A&P Ch. 12 Central Nervous System

What is the function of convolutions of the brain?

Increases surface area cortex which allows more neurons to occupy the limited space within the skull

Which two states of consciousness are between alertness and coma?

Drowsiness (lethargy) and stupor

What is cerebral edema?

swelling of brain associated with traumatic head injury; can be fatal

What are the 4 subdivisions of the motor area?

1) Primary (somatic) motor cortex 2) Premotor cortex 3) Broca's area 4) Frontal eye field

What does the caudal end of the neural tube become?

Spinal cord

What are association fibers?

Horizontal running fibers in cerebral white matter that connect different parts of same hemisphere; short association fibers connect adjacent gyri; long association fibers are bundled into tracts and connect different cortical lobes

What are the 4 general considerations of the cerebral cortex?

1) Contains three types of functional areas: • Motor areas: control voluntary movement • Sensory areas: conscious awareness of sensation • Association areas: integrate diverse information 2) Each hemisphere is concerned with contralateral (opposite) side of body 3) Lateralization (specialization) of cortical function can occur in only one hemisphere; hemispheres are not equal in function 4) Conscious behavior involves entire cortex in one way or another; no functional area of the cortex acts alone

What are the chief homeostatic controls of the hypothalamus?

1) Controls autonomic nervous system by controlling activity centers in brain stem and spinal cord • Examples: blood pressure, rate and force of heartbeat, digestive tract motility, pupil size, and many other visceral activities 2) Initiates physical responses to emotions; "heart" of the limbic system (emotional part of brain) • Ex: Perceives pleasure, fear, rage, and controls sex drive and other biological rhythms and drives 3) Regulates body temperature: initiates sweating or shivering 4) Regulates hunger in response to nutrient blood levels (glucose and amino acids) or hormones (cholecystokinin, ghrelin, and others) 5) Regulates water balance and thirst • When body fluids become too concentrated, hypothalamic neurons called osmoreceptors are activated which excite hypothalamic nuclei that trigger the release of antidiuretic hormone (ADH) from the posterior pituitary • ADH causes the kidneys to retain water • The same conditions also stimulate hypothalamic neurons in the thirst center, causing us to feel thirsty 6) Regulates sleep-wake cycles in coordination with other brain regions; it's suprachiasmatic nucleus (our biological clock) sets the timing of the sleep cycle in response to daylight-darkness cues received from the visual pathways 7) Controls endocrine system functions in two important ways: • It's releasing and inhibiting hormones control the secretion of hormones by the anterior pituitary gland • It's supraoptic and paraventricualr nuclei produce the hormones ADH and oxytocin

Name three factors that can enhance transfer of information from STM to LTM.

1) Rehearsal 2) Association 3) Heightened emotional state

What are the 3 layers of the meninges?

1) dura mater 2) arachnoid mater 3) pia mater

Where are the cell bodies of the first, second, and third order sensory neurons in the spinothalamic pathway located?

1st order - outside the spinal cord in a ganglion 2nd order - dorsal horn of spinal cord 3rd order - thalamus

How can the human brain be described and how much does it weigh?

2 good fistfuls of quivering pinkish gray tissue, wrinkled like a walnut, with a consistency of cold oatmeal; average adult brain has mass of about 1500 g (3.3 lb)

Trevor was tackled while playing football. After hitting the ground he was unable to move his lower limbs. What is a loss of motor function called? What level of his spinal cord do you think was injured (cervical, thoracic, lumbar, or sacral)? Is this a permanent injury?

A loss of motor function is called paralysis. Lower limb paralysis could be caused by a spinal cord injury in the thoracic region (between T1 and L1) If the spinal cord is transected , the result is paraplegia If the cord is only bruised, he may regain function in the limbs

What are primary brain vesicles?

As soon as the neural tube forms its anterior (rostral) end begins to expand and constructions appear that mark off the 3 primary brain vesicles (encephalo means "brain") • Prosencephalon, or forebrain • Mesencephalon, or midbrain • Rhombencephalon, or hindbrain

Describe how the brain grows embryonically

Because the brain grows more rapidly than the membranous skull it folds up to occupy the available space; initially cerebral surface is smooth, folding begins in month 6 • The midbrain and cervical flexures move the forebrain toward the brain stem • The cerebral hemispheres are forced to take a horseshoe-shaped course and grow posteriorly and laterally; as a result they grow back over and almost completely envelop the diencephalon and midbrain • By week 26, the continued growth of the cerebral hemispheres causes their surfaces to crease and fold into convolutions, which increases their surface area and allows more neurons to occupy the limited space

When Taylor begins to feel drowsy while driving, she opens her window, turns up the volume of the car stereo, and sips ice-cold water. How do these actions keep her awake?

By increasing the amount of sensory stimuli she receives, she relays this information to the reticular activating system (RAS), which in turn increases activation of the cerebral cortex

What is CSF, where is it produced, and what are its functions?

CSF is formed by the choroid plexuses as a filtrate of blood plasma. It is a watery "broth" similar in composition to plasma. It protects the brain and spinal cord from blows and other trauma, helps nourish the brain, and carries chemical signals from one part of the brain to another.

Which two areas of the adult brain have an outside layer of gray matter in addition to central gray matter and surrounding white matter?

Cerebral hemispheres and cerebellum

What are the cerebral structures of the limbic system?

Cerebral structures of the limbic system which encircle the upper part of the brain stem • Cingulate gyrus o Anterior part important function in emotions and plays role in expressing our emotions through gestures and in resolving mental conflicts when we are frustrated • Septal nuclei • Amyggdaloid body o Almond-shaped nucleus that sits on the tail of the caudate nucleus o Important function in emotions and critical in responding to perceived threats (such as angry or fearful facial expressions) with either fear or aggression • Hippocampus • Dentate gyrus • Parahippocampal gyrus

What is the fourth ventricle?

Fourth ventricle is continuous with the third ventricle via the canal-like cerebral aqueduct that runs through the midbrain • Lies in the hindbrain dorsal to the pons and superior medulla • Continuous with the central canal of the spinal cord inferiorly • 3 openings mark the walls of the fourth ventricle; these apertures connect the ventricles to the subarachnoid space, a fluid-filled space surrounding the brain: • The paired lateral apertures in its side walls • Median aperture in its roof

What is the choroid plexus?

Frond-shaped clusters of broad, thin-walled capillaries that hangs from roof of each ventricle, enclosed by pia mater and surrounding layer of ependymal cells • Capillaries are fairly permeable and tissue fluid filters continuously from bloodstream • Ependymal cells joined by tight junctions that control composition of CSF via ion pumps that set up ionic gradients that cause water to diffuse into the ventricles • Important because CFS mixes with the extracellular fluid bathing neurons and influences the composition of this fluid • Cilia of ependymal cells help to circulate CSF • Helps cleanse the CSF by removing waste products and unnecessary solutes

What are commissural fibers?

Horizontal fibers that connect corresponding gray matter of two hemispheres o These commissures allow the two hemispheres to function as a coordinated whole o The largest commissure is the corpus callosum, which lies superior to the lateral ventricles, deep within the longitundal fissure o Les prominent examples are the anterior and posterior commissures

When would you see delta waves in an EEG?

In deep sleep in normal adults

Where are motor areas located and what is their general function?

Located in posterior part of frontal lobes of each hemisphere, motor areas act to control voluntary movement

What are meninges and their function?

Meninges (singular, meninx) are three connective tissue membranes that lie just external to the CNS organs; it's functions include: o Cover and protect CNS o Protect blood vessels and enclose venous sinuses o Contain cerebrospinal fluid (CSF) o Form partitions in the skull

Mike, who is left-handed, decided to wear his favorite T-shirt to his anatomy class. On his shirt were the words "only left handed people are in their right minds". What does this statement mean?

Motor functions on the left side of the body are controlled by the right hemisphere of the brain because motor tracks from the right hemisphere cross over (in the medulla oblongata) to the left side of the spinal cord to go to the left side of the body

What are the nuclei of the midbrain and their functions?

Nuclei are also scattered in the surrounding white matter of the midbrain: 1) The corpora quadrigemina, the largest midbrain nuclei, raise 4 domelike protrustions on the dorsal midbrain surface o The superior pair, the superior colliculi, are visual reflex centers that coordinate head and eye movements when we visually follow a moving object, even if we aren't consciously looking at it o The inferior colliculi are part of the auditory relay from the hearing receptors of the ear to the sensory cortex; also act in reflexive responses to sound such as the startle reflex that causes you to turn head to unexpected noise 2) Also embedded on each side of the midbrain white matter are 2 pigmented nuclei: • Substantia nigra: located deep to the cerebral peduncle, dark color reflects high content of melanin pigment, a precursor of the neurotransmitter (dopamine) released by these neurons o Functionally linked to basal nuclei (its axons project to the putamen) and many scientists consider it to be part of the basal nuclear complex; helps to regulate motor function o Parkinson's disease is degeneration of the dopamine-releasing neurons in this area • Red nucleus: Overall nucleus that lies deep to the substantia nigra; its reddish hue is due to its rich blood supply and to the presence of iron pigment in its neurons o Red nuclei are relay nuclei in some descending motor pathways that cause limb flexion 3) Embedded in the reticular formation, a system of small nuclei scattered through the core of the brain stem

What is cephalization?

Over the course of animal evolution, the elaboration of the rostral ("toward the snout"), or anterior, portion of the CNS, along with an increase in the number of neurons in the head - has reached highest level in human brain

What are the secondary brain vesicles?

Primary vesicles give rise to the secondary brain vesicles • Forebrain divides into the telencephalon ("endbrain") and diencephalon ("interbrain") • Hindbrain constricts forming the mentencephalon ("afterbrain") and myelencephalon ("spinal brain") • Midbrain remains undivided

During which sleep stage are most skeletal muscles actively inhibited?

REM sleep

What is cerebral dominance?

Refers to hemisphere that is dominant for language (speech) • In most people (about 90%) the left hemisphere has greater control over language abilities, math, and logic o This dominant hemisphere is working when we compose a sentence, add numbers, and memorize a list • The other hemisphere (usually the right) is more free-spirited, more involved in visual-spatial skills, intuition, emotion, and artistic and musical skills (poetic, creative, and insightful) • Most people with left cerebral dominance are right handed (about 90%) o In remaining 10%, the roles of the hemispheres are reversed or the hemispheres share their functions equally • Typically right-cerebral dominant people are left handed and male o Some "lefties" who have a cerebral cortex that functions bilaterally are ambidextrous • The two cerebral hemispheres have almost instantaneous communication with each other via connecting fiber tracts as well as complete functional integration o While each hemisphere is better than the other at certain functions, neither is better at

What is spina bifida?

Results from incomplete formation of the vertebral arches and involves typically the lumbrosacral region o Technical definition is that laminae and spinous processes are missing on at least one veebra o If condition is severe, neural deviics occur as well o Spina bivida occulta - least serious type - involves one or only a few vertebra and causes no neural problems; other than a small dimple or tuft of hair over the siteo of nonfusion, it has no external manifestations o Spina bifida cystica - more common and severe form, a saclike cyst protrudes dorsally from child's spine • Cyst may contain meninges and CSP or even portions of the spinal cord and spinal nerve roots (a myelomeningocele) • The larger the cyst and more neural structure it contains, the greater the neurological impairment • In the worst case, where the inferior spinal cord is functionless, the infant experiences bowel incontinence, bladder muscle paralysis (which promotes UTI's and kidney failure), and lower limb paralysis • Infections occur continually because the cyst wall is thin and porous and tens to rupture or lead • Hydrocephalus accompanies spina bifida in 90% of cases • In past up to 70% of cases were caused by inadequate amounts of the B vitamin folic acid • Incidence has dropped significantly n the US And other countries that have introduced mandatory supplementation of folic acid in bread, flour, and pasta products

What anatomical landmark of the cerebral cortex separates primary motor areas from somatosensory areas?

The central sulcus

Which region of the brain stem is associated with the cerebral peduncles and the superior and inferior colliculi?

The midbrain

In what ways are the cerebellum and the cerebrum similar? In what ways are they different?

There are many possible answers to this question - here are a few: Similarities: Structurally, the cerebellum and cerebrum are similar in that they both have a thin outer cortex of gray matter, internal white matter, and deep gray matter nuclei. Also, both have body maps (homunculi) and large fiber tracts connecting them to the brain stem. Both receive sensory input and influence motor output. Differences: The cerebellum is almost entirely concerned with motor output, whereas the cerebrum has much broader responsibilities. Also, while a cerebral hemisphere controls the opposite side of the body, a cerebellar hemisphere controls the same side of the body.

Which ventricle is surrounded by diencephalon?

Third ventricle

Why is the thalamus called the "gateway to the cerebral cortex"?

Virtually all inputs ascending into the cerebral cortex synapse in the thalamus en route

What is subdural or subarachnoid hemorrhage

can occur following a head injury, pressure from blood may force brain stem through foramen magnum, resulting in death • Patients who are initially lucid and then begin to deteriorate neurologically are probably hemorrhaging intracranially • Intracranial hemorrhages are treated by surgically removing the hematoma (localized blood mass) and repairing the ruptured vessels

What is Lateralization of cortical functioning ?

division of labor between hemispheres • Hemispheres are not identical

What is basic pattern found in cerebrum and cerebellum?

islands of gray matter (nuclei) within white matter, as well as an outer cortex of gray matter

What is Broca's area?

o Anterior to inferior premotor area o Present in only one hemisphere (usually the left) o Motor speech area: directs muscles of speech production o Active in planning speech and other voluntary motor activities

What is the premotor cortex?

o Anterior to precentral gyrus in frontal lobe o Helps plan movements o Coordinates simultaneous or sequential actions o Controls learned, repetitious, or patterned motor skills • Playing piano or typing o Controls voluntary actions using sensory feedback • Searching for light switch in dark room o Staging area for skilled motor activities • Coordinates the movement of several muscle groups either simultaneously or sequentially, mainly by sending activating impulses to the primary motor cortex • Also influences motor activity more directly by supplying about 15% of pyramidal tract fibers

What is the anatomy of the cerebellum?

o Bilaterally symmetrical o Wormlike vermis connects its two apple-sized cerebellar hemispheres medially o Its surface is heavily convoluted with fine, transversely oriented pleatlike gyri known as folia ("leaves)" o Deep fissures subdivide each hemisphere into anterior, posterior, and flocculondular lobes • The small propeller-shaped floccuolondular lobes, situated deep to the vermis and posterior lobe, cannot be seen in surface view o Like cerebrum, has a thin outer cortex of gray matter, internal white matter, and small, deeply situated, paired masses of gray matter (most familiar are the dentate nuclei) o Several types of neurons populate the cerebellar cortex, including Purkinje cells • These large cells, with their extensively branched dendrites, are the only cortical neurons that send their axons through the white matter to synapse with the central nuclei of the cerebellum o The distinctive pattern of white matter in the cerebellum resembles a branching tree, a pattern fancifully called the arbor vitae ("tree of life") o The anterior and posterior lobes of the cerebellum, which coordinate body movements, have 3 sensory maps of the entire body as indicated by homunculi in Figure 12.16d (page 451) • The part of the cerebellar cortex that receives sensory input from a body region influences motor output to that region • The medial portions influence the motor activities of the trunk and girdle muscles • The intermediate parts of each hemisphere influence the distal parts of the limbs and skilled movements • The lateral-most parts of each hemisphere integrate information from the association areas of the cerebral cortex and appear to play a role in planning movements (rather than executing them) • The floculonodular lobes receive inputs from the equilibrium apparatus of the inner ears, and adjust posture to maintain balance

What is the pons and what is its function?

o Bulging brain stem region wedged between the midbrain and medulla oblongata o Dorsally the fourth ventricle separates it from the cerebellum o Pons means "bridge" o Composed of conduction tracts oriented in two directions: • Deep projection fibers run longitudinally and connect higher brain centers and spinal cord • The more superficial ventral fibers are oriented transversely and dorsally • They form the middle cerebellar peduncles and connect the pons bilaterally with the two sides of the cerebellum dorsally • These fibers issue form numerous pontine nuclei, which relay "conversations" between the motor cortex and the cerebellum o Several cranial nerve pairs issue form pontine nuclei including the trigeminal abducens and facial nerves o Other important pontine nuceli are part of the reticular formation and some help the medulla oblongata maintain the normal rhythm of breathing

What are ventricles?

o Central cavity of the neural tube remains continuous and enlarges in 4 areas to form the fluid-filled ventricles (ventr = little belly) of the brain

What are the major sulci that divide lobes?

o Central sulcus lies along frontal plane and separates frontal lobe from parietal lobe • Bordering the central sulcus are the precentral gyrus of frontal lobe anteriorly and postcentral gyrus of parietal lobe posteriorly o Parieto-occipital sulcus, located more posteriorly on the medial surface of the hemisphere, separates the occipital lobe from the parietal lobe o Lateral sulcus is a deep sulcus that outlines the flap-like temporal lobes and separates it from the parietal and frontal lobes

What does cerebellar processing involve?

o Cerebellum fine-tunes motor activity as follows: • Receives impulses from cerebral cortex, via relay nuclei in the brain stem, of intent to initiate voluntary muscle contraction • At same time, receives signals from proprioceptors throughout body (regarding tension in the muscles and tendons, and joint position), as well as visual and equilibrium pathways • This information enables the cerebellum to evaluate body position and momentum - where the body is and where it is going • Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction while preventing overshoot and maintaining posture • Then, via, the superior peduncles, sends "blueprint" of coordinated movement to cerebral motor cortex and also the brain stem nuclei (which in turn influences motor neurons of the spinal cord) o Just as an automatic pilot compares a plane's instrument readings with a planned course, the cerebellum continually compares the body's performance with the higher brain's intention and sends out messages to initiate appropriate corrective measures o Cerebellar injury results in loss of muscle tone and clumsy, uncertain movements

What is the cerebral cortex?

o Cerebral cortex is "executive suite" of brain and the first region of the cerebral hemispheres o Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding o Thin (2-4 mm or 1/8 inch) superficial layer of gray matter • Accounts for 40% of brain mass because its convolutions triple its surface area • Composed of neuron cell bodies, dendrites, glial cells, and blood vessels, but no axons (fiber tracts)

What are the 3 basic regions of each cerebral hemisphere?

o Cerebral cortex of gray matter superficially (looks gray in fresh tissue) o White matter internally o Basal nuclei, islands of gray matter deep within white matter

What is a CVA?

o Cerebrovascular Accidents (CVAs) • Most common nervous system disorder and third leading cause of death in North America • Also referred to as "strokes" • Occurs when blood circulation to a brain area is blocked and brain tissue dies of ischemia (a reduction of blood supply that impairs the delivery of oxygen and nutrients) • Most common cause of CVA is blood clot that blocks a cerebral artery • Clot can originate from outside the brain or form on the roughened interior wall of a brain artery narrowed by atherosclerosis • Less frequently, strokes are caused by bleeding, which compresses brain tissue • Many who survive a CVA are paralyzed on one side of body (hemiplegia); others commonly exhibit sensory deficits or have difficulty understanding or vocalizing speech • Some patients recover at least part of their lost faculties because undamaged neurons sprout new branches that spread into the injured area and take over some lost functions • Physical therapy should begin immediately to prevent muscle contractures (abnormally shortened muscles due to differences in strength between opposing muscle groups • Not all strokes are "completed"; temporary episodes of reversible cerebral ischemia, called transient ischemic attaches (TIA's) are common • TIA's last form 5 to 50 minutes and are characterized by temporary numbness, paralysis, or impaired speech • Deficits are not permanent but TIA's do constitute a "red flag" of an impending CVA • CVA like an undersea earthquake - it's not the initial tremor that does the most of the damage, it's the tsunami that later floods the coast • Similarly, the initial vascular blockage during a stroke is not usually disastrous because there are many blood vessels in the brain that can pick up the slack • Rather it's the neuron-killing events outside the initial ischemic zone that wreak the most havoc • Experimental evidence indicates that the main culprit is glutamate, an excitatory neurotransmitter, which plays a key role in learning and memory and other critical brain functions • After brain injury, neurons totally deprived of oxygen begin to disintegrate, unleashing "buckets" of glutamate • Under these conditions, glutamate acts as an excitotoxin, literally exciting surrounding cells to death • Presently most successful treatment for stroke is tissue plasminogen activator (tPA) which dissolves blood clots in brain; alternatively a mechanical device can drill into a blood clot and pull it from a blood vessel

What are ascending pathways?

o Conduct sensory pathways upward through a chain of three neurons: • First-order neuron • Their cell bodies reside in a ganglion (dorsal root or cranial) and they conduct impulses from cutaneous receptors and proprioceptors and synapses with 2nd-order neuron; impulses from facial area are transmitted by cranial nerves and spinal nerves conduct somatic sensory impulses from rest of body to CNS • Second-order neuron • Cell bodies reside in dorsal horn of spinal cord or in medullary nuclei, interneuron, axons extend to thalamus or cerebellum • Third-order neuron • Also an interneuron • Cell bodies in thalamus, axon extends to somatosensory cortex o In general, somatosensory information travels along 3 main pathways on each side of spinal cord • 2 of these pathways (the dorsal column-medial lemniscal and spinothalamic pathways) transmit impulses via the thalamus to the sensory cortex for conscious interpretation • Collectively the inputs of these sister tracts provide discriminative touch and conscious proprioception • Both pathways decussate - the first in the medulla and the second in the spinal cord • 3rd pathway, the spinocerebellar pathway, terminates in the cerebellum, and does not contribute to sensory perception • Dorsal column-medial lemniscal pathways • Mediate precise, straight-through transmission of inputs from a single type (or a few related types) a of sensory receptor that can be localized precisely on the body surface, such as discriminative touch and vibrations • These pathways are formed by the paired tracts of the dorsal white column of the spinal cord - fasiculus cuteatus and fasciulus gracialis - and the medial lemniscus • The medial lemniscus arises in the medulla and terminates in the thalamus o From the thalamus, impulses are forwarded to specific areas of the somatosensory cortex • Spinothalamic pathways • Receive input from many different types of sensory receptors and make multiple synapses in the brain stem • These pathways consist of the lateral and ventral (anterior) spinothalamic tracts • Their fibers cross over in the spinal cord • Fibers primary transmit impulses for pain and temperature, but also for coarse touch and pressure • All are sensations that we are aware of but have difficulty localizing precisely on the body surface • Spinocerebellar pathways • 3rd ascending pathway consists of the ventral and dorsal spinocerebellar tracts • Convey information about muscle or tendon stretch to the cerebellum, which uses this information to coordinate muscle activity • Do not contribute to conscious sensation • Fibers either do not decussate or else cross over twice (thus undoing the descussation)

What type of damage is seen in a stroke?

o Damage to areas of primary motor cortex, as seen in a stroke, paralyzes muscles controlled by those areas o Paralysis occurs on opposite side of body from damage o Voluntary control lost, reflex action still works o Damage to premotor area results in loss of the motor skill(s) programmed by that region but does not impair muscle strength and the ability to perform the discrete individual movements • Example: damage would still allow fingers to move, but voluntary control needed to type would be lost • Other premotor neurons can be reprogrammed to take over skill of damaged neurons • Would require practice, just as the initial learning process did

What are descending pathways and tracts?

o Deliver efferent impulses from brain to spinal cord o Motor pathways involve two neurons, referred to as upper and lower motor neurons • Upper motor neurons: pyramidal cells of the motor cortex and neurons of subcortical motor nuclei • Lower motor neurons: ventral horn motor neurons, directly innervate the skeletal muscles (their effectors) o Two groups • Direct pathways: originate mainly with the pyramidal cells located in precentral gyri; send impulses through the brain stem via the large pyramidal (corticospinal) tracts • Called "direct' because their axons descend without synapsing from the pyramidal cells to the spinal cord • There they synapse either with interneurons or with ventral horn motor neurons • Stimulation of ventral horn neurons activates the skeletal muscles with which they are associated • Direct pathway primarily regulates fast and fine (or skilled) movements such as doing needlework and writing • Indirect pathways: include brain stem motor nuclei and all mother pathways except the pyramidal pathways • Formerly lumped together as the extrapryramidal system because their nuclei of origin were presumed to be independent of the pyramidal tracts; this term is still used clinically but pyramidal tract neurons are now known to project to and influence the activity of most "extrapyramidal" nuclei; so modern anatomist refer to them as indirect or multineuronal pathways (or simply use the names of the individual motor pathways • Indirect motor pathways are complex and multisynaptic, most involved in regulating: o Axial muscles that maintain balance and posture o Muscles controlling coarse limb movements o Head, neck, and eye movements that follow objects in the visual field • Many of the activities controlled by subcortical motor nuclei depend heavily on reflex activity (ex. Rubrospinal tract) • Overall the reticulospinal and vestibulosinal tracts maintain balance by varying the tone of postural muscles • The rubospinal tracts control flexor muscles • Tectospinal tracts and superior colliculi mediate head movements in response to visual stimuli

What is the structure and main function of the reticular formation?

o Extends through central core of brain stem through the medulla oblongata, pons, and midbrain o Three broad columns of nuclei run length of brain stem • The midline raphe nuclei which are flanked laterally by • The medial (large cell) group of nuclei, and • The lateral (small cell) group of nuclei o Governs brain arousal: Has axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord o Motor branch helps control coarse limb movements and visceral motor functions

What are the 5 lobes of the cerebral hemispheres?

o Frontal - Lies in the anterior cranial fossa o Parietal o Temporal - Anterior parts fill the middle cranial fossa o Occipital o Insula -Buried deep within the lateral sulcus and forms part of its floor; covered by portions of the temporal, parietal, and frontal lobes

How do PET and MRI scans show domains?

o Functional imaging (PET and MRI) of brain show specific motor and sensory functions are located in discrete cortical areas called domains • Higher functions such as memory or language are spread over large areas of the cortex in overlapping domains • PET - positron emission tomography; shows maximal metabolic activity • MRI - magnetic resonance imaging; shows blood flow

What are the surface markings of the cerebral hemispheres?

o Gyri: elevated ridges of tissue (gyrus, plural, meaning "twisters") o Sulci: shallow grooves (sulcus = "furrows") o Fissures: deep grooves that separate large regions of the brain; more prominent gyri and fissures are important anatomical landmarks • Longitudinal fissure • Median fissure that separates cerebral hemispheres • Transverse cerebral fissure • Separates cerebrum and cerebellum bellow

What does language involve in brain function?

o Language implementation system involves practically all of the association cortex of left hemisphere o Main areas include: • Broca's area: involved in speech production • Patients with lesions in Broca's understand words, but cannot speak • Wernicke's area: involved in understanding spoken and written words • Patients with lesions in Wernicke's can speak, but words are nonsensible ("word salad") o Broca's and Wernicke's areas together with the basal nuclei form a single language implementation system that analyzes incoming and produces outgoing word sounds and grammatical structures o A surrounding set of cortical areas form a bridge between this system and the regions o f the cortex that hold concepts and ideas, which are distributed throughout the remainder of the association cortexes o Corresponding areas in the right or non-language dominant hemisphere are involved in "body language" (how you say something can drastically alter the meaning)

What are the roles of the limbic system?

o Large part of emotional or affective brain (amygdaloid body and cingulate gyrus especially important) • Recognizes angry or fearful facial expressions, assesses danger, and elicits fear response (amygdaloid body_) • Plays role in expressing emotions via gestures and resolves mental conflict (cingulate gyrus) o Limbic system links emotional responses to odors, reflect origin of much of the limbic system in our primitive "smell brain" (rhinencephalon) • Example: skunks smell bad and are repulsive o Extensive connections between limbic system and lower and higher brain regions to allow the system to integrate and respond to a variety of environmental stimli o Most output relayed via hypothalamus • Because hypothalamus is a neural clearinghouse for both autonomic (visceral) function and emotional response, it's not surprising that people under acute or unrelenting emotional stress fall prey to visceral illnesses such as high blood pressure and heartburn known as psychosomatic illnesses (illness induced by emotional stress) o Limbic system interacts with prefrontal lobes • Allows us to react emotionally to things we consciously understand to be happening • Makes us consciously aware of emotional richness in our lives • Can stop us from expressing our emotions inappropriately (logic overriding emotion) o Hippocampus and amygdaloid body also play a role in memory

What is the midbrain and what are its functions?

o Located between diencephalon and pons • Cerebral peduncles: two ventral bulges that form vertical pillars that seem to hold up the cerebrum (hence name "little feet of the cerebrum" • The crus cerebri ("leg of the cerebrum") of each peduncle contains a large pyramidal (corticospinal) motor tract descending toward the spinal cord • The superior cerebellar peduncles, also fiber tracts, connect the midbrain to the cerebellum dorsally • Running through the midbrain is the hollow cerebral aqueduct, which connects the third and fourth ventricles • It delineates the cerebral peduncles ventrally from the tectum, the midbrain's roof • Surrounding the aqueduct is the periaqueductal gray matter, which is involved in pain suppression and links the fear-perceiving amygdaloid body and the ANS pathways that control the "fight or flight" response • The periaqueductal gray matter also includes nuclei that control two cranial nerves, the oculomotor and the trochlear nuclei

What is the frontal eye field?

o Located within and anterior to premotor cortex; superior to Broca's area o Controls voluntary eye movements

What is the thalamus?

o Makes up 80% of diencephalon o Bilateral, egg-shaped, nuclei o Thalamus is Greek word meaning "hidden room" o Main thalamic function is to act as relay station for information coming into cerebral cortex • Overall, it mediates sensation, motor activities, cortical arousal, learning, and memory; gateway to the cerebral cortex o In most people, an interthalamic adhesion (intermediate mass) connects the nuclei o Afferent impulses from all senses and all parts o f the body converge on the thalamus and synapse with at least one of its nuclei o Contains 11 nuclei, named for location o Nuclei project fibers to and receive fibers from cerebral cortex o Information is sorted out and "edited" • Impulses having to do with similar functions are relayed as a group via the internal capsule to the appropriate area of the sensory cortex and to specific cortical association areas • As the afferent impulses reach the thalamus, we have a crude recognition of the sensation as either pleasant or unpleasant • However, stimulus localization and discrimination occur in the cerebral cortex o In addition to sensory inputs, virtually all other inputs ascending to the cerebral cortex funnel through the thalamic nuclei, including: • Impulses from hypothalamus for regulating emotion and visceral function (via the anterior nuclei) • Impulses from cerebellum and basal nuclei to help direct motor cortices (via the ventral lateral and ventral anterior nuclei, respectively) • Impulses for memory or sensory integration that are projected to specific association cortices (via pulvinar, lateral dorsal, and lateral posterior nuclei)

What is the epithalamus?

o Most dorsal portion of the diencephalon o Forms the roof of the third ventricle o Extending from its posterior border and visible externally is the pineal gland or body • Pineal gland secretes the hormone melatonin (a sleep inducing signal and antioxidant) and, along with the hypothalamic nuclei, helps regulate the sleep-wake cycle o The posterior commissure forms the caudal border of the epithalamus

What are the cognitive functions of the cerebellum?

o Neuroanatomy, imaging studies, and observations of patients with cerebellar injuries suggest that the cerebellum also plays a role in thinking, language, and emotion o As in the motor system, the cerebellum may compare the actual output of these systems with the expected output and adjust accordingly o Much remains to be discovered about the cerebellum's nonmotor functions

What is gray matter?

o Neuron cell bodies o Short nonmyleinated neurons

What are the lateral ventricles?

o Paired lateral ventricles are large, C-shaped chambers located deep in each hemisphere • Anteriorly, the lateral ventricles lie close together, separated only by a thin median membrane called the septum pellucidum (pellucidum = "transparent wall")

What is the limbic association area?

o Part of limbic system o Includes the cingulate gyrus, parahippocampal gyrus, and hippocampus o Provides emotional impact that makes a scene important to us and helps establish memories o Hippocampus stores memories that allow us to remember incidents

What is spinal cord protected by?

o Protected by bone, meninges, and CSF • Single layered spinal dura mater is not attached to the bony walls of the vertebral column • Between the bony vertebrae and the spinal dura mater is an epidural space filled with a soft padding of fat and a network of veins • Cerebrospinal fluid fills the subarachnoid space between the arachnoid and pia mater meninges • Inferiorly, the dural and arachnoid membranes extend to the level of S2, well beyond the end of the spinal cord • The spinal cord typically ends between L1 and L2 • For this reason, the subarachnoid space within the meningeal sac inferior to that point provides an ideal spot for removing CSF for testing (procedure called lumbar puncture) • Because the spinal cord is absent there and the delicate nerve roots drift away from the point of the needle insertion, there is little or not danger of damaging the cord (or spinal roots) beyond L3 • Inferiorly, the spinal cord terminates in a taping cone-shaped structure called the conus medullaris • The filum terminale, a fibrous extension of the conus covered by pia matter, extends inferiorly from the conus medullaris to the coccyx, where it anchors the spinal cord so its not jostled by body movements • Furthermore, the saw-toothed shelves of pia mater called denticulate ligaments secure the spinal cord to the tough dura mater meninx throughout its length • Spinal cord is about the width of a thumb for most of its length but it has obvious enlargements where the nerves serving the upper and lower limbs arise called the cervical and lumbar enlargements, respectively

Describe the spinal cord cross sectional anatomy

o Spinal cord is somewhat flattened from the front to back and two grooves mark its surface: • The wide ventral (anterior) median fissure • The narrower dorsal (posterior) median sulcus • These grooves run the length of the cord and partially divide it into right and left halves • Gray matter of the cord is located in its core, the white matter outside the core • CSF fluid-filled central canal runs the length of the spinal cord

What is the hypothalamus?

o The hypothalamus is the main visceral control and regulating center that is vital to homeostasis ; few tissues in body escape its influence o Located below thalamus, contains many nuclei (hypo = below) o Caps the brain stem and forms the inferolateral walls of the third ventricle o Merging into the midbrain inferiorly, it extends from the optic chiasma (crossover point of the optic nerves) to the posterior margin of the mammillary bodies o Infundibulum, located between the optic chiasma and mammillary bodies, is a stalk of hypothalamic tissue that connects the pituitary gland to the base of the hypothalamus

What is the third ventricle?

o Third ventricle is narrow and lies in diencephalon • Communicates with the lateral ventricles via a channel called an interventricular foramen

What are the cerebellar peduncles?

o Three paired fiber tracts - the cerebellar peduncles - connect the cerebellum to the brain stem o Virtually all fibers entering and leaving the cerebellum are ipsilateral (ispi = same) - from and to the same side of the body (unlike the contralateral fiber distribution to and from the cerebral cortex) • The superior cerebellar peduncles connecting cerebellum and midbrain carry instructions from neurons in the deep cerebellar nuclei to the cerebral motor cortex via thalamic relays • Like the basal nuclei, the cerebellum has no direct connections to the cerebral cortex • The middle cerebellar peduncles carry one-way communications from the pons to the cerebellum, advising the cerebellum of voluntary motor activities initiated by the motor cortex (via relays in the pontine nuclei) • The inferior cerebellar peduncles connect medulla and cerebellum; these peduncles convey sensory information to the cerebellum from: • Muscle proprioceptors throughout the body • The vestibular nuclei of the brain stem, which are concerned with equilibrium and balance

What happens when tumors grow on association areas?

o Tumors or other lesions of the anterior association area may cause mental and personality disorders, including loss of judgment, attentiveness, and inhibitions • Affected individual may be oblivious to social restraints, perhaps becoming careless about personal appearance, or take risks o Different problems arise for individuals with lesions in the part of the posterior association area that provides awareness of self in space • Individual may refuse to wash or dress the side of the body opposite to lesion because "that doesn't belong to me"

What are the 11 nuclei of the thalamus?

• Anterior nuclei • Impulses from hypothalamus for regulating emotion and visceral function • Medial dorsal nucleus • Lateral dorsal nucleus • Inputs for memory or sensory integration that are projected to specific association cortices • Lateral posterior nucleus • Inputs for memory or sensory integration that are projected to specific association cortices • Pulvinar • Inputs for memory or sensory integration that are projected to specific association cortices • Medial geniculate body • Important visual relay center • Lateral geniculate body • Important auditory relay center • Ventral nuclei • Ventral anterior o Impulses from the basal nuclei to help direct motor cortices • Ventral lateral o Impulses from the cerebellum to help direct motor cortices • Ventral posterolateral o Receives impulses from the general somatic sensory receptors (touch, pressure, pain, etc) • Reticular nucleus

What is the cerebellum and where is it located?

• Cauliflower like structure, exceeded in size only by cerebrum, accounts for about 11% of total brain mass • Cerebellum = "small brain" • Located dorsal to the pons and medulla (and to the intervening fourth ventricle); it protrudes under the occipital lobes of the cerebral hemisphere, from which it is separated by the transverse cerebral fissure • Processes input from cerebral motor cortex, various brain stem nuclei, and sensory receptors to provide precise, coordinated, smooth, and timed movements of skeletal muscles needed for daily living o Ex: driving, typing, playing an instrument • Plays a major role in balance • Also has role in cognitive and emotional functions • Cerebellar activity occurs subconsciously - we have no awareness of it

What are cerebral hemispheres?

• Cerebral hemispheres form superior part of brain and account for 83% of brain mass; like a mushroom cap covering the stalk of the diencephalon and top of brain stem

What are sensory areas?

• Conscious awareness of sensation • Occur in parietal, insular, temporal, and occipital lobes • Primary areas receive stimuli from associated sensory neurons • Association areas integrate and interpret information received in the primary areas for somatosensory, visual and auditory stimuli

What is cerebral white matter?

• Consists of myelinated fibers bundled into large tracts • Responsible for communication between cerebral areas, and between cortex and lower CNS • Classified according to direction they run

What is the diencephalon?

• Consists of three paired gray-matter structures that form the central core of the forebrain and is surrounded by the cerebral hemispheres: o Thalamus o Hypothalamus o Epithalamus • All three enclose third ventricle

What is the brain stem and what are its main functions?

• Consists of three regions from superior to inferior: midbrain, pons, medulla oblongata • Each structure is about an inch long and collectively account for only 2.5% of total brain mass • Tissue structure is similar to spinal cord (deep gray matter surrounded by white matter fiber tracts), however, the brain stem has nuclei of gray matter embedded in the white matter, a feature not found in the spinal cord • Controls rigidly programmed, automatic behaviors necessary for survival • Also provides a pathway for fiber tracts running between higher and lower neural centers • Additionally, brain stem nuclei are associated with 10 of the 12 pairs of cranial nerves so it is heavily involved with innervating the head

What happens when the visual cortex is damaged?

• Damage to the primary visual cortex results in functional blindness • By contrast, individuals with a damaged visual association area can see, but they do not comprehend what they are looking at

What types of seizure are there and how can they be treated?

• Epileptic seizure: torrent of electrical discharges by groups of neurons • Prevent any other messages from getting through • Victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking • Epilepsy is not associated with intellectual impairments • Epilepsy occurs in 1% of population • Genetic factors play a role, but brain injuries, stroke, infections, or tumors can also be causes • Aura (sensory hallucination) may precede seizure including taste, smell, or flashes of light (helpful because gives person time to lie down to avoid falling) • Absence seizures (formerly petit mal) • Mild seizures of young children: expression goes blank for few seconds, usually disappears by age 10 • Tonic-clonic seizures (formerly grand mal) • Most severe; last few minutes • Victim loses consciousness, bones broken during intense convulsions, loss of bowel and bladder control, and severe biting of tongue • When person awakens remains disoriented for several minutes • Control of epilepsy includes anticonvulsive drugs, vagus nerve stimulator or deep brain stimulator implantations that deliver pulses to vagus nerve or directly to brain to stabilize brain activity

What does loss of consciousness indicate?

• Except during sleep, loss of consciousness signals that brain function is impaired • Fainting or syncope ("cut short"): brief loss of consciousness • Most often due to inadequate cerebral blood flow due to low blood pressure (or ischemia) from hemorrhage or sudden, severe emotional stress • Coma: unconsciousness for extended period • Not the same as deep sleep; oxygen consumption is lowered • Factors that induce coma include 1) blows to head that cause widespread cerebral or brain stem trauma, 2) tumors or infections of the brain stem, 3) metabolic disturbances such as hypoglycemia (abnormally low blood sugar), 4) drug overdose, 5) liver or kidney failure, and 6) massive stroke causing extreme swelling of the brain or massive stroke of brain stem • Brain death: irreversible coma • Persistent vegetative state • Ethical and legal issues surround decisions on whether person is dead or alive

What is Huntington's disease?

• Fatal, hereditary disorder that strikes during middle age • Mutant huntingtin protein accumulates in brain cells and tissue dies, lading to massive degeneration of the basal nuclei and later of the cerebral cortex • Initial symptoms in many are wild, jerky, almost continuous "flapping" movements called chorea (Greek for "dance)" • Although the movements appear to be voluntary they are not • Late in the disease, marked mental deterioration occurs and is usually fatal within 15 years • The hyperkinetic manifestations are essentially opposite to those of Parkinson's (overstimulation rather than inhibition of motor drive) and is usually treated with drugs that block, rather than enhance, dopamine's effects

What are the structures of the medulla oblongata?

• Flanking the midline on the medulla's ventral aspect are two longitundal ridges called pyramids, formed by the large pyramidal (coritcospinal) tracts descending from the motor cortex • Just above the medulla-spinal cord junction most of these fibers cross over to the opposite side before continuing to the spinal cord; this crossover point is called the decussation of the pyramids • Due to this crossover, each cerebral hemisphere controls voluntary movements on opposite sides of the body • Several other structures are visible externally • The inferior cerebellar peduncles are fiber tracts that connect the medulla to the cerebellum dorsally • Situated lateral to the pyramids, the olives are oval swellings that are caused mainly by the wavy folds of gray matter of the underlying inferior olivary nuclei o These nuclei relay sensory information on the degree of stretch in muscles and joings to the cerebellum • The rootlets of the hypoglossal nerves emerge from the groove between the pyramid and olive on each side of the brain stem • Other cranial nerves associated with the medulla are the glossopharyngeal nerves and vagus nerves • Also, the fibers of the vestibulocochlear nerves synapse with the cochlear nuclei (auditory relays), and with numerous vestibular nuclei in both the ponds and medulla (the vestibular nuclei mediate responses that maintain equilibrium) • Also housed in the medulla are several nuceli associated with ascending sensory tracts; most prominent are the dorsally located nucleus gracilis and nucleus cuneatus, associated with a tract called the medial lemniscus o These serve as relay nuclei in a pathway by which general somatic sensory information ascends from the spinal cord to the somatosensory cortex

What are basal nuclei?

• Group of subcortical nuclei • Aka basal ganglia • Deepest region of cerebrum • Definition of precise structures forming basal nuclei is controversial but most anatomists agree that each hemisphere's basal nuclei include: • Caudate nucleus o Comma shaped, arches superiorly over the diencephalon; together with putamen forms striatum (so called because the fibers of the internal capsule passing through them create a striped appearance) • Putamen o Forms a lens-shaped mass with the globus pallidus that is sometimes called the lentiform nucleus but still is functionally separate from the globus pallidus • Globus pallidus • Functionally associated with the subthalamic nuclei (located on the lateral "floor" of the diencephalon) and the substantia nigra of the midbrain • Receive input from the entire cerebral cortex as well as from other subcortical nuclei and each other • Via relays through the thalamus, the output nucleus of the basal nuclei (globus pallidus) and the substantia nigra project to the premotor and prefrontal cortices and so influence muscle movements directed by the primary motor cortex • The basal nuclei have no direct access to motor pathways • Precise role has been elusive because of inaccessible location and because their motor functions overlap with those of the cerebellum • Functions of basal nuclei are thought to: • Regulate intensity of slow or stereotyped movements • Inhibit antagonistic/unnecessary movements • Play role in cognition and emotion filtering out inappropriate responses • Parkinson's disease and Huntington's disease are disorders of the basal nuclei

What is the Vestibular (Equilibrium) Cortex?

• Imaging studies show that the part of the cortex responsible for conscious awareness of balance (the position of head in space) is located on the posterior part of the insula and adjacent parietal cortex

What is the spinal cord gray matter and spinal roots?

• In cross section the gray matter of the cord looks like the letter H or a butterfly • Consists of mirror-image lateral gray masses connected by a crossbar of grey matter, the gray commissure, that encloses the central canal • The two dorsal projections of the gray matter are the dorsal (posterior) horns, and the ventral pair are the ventral (anterior) horns • The thoracic and superior lumbar segments of the cord have an additional pair of gray matter columns, the small lateral horns • All neurons whose cell bodies are in the spinal cord gray matter are multipolar • Dorsal horns consist almost entirely of interneurons • The ventral horns have some interneurons but mostly house cell bodies of somatic motor neurons • These motor neurons send their axons out to he skeletal muscles (their effector organs) via the ventral rootlets that fuse together to become the ventral roots of the spinal cord • The amount of ventral gray matter present at a given level of the spinal cord reflects the amount of skeletal muscle innervated at that level; as a result the ventral horns are largest in the limb-innervating cervical and lumbar regions for the cord and are responsible for the cord enlargements seen in those regions • Lateral horns consist mostly of the cell bodies of autonomic (sympathetic division) motor neurons that serve visceral organs • Their axons leave the cord vi the ventral root along with those of the somatic motor neurons • Because the ventral roots contain both somatic and autonomic efferent fibers, they serve both motor divisions of the peripheral nervous system • Afferent fibers carrying impulses from peripheral sensory receptors from the dorsal roots of the spinal cord that fan out as the dorsal rootlets before they enter the spinal cord • The cell bodies of the associated sensory neurons are found in an enlarged region of the dorsal root called the dorsal root ganglion or spinal ganglion • After entering the cord, the axons of these neurons may take a number of routes o Some enter the dorsal white matter of the cord directly and travel to synapse at higher cord or brain levels o Others synapse with interneurons in the dorsal horns of the spinal cord gray matter at their entry level o The dorsal and ventral roots are very short and fuse laterally to form the spinal nerves • Gray matter can be further divided according to its neurons' relative involvement in innervating the somatic and visceral regions of the body; spinal gray matter has the following 4 zones: • Somatic sensory (SS) - dorsal horn • Visceral sensory (VS) - dorsal horn • Visceral (autonomic) motor (VM) - ventral horn • Somatic motor (SM) - ventral horn

What is the structure of the spinal nerves?

• In humans, 31 pairs of spinal nerves - part of the peripheral nervous system - attach to the cord by paired roots • Each spinal cord segment is designated by the paired spinal nerves that arise from it - ex. The first thoracic cord segment (spinal cord segment T1) is where the first thoracic nerves (spinal nerve T1) emerge from the spinal cord • While each nerve pair define a segment of the cord, the spinal cord is, in fact, continuous throughout its length and its internal structure changes gradually • Each nerve exits from the vertebral column by passing superior to its corresponding vertebra via the intervertebral foramen, and travels to the body region it serves • Because the spinal cord does not reach the end of the vertebral column, its segments are located superior to where their corresponding spinal nerves emerge through the intervertebral foramina • The lumbar and sacral spinal nerve roots angle sharply downward and travel inferiorly through the vertebral canal for some distance before reaching their intervertebral foramina • The collection of nerve roots at the inferior end of the vertebral canal is called the cauda equine because it resembles a horse's tail o This strange arrangement reflects the fact that during fetal development, the vertebral column grows faster than the spinal cord, forcing the lower spinal nerve roots to "chase" their exit points inferiorly through the vertebral canal

What is the Primary somatosensory cortex?

• Located in postcentral gyri of parietal lobe just posterior to the primary motor cortex • Receives general sensory information from skin plus proprioceptors of skeletal muscle, joints, and tendons to monitor position • Capable of spatial discrimination: identification of body region being stimulated • Somatosensory homunculus: upside-down caricatures represent contralateral sensory input from body regions o Regions that have the most sensitive body areas (face and especially lips) have a greater portion of the sensory cortex devoted to it

What are key points about spinal tracts and neural pathways?

• Major spinal tracts are part of multineuron pathways • Key points about spinal tracts and pathways: o Decussation: Most pathways cross from one side of CNS to other at some point o Relay: Most pathways consist of a chain of two or three neurons (a relay) that contribute to successive tracts of the pathway o Somatotopy: Most pathways exhibit a precise spatial relationship among the tract fibers that reflects the orderly mapping of the body; ex: fibers transmitting pain and temperature from sensory receptors in superior body regions lie medial to those from inferior body regions within the same tract o Symmetry: pathways are paired symmetrically (right and left), with a member of each pair on each side of the spinal cord or brain

What are the functions of the medulla oblongata?

• Medulla has crucial role as an autonomic reflex center involved in maintaining homeostasis • Many functions overlap with hypothalamus o Hypothalamus relays instructions via medulla • Functional centers of visceral motor nuclei in medulla include: • Cardiovascular center o Cardiac center adjusts force and rate of heart contraction to meet body's needs o Vasomotor center adjusts blood vessel diameter for blood pressure regulation • Respiratory centers o Generate respiratory rhythm o Control rate and depth of breathing (with pontine centers) • Various other centers regulate: o Vomiting o Hiccupping o Swallowing o Coughing o Sneezing

What is the structure and function of the arachnoid mater?

• Middle layer with spiderweb-like extensions • Loose brain covering that never dips into the sulci at the cerebral surface • Separated from the dura mater by a narrow serous cavity, the subdural space, which contains a film of fluid • Beneath the arachnoid membrane is the wide subarachnoid space which contains CSF and largest blood vessels of brain (because the arachnoid mater is fine and elastic, these blood vessels are poorly protected) • Spiderweb like extensions span this space and secure the arachnoid mater to the underlying pia mater • Knoblike projections of the arachnoid mater called arachnoid granulations protrude superiorly through the dura mater and into the superior sagittal sinus • These granulations absorb cerebrospinal fluid into the venous blood of the sinus

What is hydrocephalus?

• Ordinarily, CSF is produced and drained at a constant rate • However, if something (like a tumor) obstructs its circulation or drainage, CSF accumulates and exerts pressure on the brain (condition called hydrocephalus or "water on the brain") • In a newborn baby with hydrocephalus, the head enlarges because the skull bones haven't yet fused • In adults, because the skull is rigid, hydrocephalus is likely to damage the brain because the accumulating fluid compresses blood vessels and crushes the soft nervous tissue • Treated by inserting a shunt into the ventricles to drain excess fluid into the abdominal cavity

What is the somatosensory association cortex?

• Posterior to primary somatosensory cortex • Integrates sensory input (temperature, pressure, etc) from primary somatosensory cortex for understanding • Determines size, texture, and relationship of parts of objects being felt o Ex. Feeling object in pocket and knowing it's a coin or keys - people with damage to this area of their brain wouldn't be able to tell this without looking at it

What is the olfactory cortex?

• Primary olfactory (smell) cortex o Found in the medial part temporal lobes in a small region called the piriform lobe which is dominated by the hooklike uncus o Afferent fibers from smell receptors in the superior nasal cavity send impulses along the olfactory tracts that are ultimately relayed to the olfactory cortices o Involved in conscious awareness of odors o Remainder of primitive rhinencephalon, which includes all parts of the cerebrum that receive olfactory signals - the orbiotofrontal cortex, uncus, and associated regions located on or in the medial aspects of the temporal lobes, and the protruding olfactory tracts and bulbs that extend to the nose • During course of evolution most of the "old" rhinencephalon has taken on new functions concerned chiefly with emotions and memory • It has become part of the "newer" emotional brain called the limbic system • The only portions of the human rhinencephalon still devoted to small are the olfactory bulbs and tracts and the greatly reduced olfactory cortices

What are the visual areas of the brain?

• Primary visual (striate) cortex located on extreme posterior tip of occipital lobe but most of it is buried deep in the calcarine sulcus in the medial aspect of the occipital lobe o Largest cortical sensory area o Receives visual information from retinas • Visual association area surrounds primary visual cortex and covers much of the occipital lobe o Communicates with the primary visual cortex, uses past visual experiences to interpret visual stimuli (color, form, movement) • Enables us to recognize a flower or a person's face o We do our "seeing" with these cortical neurons o However, complex visual processing involves the entire posterior half of the cerebral hemispheres

What is Alzheimers?

• Progressive degenerative disease of brain that results in dementia (mental deterioration) • Key proteins appear to be misfolded and malfunction in a predictable way • Memory loss, short attention span, disorientation, eventual language loss, irritability, moodiness, confusion, hallucinations • Plaques of beta-amyloid peptides form in brain (they are cut from a normal membrane precursor protein, APP, by enzymes) • One form of Alzheimer's is caused by an inherited mutation in the gene for APP, which suggests that too much beta-amyloid may be toxic • Another hallmark is presence of neurofibrillary tangles (tau protein) inside neurons which interfere with transport mechanisms • As brain cells die, brain shrinks • Particularly vulnerable brain areas include the hippocampus, the basal forebrain, and association areas of the cortex (all regions involved in thinking and memory) • Loss of neurons in the basal forebrain is associated with a shortage of the neurotransmitter acetylcholine, and drugs that inhibit breakdown of acetylcholine slightly enhance cognitive function • Approx ½ people in nursing home have Alzheimer's • Between 5-15% of people over 65 develop and for up to ½ of those people over 85 it's a major contributing factor to their death

What are multimodal association areas?

• Receive inputs from multiple sensory areas and sends output to multiple areas • In general information flows as follows: 1. Sensory receptors 2. Primary sensory cortex 3. Sensory association cortex 4. Multimodal association cortex • Allows us to give meaning to information received, store in memory, tie to previous experience, and decide on actions • Sensations, thoughts, emotions become conscious: makes us who we are • Broadly divided into three parts: anterior association area, posterior association area, and limbic association area

What are the different diagnostic procedures for accessing CNS dysfunction?

• Reflex test assesses neural function; ex. Tap with reflex hammer stretches quadriceps tendon and anterior thigh muscles contract; knee-jerk response shows that spinal cord and upper brain centers are functioning normally • Abnormal response to reflex test may indicate intracranial hemorrhage, multiple sclerosis, or hydrocephalus • New imaging techniques have revolutionized the diagnosis of brain lesions • CT and MRI scanning techniques allow quick identification of most tumors, intracranial lesions, multiple sclerosis plaques, and areas of dead brain tissue (infarcts) • PET scans can localize brain lesions that generate seizures (epileptic tissue) • New radiotracer dyes that bind to beta-amyloid promise earlier, and more reliable diagnosis of Alzheimer's • Ex: CVA patient • First, determine of stroke is due to clot or bleed by imaging the brain, usually via with CT • If stroke due to clot, tPA can be used but only within the first hours • tPA can be giving through IV but longer window of time possible if applied directly to clot using catheter guided into position o To visualize the location of the clot and catheter, dye is injected to make arteries stand out in tan -ray, a procedure called cerebral angiography • Another test to assess risk of a CVA uses ultrasound; the carotid arteries of neck, which feed most of the cerebral vessels, often narrow with age and can lead to strokes o Cheaper and less invasive than angiography; can be quickly used to examine carotid arteries and measure their blood flow

What is the Reticular Activating System?

• Sends continuous impulses to cerebral cortex to keep it conscious and alert • May explain why some students like to study in busy environment - they are stimulated by bustling environment • Filters out unimportant stimuli - repetitive, familiar, or weak (~99% of all stimuli is not relayed to consciousness) • Ex. Don't notice watch encircling wrist but would notice if the clasp broke and it fell off • LSD interferes with these sensory dampers, promoting an often overwhelming sensory overload • Inhibited by sleep centers located in the hypothalamus and other neural regions as well as alcohol, sleep inducing drugs, and tranquilizers • Severe injury (such as knock-out punch that twists the brain stem) can result in permanent unconsciousness (coma) • Although RAS is central to wakefulness, some of its nuclei are also involved in sleep, which is later discussed • Reticular formation also has a motor arm • Some of its motor nuclei project to motor neurons in the spinal cord via the reticulospinal tracts and help control skeletal muscles during coarse limb movements • Other reticular motor nuclei, such as the vasomotor, cardiac, and respiratory centers of the medulla, are autonomic centers that regulate visceral motor functions

What are ventricles and what are they filled with?

Fluid-filled chambers that are continuous to one another and to central canal of spinal cord • Filled with cerebrospinal fluid (CSF) • Lined by ependymal cells (neuroglial cells)

What can hypothalamus disorders cause?

Hypothalamic disturbances cause a number of disorders such as: • Severe body wasting • Obesity • Dehydration • Emotional imbalances • Implicated in failure to thrive: delay in growth or development when child is deprived of a warm, nurturing relationship

What are the most serious conditions affecting the CNS to developing fetus?

• Most serious conditions affecting the CNS are congenital hydrocephalus (already discussed), anencephaly, and spina bifida

Which type of fiber allows the two cerebral hemispheres to "talk to each other"

Commissural fibers (which form commissures) allow the cerebral hemispheres to "talk to each other"

The hypothalamus oversees a branch of the peripheral nervous system. Which branch?

The autonomic nervous system

Name the components of the basal nuclei

The caudate nucleus, putamen, and globus pallidus

What are the pyramids of the medulla? What is the result of decussation of the pyramids?

The corticospinal (pyramidal) tracts, the large voluntary motor tracts descending from the motor cortex. The result of decussation (crossing over) is that teach side of the motor cortex controls the opposite side of the body.

The limbic system is sometimes called the emotional-visceral brain. Which part of the limbic system is responsible for the visceral connection?

The hypothalamus is part of the limbic system and also part of the autonomic (visceral) control center

What is the explanation for the cervical and lumbar enlargements of the spinal cord?

The nerves serving the limbs arise in the cervical and lumbar enlargements

What is a contusion?

brain bruising from concussion that causes permanent neurological damage • Individual may remain conscious with cortical contusions • Severe brain stem contusions almost always cause coma, lasting from hours to a lifetime because of injury to the RAS

What 5 things does analysis of the higher brain functions include?

o Language o Memory o Brain waves and EEGs o Consciousness o Sleep and sleep-wake cycles

What happens when spinal cord is transected?

• Transection (cross section) of the spinal cord at any level results in total motor and sensory loss in body regions inferior to damage o If transection occurs between T1 and L1, both lower limbs are affected resulting in paraplegia o If occurs in cervical region, all four limbs are affected resulting in quadriplegia • Hemiplegia, paralysis of one side of the body, usually reflects brain injury vs. spinal cord injury

What is the neural tube?

Brain and spinal cord begin as this embryonic structure

What is CTE?

chronic traumatic encephalopathy

How do tracts and nerves differ? How do nuclei and ganglia differ?

Nerve is a bundle of axons in the PNS while a tract is a bundle of axons in the CNS. A nucleus is a collection of neuron cell bodies in the CNS, whereas a ganglion is a collection of neuron cell bodies in PNS.

Mrs. Lee, a neurology patient, seldom smiles, has a shuffling, stooped gait, and often spills her coffee. What degenerative brain disorder might she have?

Parkinson's disease

What is the function of the spinal cord?

• Provides two-way communication to and from brain and body • Major reflex center: reflexes are initiated and completed at spinal cord

A brain surgeon is about to make an incision. Name all the tissue layers that she cuts through from the skin to the brain.

1) skin of the scalp 2) periosteum 3) skull bone 4) dura mater 5) arachnoid mater 6) pia mater

What are the 8 subdivisions of the sensory area?

1) • Primary somatosensory cortex 2) • Somatosensory association cortex 3) • Visual areas 4) • Auditory areas 5) • Vestibular (Equilibrium) Cortex 6) • OIfactory cortex 7) • Gustatory cortex 8) • Visceral Sensory Area

What are the 4 regions of the adult brain and what do they contain?

1. Cerebral hemispheres 2. Diencephalon, consisting of • Thalamus, Hypothalamus, Epithalamus 3. Brain stem, consisting of: • Midbrain • Pons • Medulla 4. Cerebellum

What is the brain stem?

All the midbrain and hindbrain structures, except the cerebellum

What is anencephaly?

Cerebrum and part of the brain stem never develop because the neural folds fail to fuse rostrally o Child is totally vegetative, unable to see, hear, or process sensory inputs o Muscles are flaccid, no voluntary movement is possible o Mental life does not occur, death occurs soon after birth

What do the 5 secondary brain vesicles become?

Each of the 5 secondary vesicles then develops rapidly to produce the major structures of adult brain • Greatest change occurs in the telencephalon, which sprouts two lateral swellings that look like Mickey Mouse's ears; these become the two cerebral hemispheres, referred to collectively as the cerebrum • Diencephalon specializes to form the hypothalamus, thalamus, epithalamus, and retina of eye • Mesencephalon becomes the midbrain • Metencephalon becomes the pons and cerebellum • Myelencephalon becomes the medulla oblongata

What are the nucleus of the hypothalamus?

Like thalamus, contains several functionally important nuclei 1) Paraventricular nucleus • Produces oxytocin hormone 2) Dorsomedial nucleus 3) Posterior hypothalamic nucleus 4) Ventromedial nucleus 5) Mammilary bodies • Paired, pealike nuceli that bulge ventrally from the hypothalamus, are relay stations in the olfactory pathways 6) Arcuate nucleus 7) Suprachiasmatic nucleus • Our "biological clock"; regulates sleep-wake cycles 8) Supraoptic nucleus • Produces ADH hormone 9) Anterior hypothalamic nucleus 10) Preoptic nucleus

What is white matter?

Mostly myelinated with some nonmyelinated axons

Where are the structures of the limbic system?

On medial aspects of cerebral hemispheres and diencephalon

What is a transient ischemic attack (TIA) and how is it different from a stroke?

TIA is a temporary loss of blood supply to brain tissue. Different from a stroke in that resulting impairment is fully reversible. Can be sign of impending CVA.

Three-year old Jessica proudly shows you she can wiggle her left big toe in the sand. Where precisely are the pyramidal cells that allow her to perform this movement? (name the side, lobe, and region of the brain). Where are the cell bodies of the neurons that these pyramidal cells synapse with?

The pyramidal cells are in the right primary motor cortex in the frontal lobe. They synapse with the cell bodies of the ventral horn neurons in the spinal cord.

What does rostral mean?

Toward the snout/anterior

What does caudal mean?

Toward the tail/posterior

What is basic pattern found in brain stem?

additional regions of gray matter (brain nuclei) buried within the white matter

What is paresthesias?

caused by damage to dorsal roots or sensory tracts of spinal cord o Leads to sensory function loss

What is the basic pattern found in spinal cord?

central cavity surrounded by gray matter with outer white matter

What is the anterior association area (prefrontal cortex)?

o Also called prefrontal cortex o In frontal lobe o Most complicated cortical region o Involved with intellect, cognition, recall, and personality o Contains working memory needed for abstract ideas, judgment, reasoning, persistence, and planning o Slow development of these abilities in children indicates that it matures slowly and development depends on feedback from social environment

Where is the medulla oblongata?

o Also known as medulla o Most inferior part of the brain stem o Blends into spinal cord at foramen magnum o Central canal of the spinal cord continues upward into the medulla, where it broadens out to form the cavity of the fourth ventricle • The dorsal ventricular wall is formed by a thin capillary-rich membrane that forms cerebral spinal fluid called a choroid plexus which is next to the cerebellum dorsally

What are brain waves, how can they be measured, and what are the different types?

o Brain waves reflect electrical activity of higher mental functions • Normal brain functions are continuous and hard to measure o Electroencephalogram (EEG) records electrical activity that accompanies brain function • Used for diagnosing epilepsy and sleep disorders and to determine brain death o EEG measures patterns of neuronal electrical activity generated by synaptic activity in cortex • Each person's brain waves are unique • Patterns change with age, sensory stimuli, brain disease, and chemical state of body o Measures wave frequency in Hertz (Hz), numbers of peaks per second (frequency of 1 Hz means 1 peak per second) o Amplitude or intensity of wave is represented by how high the wave peaks rise and how low the troughs dip; the amplitude of brain waves reflects the synchronous activity of many neurons and not the degree of electrical activity of individual neurons o Usually brain waves are complex and low amplitude o During some stages of sleep, neurons tend to fire synchronously, producing similar, high-amplitude brain waves o Can be grouped into four classes based on Hz: • Alpha waves: (8-13 Hz)—regular and rhythmic, low-amplitude, synchronous waves indicating an "idling" brain - awake and relaxed • Beta waves: (14-30 Hz)—rhythmic, less regular waves occurring when mentally alert, concentrating on some problem or visual stimulus • Theta waves: (4-7 Hz)—even more irregular; common in children and uncommon in awake adults but may appear when concentrating • Delta waves: (4 Hz or less)—high-amplitude waves of deep sleep and when reticular activating system is suppressed, as during anesthesia; indicates brain damage in awake adult o Brain waves whose frequency is too high or too low suggest problems with cerebral cortical functions, and unconsciousness occurs at both extremes o Because spontaneous brain waves are always present, even during unconsciousness and coma, their absence - a "flat EEG" - is clinical evidence of brain death

What is the structure and function of cerebrospinal fluid?

o Cerebrospinal fluid (CSF) forms a liquid cushion of constant volume around brain o Watery filtrate from blood plasma; contains less protein than plasma and its ion concentrations are different • Ex. CSF contains more Na+, Cl-, and H+ than blood plasma and less Ca2+ and K+ than blood plasma o Functions • Gives buoyancy to CNS structures • Reduces weight of brain by 97% by floating it so it is not crushed under its own weight • Protects CNS from blows and other trauma • Helps to nourish the brain and there is some evidence that it carries out chemical signals (such as hormone and sleep- and appetite-inducing molecules) from one part of the brain to another o Normal adult CSF volume of ~150 ml is replaced every 8 hours; about 500 ml of CSF is formed daily o Once produced, CSF moves freely through the ventricles • CSF enters the subarachnoid space via the lateral and median apertures in the walls of the fourth ventricle • Cilia of ependymal cells help to circulate CSF • In the subarachnoid space, CSF bathes the outer surfaces of the brain and spinal cord and then returns to the blood in the dural sinuses via the arachnoid granulations

What is consciousness?

o Consciousness involves: • Perception of sensation • Voluntary initiation and control of movement • Capabilities associated with higher mental processing (memory, logic, judgment, etc.) o Clinically defined on continuum that grades behavior in response to stimuli: alertness, drowsiness (lethargy), stupor, and coma o Current suppositions on consciousness • Involves simultaneous activity of large cortical areas • Superimposed on other neural activities • At any time, specific neurons and neuronal pools are involved both in localized activities (such as motor control) and cognition • Holistic and totally interconnected • Information for "thought" can be claimed from many locations in the cerebrum simultaneously; Ex; retrieval of a specific memory can be triggered by several routes - a smell, place, person, etc

What is the blood brain barrier?

o Helps maintain chemically stable environment for brain • Chemical variations that occur throughout rest of body could lead to uncontrollable neuron firings o Tight junctions between capillary endothelial cells are major component and keep brain separated from many bloodborne substances; least permeable capillaries in body o Substances in blood must past through three layers before gaining entry into neurons 1. Endothelium of capillary walls 2. Basal lamina around capillaries 3. Bulbous feet of astrocytes clinging to capillaries • Astrocyte "feet" are not themselves the barrier but play a role in its regulation because they supply required signals to the endothelial cells, causing them to make tight junctions o Barrier is selective, but not absolute • Bloodborne metabolic wastes, proteins, certain toxins, and most drugs are denied entry • Small, nonessential amino acids and potassium ions are not only prevented from entering the brain but are actively pumped from the brain across the capillary endothelium • Allows certain nutrients such as glucose, essential amino acids, and some electrolytes to certain nutrients to pass by diffusion • Barrier is ineffective against fats, fatty acids, oxygen, carbon dioxide, and other fat-soluble molecules that diffuse easily through all plasma membranes • Includes alcohol, nicotine, and anesthetics o Absent in some areas surrounding the third and fourth ventricles • Ex. Vomiting center of the brain stem which monitors the blood for poisonous substances and hypothalamus which regulates water balance, body temp, and other metabolic activities o Barrier is incomplete in newborn and premature infants, and potentially toxic substances can enter the CNS and cause problems not seen in adults o Injury to the brain, whatever the cause, may result in localized breakdown of the blood brain barrier which mostly likely reflect some change in the capillary endothelial cells or their tight junctions

What is the posterior association area?

o Large region in temporal, parietal, and occipital lobes o Plays role in recognizing patterns and faces and localizing us in space o Attention to an area of space or an area of one's own body is also a function o Involved in understanding written and spoken language (includes Wernicke's area)

What is the primary (somatic) motor cortex ?

o Located in precentral gyrus of frontal lobes o Contain pyramidal cells in gyri which are large neurons that allow conscious control of precise, skilled, skeletal muscle movements • Their long axons, which project to the spinal cord, form the massive voluntary motor tracts called pyramidal tracts or corticospinal tracts • All other descending motor tracts issue from brain stem nuclei and consist of chains of two or more neurons

What does memory involve in brain function?

o Memory: storage and retrieval of information o 4 different kinds of memory • Declarative memory of facts (names, faces, words, dates) • Procedural memory of skills (playing piano) • Motor memory of motor skills (riding a bike) • Emotional memory of experiences linked to an emotion (heart pounding when you hear rattlesnake) o Two stages of declarative memory storage: • Short-term memory (STM, or working memory): temporary holding of information • Limited to seven or eight pieces of information • Long-term memory (LTM) has limitless capacity • However long-term memories can be forgotten so our memory bank changes with time • LTM ability lessens with age o Of all of the sensory inputs that flood our cerebral cortex and are processed, only about 5% is selected for transfer to STM where STM acts as temporary holding bin for data we may or may not want to retain o Information may be then transferred from STM to LTM; factors affecting transfer from STM to LTM • Emotional state: best if alert, motivated, surprised, or aroused • For shocking events transfer is almost immediate • Norepinephrine, a neurotransmitter, is involved in memory processing of emotionally charged events and is released when we are excited or "stressed out", which helps explain this phenomenon • Rehearsal: repetition and practice • Association: tying new information with old memories • Automatic memory: subconscious information stored in LTM (ex. Remembering pattern of someone's tie) o Memories transferred to LTM take time to become permanent; memory consolidation involves fitting new facts into categories already stored in cerebral cortex • Hippocampus and cortical areas of temporal lobes, thalamus, and prefrontal cortex are involved in consolidation o Specific pieces of each memory are thought to be stored near regions of the brain that need them so that new inputs can be quickly associated with the old • Accordingly, visual memories are stored in the occipital cortex, memories of music in the temporal cortex, etc

Describe developmental aspect of CNS from just before birth to old age

o One of last CNS areas to mature is the hypothalamus • Since it contains body temperature regulatory centers, premature babies have problems controlling their loss of body heat and must be kept in incubators • PET scans reveal that the thalamus and somatosensory cotex are active in 5 day old baby but the visual cortex is not • Explains why infants of this age respond to touch but have poor vision • By 11 weeks more of cortex is active and baby can reach for a rattle • By 8 months, cortex is very active and child can think about what they see • Growth and maturation of nervous system continues throughout childhood and largely reflect progressive myelination • Myelination and neuromuscular coordination progress in a superior to inferior direction and proximal to distal direction • Brain reaches max weight in young adult; over next 60 years neurons are damaged and die and brain weight and volume steadily declines, however, the number of neurons lost is only a small %; remaining neurons can change their synaptic connections, providing for continued learning throughout life • Although age brings some cognitive declines in spatial ability, speed of perception, decision making, reaction time, and working memory, losses aren't significant in healthy individual until 7th decade • Then brain becomes increasingly fragile, presumable due to less efficient calcium clearance in aging neurons (elevated Ca2+ levels are neurotoxic) • However, math skills, verbal fluency, and ability to build on experience does not decline with age, and many people continue to enjoy intellectual lives and work at mentally demanding tasks their entire life • Fewer people over 65 than you may think exhibit dementia • Many cases of "reversible dementia" are caused by prescription drug side effects, low blood pressure, poor nutrition, hormone imbalances, depression, and/or dehydration • Alcoholics and professional boxers accelerate the brain shrinking process

What are different sleep disorders and how can they be treated?

o Narcolepsy: abrupt lapse into REM sleep from awake state • Episodes last about 15 minutes • Can occur without warning and often are triggered by a pleasurable event - joke or game of poker, for example • Orexins (aka hypocretins) are maybe being destroyed by immune system; replacing orexins may be key in future treatment o Insomnia: chronic inability to obtain amount or quality of sleep needed (which can vary from 4 to 9 hours a day in healthy people) • Often reflects normal age-related changes but most common cause is psychological disturbance • May be treated by blocking orexin action

What are the stages and importance of sleep cycles?

o Sleep: state of partial unconsciousness from which person can be aroused by stimulation o Cortical activity is depressed, but brain stem activity doesn't change o Stages of sleep: • Awake • REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs • NREM • Stage 1: Relaxation begins; EEG shows alpha waves, arousal is easy • Stage 2: Irregular EEG with sleep spindles (short high-amplitude bursts); arousal is more difficult • Stage 3: Sleep deepens; theta and delta waves appear; vital signs decline • Stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur o Types of sleep: • Two major types of sleep (defined by EEG patterns) that alternative throughout most of the sleep cycle • Non-rapid eye movement (NREM) o Broken into four stages • Rapid eye movement (REM) • We pass through first two stages of NREM during the first 30-45 minutes of sleep, then move into stages 3 and 4, referred to as slow-wave sleep • Frequency of waves declines, but amplitude increases • Blood pressure and heart rate progressively decrease o At ~90 minutes in, fourth stage ends, and REM sleep begins abruptly • EEG, heart rate, respiratory rate, blood pressure, and GI motility change • Temporary paralysis, except for rapid eye movements, keeps us from acting out our dreams • Oxygen consumption, heart rate, and breathing increase; increase can be greater than when awake • Most dreaming occurs in REM o How sleep is regulated • Alternating cycles of sleep and wakefulness reflect natural circadian (24-hour) rhythm • The hypothalamus is responsible for the timing of the sleep cycle • Its suprachiasmatic nucleus (a biological clock) regulates its preoptic nucleus (a sleep-inducing center) • By inhibiting the brain stem's reticular activating system (RAS), the preoptic nucleus puts the cerebral cortex to sleep • However, sleep is much more than simply turning off the arousal system • RAS centers not only help maintain the awake state but also mediate some sleep stages, especially dreaming sleep • Just before we wake, hypothalamic neurons release peptides called orexins, which act as "wake up" chemicals. • As a result, certain neurons of the brain stem reticular formation fire at maximal rates, arousing the sleepy cortex • A large number of chemical substances in the body cause sleepiness, but the relative importance of these various sleep-inducing substances is not known o Importance of sleep • Slow-wave sleep (NREM stages 3 and 4) presumed to be restorative stage, the time when most neural activity can wind down to basal levels • When deprived of sleep we spend more time than usual in slow-wave sleep • REM sleep may: • Give brain opportunity to analyze day's events and work through emotional events or problems • Eliminate unneeded synapses that were formed (dream to forget) • People deprived of REM sleep become moody and depressed • Daily sleep requirements decline with age • Infants 17-18 hours per day • Teens 8.5 - 9.5 • Adults 7 - 8 • Stage 4 sleep declines steadily and may disappear after age 60

What is somatotopy?

o Somatotopy: all muscles of body can be mapped to area on primary motor cortex • Most of the neurons in these gyri control muscles in body areas having the most precise control - face, tongue, and hands, and consequently these regions are disproportionately large • Motor homunculi: upside-down caricatures represent contralateral motor innervation of body regions (left side of brain controls right side of body and vice-versa) • Muscles are controlled by more than one area of the cortex and each area of the cortex controls more than one muscle; individual pyramidal motor neurons control muscles that work together in a synergistic way to perform a given movement (ex: neurons controlling arm and elbow movement work together but neurons controlling arm movement and trunk movement do not cooperate)

What is the gross anatomy of the spinal cord?

o Spinal cord is enclosed in vertebral column • Begins at the foramen magnum • Ends at L1 or L2 vertebra • 42 cm long (17 inches) • 1.8 cm or ¾ inch think

What is spastic paralysis?

occurs if only the upper motor neurons of the primary motor cortex (or their axons in the spinal cord) are damaged; spinal motor neurons remain intact and spinal reflex activity continues to stimulate the muscles irregularly; muscles remain healthy but are no longer subject to voluntary control; often muscles shorten permanently

What is flaccid paralysis?

occurs when spinal cord or ventral roots are injured; nerve impulses don't reach the affected muscles, which consequently cannot move voluntary or involuntary; muscles atrophy

What is a concussion?

temporary alteration in function; even mild can be damaging, especially if occur more than once

What is amyotrophic lateral sclerosis (ALS)?

• Aka Lou Gehrig's disease • Devastating neuromuscular condition that progressively destroys ventral horn motor neurons and fibers of the pyramidal tracts (a major motor pathway) • As disease progresses the victim loses the ability to speak, swallow, and breathe • Death typically occurs within 5 years • Caused by environmental and genetic factors • In 10% of cases mutations are inherited • Spontaneous mutations involved in the rest o Recently mutations have been localized to genes that are involved in RNA processing o Exact mechanism isn't clear but presence of excess extracellular glutamate suggest that excitetoxic cell death is involved • Riluzole, a drug that interferes with glutamate signaling, is the only available life-prolonging treatment

What is spinal shock?

• Anyone with spinal cord injury must be watched for symptoms of spinal shock, a transient period of functional loss that follows the injury o Immediately depresses all reflex activity caudal to the lesion site; bowel and bladder reflexes stop, blood pressure falls, and all muscles (somatic and visceral alike) below the injury are paralyzed and insensitive o Neural function usually returns within a few hours following injury; if function doesn't resume within 48 hours, paralysis is probably permanent

What is cerebral palsy?

• Cerebral palsy is neuromuclar disability in which the voluntary muscles are poorly controlled or paralyzed as a result of brain damage • May be caused by temporary lack of oxygen during difficult delivery or many other factors • In addition to spasticity, speech difficulties and other motor impairments, about ½ have seizures, ½ are intellectually disabled, and 1/3 have some degree of deafness • Visual impairment also common • Does not get worse over time but deficits are irreversible • Largest single cause of physical disability in children, affects 3 out of every 1,000 births

What is the spinal cord white matter?

• Composed of myelinated and nonmyelinated nerve fibers that allow communication between different parts of the spinal cord and between the cord and brain • Fibers run in 3 directions: • Ascending - up to higher centers (sensory inputs) • Descending - down to the cord from the brain or within the cord to lower levels (motor outputs) • Transverse - across from one side of the cord to the other (commissural fibers) • Ascending and descending tracts make up most of the white matter • White matter on each side of the cord is divided into three white columns, or funiculi, named according to their position as dorsal (posterior), lateral, and ventral (anterior) funiculi • Each funiculus contains several fiber tracts and each tract is made up of axons with similar destinations and functions • With a few exceptions, the names of the spinal tracts reveal both their origin and destination o Ascending Tracts • Dorsal white column • Fasciulus gracilis • Fasciculus cuneatus • Spinocerebellar tracts • Dorsal • Ventral • Spinothalamic tracts • Lateral • Ventral o Descending Tracts • Corticospinal tracts (pyramidal tracts) • Lateral • Ventral • Rubospinal tract • Reticulospinal tracts • Medial • Lateral • Vestibulospinal tract • Tectospinal tract

What types of amnesia can occur?

• Damage to hippocampus or surrounding temporal lobe structures on either side result in only slight memory loss • Bilateral destruction causes widespread amnesia • Anterograde amnesia: consolidated memories are not lost, but new inputs are not associated with old one • Person lives in the here and now • Memory of conversations from just 5 minutes before would not be remembered • Retrograde amnesia: loss of memories formed in the distant past

What is the structure and function of the pia mater?

• Delicate connective tissue that clings tightly to brain like plastic wrap, following every convolution • Contains many tiny blood vessels that feed brain • Small arteries entering the brain tissue carry ragged sheaths of pia mater inward with them for short distances

What is poliomyelitis?

• Destruction of ventral horn motor neurons by poliovirus • Virus typically enters body in feces-contaminated water • Early symptoms are fever, headache, muscle pain, and weakness, and loss of certain somatic reflexes • Later, paralysis develops and the muscles served atrophy • Victim may die from paralyzed respiratory muscles or cardiac arrest • Vaccines have nearly eradicated disease • Survivors often develop postpolio syndrome many years later from neuron loss • Symptoms include extreme lethargy, sharp burning pains in muscles, and progressive weakness and atrophy of muscles • Cause is unknown but likely because the compensating neurons for those damaged initially in the disease begin to degenerate as everyone continues to lose neurons throughout life

What are the fiber tracts of the limbic system?

• Fiber tracts connecting limbic system structures • Fornix ("arch") • Anterior commissure

What are the auditory areas of the brain?

• Found in the superior margin temporal lobes next to the lateral sulcus • Primary auditory cortex o Interprets information from inner ear as pitch, loudness, and location • Auditory association area o More posterior, stores memories of sounds and permits perception of sound stimulus o Wernicke's area includes parts of the auditory cortex

What is the visceral sensory area?

• In the cortex of the insula just posterior to the gustatory cortex • Involved in conscious perception of visceral sensations o Upset stomach, full bladder, feeling your lungs will burst if you hold your breath too long

What is meningitis, how is it diagnosed, and what can it lead to?

• Meningitis: inflammation of the meninges • May be caused by viral or bacterial infection that could dangerously spread to CNS • Meningitis is usually diagnosed by observing microbes in a sample of CSF obtained via lumbar puncture (spinal tap) • May spread to CNS, which would lead to inflammation of the brain, referred to as encephalitis

What is the brain protected by?

• Nervous tissue is very delicate but brain is protected by bones, membranes the meninges), and cerebrospinal fluid, and blood brain barrier protects the brain from harmful substances in the blood

What is paralysis?

• Paralysis: caused by damage to ventral roots or ventral horn cells o Leads to motor function loss o Two types of paralysis: flaccid or spastic

What is the composition of dura mater and its function?

• Strongest, leathery layer ("durable") • Made up of two layers of fibrous connective tissue • Periosteal layer attaches to inner surface of skull (the periosteum) - there is no dura periosteal layer surrounding the spinal cord • Meningeal layer: true external covering of brain o Continues caudally in the vertebral canal as the spinal dura mater • Two layers are mostly fused, but separate in certain areas to form dural venous sinuses that collect venous blood from the brain and direct it to the internal jugular veins of the neck • In several places, the meningeal dura mater extends inward to form flat partitions that subdivide the cranial cavity • These dural septa, which limit excessive movement of the brain within the cranium, include the following: o Falx cerebri: A large sickle-shaped fold that dips into the longitudinal fissure between the cerebral hemispheres; anteriorly it attaches to the crista galli of the ethmoid bone o Falx cerebelli: Continuing inferiorly from the posterior falx cerebri, this small midline partition runs along the vermis of the cerebellum o Tentorium cerebelli: Resembling a tent over the cerebellum, this nearly horizontal dural fold extends into the transverse fissure between the cerebral hemispheres (which it helps to support) and the cerebellum

What are projection fibers?

Vertical fibers that connect hemispheres with lower brain or spinal cord o Internal capsule: projection fibers on each side of brain stem form compact band • Passes between thalamus and some of basal nuclei o Corona radiata: projection fibers that radiate through cerebral white matter to cortex

What are the diencephalic structures of the limbic system?

• Anterior thalamic nuclei (flanking 3rd ventricle) • Hypothalamus • Mammillary body

What is the • Gustatory cortex ?

• Located in the insula just deep to the temporal lobe • Involved in perception of taste

What is a function brain system and what are two examples?

• Networks of neurons that work together but span wide areas of brain o Limbic system o Reticular formation

What is Parkinson's disease?

• Typically strikes people in their 50's and 60's • Degeneration of dopamine-releasing neurons of substantia nigra (midbrain nuclei) • Basal nuclei deprived of dopamine become overactive, resulting in tremors at rest (exhibited by "pill-rolling" movements of the fingers and wrist), a forward-bent walking posture and shuffling gait, and a stiff facial expression; they are slow at initiating and executing movement • Cause unknown, but theories include abnormalities in certain mitochondrial proteins and protein degradation pathways • Treatments include: • L-dopa (dopamine precursor) which passes through the blood barrier and converted into dopamine, which helps alleviate some symptoms • Mixing L-dopa with drugs that inhibit the breakdown of dopamine can prolong the effectiveness as more neurons die off and L-dopa becomes ineffective • Deep brain stimulation via implanted electrodes shuts down abnormal brain activity and can alleviate tremors (expensive and risky but works for patients who no longer respond to drug therapy) • Another future treatment possibly could be using gene therapy to insert into adult brain cells the genes that would cause them to secret the inhibitory neurotransmitter GABA; GABA then inhibits the abnormal brain activity just as the electrical stimulation does • Replacing dead or damaged cells by implanting stem cells is promising but results to date are no better than the conventional treatments

Developmental Aspects of the Nervous System

• Starting in the 3 week old embryo: 1. The ecotoderm (cell layer at the dorsal surface) thickens along the dorsal midline axis of the embryo to form the neural plate a. The neural plate invaginates, forming a neural groove flanked by neural folds 2. Small groups of enural fold cells migrate laterally from between the surface ectoderm and the neural groove, forming the neural crest a. Neural crest cells give rise (among other things) to some neurons destined to reside in ganglia 3. As the neural groove deepens, the superior edges of the neural folds fuse, forming the neural tube, which soon detaches from the surface ectoderm and sinks into a deeper position • The neural tube, formed by the 4th week of pregnancy, differentiates rapidly into the CNS o The brain forms rostrally, and the spinal cord develops from the caudal portion of neural tube • By week 6, each side of the developing spinal cord as 2 recognizable clusters of neuroblasts that have migrated outward from the original neural tube: a dorsal alar plate and a ventral basal plate o Alar plate neuroblasts become interneurons o Basal plate neuroblasts deveop into motor neurons and sprout axons that grow out to the effector organs o Axons that emerge from alar plate cells (and some basal palte cells) form the white matter of the cord o As development progresses, these plates expand dorsally and ventrally to produce the H-shaped central mas of gray matter in adult spinal cord o Neural crest cells that come to lie alongside the cord form the dorsal root ganglia containing sensory neuron cell bodies • These sensory neurons send their axons into the dorsal aspect of the cord o As brain and spinal cord grow and mature through prenatal period, gender specific areas appear • Ex: certain hypothalamic nuclei concerned with regulating typical male sexual behavior and clusters of neurons in the spinal cord that serve the external genitals are much larger in males • The key to CNS gender-specific development is whether or not the fetus is secreting testosterone • The causes of other gender differences in the adult brain (for example, in the corpus callosum and language and auditory areas of the cerebral cortex) are not as clear, and may be due to life experiences more than hormones o Maternal exposure to radiation, various drugs, alcohol, and infections can harm the development CNS, particularly during the initial formative stages • Ex: Rubella (German measles) often leads to deafness and other types of NS damage • Smoking decreases the amount of oxygen in blood and can cause brain damage