Chapter 12: The Central Nervous System

brain regions and organization

Four adult brain regions: (1) cerebral hemispheres (2) diencephalon (3) brain stem (midbrain, pons, and medulla oblongata) (4) cerebellum a slice of brain tissue reveals patterns of darker and lighter areas called: - Gray matter - consists of short, nonmyelinated neurons and neuron cell bodies - white matter - consists mostly of myelinated axons with some nonmyelinated axons, primarily in fiber tracts. The dense coating of fatty myelin is what gives white matter its color Gray and white matter have a unique distribution in the brain; the basic pattern of the CNS is a central cavity surrounded by gray matter, external to which is white matter (1) The spinal cord exhibits this basic pattern. This pattern changes with ascent into the brain stem (2) the brain stem has additional gray matter nuclei scattered within the white matter (3) the cerebral hemispheres and the cerebellum have an outer layer or "bark" of gray matter called a cortex

The spinal cord is

a reflex center and conduction pathway

somatosensory association cortex

lies just posterior to the primary somatosensory cortex and has many connections with it major function is to integrate sensory inputs (temperature, pressure, etc.) relayed to it via the primary somatosensory cortex to produce an understanding of an object being felt: its size, texture, and the relationship of its parts EX: when reaching into pocket, somatosensory association cortex uses stored memories of past sensory experiences to perceive the objects you feel as coins or keys; someone with damage to this area could not recognize these objects without looking for them

midbrain

located b/t the diencephalon and pons CEREBRAL PEDUNCLES form vertical pillars that seem to hold up the cerebrum the crus cerebri of each peduncle contains a large pyramidal motor tract descending toward the spinal cord the superior cerebellar peduncles (fiber tracts) connect the midbrain to the cerebellum dorsally running through it is the hollow cerebral aqueduct, which connects the third and fourth ventricles; it delineates the cerebral peduncles ventrally from the tectum (midbriain's roof); surrounded by the periaqueductal gray matter (involved in pain suppression and links the fear-perceiving amygdaloid body and ANS pathways that control the "fight-or-flight" response (also includes nuclei that control two cranial nerves, the oculomotor and the trochlear nuclei) nuclei scattered in the surrounding white matter of the midbrain (the CORPORA QUADRIGEMINA), the largest midbrain nuclei, raise four domelike protrusions on the dorsal midbrain surface SUPERIOR COLLICULI are visual reflex centers that coordinate head and eye movements when we visually follow a moving object, even if we are not consciously looking at it 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 your head toward an unexpected noise the substantia nigra and red nucleus (both pigmented nuclei embedded in each side of the midbrain white matter) - substantia nigra is located deep to the cerebral peduncle, its dark color reflects a high content of melanin pigment, a precursor of the neurotransmitter (dopamine) released by these neurons; functionally linked to the basal nuclei; - RED NUCLEUS hue is due to its rich blood supply and to the presence of iron pigment in its neurons; relay nuclei in some descending motor pathways that cause limb flexion, and they are embedded in the reticular formation, a system of small nuclei scattered through the core of the brain stem

Frontal eye field

located partially in and anterior to the premotor cortex and superior to Broca's area controls voluntary movements of the eyes

the cerebellum adjusts...

motor output, ensuring coordination and balance accounts for 11% of total brain mass located dorsal to the pons and medulla protrudes under the occipital lobes of the cerebral hemispheres, from which it is separated by the transverse cerebral fissure by processing inputs received from the cerebral motor cortex, various brain stem nuclei, and sensory receptors, the cerebellum provides the precise timing and appropriate patterns of skeletal muscle contraction for smooth, coordinated movements and agility needed for our daily living - driving, typing, and instruments cerebellar activity occurs subconsciously - we have no awareness of it

diagnostic procedures for assessing CNS dysfunction

reflex tests - a tap of reflex hammer stretches your quadriceps tendon and your anterior thigh muscles contract; produces knee-jerk response, which is a basic screening test for spinal cord and upper brain centers - abnormal responses to a reflex test may indicate such serious disorders as intracranial hemorrhage, multiple sclerosis, or hydrocephalus; they indicate that more sophisticated neurological tests are needed to identify the problem new imaging techniques have revolutionized the diagnosis of brain lesions - together various 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), and radio tracer dyes that bind to beta-amyloid allow earlier, more reliable diagnosis of alzheimer's disease

Spinal Cord - cross sectional anatomy

somewhat flattened from front to back and two grooves mark its surface - he wide VENTRAL (ANTERIOR) MEDIAN FISSURE and the narrower DORSAL (POSTERIOR) MEDIAN SULCUS; these grooves run the length of the cord and partially divide it into right and left halves central canal: cerebrospinal-fluid filled, runs the length of the spinal cord Gray Matter and Spinal Roots

gustatory cortex

taste a region involved in perceiving taste stimuli, located in the insula just deep to the temporal lobe

Sleep and Sleep-Wake Cycles

sleep is defined as a state of partial unconsciousness from which a person can be aroused by stimulation - distinguishes sleep from coma (a state of unconsciousness from which a person cannot be aroused by even the most vigorous stimuli) cortical activity is depressed during sleep, but brain stem functions continue, such as control of respiration, heart rate, and blood pressure; even environmental monitoring continues to some extent, as illustrated by the fact that strong stimuli ("things that go bump in the night") immediately arouse us TYPES OF SLEEP two types that alternate through most of the sleep cycle - non-rapid eye movement (NREM) sleep ** during the first 30-45 minutes of the sleep cycle, EEGs show that we pass through the first two stages of NREM sleep and into NREM stages 3 and 4 (called slow-wave sleep) ** as we pass through these stages and slip into deeper and deeper sleep, the frequency of the EEG waves declines, but their amplitude increases; blood pressure and heart rate also progressively decrease - about 90 minutes after sleep begins, after reaching stage 4, EEG pattern changes abruptly; becomes very irregular and backtracks quickly through the stages until alpha waves (more typical of the awake state) reappear, indicating the onset of REM sleep; this brain wave change is coupled with increases in heart rate, respiratory rate, and blood pressure and a decrease in GI motility - rapid eye movement (REM) sleep ** oxygen use by the brain is tremendous during REM - greater than during the awake state ** eyes move rapidly under the eyelids ** most of the body's skeletal muscles are actively inhibited and go limp ** most dreaming occurs; this temporary paralysis prevents us from acting out our dreams HOW SLEEP IS REGULATED - the alternating cycles of sleep and wakefulness reflect a natural circadian (24 hr) rhythm - hypothalamus is responsible for the timing of the sleep cycle - its suprachiasmatic nucleus (a biological clock) regulates its prep-tic nucleus (a sleep-inducing center) - by inhibiting the brain stem's reticular activating system, the rep-tic 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 (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 IMPORTANCE OF SLEEP - don't know why we sleep - during sleep we may consolidate new memories and discard memories that are no longer accessed (in other words, we forget) - presumed to be restorative - the time when most neural activity can wind down to basal levels - when deprived of sleep, we spend more time than usual in both REM and slow-wave sleep during the next sleep episode in an attempt to catch up

Folding during development determines...

the complex structure of the adult brain

Degenerative Brain Disorders

Alzheimer's disease (AD) Parkinson's disease Huntington's disease

olfactory cortex

PRIMARY OLFACTORY (SMELL) CORTEX lies on the medial aspect of the temporal lobe in a small region called the piriform love which is dominated by the hooklike uncus afferent fibers from smell receptors in the superior nasal cavity send impulses along the olfactory tracts that are ultimately relayed to the olfactory cortices; the outcome is conscious awareness of different odors this cortex is part of the primitive RHINENCEPHALON, which includes all parts of the cerebrum that receive olfactory signals - the orbitofrontal cortex, uncus, and associated regions located on or in the medial aspects of the temporal loves, and the protruding olfactory tracts and bulbs that extend to the nose - during course of evolution, most of the "old" rhinencephalon takes on new functions concerned chiefly with emotions and memory; become part of the "newer" emotional brain, called the limbic system explains why certain odors can evoke strong emotions

Huntington's disease

a fatal hereditary disorder strikes during middle age mutant huntington protein accumulates in brain cells and the tissue dies, leading 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; involuntary movements late in the disease, marked mental deterioration occurs progressive and usually fatal within 15 years the hyperkinetic manifestations of Huntington's disease are essentially the opposite of parkinson's disease (overstimulation rather than inhibition of the motor drive) usually treated with drugs that block, rather than enhance, dopamine effects

The Limbic System

a group of structures located on the medial aspect of each cerebral hemisphere and diencephalon; cerebral structures encircle the upper part of the brain stem includes the AMYGDALOID BODY (almond shaped nucleus that sits on the tail of the caudate nucleus, and other parts of the rhinencephalon in the diencephalon, the main limbic structures are the hypothalamus and the anterior thalamic nuclei; the FORNIX and other fiber tracts link these symptom regions together our emotional-visceral brain amygdaloid body and the anterior part of the cingulate gyrus important in emotions amygdaloid body is critical for responding to perceived threats (such as angry or fearful facial expressions) with fear or aggression the cingulate gyrus plays a role in expressing our emotions through gestures and in resolving mental conflicts when we are frustrated odors often trigger emotional reactions and memories; these responses reflex the origin of much of the limbic system in the primitive "smell brain"; reactions to odors often recall memories of emotion-laden events extensive connections b/t the limbic system and lower and higher brain regions allow the system to integrate and respond to a variety go environmental stimuli most limit system output is relayed through the hypothalamus (the neural clearinghouse for both autonomic (visceral) function and emotional response) - explains why some people under acute or unrelenting emotional stress fall prey to visceral illnesses (high blood pressure, heartburn) PSYCHOSOMATIC ILLNESSES: disorders with physical symptoms that originate from emotional causes interacts with the prefrontal cortex, has intimate relationship b/t our feelings (mediated by the emotional brain) and our thoughts (mediated by the cognitive brain) - as a result, we (1) react emotionally to things we consciously understand to be happening, and (2) are consciously aware of the emotional richness of our lives communication b/t the cerebral cortex and limbic system explains why emotions sometimes override logic and, conversely, why reason can stop us from expressing our emotions inappropriately HIPPOCAMPUS and amygdaloid body play a role in memory

cerebral hemisphere have three basic regions

a superficial cerebral cortex of gray matter, which looks gray in fresh brain tissue internal white matter basal nuclei, islands of gray matter situated deep within the white matter

medulla oblongata

aka the medulla the most inferior part of the brain stem STRUCTURE: - two longitudinal ridge scaled PYRAMIDS (formed by large pyramidal tracts descending from the motor cortex) - decussation of the pyramids : crossover point where most fibers cross over to the opposite side before continuing into the spinal cord; results with each cerebral hemisphere chiefly controls the voluntary movements of muscles on the opposite side of the body - inferior cerebellar peduncles are fiber tracts that connect the medulla to the cerebellum dorsally - the olives are oval swellings caused by the wavy folds of gray matter of the underlying INFERIOR OLIVARY NUCLEI (these relay sensory info on the degree of stretch in muscles and joints to the cerebellum - rootlets of the hypoglossal nerves emerge from the groove b/t the pyramid and olive on each side of the brain stem - other cranial nerves associated w/ the medulla are the glossopharyngeal nerves and vagus nerves - the fibers of the vestibulocochlear nerves synapse with the COCHLEAR NUCLEI (auditory relays) and w/ numerous VESTIBULAR NUCLEI (which mediate responses that maintain equilibrium) in both the pons and medulla - houses several nuclei associated w/ ascending sensory tracts (the NUCLEUS GRACILIS and NUCLEUS CUNEATUS) which serve as relay nuclei in a pathway by which general somatic and proprioceptive sensory info ascends from the spinal cord to the somatosensory cortex FUNCTIONS: - autonomic reflex center involved in maintaining homeostasis - contains these important functional groups of visceral motor nuclei: *** CARDIOVASCULAR CENTER: includes the CARDIAC CENTER, which adjusts the force and rate of heart contraction to meet the body's needs, and the VASOMOTOR CENTER, which changes blood vessel diameter to regulate blood pressure *** RESPIRATORY CENTERS: generate the respiratory rhythm and (together with pontine centers) control the rate and depth of breathing *** VARIOUS OTHER CENTERS: additional centers regulate such activities as vomiting, hiccuping, swallowing, coughing, and sneezing

Cerebral Cortex: sensory areas

areas concerned with conscious awareness of sensation, the sensory areas of the cortex, occur in the parietal, insular, temporal, and occipital lobes -primary somatosensory cortex -somatosensory association cortex -visual areas -auditory areas -vestibular (equilibrium) cortex -olfactory cortex -gustatory cortex -visceral sensory area

brain folding

b/c the brain grows more rapidly than the membranous skull that contains it, it folds up to occupy the available space the midbrain and cervical flexures move the forebrain toward the brain stem the cerebral hemisphere 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

cerebellar anatomy

bilaterally symmetrical VERMIS connects its two apple-sized cerebellar hemisphere medially; surface is heavily convoluted, with fine, transversely oriented pleat like gyri (FOLIA) deep fissures subdivide each hemisphere into anterior, posterior, and flocculonodular lobes flocculonodular lobes cannot be seen in a surface view has a thin outer cortex of gray matter, internal white matter, and small, deeply situated, paired masses of gray matter (dentate nuclei) several types of neurons populate the cerebellar cortex, including PURKINJE CELLS (extensively branched dendrites, are the only cortical neurons that send axons through the white matter to synapse with the central nuclei of the cerebellum) distance white pattern in the cerebellum resembles a branching tree, called the ARBOR VITAE anterior and posterior lobes of cerebellum have 3 sensory maps of the entire body as indicated by the homunculi. 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 later almost 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 flocculonodular lobes receive inputs from the equilibrium apparatus of the inner ears, and adjust posture to maintain balance

Brain Wave Patterns and the EEG

brain waves reflect the electrical activity on which higher mental functions are based because normal brain function involves continuous electrical activity of neurons ELECTROENCEPHALOGRAM (EEG): records some aspects of the above activity; used for diagnosing epilepsy and sleep disorders, in research on brain function, and to determine brain death - made by placing electrodes on the scalp and connecting the electrodes to an apparatus that measures voltage differences b/t various cortical areas BRAIN WAVES; patterns of neuronal electrical activity recorded; generated by synaptic activity at the surface of the cortex, rather than by action potentials in the white matter each of us has a brain wave pattern that is as unique as our fingerprints - can group them into the four frequency classes - each wave is a continuous train of peaks and troughs, and the wave frequency, expressed in Herts (Hz) is the number of peaks in one second. A frequency of 1 Hz means that one peak occurs each second the amplitude or intensity of any wave is represented by how high the wave peaks rise and how low the troughs dip. - reflects the synchronous activity of many neurons and not the degree of electrical activity of individual neurons brain waves are complex and low amplitude during some stages of sleep, neurons tend to fire synchronously, producing similar, high-amplitude brain waves Alpha Waves: relatively regular and rhythmic, low-amplitude, synchronous waves; indicate a brain that is "idling" (a calm, relaxed state of wakefulness) Beta Waves: rhythmic, but less regular than alpha waves and with a higher frequency; occur when we are mentally alert, as when concentrating on some problem or visual stimulus Theta Waves: more irregular; common in children, uncommon in awake adults but may appear when concentrating Delta Waves: high-amplitude waves seen during deep sleep and when the reticular activating system is suppressed, such as during anesthesia; in awake adults, they indicate brain damage brain waves whose frequency is too high or too low to suggest problems with cerebral cortical functions, and unconsciousness occurs at both extremes since spontaneous brain waves are always present, even during consciousness and coma, their absence -a "flat EEG" - is clinical evidence of brain death

second - order neurons

cell bodies reside in the dorsal horn of the spinal cord or in medullary nuclei they transmit impulses to the thalamus or the cerebellum where they synapse

Thalamus

consist of bilateral egg-shaped nuclei, which form the superolateral walls of the third ventricle inter thalamic adhesion (intermediate mass) connects the nuclei greek word meaning "inner room" makes up 80% of the diencephalon the relay station for information coming into the cerebral cortex large number of nuclei, most named according to their location; each nucleus has a functional specialty, and each projects fibers to and receives fibers from a specific region of the cerebral cortex afferent impulses from all senses and all parts of the body converge on the thalamus and synapse with at least one of its nuclei 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 assiociation areas as the afferent impulses reach the thalamus, we have a crude recognition of the sensation as pleasant or unpleasant; however, specific stimulus localization and discrimination occur in the cerebral cortex in addition to sensory inputs, virtually all other inputs ascending to the cerebral cortex funnel through thalamic nuclei, including: - inputs that help regulate emotion and visceral function from the hypothalamus - instructions that help direct the activity of the motor cortices from the cerebellum and basal nuclei - inputs for memory or sensory integration that are projected to specific association cortices (via pulvinar, lateral dorsal, and lateral posterior nuclei) plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory

spinocerebellar pathways

consists of the ventral and dorsal spinocerebellar tracts they convey information about muscle or tendon stretch to the cerebellum, which uses this info to coordinate skeletal muscle activity do not contribute to conscious sensation the fibers of the spinocerebellar pathways either do not decussate or else cross over twice (thus undoing the decussation)

ventricles

continuous with one another and with the central canal of the spinal cord the hollow ventricular chambers are filled with cerebrospinal fluid and lined by ependymal cells (type of neuroglia) the paired LATERAL VENTRICLES, one deep within each cerebral hemisphere, are large C-shaped chambers that reflect the pattern of cerebral growth; anteriorly, the lateral ventricles lie close together, separated only by a thin median membrane called the SEPTUM PELLUCIDUM ("transparent wall") - each lateral ventricle communicates with the narrow THIRD VENTRICLE in the diencephalon via a channel called an INTERVENTRICULAR FORAMEN Third ventricle is continuous with the FOURTH 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 - three openings mark the walls of the fourth ventricle: *** the paired lateral apertures in its side walls *** the median aperture in its roof these apertures connect the ventricles to the subarachnoid space (a fluid-filled space surrounding the brain)

The cerebral hemispheres consist of...

cortex, white matter, and the basal nuclei cerebral hemispheres: form the superior part of the brain and are the most conspicuous parts of an intact brain; together they account for about 83% of total brain mass; cover and obscure the diencephalon and the top of the brain stem gyri: elevated ridges of tissue separated by sulci sulci: shallow grooves - mark nearly the entire surface of the cerebral hemispheres - divide hemisphere into 5 lobes: frontal, parietal, temporal, occipital, and insula (all except for last are cranial bones) -central sulcus lies in frontal plane and separates the frontal lobe from the parietal lobe - precentral gyrus border the central sulcus anteriorly and the post central gyrus posteriorly -parieto-occipital sulcus separates the occipital lobe from the parietal lobe -lateral sulcus outlines the flaplike temporal love and separates it from the parietal and frontal loves - insula is buried deep within the lateral sulcus and form part of its floor; covered by portions of the temporal, parietal, and frontal lobes fissures: deeper grooves - separate large regions of the brain median longitudinal fissure - separates the cerebral hemispheres transverse cerebral fissure - separates the cerebral hemispheres from the cerebellum

four key parts to spinal tracts and pathways

decussation - most pathways cross from one side of the CNS to the other (decussate) at some point along their journey relay - most pathways consist of a chain of two or three neurons (A relay) that contribute to successive tracts of the pathway somatotopy - most pathways exhibit somatotopy, a precise spatial relationship among the tract fibers that reflects the orderly mapping of the body. EX: fibers transmitting pain and temperature information from sensory receptors in superior body regions lie medial to those from inferior body regions within the same tract symmetry - all pathways and tracts are paired symmetrically (right and left) with a member of the pair present on each side of the spinal cord or brain

auditory areas

each PRIMARY AUDITORY CORTEX is located in the superior margin of the temporal love next to the lateral sulcus. Sound energy exciting the hearing receptors of the inner ear causes impulses to be transmitted to the primary auditory cortex, where they are interpreted as pitch, loudness, and location posterior AUDITORY ASSOCIATION CORTEX then permits the perception of the sound stimulus, which we "hear" as speech, a scream, music, thunder, and so on; memories of sounds heard in the past appear to be stored here for reference; WERNICKE'S AREA includes parts of the auditory cortex

The Spinal Cord gross anatomy and protection

enclosed in the vertebral column extends from the foramen magnum of the skull to the first or second lumbar vertebra provides a two-way conduction pathway to and from the brain major reflex center: spinal reflexes are initiated and completed at the spinal cord level protected by bone, meninges, and cerebrospinal fluid the single-layered SPINAL DURA MATER is not attached to the bony walls of the vertebral column EPIDURAL SPACE: b/t the bony vertebrae and the spinal dura mater; filled with a soft padding of fat and a network of veins cerebrospinal fluid fills the subarachnoid space b/t the arachnoid and pia mater meninges subarachnoid space within the meningeal sac inferior to this point provides an ideal spot for removing cerebrospinal fluid for testing (called LUMBAR PUNCTURE) little to no danger of damaging the spinal cord or spinal rifts beyond L3 because the spinal cord is absent there and the delicate roots drift away from the point of needle insertion CONUS MEDULLARIS: inferiorly, the spinal cord terminates in a tapering cone-shaped structure FILUM TERMINALE: a fibrous extension of the conus covered by pia mater, extends inferiorly from the conus medullaris to the coccyx, where it anchors the spinal cord so it is not jostled by body movements CERVICAL and LUMBAR ENLARGEMENTS: areas of enlargement where the nerves serving the upper and lower limbs arise on the spinal cord 31 pairs of spinal nerves (part of PNS) each spinal cord segment is designated by the paired spinal nerves that arise from it - EX: the first thoracic cord segment (T1) is where the first thoracic nerves emerge from the spinal cord each nerve pair defines a segment of the cord, but the cord is continuous throughout its length and its internal structure changes gradually each nerve exits the vertebral column by passing adjacent to its corresponding vertebra via the intervertebral foramen, and travels to the body region it serves - the spinal cord segments are located superior to where their corresponding spinal nerves emerge through the intervertebral foramina CAUDA EQUINA: the collection of nerve roots at the inferior end of the vertebral canal

Consciousness

encompasses perception of sensations, voluntary initiation and control of movement, and capabilities associated with higher mental processing (memory, logic, judgement, perseverance, etc) defined on a continuum that grades behavior in response to stimuli as (1) alertness, (2) drowsiness or lethargy (which proceeds to sleep) (3) stupor, and (4) coma - alertness is the highest state of consciousness and cortical activity, and coma the most depressed difficult to define; reducing our response to a glorious sunset to a series of interactions b/t dendrites, axons, and neurotransmitters does not capture what makes that event so special suppositions: - consciousness involves simultaneous activity of large areas of the cerebral cortex - it is superimposed on other types of neural activity; at any time specific neurons and neuronal pools are involved both in localized activities (such as motor control) and in cognition - it is holistic and totally interconnected; info 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, a place, a particular person, etc.

The Reticular Formation

extends through the central core of the medulla oblongata, pons, and midbrain composed of loosely clustered neurons in what is white matter - neurons form three broad columns along the length of the brain stem (1) the midline RAPHE NUCLEI flanked laterally by (2) the MEDIAL (LARGE CELL) GROUP OF NUCLEI and (3) the LATERAL (SMALL CELL) GROUP OF NUCLEI reticular neurons have furlong axonal connections individual reticular neurons project to the hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord, making reticular neurons ideal for governing the arousal of the brain as a whole RETICULAR ACTIVATING SYSTEM (RAS): the neurons of the part of the reticular formation - send a continuous stream of impulses to the cerebral cortex, keeping the cortex left and conscious and enhancing its excitability impulses from all the gray ascending sensory tracts synapse with RAS neurons, keeping the active and enhancing their arousing effect on the cerebrum RAS also filters this flood of sensory inputs; repetitive, familiar, or weak signals are filtered out, but unusual, significant, or strong impulses do reach consciousness The RAS and the cerebral cortex disregard 99% of all sensory stimuli is unimportant; if this filtering does not occur, the sensory overload would drive us crazy -the drug LSD interferes with these sensory dampers, promoting an often overwhelming sensory overload RAS is inhibited by sleep centers located in the hypothalamus and other neural regions, and is depressed by alcohol, sleep-induced drugs, and tranquilizers although RAS is central to wakefulness, some of its nuclei are involved in sleep 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

cerebellar processing

fine-tunes motor activity as follows: 1. the motor areas of the cerebral cortex, via relay nuclei in the brain stem, notify the cerebellum of their intent to initiate voluntary muscle contractions 2. at the same time, the cerebellum receives info from proprioceptors throughout the body (regarding tension in the muscles and tendons, and joint position) and from visual and equilibrium pathways; this info enables the cerebellum to evaluate body position and momentum - where the boy is and where it is going 3. the cerebellar cortex calculates the best way to coordinate the force, direction, and extent of muscle contraction to prevent overshoot, maintain posture, and ensure smooth, coordinated movements 4. Then, via the superior peduncles, the cerebellum dispatches to the cerebral motor cortex its "blueprint" for coordinating movement. Cerebellar fibers also send info to brain stem nuclei, which in turn influence motor neurons of the spinal cord cerebellum continually compares the body's performance with the higher brain's intention and sends out messages to initiate appropriate corrective measures cerebellar injury results in loss of muscle tone and clumsy, uncertain movements

Epithalamus

forms the roof of the third ventricle PINEAL GLAND or BODY extends from its posterior border and visible externally - secretes hormone melatonin and helps regulate the sleep-wake cycle posterior commissure forms the caudal border of the epithalamus

third - order neurons

have cell bodies in the thalamus relay impulses to the somatosensory cortex of the cerebrum (there are no third - order neurons in the cerebellum)

traumatic brain injuries

head injuries are a leading cause of accidental death in North America EX: you forget to fasten your seatbelt and then rear-end another car; head moves and then stops suddenly and hits the windshield; brain damage is caused not only by localized injury at the site of the blow, but also by the ricocheting brain hitting the opposite end of the skull CONCUSSION: an alteration in brain function, usually temporary, following a blow to the head; victim may be dizzy or lose consciousness - typically mild and short-lived mild concussions can be damaging, and multiple concussions over time produce cumulative damage CONTUSION: more serious concussions that can bruise the brain and cause permanent neurological damage - in cortical contusions, individual may remain conscious - severe brain stem contusions cause coma, lasting from hours to a lifetime b/c of injury to the reticular activating system following a head injury, death may result from SUBDURAL or SUBARACHNOID HEMORRHAGE (bleeding from ruptured vessels into those spaces) - individuals who are initially lucid and then begin to deteriorate neurologically may be hemorrhaging intracranially blood accumulating in the skull increases intracranial pressure and compresses brain tissue - if the pressure forces the brain stem inferiorly through the foramen magnum, control of blood pressure, heart rate, and respiration is lost intracranial hemorrhages are treated by surgically removing the hematoma (localized blood mass) and preparing the ruptured vessels CEREBRAL EDEMA: swelling of the brain; aggravates the injury; can be fatal in and of itself

indirect pathways

include the brain stem motor nuclei and all motor pathways except the pyramidal pathways formerly lumped together as the extrapsramidal system because their nuclei of origin were presumed to be independent of ("extra to") the pyramidal tracts pyramidal tract neurons are now known to project to and influence the activity of most "Extrapyramidal" nuclei, so modern anatomists refer to them as indirect, or multi neuronal, pathways or simply use the names of the individual motor pathways complex and multi synaptic. most involved in regulating: - axial muscles that maintain balance and posture -muscles controlling coarse limb movements -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 the reticulospinal and vestibulospinal tracts maintain balance by varying the tone of postural muscles the rubrospinal tracts control flexor muscles, whereas the tectospinal tracts and the superior colliculi mediate head movements in response to visual stimuli

Cerebral Cortex: Motor areas

lie in the posterior part of the frontal lobes: - primary motor cortex -premotor cortex - broca's area - frontal eye field

Broca's area

lies anterior to the inferior region of the premotor area - considered to be (1) present in one hemisphere only (usually the left) and (2) a special motor speech area that directs the muscles involved in speech production -also becomes active as we prepare to speak and even as we think about (plan) many voluntary motor activities other than speech

dorsal column - medial lemniscal pathways

mediate precise, straight-through transmission of inputs from a single type (or a few related types) of sensory receptor that can be localized precisely on the body surface, such as discriminative touch and vibrations transmits information from proprioceptors formed by the paired tracts of the dorsal white column of the spinal cord - FASCICULUS CUNEATUS and FASCICULUS GRACILIS - and the MEDIAL LEMNISCUS medial lemniscus arises in the medulla and terminates in the thalamus, from there impulses are forwarded to specific areas of the somatosensory cortex

The brain stem consists of

midbrain pons medulla oblongata account for 2.5% of total brain mass tissues consist of 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 brain stem centers produce the rigidly programmed, automatic behaviors necessary for survival provides a pathway for fiber tracts running between higher and lower neural centers brain stem nuclei are associated with 10 of the 12 pairs of cranial nerves, so the brain stem is heavily involved with innervating the head

Cerebral Cortex: multimodal association areas

most of the cortex consists of complexly connected multimodal association areas that receive inputs from multiple senses and send outputs to multiple areas information flows as follows: sensory receptors -- primary sensory cortex -- sensory association cortex -- multimodal association cortex allows us to give meaning to the information that we receive, store it in memory, tie it to previous experience and knowledge, and decide what action to take; those decisions are related to the premotor cortex, which in turn communicates with the motor cortex seems to be where sensations, thoughts, and emotions become conscious; makes us who we are along with feelings of panic, these perceptions are woven into a seamless whole, which recalls instructions about what to do in this situation; results in premotor and primary motor cortices direct your legs to propel you to shower divided into three parts: - anterior association area *** in the frontal lobe *** aka prefrontal cortex *** most complicated cortical region; involved w/ intellect, complex learning abilities (cognition), recall, and personality *** contains working memory, necessary for abstract ideas, judgement, reasoning, persistence, and planning; abilities develop slowly in children, which implies that the prefrontal cortex matures slowly and depends heavily on feedback from our social environment - posterior association area *** large region encompassing parts of the temporal, parietal, and occipital lobes *** plays role in recognizing patterns and faces, localizing us and our surroundings in space, and binding different sensory inputs into a coherent whole (Awareness of a scene for example) *** attention to an area of space or an area of one's own body *** involved in understanding written and spoken language - limbic association area *** includes the cingulate gyrus, parahippocampal gyrus, and hippocampus *** provides the emotional impact that makes a scene important to us (EX. sense of danger when acid splashes legs) *** hippocampus establishes memories that allow us to remember this incident

Hypothalamus

named for its position below the thalamus caps the brain stem and forms the inferolateral walls of the third ventricle contains many functionally important nuclei MAMMILLARY BODIES relay stations in the olfactory pathways INFUNDIBULUM, a stalk of hypothalamic tissue that connects the PITUITARY GLAND to the base of the hypothalamus the main visceral control center of the body and is vitally important to overall body homeostasis few tissues in the body escape its influence. Its chief homeostatic roles are to: - control the autonomic nervous system ** hypothalamus regulates ANS activity by controlling the activity of centers in the brain stem and spinal cord; influences blood pressure, rate and force of heartbeat, digestive tract motility, eye pupil size, etc. - instate physical responses to emotions ** hypothamalus lies at the heart of the limbic system (emotional part of the brain); contains nuclei involved in perceiving pleasure, fear, and rage, and those involved in biological rhythms and drives (Sex drives); acts through ANS pathways to initiate most physical expressions of emotion (EX: a fearful person has a pounding heart, high blood pressure, pallor, sweating, and a dry mouth) - regulate body temperature ** hypothalamus has body's thermostat; hypothalamic neurons motor blood temp and receive input from other thermoreceptors in the brain and body periphery; hypothalamus initiates cooling (sweating) or heat-generating actions (Shivering) as needed to maintain a relatively constant body temp -regulate food intake ** in response to changing blood levels of certain nutrients (glucose and amino acids) or hormones (CCK, ghrelin, etc.), hypothalamus regulates feelings of hunger and satiety -regulate water balance and thirst ** hypothalamic neurons called OSMORECEPTORS are called when body fluids become too concentrated; they excite hypothalamic nuclei that trigger the release of antidiuretic hormone (ADH) from the posterior pituitary; ADH causes the kidney's to retain water; same conditions stimulate hypothalamic neurons in the thirst center, causing us to feel thirsty and drink more fluids - regulate sleep-wake cycles ** acting w/ other brain regions, the hypothalamus helps regulate sleep; its suprachiasmatic nucleus sets the timing of the sleep cycle primarily in response to daylight-darkness cues received from the visual pathways - control endocrine system function ** acts as the helmsman of the endocrine system in two important ways: releasing and inhibiting hormones control the secretion of hormones by the anterior pituitary gland AND its supraoptic and paraventricular nuclei produce the hormones ADH and oxytocin

cognitive functions of the cerebellum

neuroanatomy, imaging studies, and observations of patients w/ cerebellar injuries suggest that the cerebellum also plays a role in thinking, language, and emotion as in the motor system, the cerebellum may compare the actual output of these systems with the expected out and adjust accordingly

direct (pyramidal) pathways

originate mainly with the pyramidal cells located in the precentral gyri these neurons send impulses through the brain stem via the large pyramidal (corticospinal) tracts 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 the ventral horn neurons activates the skeletal muscles with which they are associated. The direct pathway primarily regulates fast and fine (or skilled) movements such as texting or playing an instrument

spinothalamic pathways

receive input from many different types of sensory receptors and make multiple synapses in the brain stem consist of the lateral and ventral (anterior) spinothalamic tracts fibers cross over in the spinal cord the fibers primarily 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

primary somatosensory cortex

resides in the post central gyrus of the parietal lobe, posterior to the primary motor cortex neurons in this gyrus receive info from the general (Somatic) sensory receptors in the skin and from proprioceptors, located in skeletal muscles, joints, tendons, inform the brain of the body's position in space neurons then identify the body region being stimulated, an ability called spatial discrimination the amount of sensory cortex devoted to a particular body region is related to that region's sensitivity (how many receptors it has), not its size the face (especially the lips) and fingertips are the most sensitive body areas, so these regions are the largest parts of the somatosensory homunculus

Parkinson's Disease

results from a degeneration of the dopamine-releasing neurons of the substantia nigra; as these neurons deteriorate, the dopamine-deprived basal nuclei they target become overactive afflicted individuals have a persistent tremor at rest, a forward bent walking posture and shuffling gait, and a stiff facial expression; they are slowly initiating and executing movement becomes more common with age cause is still unknown, but multiple factors may interact to destroy dopamine-releasing neurons -recent evidence points to abnormalities in certain mitochondrial proteins and protein degradation pathways - the drug L-dopa helps to alleviate some symptoms; it passes through the blood brain barrier and is then converted into dopamine - however, as more neurons die off, L-dopa becomes ineffective; mixing it with other drugs can prolong its effectiveness - early in the disease, these drugs alone slow the neurological deterioration to some extend and delay the need to administer L-dopa deep brain stimulation via implanted electrodes shuts down abnormal brain activity and can alleviate tremors; this treatment (for those who no longer respond to drug therapy) is expensive and risky, but it works - another treatment possible is to use gene therapy to insert into adult brain cells the genes that would cause them to secrete the inhibitory neurotransmitter GABA which 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 more conventional treatments

Cerebral White Matter

second of the three basic regions of each cerebral hemisphere responsible for communication b/t cerebral areas and b/t the cerebral cortex and lower CNS centers consists largely of myelinated fibers bundled into large tracts; they're classified according to the direction in which they run as association, commissural, or projection association fibers - connect different parts of the same hemisphere - short association fibers connect adjacent gyri - long association fibers are bundled into tracts and connect different cortical lobes - run horizontally commissural fibers - connect corresponding gray areas of the two hemispheres - COMMISSURES allow the two hemispheres to function as a coordinated whole - largest commissure is the CORPUS CALLOSUM - less prominent examples are the ANTERIOR and POSTERIOR COMMISSURES projection fibers - either enter the cerebral cortex from lower brain or cord centers or descend from the cortex to lower areas - sensory information reaches the cerebral cortex and motor output leaves it through these projection fibers; they tie the cortex to the rest of the nervous system and to the body's receptors and effectors - run vertically - at the top of the brain, these fibers on each side form a compact band (the INTERNAL CAPSULE) that passes b/t the thalamus and some of the basal nuclei; superior to that point, the fibers radiate fanlike through the cerebral white matter to the cortex (called the CORONA RADIATA)

Neuronal pathways carry?

sensory and motor information to and from the brain all major spinal tracts are part of multi neuron pathways that connect the brain to the body periphery; these ascending and descending pathways contain not only spinal cord neurons but also parts of peripheral neurons and neurons in the brain the pathways to and from the head are similar to those of the trunk and limbs with TWO EXCEPTIONS: - the axons of the tracts servicing the head are located in cranial nerves - the cell bodies are located in the brain stem rather than in the spinal cord diffusion tensor MRI allows visualization of fiber tracts in the CNS - these images are artificially colored to show the direction of the fiber

Cerebrovascular Accidents (CVAs)

single most common nervous system disorder and 3rd leading cause of death in North America also called strokes occurs when blood circulation to a brain area is blocked and brain tissue dies of ISCHEMIA (a reduction of blood supply that impairs delivery of oxygen and nutrients) most common cause is a blood clot that blocks a cerebral artery; a clot can originate outside the brain (EX: the heart) 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 CVA are paralyzed on one side of the body (hemiplegia); others commonly exhibit sensory defects or have difficult understanding or vocalizing speech Some patients recover at least part of their lost faculties, b/c undamaged neurons sprout new branches that spread into the injured area and take over some lost functions if motor function is impaired, PT should start ASAP to prevent muscle contractures (abnormally shortened muscles due to differences in strength b/t opposing muscle groups) not all strokes are "completed" ; temporary episodes of transient ischemic attacks (TIAs, reversible cerebral ischemia) are common - last 5 to 50 minutes - characterized by temporary numbness, paralysis, or impaired speech; these deficits are not permanent, but do constitute "red flags" that warn of impeding, more serious CVAs like an undersea earthquake; its not the initial temblor that does the most damage, it's the tsunami that floods the coast later - similarly, the initial vascular blockage during as stroke is not usually disastrous b/c there are many blood vessels in the brain that can pick up the slack; rather, its the neuron-killing events outside the initial ischemic zone that wreak the most havoc main culprit is glutamate, an excitatory neurotransmitter - plays a role in learning and memory and other critical brain functions - after brain injury, neurons totally deprived of oxygen begin to disintegrate, unleashing the cellular equivalent of a tidal wave of glutamate; under these circumstances, glutamate acts as an excitotoxin (exciting surrounding cells to death) most successful treatment for stroke is tissue plasminogen activator (tPA) which dissolves blood clots in the brain - alternate: a mechanical device can drill into a blood clot and pull it from a blood vessel like a cork from a bottle

Language

such an important function of the brain that it involves practically all of the association cortex on the left side in one way or another aphasias (the loss of language abilities due to damage to specific areas of the brain) pointed to two critically important regions: Broca's area and Wernicke's area patients with lesions involving BROCA'S AREA can understand language but have difficulty speaking (and sometimes cannot write or type or use sign language) patients with lesions involving WERNICKE'S AREA are able to speak but produce a type of nonsense often referred to as "word salad"; have great difficulty understanding language 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 a surrounding set of critical areas forms a bridge b/t this system and the regions of cortex that hold concepts and ideas, which are distributed throughout the remainder of the association cortices the corresponding areas in the right or non-language-dominant hemisphere are involved in "body language" - the nonverbal emotional components of language - these areas allow the lilt or tone of our voice and our gestures to express our emotions when we speak, and permit us to comprehend the emotional content of what we hear

The diencephalon includes

thalamus hypothalamus epithalamus forming the central core of the forebrain and surrounded by the cerebral hemispheres, the diencephalon consists largely of three paired structures (mentioned above); these gray matter areas enclose the third ventricle

Cerebral Cortex

the "executive suite" of the nervous system, where our conscious mind is found enables us to be aware of ourselves and our sensations, to communicate, remember, understand, and initiate voluntary movements composed of gray matter: neuron cell bodies, dendrites, associated glia and blood vessels, but no fiber tracts contains billions of neurons arranged in six layers 40% of brain mass its many convolutions effectively triple its surface area specific motor and sensory functions are localized in discrete cortical areas called domains; however, many higher mental functions, such as memory and language, appear to be spread over large areas of the cortex in overlapping domain FOUR GENERALIZATIONS: - contains three kinds of functional areas: motor areas, sensory areas, and association areas (not the same with neurons; all are interneurons in the cortex) - each hemisphere is chiefly concerned with the sensory and motor functions of the contralateral (opposite) side of the body - although largely symmetrical in structure, the two hemispheres are not entirely equal in function; instead, there is lateralization (specialization) of critical functions - approach is gross oversimplification; no functional area of the cortex acts alone, and conscious behavior involves the entire cortex in one way or another

the brain and spinal cord begin as an embryonic structure called

the NEURAL TUBE -as soon as it forms, its anterior (rostral) end begins to expand and constrictions appear that mark off the three PRIMARY BRAIN VESICLES ** prosencephalon - forebrain - divides into the telencephalon ("end brain") and diencephalon ("interbrain") ** mesencephalon - midbrain ** rhombencephalon - hindbrain - constricts, forming the metencephalon ("after brain") and myelencephalon ("spinal brain") the remaining caudal, or posterior, portion of the neural tube becomes the spinal cord the primary vesicles give rise to the SECONDARY BRAIN VESICLES - each of the 5 secondary vesicles then develops rapidly to produce the major structures of the adult brain -greatest change occurs in the telencephalon, which sprouts two lateral swellings that look like Mickey Mouse's ears; these two become the two cerebral hemispheres, referred to as the CEREBRUM - the diencephalon specializes to form the hypothalamus, thalamus, epithalamus, and retina of the eye -less dramatic changes occur in the mesencephalon, metencephalon, and myelencephalon as these regions transform into the midbrain, the pons and cerebellum, and the medulla oblongata - all these midbrain and hindbrain structures (Except the cerebellum) form the BRAIN STEM the central cavity of the neural tube remains continuous and enlarges in four areas to form the fluid-filled ventricles of the brain

Pons

the bulging brain stem region wedged b/t the midbrain and the medulla oblongata; dorsally, the ventricle separates it from the cerebellum chiefly composed of conduction tracts; oriented in two different directions: - the deep projection fibers run longitudinally as part of the pathway b/t higher brain centers and the spinal cord - more superficial ventral fibers are oriented transversely and dorsally; form the middle cerebellar peduncles and connect the pons bilaterally with the two sides of the cerebellum dorsally; these fibers issue from numerous pontine nuclei, which relay "conversations" b/t the motor cortex and cerebellum several cranial nerve pairs issue from pontine nuclei, including trigeminal, abducens, and facial nerves

visceral sensory area

the cortex of the insula just posterior to the gustatory cortex is involved in conscious perception of visceral sensations includes upset stomach, full bladder, and the feeling that your lungs will burst when you hold your breath too long

descending pathways and tracts

the descending pathways that deliver efferent impulses from the brain to the spinal cord are divided into two groups: (1) the direct pathways - the pyramidal tracts (2) the indirect pathways - essentially all of the others motor pathways involve two neurons, referred to as the upper and lower motor neurons: - upper motor neurons - the pyramidal cells of the motor cortex and the neurons of subcortical motor nuclei -lower motor neurons - the ventral horn motor neurons. These directly innverate the skeletal muscles (their effectors)

The interconnected structures of the brain allow higher mental functions

the mind = "inner space"

vestibular (equilibrium) cortex

the part of the cortex responsible for conscious awareness of balance (the position of the head in space) is located in the posterior part of the insula and adjacent parietal cortex

visual areas

the primary visual (striate) cortex is seen on the extreme posterior tip of the occipital lobe, but most of it is buried deep in the calcimine sulcus in the medial aspect of the occipital lobe primary visual cortex is the largest cortical sensory area; receives visual info that originates on the retina of the eye; the visual space on the opposite side of the body is mapped to the primary visual cortex just like the body surface is mapped onto the somatosensory cortex VISUAL ASSOCIATION AREA: surrounds the primary visual cortex and covers much of the occipital lobe; communicating with the primary visual cortex, this area uses post visual experiences to interpret visual stimuli (color, form, and movement), enabling us to recognize a flow or a person's face and to appreciate what we are seeing (We do our "Seeing" with these cortical neurons) complex visual processing involves the entire posterior half of the cerebral hemispheres

Memory

the storage and retrieval of information are essential for learning and incorporating our experiences into behavior and are an integral part of our consciousness different kinds of memory: - declarative (fact)memory (names, faces, words, and dates) - procedural (skills) memory (piano playing) - motor memory (riding a bike) - emotional memory (your pounding heart when you hear a rattlesnake nearby) Declarative memory storage involves two distinct stages: - short term memory (STM): working memory, the preliminary step, as well as the power that lets you look up a telephone number, dial it, and then never think of it again; limited to 7 or 8 chunks of information, such as the digits of a telephone number or the sequence of words in an elaborate sentence - long term memory (LTM): limitless capacity, remember many lyrics to songs, can be forgotten, so our memory bank continually changes with time, our ability to store and retrieve info declines w/ aging do not remember or consciously notice much of what is going on around us As sensory inputs flood into our cerebral cortex, they are processed - 5% of this info is selected for transfer to STM which serves as a temporary holding bin for data that we may or may not want to retain - info is then transferred from STM to LTM. Factors influencing this transfer include: ** emotional state: we learn best when we are alert, motivated, surprised, or aroused. EX: when we witness shocking events, transferal is almost immediate. Norepinephrine, a neurotransmitter involved in memory processing of emotionally charged events, is released when we are excited or "stressed out" ** Rehearsal: rehearsing or repeating the material enhances memory ** Association: tying "new" information to "old" information already stored in LTM appears to be important in remembering facts ** Automatic memory: not all impressions that become part of LTM are consciously formed. A student concentrating on a lecturer's speech may record an automatic memory of the pattern of the lecturer's tie memories transferred to LTM take time to become permanent the process of MEMORY CONSOLIDATION involves fitting new facts into the categories of knowledge already stored in the cerebral cortex. The hippocampus and surrounding temporal cortical areas play a major role in memory consolidation by communicating with the thalamus and the prefrontal cortex specific pieces of each memory thought to be stored near regions of the brain that need them so 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.

cerebellar peduncles

three paired fiber tracts (the cerebellar peduncles) connect the cerebellum to the brain stem; virtually all fibers entering and leaving the cerebellum are IPSILATERAL (From and to the same side of the body) - 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; 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; convey sensory info to the cerebellum from (1) muscle proprioceptors throughout the body and (2) the vestibular nuclei of the brain stem, which are concerned with equilibrium

Ascending Pathways to the Brain

typically conduct sensory impulses upward through chains of three successive neurons (first-, second-, and third - order neurons) second - and third - order neurons are interneurons somatosensory information travels along three main pathways on each side of the spinal cord; two of these pathways (the dorsal column-medial lemniscal and spinothalamic pathways) transmit impulses via the thalamus to the sensory cortex for conscious interpretation 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 the third pathway, the spinocerebellar pathway, terminates in the cerebellum, and does not contribute to sensory perception

Cerebral Cortex: Lateralization of cortical functioning

use both cerebral hemispheres for almost every activity, and the hemispheres appear nearly identical; still have a division of labor, and each hemisphere has abilities not shared by its partner (called LATERALIZATION) one cerebral hemisphere or the other "dominates" each task, the term CEREBRAL DOMINANCE designates the hemisphere that is dominant for language - 90% of people has left hemisphere with greater control over language abilities, math, and logic; this so called dominate hemisphere is working when we compose a sentence, add numbers, and memorize a list - the other hemisphere (the right) is more free-spirited, involved with visual-spatial skills, intuition, emotion, and artistic and musical skills; the poetic, creative, "ah-ha!" (insightful) side of nature most people w/ left cerebral dominance are right-handed, the remaining 10% of people have the roles of the hemispheres reversed or the hemispheres share their functions equally typically right-cerebral-dominant people are left-handed; some lefties who have a cerebral cortex that functions bilateral ate ambidextrous the two cerebral hemispheres have almost instantaneous communication with each other via connecting fiber tracts and complete functional integration; neither is better at everything

First-order neurons

whose cell bodies reside in a ganglion (dorsal root or cranial), conduct impulses from the cutaneous receptors of the skin and from proprioceptors to the spinal cord or brain stem, where they synapse with second-order neurons impulses from the facial area are transmitted by cranial nerves, and spinal nerves conduct somatic sensory impulses from the rest of the body to the CNS

Basal Nuclei

the third basic region of each hemisphere a group of subcortical nuclei also called BASAL GANGLIA primarily involved in the control of movement include the CAUDATE NUCLEUS, PUTAMEN, and GLOBUS PALLIDUS functionally associated with the SUBTHALAMIC NUCLEI and the SUBSTANTIA NIGRA of the midbrain receive input from the entire cerebral cortex and form other subcortical nuclei and each other via relays through the thalamus, the output nucleus of the basal nuclei and the substantial migration project to the premotor and prefrontal cortices and so influence muscle movements directed by the primary motor cortex have no direct access to motor pathways play a role in cognition and emotion filter out incorrect or inappropriate responses, passing only the best response on to the cortex in motor activity, they are particularly important in starting, stopping, and monitoring the intensity of movements executed by the cortex, especially those that are relatively slow or stereotyped, such as arm-swinging during walking they inhibit antagonistic or unnecessary movements disorders: Huntington's disease and Parkinson's disease

Alzeheimers disease (AD)

- a progressive degenerative disease of the brain, ultimately results in dementia (mental deterioration) - AD patients represent half of the people living in nursing homes - b/t 5 and 15% of people over 65 develop this condition, half of them over 85 it is the major cause in their death - exhibit memory loss over a period of several years - examination of brain tissue reveals senile plaques littering the brain like shrapnel b/t neurons; the plaques consist of extracellular aggregations of beta-amyloid peptide, which cut from a normal membrane precursor protein (APP) by enzymes - one form is caused by an inherited mutation in the gene for APP, which suggests that too much beta-amyloid may be toxic; clinical trials focus on the immune system to clear away this peptide - another form is the presence of neurofibrillary tangles inside neurons; these tangles involve a protein called tau, which functions like railroad ties to bind microtubule "tracks" together; in brain of AD patients, tau abandons its microtubule - stabilizing role and grabs on to other tau molecules, forming spaghetti-like neurofibrillary tangles, which kill the neurons by disrupting their transport mechanisms - both plaques and tangles come about b/c proteins that comprise them have misfiled (they clump together and catalyze misfolding of normally folded copies of the same proteins); evidence suggests this misfolding spreads from one region to another, explaining different types of dimension and their progression, as neurons in more brain regions die as brain cells die, their functions are lost and the brain shrinks; vulnerable areas include the hippocampus, the basal forebrain, and association areas of the cortex. all regions involved with thinking and memory - additionally, neurons that use ACh are vulnerable, and their loss is associated with a shortage of ACh

premotor cortex

- in the frontal lobe - helps plan movements; selects and sequences basic motor movements into more complex tasks, such as playing a musical instrument - using highly processed sensory info received from other cortical areas, it can control voluntary actions that depend on sensory feedback, such as feeling for a light switch in a dark room - coordinates the movement of several muscle groups either simultaneously or sequentially, mainly by sending activating impulses to the primary motor cortex - influences motor activity more directly by supplying about 15% of pyramidal tract fivers; staging area for skilled motor activities

primary motor cortex

-(somatic) located in the precentral gyrus of the frontal lobe of each hemisphere -large neurons (pyramidal cells) in these gyri allow us to consciously control the precise or skilled voluntary movements of our skeletal muscles; long axons that project to spinal cord form the massive voluntary motor tracts (pyramidal tracts or corticospinal tracts) - entire body is represented spatially in the primary motor cortex of each hemisphere (called SOMATOTOPY); body is presented upside down - most of the neurons in these gyri control muscles in body areas having the most precise control - the face, tongue, and hands; these regions are disproportionately large in the caricature-like MOTOR HOMUNCULUS (useful to show that broad areas of the primary cortex are devoted to the leg, arm, torso, and head, but neuron organization within those broad areas is much more diffuse than initially imagined) - left primary motor gyrus controls muscles on right side of body and vise versa