Chapter 13: Brain and Cranial Nerves

Arachnoid Mater

Arachnoid Membrane, and arachnoid trabeculae (connects to pia mater). Provides smooth covering.

Vermis:

Band of cortex that separates cerebellar hemispheres

Fourth Ventricle

Begins in metencephalon and extends to superior portion of medulla oblongata. Later narrows and becomes central canal for spinal cord

Basal Nuclei Components

Caudate Nucleus Lentiform which is subdivided into globus pallidus and a lateral putamen Internal Capsule which consist of axon bundles that link cerebral cortex to diencephalon and brain stem Page 443 for role of basal nuclei in movement

Theta Waves

During sleep and occur in children and frustrated adults. If occuring under other circumstances could be brain disorder such as tumors.

Free Nerve Roots

Extend through tissues and can be stimulated in many different ways. Touch, pain, temperature, chemical exposures, etc. Branching tips of sensory neurons. Not protected and most common in skin.

Gyri

Folds in cerebral cortex that increase surface area

Purkinje Cells

Found in cerebellar cortex and are highly branched. Info about motor commands issued at conscious and subconscious levels come here after being relayed by nuclei in pons or cerebellar nuclei. Axons project onto white mater of cerebellum and receive info from up to 20,000 axons.

Choroid Plexus

Found in each ventricle and has combination of specialized ependymal cells and capillaries for CSF production/maintenance.. 500 mL/day 150 mL at any moment Waste removal as well.

Thermoreceptors

Free nerve endings in dermis, skeletal muscles, in liver and hypothalamus, can detect temp. Cold receptors are far more numerous than warm.

Motor Homunculus

Functional map of cortical areas Proportions of this "map" are devoted to a specific region of cortex and is proportional to the number of motor units dedicated to that control

Interventricular Foramen

How lateral ventricles communicate with third ventricle

Lateral Ventricle

In each cerebral hemisphere

Dura Mater

Outer layer fused to periosteum layer of cranial bones (no epidural space) Endosteal (outer) and Meningeal (inner).. contains fluids, blood vessels, large dural sinuses that collect blood from veins in brain

Nociceptors

Pain receptors. Free nerve endings with large receptive fields. Type A Fibers: carry sensations of fast pain (deep cut or injection). Reach CNS quick and trigger somatic reflexes. Receive conscious attention and help us localize the pain. Type C Fibers: carry slow pain such as burning and aching. Activate reticular info in thalamus and we have general idea of where it is coming from.

Red Nucleus:

Receives info from cerebellum and cerebrum and issues subconscious motor commands that affect upper limb position

Referred Pain

Sensation of pain in a part of the body besides the actual source. Ex: heart attack victims feel pain in left arm.

Lamellated Corpuscles

Sensitive to deep pressure. Most sensitive to high frequency vibrations and pulsing. Single dendrite and cell itself has many layers of collagen fibers. Fibrous layers shield dendrite from other sitmuli Found in deep layer of dermis in fingers, mammary glands. Found in visceral sensory info in pancreas and walls of urethra.

Diencephalon

Structural and functional link between cerebral hemispheres and the rest of CNS.

Performing movement is adjusted by Basal Nuclei in 2 ways:

Talks to primary motor cortex, cerebellum and other nuclei in medial/.lateral pathways 1. Alter sensitivity of pyramidal cels to adjust output in corticospinal tracts 2. Change excitatory/ inhibitory output of medial/lateral tracts

Corpus Callosum

Thick tract of white matter that connects cerebral hemispheres

How does CSF reach arachnoid spaces?

Through two lateral apertures and a single median aperture in roof of 4th ventricle.

Pia mater

Stuck to every portion of the brain. Bound by astrocyte process.

Third order neurons

synapse in the primary sensory cortex

Corticibulbar Tracts

synapse on lower motor neurons in motor nuclei. Conscious control over muscles in eye, jaw, face, neck and pharynx

Tactile Discs and Merkel Receptors

Tactile: fine touch pressure receptors and extremely sensitive tonic receptors. Single myelinated afferent fiber makes contact with Merkel cells--> large epithelial cells in stratum basale

Right Cerebral Hemipshere

Analyzes sensory info and relates body to the sensory environment. Helps you identify familiar things. Spatial visualization and analysis.

Anatomy of Cerebellum

Anterior and posterior lobes. Has two hemispheres and is covered by layer of gray mater- cerebellar cortex.

Cerebellum In Depth

Automatic processing that coordinates learned and reflexive patters at subconscious level. Proprioceptive, visual, tactile, balance, and auditory sensations. Two Primary Functions: Adjusting to Postural Muscles in the Body- coordinates rapid automatic adjustments to maintain balance and equilibrium.. modifies activities of motor centers in brain stem. Programming and Fine-Tuning Movements at the Conscious/Unconscious Levels- regulates motor activity along cerebral cortex, basal nuclei, motor centers in brain stem. Makes adjustments to proprioceptors so make movements smooth.

Rabies

Bite by rabid animal, injects virus into peripheral tissues on axons and enter synaptic knob. Retrograde flow then carries virus into CNS and can be fatal.

Cerebral Palsy

CP is disorder affecting voluntary motor performance. Appear during infancy and early childhood. Could be caused by trauma, stressful birth, maternal exposure to drugs or genetic defect

Posterior Column Pathway

Carries sensations that are highly localized to touch, pain, temp, vibrations and proprioceptors. Begins in peripheral receptor and ends in primary sensory cortex of cerebral hemipshere. Touch felt on right side--> sensory nerves ascend on right side to fasiculus gracilis and fasiculus cueatus-->cross over to other side with help of 2nd order neurons and then carried up by medial lemniscus--> sensation enters ventral nuclei in thalamus

Spinothalamic Pathway: Anterior Spinothalamic Tracts

Carry crude touch and pressure sensations to second order neurons. Sensations felt on left side use interneurons/ 2nd order neurons of spinal cord to go to opposite side before reaching brain.

Spinothalamic Pathway: Lateral Spinothalamic Tracts

Carry pain and temperature sensations to secondary neurons. Sensations felt on left side use interneurons/2nd order neurons of spinal cord to go to opposite side before reaching brain.

Spinocerebellar Pathway

Cerebellum receives info from proprioceptors about position of skeletal muscles tendons and joints. DO NOT CROSS OVER however, anterior spinocerebellar tract does receive info that crosses over and is taken up to pons and cerebellum by spinocerebellar pathway

Cerebrum:

Cerebral Hemispheres (highly folded and covered in superficial layer of gray matter called Cerebral Cortex). Functions: conscious thought, memory storage, and processing, sensory processing, regulation of skeletal muscle contractions.

What does Cerebellum do as you move?

Communicates with basal nuclei and primary motor cortex as movement occurs it monitors proprioceptors and vestibular info and compares arriving sensations with those experienced with prior movements. Can then adjust activities of upper motor neurons involved.

CSF role..

Completely surrounds and bathes CNS. Circulates through and fills central canal of spinal cord. Allows diffusion between interstitial fluid of CNS across the ependymal cells. Replaced every 8 hours.

Pons

Connects cerebellum to brain stem. Tracts and relay centers contains nuclei in somatic and visceral motor control

Medulla Oblongata Components and Function

Contains nuclei associated with 5 cranial nerves .. Gray Matter: Nucleus gracilis, nucleus cuneatus- Relay somatic sensory information to the thalamus Olivary Nuclei- Located within the olives; relay info to the cerebellum Autonomic Reflex Center- cardiac, vasomotor, respiratory rhythmicity Other Nuclei/Centers- contain sensory and motor nuclei of cranial nerves. Relay sensory info from spin to higher centers White Matter: Ascending and Descending Tracts: Link brain to spine.

What protects the brain?

Cranial Meninges (dura, arachnoid, pia matter) and CSF

Dural Folds

Created by dura mater extending into cranial cavity. Additional stabilization and support.

Substania Nigra

Darkly pigment cells that adjust to activity of basal nuclei of cerebrum

Fissures

Deep grooves that subdivide the cerebral hemispheres

Multiple Sclerosis

Demyelination of axons in optic nerve, brain and spinal cord. Signs and symptoms include minor vision loss, loss of coordination speech balance and muscle control. Is progressive 1/3 of the time.

Cerebellar Peduncles

Tracts that link cerebellum to brain stem, cerebrum and spinal cord. Superior, Middle, Inferior

Tonic Receptors

Type of receptors that always generate action potentials at a frequency that reflects background level stimulation. Higher stimuli, more frequent action potentials

How does somatic nervous system control skeletal muscles?

Upper and lower motor neurons. Upper: cell bodies lie in a CNS processing center.. synapses on lower Lower: cell bodies lie in nucleus of brain stem or spinal cord

Lateral Pathways:

Upper motor neurons in this pathway are in red nucleus, which receives info from cerebrum and cerebellum to adjust upper limb position and background muscle tone. Axons in this pathway cross over at rubrospinal tracts which are small and go to cervical spinal cord to provide the control over distal upper limb muscles

Medial Pathways:

Upper motor neurons in this pathway are located in vestibular nuclei, the supior/inferior colliculi and the reticular info.

Electrical Activity of two hemispheres

Usually line up and when they dont it can help pinpoint damage and cause disorders such as seizures

Delta Waves

Very large amplitude and happen during sleep.

Alpha Waves

Waves when awake but disappear during sleep and vanish when concentrating on specific thing

Interconnecting the Brain

White matter interconnects cerebral hemispheres, and links cerebrum to rest of brain.

Arbor Vitae

White matter of cerebellum that forms the tree of life

Major Midbrain landmarks: Corpora Quadrigemina

are two pairs of sensory nuclei located on roof of midbrain Superior Colliculus-visual inputs from thalamus and controls reflex movements of eyes, head, neck in response to visual stimuli Inferior Colliculus- Same as superior except with auditory.

Hypothalamus

floor of Diencephalon. Contains centers involved in emotions, autonomic function and hormone production.

Cerebral Hemispheres General Facts:

Each hemisphere receives sensory info and sends motor commands to opposite side of the mody Many differences exist between different hemispheres No specific function is assigned to a specific region. There is overlap.

First order neurons

Enter spine and synapse on second order neurons within posterior gray horns

Diencephalon Consists of..

Epithalamus, (left right) thalamus, and hypothalamus

Thalamus Components and Functions

Final relay point for ascending sensory information that is projected to cerebral cortex. Acts as filter only passing a small portion on to cerebral hemispheres. Nuclei/Group: Anterior-Limbic system Medial-Integrates sensory info for projection onto frontal lobes Ventral-Projects sensory info to primary sensory cortex; relays info from cerebellum and basal nuclei to motor area of cerebral cortex Posterior: Pulvinar-->integrates sensory info for projection to association of cerebral cortex -Lateral Geniculate--> Project visual info to visual cortex -Medial Geniculate--> Project auditory info to auditory cortex Lateral- Integrates sensory info and influences emotion

Tactile Corpuscles

Fine touch, pressure and low frequency vibrations Fairly large and most abundant in eyelids, lips, finer tips, nipples.

Arachnoid Granulations?

Fingerlike extensions of arachnoid membrane that penetrate meningeal layer of dura mater and extend to superior sagittal sinus. Here CSF is absorbed into venous circulation

CSF getting to brain and spine?

Flows through subarachnoid space surrounding brain, spine and cauda equina.

Falx Cerebri

Fold of dura mater projecting between cerebral hemispheres.

Folia

Folds on surface of cerebellar surface. Not very prominent

Ventricles

Form during development of brain. Filled with CSF and lined with ependymal cells.

More on Limbic System:

Fornix is the tract of white matter connecting hippocampus and hypothalamus Amygdaloid Body helps regulate heart beat, control of fight of flight response and linking emotions to memory Hippocampus important in learning and storage/ retrieval of long-term memories

Preparing for Movement

Frontal lobes decide--> motor association areas--> basal nuclei/cerebellum--> motor fibers

Left Cerebral Hemisphere

General interpretive and speech centers. Language centers for speech, writing, analytical skills like math and logic.

Cerebellum Components and Functions:

Gray Matter: Cerebellar Cortex & Nuclei- Involuntary coordination and control of ongoing body movements White Matter: Arbor Vitae- Connects cerebellar cortex and nuclei with cerebellar peduncles Superior Peduncle-Link cerebellum to midbrain, diencephalon and cerebrum Middle Peduncle- Transverse fibers and carry communications between cerebellum and pons Inferior Peduncle- Link cerebellum with the medulla oblongata and spinal cord Transverse Fibers-Interconnect pontine nuclei with the cerebellar hemisphere on opposite side

Components and Functions of Midbrain

Gray Matter: Tectum--> superior colliculi- integrate visual info and cause reflexes -->Inferior colliculi- Auditory info integration and cause reflexes Walls and Floor--> Red Nuclei- subconscious control of upper limb position -->Sunstania Nigra- regulates basal nuclei activity --> Reticular Formation- processes incoming sensations and outgoing motor commands automatically. RAS control and involuntary motor responses to stimuli -->Other nuclei and Centers- associated with cranial nerve III and IV White Matter: Cerebral Peduncles- Connect primary motor cortex with motor neurons in brain and spine. Carry ascending sensory info to thalamus.

Beta Waves

Higher frequency and appear during concentration and stress.

Hypothalamus and Nuclei

Important control and integrative centers stimulated by A)sensory info from cerebrum, brain stem and spinal cord. B) changes in composition of CSF and intestinal fluid. C) chemical stimuli in circulating blood. Have connections to pituitary glands at infundibulum and secrete hormones. Have mamillary bodies that control feeding reflexes Nuclei (control cardiovascular and vasomotor centers of medulla oblongata) Preoptic Area: regs body temp by coordinating adjustments in blood flow and sweat gland activity. Suprachiasmatic Nucleus:Coordinates day-night cycles

Components of Limbic System

In Diencephalon: Hypothalamus, mamillary body and anterior group of thalamic nuclei (relay info from mamillary body to cingulate gyrus) In Cerebrum: Limbic Lobe Cingulate gyrus Parahippocampal gyrus

Association Fibers

Interconnect areas of neural cortex Arcute Fibers are shortest type and curve in arc to connect gyrus' Longitudinal Fasciculi are longer fibers and form in discrete bundles. Connect frontal lobes to other cerebral hemispheres

Commissural Fibers

Interconnect cerebral hemispheres. Projection Fibers connect cerebral cortex to diencephalon, brain stem, cerebellum, and spinal cord. All these ascending and descending projection fibers form a mass called internal capsule.

Limbic System

Known as motivational center Group of tracts and nuclei located in Cerebrum and Diencephalon. It is a functional group. 1. Establishing emotions 2. Linking conscious and intellectual functions of cerebral cortex with unconscious and autonomic functions of brain stem 3. Memory storage and retrieval

Dural Sinuses

Large collecting veins located within dural folds.

Superior Sagittal Sinus

Largest dural sinus

Corticospinal Pathway

Like a pyramid system and originate in pyramidal cells in primary motor cortex. Cary info (descending) to brain stem and spinal cord (lower motor neurons) that control skeletal muscle

Third Ventricle

Located in Diencephalon

Who has Somatic Control?

Many parts of the brain. Brain stem and Spine: Simple cranial and spinal reflexes Pons and Medulla Oblongata: Balance reflexes and more complex respiratory reflexes Hypothalamus: Motor patters related to eating, drinking, sex and modifies respiratory reflexes Thalamus and Midbrain: Reflexes in response to visual/auditory stimuli Basal Nuclei: Modify voluntary reflexive motor patterns at subconscious level Cerebral Cortex: Plans and initiates voluntary motor activity Cerebellum: Coordinates complex motor patterns involving cerebral cortex and basal nuclei as well as nuclei in medial and lateral pathways

Brain Stem:

Midbrain, pons, medulla oblongata

Performing for Movement

Motor association areas/ Basal nuclei--> primary motor cortex-->lower motor neurons

Root Hair Plexus

Nerve endings where hair is. Monitor distortions and movements across body surfaces. Movement of hair runs down follicle and generates action potentials. Best at detecting initial contact

Cerebral Cortex: Motor Cortex

Neurons here called pyramidal cells because cell bodies resemble little pyramids Somatic Motor Association area is responsible for coordination of learned movements

Cerebral Cortex: Sensory Cortex

Neurons in primary sensory cortex receive somatic sensory info such as touch, pressure, pain, vibration, taste and temp Somatic Association Area: monitors activity in primary sensory cortex. Can recognize light touch such as mosquito landing on you

Parkinsons Disease

Neurons of Substantia nigra being damaged or secrete less dopamine. Basal nuclei becomes more active and produces more muscle tone which leads to stiffness and rigidity. Difficulty starting voluntary movements because opposing muscle groups do not relax.

Phasic Receptors

Normally inactive receptors but become active for short time in response to a change in condition

Midbrain

Nuclei that process visual and auditory info and control reflexes. Also help maintain consciousness.

Basal Nuclei

Of cerebrum, performs subconscious adjustment and refinement of ongoing voluntary movements Masses of gray matter, deep to floor of lateral ventricle. Subconscious control of muscle tone, help coordinate learned movement patters. Do not initiate movements to give pattern and rhythm to trunk and proximal limbs.

Septum Pellucidum

Partition that separates the two lateral ventricles.

Spinothalamic Pathway

Pathway that provides conscious sensations of poorly localized (crude) touch, pressure, pain and temp. Contains first, second and third order neurons.

Ataxia

Permanent damage by trauma or stroke. Can be temporarily affected by alcohol. Disturbance of muscle coordination and individual cannot sit or stand without assistance.

Primary Motor Cortex Damage?

Person loses ability to exert fine control over skeletal muscles. Come voluntary control is possible through basal nuclei but becauee corticospinal tracts is inoperative there can be no feedback for fine tuning. Can walk, stand and balance but all movements are awkward and poorly controlled.

Anterior Commissure and Corpus Callosum

Play a role in helping communication between left and right hemipsheres

Second order neurons

Posterior gray horns and cross opposite side of spinal cord before ascending to the thalamus. Synapse in ventral nuclei of thalamus

Cerebral Cortex is divided into Lobes

Precentral Gyrus- anterior to central sulcus and contains primary motor cortex. Motor neurons control voluntary movements Central Sulcus- Divides frontal and parietal lobes Postcentral Gyrus- posterior to central sulcus. Primary sensory cortex that receives sensory info that reaches conscious awareness Lateral Sulcus- separates frontal and temporal lobes

Cerebral Cortex:

Primary motor cortex: issues voluntary commands to skeletal muscles Primary Sensory Cortex: receives general somatic sensory info. Each region is connected to nearby association areas

Cerebral Cortex: Visual Cortex

Primary: receives info from lateral geniculate nuclei Visual Association Area: monitors patterns of activity in visual cortex and interprets. Ex. see letters c, a, r.. recognize it as car

Cerebral Cortex: Auditory Cortex

Primary: responsible for monitoring sound info Auditory Association area: monitors sensory activity in auditory cortex and recognizes sounds such as words

ALS

Progressive degenerative disorder affecting morot neurons in spinal cord. Degeneration affects upper and lower neurons. Lou Gehrig disease and causes atrophy and could be caused by defect in axonal transport

Alzheimers Disease

Progressive, loss of higher-order cerebral functions. Symptoms occur with old age. Areas with memory processing highly effected

Linked to Mechanoreceptors and Chemoreceptors are the following

Proprioceptors: Monitors positions of joints and muscles. Most structurally and functionally complex. Ex. muscle spindle Baroreceptors: Detect pressure changes in walls of blood vessels, portions of digestive, repo, and urinary systems. Tactile Receptors: Provide sensations of touch, pressure and vibration. Either extremely sensitive fine touch receptors or crude touch receptors that provide not so detailed info

Cerebral Cortex: Gustatory Cortex

Receives info from taste receptors

Cerebral Cortex: Olfactory Cortex

Receives sensory info from olfactory receptors

Adaptation

Reduction in sensitivity due to presence of constant stimuli. Peripheral: Occurs when level of receptor activity changes. Reacts strongly at first then decreases. Central: Occurs along sensory pathways in CNS a few seconds after exposure to stimuli.

Thalamus

Relay and processing center of sensory information

Chemoreceptors

Respond to water-soluble and lipid-soluble substances dissolved in body fluids (plasma, intestinal fluid, CSF)

Tracts within Medial Pathways

Reticulospinal Tracts: axons from reticular info from upper motor neurons. Reticular info receives info from almost every ascending and descending pathway. Vestibulospinal Tracts: Receive sensory info from inner eat about position and movement of head. Respond to changes in head orientation by issuing motor commands and can alter position of neck, eyes, head and limbs Tectospinal Tracts: Upper motor neurons of superior and inferior colliculi of midbrain. Direct reflexive changes in head, neck, and upper limbs in response to bright lights, loud noises and sudden movements

Epithalamus:

Roof of Diencephalon superior to the third ventricle. Extensive area of Choroid plexus that extend through intraventricular foramina. Pineal glad found here-- secretes melatonin (sleep and regulation of reproductive function) Optic Chiasm--Optic nerves connect to brain

Ruffini Corpuscles

Sensitive to pressure of reticular deep dermis. Tonic and show little adaptation. Dendrites woven in collagen fibers with afferent fiber as well. Any stretching, compressing, twisting, etc. activates afferent fiber

Mechanoreceptors

Sensitive to stimuli that distorts plasma membranes. Membranes contain chemically gated ion channels that open in response to stress, compression, twisting, etc.

Primary Fissure

Separate anterior and posterior lobes

Tentorium Cerebelli

Separates cerebral hemispheres from cerebellum

Who issues motor commands?

Several centers located in cerebrum, diencephalon, and brain stem. Issued by medial pathways, help gross control of trunk and proximal limb muscles. OR lateral pathways, control distal limb muscles and more precise movements.

Sulci

Shallow depressions in cerebral cortex that separate adjacent gyri

Aqueduct of the Midbrain

Slender canal in midbrain connects third to fourth ventricle.

Reticular Activating System (RAS)

Specialized part of reticular info. Stimulation makes you more alert and attentive. Damage produces unconscious.

Cerebral Cortex: Integrative Centers

Speech center (Boca Area) Prefrontal Cortex: Coordinates info relay from association areas of cortex. Helps in predicting consequences of events or actions Frontal Eye Field: Controls learned eye movements General Interpretive Area: (Wernicke Area) Receives info from all sensory association areas. Typically in left hemisphere. Essential role in personality.

Cerebellum

partially hidden by cerebral hemispheres. 2nd largest structure in brain.. coordination and modulation of motor commands from cerebral cortex

Medulla Oblongata

relays sensory info to the rest of the brain stem and thalamus. Major centers for regulating autonomic function.. Heart Beat and Blood Pressure

Pons Components and Functions:

reticular info found here.. loosely organized gray matter containing nuclei and centers that regulate vital autonomic functions. Gray Matter: Nuclei Associated w/ Cranial Nerves V, VI, VII, VIII-Relay sensory information and issue somatic motor commands Apneustic and Pneumotaxic Centers- Adjust activities of the respiratory rhythmicity centers of medulla oblongata. Relay Centers- relay sensory and motor information of the cerebellum White Matter: Ascending Tracts- Carry sensory information from nucleus cuneatus and nucleus gracilis to thalamus Descending Tracts: Carry motor commands from higher centers to motor nuclei of cranial or spinal nerves Transverse Fibers- Interconnect processing centers in the cerebellar hemispheres

Lateral Coricospinal Tracts

roughly 85% of these corticospinal axons cross over to here before reaching 1st order neurons, posterior gray horn to anterior gray horn before going out to muscles. Other 15% descending that are not crossed does cross over in anterior white commissure before synapsing on lower motor neurons in anterior gray horn