The central Nervous System

o Originates from the neural tube during embryonic development The neural tube starts as an open groove along the top surface of the embryo,

then nervous tissue grows around it and encloses it The neural tube becomes the ventricles of the brain and the central canal of the

spinal cord

Regions and Divisions of the CNS

4 major divisions of the Braino Cerebral hemispheres (or cerebrum)o Diencephalono Brain stem (midbrain, pons, and medulla)o Cerebellum

Regions and Organization of the CNS

Spinal cordo Central cavity surrounded by a gray matter core o External white matter composed of myelinated fiber tracts

Braino Similar pattern with additional areas of gray mattero Nuclei in cerebellum and cerebrumo Cortex of cerebellum and cerebrum

Ventricles of the Brain

Connected to one another and to the central canal of the spinal cord Lined by ependymal cells Contain cerebrospinal fluid

o Two C-shaped lateral ventricles in the cerebral hemisphereso Third ventricle in the diencephalono Fourth ventricle in the hindbrain, dorsal to the pons, develops from the lumen of the

neural tube

The Brain

1. Cerebral hemispheres ~ 83% of the masso Elevated ridges are gyri and grooves are sulcio Foldings increase the surface area for neurons

Total surface area is about 2.5ft2

As humans evolved, we developed our analytical skills and our ability to manipulate facts; our ability to retain and remember information has also increased; as humans evolved, our brains got larger

But, the cerebral hemispheres enlarged at a much faster pace than the rest of the brain; Why?

Takes more neurons to do these “higher thinking” skillso The neurons involved in the higher thinking skills are in the superficial layer of the

cortex, so it is there that the expansion of the brain has been most pronounced (see it in the folds of the cortex)

Deeper grooves (fissures) separate the larger regions (lobes) of the brain; 4 of them are named for the bones that they cover: frontal, parietal, temporal, occipital, plus there is a 5th region (insula) which is under the frontal, parietal, and temporal regions

Deeper grooves (fissures) separate large regions of the brain as well There are 2 deep fissures: the longitudinal fissure which separates the cerebrum

into right and left cerebra and the transverse cerebral fissure which separates the cerebrum from the cerebellum

Cerebral cortexo Covers the outer 2 – 4 mm of the cerebral hemispheres and is composed of gray matter,

with no fiber tracts; specific motor and sensory functions are localized in discrete cortical areas called domains

o It is where our conscious mind is found and enables us to Be aware of ourselves and our sensations To communicate, remember, and understand To initiate voluntary movement

o The higher mental functions (memory, language) may have overlapping domains and are spread over large areas of the cortex

o Each cerebral hemisphere is concerned with the sensory and motor functions of the opposite half of the body; but the halves are not entirely equal in function; there is a specialization of cortical functions

o Thick band of axons (corpus callosum) enables communication between the right and left cerebral cortex

o Domain Information Remember, no functional area acts alone (the following is a gross

oversimplification) 1.Primary Somatic Motor Cortex – (located in the back portion of the frontal

region) Allows us to consciously control the precise voluntary movements of

our skeletal muscles Each part of the body is represented in a different part of the primary

motor cortex

2.Premotor cortex – just anterior to the precentral gyrus in the frontal lobe Controls the learned motor skills of a repetitious or patterned nature,

(playing the piano or typing, for ex) Also involved in planning movements, such as moving an arm through a

maze to grab a hidden ball 3.Broca’s Area – anterior to the premotor cortex but lateral to cerebrum

Present in only one hemisphere, usually the left Directs the muscles involved with speech and in planning to speak

4.Frontal eye field (anterior to the premotor cortex and superior to Broca’s area)

Controls voluntary movement of the eyes 6.Primary somatosensory cortex (postcentral gyrus of the parietal lobe, just

posterior to the primary motor cortex) Receives information from the sensory receptors in the skin,

proprioreceptors (position sense receptors) in the skeletal muscles, joints, and tendons

Amount of sensory cortex devoted to a particular body region is related to the number of sensory receptors in that region, not to the size of the body region

In humans, the face (esp. the lips) and fingertips are the most sensitive, so they get most of the area of the somatosensory cortex; see figure 12.9

7.Somatosensory association cortex (posterior to the primary somatosensory cortex)

Integrates sensory input related to it via the primary somatosensory cortex in order to understand the object being felt, its size, texture, and relationship of its parts (feeling keys in your pocket allows you to relate stored memories of past sensory experiences to perceive the objects as keys; someone with damage to this area would have to look at the keys to perceive them as keys…)

8.Visual areas; primary visual cortex (extreme posterior tip of the occipital lobe) Receives sensory input from the retina of the eye Visual association area surrounds the primary visual cortex and covers

much of the occipital lobe Use past visual experiences to interpret visual stimuli (color, form,

movement) so that we can recognize a person’s face, etc Primary visual cortex recognizes the letters c, a, and r and knows that

car means car; a damaged visual association area would perceive no meaning from c, a, r (the symbols for car)

9.Auditory areas; primary auditory cortex (superior margin of the temporal lobe)

Sound energy exciting the inner ear hearing receptors cause impulses to be transmitted to the primary auditory cortex where they are interpreted in terms of pitch, loudness and location

Auditory association area then permits the perception of the sound stimulus, which we hear as speech or music, etc (memories of sounds heard in the past seem to be stored here for reference)

If the primary auditory cortex is OK, but the auditory association area were damaged, you could hear and understand the words “sit” and “here”, but the phrase “sit here” would bewilder you…

10.Olfactory (smell) cortex (medial aspect of the temporal lobe) Afferent fibers from the smell receptors in the superior nasal cavities

send impulses along the olfactory tracts that relayed to the olfactory cortex;

Conscious awareness of different odors 11.Gustatory (taste) cortex (located in the insula just deep to the temporal lobe) 12.Visceral sensory area (in the insula); concerned with visceral sensations like

an upset stomach, full bladder, etc. 13.Vestibular (equilibrium) cortex (insula, most likely) 14.Multimodal Association Areas (3)

Receives input from multiple senses and sends outputs to multiple areas Information flows from sensory receptors to the appropriate primary

sensory cortex to a sensory association cortex to the multimodal association cortex

Allows us to give meaning to the information that we receive, store it in memory if needed, tie it to previous experience and knowledge, and decide what action to take

Final decision is relayed to the premotor cortex and then to the primary motor cortex

a.Anterior association area- in the prefrontal cortex, anterior portion of the frontal lobe;

o Most complex; is invloved with intellect, complex learning abilities, recall and personality

o Contains working memory, abstract ideas, judgment, reasoning, persistence and planning

o The prefrontal cortex matures slowly and is heavily dependent on positive and negative feedback from one’s social environment!

b.posterior association area/Wernicke’s area (large, encompassing parts of the temporal, parietal and occipital lobes)

o Recognizes patterns and faces, localizes us to our surroundings in space

o Binds the different sensory inputs into a coherent wholeo (Patients with damage to the parietal region of this area refuse

to wash or dress the left side of the body b/c it doesn’t “belong” to them)

c.Limbic association area – group of structures located on the medial aspect of each cerebral hemisphere and diencephalon

o Includes the cingulated gyrus, the parahippocampal gyrus, the hippocampus, and the amygdala

o The fornix is the white matter that links these limbic system regions together

o Provides the emotional impact; tells us what it is about a particular occurrence that is important to us

o Recognizes anger, fearful facial expressions, assesses danger, and elicits the fear response

o Allows us to express our emotions through gestures and resolve mental conflicts when we’re frustrated

o Odors can trigger emotional responses and memories hereo Translates emotional stress to visceral functions (high blood

pressure, for ex)o Translates our conscious understanding of an occurrence to an

emotional reaction to that evento Communication b/w the limbic system and cerebral cortex

explains why sometimes emotions override logic, and why reason can sometimes stop us from expressing our emotions in inappropriate situations

o Stroke Damage to Cortex Areas Stroke is caused by a blockage or rupture in a blood vessel going to the brain Stroke damage to the primary motor cortex would cause loss of use of the

voluntary skeletal muscles controlled by the damaged domain (but only the ability to control those muscles; the muscles would still contract, you just wouldn’t have any control over them)

Stroke damage to the premotor cortex results in loss of motor skills programmed in that region, but you can still control the individual movements and the muscle strength is intact; you could reprogram the lost skill, with a lot of practice

Cerebral White Mattero Responsible for communication b/w the cerebral areas and b/w the cerebral cortex and

the lower CNS centers; consists of myelinated fibers bundled into large tracts A. commissures- largest is the corpus callosum; connects right and left cerebral

hemispheres B. association fibers – connects different parts of the same hemisphere

C. projection fibers – connects the cerebral hemispheres with the lower brain or spinal cord centers

Basal Nucleio Deep within the cerebral white matter (beneath the floor of the lateral ventricles) are

the basal nuclei – collections of neuron soma (cell bodies)o Precise role is undetermined, but they seem to be involved with the subconscious

control of skeletal muscle tone and coordination of learned movement patterns (they don’t initiate movements, but once underway, they provide the general pattern and rhythm, esp. for movements of the trunk and proximal limbs)

o When you walk, the basal nuclei control the cycles of arm and thigh movements that occur between the time you decide to “start” walking and the time you give the “stop” order

o Parkinson’s… Lateralization of Cortical Function

o Lateralization Division of labor between hemispheres

o Cerebral dominance Designates the hemisphere dominant for language (left hemisphere in 90% of

people)o Left hemisphere

Controls language, math, and logico Right hemisphere

Insight, visual-spatial skills, intuition, and artistic skillso Left and right hemispheres communicate via fiber tracts in the cerebral white matter

Diencephalono Three paired structures

Thalamus 80% of diencephalon; an egg-shaped mass of gray matter connected by

an intermediate mass Forms the superolateral walls of the third ventricle Contains several nuclei, named for their location Nuclei project and receive fibers from the cerebral cortex Relays information from the basal nuclei to the cerebral cortex Thalamic Function

o Gateway to the cerebral cortexo Sorts, edits, and relays information

Afferent impulses from all senses and all parts of the body

Impulses from the hypothalamus for regulation of emotion and visceral function

Impulses from the cerebellum and basal nuclei to help direct the motor cortices

o Mediates sensation, motor activities, cortical arousal, learning, and memory

Hypothalamus Forms the inferolateral (lower side) walls of the third ventricle Contains many nuclei

o Example: mammillary bodies- relays in olfactory pathways Paired anterior nuclei Olfactory relay stations

Infundibulum—stalk that connects to the pituitary gland Hypothalamic Fucntion

o Autonomic control center for many visceral functions (e.g., blood pressure, rate and force of heartbeat, digestive tract motility)

o Center for emotional response: Involved in perception of pleasure, fear, and rage and in biological rhythms and drives (part of the limbic system, in that they are connected)

o Regulates body temperature, food intake, water balance, and thirst (the body’s thermostat in in the hypothalamus)

o Regulates feelings of hunger, water balance and thirsto Regulates sleep and the sleep cycleo Controls release of hormones by the anterior pituitaryo Produces posterior pituitary hormones

Epithalamus Most dorsal portion of the diencephalon; forms roof of the third

ventricleo Pineal gland —extends from the posterior border and secretes

melatonin, a sleep-inducing hormone Melatonin—helps regulate sleep-wake cycles together

with the hypothalamic nucleio Gray matter; encloses the third ventricle

Brain Stemo Three regions

Midbrain Pons Medulla oblongata

o Provides a pathway for fiber tracts running between higher and lower neural centerso Similar structure to spinal cord but contains embedded nuclei (gray matter surrounded

by white matter and the white matter has embedded nuclei of gray matter)o Controls automatic behaviors necessary for survival

o Contains fiber tracts connecting higher and lower neural centerso Associated with 10 of the 12 pairs of cranial nerves

Midbraino Located between the diencephalon and the pons

A.Cerebral peduncles (“little feet” of the cerebrum; holds up the cerebrum) Contains pyramidal motor tracts (descending, moving toward the spinal

cord); other nerve tracts connect the midbrain to the cerebellum B.Cerebral aqueduct

Channel between third and fourth ventricles C.Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) D.Corpora quadrigemina —domelike dorsal protrusions

Superior colliculi—visual reflex centers; coordinate head and eye movements when looking at a moving object

Inferior colliculi—auditory relay centers from the hearing receptors of the ear to the sensory cortex; allows you to turn your head toward an unexpected sound

E.Substantia nigra —functionally linked to basal nuclei; embedded in each side of the midbrain white matter; dark in color b/c of melanin, a precursor to dopamine (degeneration of the dopamine-releasing neurons here is the ultimate cause of Parkinson’s)

F.Red nucleus —relay nuclei for some descending motor pathways and part of reticular formation; also embedded in the side of the midbrian; lots of iron, due to rich blood supply; receives info from the cerebrum and cerebellum and issues subconscious motor commands that affect upper limb positions

Ponso Bulging brain stem region wedged b/w the midbrain and medullao Forms part of the anterior wall of the fourth ventricleo Fibers of the pons

Connect higher brain centers and the spinal cord Relay impulses between the motor cortex and the cerebellum; conduction tracts

run in 2 directionso Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial)o Nuclei that help maintain normal rhythm of breathing

Medulla Oblongatao Continuous with the spinal cord at foramen magnumo Forms part of the ventral wall of the fourth ventricleo All communication between the brain and spinal cord involves tracts that traverse

through the medulla Descending motor tracts are called pyramids, which cross over to the opposite

side of the medulla before entering the spinal cord; so motor signals that enter

from the left side of the cerebrum go to voluntary muscles on the right side of the body

Also tracts that connect the medulla to the cerebellumo Inferior olivary nuclei—relay sensory information from muscles and joints to cerebellumo Cranial nerves VIII, X, and XII are associated with the medullao Vestibular nuclear complex—mediates responses that maintain equilibriumo Several nuclei (e.g., nucleus cuneatus and nucleus gracilis) relay sensory informationo Autonomic reflex centerso Cardiovascular center

Cardiac center adjusts force and rate of heart contraction Vasomotor center adjusts blood vessel diameter for blood pressure regulation

o Respiratory centers Generate respiratory rhythm Control rate and depth of breathing, with pontine centers

o Additional centers regulate Vomiting Hiccuping Swallowing Coughing Sneezing

The Cerebellumo 10% of brain masso Dorsal to the pons and medullao When nerve impulses from the motor cortex descend to the spinal cord to initiate

voluntary movements, nerve impulses are also sent to the cerebellum about these intended movements.

o The cerebellum unconsciously coordinates adjustments to maintain balance and equilibrium

o Proprioceptors provide sensory information as to the current limb positiono To ensure smooth, coordinated movements, the cerebellum compares the intended

movements with current limb positiono Nerve tracts between the cerebellum and the spinal cord do NOT cross over; the left

side of the cerebellum controls the left side of the bodyo Nerve messages from the cerebellum to the cerebrum go through the thalamus

meaning there is no direct connection for ascending messages between the cerebellum and cerebral cortex

o Two hemispheres connected by vermiso Each hemisphere has three lobes

Anterior, posterior, and flocculonodularo Folia—transversely oriented gyrio Arbor vitae—distinctive treelike pattern of the cerebellar white matter

o Cognitive Function Recognizes and predicts sequences of events during complex movements But, has a broader role in a number of key cognitive functions, including

attention and the processing of language and music Plays a role in nonmotor functions such as word association and puzzle

solving

Protection of the Brain and Spinal Cord

Bone (skull) or vertebrae Membranes (meninges)

o Cover and protect the CNSo Protect blood vessels and enclose venous sinuseso Contain cerebrospinal fluid (CSF)o Form partitions in the skullo Three layers

Dura mater Strongest meninx Two layers of fibrous connective tissue (around the brain) separate to

form dural sinuses Arachnoid mater

Middle layer with weblike extensions Separated from the dura mater by the subdural space Subarachnoid space contains CSF and blood vessels Arachnoid villi protrude into the superior sagittal sinus and permit CSF

reabsorption Pia mater

Layer of delicate vascularized connective tissue that clings tightly to the brain

Watery cushion (cerebrospinal fluid) Blood-brain barrier

The Spinal Cord

We have 31 pairs of spinal nerves attached to the cord by paired roots Each nerve exits from the vertebral cloumn by passing superior to its corresponding vertebra via

the intervertebral foramina Cord is about the width of a thumb Because it ends at L2, the last few lumbar and sacral spinal nerve roots angle sharply downward

and travel inferiorly through the vertebral canal for some distance before reaching their intervertebral foramina

The collection of nerve roots at the inferior end of the vertebral canal is called the cauda equina (“horse’s tail”) (during fetal development – age 4, the vertebral column grows faster than the spinal cord, so the lower spinal nerve roots have to chase their exit points inferiorly through the vertebral canal)

A spinal tap or lumbar puncture is a withdrawal of CSF for testing from the subarachnoid spaceo Needle is inserted b/w L3 and L5 with little danger of damaging the cord or spinal nerve

roots b/c the cord terminates at L2 and the nerves have moved out of the way Gray Matter of the Spinal Cord

o In cross section, looks like a butterflyo 2 extensions called roots that protrude from each side of the spinal cord

The ventral roots contain axons of motor neurons that are leaving the spinal cord on their way to effectors (muscles or glands)

The dorsal roots contain axons of sensory neurons that are found in the dorsal root ganglion just outside the spinal cord; and they are bringing sensory information from sensory receptors to the CNS

The 2 roots come together and form the spinal nerves that extend out from the spinal cord

o The amount of gray matter present at a given level of the spinal cord reflects the amount of skeletal muscle innervated at that level

White Matter of the Spinal Cordo Allow for communication b/w different areas of the spinal cord and b/w the cord and

brain Ascending fibers – sensory; travel up to higher parts of spinal cord or brain Descending fibers – motor outputs; travel down from brain or from higher levels

of spinal cord Transverse fibers – travel from one side of cord to other

Generalizations for Pathways of Spinal Cordo Most cross from one side of the CNS to the other at some point along their journeyo Most pathways consist of a chain of 2 – 3 neuronso Most exhibit somatotophy – a precise spatial relationship among the tract fibers that

reflects the orderly mapping of the body (fibers from legs are medial to fibers from arms, for ex)

o All pathways and tracts are paired ( r and l) with a member of each pair present on each side of the spinal cord or brain

Ascending Pathwayo First Order Neuron – all ascending pathways (sensory pathways going to brain) start at

the sensory receptor (dendrite location) and travel to the dorsal root ganglion (location of the sensory neuron soma)

o Second Order Neuron – next connecting neuron soma is either in the spinal cord gray matter or in the medulla

o Third Order Neuron – the next and final connection is in the thalamus with axons going to cerebrum

(if final destination is the cerebellum, there is no third order neuron) Descending Pathway

o Motor pathways invlove 2 or 3 neuronso Upper motor neuron – neuron in the cerebral cortex with a long axon running down

through the brain stem, down the spinal cord where it synapses with either the interneuron and then the lower motor neuron going to the skeletal muscle

Spinal Nerveso 31 pairs of mixed nerves named according to their point of issue from the spinal cord

8 cervical (C1–C8) 12 thoracic (T1–T12) 5 Lumbar (L1–L5) 5 Sacral (S1–S5) 1 Coccygeal (C0)

o Roots Each spinal nerve connects to the spinal cord via two roots Ventral roots

Contain motor (efferent) fibers from the ventral horn motor neurons Fibers innervate skeletal muscles)

Dorsal roots Contain sensory (afferent) fibers from sensory neurons in the dorsal

root ganglia Conduct impulses from peripheral receptors

Dorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the intervertebral foramina

o Rami Each spinal nerve branches into mixed rami Dorsal ramus Larger ventral ramus Meningeal branch Rami communicantes (autonomic pathways) join to the ventral rami in the

thoracic region All ventral rami except T2–T12 form interlacing nerve networks called plexuses

(cervical, brachial, lumbar, and sacral) The back is innervated by dorsal rami via several branches Ventral rami of T2–T12 as intercostal nerves supply muscles of the ribs,

anterolateral thorax, and abdominal wallo Cervical Plexus

Formed by ventral rami of C1–C4 Innervates skin and muscles of the neck, ear, back of head, and shoulders

Phrenic nerve Major motor and sensory nerve of the diaphragm (receives fibers from

C3–C5) Spinal nerves C1-4 Innervates muscles attached to hyoid bone and neck Contains phrenic nerve which innervates diaphragm

o Brachial Plexus Formed by ventral rami of C5–C8 and T1 (and often C4 and T2) It gives rise to the nerves that innervate the upper limb Major branches of this plexus:

Roots—five ventral rami (C5–T1) Trunks—upper, middle, and lower Divisions—anterior and posterior Cords—lateral, medial, and posterior

Nerves Axillary—innervates the deltoid, teres minor, and skin and joint capsule

of the shoulder Musculocutaneous—innervates the biceps brachii and brachialis and

skin of lateral forearm Median—innervates the skin, most flexors and pronators in the

forearm, and some intrinsic muscles of the hand Ulnar—supplies the flexor carpi ulnaris, part of the flexor digitorum

profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand

Radial—innervates essentially all extensor muscles, supinators, and posterior skin of limb

o Lumbar Plexus Arises from L1–L4 Innervates the thigh, abdominal wall, and psoas muscle Femoral nerve—innervates quadriceps and skin of anterior thigh and medial

surface of leg Obturator nerve—passes through obturator foramen to innervate adductor

muscleso Sacral Plexus

Arises from L4–S4 Serves the buttock, lower limb, pelvic structures, and perineum Sciatic nerve

Longest and thickest nerve of the body Innervates the hamstring muscles, adductor magnus, and most muscles

in the leg and foot Composed of two nerves: tibial and common fibular

o Innervation of Skin by Spinal Nerves Dermatome: the area of skin innervated by the cutaneous branches of a single

spinal nerve All spinal nerves except C1 participate in dermatomes Most dermatomes overlap, so destruction of a single spinal nerve will not cause

complete numbnesso Innervation of Joints

Just know that they do innervate joints

Peripheral Nervous System

All neural structures outside the braino Sensory receptors

Specialized to respond to changes in their environment (stimuli) Activation results in graded potentials that trigger nerve impulses Sensation (awareness of stimulus) and perception (interpretation of the

meaning of the stimulus) occur in the brain Classification of Receptors

Based on:o Stimulus type

Mechanoreceptors—respond to touch, pressure, vibration, stretch, and itch

Thermoreceptors—sensitive to changes in temperature Photoreceptors—respond to light energy (e.g., retina) Chemoreceptors—respond to chemicals (e.g., smell,

taste, changes in blood chemistry) Nociceptors—sensitive to pain-causing stimuli (e.g.

extreme heat or cold, excessive pressure, inflammatory chemicals)

o Location 1. Exteroceptors

Respond to stimuli arising outside the body Receptors in the skin for touch, pressure, pain,

and temperature Most special sense organs

2. Interoceptors (visceroceptors) Respond to stimuli arising in internal viscera

and blood vessels Sensitive to chemical changes, tissue stretch,

and temperature changes 3. Proprioceptors

Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles

Inform the brain of one’s movementso Structural complexity

o Peripheral nerves and associated gangliao Motor endings

From Sensation to Perceptiono Survival depends upon sensation and perceptiono Sensation: the awareness of changes in the internal and external environmento Perception: the conscious interpretation of those stimuli

Main Aspects of Sensory Perceptiono Feature abstraction—identification of more complex aspects and several stimulus

propertieso Quality discrimination—the ability to identify submodalities of a sensation (e.g., sweet

or sour tastes)o Pattern recognition—recognition of familiar or significant patterns in stimuli (e.g., the

melody in a piece of music) Perception of Pain

o Warns of actual or impending tissue damageo Stimuli include extreme pressure and temperature, histamine, K+, ATP, acids, and

bradykinin o Impulses travel on fibers that release neurotransmitters glutamate and substance Po Some pain impulses are blocked by inhibitory endogenous opioids

Spinal Cordo Extends from foramen magnum to 2nd lumbar vertebrao Protected by vertebral columno Spinal nerves allow movemento If damaged paralysis can occur

Gray and White Matter in Spinal Cordo Gray Matter:

center of spinal cord looks like letter H or a butterfly Posterior horns:

contain axons which synapse with interneurons Anterior horns:

contain somatic neurons Lateral horns:

contain autonomic neurons Central canal:

fluid filled space in center of cord

o White Matter: outside of spinal cord contains myelinated fibers

Spinal Nerveso Arise along spinal cord from union of dorsal roots and ventral rootso Contain axons sensory and somatic neuronso Located between vertebrao Categorized by region of vertebral column from which it emerges (C for cervical)o 31 pairso Organized in 3 plexuseso Structure

Cordlike organ of the PNS Bundle of myelinated and unmyelinated peripheral axons enclosed by

connective tissue Connective tissue coverings include: Endoneurium—loose connective tissue that encloses axons and their myelin

sheaths Perineurium—coarse connective tissue that bundles fibers into fascicles Epineurium—tough fibrous sheath around a nerve

o Classification Most nerves are mixtures of afferent and efferent fibers and somatic and

autonomic (visceral) fibers Pure sensory (afferent) or motor (efferent) nerves are rare Types of fibers in mixed nerves:

Somatic afferent and somatic efferent Visceral afferent and visceral efferent

Peripheral nerves classified as cranial or spinal nerves Ganglia

o Contain neuron cell bodies associated with nerves Dorsal root ganglia (sensory, somatic) (Chapter 12) Autonomic ganglia (motor, visceral) (Chapter 14)

Regeneration of Nerve Fiberso Mature neurons are amitotico If the soma of a damaged nerve is intact, axon will regenerateo Involves coordinated activity among:

Macrophages—remove debris Schwann cells—form regeneration tube and secrete growth factors Axons—regenerate damaged part

o CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration

Cranial Nerves

o Twelve pairs of nerves associated with the brain o Most are mixed in function; two pairs are purely sensoryo Each nerve is identified by a number (I through XII) and a name

“On occasion, our trusty truck acts funny—very good vehicle anyhow”o I: Olfactory Nerves

Arise from the olfactory receptor cells of nasal cavity Pass through the cribriform plate of the ethmoid bone Fibers synapse in the olfactory bulbs Pathway terminates in the primary olfactory cortex Purely sensory (olfactory) function

o II: The Optic Nerves Arise from the retinas Pass through the optic canals, converge and partially cross over at the optic

chiasma Optic tracts continue to the thalamus, where they synapse Optic radiation fibers run to the occipital (visual) cortex Purely sensory (visual) function

o III: The Oculomotor Nerves Fibers extend from the ventral midbrain through the superior orbital fissures to

the extrinsic eye muscles Functions in raising the eyelid, directing the eyeball, constricting the iris

(parasympathetic), and controlling lens shapeo IV: The Trochlear Nerves

Fibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle

Primarily a motor nerve that directs the eyeballo V: The Trigeminal Nerves

Largest cranial nerves; fibers extend from pons to face Three divisions

Ophthalmic (V1) passes through the superior orbital fissure Maxillary (V2) passes through the foramen rotundum Mandibular (V3) passes through the foramen ovale

Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

o VI: The Abducens Nerves Fibers from the inferior pons enter the orbits via the superior orbital fissures Primarily a motor, innervating the lateral rectus muscle

o VII: The Facial Nerves Fibers from the pons travel through the internal acoustic meatuses, and emerge

through the stylomastoid foramina to the lateral aspect of the face Chief motor nerves of the face with 5 major branches

Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands

Sensory function (taste) from the anterior two-thirds of the tongueo VIII: The Vestibulocochlear Nerves

Afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla border

Mostly sensory function; small motor component for adjustment of sensitivity of receptors

o IX: The Glossopharyngeal Nerves Fibers from the medulla leave the skull via the jugular foramen and run to the

throat Motor functions: innervate part of the tongue and pharynx for swallowing, and

provide parasympathetic fibers to the parotid salivary glands Sensory functions: fibers conduct taste and general sensory impulses from the

pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors

o X: The Vagus Nerves The only cranial nerves that extend beyond the head and neck region Fibers from the medulla exit the skull via the jugular foramen Most motor fibers are parasympathetic fibers that help regulate the activities of

the heart, lungs, and abdominal viscera Sensory fibers carry impulses from thoracic and abdominal viscera,

baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx

o XI: The Accessory Nerves Formed from ventral rootlets from the C1–C5 region of the spinal cord (not the

brain) Rootlets pass into the cranium via each foramen magnum Accessory nerves exit the skull via the jugular foramina to innervate the

trapezius and sternocleidomastoid muscleso XII: The Hypoglossal Nerves

Fibers from the medulla exit the skull via the hypoglossal canal Innervate extrinsic and intrinsic muscles of the tongue that contribute to

swallowing and speech

Muscular System Functions

o 1. Movemento 2. Maintain postureo 3. Respirationo 4. Production of body heato 5. Communicationo 6. Heart beato 7. Contraction of organs and vessels

Types of Muscleso 1. Skeletalo 2. Cardiaco 3. Smooth

Abilities of Skeletal Muscleso Contractility:

ability to shorten o Excitability:

respond to stimuluso Extensibility:

can stretcho Elasticity:

recoil Skeletal Muscle Characteristics

o Makes up 40% of body weighto Named because attached to bones (skeleton)o Many nuclei per cell (near periphery)o Striatedo Longest of muscle types

Skeletal Muscle Structures – Connective Tissue Coveringso Epimysium:

connective tissue that surrounds entire skeletal muscle (outside)

o Muscle fasciculus: bundle of muscle fibers

o Perimysium: connective tissue around each muscle fasciculus

o Muscle fiber: - skeletal muscle cells - many nuclei

o Endomysium: connective tissue that surrounds each muscle fiber

Skeletal Muscle Structures – Muscle Fiber Structureo Myofibril:

thread-like proteins that make up muscle fiberso Myofilament:

- proteins that make up myofibrils - Ex. actin and myosin

o Sarcoplasm: cytoplasm of muscle fiber (cell)

o Sarcolemma: - cell membrane - contains T-tubules

o T-tubules (transverse): - wrap around sarcomeres at A band - associated with sarcoplasmic reticulum

o Sarcoplasmic reticulum: - type of SER - surrounds myosin - stores and releases Ca2+

Skeletal Muscle structures – Actin and Myosin Myofilamentso Actin:

- thin myofilament - resemble 2 strands of pearls

o Myosin: - thick myofilament - resemble golf clubs

o Troponin: attachment site on actin for Ca2+

o Tropomyosin: - filament on grooves of actin - attachment site on actin for myosin

Skeletal Muscle Structures- Sarcomereso Sarcomere:

- contractile unit - contains actin and myosin

o Z disk: protein fibers that form attachment site for actin

o H zone: - center of sarcomere - contains only myosin

o I band: contains only actin

o A band: where actin and myosin overlap

o M line: where myosin are anchored

Nerve Supplyo Motor neuron:

nerve cells that carry action potentials to muscle fiberso Neuromuscular junction (synapse):

where nerve cell and muscle fiber meeto Presynaptic terminal:

end of nerve cell (axon) o Postsynaptic membrane:

muscle fiber membraneo Synpatic cleft:

space between presynpatic terminal and postsynaptic membrane

o Synaptic vesicle: - in presynaptic terminal - store and release neurotransmitters

o Neurotransmitter: - chemicals that stimulate or inhibit a muscle fiber

- Ex. Acetylcholineo Motor unit:

group of muscle fibers that motor neuron stimulates Steps in Muscle Contraction

o Sliding Filament Theory 1. An action potential travels down motor neuron to

presynaptic terminal causing Ca2+ channels to open. 2. Ca2+ causes synaptic vesicles to release acetylcholine into

synaptic cleft. 3. Acetylcholine binds to receptor sites on Na+ channels, Na+

channels open, and Na+ rushes into postsynaptic terminal (depolarization).

4. Na+ causes sarcolemma and t-tubules to increase the permeability of sarcoplasmic reticulum which releases stored calcium.

5. Ca2+ binds to troponin which is attached to actin. 6. Ca2+ binding to troponin causes tropomyosin to move

exposing attachment sites for myosin. 7. Myosin heads bind to actin. 8. ATP is released from myosin heads and heads bend toward

center of sarcomere. 9. Bending forces actin to slide over myosin. 10. Acetylcholinesterase (enzyme breaks down acetylcholine) is

released, Na+ channels close, and muscle contraction stops. ATP and Muscle Contractions

o Energy for muscle contractions supplied by ATPo Energy is released as ATP → ADP + Po ATP is stored in myosin headso ATP helps form cross-bridge formation between myosin and actin o New ATP must bind to myosin before cross-bridge is releasedo Rigor mortis:

person dies and no ATP is available to release cross-bridges o ATP is made in mitochondria from aerobic or anaerobic respiration.o During a muscle contraction, H zone and I band shorten but A band

stays the same.o Striations of skeletal and cardiac muscle are due to sarcomeres (actin

and myosin). Terms

o Threshold: weakest stimulus needed to produce a response

o All or None Law: muscle contracts or doesn’t (no in between)

o Twitch: rapid contraction and relaxation of a muscle

o Tetanus: muscle remains contracted

o Isometric: amount of tension increases (weight)

o Isotonic: amount of repetitions increases

o Tone: constant tension over a long period of time

Slow and Fast Twitch Fiberso Humans have both types of fiberso Distribution of fibers is genetically determined

o Neither type can be converted but capacity can be increased through intense exercise

o Slow Twitch Fibers Contract slowly Fatigue slowly Long distance runners Use aerobic respiration Energy from fat Dark meat Red or dark because of myoglobin Myoglobin: helps O2 bind in muscle

o Fast Twitch Fibers Contract quickly Fatigue quickly Sprinters Use anaerobic respiration Energy from glycogen White meat

Skeletal Muscle Anatomyo Origin:

nonmovable end o Insertion:

movable end o Belly:

middle o Synergists:

muscles that work together o Antagonist:

muscles that oppose each other Muscle Nomenclature

o Muscles are named according to Location Origin/insertion Size Shape Function

Cardiac Muscle Characteristicso Hearto 1 centrally located nucleus/cello Striatedo Rich in mitochondria

o Intercalated disks: special cell junctions that allow cells to act as a unit

Smooth Muscle Characteristicso Found on organso 1 centrally located nucleus/cello Not striatedo Less actin and myosino Under involuntary control

Autonomic Nervous System

The ANS consists of motor neurons that: o Innervate smooth and cardiac muscle and glandso Make adjustments to ensure optimal support for body activitieso Operate via subconscious control

Other nameso Involuntary nervous system o General visceral motor system

Somatic and Autonomic Nervous Systemo The two systems differ in

Effectors Somatic nervous system

o Skeletal muscles ANS

o Cardiac muscleo Smooth muscleo Glands

Efferent pathways (and their neurotransmitters) Somatic nervous system

o A, thick, heavily myelinated somatic motor fiber makes up each pathway from the CNS to the muscle

ANS pathway is a two-neuron chaino Preganglionic neuron (in CNS) has a thin, lightly myelinated

preganglionic axono Ganglionic neuron in autonomic ganglion has an unmyelinated

postganglionic axon that extends to the effector organ Target organ responses to neurotransmitters

Somatic nervous systemo All somatic motor neurons release acetylcholine (ACh)o Effects are always stimulatory

ANS

o Preganglionic fibers release ACh o Postganglionic fibers release norepinephrine or ACh at

effectorso Effect is either stimulatory or inhibitory, depending on type of

receptors Divisions of the ANS

o 1. Sympathetic divisiono 2. Parasympathetic divisiono Dual innervation

Almost all visceral organs are served by both divisions, but they cause opposite effects

Role of the Parasympathetic Divisiono Promotes maintenance activities and conserves body energyo Its activity is illustrated in a person who relaxes, reading, after a meal

Blood pressure, heart rate, and respiratory rates are low Gastrointestinal tract activity is high Pupils are constricted and lenses are accommodated for close vision

o Mobilizes the body during activity; is the “fight-or-flight” systemo Promotes adjustments during exercise, or when threatened

Blood flow is shunted to skeletal muscles and heart Bronchioles dilate Liver releases glucose

ANS Anatomy

Division Origin of Fibers Length of Fibers Location of Ganglia

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o