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Hole’s Human Anatomy and Physiology

Eleventh Edition

Shier w Butler w Lewis

Chapter

Chapter 11: Nervous System II

Meninges • membranes surrounding CNS

• protect CNS

• three layers

1. dura mater

2. arachnoid mater

3. pia mater

Meninges

dura mater • Outer most • Tough, white connective tissue • Contains blood vessels and nerves

arachnoid mater • Middle layer • Thin, weblike • Sub-arachnoid space below which is filled with cerebrospinal fluid

pia mater • Innermost • Thin delicate connective tissues • Many nerves and blood vessels for nourishment • Dips into grooves and contours of brain

Meninges of the Spinal Cord

Space between vertebrae and dura mater is called epidural space and is filled with loose connective tissue and fat.

Epidural used for pain

during childbirth

Meningitis

• infection within the meninges

• 2 types – viral and bacterial

Meningitis

•May be diagnosed by drawing CSF from sub-arachnoid space at the lumbar region in a procedure called a lumbar puncture. This procedure is also called a spinal tap.

Major Divisions of the Brain

Also classified as:

Ventricles

• interconnected cavities

•lateral ventricles •third ventricle •fourth ventricle •cerebral aqueduct

• within cerebral hemispheres and brain stem

• continuous with central canal of spinal cord

• filled with cerebrospinal fluid (CSF)

Cerebrospinal Fluid

• secreted by choroid plexus

• circulates in:

•Ventricles •central canal of spinal cord •subarachnoid space

• completely surrounds brain and spinal cord

• clear liquid

• nutritive and protective

• helps maintain stable ion concentrations in CNS

Ommaya Reservior

Spinal Cord

• slender column of nervous tissue continuous with brain

• extends downward through vertebral canal

• begins at level of foramen magnum and terminates near first and second lumbar

Cross Section of Spinal Cord

Functions of Spinal Cord

• center for spinal reflexes

• conduit for nerve impulses to and from the brain

Reflex Arcs

Reflexes – automatic, subconscious responses to stimuli within or outside the body

General Components of a Spinal Reflex

Tracts of the Spinal Cord

• Ascending tracts conduct sensory impulses to the brain

• Descending tracts conduct motor impulses from the brain to motor neurons reaching muscles and glands

Functions • interprets sensations • determines perception • stores memory • reasoning • makes decisions • coordinates muscular movements • regulates visceral activities • determines personality

Major Parts • cerebrum

• two hemispheres

• basal nuclei • • diencephalon

• brainstem

• cerebellum

Brain Development

Three Major Vesicles 1. Forebrain 2. Midbrain 3. Hindbrain

Brain Development

Structure of Cerebrum

• corpus callosum • connects cerebral hemispheres

• convolutions • bumps or gyri

• sulci • grooves

• longitudinal fissure • separates hemispheres

• transverse fissure • separates cerebrum from cerebellum

Lobes of Cerebral Hemispheres

• Frontal

• Parietal

• Temporal

• Occipital

• Insula

Functions of the Cerebrum

• interpreting impulses

• initiating voluntary movements

• storing information as memory

• retrieving stored information

• reasoning

• seat of intelligence and personality

Functional Regions of Cerebral Cortex

Cerebral Cortex – thin layer of gray matter that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system

Sensory Areas

• Cutaneous Sensory Area • parietal lobe • interprets sensations on skin

• Visual Area • occipital lobe • interprets vision

• Auditory Area • temporal lobe • interprets hearing

• Sensory Area for Taste • near bases of the central sulci

•Sensory Area for Smell •arise from centers deep within the cerebrum

Sensory Areas

Association Areas

• regions that are not primary motor or primary sensory areas • widespread throughout the cerebral cortex • analyze and interpret sensory experiences • provide memory, reasoning, verbalization, judgment, emotions

Association Areas

Frontal Lobe Association Areas • concentrating • planning • complex problem solving

Parietal Lobe Association Areas • understanding speech • choosing words to express thought

Temporal Lobe Association Areas • interpret complex sensory experiences • store memories of visual scenes, music, and complex patterns

Occipital Lobe Association Areas

• analyze and combine visual images with other sensory experiences

Hemisphere Dominance

• The left hemisphere is dominant is most individuals

• Dominant hemisphere controls

• speech • writing • reading • verbal skills • analytical skills • computational skills

• Nondominant hemisphere controls

• nonverbal tasks • motor tasks • understanding and interpreting musical and visual patterns • provides emotional and intuitive thought processes

Memory

Short Term • working memory • closed neuronal circuit • circuit is stimulated over and over • when impulse flow ceases, memory does also

• unless it enters long-term memory via memory consolidation

Long Term • changes structure or function of neurons • enhances synaptic transmission

Motor Areas

• Primary Motor Areas • frontal lobes • control voluntary muscles

• Broca’s Area • anterior to primary motor cortex • usually in left hemisphere • controls muscles needed for speech

• Frontal Eye Field • above Broca’s area • controls voluntary movements of eyes and eyelids

Motor Areas

Functions of the Cerebral Lobes

Basal Nuclei

• masses of gray matter • deep within cerebral hemispheres • caudate nucleus, putamen, globus pallidus • produce dopamine • control certain muscular activities

• primarily by inhibiting motor functions

Diencephalon

• between cerebral hemispheres and above the brainstem • surrounds third ventricle

• thalamus • hypothalamus • optic tracts • optic chiasma • infundibulum • posterior pituitary • mammillary bodies • pineal gland

Diencephalon

Thalamus • gateway for sensory impulses heading to cerebral cortex • receives all sensory impulses (except smell) • channels impulses to appropriate part of cerebral cortex for interpretation

Hypothalamus • maintains homeostasis by regulating visceral activities • links nervous and endocrine systems

Diencephalon

Consists of • portions of frontal lobe • portions of temporal lobe • hypothalamus • thalamus • basal nuclei • other deep nuclei

Functions • controls emotions • produces feelings • interprets sensory impulses

Limbic System

Brain Stem

Three Parts 1. Midbrain 2. Pons 3. Medulla Oblongata

Midbrain

• between diencephalon and pons • contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain • cerebral aqueduct • cerebral peduncles – bundles of nerve fibers • corpora quadrigemina – centers for visual and auditory reflexes

• rounded bulge on underside of brainstem • between medulla oblongata and midbrain • helps regulate rate and depth of breathing • relays nerve impulses to and from medulla oblongata and cerebellum

Medulla Oblongata

• enlarged continuation of spinal cord • conducts ascending and descending impulses between brain and spinal cord • contains cardiac, vasomotor, and respiratory control centers • contains various nonvital reflex control centers (coughing, sneezing, swallowing, vomiting)

Reticular Formation

• complex network of nerve fibers scattered throughout the brain stem • extends into the diencephalon • connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum • filters incoming sensory information • arouses cerebral cortex into state of wakefulness

Types of Sleep

Slow Wave • non-REM sleep • person is tired • decreasing activity of reticular system • restful • dreamless • reduced blood pressure and respiratory rate • ranges from light to heavy • alternates with REM sleep

Rapid Eye Movement (REM) • paradoxical sleep • some areas of brain active• heart and respiratory rates irregular • dreaming occurs

Cerebellum

• inferior to occipital lobes • posterior to pons and medulla oblongata • two hemispheres • vermis connects hemispheres • cerebellar cortex – gray matter • arbor vitae – white matter • cerebellar peduncles – nerve fiber tracts • dentate nucleus – largest nucleus in cerebellum • integrates sensory information concerning position of body parts • coordinates skeletal muscle activity • maintains posture

Major Parts of the Brain

Peripheral Nervous System

Subdivided into 2 branches:

1. Sensory Divison

2. Motor Divison

PNS: Motor Division

Subdivided into 2 branches: 1. Somatic NS – from CNS to skin and skeletal muscles

2. Autonomic NS – from CNS to smooth muscle, cardiac

muscle and endocrine glands

Peripheral Nervous System

1. Cranial nerves arising from the brain 2. Spinal nerves arising from the spinal cord

Both have • Somatic fibers connecting to the skin and skeletal muscles

• Autonomic fibers connecting to viscera

Includes:

Nerve Fiber Classification

• Sensory Nerves – conduct impulses into brain or spinal cord

• Motor Nerves – conduct impulses to muscles or glands

• Mixed Nerves – contain both sensory nerve fibers and motor nerve fibers; most nerves

A nerve is a cord-like bundle of axons wrapped in connective tissue. There are 3 types of nerve fibers.

Two Subdivisions of spinal and cranial nerves: These are the 2 subdivisions of Sensory division of PNS

1. General – fibers associated with general structures such as the

skin, skeletal muscles, glands, and viscera. 2. Special – fibers associated with more specialized structures such

as eyes and ears

General somatic efferent fibers • carry motor impulses from CNS to skeletal muscles

General visceral efferent fibers • carry motor impulses away from CNS to smooth muscles and glands

General somatic afferent fibers • carry sensory impulses to CNS from skin and skeletal muscles

General visceral afferent fibers • carry sensory impulses to CNS from blood vessels and internal organs

Special somatic efferent fibers • carry motor impulses from brain to muscles used in chewing, swallowing, speaking, and forming facial expressions

Special visceral afferent fibers • carry sensory impulses to brain from olfactory and taste receptors

Special somatic afferent fibers • carry sensory impulses to brain from receptors of sight, hearing, and equilibrium

Cranial Nerves

12 pairs of cranial nerves

2 pair to/from forebrain

10 pairs to/from brain stem

Cranial Nerves

I. Olfactory – sense of smell - sensory only

II. Optic – sense of vision - sensory only

III. Oculomotor – innervates eye muscles - motor only

IV. Trochlear – innervates eye muscles - motor only

V. Trigeminal – largest sensory from face motor to chewing muscles -

VI. Abducens – innervates eye muscles - motor only

Cranial Nerves

VII. Facial – innervates muscles of facial expression sensory taste - mixed

VIII. Vestibulocochlear – sense of hearing and equilibrium - sensory only

IX. Glossopharyngeal – moves tongue and pharynx muscles - mixed

X. Vagus – innervates visceral smooth muscle - mixed

XI. Accessory – innervates neck muscles - motor only

XII. Hypoglossal – moves tongue - motor only

Spinal Nerves

• ALL mixed nerves

• 31 pairs • 8 cervical • 12 thoracic • 5 lumbar • 5 sacral • 1 coccygeal

Spinal Nerves

Dorsal root (posterior or sensory root) • axons of sensory neurons in the dorsal root ganglion

Dorsal root ganglion • cell bodies of sensory neurons whose axons conduct impulses inward from peripheral body parts

Spinal Nerves

Ventral root (anterior or motor root) • axons of motor neurons whose cell bodies are in spinal cord

Spinal nerve • union of ventral root and dorsal root

Nerve Plexus

Nerve plexus – complex networks formed by anterior branches of spinal nerves; fibers of various spinal nerves are sorted and recombined

Cervical Plexus - contribute to neck & phrenic (diaphragm) nerves

Brachial Plexus – upper limbs

Lumbar Plexus – anterior and medial thigh

Sacral Plexus – posterior lower limb

Somatic NS vs. Autonomic NS

Somatic NS

One motor neuron

No ganglia

Uses acetylcholine

Effector = skeletal muscle

Autonomic NS

Two motor neurons

Synapse between neurons occur within a

ganglion

Effectors = smooth muscle, cardiac muscle, &

glands 2 divisions:

○ Sympathetic ○ Parasympathetic

Autonomic Nervous System

• functions without conscious effort • controls visceral activities • regulates smooth muscle, cardiac muscle, and glands • efferent fibers typically lead to ganglia outside CNS

Two Divisions • sympathetic – prepares body for fight or flight situations • parasympathetic – prepares body for resting and digesting activities

Sympathetic Division

Preganglionic neuron = short Postganglionic neuron = long Norepinephrine is the neurotransmitter used.

Life-Span Changes

• Brain cells begin to die before birth • Over average lifetime, brain shrinks 10% • Most cell death occurs in temporal lobes • By age 90, frontal cortex has lost half its neurons • Number of dendritic branches decreases • Decreased levels of neurotransmitters • Fading memory • Slowed responses and reflexes • Increased risk of falling • Changes in sleep patterns that result in fewer sleeping hours

Clinical Application

Cerebral Injuries and Abnormalities Concussion

• brain jarred against cranium • loss of consciousness • temporary loss of memory • mental cloudiness • headache • recovery usually complete

Cerebral Palsy • motor impairment at birth • caused by blocked cerebral blood vessels during development • seizures • learning disabilities

Cerebrovascular Accident • stroke • sudden interruption in blood flow • brain tissues die

End here – rest are

extras

Parasympathetic Division

Preganglionic neuron = long Postganglionic neuron = short Acetylcholine is the neurotransmitter used.

Autonomic Nerve Fibers

• all are neurons are motor (efferent)

• preganglionic fibers • axons of preganglionic neurons • neuron cell bodies in CNS

• postganglionic fibers • axons of postganglionic neurons • neuron cell bodies in ganglia

• thoracolumbar divison – location of preganglionic neurons

• preganglionic fibers leave spinal nerves through white rami and enter paravertebral ganglia • paraverterbral ganglia and fibers that connect them make up the sympathetic trunk

• postganglionic fibers extend from sympathetic ganglia to visceral organs • postganglionic fibers usually pass through gray rami and return to a spinal nerve before proceeding to an effector • Exception: preganglionic fibers to adrenal medulla do not synapse with postganglionic neurons

Parasympathetic Division

• craniosacral division – location of preganglionic neurons

• ganglia are near or within various organs

• terminal ganglia • short

postganglionic fibers • continue to specific muscles or glands

• preganglionic fibers of the head are included in nerves III, VII, and IX

• preganglionic fibers of thorax and abdomen are parts of nerve X

Autonomic

Neurotransmitters

Cholinergic Fibers • release acetylcholine • preganglionic sympathetic and parasympathetic fibers • postganglionic parasympathetic fibers

Adrenergic Fibers

• release norepinephrine • most postganglionic sympathetic

Actions of Autonomic

Neurotransmitters

• depend on receptors in the membrane

Cholinergic receptors • bind to acetlycholine • muscarinic

• excitatory • slow

• nicotinic • excitatory • rapid

Adrenergic Receptors • bind to epinephrine and norepinephrine • alpha and beta

• both elicit different responses on various effectors

Insert figure 11.39

Actions of Autonomic Neurotransmitters

Control of Autonomic

Activity

• Controlled largely by CNS

• Medulla oblongata regulates cardiac, vasomotor and respiratory activities

• Hypothalamus regulates visceral functions, such as body temperature, hunger, thirst, and water and electrolyte balance

• Limbic system and cerebral cortex control emotional responses

Cranial Nerves I and II

Olfactory (I) • sensory • fibers transmit impulses associated with smell

Optic (II) • sensory • fibers transmit impulses associated with vision

Cranial Nerves III and IV

Trochlear (IV) • some sensory

• proprioreceptors • primarily motor • motor impulses to muscles that move the eyes

Oculomotor (III) • some sensory

• proprioreceptors • primarily motor • motor impulses to muscles that

• raise eyelids • move the eyes • focus lens •adjust light entering eye

Cranial Nerve V

Trigeminal (V) • mixed • opthalmic division

• sensory from surface of eyes, tear glands, scalp, forehead, and upper eyelids

• maxillary division • sensory from upper teeth, upper gum, upper lip, palate, and skin of face

• mandibular division • sensory from scalp, skin of jaw, lower teeth, lower gum, and lower lip • motor to muscles of mastication and muscles in floor of mouth

Cranial Nerves VI and VII

Abducens (VI) • primarily motor • motor impulses to muscles that move the eyes • some sensory with proprioreceptors

Facial (VII) • mixed • sensory from taste receptors • motor to muscles of facial expression, tear glands, and salivary glands

Cranial Nerves VIII and IX

Vestibulocochlear (VIII) • sensory • vestibular branch

•sensory from equilibrium receptors of ear

• cochlear branch •sensory from hearing receptors

Glossopharyngeal (IX) • mixed • sensory from pharynx, tonsils, tongue, and carotid arteries • motor to salivary glands and muscles of pharynx

Cranial Nerve X

Vagus (X) • mixed • somatic motor to muscles of speech and swallowing • autonomic motor to viscera of thorax and abdomen • sensory from pharynx, larynx, esophagus, and viscera of thorax and abdomen

Cranial Nerves XI and XII

Accessory (XI) • primarily motor • cranial branch

• motor to muscles of soft palate, pharynx, and larynx

• spinal branch •motor to muscles of neck, and back; some proprioreceptor

Hypoglossal (XII) • primarily motor • motor to muscles of the tongue; some proprioreceptor

Cervical Plexuses

Nerve plexus – complex networks formed by anterior branches of spinal nerves; fibers of various spinal nerves are sorted and recombined

Cervical Plexus • formed by anterior branches of C1-C4 • lies deep in the neck • supply muscles and skin of the neck • C3 – C5 contribute to phrenic nerves

Brachial Plexuses

• C5-T1 • lies deep within shoulders • musculocutaneous nerves

• supply muscles of anterior arms and skin of forearms

• ulnar and median nerves • supply muscles of forearms and hands • supply skin of hands

•radial nerves • supply posterior muscles of arms and skin of forearms and hands

• axillary nerves • supply muscles and skin of anterior, lateral, and posterior arms

Lumbosacral Plexuses

• T12 – S5

• extend from lumbar region into pelvic cavity

• obturator nerves • supply motor impulses to adductors of thighs

• femoral nerves • supply motor impulses to muscles of anterior thigh and sensory impulses from skin of thighs and legs

• sciatic nerves • supply muscles and skin of thighs, legs, and feet

Plexuses

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