Nervous System II

Meninges• membranes surrounding CNS• protect CNS• three layers

• dura mater – outer, tough• arachnoid mater - weblike• pia mater – inner, delicate

Meninges of the Spinal Cord

Ventricles• interconnected cavities• within cerebral hemispheres and brain stem• continuous with central canal of spinal cord• filled with cerebrospinal fluid (csf)

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

Cerebrospinal Fluid

• secreted by choroid plexus• circulates in ventricles, central canal of spinal cord, and subarachnoid space• completely surrounds brain and spinal cord• clear liquid• nutritive and protective• helps maintain stable ion concentrations in CNS

Spinal Cord Structure• extends foramen magnum to 2nd lumbar vertebra

Cross Section of Spinal Cord

Spinal Cord Functions

• center for spinal reflexes

• conduit for nerve impulses to and from the brain

Reflex ArcsReflexes – automatic, subconscious responses to stimuli

Knee-jerk Reflex• helps maintain posture

Withdrawal Reflex• protective

Crossed-Extensor Reflex

• flexor muscles contract• flexor muscles on opposite side inhibited• extensor muscles on opposite side contract for balance

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

Ascending Tracts• fasciculus cuneatus• lateral spinothalamic

Corticospinal Tract

Brain

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

Major Parts• cerebrum

• two cerebellar hemispheres• diencephalon• brain stem• cerebellum

Brain Development

Three Major Vesicles1. Forebrain2. Midbrain3. Hindbrain

Forebrain (prosencephalon)• anterior portion (telencephalon)

• cerebrum• basal ganglia

• posterior portion (diencephalon)• thalamus• hypothalamus• posterior pituitary• pineal gland

Brain Development

Midbrain (mesencephalon)

• midbrain

Hindbrain (rhombencephalon)• anterior portion (metencephalon)

• cerebellum• pons

• posterior portion (myelencephalon)• medulla oblongata

Structure of Cerebrum

• corpus callosum• connects hemispheres

• convolutions • bumps or gyri

• sulci• grooves

• longitudinal fissure• separates hemispheres

• transverse fissure• separates cerebrum from cerebellum

Lobes of Cerebrum

• Frontal• Parietal• Temporal• Occipital• Insula

Functions of Cerebrum

• interpretation• initiating voluntary movements• storing memory• retrieving memory• reasoning• center for 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

Motor Areas• Primary Motor Areas

• frontal lobes• control voluntary muscles

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

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

Motor Areas

Sensory Areas

• Cutaneous Sensory Area

• parietal lobe• interprets sensations on skin

• Visual Area• occipital lobe• interprets vision

• Auditory Area• temporal lobe• interprets hearing

Sensory Areas

Association Areas• regions of cortex 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• problem solving• judging

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

Temporal Lobe Association Areas• remember visual scenes• remember music• remember complex patterns

Occipital Lobe Association Areas• combine visual images with other sensory experiences

Hemisphere Dominance

• In over 90% of population, left hemisphere is dominant

• 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 circuit• circuit is stimulated over and over• when impulse flow stops, memory disappears

Long Term• changes structure and function of neurons• enhanced synaptic transmission

Basal Nuclei

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

Diencephalon• between cerebral hemispheres and brainstem• surrounds third ventricle

• thalamus• hypothalamus• optic tracts• optic chiasm• 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

Limbic System

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

Functions• controls emotions• produces feelings• interpret sensory impulses

Brain Stem

Three Parts1. Midbrain2. Pons3. 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

Pons

• 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, 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• 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)• 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

Peripheral Nervous System

• Cranial nerves arising from the brain• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

• Spinal nerves arising from the spinal cord• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

Structure of a Peripheral Nerve

Nerve Fiber Classification

• Sensory Nerves – conduct impulses into CNS• Motor Nerves – conduct impulses to muscles or glands• Mixed Nerves – contain both sensory nerve fibers and motor nerve fibers; most nerves

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

Nerve Fiber Classification

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

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

Oculomotor (III)• primarily motor• motor impulses to muscles that

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

Cranial Nerve VTrigeminal (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 VIIAbducens (VI)

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

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• sensory from equilibrium receptors of ear• 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• motor to muscles of soft palate, pharynx, larynx, neck, and back

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

Spinal Nerves

• mixed nerves• 31 pairs

• 8 cervical (C1 to C8)• 12 thoracic (T1 to T12)• 5 lumbar (L1 to L5)• 5 sacral (S1 to S5)• 1 coccygeal (Co)

Spinal NervesDorsal root

• axons of sensory neurons in the dorsal root ganglion

Dorsal root ganglion • cell bodies of sensory neurons

Ventral root• axons of motor neurons whose cell bodies are in spinal cord

Spinal nerve• union of ventral root and dorsal root

Dermatome• an area of skin that the sensory nerve fibers of a particular spinal nerve innervate

Cervical Plexus

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

Cervical Plexus• C1-C4• lies deep in the neck• supply muscles and skin of the neck• contribute to phrenic nerve

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

• supply muscles of anterior arms and skin of forearms

• ulnar 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 superior, lateral, and posterior arms

Lumbosacral Plexus

• T12 – S5• extend from lumbar region into pelvic cavity• obturator nerves

• supply adductors of thighs

• femoral nerves• supply muscles and skin of thighs and legs

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

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

Autonomic Nerve Fibers

• all 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

Sympathetic Division

• 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

Sympathetic Division• 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

• preganglionic fibers to adrenal medulla do not synapse with postganglionic neurons

Sympathetic Division

Parasympathetic Division

• craniosacral division – location of preganglionic neurons

• ganglia are near or within various organs

• short postganlionic fibers

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

• preganglionic fibers of thorax and abdomen in X

Parasympathetic Division

Autonomic NeurotransmittersCholinergic Fibers

• release acetylcholine• preganglionic sympathetic fibers• preganglionic parasympathetic fibers• postganglionic parasympathetic fibers

Adrenergic Fibers• release norepinephrine• postganglionic sympathetic fibers

Actions of AutonomicNeurotransmitters

• depend on receptor

Cholinergic receptors• bind to acetlycholine• muscarinic

• excitatory • nicotinic

• excitatory

Adrenergic Receptors• bind to norepinephrine• alpha

• different responses on various effectors

• beta• different responses on various effectors

Insert figure 11.39Actions of Autonomic

Neurotransmitters

Control of Autonomic Activity

• Controlled largely by CNS• Medulla oblongata regulates cardiac, vasomotor and respiratory activities• Hypothalamus regulates visceral functions• Limbic system and cerebral cortex control emotional responses

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 lobe has lost half its neurons• Number of dendritic branches decreases• Decreased levels of neurotransmitters• Fading memory• Slowed responses and reflexes• Changes increase risk of falling• Sleep problems common

Clinical ApplicationCerebral 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• seizues• learning disabilities

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

TABLES FOR CHAPTER 11