Chapter 10

The Nervous System

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Objectives

List the organs and divisions of the nervous system and describe the generalized functions

Identify the major types of cells in the nervous system and discuss the function of each

Identify the major anatomical components of the brain and spinal cord and briefly comment on the function of each

Identify and discuss the coverings and fluid spaces of the brain and spinal cord

Compare and contrast spinal and cranial nerves

Discuss the structure and function of the two divisions of the autonomic nervous system

Describe major nervous system disorders

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Nervous System

1. Central nervous system (CNS) - brain and spinal

cord

2. Peripheral nervous

system (PNS) - all nerves

Autonomic nervous system

(ANS)

Somatic nervous system

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Central Nervous System

Contains:

Brain

Spinal cord

Made of gray and white matter

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Brainstem

Made up of 3 parts: medulla oblongata, pons, and midbrain

Medulla- regulates the vital functions of heart rate, breathing,

and BP; regulates reflexes of coughing, sneezing, swallowing,

and vomiting

Pons- contains respiratory centers that work with those in

medulla

Midbrain- contains centers for visual reflexes, auditory reflexes,

and righting (equilibrium) reflexes

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Cerebellum

Second largest part of the

human brain

Function

Regulates coordination of

voluntary movement, muscle

tone, stopping movements, and

equilibrium

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Diencephalon

Consist of hypothalamus, thalamus, and pineal gland

Control the functioning of most internal organs

Controls hormone secretion by anterior and posterior pituitary glands

Contains centers for controlling appetite, wakefulness, pleasure, etc.

Hypothalamus

Contributes to healthy survival

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Thalamus

Dumbbell-shaped mass of gray

matter extending into each

cerebral hemisphere

Superior to the hypothalamus

Inferior to the cerebrum

Relays and integrates sensory

impulses to cerebrum

Produces emotions of

pleasantness or unpleasantness

associated with sensations

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Cerebrum

Largest part of the human brain

Consists of two hemispheres

separated by longitudinal fissure

Outer layer of gray matter is the

cerebral cortex

Interior composed mainly of white

matter

Functions of the cerebrum:

mental processes of all types, including sensations,

consciousness, memory, and

voluntary control of movements

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Central Nervous System

Outer portion: Columns of white matter, composed of

bundles of myelinated nerve fibers

Interior portion: Gray matter made up mainly of neuron dendrites and cell bodies

Spinal cord tracts provide two-way conduction paths - ascending and descending

Spinal cord contains all spinal cord reflexes; sensory and motor tracts conduct impulses to and from the brain

Spinal Cord:

Cross-section of spinal cord

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Peripheral nervous system

Also known as (PNS) - all nerves outside of brain

and spinal cord

Contains:

1. Autonomic nervous system (ANS)

2. Somatic nervous system

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Autonomic Nervous System

The ANS- consists of motor neurons that conduct impulses

from the spinal cord or brainstem to the following tissues:

1. Cardiac muscle tissue

2. Smooth muscle tissue

3. Glandular epithelial tissue

Consists of two main divisions:

Sympathetic nervous system- “Fight or Flight”

Parasympathetic nervous system

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Autonomic Nervous System

Sympathetic nervous system

Serves as the emergency or stress system,

controlling visceral effectors during strenuous

exercise and when strong emotions (anger, fear,

hate, or anxiety) are elicited

Group of changes induced by sympathetic control

is called the fight-or-flight response

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Autonomic Nervous System

Parasympathetic nervous system

Function - dominates control of many visceral

effectors under normal, everyday conditions

What are visceral effectors referring to?

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Autonomic Nervous System

Motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue

Regulates body’s automatic or involuntary functions

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Autonomic Nervous System

Autonomic neurotransmitters

Cholinergic fibers – pre-ganglionic axons of

parasympathetic and sympathetic systems release

acetylcholine

Adrenergic fibers - axons of sympathetic postganglionic

neurons release norepinephrine (noradrenaline)

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Somatic Nervous System

Also part of peripheral nervous system

Voluntary action signaling of the nervous system

to the voluntary muscles

https://www.youtube.com/watch?v=pEezpi9g6_w

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Peripheral Nervous System

Cranial nerves 12 pairs - attached to undersurface of the brain

Connect brain with the neck and structures in the thorax and abdomen

The Cranial Nerves

I Olfactory

II Optic

III Oculomotor

IV Trochlear

V Trigeminal

VI Abducens

VII Facial

VIII Acoustic

IX Glossopharyngeal

X Vagus

XI Spinal accessory

XII Hypoglossal

“On Old Olympus’ Tiny

Tops, A Finn And German

Viewed Some Hops”

The Cranial Nerves

I Olfactory Sense of smell

II Optic Vision

III Oculomotor Eye movements

IV Trochlear Eye movements

V Trigeminal Sensation of face, scalp, teeth

VI Abducens Eye movements

VII Facial Sense of taste

VIII Acoustic Hearing, sense of balance

IX Glossopharyngeal Swallowing

X Vagus Sensations of throat, slowing of HR

XI Spinal accessory Shoulder shrug

XII Hypoglossal Tongue movements

NERVE FUNCTION

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Peripheral Nervous System

Spinal nerves: contain dendrites of sensory neurons and axons of motor neurons

Conduct impulses necessary for sensations and voluntary movements

Skin surface area supplied by a single nerve is called a dermatome

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Transmission

How do the signals get around?

video

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Neurons (nerve fibers)

1. Cell body: contains the

nucleus, essential for the life of

the neuron

2. Dendrites – processes that

transmit impulses toward the

cell body

3. Axon - elongated projection

that conducts impulses away

from the cell

4. Protected by the myelin

sheath: made of Schwann

cells

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Nerves

Bundle of peripheral axons

Tract – bundle of central

axons

White matter- brain or

cord tissue composed

primarily of myelinated

axons (tracts)

Gray matter- brain or

center of spinal cord

tissue composed

primarily of cell bodies

and unmyelinated fibers

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Neurons

Neurons classified according to function or direction of

impulse

Sensory neurons (afferent neurons): conduct

impulses to the spinal cord and brain

Motor neurons (efferent neurons): conduct impulses

away from brain and spinal cord to muscles and glands

Interneurons: conduct impulses from sensory neurons

to motor neurons; also called central or connecting

neurons

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Glia (neuroglia) Support cells: bring cells of nervous tissue together

structurally and functionally

Three main types of connective tissue cells of the CNS:

1. Astrocytes

2. Microglia

3. Oligodendrocytes

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Neuron signaling

1. Reception – the information is received

2. Transmission – an electrical process send

information from the afferent (sensory) neurons to

the interneurons in the CNS

3. Integration – the information is processed

4. Transmission – interneurons transmit information to

efferent (motor) neurons then to muscles or glands

5. Actual response

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The Synapse

Definition - the place where impulses are transmitted from one neuron to another

Synapse made of three structures - synaptic knob, synaptic cleft, and plasma membrane

Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron

http://www.news-medical.net/health/What-is-the-Nervous-System.aspx

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The Synapse

Names of neurotransmitters - acetylcholine,

(catecholamines; norepinephrine, dopamine,

and serotonin), endorphins, enkephalins, nitric

oxide (NO), and other compounds

Parkinson disease (PD) - characterized by

abnormally low levels of dopamine in motor

control areas of the brain; patients usually

exhibit involuntary trembling and muscle rigidity

Parkinsonism

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Reflex A reflex is an involuntary or automatic, one way action that

your body does in response to something - without you even having to think about it

Nerve impulses are conducted from afferent receptors to effector receptors over neuron pathways or reflex arcs

Five essential parts:

1. Receptors- detect a change and generate impulses

2. Sensory neurons- transmit impulses from receptors to the CNS

3. CNS- contains one or more synapses

4. Motor neurons- transmit impulses from the CNS to the effector

5. Effector- performs its characteristic action

Patellar reflex

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Disorders of nervous tissue Multiple sclerosis

Characterized by myelin loss in central nerve fibers and

resulting conduction impairments

Tumors

General name for nervous system tumors is neuroma

Most neuromas are gliomas, glial tumors

Multiple neurofibromatosis - characterized by numerous

benign tumors

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Brain disorders

Destruction of brain tissue

Cerebrovascular accident (CVA) – 2 types hemorrhage

from or cessation of blood flow through cerebral blood

vessels; a “stroke”

Cerebral palsy (CP) - condition in which damage to motor

control areas of the brain before, during, or shortly after birth

causes paralysis (usually spastic) of one or more limbs

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Brain disorders Dementia - progressive loss of memory, shortened

attention span, personality changes, reduced intellectual

capacity, motor control deficit

Alzheimer disease (AD) - brain disorder of the middle and

late adult years characterized by dementia

Huntington disease (HD) - inherited disorder characterized

by chorea (purposeless movement) progressing to severe

dementia

HIV (also causes AIDS) can infect neurons and thus cause

dementia

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Brain disorders Seizure disorders

Seizure - sudden burst of abnormal neuron activity that results in temporary changes in brain function

Epilepsy - many forms, all characterized by recurring seizures

Electroencephalogram - graphic representation of voltage changes in the brain used to evaluate brain activity

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Peripheral Nerve disorders

Neuritis - general term referring to nerve inflammation

Sciatica is inflammation of the sciatic nerve that innervates

the legs

Neuralgia, or muscle pain, often accompanies neuritis

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Peripheral Nerve disorders

Trigeminal neuralgia - recurring episodes of stabbing pain along one or more branches of the trigeminal (fifth cranial)

nerve in the head

Bell palsy - paralysis of facial features resulting from damage to the facial (seventh cranial) nerve

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Peripheral Nerve disorders

Herpes zoster or shingles

Viral infection caused by chickenpox virus that has invaded

the dorsal root ganglion and remained dormant until an

episode of shingles

Usually affects a single dermatome, producing characteristic

painful plaques or vesicles

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Disorders of the

Autonomic Nervous System Stress-induced disease

Prolonged or excessive response to stress can disrupt normal functioning throughout the body

Examples of stress-induced conditions include heart

disease, digestive problems, and reduced resistance to disease