Lecture Medical assisting: Administrative and clinical procedures with anatomy and physiology (4e) – Chapter 25

A ll ri g ht s re se rv e d .• Three types of neurons – Afferent or sensory nerves • Sensory information from environment or inside body to CNS for interpretation – Efferent or motor ner

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© 20 11 T he M c Graw - Hi ll C o m p anie s, Inc A ll ri g ht s re se rv e d

25

The Nervous

System

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Learning Outcomes

25.1 Explain the difference between the central

nervous system and the peripheral nervous system.

25.2 Describe the functions of the nervous

system.

25.3 Describe the structure of a neuron.

25.4 Describe the function of a nerve impulse and

how a nerve impulse is created.

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25.5 Describe the structure and function of a

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25.9 Describe the location and function of

cerebrospinal fluid.

25.10 Define reflex and list the parts of a reflex arc.

25.11 List the major divisions of the brain and give

the general functions of each.

25.12 Explain the functions of the cranial and

spinal nerves.

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25.13 Describe the differences between the

somatic nervous system and autonomic nervous system.

25.14 Explain the two divisions of the autonomic

nervous system.

25.15 Describe the causes, signs and symptoms,

and treatments of various diseases and disorders of the nervous system

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maintaining balance within those systems

Disorders are numerous and often

difficult to diagnose and treat

Disorders are numerous and often

difficult to diagnose and treat

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General Functions of the NS

• Somatic nervous system (SNS)

– Skeletal or voluntary muscles

• Autonomic nervous system

(ANS)– Automatic functions

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• Three types of neurons

– Afferent or sensory nerves

• Sensory information from environment or inside body to CNS for interpretation

– Efferent or motor nerves

• Impulses from CNS to PNS to allow for movement or action

– Interneurons

• Interpretive neurons between afferent and efferent nerves in the CNS

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Apply Your Knowledge

Match the following:

_ Somatic nervous system A Motor nerves

_ Autonomic nervous system B Governs skeletal or voluntary

muscles

_ Afferent nerves C Governs respiratory and GI

systems

_ Efferent nerves D Go-betweens or interpreters

_ Interneurons E Sensory nerves

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• Neurons lose their ability to divide

– If destroyed, not replaced

• Neuralgia

– Support cells for neurons that can divide

– Astrocytes – anchor blood vessels to nerves

– Microglia – act as phagocytes

– Oligodendrocytes – assist with production of myelin

sheath

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Neurons have a cell

body and processes

called nerve fibers that

extend from the cell

body

Neurons have a cell

body and processes

called nerve fibers that

extend from the cell

body

 Dendrites – short

 Receive nerve impulses

for the neuron

 Axons – long

 Send nerve impulses

away from the cell body

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• White matter – axons with myelin sheath

– Schwann cells

• Wrap around some axons

• Cell membranes contain myelin

• Myelin insulates axons and enables axons to send nerve impulses more quickly

• Gray matter – axons without myelin sheath

Schwann

cells

Axon

Dendrites

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True or False:

_ Effectors are neurons

_ Neurons can reproduce

_ Astrocytes anchor blood vessels to nerve cells

_ Microglia act as phagocytes

_ Oligodendrocytes are reproductive cells

_ Repolarization is the return to the resting state

They are the muscles or glands.

Neurons cannot reproduce.

They take part in myelin production.

GOOD JOB!

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Nerve Impulse

• Membrane potential

– Neuron cell membrane at rest is in a polarized state

• Inside of cell membrane is negative

• Outside of cell membrane is positive due to more Na + and K + – As Na+ and K+ move into the cell, the membrane

becomes depolarized

• Inside becomes more positive

• Action potential (nerve impulse) is created

– Repolarization occurs when K+ and later Na+ move to

the outside of the cell membrane

• Return of the cell to polarized (resting) state

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• Impulse travels down axon to synaptic knob

– Vesicles or small sacs in synaptic knob

• Produce chemicals called neurotransmitters

– Neurotransmitters are released by synaptic knob

• Allow impulse transmission to postsynaptic structures

– Dendrites – Cell bodies – Axons of other neurons

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• Functions of neurotransmitters

– Cause muscles to contract or relax

– Cause glands to secrete products

– Activate or inhibit neurons

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What is the function of neurotransmitters?

ANSWER: Neurotransmitters cause muscles to

contract or relax, cause glands to secret products,

activate neurons to send nerve impulses, or inhibit

neurons from sending them.

Right

!

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Central Nervous System

• Includes the spinal cord and brain

• Blood-brain barrier

– Protects layers of the membranes of the

CNS– Formed by tight capillaries

• Prevents unwanted substances from entering the CNS tissues

• Inflammation can make more permeable

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• Meninges –protect brain and spinal cord

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• Between arachnoid mater and pia mater

• Contains cerebrospinal fluid (CSF)

• Cushions CNS

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Spinal Cord

• Slender structure continuous with

the brain

• Descends into the vertebral canal

and ends around the level of the

first or second lumbar vertebra

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• Gray matter

– Inner tissue with darker color

– Contains neuron cell bodies and their

dendrites – Divisions are called horns

– Central canal runs down the entire length

of the spinal cord through the center of the gray matter Cord/NerveSpinal

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• White matter

– Outer tissue

– Contains myelinated axons

– Divisions are called columns (funiculi)

• Columns contain groups of axons called nerve tracts

Spinal Cord/Nerve Spinal Cord/Nerve

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• One function of the spinal cord is to carry sensory

information to and from the brain

• Ascending tracts

– Carry sensory information up to the brain

• Descending tracts

– Carry motor information down from the brain to

muscles and glands

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• Reflexes

– Another function of the spinal cord is to participate in

reflexes

– Reflex – a predictable, automatic response to stimuli

Interneurons

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Cerebrum

• Largest section

• Two cerebral hemispheres

– Connected by a thick bundle of nerve fibers called

the corpus callosum

– Longitudinal fissure between hemispheres

• Sulci – grooves on surface

• Gyri or convolutions – bumps of brain matter

between sulci

Brain

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• Interpret sensory information

• Initiate body movements

• Stores memories and creates emotions

• Ventricles

– Interconnected cavities within the brain

– Filled with CSF

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Diencephalon

• Between the cerebral hemispheres superior to the brain

stem

• Thalamus

– Relay station for sensory information going to the

cerebral cortex for interpretation

• Hypothalamus

– Maintains homeostasis by regulating vital activities

Brain

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Brain Stem

• Connects the cerebrum to

the spinal cord

• Midbrain

– Just beneath diencephalon – Controls both visual and auditory reflexes

• Pons

– Rounded bulge on underside of brain stem – Between midbrain and medulla oblongata

– Controls many vital activities, such as heart rate, blood pressure, and breathing

Brain

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– Complex skeletal muscle contractions that are

needed for body movements– Fine movements

Brain

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Preventing Brain and Spinal Cord Injuries

• Always wear seat belts

• Follow safety rules on

 Follow traffic rules and

signs while walking, biking, or driving

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Match the following:

_ Meninges A Carry motor information from brain

_ Ascending tracts B Stores memories and creates emotions

_ Descending tracts C Grooves on the surface of the cerebrum

_ Cerebral cortex D Carry sensory information to the brain

_ Hypothalamus E Predictable, automatic response to stimuli

_ Sulci F Maintains homeostasis

_ Cerebellum G Coordinates skeletal muscle contractions

_ Reflexes H Protects the brain and spinal cord

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Peripheral Nervous System

• Nerves that branch off

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Cranial Nerves

I Olfactory nerves

– Carry smell information to the brain for

interpretation

II Optic nerves

– Carry visual information to the brain for

interpretation

III Oculomotor nerves

– Found within the muscles that move the eyeball,

eyelid, and iris

IV Trochlear nerves

– Act in the muscles that move the eyeball

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V Trigeminal nerves

– Carry sensory information from the surface of the

eye, the scalp, facial skin, the lining of the gums, and the palate to the brain for interpretation

– Also found within the muscles needed for chewing

VI Abducens nerves

– Act in the muscles that move the eyeball

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VII Facial nerves

– Found in the muscles of facial expression as

well as in the salivary and tear glands– Also carry sensory information from the tongueVIII Vestibulocochlear nerves

– Carry hearing and equilibrium information from

the inner ear to the brain for interpretation

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IX Glossopharyngeal nerves

– Carry sensory information from the throat and

tongue to the brain for interpretation– Also act in the muscles of the throat

X Vagus nerves

– Carry sensory information from the thoracic and

abdominal organs to the brain for interpretation– Also found within the muscles in the throat,

stomach, intestines, and heart

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XI Accessory nerves

– Found within the muscles of the throat, neck,

back, and voice boxXII Hypoglossal nerves

– Found within the muscles of the tongue

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Spinal Nerves

• Peripheral nerves originating from the spinal cord

• 31 pairs of spinal nerves

– 8 pairs of cervical nerves (C1 through C8) – 12 pairs of thoracic nerves (T1 through

T12) – 5 pairs of lumbar nerves (L1 through L5) – 5 pairs of sacral nerves (S1 through S5) – 1 pair of coccygeal nerves (C0)

Spinal Nerves

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• Dermatome

– Skin segment innervated by spinal nerve

– C1 is not associated with a dermatome

• Ventral root

– Axons of motor neurons only

• Dorsal root

– Axons of sensory neurons only

– Dorsal root ganglion

• Contains cell bodies of sensory neurons

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• Main portions of spinal nerves fuse to form nerve

plexuses

– Cervical – supply skin and muscles of neck

• Phrenic nerve originates from this plexus and controls the diaphragm

– Brachial – control muscles in the arms

– Lumbosacral – lower abdomen, external genitalia,

buttocks, thighs, legs, and feet

• Sciatic nerve originates from this plexus and controls muscles of legs

Spinal Nerves

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Somatic Nervous System

• Nerves that connect the CNS to skin and

skeletal muscle

• “Voluntary” nervous system

– Controls skeletal muscles, which are under voluntary

control

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Autonomic Nervous System

• Nerves that connect the CNS to organs and

other structures

• “Involuntary” nervous system

• Motor neurons located in ganglia

– Neuron cell bodies outside the CNS

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• Sympathetic division

– “Fight or flight” – Prepares body for stressful or

emergency situations– Neurons release neurotransmitter norepinephrine

• Increases heart and breathing rates

• Slows down muscles of the stomach and intestines

• Dilates pupils

• Constricts blood vessels – increases blood pressure

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• Parasympathetic division

– Prepares body for rest and digesting

– Controls most of the body’s organs

– Releases acetylcholine

• Slows heart and breathing rates

• Constricts pupils

• Activates muscles of stomach and intestine

– No communication with blood vessels

• Sympathetic and parasympathetic divisions are

antagonistic

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