Chapter 14: Peripheral Nervous System

PowerPoint by John McGillSupplemental Notes

by Beth Wyatt

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I. SPINAL NERVES

• OVERVIEW• DEFINITION

• Nerves That Extend Off the Spinal Cord (Emerge From the Spinal Cavity)

• NUMBER: 31 Pair

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I. SPINAL NERVES•C1-C8

•CERVICAL NERVES

•T1-T12•THORACIC NERVES

•L1-L5•LUMBAR NERVES

•SACRAL NERVES•S1-S5

•COCCYGEAL NERVES•1 PAIR

• They are NOT “named.”• LETTERS

• INDICATE REGIONS OF VERTEBRAL COLUMN

• NUMBERS• INDICATE HOW MANY OF

EACH TYPE (EACH PAIRED)

SPINAL NERVES are IDENTIFIED BY LETTERS AND

NUMBERS

SPINAL NERVES are IDENTIFIED BY LETTERS AND NUMBERS

• THE LETTERS AND NUMBERS INDICATE WHERE THE NERVES EXIT SPINAL CAVITY•C1-C7 Exit Above C1-C7

Vertebrae•C8 Exits Below C7 Vertebra•Thoracics and Lumbars Exit Below

Their Respective Vertebrae•Sacrals Exit Through Openings in

Sacrum•Coccygeals Pass Over Coccyx

CAUDA EQUINA ( Horse’s Tail )

• Describes the Appearance of the Bottom of the Spinal Cord

• Reason: Spinal Cord Ends at Bottom of the 1st Lumbar Vertebra;

CAUDA EQUINA ( Horse’s Tail )

• Means That Lumbar, Sacral, and Coccygeal Nerves Hang in a Bundle at the Bottom of the SC Before Exiting at Their Respective Locations

• Causes the Bottom of the Spinal Cord to Resemble a Cauda Equina

SPINAL NERVES ARE MIXED NERVES

• The spinal nerves carry both sensory and motor messages and are called “mixed nerves.”

SPINAL NERVE STRUCTURE

• NERVE ROOTS: Join Spinal Nerves to Spinal Cord• VENTRAL ROOTS

• NF OF EFFERENT NEURONS

• DORSAL ROOTS• NF OF AFFERENT NEURONS

SPINAL NERVE ROOTS

RAMI (RAMUS)• The Major Branches of a Spinal Nerve• Each Spinal Nerve Has 2 Rami

RAMI (RAMUS) DESCRIPTION• The spinal nerve trunk

emerges laterally from the intervertebral foramen

• The trunk divides into two major branches (The anterior (ventral) and posterior (dorsal) primary rami (ramus, singular))

• The posterior primary rami go to the back.

• The anterior primary rami go to the sides and front of the body, and to the upper and lower members.

DORSAL RAMUS• AREAS SUPPLIED

•Provides Nerve Supply to Posterior Head, Neck, and Trunk

•Contains Both Afferent and Efferent (Somatic) Nerve Fibers

VENTRAL RAMUS (More Complex)

• AREAS SUPPLIED•Lateral and Anterior Neck and

Trunk as well as Extremities•Contains Both Afferent and

Efferent (Somatic & Autonomic) Nerve Fibers

VENTRAL RAMUS (More Complex)

• NERVE PLEXUSES are only found on ventral rami

• DEFINITION• Complex Nerve Network• The Ventral Rami of

Most Spinal Nerves Form Plexuses (Not T2 ‑ T12)

• Formed when the Ventral Rami of Several Spinal Nerves Exchange Fibers

• (Fibers Recombine) to Form New Nerves that Supply Specific Areas

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VENTRAL RAMUS (Comments from the text)

• Fibers of several rami join to form individual nerves.

• Each nerve emerging from a plexus contains all the fibers that innervate a body region.

• Destination is basis for nerve’s name.• The plexus reduces the number of

nerves needed to supply a body part.• Since plexi are composed of fibers from

different spinal nerves, damage to one spinal nerve does not mean a complete loss of function in a body region

• But Instead, Partial Loss of Function in Several Areas

MAJOR PLEXUSES (ALL ARE PAIRED): CERVICAL PLEXUS

• CERVICAL PLEXUS•Formed by the Ventral Rami of

C1‑C4 and a Branch of Ventral Ramus of C5

•Provides Nerve Supply to Neck and Upper Shoulders and Part of Head

CERVICAL PLEXUS

MAJOR PLEXUSES (ALL ARE PAIRED):BRACHIAL PLEXUS

• BRACHIAL PLEXUS•Formed by the Ventral Rami of

C5‑T1•Provides Nerve Supply to Lower

Shoulders and Arms

BRACHIAL PLEXUS

MAJOR PLEXUSES (ALL ARE PAIRED): LUMBAR PLEXUS

• LUMBAR PLEXUS•Formed by the Ventral Rami of

L1‑L4

• SACRAL PLEXUS•Formed by the Ventral Rami of L4,

L5, & S1‑S4

• *Note: Together the Lumbar and the Sacral Plexuses (also the Coccygeal Plexus) Are Known as the Lumbosacral Plexus that Provides Nerve Supply to the Lower Trunk and the Legs

LUMBOSACRAL PLEXUS

Plexus Notes

• * Coccygeal Plexus: Formed by S4, S5, and Coccygeal Nerves

GENERALIZATIONS ABOUT SPINAL NERVES

• Spinal Nerves Are Not Named; •However, the Nerves That Emerge

From Plexuses Often Are Named•Examples: Phrenic Nerve, Sciatic

Nerve

• There is a Close Relationship Between Where a Spinal Nerve Exits the Spinal Cavity and the Area the Nerve Supplies

CRANIAL NERVES

• DEFINITION• Nerves That

Attach to the Undersurface of the Brain (Mainly the Brainstem)

• 12 Pair

CRANIAL NERVES

• IDENTIFICATION• By Names and

Numbers

• NAMES• MAY INDICATE

NERVE’S FUNCTION• MAY INDICATE AREA

THE NERVE SUPPLIES

• NUMBERS• ROMAN NUMERALS• ORDER IN WHICH

NERVE EMERGES FROM ANTERIOR TO POSTERIOR

NERVE TYPES• Some Cranial Nerves Are Mixed,

Some Are Sensory, Some Are Motor • Saying to Remember Nerve Types:

Some Say Marry Money, But My Brothers Say Bad Business Marry Money

• MIXED NERVES: V, VII, IX, X• SENSORY NERVES: I, II, VIII• MOTOR NERVES: III, IV, VI, XI, XII

NAMES, NUMBERS, FUNCTIONS

CRANIAL NERVE I • OLFACTORY NERVE

• Sensory• Function: Smell

CRANIAL NERVE II

• OPTIC NERVE• Sensory• Function:

Vision

CRANIAL NERVE III • OCULOMOTOR

NERVE• Motor• Functions:

• Eye Movements

• Regulation of Pupil Size

• Accomodation

CRANIAL NERVE IV

• TROCHLEAR NERVE • Motor• Function: Eye Movements

CRANIAL NERVE V

• TRIGEMINAL NERVE • Mixed• Functions:

• Sensory: Sensations of Head and Face• Motor: Chewing

CRANIAL NERVE V

CRANIAL NERVE VI

• ABDUCENS NERVE•Motor•Function: Lateral Eye Movements

CRANIAL NERVE VII

• FACIAL NERVE •Mixed•Functions:

•Sensory: Taste•Motor:

– Facial Expressions

– Secretion of Saliva and Tears

CRANIAL NERVE VIII

• Vestibulocochlear• Sensory Functions: Hearing and Equilibrium

CRANIAL NERVE IX• GLOSSOPHARYNGEAL

NERVE• Mixed• Functions:

• Sensory: Taste (and General Sensations of Tongue)

• Motor: Swallowing, Secretion of Saliva

• NOTE: This nerve is also involved in the reflexes of BP and respiration.

CRANIAL NERVE X• X VAGUS NERVE

• Mixed• Functions:

• Sensory: Sensations in Organs Supplied

• Motor: Movements of Organs Supplied (i.e., Slows Heart, Increases Peristalsis)

CRANIAL NERVE XI• ACCESSORY NERVE

Motor• Functions:• Turning Movements

of Head• Shoulder

Movements• Movements of

Organs Supplied• Voice Production

CRANIAL NERVE XII

• HYPOGLOSSAL NERVE• Motor• Function: Tongue Movements

Saying Used to Remember the Names of the Cranial

Nerves• On• Old• Olympus‘• Tiny• Tops• A

• Friendly• Viking• Grew• Vines• And• Hops” 

• On• Old• Olympus‘• Tiny• Tops• A

• Friendly• Viking• Grew• Vines• And• Hops” 

• Only• Old• Octopi• Trade• Tracks• At• Friendly

• Vertebrate• Grasslands• In• Vagus• Ad• Hoc

III. FUNCTIONAL DIVISIONS OF THE PERIPHERAL NERVOUS SYSTEM

• Based on Direction in Which Neurons Conduct Nerve Impulses•AFFERENT (SENSORY) DIVISION

•aa, like baa•Af = toward•Consists of all Afferent Neurons• Includes all Spinal Nerves (Afferent

Fibers)as well as Cranial Nerves Which are Sensory and Mixed (Afferent Fibers)

III. FUNCTIONAL DIVISIONS OF THE PERIPHERAL NERVOUS SYSTEM

•EFFERENT (MOTOR) DIVISION•ee, like Lee or eff, like Jeff•Ef = away from•Consists of all Efferent Neurons• Includes all Spinal Nerves (Efferent

Fibers)as well as Cranial Nerves Which are Motor and Mixed (Efferent Fibers)

Two Efferent Subdivisions OF THE PERIPHERAL NERVOUS SYSTEM

•Two Subdivisions (Based on Effectors)– SOMATIC MOTOR NERVOUS SYSTEM

• Effectors are Voluntary: Skeletal Muscles

– THE AUTONOMIC NERVOUS SYSTEM (Sympathetic & Parasympathetic

• Effectors are Involuntary: Cardiac Muscle, Smooth Muscle, and Glands

ANS has 2 Divisions:Sympathetic and Parasympathetic

• SYMPATHETIC DIVISION• THORACOLUMBAR• Nerves of the

Sympathetic Division Branch from Thoracic Spinal Nerves (T1‑T12) and from some Lumbar Spinal Nerves (L1‑L4)

• Explanation: Spinal Nerves are Mixed, Their Efferent Nerve Fibers are Somatic and Autonomic; The Autonomic Fibers are Sympathetic Nerves

ANS has 2 Divisions:Sympathetic and Parasympathetic

• PARASYMPATHETIC DIVISION• CRANIOSACRAL• Nerves of the Parasympathetic

Division Branch from some Cranial Nerves (III, VII, IX, X, XI) and from some Sacral Spinal Nerves (S2‑S4)

• Explanation: Cranial Nerves III and XI are Motor, the Remaining Cranial Nerves Listed (VII, IX, X) are Mixed; Spinal Nerves are Mixed; Efferent Fibers in All These Nerves are Somatic and Autonomic; The Autonomic Fibers are Parasympathetic Nerves

b. FUNCTIONS OF THE ANS

• OVERVIEW OF ANS FUNCTIONS•ANS REGULATES AUTONOMIC

EFFECTORS IN WAYS THAT MAINTAIN HOMEOSTASIS

•BOTH DIVISIONS:•CONTINUALLY CONDUCT NI'S TO

AUTONOMIC EFFECTORS (TONICALLY ACTIVE)

b. FUNCTIONS OF THE ANS

• EXERT ANTAGONISTIC INFLUENCES ON AUTONOMIC EFFECTORS

– Ex: If Sympathetic Division Stimulates an Autonomic Effector, then the Parasympathetic Division will Inhibit the Autonomic Effector

– *NOTE: ACTUAL EFFECT DEPENDS ON WHICH DIVISION DOMINATES (SITUATION)

•ANS INFLUENCED BY CEREBRAL CORTEX AND HYPOTHALAMUS

FUNCTIONS OF SYMPATHETIC DIVISION

• MAJOR FUNCTION• DURING STRESS PRODUCES THE FIGHT OR

FLIGHT REACTION• (SERVES AS THE BODY'S EMERGENCY

SYSTEM)

•Dominates during Stress (Physical or Psychological)

•During Stress Produces "Fight or Flight“ Reaction

Fight or Flight" Reaction

• A Collection of Changes in Autonomic Effectors which are Designed to Prepare the Individual to Respond to the Stress

• The Major Goal of all the Changes is to Get Skeletal Muscles Prepared to Expend Maximum Energy

SUMMARY OF MAJOR CHANGES THAT OCCUR IN THE FIGHT OR FLIGHT REACTION:

• *CARDIAC MUSCLE: • Rate/Strength of Heartbeat Increases

• *SMOOTH MUSCLE: • Of Blood Vessels

• Coronary, Skeletal Muscle: Dilate• Digestive Organ:

• Constrict• Of Hollow Organs

• Respiratory Airways: Dilate• Digestive Tract: Peristalsis Decreases

• *GLANDS• Sweat Glands: Production of Sweat Increases• Liver: Glycogen -----> Glucose• Adrenal Medulla: Secretion of Epinephrine

(Adrenalin) Increases

SYMPATHETIC DURING NONSTRESS

• DOMINATES SOME AUTONOMIC EFFECTORS

• MAINTAINS THEIR NORMAL FUNCTION• Ex: Cardiac Muscle

FUNCTIONS OF PARASYMPATHETIC DIVISION• DOMINATES MOST

AUTONOMIC EFFECTORS DURING NONSTRESS•Rest and Repair Division•Promotes Normal Digestive

System Activities•(For Example: Peristalsis and

Elimination)

• http://www.octc.kctcs.edu/gcaplan/anat/Notes/API%20Notes%20M%20%20Peripheral%20Nerves.htm

• http://www.teaching-biomed.man.ac.uk/resources/wwwcal/cranial_nerves/page2.asp