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Nervous System: Peripheral Nerves

Nervous system divisions


I). Cranial Nerves

A). 12 nerves  Have both somatic and autonomic functions.


cranial nerves

B). Summary Anterior of the Brain to Posterior

I. Olfactory


nerves for smell

olfactory nerve
II. Optic


nerve for vision.

optic nerve
III. Oculomotor

Somatic & Parasympathetic:

 control of extrinsic eye muscles and pupil dilation.


oculomotor nerve
IV. Trochlear


control of muscles that surround the eye.

trochlear nerve
V. Trigeminal

Sensory & Somatic

control of facial nerves and muscles for chewing.


Trigeminal  Nerrve
VI. Abducens


muscle control of lateral movement of the eyeball.


Abducens Nerve
VII. Facial

Sensory, Somatic & Parasympathetic

control over facial expression and taste.


Facial Nerve
VIII. Vestibulocochlear or Auditory Nerve


 nerve for hearing.


Vestibulocochlear or Auditory Nerve
IX. Glossopharyngeal

Sensory, Somatic & Parasympathetic

control over taste, the tongue and the pharynx.


Glossopharyngeal Nerve
X. Vagus

Primary Parasympathetic

 nerve with some Somatic and Sensory functions. Controls visceral organs.


Vagus nerve
XI. Accessory


control over larynx, pharynx and sternocleidomastoid muscles


Accesory Nerve
XII. Hypoglossal


control over the tongue.

Hypoglossal Nerve

II). Spinal Nerves

Spinal Nerves

A). 31 pairs of spinal nerves 

bullet Spinal roots
bullet Rami
bullet Nerve Plexus are interlaced nerve networks that form when the rami join together.
spinal nerves

B). Somatic and Sensory nerves

1). C1 to C8 cervical nerves

a). Cervical plexus

bulletDeep in neck under sternocleidomastoid muscle.
bulletWorks muscles in the neck, scapulae, trapezius, and diaphragm. (C3 to C4)
bulletSensory skin in neck, ear, and chest.

b). Brachial plexus

bulletFound partly in the neck and axilla. 
bullet All of the nerves that innervate the upper limbs. (C5 to C8)
brachial plexuses and nerves of the arm


i). Axillary nerve: Deltoid & Teres minor

ii). Musculocutaneous nerve: Biceps brachii, brachialis and skin.

iii). Median nerve: Flexor muscles, wrist & fingers.

iv). Ulnar nerve: flexors not covered by median nerve. (Funny bone pain)

v). Radial nerve: Extensor muscle and skin.

2). T1 to T 12 thoracic nerves

a). Intercostal nerves

bulletSupply intercostal muscles, abdominal wall and branch into the skin.

3). L1 to L 5 lumbar nerves

a). Lumbar plexus

bulletL1 to L4 Innervates abdominal wall and interior and medial thigh.

i). Femoral nerve: Skin and quadriceps.

ii). Obturator nerve: Adductor muscles

iii).  Saphenous nerve

Lumbosacral plexus and nerves of the leg


4). S1 to S5 sacral nerves

a). Sacral plexus

bulletL4 to S4 Buttock and lower limb

i). Sciatic nerve: Posterior thigh, hamstrings, flexors and extensors

ii). Tibial nerve: part of sciatic Posterior calf and foot.

iii). Common fibular nerve (peroneal): part of sciatic. Knee joint and anterolateral lower leg muscles.

5). C0 coccygeal nerve

III). Innervation of joints

Hiltonís Law:

Any nerve serving a muscle producing

movement at a joint also innervates the

joint itself and the skin over that joint.


IV). Innervation of skin




V). Reflex Arc

Reflex Arc


stimulus receptor
sensory neuron  integration center
motor neuron effector


A). Definition

A reflex is involuntary rapid predictable motor response to a stimulus.

It is a spinal response that occurs without any input from the brain.


B). Necessary Components

1). Receptor

2). Sensory neuron

3). Integration Center:

4). Motor neuron:

5). Effector:


C). Classification

1). Autonomic:

2). Somatic:


D).  Types

1).  Spinal reflexes

a). Stretch & Deep Tendon

bullet Control the rate and amount of stretch by contracting and relaxing muscle.
bulletMuscle tone is adjusted reflexively in response to posture

i).  Stretch Reflex:

bullet Muscle contraction in response to muscle stretch or increased length.

ii).  Deep Tendon Reflex:

bulletMuscle lengthening in response to muscle contraction or shortening.

ie. Patellar (Knee jerk response)


bullet Strike patellar tendon (stimulus)
bullet Stretches the quadriceps muscle (receptor)
bullet Stimulates muscle spindle (sensory neuron)
bullet Afferent impulse to spinal column (integration center)
bullet Impulses inhibit contraction of antagonist muscle (motor neuron)
bullet Results in contraction of quadriceps and inhibition of hamstring. (effector)

b). Flexor Reflex

bullet Withdrawal of body part in response to a painful stimulus. (either real of perceived)

c). Crossed Extensor Reflex

bullet Withdrawal of body part while simultaneously extending the opposite of the body to maintain support.

d). Superficial Reflexes

bullet Response to gentle cutaneous stimulation.

ie. Plantar Reflex:


VI.  Autonomic Nervous System

(parasympathetic & sympathetic)

if you could control this system think in terms of:

Fight or flight:   what do you do when there is a tiger in the room

Maintenance:  what do you do when you are "vegging out" on the Lazy Boy.

A). Summary

bulletInvoluntary nervous system or visceral motor nervous system.
bulletFunctions in coordination with the somatic and sensory system and higher brain functions.
bulletBoth systems are fully integrated.


Dual system with the parasympathetic and sympathetic system innervating the same organs but causing opposite effects.

bullet Sympathetic:  Fight or Flight (tiger in the room)
bullet Parasympathetic: Maintenance ("vegging out" on the Lazy Boy)

B). Comparison to Somatic Nervous System

1). Effectors


bulletSkeletal muscle (only)


bulletSmooth muscle
bulletCardiac muscle

2). Efferent Pathways

Somatic: cell body in CNS axon attaches to skeletal muscle.

bulletConduction of impulses very fast

Autonomic: 2 neuron chain

bulletCell body of first neuron in the CNS
bullet2nd neuron outside CNS and attached to effector organ.
bulletConduction of impulses slower.

2). Neurotransmitter Effects

Somatic: Always excitatory

Autonomic: Excitation or Inhibition


C). Differences in Parasympathetic & Sympathetic Divisions

1). Functional Role

Parasympathetic: Maintenance functions

bullet Conserves & stores energy

Sympathetic: Prepares the body for emergencies

Intense muscular activity
Fight or Flight

2). Origin sites

Parasympathetic: Brain & Sacral Spinal Cord

Sympathetic: Thoracic-Lumbar Spinal Cord

3). Length of ganglionic fibers

4). Neurotransmitters

Parasympathetic: Acetylcholine

Sympathetic: Some Acetylcholine in preganglia (first neuron that connects to the second neuron) but postganglia release Norepinephrine (common term Adrenaline) this goes to the effectors.


D). Parasympathetic Division (Maintenance division)

(When you are "vegging out" on the lazy boy you do not want your heart racing.  This is a time to digest your hamburger and lounge around)

1). Parasympathetic fibers do not run in spinal nerves. (Vagus nerve is a cranial nerve, so are many of the parasympathetic nerves)

2). Nerves arise from the cranial, (brainstem) and the sacral region.

3). Nerves involved

i). Oculomotor nerves: constrict pupils focus on objects

ii). Facial nerves: activates glands

lacrimal glands & salivary glands

(Think of the oppisite when you are exicited your mouth dries up because the last thing you need is to process food)

iii). Glossopharyngeal nerves: salivary glands

iv). Vagus nerves:

Serves most of the visceral organs

Cardiac plexus: Slows the heart rate
Pulmonary plexus
Esophageal plexus: liver, gallbladder, stomach, small intestine, kidneys, pancreas, large intestine. (This is independent of the spinal cord)

5). Sacral nerves: pelvic organs, bladder, genitals & large intestine.

E). Sympathetic Division (fight or flight)

Innervates visceral organs, adrenal glands, sweat glands and hair raising glands and vascular smooth muscle.

When the tiger is in the room you do not want blood and energy going tot he visceral organs to digest your dinner you want blood going to the muscles (vascular dilation) and when you are running you are producing heat so you need to sweat)


Functions of Sympathetic and Parasympathetic Divisions

Look at this table and think of how to balance resources when there is a tiger in the room. 





Relaxing in the lazy boy

There is a tiger in the room

Cellular metabolism



Sweat gland,

Adrenal Glands,

Hair raising muscle






Heart muscle

Heart rate




Blood vessels



Blood Vessels


Constricts visceral

Dilates skeletal muscle

Mental alertness




Promotes voiding

Inhibits voiding