PERIPHERAL NERVOUS SYSTEM

PNS

Provides the relays to the central nervous system. It picks up sensory information from the environment and translates it to the CNS.

The stimulus received by the PNS can be classified into five types.

Classification of stimulus

Mechanoreceptors respond to mechanical force such as touch, pressure (including BP), vibration, and stretch.

Thermo receptors- are sensitive to temperature changes.

Photoreceptors- such as those of the retina and the eye, respond to light energy.

Chemorecptors- respond to chemicals in chemical solutions. (molecules that can be smelled, or tasted, etc)

Noicreceptors- respond to stimulus that result from pain. Such as loud noise, extreme cold, pressure, and inflammatory chemicals.

Classification by location

Exteroceptors- sensitive to stimuli that occurs outside of the body. Needless to say, these receptors are found mostly on the body surface.

Interoceptors- respond to stimulus within the body. They monitor everything from chemical change, tissue stretch, and temperature. They can make us feel pain, hunger, and discomfort, but we are usually unaware of it.

Proprioceptors- Located in the skeletal muscles and joints , tendons and ligaments, and in connective tissue that covers the skeleton and muscle only.

They serve the same function as interoceptors.

Complexity

Most PNS structures are simple, meaning that they are usually just a modified dendritic cell.

The Few that are complex however, are what we associated as our sensory organs like the eyes.

Sensory Integration: from sensation to perception

Human survival depends not only on sensation, but the perception of that sensation.

For example If you get smacked on the arm, you sense pressure, but you perceive that pressure as pain.

General organization of the somatosensory system

The somatosensory system is a system that serves the limbs of the body. The three main levels at which this is operated is as follows: Receptor level: sensory receptors (tells you

what) Circuit level: Ascending pathway (Sends

impulse to proper channel) Perceptual level: Neuronal circuits in the

cerebral cortex (tells you how to perceive the stimulus.)

Structural Classification of nerves

A nerve is a cordlike organ that is part of the peripheral nervous system. The consist of parallel bundles of peripheral axons, enclosed by successive wrappings of connective tissue.

Regeneration of Nerve Fibers

1. When a nerve is severed or crushed, Wallerian degeneration (cell destruction and the destruction of cells around the severed cell) occurs.

2. After debris is disposed of, Shwann cells proliferate and macrophages are released into the injury site.

3. Then the regenerated axons will sprout across the gap and to their original contacts.

Cranial nerves

There are 12 sets of nerves that associate themselves with the brain.

They are: Olfactoral Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulocochlear Glossopharyngeal Vagus Accessory Hypoglossal

Cranial Nerves: Olfactory

Sensory nerves that control smell. Runs from the nasal mucosa to the olfactoral bulb.

Cranial Nerves: Optic

Because the sensory nerves of vision develops outside the brain, it is a brain tract.

Cranial Nerves: Oculomotor

Sensory nerve that supplies nerves that innervate muscles that control eye movement.

Cranial Nerves: Trochlear

Means “pulley” and innervates muscles that are in a pulley shaped muscle in the orbit (eye area).

Cranial Nerves: Trigeminal

Three branches that supply sensory fibers to the face and motor fibers to the to the chewing muscles.

Cranial Nerves: Abducens

Controls the muscles that abduct the eyeball (move it laterally)

Cranial Nerves: Facial

A large nerve that innervates the muscles of the face. (and other things as well)

Cranial Nerves: Vestibulocochlear

Sensory nerve for hearing and balance. A.K.A. the auditory nerve.

Cranial Nerves: Glossopharyngeal

Means “tongue and pharynx”. Innervates the tongue and throat.

Cranial Nerves: Vagus

Means “wanderer” The only cranial nerve that extends to the thorax and the abdomen.

Cranial Nerves: Accessory

An accesory (helper) nerve that assists the vagus nerve.

Cranial Nerves: Hypoglossal

Runs inferior to the tongue and innervates the tongue muscles.

Spinal nerves

There are 31 pairs of spinal nerves that innervate the body. Each of those spinal nerves contain thousands of nerves. There are 8 pairs of cervical spinal

nerves There are 12 pairs of thoracic spinal

nerves There are 5 pairs of lumbar spinal

nerves There are 5 pairs of sacral spinal

nerves There is 1 pair of coccygeal nerves.

Nerve plexus

Are bundles of nerves that occur in the cervical, thoracic, lumbar, and sacral regions that are designed to innervate primarily the limbs.

Branches of the cervical plexus: Cutaneous branches

Branch Lesser occipital

C2 Greater auricular

C2, C3 Transverse

Cervical C2, C3

Supraclavicular C3, C4

Structure served Skin on

posterolateral aspect of neck

Skin of ear, skin over parotid gland

Skin on the anterior aspect of neck

Skin of the shoulder and the clavicular region

Branches of the cervical plexus: motor branches

Branch Ansa Cervicalis

C1-C3 Segmental and other

muscular branches C1-C5

Phrenic C3-C5

Structure Served Infrahyoid muscle

of the neck Deep muscles of

the neck, portions of the scalenes, levator, scapulae, trapezius, and sternonucleiodmastoid muscles

Diaphragm

Branches of the brachial plexus

Nerve Musculocutaneous

C5-C7

Median: (2) branches MedialC8-T1 lateral C5-C7

Structure served Muscular branches;

flexor muscles in anterior arm In cutaneous branches: controls skin on arm.

Flexor muscles of the forearm. Digits of the fingers.

Cutaneous: skin of 2/3 of hand and palm.

Nerve Ulnar

C8-T1

Structure served Flexor muscles of

the anterior forearm; interisitc muscles of the lateral palm. Cutaneous branches: skin of the posteriolateral surface of the entire limb

Nerve Radial

C5-C8, T1

Structure Served Posterior muscles

of the arm and forearm; most intrinsic muscles of the hands. Cutaneous: posteriolateral surface of the hand.

Nerve Axillary

C5,C6

Dorsal Scapular C5

Structure Served Deltoid and teres

minor muscles. Cutaneous: some skin of the shoulder

Rhomboid muscles and levator scapulae.

Nerve Long Thoracic

C5-C7 Subscapular

C5, C6 Suprascapular

C5, C6

Pectoralis C5-T1

Structure Served Serratus anterior

muscle

Teres major and subscapularis muscle

Shoulder joint; supraspinatus and infraspinas muscles

Pectoralis major and minor muscles

Branches of the Lumbar plexus Nerve Femoral

L2-L4

Obturator L2-L4

Structure served Skin of anterior and

medial thigh. Medial leg and foot. Hip, knees, and joints.

Motor to adductor magnus, longus, and brevis, obturator, skin for medial thigh, and for hip and knee joints

Nerve Lateral femoral

cutaneous. L2, L3

Iliohypogastric L1

Structure served Skin of lateral

thigh; some sensory branches to peritoneum.

Skin of lower abdomen and hip; muscles of anterolateral abdominal wall

Nerve Ilioiguinal

L1

Structure Served Skin of external

genitalia, and proximal medial aspect of the thigh; inferior abdominal muscles

Nerve Genitofemoral

Structure Served Skin of scrotum in

males, of labia majora in females, and of anterior thigh; inferior to middle portion of inguinal region; cremaster muscles in males.

Branches of sacral plexus

Nerve Sciatic nerve

Tibial (including sural, medial and lateral plantar, and medial calcaneal branches) L4-S3

Structure Served Cutaneous

branches: to skin of posterior surface of leg and sole of foot

Motor branches: posterior of adductor magnus, triceps surae, tibulis

Common fibular (superficial and deep branches) L4-S2

Cutaneous: to skin of anterior and lateral surface of the leg and dorsum of foot

Motor branches: short head of biceps femoralis of the thigh; extensor muscles of the toes.

Nerve Superior Gluteal

L4, L5, S1

Inferior Gluteal L5-S2

Structure served Motor branch to

gluteus medius and minimus

Motor branch to gluteus maximus

Posterior femoral cutaneous S1-S3

Pudendal S2-S4

Skin of the buttock, and posterior thigh

Supplies most of the skin muscles, anus, clitoris, labia, vaginal mucosa (females), scrotom and penis in males.