Biology 211Anatomy & Physiology I

Dr. Thompson

The Peripheral Nervous System

Recall: All organs are composed of Epithelial tissue Muscle tissue Connective tissue Nervous tissue

Nervous tissue: Excitable cells (neurons) Nonexcitable (supporting) cells

Connective tissue: Meninges in central nervous system Endoneurium Perineurium in peripheral nervous system Epineurium

Epithelium found only in blood vessels of PNSMuscle (smooth)

Cells of Nervous Tissue:

1) Excitable cells = Neurons Carry electrical signals from one place to another Pass these signals to other cells

2) Nonexcitable cells = Glia in CNS Satellite cells Schwann cells

in PNS

In Peripheral Nervous System:

Neuron cell bodies grouped into ganglia (single = ganglion)

Axons grouped into nerves

Nerve:

Each axon surrounded by Schwann cells, which may or may not form a myelin sheath.

Outside the Schwann cells, each axon is surrounded by layer of connective tissue called endoneureum

Axons (surrounded by Schwann cells and endoneureum) form bundles called fascicles, each of which is surrounded by a thicker layer of connective tissue called perineureum

Fascicles group together to form a nerve, which is surrounded by an eventhicker layer of connective tissue called epineureum

Cranial Nerves connect to the brain. Three carry only sensory information, five carry mostly motor information (with a small amount of sensory), and four carry both motor and sensory information

Spinal Nerves connect to the spinal cord. All of these carry both motor and sensory information

Cranial Nerves:

- Originate from the brain-Pass through foramina in the skull to reach the periphery

12 pairs, numbered from superior to inferior.

They carry the special senses (smell, vision, hearing, taste, and equilibrium)They carry sensory information from the head, face, and much of the neck.They carry motor innervation to muscles of the eye, face, larynx, and tongue; some muscles of the neck and back.One (CN X) carries autonomic information to organs of the thorax and abdomen.

You will not be asked to identify cranial nerves on either diagrams or specimens

The names, functions, origins, terminations, foramina, and effects of damage are listed and described in your Saladin text for all of the cranial nerves.

Using this information, you will be expected to know

a) The names and numbers of all 12 pairs of cranial nerves, including the subdivisions of cranial nerve V

b) The foramen through which each cranial nerve passes

c) The primary functions of each cranial nerve

d) The effects of damage to each cranial nerve

Using this information, you will be expected to know

a) The names and numbers of all 12 pairs of cranial nerves, including the subdivisions of cranial nerve V

b) The foramen through which each cranial nerve passes

c) The primary functions of each cranial nerve

d) The effects of damage to each cranial nerve

Example: The abducens nerve (VI) originates from the pons and exits the skull through the superior orbital fissure. It innervates the lateral rectus muscle which causes the eye to rotate laterally. Injury to this nerve on either side causes an inability to rotate that eye laterally, and unopposed function of the other muscles often cause the eye rotate medially.

- Pass between vertebrae through intervertebral foramina to reach the periphery

Spinal Nerves:

- Originate from the spinal cord by dorsal and ventral roots

Spinal Nerves:

- Originate from the spinal cord by dorsal and ventral roots

- Pass between vertebrae through intervertebral foramina to reach the periphery

- 31 pairs, numbered from superior to inferior in each region of the back

Naming Spinal Nerves:

Cervical nerves #1 through #7 leave the vertebral canal through the intervertebral foramina ABOVE the vertebrae with the same numbers.Example: Cervical nerve #3 passes above cervical vertebra #3 (between cervical vertebra #2 and #3)

Cervical nerve #8 leaves the vertebral canal through the intervertebral foramen between cervical vertebra #7 and thoracic vertebra #1 .

Naming Spinal Nerves:

Cervical nerve #8 leaves the vertebral canal through the intervertebral foramen between cervical vertebra #7 and thoracic vertebra #1 .

All thoracic, lumbar, and sacral nerves plus the single coccygeal nerve leave the vertebral canal through the intervertebral foramina BELOW the vertebrae with the same numbers.Example: Thoracic nerve #3 passes below thoracic vertebra #3 (between thoracic vertebra #3 and #4)

Spinal nerves passing through intervertebral foramina

Spinal nerve passing through intervertebral foramina

Immediately distal to the intervertebral foramen, each spinal nerve divides into a dorsal ramus and a ventral ramus.

Both rami are mixed, carrying both afferent & efferent information

Dorsal rami of all spinal nerves innervate the muscles and the skin of the back at their level.

For example: the dorsal ramus of nerve thoracic-2 innervates the muscles and skin of the back at the level of vertebra thoracic-2

Ventral rami of spinal nerves Thoracic 2 -12 innervate muscles and skin of body wall (thorax and abdomen)

Ventral rami of spinal nerves Thoracic 2 -12 innervate muscles and skin of body wall (thorax and abdomen)

But:Ventral rami of all other spinal nerves Cervical 1-8, Thoracic 1, Lumbar 1-5, Sacral 1-5 enter into plexes (singular = plexus)

A plexus is an interchange which allows nerves from different spinal cord levels to combine to serve common structures.

1. Each nerve distal to a plexus carries axons to & from more than one level of the spinal cord.

Example: Radial nerve carries information to & from five levels of the spinal cord: C5, C6, C7, C8, T1

1. Each nerve distal to a plexus carries axons to / from more than one level of the spinal cord. Example: Radial nerve carries information to and from five levels of the spinal cord: C5, C6, C7, C8, T1

2. Axons carrying information to / from a single spinal cord level are distributed through more than one nerve distal to the plexus

Example: Spinal cord level C7 sends and receives information through more than 20 different nerves

Four plexes:

Cervical plexus

Brachial plexus

Lumbar plexus

Sacral plexus

Cervical Plexus

Originates from ventral rami of nerves C1, C2, C3, C4 (+C5)

Carries efferent neurons to many muscles of the neck.

Carries afferent neurons from skin of the neck, shoulder, and scalp near ear

Brachial Plexus

Originates from ventral rami of nerves C5, C6, C7, C8, T1, (+C4)

Carries efferent neurons to muscles of the shoulder, arm, forearm, and hand

Carries afferent neurons from skin of the shoulder, arm, forearm, and hand

Lumbar Plexus

Originates from ventral rami of nerves L1, L2, L3, L4, (L5)

Carries efferent neurons to muscles of the anterior pelvis, anterior and medial thigh

Carries afferent neurons from skin of the anterior pelvis, anterior and medial thigh, and medial leg.

Sacral Plexus

Originates from ventral rami of nerves (L4), L5, S1, S2, S3, S4, (S5, Cx1)

Carries efferent neurons to muscles of the posterior pelvis, posterior thigh, anterior and posterior leg, and foot

Carries afferent neurons from skin of the posterior pelvis, posterior thigh, anterior and posterior leg, and foot.

We will go into greater detail about the bracheal plexus, but you will not be held responsible for details of the cervical, lumbar, or sacral plexes EXCEPT:

You need to know which spinal nerves contribute their ventral rami to each plexus.

You need to know which plexus gives rise to each of the following nerves, and which area of the body each of them innervates:

Ansa cervicalis Femoral Obturator Fibular (common peroneal) Phrenic Genitofemoral Pudendal Inferior and superior gluteal Tibial (Sciatic)

Summary of the Brachial Plexus

Roots

Trunks Upper Middle Lower

Divisons

Anterior

Posterior

Cords: Lateral PosteriorMedial

More than 20 nerves leave the brachial plexus to supply both afferent (sensory) and efferent (motor) innervation to the shoulder, arm, forearm, hand, and parts of the neck and thoracic wall.

We will follow five of these:

1. Musculocutaneous nerve: Arises from the lateral cord of the brachial plexus.

Innervates muscles of the anterior compartment of the arm; skin of lateral forearm

1. Musculocutaneous nerve: Arises from the lateral cord of the brachial plexus.Innervates muscles of the anterior compartment of the arm; skin of lateral forearm

2. Ulnar Nerve: Arises from the medial cord of the brachial plexus.

Innervates muscles in the anterior compartment of the forearm & some intrinsic muscles of the hand; skin on medial third of hand (both anterior and posterior surfaces)

2. Ulnar nerve: Arises from the medial cord of brachial plexus. Innervates muscles of the anterior compartment of forearm & some muscles of hand; skin on medial third of hand (posterior & anterior)

3. Median Nerve: Arises from medial AND lateral cords of the brachial plexus.

Innervates muscles in the anterior compartment of the forearm & some intrinsic muscles of the hand; skin on anterior surface of lateral two-thirds of hand

4. Radial Nerve: Arises from posterior cord of brachial plexus.

Innervates muscles in posterior compartment of arm & posterior compartment of forearm; skin on posterior surface of lateral two-thirds of hand & skin on posterior surfaces of forearm and arm

3. Median Nerve: Arises from medial AND lateral cords of the brachial plexus. Innervates muscles in the anterior compartment of the forearm & some muscles of hand; skin on anterior surface of lateral two-thirds of hand

4. Radial Nerve: Arises: posterior cord of brachial plexus.Innervates muscles in posterior compartments of arm & forearm; skin on posterior surface of lateral two-thirds of hand & skin on posterior surfaces of forearm and arm

5. Axillary Nerve: Arises from posterior cord of brachial plexus.

Innervates shoulder joint, deltoid and teres minor muscles; skin of shoulder

Cutaneous Innervation

Axillary

Ulnar

Musculocutaneous

Radial

Anterior Posterior

Median

(Medial antebrachial cutaneous)