Limb Plexus - Functional NeuroAnatomy 1

What is a plexus ? So what is a nerve plexus ?

• A plexus is a network.

• Nerve plexus is a network of nerves innervating limbs.

Can you describe the divisions of the spinal cord ?

• CNS: brain & spinal cord

• PNS: spinal nerves, cranial nerves, peripheral nerves, ganglia.

What is the CNS protected by ? Explain ?

• The CNS is protected by bone.

• The brain is covered by the skull and the spinal cord is protected by the vertebral column.

What is a Myotome ?

A myotome is all the skeletal muscles innervated by a single spinal nerve ?

So is each skeletal muscle innervated by one spinal nerve ?

• No, although the myotome is all the skeletal muscles innervated by a single spinal nerve, it is important to know that each skeletal muscle is innervated by more than 1 spinal nerve.

Where does the spinal nerve leave ? Does it leave in one section ?

• The spinal nerve is a nerve that leaves the spinal cord.

• It does not leave the spinal cord in one section.

• One leaves the front and the other is connected to the back.

• These are called roots - anterior root (ventral) an posterior root (dorsal).

• They unite to form the spinal nerve which leaves the vertebral column.

• Divides into 2 divisions called the anterior ramus / division and the posterior ramus / divivision.

What is the function of the anterior and posterior ramus ?

• To supply the muscles and the skin.

Where do the limb develop from in an embryo ? How are they supplied ?

• Limbs develop from body segments.

• The anterior rami branch - combine - and rebranch, to form plexuses.

What is the main function of the brachial plexus ? What about the lumbar and the sacral plexus ?

Brachial plexus - are the main nerves in supplying the upper limb.

Lumbar and sacral plexus - are the main nerves in supplying the lower limb.

What comes from the plexuses ? What does this serve ?

Plexuses divide into peripheral / limb nerves that innervate the muscles and the skin.

Lumbar plexus: Derived from what ? Innervate what ? Branches ?

• Derived from the anterior rami of L1-L3, most of L4.

• Innervate the lower limb and parts of the trunk.

• Branches: Femoral artery and the Obturator artery (that innervates the inside / medial part of the thigh)

Sacral Plexus: Components ? Branches ? Musculature branches ?

Components: Lumbosacral trunk (L4-L5), Anterior Rami / divisions of S1-S4

Branches: Sciatic Nerve (largest nerve in the body)

From these plexuses they split off into smaller branches that innervate muscles that are nearby.

Musculature branches:

• Cuff of muscles of the hip joint

• Muscles of the gluteal region

Brachial plexus: where does the word brachium come from ? What does it innervate ? What is it ?

• Brachial comes from the word brachium which means arm.

• It innervates muscles of the upper limb.

• What is it ? It is a union of the anterior rami / divisions of the spinal cord. (C5,C6,C7,C8.T1) - 5 rami

What can we use to remember the brachial plexus in our study ?

It is the union of 5 rami, and it starts with C5

Can you explain verbally the division of the networks ?

Because we have a network, we try to divide the network into sections, and then give these sections names.

What is the name of these subdivisions ?

• Roots: start of something, union of anterior rami C5-T1.

• The roots unite to have trunks (superior, medial, inferior)

• The roots divide to form divisions (anterior and posterior)

• Divisions combine to form Cords (medial,lateral and posterior)

• The cord split into branches which are the main nerves supplying the upper limb

Roots: how are they formed? where do you find them ?

• Roots are formed by the union of the anterior rami C5-T1.

• You will find them in the neck region.

Trunks: how do they form ? Distinguish between C5-T1 ? Where do you find trunks ?

• Trunks form from the union of the roots

• C5 + C6 = superior trunk

• C7 = middle trunk

• C8 + T1 = inferior trunk

• You find the trunks : underneath the clavicle running from the neck to the axilla (pyramid-shaped space in the armpit)

How are divisions formed ? Types ?

Divisions form from the division of the trunks. We have the 

• anterior divisions

• posterior divisions

How do cords form ? Where do they form ? Where are they located ?

• Cords form through the union of the divisions.

• They form at the axilla.

• They surround the artery.

How are the cords given their name ?

they are given there name according to their location around the artery.

What is the name of the 3 cords we learned about ? How do they form ?

• The anterior branch of the upper and middle trunk form the lateral cord.

• The anterior branch of the lower limb forms the medial cord.

• The posterior branches of all three limbs forms the posterior cord

What can a particular spinal nerve do ?

A particular spinal nerve can contribute to several nerves.

What is so special about the median nerve ?

It has contributions from all 5 spinal nerves.

What is a myotome ?

These are all the muscles innervated by a single spinal nerve coming from 1 segment of the spinal cord.

List 5 movements that occur in the hand and what spinal nerve innervates that movement ?

1. C5: abduction of the arm (performed by deltoid muscle which is innervated by the axillary nerve)

2. C(5)6: Flexion of elbow

3. C(6)7(8): Extension of elbow

4. C8: Flexion of fingers

5. T1: Abduction and adduction of fingers

Brachial Plexus Injuries: what is a condition associated with damage to C5-C6 ? When does it happen ? What movements are effected ?

• Condition: Erb Duchenne palsy / Waiters tip

• When does it happen ? It can happen during birth trauma when assistance is required and it causes an increase angle between neck and shoulder, this will damage brachial plexus. Can also happen in Motor bike RTA - forced lateral flexion of the neck causing traction (pull) of opposite shoulder. Could also be fall from height.

• Movements effected ? Abduction of the arm and Flexion of the elbow.

What happens if there is damage to the lower trunks: name a condition ? How does this happen ? What nerves are damaged ? What movements are affected ?

• Klumpke’s palsy (damage to C8,T1).

• Occurs if there is excessive abduction and traction (pull) of the arm, for examples, if a person is falling from a height and grabs onto an object to save themself.

• Flexion of the fingers and abduction and adduction of the fingers are affected to damage to C8 and T1.

What motor loss occurs ? What is a sign ?

Hand instrinsic muscles (completely inside origin and insertion included) are weakened.

Sign = claw hand deformity