Lab 4.3

peripheral nervous system

essential for understanding how the body senses, moves, and communicates with itself

how many pairs of spinal nerves form the fusion  of the anterior and posterior roots of spinal cord 

31 

function of the 31 pairs of spinal nerves

forms from the fusion of the anterior and posterior roots of the spinal cord;

8 pairs of

cervical spinal nerves

12 pairs of

thoracic spinal nerves

5 pairs of

lumbar spinal nerves

5 pairs of

sacral spinal nerves

1 pair of

coccygeal spinal nerves

mixed nerve

Each spinal nerve carries both motor all sensory axons,

function of anterior roots

carry motor axons emerging from the spinal cord

function of posterior roots

carry sensory axons to the spinal cord

when the anterior and posterior roots fuse to form the spinal nerve they become?

posterior ramus (plural: rami), an anterior ramus, and a small meningeal branch

posterior rami

serve the skin, joints, and musculature of the posterior trunk

small meningeal branches

reenter the vertebral canal to innervate spinal structures

larger anterior rami

travel anteriorly to supply the muscles of the upper and lower limbs, the anterior thorax and abdomen, and part of the back.

what rami differs for each section of the trunk; the thoracic region forms the intercostal nerves, while in the cervical, lumbar, sacral, and coccygeal regions form the four different plexuses

anterior rami 

intercostal nerves

anterior rami of the thoracic spinal nerves travel between the ribs as 11 separate pairs of intercostal nerves

function of intercostal nerves

innervate the intercostal muscles, the abdominal muscles, and the skin of the chest and abdomen

sensory function of intercostal nerves

branches to the skin are the most common routes of viral migration in the painful disease known as shingles!

motor function of intercostal nerves

innervate the internal oblique, external oblique, and transverse abdominal muscle.

cervical plexus

consists of the anterior rami of C1–C4 spinal nerves with small contributions from C5.

what is the function of the branches of cervical plexus

serve the skin of the head and neck and certain neck muscles. 

where do most cervical plexus nerves emerge from or around

sternocleidomastoid muscle

spinal nerves of lesser occipital nerve

C2 and C3

motor of lesser occipital nerve

none

sensory of lesser occipital nerve

External ear and lateral scalp and upper neck

location of lesser occipital nerve 

Travels along the posterior border of the SCM toward the occipital bone

nearby structures of lesser occipital nerve

External jugular vein

cranial nerve association of lesser occipital nerve

none

etymology of lesser occipital nerve

Occipital refers to the back of the skull

visualization tip for lesser occipital nerve

Place your hand behind your ear and trace up to the occipital area

spinal nerves of ansa cervicalis

C1 to C3

motor of ansa cervicalis

Omohyoid, sternohyoid, and sternothyroid muscles

sensory of ansa cervicalis

none

location of ansa cervicalis

Loops around the anterior surface of the SCM, superficial to the internal jugular vein

nearby structures of ansa cervicalis

Internal jugular vein and carotid sheath

cranial nerve association for ansa cervicalis

Travels briefly with cranial nerve XII (hypoglossal)

etymology of ansa cervicalis 

"Ansa" means loop, "cervicalis" means of the neck

visualization tip for ansa cervicalis

Picture a necklace loop resting over the front of your neck

spinal nerves of supraclavicular nerve

C3 and C4

motor of supraclavicular nerve

none

sensory of supraclavicular nerve

Skin over the clavicle, shoulder, and upper chest

location of supraclavicular nerve

Emerges around the middle third of the SCM and travels toward the clavicle

nearby structures of supraclavicular nerve 

Clavicle and superficial veins

cranial nerve association of supraclavicular nerve

none

etymology of supraclavicular nerve

Supra means above, clavicular refers to the clavicle

visualization tip of supraclavicular nerve

Imagine a shoulder strap crossing from neck to chest

spinal nerves for transverse cervical nerve

C2 and C3

motor of transverse cervical nerve

none

sensory transverse cervical nerve

Anterior and lateral skin of the neck

location of transverse cervical nerve

Travels horizontally across the middle of the SCM

nearby structures of transverse cervical nerve

External jugular vein

cranial nerve association for transverse cervical nerve

none

etymology of transverse cervical nerve

Transverse means across, cervical refers to the neck

visualization tip for transverse cervical nerve 

Trace a horizontal line from under your chin across the neck

spinal nerve for greater auricular nerve

C2 and C3

motor for greater auricular nerve

none

sensory for greater auricular nerve

Skin over the parotid gland, mastoid region, and external ear

location of greater auricular nerve

Ascends vertically over the anterior border of the SCM toward the ear

nearby structures for greater auricular nerve

Parotid gland and external jugular vein

cranial nerve association for greater auricular nerve 

none 

etymology for greater auricular nerve

Auricular means related to the ear

visualization tip for greater auricular nerve

Trace a path from your jaw up to your earlobe

spinal nerves for phrenic nerve

C3,C4, and C5

motor phrenic nerve

diaphragm

sensory of phrenic nerve

Central diaphragm and surrounding pleura

location of phrenic nerve

Descends vertically along the anterior surface of the anterior scalene muscle, deep to the SCM

nearby structures for phrenic nerve

Internal jugular vein, vagus nerve, subclavian vessels

cranial nerve association for phrenic nerve

Travels near but separate from the vagus nerve

etymology for phrenic nerve

From Greek “phren” meaning diaphragm

mnemonic for phrenic nerve

C3 4 and 5 keep the diaphragm alive

visualization tip for phrenic nerve

Imagine a lifeline running from your neck down into your chest, enabling each breath

brachial plexus

anterior rami of C5–T1 spinal nerves ⇒ then each spinal nerve contribute to the formation of three large trunks ⇒ then each trunk is divided into two divisions (an anterior and a posterior) ⇒ then each division contributes to the formation of the three cords ⇒ each cord contributes to the formation of each of the five nerve branches

how can the brachial plexus be easy identified

by the M or W shape it resembles on the anterior side via the lateral and medial cords. While the posterior cord resembles a V on the posterior side of the M or W.

where does the brachial plexus pass

over the 1st rib into the axilla and innervates the upper limb and some muscles of the neck and shoulder

trunks

The first structures formed in each brachial plexus are its three large

superior trunk

formed by the C5 and C6 spinal nerves

middle trunk

formed by the C7 spinal nerve

inferior trunk 

formed by the C8 and T1 spinal nerves

divisions

• Each trunk splits into an anterior and posterior divisions that contribute to the cords. 

  • Anterior and posterior divisions of the superior trunk

  • Anterior and posterior divisions of the middle trunk

  • Anterior and posterior divisions of the inferior trunk

cord rule 1

Formed by a contribution of one division, specifically the anterior division of the inferior trunk forms the medial cord, which descends in the medial arm. 

medial cord

formed by anterior division of the inferior trunk

cord rule 3

Formed by the contribution of two divisions, specifically the anterior divisions of the superior and middle trunks unite to form the lateral cord, which descends in the lateral arm. 

lateral cord

formed by the anterior divisions of the superior and middle trunks unite

cord rule 3

Formed by the contribution of three divisions, specifically the posterior divisions of all three trunks unite to form the posterior cord, which is located in the posterior arm.

posterior cord

formed by posterior divisions of all three trunks

nerve branches

Several nerves originate from the brachial plexuses’ cords and trunks, including the following:

lateral cord nerve

musculocutaneous nerve

musculocutaneous nerve

It is the distal continuation of the lateral cord and located in the lateral arm.

motor of musculocutaneous nerve

Serves the anterior arm muscles (musculo-) that flex the forearm (such as the biceps brachii, brachialis, and coracobrachialis muscles).

sensory of musculocutaneous nerve

Serves the skin (-cutaneous) of the anterolateral forearm and elbow joint

location of musculocutaneous nerve

deep to the biceps brachii muscle, but superficial to the brachialis muscle

• is the lateral side of the M shape this plexus resemble

posterior cords nerves 

• axillary nerve 

• radial nerve 

axillary nerve

A short branch of the posterior cord. It travels by the subscapularis muscle and pierces posteriorly between the teres minor and major muscles.

• It is the shorter branch of the V shape this plexus resembles

motor of axillary nerve

It serves structures near the axilla, including the deltoid and teres minor muscles. It makes sense, since they are all near each other. 

sensory of axillary nerve

It serves the skin around the axillary region.

radial nerve

it is the distal continuation of the posterior cord and is located in the posterior upper limb.

• It travels on the radial groove found on the posterior side of the humerus bone.

• As it travels down the arm it will then migrate laterally as it reaches the forearm.

• It is the longer branch of the V shape this plexus resembles.

motor of radial nerve

It serves the muscles that extend the arm, forearm and hand.

sensory of radial nerve

serves the joints of the elbow, wrist, hand, the skin on the posterior arm and forearm, lateral forearm, wrist, and hand (which makes sense since the radius is always located laterally). 

median nerve

This is the only nerve in the brachial plexus that is formed from the fusion of portions of two cords, namely the medial and lateral cords. It is named as such because it travels approximately down the middle of the arm and forearm. 

• It is the middle part of the M shape this plexus resembles.