Spinal Nerves

Cervical plexus

Brachial plexus

Objectives• Describe how spinal nerves are formed.• Make a list of contributing roots to cervical plexus.• Discuss the general arrangement.• Describe the location of this plexus.• Make a list of the out coming nerves..• Point out the point where the major cutaneous nerves

emerge.• Describe the brachial plexus• Make a list of contributing spinal nerves.• Discuss the general arrangement of this plexus.• Locate the plexus in the axilla and note important relations

to blood vessels.• Make a list of the terminal main branches of brachial plexus.

Spinal Nerves• The spinal cord is functionally segmented• Each segment gives of a pair of spinal nerves

(31)• 8 cervical, 12 thoracic, 5 lumbar, 5 sacral &

one coccygeal• Each nerve has a dorsal (sensory) root & a

ventral motor root• The dorsal has a ganglion containing

pseudounipolar neurons

• Each spinal nerve arises as rootlets which then combine to form dorsal (posterior) & ventral (anterior) roots.

• Two roots merge laterally and form the spinal nerve.

• Dorsal (posterior) root has a ganglion (dorsal root/sensory ganglion) that contains the cell bodies of the sensory neurons

• Each spinal nerve then divides into a smaller dorsal and a larger ventral ramus

Spinal nerve Typical spinal nerve divides into:• 1- Dorsal ramus which supplies structures on

the back• 2- White ramus communicans to sympathetic trunk and Grey ramus communicans from the sympathetic trunk• 3- Collateral branch• 4- Ventral ramus• 5- Lateral branch• 6- Anterior branch

Main Branches of the spinal nerve

• Dorsal Ramus: innervate deep muscles of the trunk responsible for movements of the vertebral column and skin near the midline of the back.

• Ventral Ramus: what they innervate depends upon which part of the spinal cord is considered. Thoracic region: form intercostal nerves that

innervate the intercostal muscles and the skin over the thorax

Remaining spinal nerve ventral rami (roots of the plexus): form five plexuses (intermingling of nerves).

Ventral rami of C1-C4= cervical plexus Ventral rami of C5-T1= brachial plexus Ventral rami of L1-L4= lumbar plexus Ventral rami of L4-S4= sacral plexus Ventral rami of S4 and S5= coccygeal plexus

• Communicating Rami: communicate with sympathetic chain of ganglia.

Dermatomes

• Dermatome is: A specific segment of skin supplied by a single spinal nerve.

• All spinal nerves except for C1 innervate a segment of skin, and so each of these nerves is associated with a dermatome.

• The skin of the body may be divided into sensory segments that collectively make up a dermatome map.

Dermatomes

• Cutaneous areas supplied by adjacent spinal nerves overlap. There is therefore little or no sensory loss after interruption of a single spinal nerve or dorsal root

Cervical Plexus

• Is made of the anterior rami of C1-4• Ansa cervicalis: is a nerve loop made of superior

root C1-2 and inferior root C2-3• Ansa cervicalis and anterior ramus of C1 supply infrahyoid muscle• Phrenic nerve arises from C3-5

Cervical Plexus

Sensory branches of cervical plexus include:

• Lesser occipital nerve• Great auricular nerve• Transverse cervical nerve• Supraclavicular nerves

Brachial Plexus• It is formed by the ventral rami of C5-T1• C5-6 form upper trunk• C7 continues as middle trunk• C8-T1 form the lower trunk• Each trunk divides into anterior and posterior divisions

FORMATION OF BRACHIAL PLEXUS • It is formed in the posterior triangle of the neck.• Divisions:

• The plexus is divided into :– Roots– Trunks– Divisions– Cords– Terminal branches

•

TRUNKS• Upper trunk– Union of the roots of

C5 & 6

• Middle trunk– Continuation of the

root of C7

• Lower trunk– Union of the roots of

C8 & T1

DIVISIONS & CORD

• Each trunk divides into anterior and posterior division

• Posterior cord:– From the three posterior divisions

• Lateral cord:– From the anterior divisions of the

upper and middle cords

CORDS & BRANCHES

• Medial cord – It is the continuation

of the anterior division of the lower trunk

Branches All three cords will give

branches, those will supply their respective regions

BRANCHES • (A) From Roots:1. C5: Nerve to rhomboids (dorsal scapular nerve).

2. C5,6 &7: Long thoracic nerve

(B) From Trunk (upper trunk): 1. Nerve to subclavius

2. Suprascapular nerve (supplies supraspinatus & infraspinatus)

Lateral Cord(2LM) .Lateral pectoral n.Lateral root to median n.Musculocutaneous n

Posterior Cord(ULTRA) .Upper subscapular n.Lower subscapular n.Thoracodorsal n.Radial n .Axillary n

Medial cord(4MU) .Medial pectoral n..Medial root to median n..Medial cutaneous n of arm..Medial cutaneous n of forearm..Ulnar n.

C5

C6

C7

C8T1

(C)BRANCHES From Cords

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