Spinal Nerves - Cervical and Brachial Plexuses

Question 1

Components of the Spinal Nerve

Answer 1

Dorsal horn and ventral horn merge to form the spinal nerve.
Dorsal horn contains sensory nerve cells.
Ventral horn contains motor nerve cells.
Part of the peripheral nervous system.

Question 2

How many pairs of spinal nerves are there and how many belong to each area?

Answer 2

31 pairs of spinal nerves.
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal

Question 3

Spinal Nerve Supply and Entry

Answer 3

Combination of somatic sensory and somatic motor info and visceral sensory and visceral motor info.
Sensory axons enter the spinal cord as dorsal nerve root.
Motor fibers enter as the ventral nerve root.

Question 4

Somatic System - Myotomes

Answer 4

Group of muscles that the ventral root of a single spinal nerve innervates.
Organized into segments because the share a common origin.

Question 5

Myotome Testing

Answer 5

Difficult. Muscles can be innervated by more than one nerve and by nerves that originate from different spinal cord levels.
Check ability to perform a specific action and muscle weakness. Provides info on type of movements that will be affected.

Question 6

Somatic System - Dermatomes

Answer 6

Area of the skin that the dorsal root of a single nerve innervates.
Clinically important to identify where there has been damage to the spinal cord.
From occipital protuberance to the perineal area.

Question 7

Myotome Levels

Answer 7

C5: Elbow flexors
C6: Wrist extensors
C7: Elbow extensors
C8: Finger flexors
T1: 5th digit abductors
L2: Hip flexors
L3: Knee extensors
L4: Ankle dorsiflexors
L5: Long toe extensors
S1: Ankle plantar flexors

Question 8

Spinal Nerve Locations

Answer 8

First nerve C1 emerges between C1 and the occipital bone.
Second nerve C2, between C1 and C2.
C8 emerges between C7 and T1.
Thoracic and lumbar nerves emerge between the same vertebra and the one below.
Sacral nerves emerge from sacral foramina.

Question 9

Nerve Plexuses (4) - Definition

Answer 9

Axons from different spinal nerves come together into a systemic nerve.
Network of nerve fibers with no associated cell bodies.
Cervical level: cervical plexus, brachial plexus.
Lumbar level: lumbar plexus
Sacral level: sacral plexus

Question 10

Cervical Plexus - Function and Location

Answer 10

Supplies innervation to some structures in the neck and trunk.
Located in posterior triangle of neck, behind sternocleidomastoid.
Formed by the ventral rami of cervical spinal nerves C1-C4.

Question 11

Cervical Plexus - Branches (supply)

Answer 11

Gives rise to numerous branches which supply structures in head and neck.
Muscular branches: deep to the sensory branches. Supply muscles of neck, back and diaphragm.
Sensory branches: Supply skin of neck, upper thorax, scalp and ear.

Question 12

Muscular Branches - Nerves

Answer 12

Phrenic nerve
Nerves to geniohyoid and thyrohyoid
Ansa cervicalis
Minor muscular branches

Question 13

Cervical Plexus - Phrenic Nerve

Answer 13

Arises from anterior rami of C3-C5.
Provides motor innervation to the diaphragm. C3,4,5 keeps the diaphragm alive.

Question 14

Cervical Plexus - Spinal Nerves to Geniohyoid and Thyrohyoid

Answer 14

C1 spinal nerve gives rise to geniohyoid and thyrohyoid. Travel with the hypoglossal nerve(cranial nerve) to reach their respective muscles.

Question 15

Cervical Plexus - Ansa Cervicalis (branches 4, roots, function)

Answer 15

Loop of nerves formed by nerve roots C1-C3.
Gives 4 muscular branches:
- superior belly of omohyoid muscle
- inferior belly of omohyoid muscle
- sternohyoid
- sternothyroid
Important function for swallowing and speech.

Question 16

Cervical Plexus - Sensory Branches (4)

Answer 16

Greater auricular nerve
Transverse cranial nerve
Lesser occipital nerve
Supraclavicular nerve

Question 17

Cervical Plexus - Greater Auricular Nerve

Answer 17

Formed by C2 and C3 roots.
Provides sensation to external ear and skin over parotid gland.

Question 18

Cervical Plexus - Transverse Cervical Nerve

Answer 18

Formed by C2 and C3 fibers.
Supplies sensation to the anterior neck and upper sternum.

Question 19

Cervical Plexus - Lesser Occipital Nerve

Answer 19

From C2 root, with C3 contributions in some people.
Also named Arnold’s nerve.
Supplies cutaneous sensation to posterosuperior scalp.

Question 20

Cervical Plexus - Supraclavicular Nerve

Answer 20

Group of nerves formed from C3 and C4 roots.
Provide sensation to the skin overlying the supraclavicular fossa, upper thoracic region and sternoclavicular joint.

Question 21

Brachial Plexus - Function, Formation

Answer 21

Supplies the skin and musculature of the upper limb.
Begins at root of neck, passes through axilla and runs through upper limb.
Formed by ventral rami of spinal nerves C5-T1.

Question 22

Brachial Plexus - Division (5)

Answer 22

• Roots
• Trunks
• Divisions
• Cords
• Branches
  Read That Damn Cadaver Book

Question 23

Brachial Plexus - Roots

Answer 23

Refer to the anterior rami of spinal nerves C5, C6, C7, C8, T1.
Leave the spinal cord via the intervertebral foramina.

Question 24

Brachial Plexus - Branches from the Roots (2)

Answer 24

Only motor info.
Dorsal Scapular Nerve: from C5. Supplies rhomboids major and minor, levator scapulae.
Long Thoracic Nerve: from C5, C6 and C7. Supplies serratus anterior.

Question 25

Brachial Plexus - Trunks (3)

Answer 25

Roots converge to form 3 trunks:
Superior: from C5 and C6
Middle: from C7
Inferior: from C8 and T1

Question 26

Brachial Plexus - Branches from the Trunks (2)

Answer 26

Motor info only.
Subclavius: from (C4) C5 and C6. Supplies subclavius.
Suprascapular: from (C4) C5 and C6. Supplies supraspinatus, infraspinatus, articular filaments to shoulder and acromioclavicular joint.

Question 27

Brachial Plexus - Divisions

Answer 27

Each trunk splits into 2 divisions:
Anterior: division moves anteriorly
Posterior: division moves posteriorly
Pass into the axilla. Recombine into cords.
No branches coming from the divisions.

Question 28

Brachial Plexus - Cords (3)

Answer 28

Named by their position relative to axillary artery.
Lateral cord: Formed by anterior divisions of superior and middle trunks.
Posterior cord: Formed by posterior divisions of superior, middle and inferior trunks.
Medial Cord: Formed by anterior division of inferior trunk.

Question 29

Brachial Plexus - Branches from the Cords (Anterior Divisions, Motor Function) (2)

Answer 29

Lateral Pectoral Nerve: Lateral cord, From C5, C6 and C7. Supplies pec major.
Medial Pectoral Nerve: Medial cord, from C8 and T1. Supplies pec minor.

Question 30

Brachial Plexus - Branches from the Cords (Anterior Divisions, Cutaneous Function) (2)

Answer 30

Medial Brachial Cutaneous Nerve (arm): Medial cord, from T1. Supplies skin and fascia on medial side of proximal half of arm.
Medial Antebrachial Cutaneous Nerve (forearm): Medial cord, T1. Supplies skin and fascia on lower part of biceps, medial side of forearm, medial side of posterior forearm.

Question 31

Brachial Plexus - Branches from the Cords (Posterior Divisions, Motor Function) (2)

Answer 31

Upper and Lower Subscapular Nerves: Posterior cord. C4, C5, C6, C7. Supplies teres major.
Thoracodorsal Nerve: Posterior cord. C6, C7, C8. Supplies latissimus dorsi.

Question 32

Brachial Plexuses - Branches

Answer 32

In axilla and proximal upper limb.
Cords give rise to 5 major branches:
Musculocutaneous
Axillary
Median
Radial
Ulnar
Provide innervation to muscles and skin in the upper limb.

Question 33

Brachial Plexus - Branches - Axillary Nerve

Answer 33

Roots: C5, C6.
Cords: posterior
Motor function: teres minor, posterior deltoid.
Sensory function: superior lateral cutaneous nerve of arm: lower deltoid and lateral head of tricep.

Question 34

Brachial Plexus - Branches - Musculocutaneous Nerve

Answer 34

Roots: C5, C6, C7
Cord: Lateral

Question 35

Brachial Plexus - Branches - Musculocutaneous Nerve

Answer 35

Roots: C5, C6, C7
Cord: Lateral
Motor function: brachialis, biceps brachii, coracobrachialis.
Sensory function: Lateral cutaneous branch of forearm: Lateral half of anterior and posterior (small) forearm.

Question 36

Brachial Plexus - Branches - Median Nerve

Answer 36

Roots: (C5), C6 to T1.
Cords: lateral cord and part of medial cord.
Motor Function: Forearm flexor muscles, thenar muscles, two lateral lumbricals (index and middle finger).
Sensory Function: Palmar cutaneous branch: Lateral palm. Digital cutaneous branch: lateral 3,5 fingers on palmar surface of hand.

Question 37

Brachial Plexus - Branches - Radial Nerve

Answer 37

Root: C5 - T1.
Cord: Posterior.
Motor function: triceps brachii, posterior compartment of wrist and fingers.
Sensory function: Posterior cutaneous nerve of arm: posterior proximal third of arm. Lower lateral cutaneous nerve of forearm: lower lateral part of arm and forearm. Posterior cutaneous nerve of forearm: Dorsum of forearm.

Question 38

Brachial Plexus - Branches - Ulnar Nerve

Answer 38

Root: C8 and T1.
Cord: Medial.
Motor function: muscles of the hand (except thenar and two lumbricals). Flexor carpi ulnaris and medial half of flexor digitorum profundus.
Sensory Function: Palmar cutaneous branch: medial palm. Dorsal branch: dorsum of hand, dorsal 5th finger and adjacent half of 4th finger. Deep branch: wrist joint.

Question 39

Anecdotes to remember the Brachial Plexus

Answer 39

3 Y’s
2 E’s
1 X
3 musketeers assassinated 5 rats 5 mice and 2 unicorns.
3 musketeers: musculocutaneous C5, C6, C7.
Assassinated: Axillary, C5, C6 (finger gun).
5 Rats: radial, C5-T1.
5 Mice: median C5(C6) - T1.
2 Unicorns: ulnar C8, T1.