1. No. 30
1. Cervical Plexus
2. Brachial Plexus

2. Chapter 3 The Peripheral Nervous System
Introduction:
The peripheral nervous system is the nervous structures outside the brain and spinal cord. It is composed of nerves and ganglia, and usually divided into three portions according to their origins and distribution:
(1) Spinal nerves (31 pairs):
They attach to the spinal cord and make their exit through the intervertebral foramina.
(2) Cranial nerves (12pairs):
They attach to the brain and make their exit through the skull.

3. (3) Visceral nerves:
A further part of the peripheral nervous system which is not a separate morphological entity but a grouping of special nerve components which travel within certain spinal and cranial nerves to innervate smooth muscle, cardiac muscle and gland, that is the visceral nervous system.

4. According to the difference of subject innervated by the nerves, the peripheral nervous system is divided the somatic nerves (supply the body surface, bones, joints, and skeletal muscle) and visceral nerves (are distributed in the viscera, heart, vessels, and smooth muscles).

5. In the peripheral nerves (the somatic and visceral nerves), there are two nerve fibers called afferent nerves (sensory nerves) and efferent nerves (motor nerves).
The visceral efferent (motor) nerve is also called the vegetative nervous system or autonomic nervous system and is further divided into sympathetic nerve and parasympathetic nerve.

6. Section 1 The Spinal Nerve
Introduction:
1. The formation, division, fibrous components of spinal nerves
(1) Formation of the spinal nerves
The spinal nerves, 31 pairs in number, are formed from the union of ventral (anterior) and dorsal (posterior) roots that leave or enter the spinal cord.
The anterior root contains motor fibers arising from the large motor cells of the anterior and lateral horns of the gray matter.

8. The posterior root contains sensory fibers which are the central processes of the pseudounipolar neurons in the spinal ganglion.
So the spinal nerves are mixed nerves.
Spinal ganglion:
The spinal ganglion contains cell bodies of pseudounipolar neurons, their peripheral processes are united with the anterior root to form the spinal nerve at the intervertebral foramen.

9. (2) The division of spinal nerves
There are 31 pairs of spinal nerves, including 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral, and 1 pair of coccygeal nerves.
The spinal nerves leave the vertebral canal by passing through the intervertebral foramina.
All spinal nerves emerge from the intervertebral foramina between adjoining vertebrae, but the 1st cervical nerve exits between the occipital bone and the atlas.
The 8th cervical nerve emerges between the seventh cervical and the first thoracic vertebrae.
The first four of the sacral nerves make their exit through foramina in the sacrum, the fifth and the coccygeal nerves emerge from the sacral hiatus.

10. The spinal nerves consist of four components:
(3) Fibrous components of spinal nerve
The spinal nerves consist of four components:
① The somatic sensory (afferent) fibers
The fibers come from the pseudounipolar neurons in the spinal ganglion. The central processes of pseudounipolar neurons constitute the posterior roots of spinal nerves to go into the spinal cord, while their peripheral processes enter into the spinal nerves to distribute the skin, skeletal muscles, muscular tendon, and the joints of the trunk and limbs, conducting impulses of the superficial sensations of skin (sensations of pain, thermal and tactile) and the deep (proprioceptive) sensations of muscles, tendon, and joints (sensations of the body posture, movement, vibration) into the center.

11. ② The visceral sensory (afferent) fibers
They are also from the pseudounipolar neurons in the spinal ganglion. The central processes form the posterior roots of the spinal nerves to go into the spinal cord, while their peripheral processes distribute the viscera, heart, blood vessels, and glands.
③ The somatic motor (efferent) fibers
The somatic motor fibers coming from the anterior horn of spinal cord, distribute to the skeletal muscles to control their voluntary movement.

12. ④ The visceral motor (efferent) fibers
The visceral motor fibers coming from the lateral horn in the thoracolumbar segments (sympathetic nerve center) and sacral parasympathetic nucleus (parasympathetic nerve center) of spinal cord, distribute the viscera, heart and blood vessels, and glands to innervate the movements of cardiac and smooth muscles, and to control the secretion of glands.

13. 2. Branches of the spinal nerves
Immediately after leaving the foramen, the spinal nerve is divided into:
①The dorsal (posterior) branch: for the supply of muscles and skin of the posterior part of the body. The posterior branches are generally smaller than the anterior, but the posterior branch of the second cervical nerve is larger, its cuteneous branch called the greater occipital nerve, supplies the skin of the occiput.
②The anterior branch: for the supply of structures of the limbs, the lateral and ventral trunk.

14. ③The meningeal branch: supplies the dura matter.
④The communicating branches: connects with the sympathetic trunk.
Except for the anterior branches of thoracic nerves which are quite separated from each other, the anterior branches of other spinal nerves form intricate plexus before supplying a part of body.
They are named the cervical plexus, the brachial plexus, the lumbar plexus and the sacral plexus.

15. Ⅰ. The Cervical Plexus Ⅰ) The Formation of Cervical Plexus
It is formed by the anterior branches of the four upper cervical nerves (C1-4).
Ⅱ) Location of Cervical Plexus
It is situated deeply in the upper part of the neck, rested on the levator scapulae and scalenus medius and is covered by the sternocleiodmastoid.
Ⅲ) The Branches of Cervical Plexus
Its branches may be divided into two groups, superficial and deep.

16. 1. The superficial branches
They emerge near the middle of the posterior border of the sternocleidomastoid and have fan-shaped distribution.
1) The lesser occipital nerve(C1). It is distributed to the skin of occiput and behind the auricle.
2) The greater auricular nerve(C2-3). It supplies much of the external ear and some skin around the auricle.
3) The transverse nerve of neck(C2-3). It is distributed to the skin of the anterior part of the neck.
4) The supraclavicular nerves(C2-4). They are distributed to the skin at the upper portion of the chest, the base of the neck and the shoulder.

18. 2. The deep branches
The phrenic nerve (C3-5)
It descends to the root of the neck, running obliquely across the front of the scalenus anterior, then passes between the subclavian artery and vein to enter the chest. Within the chest it descends in front of the root of the lung between the pericardium and the mediastinal pleura to the diaphragm.

20. The motor fibers supply the diaphragm, the sensory fibers are distributed to the diaphragmatic peritoneum, the diaphragmatic and mediastinal pleurae and the pericardium. The sensory fibers of the right phrenic nerve is also distributed to the liver, the gallbladder and the biliary system.

22. Ⅱ. The Brachial Plexus
Ⅰ) The Formation and Location of Brachial Plexus
The brachial plexus is formed by the union of the anterior branches of the four lower cervical nerves (C5-8) and great part of the anterior branch of the first thoracic nerve (T1).
It extends from the lower part of the side of the neck to the axilla.
Three trunks: between the scalenus anterior and scalenus medium.
Superior trunk (C5-6),
Middle trunk (C7),
Inferior trunk (C8, T1).

23. Divisions: beneath the clavicle, each of these trunks is divided into two divisions—an anterior and posterior divisions. ↓
Cords: in the axilla.
Lateral cord: the anterior divisions of the superior and middle trunks unite to form.
Medial cord: the anterior division of the inferior trunk.
Posterior cord: the posterior divisions of all the three trunks to from.

25. Ⅱ) The Branches of Brachial Plexus
1. The branches above the clavicle
1) The long thoracic nerve: supplies the serratus anterior→”winging of the scapula”.
2) The suprascapular nerve: supplies the supraspinatus and the infraspinatus.
3) The dorsal scapular nerve: supplies the levator scapulae and rhomboideus.

27. 2. The branches below the clavicle
1) The subscapular nerve (C5-7)
It originates from the posterior cord of the brachial plexus, supplies the subscapularis and teres major.
2) The thoracodorsal nerve (C6-8)
It arises from the posterior cord of the brachial plexus, supplies the latissimus dorsi.
3) The lateral and medial pectoral nerves (anterior thoracic nerves) (C5-T1)
They arise from the lateral and medial cords and supply the pectoralis major and pectoralis minor.
4) The axillary nerve (C5-6)

30. Arision:
It arises from the posterior cord.
Route:
It passes backward with the posterior humeral circumflex vessels through the quadrangular space and winds round the surgical neck of the humerus to reach the deltoid muscle.
Branches and their distribution:
Muscular branches supplies the deltoid and teres major, and cutaneous branch to the skin over the deltoid.
Clinical significance:
This nerve may be injured in fracture of the humeral neck or in dislocation of the shoulder joint.
The deltoid is paralyzed and wasting.
A small patch of anesthesia over this muscle may also occur.

32. 5) The musculocutaneous nerve (C5-7)
It arises from the lateral cord of the brachial plexus and perforates through the coracobrachialis, then descends between the biceps brachii and the brachialis and gives off some branches to supply these three muscles.
A little above the elbow, it pierces the deep fascia between the tendon of the biceps and the brachioradialis as the lateral antebrachial cutaneous nerve which supplies the skin of the lateral side of the forearm.

34. It is lateral to the brachial artery—in the upper part of the arm.
6) The median nerve (C6-8, T1)
Arision:
It arises by two roots, one from the lateral and another from the medial cord of the brachial plexus, which embrace the axillary artery and unite each other in front or on the lateral side of the vessel.
Route:
It descends along the medial side of the biceps with the brachial artery.
It is lateral to the brachial artery—in the upper part of the arm.
It crosses the brachial artery anteriorly and posteriorly at the middle part of the arm.
It lies on the medial side of the artery to the cubital fossa.

36. It enters the forearm, by passing between the two heads of the pronator teres, and descends deep to the flexor digitorum superficialis, lying on the flexor digitorum profundus, to the wrist, lying between the tendons of the flexor carpi radialis and palmaris longus, then passes beneath the flexor retinaculum into the palm of the hand and is covered by the palmar aponeurosis.

37. Branches and their distribution:
①It has no branches in the arm.
②In the forearm: it supply the both pronators (protonator teres and pronator quadatus) and most of the flexor muscles (flexor carpi radialis, palmaris longus, flexor digiturum superficialis, flexor pollicis longus and lateral half of the flexor digitorum) except the brachioradialis, the flexor carpi ulnaris and the medial half of the flexor digitorum profundus.

39. ③Before reaching the flexor retinaculum, it gives rise to a small palmar cutaneous branch to the skin of the thenar and central part of the palm.
④In the palm, it divides into a recurrent branch and three common palmar digital nerves.
The recurrent branch innervates the thenar muscles except for the adductor pollicis.
Each of common palmar digital nerves divides into proper palmar digital nerves for the skin of the palmar aspect of the thumb, second, third and the lateral half of the fourth fingers, as well as the skin on the dorsum of the middle and terminal phalanges.
⑤It also contributes muscular branches to the first and second lumbricales.

41. Clinical significance:
An injury to the median nerve in the forearm can result in:
① A loss of pronation of the forearm, flexion of the second, the third fingers and the distal phalanx of the thumb and opposition of the thumb.
② Wrist flexion is severely affected.
③ The thenar muscles are paralyzed, so that the thumb becomes to lie in the same plane as the other digits, it is just an “ape-like” hand.
④ There is also a loss or weakness of sensation from the skin of the radial part of the palmar surface of the thumb, index, middle and radial half of the ring finger.

42. It arises from the medial cord of the brachial plexus. Route:
7) The ulnar nerve (C7-T1)
Arision:
It arises from the medial cord of the brachial plexus.
Route:
At first it lies to the medial side of the brachial artery, about the middle of the arm it pierces the medial intermuscular septum and descends to pass along the groove between the medial epicondyle of humerus and the olecranon, here the ulnar nerve is superficial and easily palpable against the bone, so that, it is easily injured. It enters the forearm between the heads of the flexor carpi ulnaris, and runs downward deep to this muscle on the flexor digitorum profundus with the ulnar artery at its medial side to the wrist.

45. Branches and their distribution:
① In the arm, the ulnar nerve has no branch.
② At the wrist, it crosses the anterior surface of the flexor retinaculum and immediately divides into a superficial branch and a deep palmar branch.
The superficial branch is cutaneous branch, it provides:
*A proper digital nerve to the skin of ulnar side of the little finger and the skin of hypothenar.
*A common palmer digital nerve divides into two proper palmardigital nerves for the skin of contiguous sides of fourth and fifth fingers.

47. The deep palmar branch is muscular branch, it supplies the muscles of hypothenar, the third and the fourth lumbricales, the adductor pollicis and interossei.
③ About 5 cm above the wrist, it gives off a dorsal branch, distribute to the ulnar half of the dorsum of the hand and the posterior surface of the ulnar one and half fingers.

50. Clinical significance:
Ulnar nerve may be damaged at the elbow or the wrist. It results in:
① Interfering with the flexion of the ring and little fingers, metacarpophalangeal joints.
② The extension of the interphalangeal joints, adduction of the thumb is lost.
③ There is also a loss of abduction and adduction of the fingers.
④ The hand is known as “clawhand”.
⑤ The sensation from the skin of the hypothenar and the little finger is lost.

51. It is the continuation of the posterior cord. Route:
8) The radial nerve (C5-T1)
Arision:
It is the continuation of the posterior cord.
Route:
In the axilla, it is placed behind the axillary artery.
Then it runs between the lateral and medial heads of the triceps brachii, and passes along the radial groove.
When it reaches the lower one third of the humerus, the radial nerve pierces the lateral intermuscular septum and continues inferiorly between the brachialis and brachioradialis at the level of the lateral epicondyle of the humerus, where it divides into deep and superficial branches.

53. Branches and their distribution:
① Superficial branch:
At about the junction of the middle and lower one third of the forearm, it continues downwards to the dorsum of the hand. Here it distributes to the skin on the radial side of the dorsum of the hand, and on the proximal digits of the lateral two and half fingers.

55. ② Deep branch:
It pierces through the supinator, curves around the lateral side of the radius to enter the posterior fascial compartment of the forearm.
It distributes the brachioradialis and the extensors of the forearm.
In the arm, the radial nerve also supplies the triceps brachii and the skin on the dorsum of the arm.

56. Clinical significance:
Injury to the radial nerve in the upper or middle part of the arm results in:
① The paralysis of the triceps brachii, brachioradialis, supinator and extensors of the wrist, thumb and fingers.
② The “Wristdrop”.
③ Loss of sensation in the areas of skin supplied by this nerve.