no. 30 1. cervical plexus 1. cervical plexus 2. brachial plexus 2. brachial plexus
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No. 30 1. Cervical Plexus 2. Brachial Plexus
Chapter 3 The Peripheral Nervous SystemIntroduction: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) 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.
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).
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.
Section 1 The Spinal NerveIntroduction: 1. The formation, division, fibrous components of spinal nerves (1) Formation of the spinal nervesThe 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.
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.
(2) The division of spinal nervesThere 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.
(3) Fibrous components of spinal nerveThe spinal nerves consist of four components: The somatic sensory (afferent) fibersThe 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.
The visceral sensory (afferent) fibersThey 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. The somatic motor (efferent) fibersThe somatic motor fibers coming from the anterior horn of spinal cord, distribute to the skeletal muscles to control their voluntary movement.
The visceral motor (efferent) fibersThe 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.
2. Branches of the spinal nervesImmediately after leaving the foramen, the spinal nerve is divided into: The 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. The anterior branch: for the supply of structures of the limbs, the lateral and ventral trunk.
The meningeal branch: supplies the dura matter. The 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.
. The Cervical Plexus ) The Formation of Cervical PlexusIt is formed by the anterior branches of the four upper cervical nerves (C1-4). ) Location of Cervical PlexusIt is situated deeply in the upper part of the neck, rested on the levator scapulae and scalenus medius and is covered by the sternocleiodmastoid. ) The Branches of Cervical PlexusIts branches may be divided into two groups, superficial and deep.
1. The superficial branchesThey 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.
2. The deep branchesThe 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.
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.
. The Brachial Plexus ) The Formation and Location of Brachial PlexusThe 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).
Divisions: beneath the clavicle, each of these trunks is divided into two divisionsan 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.
) The Branches of Brachial Plexus 1. The branches above the clavicle 1) The long thoracic nerve: supplies the serratus anteriorwinging of the scapula. 2) The suprascapular nerve: supplies the supraspinatus and the infraspinatus. 3) The dorsal scapular nerve: supplies the levator scapulae and rhomboideus.
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)
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.
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 t