Cervical Plexus
The cervical plexus is a relatively small plexus originating from spinal nerves C1–C4.
Branches derived from this plexus innervate superficial neck structures, including several of the muscles attached to the hyoid bone. The cervical plexus innervates the skin of the neck and posterior portion of the head. The phrenic nerve, which originates from spinal nerves C3–C5, is derived from both the cervical and brachial plexus. The phrenic nerves descend along each side of the neck to enter the thorax. They descend along the sides of the mediastinum to reach the diaphragm, which they innervate. Contraction of the diaphragm is largely responsible for the ability to breathe.
Lumbar and Sacral Plexuses
The lumbar plexus originates from the ventral rami of spinal nerves L1–L4 and the sacral plexus from L4 to S4. Because of their close, overlapping relationship and their similar distribution, however, the two plexuses often are considered together as a single lumbosacral plexus (L1–S4). Four major nerves exit the lumbosacral plexus and enter the lower limb: the obturator, femoral, tibial, and common fi bular (peroneal) nerves. Other lumbosacral nerves supply muscles of the lower back, hip, and lower abdomen and the skin of the hip and thigh. The tibial and common fi bular nerves originate from spinal segments L4–S3 and are bound together within a connective tissue sheath for the length of the thigh. The two nerves bound together are referred to jointly as the sciatic nerve. The sciatic nerve is by far the largest peripheral nerve in the body. It passes through the greater sciatic notch in the coxal bone and descends in the posterior thigh to the back of the knee, where the tibial and common fibular nerves separate from each other. The sciatic nerve supplies the posterior thigh muscles, the tibial nerve supplies the posterior compartment of the leg, and the common fibular supplies the anterior and lateral compartments. Branches of the two nerves combine to form the sural nerve, which supplies the skin on the posterior and lateral leg.
Coccygeal Plexus
The coccygeal plexus is a very small plexus formed from the ventral rami of spinal nerve S5 and the coccygeal nerve (Co). This small plexus supplies the muscles of the pelvic floor and the skin over the coccyx. The dorsal rami of the coccygeal nerves also innervate some skin over the coccyx.
3.4 Clinical correlates
and, if this region of the elbow is banged against a hard object, temporary ulnar nerve damage may occur. This damage results in painful tingling sensations radiating down the ulnar side of the forearm and hand. Because of this sensation, this area of the elbow is often called the funny bone or crazy bone.
Median Nerve Damage
Damage to the median nerve occurs most commonly where it enters the wrist through the carpal tunnel. This tunnel is created by the concave organization of the carpal bones and the retinaculum on the anterior surface of the wrist. None of the connective tissue components of the carpal tunnel expand readily. The tendons passing through the carpal tunnel may become inflamed and enlarged as a result of repetitive movements. This inflammation can produce pressure within the carpal tunnel, thereby compressing the median nerve and resulting in numbness, tingling, and pain in the fingers. The thenar muscles, innervated by the median nerve, have reduced function, resulting in weakness in thumb flexion and opposition. This condition is referred to as carpal tunnel syndrome. Carpal tunnel syndrome is common among people who perform repetitive movements of the wrists and fingers, such as keyboard operators. Surgery is often required to relieve the pressure.
Self-Assessment Exercises
• Describe the spinal nerves.
• Discuss the spinal reflex arc.
Activity
i. In the histology laboratory, observe and recognize the microscopic slides of a nerve and its connective tissue coverings.
ii. In the gross anatomy laboratory/ dissection room, identify the major spinal nerve plexuses – cervical, brachial, lumbar and sacral plexuses.
4.0 Conclusion
The five major plexuses are the cervical (C1–C4), brachial (C5– T1), lumbar (L1–L4), sacral (L4–S4), and coccygeal (S5 and coccygeal nerve). The lumbar and sacral plexuses are often considered together as the lumbosacral plexus. A major nerve of the cervical plexus is the phrenic nerve. The major nerves of the brachial plexus are the axillary, radial, musculocutaneous, ulnar, and median nerves.
5.0 Summary
Individual axons are surrounded by the endoneurium. Groups of axons, called fascicles, are bound together by the perineurium. The fascicles form the nerve and are held together by the epineurium.
Eight cervical, 12 thoracic, 5 lumbar, 5 sacral pairs, and 1 coccygeal pair make up the spinal nerves. The distribution of spinal nerves to skeletal muscles has a top-to bottom pattern in which superior nerves supply superior muscles and inferior nerves supply inferior muscles.
Spinal nerves have specific cutaneous distributions called dermatomes. Spinal nerves branch to form rami. The dorsal rami supply the muscles and skin near the midline of the back.
6.0 Tutor Marked Assignments
1. Which of these is a correct count of the spinal nerves?
a. 9 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal b. 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal c. 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal d. 8 cervical, 11 thoracic, 4 lumbar, 6 sacral, 1 coccygeal e. 7 cervical, 11 thoracic, 5 lumbar, 6 sacral, 1 coccygeal 2. Given these structures:
1. dorsal ramus 2. dorsal root 3. plexus 4. ventral ramus 5. ventral root
Choose the arrangement that lists the structures in the order that an action potential passes through them, given that the action potential originates in the spinal cord and propagates to a peripheral nerve.
a. 2,1,3 b. 2,3,1 c. 3,4,5 d. 5,3,4 e. 5,4,3
3. Damage to the dorsal ramus of a spinal nerve results in a. loss of sensation.
b. loss of motor function.
c. both a and b.
4. A dermatome
a. is the area of skin supplied by a pair of spinal nerves.
b. exists for each spinal nerve except C1.
c. can be used to locate the site of spinal cord or nerve root damage.
d. all of the above.
5. A collection of spinal nerves that join together after leaving the spinal cord is called a a. ganglion.
b. nucleus.
c. projection nerve.
d. plexus.
6. Which of these nerves arises from the cervical plexus?
a. median
b. musculocutaneous c. phrenic
d. obturator e. ulnar sheath.
7. The sciatic nerve is actually two nerves combined within the same. The two nerves are the a. femoral and obturator.
b. femoral and gluteal.
c. common fibular (peroneal) and tibial.
d. common fibular (peroneal) and obturator.
e. tibial and gluteal.
7.0 References and other resources
1. Hutchinson, M., Mallat, J., Marieb, E.N., Wilhelm P.B. (2007). A Brief Atlas of the Human Body. Sna Franscisco: Pearson Education Inc.
2. Katherine M. A. Rogers and William N. Scott (2011) Nurses! Test Yourself in Anatomy and Physiology
3. Kathryn A. Booth, Terri. D. Wyman (2008) Anatomy, Physiology, and Pathophysiology for Allied Health
4. Keith L Moore, Persuade T.V.N (2018), The Developing Human Clinically Oriented Embryology 11th Edition Lippincott Williams & Wilkins
5. Kent M. Van De Graff, R.Ward Rhees, Sidney Palmer (2010) Schaum‘s Outline of human Anatomy and Physiology 3rd edition.
6. Philip Tate (2012) Seeley‘s Principles of Anatomy & Physiology 2nd ed.
7. Sadler T.W (2012), Langman‘s Medical Embryology 12th edition.
8. Seeley‘s Principles of Anatomy & Physiology, Second edition Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY 10020. Copyright c 2012- Chapter 17&18
UNIT 3 AUTONOMIC NERVOUS SYSTEM