2. The Nervous System
The nervous system can be defined as the network of nerve cells and fibers
that sends messages for controlling movement and feeling between the
brain and the other parts of the body. This nervous system is divided into
two main parts, the central nervous system (CNS), which consists of the
brain and spinal cord , and the peripheral nervous system (PNS) , which
consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves and their
associated ganglia.
Functionally, the nervous system can be further divided into the somatic
nervous system, which controls voluntary activities, and the autonomic
nervous system, which controls involuntary activities.
3. functions of the nervous system
The three basic functions of the nervous system:
Motor output: Respond via muscle or glandular action
Sensory input: Receive sensations from inside and outside the
body
Integration: Process and interpret sensations and make
decisions
The nervous system, together with the endocrine system,
controls and integrates the activities od the different parts of
the body.
5. Nerve plexus
plexus /pleksəs/ noun a network of nerves, blood vessels or lymphatics.
A nerve plexus is a system of connected nerve fibers that link spinal nerves
with specific areas of the body. Fibers in a plexus connect the spinal cord and
the body by grouping themselves into one larger nerve. The human body
consists of several nerve plexuses, including the brachial plexus, the cervical
plexus, the coccygeal plexus, the lumbar plexus, the sacral plexus, and the
solar plexus.
A plexus is like an electrical junction box, which distributes wires to different
parts of a house. In a plexus, nerve fibers from different spinal nerves (which
connect the spinal cord to the rest of the body) are sorted. The fibers are
recombined so that all fibers going to a specific body part are put together
one nerve. Damage to nerves in the major plexuses causes problems in the
arms or legs that these nerves supply.
6. NERVE PLEXUS
ANATOMY
The nerve plexus is actually made up
of a multitude of nerve branches.
These branches come from the spinal
nerves, except for the thoracic spinal
nerves 2 through 12. The remaining
nerves donate their anterior rami,
which branch off from the spinal
nerves only to adjoin with each other
. A nerve plexus is composed of
afferent and efferent fibers that arise
from the merging of the anterior
rami of spinal nerves and blood
vessels.
7. NERVE PLEXUS STRUCTURE
Once they connect, they break off again and develop the network of
nerve fibers known as the nerve plexus. There are actually 4 of these
nerve plexuses in the human body, the brachial plexus, cervical plexus,
the sacral plexus and the lumbar plexus.
At the root of the limbs, the anterior rami join one another to form
complicated nerve plexus. The cervical and brachial plexuses are
found at the root of the upper limbs, and the lumbar and sacral
plexuses are found at the root of the lower limbs.
The nerves which come out of the various plexus are typically named
either for the specific area which they innervate or the basic course
which can be traced along the way.
8. The main function of a nerve plexus
The main function of a nerve plexus is to ensure that all areas of the
body are innervated, thereby equipping each region with the ability
to send and receive messages from the peripheral nervous system.
The different plexuses are charged with innervating different portions
of the body and help to control the functions unique to each portion.
A nerve plexus is formed during development, when disparate
muscles of the skeleton fuse together and result in large muscles
requiring innervation . The nerves that arise from the plexuses have
both sensory and motor functions. These functions include muscle
contraction, the maintenance of body coordination and control, and
the reaction to sensations such as heat, cold, pain and pressure.
10. 1. Spinal plexus
At each vertebral level, paired spinal
nerves leave the spinal cord via
the intervertebral foramina of the
vertebral column.
There are five spinal nerve plexuses
11. 1.a. Cervical plexus
The cervical nerve plexus is a junction of small
nerve fiber network that transports sensory
information to the shoulder, neck and the head.
It continues until pharynx and is enclosed deep
within the neck. It extends further up to the
pharynx. The cervical plexus is an important part
of the peripheral nervous system (PNS) which is
a part of nervous system located outside the
spinal cord and brain.
Cervical Plexus—Serves the Head, Neck and
Shoulders
The cervical plexus is formed by the ventral rami
of the upper four cervical nerves and the upper
part of fifth cervical ventral ramus. The network
of rami is located deep within the neck.
12.
13.
14.
15. The cervical plexus is an arrangement of sensory and motor fibers, formed from the ventral rami of spinal nerves C1 to C4.
The cutaneous branches of cervical plexus are:
Lesser occipital nerve innervate the skin of the occipital region
Great auricular nerve innervate outer ear & ear canal
Transverse cervical nerve innervate the anterior aspect of the neck
Supraclavicular nerves innervate the shoulder and the upper thorax
16. Lesser occipital (C2):
Along the posterior border of SCM
Supplies skin & subcutaneous tissue at the insertion of
the muscle
17. Great auricular (C2,3):
Ascends in the direction of the auricle
Supplies the auricle (except the upper ½ of lateral surface) &
skin over the angle of mandible
18. Anterior cervical cutaneous[Transverse cervical
nerve ] (C2,3)
Crosses SCM horizontally forward
Supplies skin & subcutaneous tissues of the cylinder of the
neck, so it transmits sensory information from the skin of
the anterior and lateral aspects of the neck.
19. Supraclavicular nerves
The supraclavicular nerves are three groups of nerves that
arise from the third and the fourth cervical nerves, via the
cervical plexus, to provide sensory innervation of the skin
above and below the clavicle.
Once They pass through the platysma, the multiple fibers
become arranged into three groups termed medial,
intermediate, and lateral according to their position.
As well as the skin, the medial supraclavicular nerve
innervates part of the sternoclavicular joint.
The three groups and their innervation are:
1. Medial; skin over manubrium sterni
2. Intermediate; skin over the pectoral region down to the
sternal angle
3. Lateral; skin over deltoid as far as the distal 1/2 of muscle
20. Muscular (motor) branches of cervical plexus are:
Ansa cervicalis innervate various hyoid attaching muscles
Phrenic nerve innervate diaphragm & pericardium
Segmental branches that innervate anterior and middle
scalenes
21. Superior root of Ansa cervicalis
Branches of the cervical spinal nerves 1(C1) and 2 (C2) travel in the hypoglossal nerve. These nerves
separate in the carotid triangle to form the superior root of the Ansa cervicalis.
The superior root travels around the occipital artery and then descends on the carotid sheath.
Branches of the superior root then travel to the superior belly of the omohyoid muscle and the upper
parts of the sternothyroid and sternohyoid muscles. It is then joined by the inferior root, creating a
loop.
22. Inferior root of Ansa cervicalis
The inferior root of the Ansa cervicalis (also known as the descendens cervicalis) is formed by
fibers from the cervical spinal nerves C2 and C3.
The inferior root of the Ansa cervicalis then branches off to the inferior belly of the omohyoid
muscle, and the lower parts of the sternothyroid and sternohyoid muscles.
23. Phrenic nerve
The phrenic nerve arises from the ventral primary rami of spinal nerves of the cervical plexus (C3-C5). It
supplies the skeletal muscles of the respiratory diaphragm and provides cutaneous innervation to the
diaphragmatic pleura. A few fibers are distributed to the pericardium as well as the surrounding
mediastinal and costal pleurae.
24. Greater occipital nerve
The greater occipital nerve is a branch of the
posterior ramus of the 2nd cervical nerve.
The 1st cervical nerve has no cutaneous branch.
The skin of the front and sides of the neck is
supplied by anterior rami of cervical nerves 2 to 4
through branches of the cervical plexus. The
branches emerge from beneath the posterior border
of the sternocleidomastoid muscle.
The greater occipital nerve is the medial branch of
the dorsal primary ramus of the second cervical
nerve. It supplies the muscles of the posterior neck,
the semispinalis capitis muscle, the multifidus
cervicis muscle and the skin on the posterior scalp. It
also provides meningeal branches to the posterior
cranial fossa and pain and proprioceptive branches
to the first cervical nerve for the suboccipital
muscles.
25. Suboccipital nerve
The suboccipital nerve is the dorsal division of the first cervical spinal nerve. It innervates the
rectus capitis posterior major, obliquus capitis superior , and oblique capitis inferior, which
together form the boundaries of the suboccipital triangle, as well as the rectus capitis posterior
minor.
It is so named due to its leaving the spinal cord between the occipital bone of the skull and the
first cervical vertebra.
26.
27. Notes :
The cervical plexus is different from the brachial plexus that it is do not have roots or cords .
The cervical plexus is not regular as the brachial plexus.
The accessory nerve supplies the sternocleidomastoid and trapezius muscles.
The hypoglossal nerve supplies the intrinsic and extrinsic muscles of the tongue, except the
palatoglossus muscles.
C1 has four branches in the neck are:
1. Meningeal branch
2. Superior ramus of Ansa cervicalis
3. Nerve to thyrohyoid
4. Nerve to geniohyoid
These nerves distributed by the hypoglossal nerve
