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.b. the brachial plexus
The brachial plexus is formed by the ventral
rami of C5–C8 and the T1 spinal nerves, and
lower and upper halves of the C4 and T2
spinal nerves. The plexus extends toward the
armpit (axilla).
The Brachial Plexus is located on the right
and left side of your neck, between the neck
and shoulder area. It is a group of nerves
that run from the spinal cord through the
arm to the wrist and hand.
The brachial nerve plexus supplies nerves to
the arms, chest, hands, and shoulders. It runs
from the spinal cord through the chest and
shoulders before reaching the armpit; from
there, it descends down the arm and into the
hand. The brachial nerve is comprised of a
series of branches, cords, divisions, roots,
and trunks.
12.
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18.
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27.
28. Roots:The ventral rami of spinal nerves C5 to T1 are referred to as the "roots" of the plexus. The
typical spinal nerve root results from the confluence of the ventral nerve rootlets originating in the
anterior horn cells of the spinal cord and the dorsal nerve rootlets that join the spinal ganglion in the
region of the intervertebral foramen.The roots emerge from the transverse processes of the cervical
vertebrae immediately posterior to the vertebral artery, which travels in a cephalocaudad direction
through the transverse foramina. Each transverse process consists of a posterior and anterior tubercle,
which meet laterally to form a costotransverse bar. The transverse foramen lies medial to the
costotransverse bar and between the posterior and anterior tubercles. The spinal nerves that form the
brachial plexus run in an inferior and anterior direction within the sulci formed by these structures.
29. Divisions:Each trunk splits into an anterior division and a posterior division.
These separate the innervation of the ventral and dorsal aspect of the upper limb.
The anterior divisions usually supply flexor muscles. The posterior divisions usually
supply extensor muscles.
30. Cords:The cords are referred to as the lateral, posterior, and medial cord, according to their
relationship with the axillary artery, as seen in the image below. The cords pass over the first rib
close to the dome of the lung and continue under the clavicle immediately posterior to the
subclavian artery.Diagram showing basic relationships of the brachial plexus to the pectoralis minor
muscle and the axillary artery, which is a continuation of the subclavian artery.View Media
GalleryThe anterior divisions of the upper and middle trunks unite to form the lateral cord, which is
the origin of the lateral pectoral nerve (C5, C6, C7).The anterior division of the lower trunk forms the
medial cord, which gives off the medial pectoral nerve (C8, T1), the medial brachial cutaneous nerve
(T1), and the medial antebrachial cutaneous nerve (C8, T1). The posterior divisions from each of the
3 trunks unite to form the posterior cord.The upper and lower subscapular nerves (C7, C8 and C5,
C6, respectively) leave the posterior cord and descend behind the axillary artery to supply the
subscapularis and teres major muscles. The thoracodorsal nerve to the latissimus dorsi (also known
as the middle subscapular nerve, C6, C7, C8) also arises from the posterior cord, as seen in the
image below.
31. Trunks:Shortly after emerging from the intervertebral foramina, the 5 roots
(C5-T1) unite to form 3 trunks. The trunks of the brachial plexus pass between the
anterior and middle scalene muscles.The ventral rami of C5 and C6 unite to form
the upper trunk. The suprascapular nerve and the nerve to the subclavius arise
from the upper trunk. The suprascapular nerve contributes sensory fibers to the
shoulder joint and provides motor innervation to the supraspinatus and
infraspinatus muscles.The ventral ramus of C7 continues as the middle trunk. The
ventral rami of C8 and T1 unite to form the lower trunk.
32. Branches :
1- Musculocutaneous nerve
branch
The musculocutaneous nerve is a mixed
nerve containing sensory and motor axons.
The musculocutaneous nerve is derived from
the lateral cord. The musculocutaneous nerve
leaves the brachial plexus sheath high in the
axilla at the level of the lower border of the
teres major muscle and passes into the
coracobrachialis muscle. It innervates the
muscles in the flexor compartment of the
arm and carries sensation from the lateral
(radial) side of the forearm. (See the image
below.)
33. 2-Ulnar nerve branch
The ulnar nerve is derived from the
medial cord. Motor innervation is
mainly to intrinsic muscles of the hand
(as seen in the image below). Sensory
innervation is to the medial (ulnar) 1.5
digits (little finger, half of the ring
finger)
2
34. 3-Median nerve branch
The median nerve is derived from the lateral
and medial cords. Motor innervation is to most
flexor muscles in the forearm and intrinsic
muscles of the thumb (thenar muscles), as seen
in the image below. Sensory innervation is to
the lateral (radial) 3.5 digits (thumb, index and
middle fingers, half of the ring finger).
3
35. 4-Axillary nerve branch
The axillary nerve is derived from the posterior
cord. The axillary nerve leaves the brachial
plexus at the lower border of the subscapularis
muscle and continues along the inferior and
posterior surface of the axillary artery as the
radial nerve. The axillary nerve serves as motor
innervation to the deltoid and teres minor
muscles, as seen in the image below. These act
at the glenohumeral joint. Sensory innervation
is from the skin just below the point of the
shoulder. The axillary nerve continues as the
superior lateral brachial cutaneous nerve of the
arm
4
36. 5-Radial nerve branch
The radial nerve is also derived from the
posterior cord. The radial nerve
continues along the posterior and
inferior surface of the axillary artery and
innervates the extensor muscles of the
elbow, wrist, and fingers, as seen in the
image above. Sensory innervation is from
the skin on the dorsum of the hand on
the radial side.
5
37. Additional branches In addition to the 5 terminal branches described above, numerous
preterminal or collateral branches leave the plexus at various points along its length.
1- Dorsal scapular nerve : The dorsal scapular nerve is derived from the C5 root just after its exit from the
intervertebral foramen. It serves as the motor nerve to the rhomboids major and minor musclesLong thoracic
nerve
2- The long thoracic nerve: is derived from C5, C6, and C7 roots immediately after their emergence
from the intervertebral foramina. The long thoracic nerve crosses the first rib and then descends through the
axilla behind the major branches of the plexus. It innervates the serratus anterior muscle.
3- Phrenic nerve: the phrenic nerve arises from C3, C4, and C5 root levels, although chiefly from the C4
nerve root. It crosses the anterior scalene from lateral to medial and extends into the thorax between the
subclavian vein and artery.
4- Subclavius muscle nerve : The nerve to the subclavius muscle is a small filament that arises from
the upper trunk. It descends to the subclavius muscle in front of the subclavian artery and the lower trunk of the
plexus.
38. 5- Suprascapular nerve :The suprascapular nerve arises from the upper trunk formed by
the union of the fifth and sixth cervical nerves. It innervates the supraspinatus muscles and
infraspinatus muscles. It runs laterally beneath the trapezius and the omohyoideus and enters the
supraspinatus fossa through the suprascapular notch, below the superior transverse scapular
ligament; it then passes beneath the supraspinatus and curves around the lateral border of the
spine of the scapula to the infraspinatus fossa.
6- Lateral pectoral nerve: The lateral pectoral nerve arises from the lateral cord of
the brachial plexus, from the fifth, sixth, and seventh cervical nerves. It passes across the axillary
artery and vein, pierces the coracoclavicular fascia, and is distributed to the deep surface of the
pectoralis major. It sends a filament to join the medial anterior thoracic and forms with it a loop in
front of the first part of the axillary artery. This nerve innervates the clavicular head of the pectoralis
major muscle.
7- Medial pectoral nerve: The medial pectoral nerve arises from the medial cord
from the eighth cervical and first thoracic nerve. It passes behind the first part of the axillary artery,
curves forward between the axillary artery and vein, and unites in front of the artery with a filament
from the lateral nerve. It then enters the deep surface of the pectoralis minor, where it divides into a
number of branches, which supply the muscle. Several branches of the medial pectoral nerve pierce
the muscle and end in the pectoralis major, which supply the muscle.The medial and lateral pectoral
nerve often join together to act as a single nerve innervating the pectoralis major and minor
muscles
39. 8- Medial brachial cutaneous nerve: The medial brachial cutaneous nerve is the
smallest branch of the brachial plexus; arising from the medial cord, it receives its fibers from the
eighth cervical and first thoracic nerves. It passes through the axilla, at first lying behind and then
medial to the axillary vein, and communicates with the intercostobrachial nerve . The medial brachial
cutaneous nerve descends along the medial side of the brachial artery to the middle of the arm,
where it pierces the deep fascia, and is distributed to the skin of the back of the lower third of the
arm, extending as far as the elbow, where some filaments are lost in the skin in front of the medial
epicondyle, and others over the olecranon. It communicates with the ulnar branch of the medial
antebrachial cutaneous nerve. The medial brachial cutaneous nerve carries sensation from the lower
medial portion of the arm.
9- Medial antebrachial cutaneous nerve :The medial antebrachial cutaneous
arises from the medial cord of the brachial plexus. It derives its fibers from the eighth cervical and first
thoracic nerves and at its commencement is medial to the axillary artery. It gives off near the axilla a
filament that pierces the fascia and supplies the integument covering the biceps brachii, nearly as far
as the elbow. The nerve then runs down the ulnar side of the arm medial to the brachial artery, pierces
the deep fascia with the basilic vein, about the middle of the arm, and divides into a volar and an
ulnar branch
41. Blood Supply of the Brachial Plexus
The blood supply of the brachial plexus is based largely on the
subclavian (which becomes the axillary) artery and its branches,
and variations exist. Generally, the vessels involved are the
vertebral, the ascending and deep cervical, and the superior
intercostal arteries. The cord and rootlets of the cervical nerves
are supplied by the anterior and posterior spinal branches of the
vertebral artery. The trunks of the plexus are supplied by muscular
branches of the ascending and deep cervical arteries and superior
intercostals , and occasionally by the subclavian itself.
42. Brachial Plexus Block
Brachial Plexus Block Injection of an anesthetic solution into or
immediately surrounding the axillary sheath interrupts nerve impulses
and produces anesthesia of the structures supplied by the branches of
the cords of the plexus. Combined with an occlusive tourniquet
technique to retain the anesthetic agent, this procedure enables
surgeons to operate on the upper limb without using a general
anesthetic. The brachial plexus can be anesthetized using a number of
approaches, such as interscalene, supraclavicular, and axillary.
43. Brachial Plexus Injuries
Injuries to the brachial plexus affect movements and cutaneous sensations in the upper
limb. Disease , stretching, and wounds in the lateral cervical region (posterior triangle of
the neck) or in the axilla may produce brachial plexus injuries .Signs and symptoms
depend on which part of the plexus is involved. Injuries to the brachial plexus result in
loss of muscular movement paralysis) and loss of cutaneous sensation (anesthesia). In
complete paralysis, no movement is detectable. In incomplete paralysis, not all muscles
are paralyzed; therefore, the person can move, but the movements are weak compared
to those on the uninjured side. Injuries to superior parts of the brachial plexus (C5 and
C6) usually result from an excessive increase in the angle between ,the neck and the
shoulder. These injuries can occur in a person who is thrown from a motorcycle or a
horse and lands on the shoulder in a way that widely separates the neck and shoulder
When thrown, the person’s shoulder often hits something (e.g., a tree or the ground)
and stops, but the head and trunk continue to move.
44. Brachial Plexus Injuries
This stretches or ruptures superior parts of the brachial plexus or avulses (tears) the roots
of the plexus from the spinal cord. Injury to the superior trunk is apparent by the
characteristic position of the limb (“waiter’s tip position”) in which the limb hangs by the
side in medial rotation .Upper brachial plexus injuries can also occur in a newborn when
excessive stretching of the neck occurs during delivery As a result of injuries to the
superior parts of the brachial plexus (Erb-Duchenne palsy), paralysis of the muscles of
the shoulder and arm supplied by C5–C6 occurs. The usual clinical appearance is an
upper limb with an adducted shoulder, medially rotated arm, and extended elbow. The
lateral aspect of the upper limb also experiences loss of sensation. Chronic microtrauma
to the superior trunk of the brachial plexus from carrying a heavy backpack can produce
motor and sensory deficits in the distribution of the musculocutaneous and radial nerves.
45. Brachial Plexus Injuries
Injuries to inferior parts of the brachial plexus (Klumpke paralysis)
are much less common. These injuries may occur when the upper
limb is suddenly pulled superiorly—for example, when a person
grasps something to break a fall or when a baby’s limb is pulled
excessively during delivery .These events injure the inferior trunk of
the plexus (C8 and T1) and may avulse the roots of the spinal
nerves from the spinal cord. The short muscles of the hand are
affected and a claw hand results
