Lecture Human anatomy and physiology - Chapter 13: The peripheral nervous system and reflex activity (part c)

PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College

CHAPTER

13

The Peripheral
Nervous
System and
Reflex Activity:
Part C
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Spinal Nerves
• 31 pairs of mixed nerves named according to
their point of issue from the spinal cord
• 8 cervical (C1–C8)
• 12 thoracic (T1–T12)
• 5 Lumbar (L1–L5)
• 5 Sacral (S1–S5)
• 1 Coccygeal (C0)
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Cervical plexus
Brachial plexus
Cervical

enlargement
Intercostal
nerves

Cervical
nerves
C1 – C8

Thoracic
nerves
T1 – T12

Lumbar
enlargement
Lumbar plexus

Sacral plexus
Cauda equina
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Lumbar
nerves
L1 – L 5
Sacral nerves
S1 – S 5
Coccygeal nerve Co1
Figure 13.6


Spinal Nerves: Roots

• Each spinal nerve connects to the spinal cord
via two roots
• Ventral roots
• Contain motor (efferent) fibers from the ventral
horn motor neurons
ã Fibers innervate skeletal muscles)

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Spinal Nerves: Roots
• Dorsal roots
• Contain sensory (afferent) fibers from sensory
neurons in the dorsal root ganglia
• Conduct impulses from peripheral receptors

• Dorsal and ventral roots unite to form spinal
nerves, which then emerge from the vertebral
column via the intervertebral foramina

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Dorsal root
ganglion
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Spinal nerve

Gray matter
White matter
Ventral root
Dorsal root

Dorsal and
ventral rootlets
of spinal nerve

Rami communicantes
Sympathetic trunk
ganglion

Anterior view showing spinal cord, associated nerves, and vertebrae.
The dorsal and ventral roots arise medially as rootlets and join
laterally to form the spinal nerve.
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Figure 13.7 (a)


Spinal Nerves: Rami
• Each spinal nerve branches into mixed rami
• Dorsal ramus
• Larger ventral ramus
• Meningeal branch
• Rami communicantes (autonomic pathways)
join to the ventral rami in the thoracic region

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Spinal Nerves: Rami
• All ventral rami except T2–T12 form interlacing
nerve networks called plexuses (cervical,
brachial, lumbar, and sacral)
• The back is innervated by dorsal rami via
several branches
• Ventral rami of T2–T12 as intercostal nerves
supply muscles of the ribs, anterolateral
thorax, and abdominal wall

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Dorsal ramus
Ventral ramus
Spinal nerve
Rami communicantes
Sympathetic trunk
ganglion

Intercostal nerve
Dorsal root
ganglion
Dorsal root
Ventral root
Branches of intercostal
nerve

• Lateral cutaneous
• Anterior cutaneous
Sternum

(b) Cross section of thorax showing the main roots and
branches of a spinal nerve.
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Figure 13.7 (b)


Cervical Plexus
• Formed by ventral rami of C1–C4
• Innervates skin and muscles of the neck, ear,
back of head, and shoulders
• Phrenic nerve
• Major motor and sensory nerve of the
diaphragm (receives fibers from C3–C5)

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Ventral rami

Segmental
branches
Hypoglossal
nerve (XII)
Lesser occipital
nerve

Greater auricular
nerve
Transverse
cervical nerve
Ansa cervicalis
Accessory nerve (XI)
Phrenic nerve

Ventral
rami:
C1
C2
C3
C4
C5

Supraclavicular
nerves
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Figure 13.8


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Table 13.3


Brachial Plexus
• Formed by ventral rami of C5–C8 and T1 (and often C4

and T2)
• It gives rise to the nerves that innervate the upper
limb
• Major branches of this plexus:
• Roots—five ventral rami (C5–T1)
• Trunks—upper, middle, and lower
• Divisions—anterior and posterior
• Cords—lateral, medial, and posterior
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Posterior
divisions

Cords

Roots (ventral rami):
C4
C5

Dorsal scapular
Nerve to
subclavius
Suprascapular

C6
C7

Lateral

C8

Posterior

T1

Medial
Axillary
Musculocutaneous
Radial
Median
Ulnar

Upper
Middle

Trunks

Lower
Long thoracic
Medial pectoral
Lateral pectoral
Upper subscapular
Lower subscapular
Thoracodorsal
Medial cutaneous
nerves of the arm
and forearm

(a) Roots (rami C5 – T1), trunks, divisions, and cords

Anterior
divisions
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Posterior
divisions

Trunks

Roots
Figure 13.9 (a)


Anterior
divisions

Posterior
divisions

Major terminal
branches
(peripheral nerves)
Musculocutaneous
Median
Ulnar
Radial
Axillary

Trunks

Cords

Roots

Divisions
Anterior

Lateral

Posterior

Medial

Anterior
Posterior

Posterior

Anterior
Posterior

Trunks

Upper

Roots
(ventral
rami)
C5

C6

Middle

C7
C8

Lower

T1

(d) Flowchart summarizing relationships within the
brachial plexus

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Figure 13.9 (d)


Brachial Plexus: Nerves
• Axillary—innervates the deltoid, teres minor, and skin
and joint capsule of the shoulder
• Musculocutaneous—innervates the biceps brachii
and brachialis and skin of lateral forearm
• Median—innervates the skin, most flexors and
pronators in the forearm, and some intrinsic muscles
of the hand
• Ulnar—supplies the flexor carpi ulnaris, part of the
flexor digitorum profundus, most intrinsic muscles of
the hand, and skin of medial aspect of hand

• Radial—innervates essentially all extensor muscles,
supinators, and posterior skin of limb
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Axillary
nerve

Anterior
divisions

Posterior
divisions

Trunks

Roots

Humerus
Radial nerve
Musculocutaneous nerve
Ulna
Radius
Ulnar nerve
Median nerve
Radial nerve (superficial branch)
Dorsal branch of ulnar nerve
Superficial branch of ulnar nerve
Digital branch of ulnar nerve
Muscular branch

Median nerve
Digital branch
(c) The major nerves of the upper limb
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Figure 13.9 (c)


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Table 13.4


Lumbar Plexus
• Arises from L1–L4
• Innervates the thigh, abdominal wall, and
psoas muscle
• Femoral nerve—innervates quadriceps and
skin of anterior thigh and medial surface of leg
• Obturator nerve—passes through obturator
foramen to innervate adductor muscles

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Ventral rami

Iliohypogastric
Ilioinguinal

Ventral
rami:
L1
L2

Genitofemoral

L3

Lateral femoral
cutaneous
Obturator

L4

Femoral
Lumbosacral
trunk

L5

(a) Ventral rami and major branches
of the lumbar plexus

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Iliohypogastric
Ilioinguinal
Femoral
Lateral femoral

cutaneous
Obturator
Anterior femoral
cutaneous
Saphenous

(b) Distribution of the major nerves from
the lumbar plexus to the lower limb
Figure 13.10


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Table 13.5


Sacral Plexus
• Arises from L4–S4
• Serves the buttock, lower limb, pelvic structures, and
perineum
• Sciatic nerve
• Longest and thickest nerve of the body
• Innervates the hamstring muscles, adductor magnus,
and most muscles in the leg and foot
• Composed of two nerves: tibial and common fibular

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Ventral rami

Ventral rami:
L4

Superior
gluteal
Lumbosacral
trunk
Inferior
gluteal
Common
fibular
Tibial
Posterior
femoral
cutaneous
Pudendal
Sciatic

L5
S1
S2
S3
S4
S5
Co1

Ventral rami and major branches
of the sacral plexus
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Figure 13.11 (a)


Superior gluteal
Inferior gluteal
Pudendal
Sciatic
Posterior femoral
cutaneous
Common fibular
Tibial
Sural (cut)
Deep fibular
Superficial fibular
Plantar branches
(b) Distribution of the major nerves from
the sacral plexus to the lower limb
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Figure 13.11 (b)


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Table 13.6