1. The Peripheral Nervous
Chapter 13
The Peripheral Nervous
System (PNS)
Part B

2. Thirty-one pairs of mixed nerves Arise from the spinal cord
Spinal Nerves
Thirty-one pairs of mixed nerves
Arise from the spinal cord
Supply all parts of the body except the head
Are named according to their point of issue
8 cervical (C1-C8)
12 thoracic (T1-T12)
5 lumbar (L1-L5)
5 sacral (S1-S5)
1 coccygeal (Co1)

3. Spinal Nerves
Figure 13.6

4. Each nerve connects to the cord via two roots
Spinal Nerves: Roots
Each nerve connects to the cord via two roots
Each root forms rootlets that attach it to the cord
The two roots include the ventral & the dorsal roots
Ventral roots:
Contain motor (efferent) fibers
Arise from the anterior horn (spinal cord grey matter)
Dorsal roots:
Contain sensory (afferent) fibers
Arise from sensory neurons (in dorsal root ganglion)

5. Spinal Nerves: Roots
Figure 13.7a

6. The spinal nerves result from the union of the dorsal & ventral roots
Spinal Nerves: Rami
The spinal nerves result from the union of the dorsal & ventral roots
They are short and branch into three or four mixed rami
These rami include:
Small dorsal ramus
Larger ventral ramus
Tiny meningeal branch
Rami communicantes

7. The tiny meningeal branch reenters the canal to innervate:
Spinal Nerves: Rami
The tiny meningeal branch reenters the canal to innervate:
The meninges
The blood vessels within the meninges
The rami communicantes:
Located at the base of the ventral rami
Found in the thoracic region
Contain autonomic (visceral) nerve fibers

9. Only & all ventral rami except T2-T12 form:
Nerve Plexuses
Only & all ventral rami except T2-T12 form:
Interlacing nerve networks called plexuses
Plexuses are found in the following regions:
Cervical
Brachial
Lumbar
Sacral
Each resulting plexus contains:
Fibers from several spinal nerves

10. Fibers travel to the periphery via:
Nerve Plexuses
Fibers travel to the periphery via:
Several different routes
Each muscle receives:
A nerve supply from more than one spinal nerve
Therefore, damage to one spinal segment:
Cannot completely paralyze a muscle

11. Spinal Nerve Innervation:
The back is innervated by:
Dorsal rami (via several branches)
The thorax is innervated by:
Ventral rami T1-T12 (as intercostal nerves)
Intercostal nerves supply:
Muscles of the ribs
Anterolateral thorax
Abdominal wall

12. The most important nerve of this plexus is: The phrenic nerve:
Cervical Plexus
The cervical plexus is formed by:
Ventral rami of spinal nerves C1-C4
Most branches are cutaneous nerves of:
The neck
The head
The shoulders
The most important nerve of this plexus is:
The phrenic nerve
The phrenic nerve:
The major motor & sensory nerve of the diaphragm

13. Cervical Plexus

14. Brachial Plexus Formed by: It gives rise to:
Spinal nerves C5-C8 and T1
C4 and T2 may also contribute to this plexus
It gives rise to:
Nerves that innervate the upper limb

15. Brachial Plexus Comprises four major groups of branches:
Rami (misleadingly called roots):
Five ventral rami (C5-T1)
They unite to form trunks
Trunks:
Include:
Upper trunk
Middle trunk
Lower trunk
Each trunk divides immediately into two divisions

16. Brachial Plexus: Nerves
Figure 13.9b

17. Brachial Plexus
Figure 13.9a

18. Brachial Plexus Divisions: Include: Anterior division
Posterior division
Serve the front and back of the limb, respectively
Give rise (in axilla) to three large fiber bundles called cords
Cords:
Lateral
Medial
Posterior

19. Brachial Plexus: Upper limb Nerves
The brachial plexus ends in the axilla
Its three cords give rise to the main nerves of the upper limb
The five especially important of these nerves are:
Axillary :– innervates:
Deltoid
Teres minor
Musculocutaneous:– Sends fibers to:
Biceps brachii
Brachialis
Coracobrachialis

20. Brachial Plexus: Upper limb Nerves
Median :– branches to:
Flexor muscles of anterior arm
Ex. Flexor carpi radialis
Ulnar :– supplies:
Ex. Flexor carpi ulnaris
Radial :– innervates:
Extensor (posterior) muscles of arm
Ex. Extensor carpi radialis

21. Brachial Plexus: Distribution of Nerves
Figure 13.9c

22. Brachial Plexus: Nerves
Figure 13.9b

23. Lumbar Plexus Arises from L1-L4 Innervates: The major nerves are:
Thigh (anterior & medial)
Abdominal wall
Psoas muscle
The major nerves are:
The femoral
The obturator

24. Lumbar Plexus
Figure 13.10

25. Arises from spinal nerves L4-S4 Serves:
Sacral Plexus
Arises from spinal nerves L4-S4
Serves:
Buttock
Lower limb
Pelvic structures
The perineum

26. The sciatic is actually composed of two nerves:
Sacral Plexus
The major nerve is:
The sciatic
The longest & thickest nerve of the body
The sciatic is actually composed of two nerves:
The tibial nerve
The common fibular (peroneal) nerve

27. Sacral Plexus
Figure 13.11

28. Innervation of the Skin (Dermatomes)
A dermatome is:
The area of skin innervated by:
The cutaneous branches of a single spinal nerve
All spinal nerves participate in dermatomes except:
The 1st cerviacal spinal nerve (C1)

29. Dermatomes
Figure 13.12

30. Reflexes Reflexes: A reflex is: Reflexes may be:
Are a category of control systems in the body
A reflex is:
A rapid, predictable motor response to a stimulus
Reflexes may be:
Inborn (intrinsic):
Ex. Response to splashing hot water on one’s arm
Learned (acquired):
Ex. Sequences of reaction during driving

31. Reflexes Awareness of reflex responses: Reflexes involve only:
Acknowledged:
Ex. Dropping a pot of a boiling water
Passed unnoticed:
Ex. Visceral reflexes controlled by brain stem & spinal cord
Reflexes involve only:
Peripheral nerves
The spinal cord
Higher brain centers as well

32. Reflex Arc Highly specific neural paths over which reflexes occur
Reflex arc components:
Receptor
Sensory neuron
Integration center
Motor neuron:
Effector
Classification:
Somatic reflexes: activates skeletal muscles
Autonomic (visceral) reflexe: activates visceral effectors

33. Reflex Arc
Figure 13.14