1. Neuro-anatomy Nerve PlexusesBy
Khaled Na3im

2. The C.N.S = Brain + Spinal Cord
C.N.S tissue is enclosed within the skull and vertebral column
The C.N.S.is protected by bones, meninges, and cerebrospinal fluid (CSF)
Epidural space is the space between the bones and the Dural sheath (dura mater)

3. THE MENINGES
The meninges are a set of 3 connective tissue layers that surround the brain and spinal cord.
The dura mater – toughest & outermost
The arachnoid mater – middle layer containing most major blood vessels and cerebrospinal fluid.
The pia mater – inner most layer with fine blood vessels.

4. Meninges

5. Spinal Cord
Cervical and lumbosacral enlargements – sites where nerves serving the limbs emerge
Conus medullaris – terminal portion of the spinal cord
Cauda equina – collection of nerve roots at the inferior end of the vertebral canal
Spinal nerves – 31 pairs

6. Spinal Gray Matter
Gray matter consists of neurons, unmyelinated processes, and neuroglia
Gray commissure – connects masses of gray matter; encloses central canal
Posterior (dorsal) horns – interneurons (sensory)
Anterior (ventral) horns – some interneurons but mostly somatic motor neurons
Lateral horns – contain autonomic nerve fibers

7. Gray Matter and Spinal Roots

8. Cross Section of Spinal Cord

9. Reflex Arc
Basic functional unit of nervous system and simplest portion capable of receiving a stimulus and producing a response
Automatic response to stimulus, occurs without conscious thought.
Components
Action potentials produced in sensory receptors transmitted to
Sensory neuron. To-
Interneurons. To-
Motor neuron. To-
Effector organ which responds with a reflex

10. Variety of Reflexes
Some integrated within spinal cord; some within brain
Some involve excitatory neurons yielding a response; some involve inhibitory neurons that prevent an action
Higher brain centers can influence, suppress, or exaggerate reflex responses

11. Spinal Nerve Organization
Dorsal half – sensory roots and ganglia
Ventral half – motor roots
Dorsal & ventral roots fuse laterally to form spinal nerves

12. Cross-Sectional Anatomy of Spinal Cord

13. Spinal Nerves 8 cervical (C1-C8) 12 thoracic (T1-T12) 5 Lumbar (L1-L5)
31 pairs of mixed nerves supply all parts of body except head
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 (C0)

14. Spinal Nerve
Each spinal nerve connects to the spinal cord via two medial roots
Each root forms a series of rootlets that attach to the spinal cord
Ventral roots arise from the ventral horn and contain motor (efferent) fibers
Dorsal roots arise from sensory neurons in the dorsal root ganglion and contain sensory (afferent) fibers

15. Spinal Nerves: Roots

16. Nerve Plexuses
All ventral rami except T2-T12 form interlacing networks called plexuses
Plexuses are found in the:
cervical,
brachial,
lumbar,
and sacral regions
Each resulting branch of a plexus contains fibers from several spinal nerves
Each muscle receives a nerve supply from more than one spinal nerve
Damage to one spinal segment cannot completely paralyze a muscle

17. Cervical Plexus The cervical plexus is formed by ventral rami of C1-C4
Most branches are cutaneous nerves of the neck, ear, back of head, and shoulders
The most important nerve of this plexus is the phrenic nerve - the major motor and sensory nerve of the diaphragm

18. Cervical Plexus
Figure 13.8

19. Brachial Plexus
Formed by ventral rami of C5-C8 and T1 (C4 and T2 may also contribute to this plexus)
It gives rise to the nerves that innervate the upper limb ( except trapezes is supplied by accessory nerve and skin of tip of shoulder )
The major ones :
Axillary n Nerve to serratus ant.
Radial n Nerve to L.D.
Musculocutaneous n.
Ulnar n Median n.

20. Brachial Plexus C4 from cervical plus C5-T1 Five ventral rami form
three trunks that separate into six divisions then form
three cords that give rise to:
Branches/nerves
Axillary
Radial
Musculocutaneous
Ulnar
Median
Smaller nerves, too.

21. Brachial Plexus: Distribution of Nerves

22. Lumbosacral Plexus (Lumbar and Sacral Plexuses)
Arises from L1-L4 & L4-S4 and innervates the thigh, abdominal wall, psoas muscle, the buttock, lower limb, pelvic structures, and the perineum
The major nerves are the
Femoral (Lumbar)
Obturator (Lumbar)
Sciatic (Sacral)
Tibial
Common fibular (peroneal)

25. Questions Which of the following is NOT a nerve plexus?
The thoracic rami 
The lumbosacral plexus 
The cervical plexus  
The brachial plexus 

26. Questions
Which of the following nerves does NOT arise from the brachial plexus? 
The musculocutaneous nerve 
The radial nerve 
The axillary nerve 
The ulnar nerve 
The phrenic nerve

27. Questions
The muscle fiber or gland cell that responds to the efferent impulses is known as the  
Effector  
Motor neuron 
Integration center 
Sensory neuron 
Receptor

28. Questions
The basic pattern of the CNS in the spinal cord is a central cavity surrounded by a gray matter core and a white matter layer lying outside of that.   True  False

29. Questions
Although the pairs of spinal nerves correspond to the number of vertebrae in the each area, there are eight pairs of cervical cranial nerves, but only seven cervical vertebrae.   True  False

30. Questions
Each muscle in a limb receives its nerve supply from one spinal nerve.   True  False

31. Questions
A sensory nerve transmits afferent impulses to the CNS.   True  False