1. Exercise 15: Spinal Cord and Spinal Nerves

2. 1. Spinal Cord Extends from the foramen magnum of the skull to the
first or second lumbar vertebra
(L1& L2)
31 pairs of spinal nerves arise from the spinal cord
Cauda equina is a collection of spinal nerves at the inferior end
The cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina

3. 2. Spinal Cord Anatomy
Figure 7.21

4. 2. Another spinal cord picture
Dorsal ramus
of spinal nerve
Ventral ramus of spinal nerve

5. The Spinal Nerves-
immediately after being formed the spinal nerves split into dorsal and ventral rami.
Figure 7.25b

6. 3. Gross Anatomy of Spinal Cord
Thicker at the neck and end of the cord (cervical and lumbar enlargements)
Reason: large group of nerves leave the cord to serve the arms and legs .

7. Spinal Cord Anatomy Meninges cover the spinal cord
Spinal nerves leave at the level of each vertebrae
Dorsal root
Associated with the dorsal root ganglia—collections of cell bodies outside the central nervous system
Ventral root
Contains axons

8. Spinal Cord Anatomy Internal gray matter is mostly cell bodies
Dorsal (posterior) horns
Anterior (ventral) horns
Gray matter surrounds the central canal
Central canal is filled with cerebrospinal fluid
Exterior white mater—conduction tracts
Dorsal, lateral, ventral columns

9. Spinal Cord Anatomy Up close view of cervical enlargement
Figure 7.20 (1 of 2)

10. Spinal Cord Anatomy Up close view of lumbar enlargement
Figure 7.20 (2 of 2)

11. Spinal Nerves and Nerve Plexuses

12. 4. Spinal Nerves
31 nerves connecting the spinal cord and various body regions.
8 paired cervical nerves
12 paired thoracic nerves
5 paired lumbar nerves
5 paired sacral nerves
1 pair of coccygeal nerves

13. Spinal Nerves
There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs
Formed by the combination of the ventral and dorsal roots of the spinal cord
Named for the region from which they arise
Figure 7.25a

14. 5.Anatomy of Spinal Nerves
Spinal nerves divide soon after leaving the spinal cord
Dorsal rami—serve the skin and muscles of the posterior trunk
Ventral rami—form a complex of networks (plexus) for the anterior

15. 5.& 7. Plexuses Sacral Plexus
Plexus- ventral rami C1-T1 and T12-S4 branch extensively and join one another lateral to the vertebral column forming complicated nerve plexuses that serve motor and sensory needs
***Except for T2 to T12,
Ventral Rami from C1- T1 form Cervical & Brachial plexuses
Ventral rami from L1-S4 form Lumbar and Sacral plexuses
6. Serve motor and sensory needs of the limbs
Ventral rami from T2-T12 do not form plexuses..they serve the muscles of intercostal spaces and the skin and muscles of the anterior and lateral trunk
Sacral Plexus

16. This diagram shows the nerves leaving from the vertebral canal
Note: There are 7 cervical vertebrae but 8 pairs of cervical nerves.
C1 – C7 emerge above the vertebrae for which they are named.
C8 emerges between C7 and T1.
The remaining spinal nerve pairs emerge below the same numbered vertebra.

17. PNS: The Spinal Nerves
Look how the dorsal and ventral roots merge to form the spinal nerve then split again to form the ventral and dorsal rami
Figure 7.25b

18. Table 7.2 (1 of 2)

19. Table 7.2 (2 of 2)

20. 6. Spinal Nerves
Each connects to the spinal cord by 2 roots – dorsal and ventral.
Ventral roots are motor while dorsal roots are sensory.

21. Dorsal root – sensory function Ventral root – motor function6.
Dorsal root – sensory function
Ventral root – motor function
Dorsal Root
Figure 7.22
Ventral root

22. Dorsal root – sensory function
Ventral root – motor function

23. Cervical Plexus-
Important nerve= phrenic nerve which serves the diaphragm and muscles of shoulder and neck

24. Major Peripheral Nerves of the Upper Limbs
The brachial plexus branches into 5 major peripheral nerves of the upper limbs :
Axillary
Radial
Median
Musculocutaneous
Ulnar
Figure 7.26a

25. Major Peripheral Nerves of the Lower Limbs
The nerves from the lumbar plexus serve the abdominal region and the anteromedial thigh.
Important nerves:
Femoral
Obturator
Figure 7.26b

26. Major Peripheral Nerves Lower Limbs
Sacral plexus – supply buttock, posterior thigh, and almost all leg and foot.
Important Nerves:
The sciatic nerve – largest nerve in the body; divides into common fibular nerve and tibial nerve.
Superior and Inferior Gluteal
Figure 7.26c

27. 8.

28. Table 7.2 (2 of 2)

29. Extra/ More information on the brain

30. Spinal Cord
Functions to transmit messages to and from the brain (white matter) and to serve as a reflex center (gray matter).
extends about 17”
diameter of your thumb
Thicker at the neck and end of the cord (cervical and lumbar enlargements) b/c of the large group of nerves connecting these regions of the cord w/ the arms and legs.

31. Spinal Cord
The cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina.

32. Spinal Cord Notice the gross features of the spinal cord on the right.
31 pairs of spinal nerves attach to the cord by paired roots and exit from the vertebral canal via the intervertebral foramina.

33. Cross Sectional Anatomy of the Spinal Cord
Flattened from front to back.
Anterior median fissure and posterior median sulcus partially divide it into left and right halves.
Gray matter is in the core of the cord and surrounded by white matter.

34. Resembles a butterfly.
2 lateral gray masses connected by the gray
commissure.
Posterior projections are the posterior or dorsal horns.
Anterior projections are the anterior or ventral horns.
In the thoracic and lumbar cord, there also exist lateral horns.

35. Gray Matter Posterior horns contain interneurons.
Anterior horns contain some
interneurons as well as the cell
bodies of motor neurons.
These cell bodies project their axons via the ventral roots of the spinal cord to the skeletal muscles.
The amount of ventral gray matter at a given level of the spinal cord is proportional to the amount of skeletal muscle innervated.

36. Gray Matter
Lateral horn neurons are sympathetic motor neurons serving visceral organs.
Their axons also exit via the ventral root.
Afferent sensory fibers carrying info from peripheral receptors form the dorsal roots of the spinal cord. The somata of these sensory fibers are found in an enlargement known as a dorsal root ganglion.
The dorsal and ventral roots fuse to form spinal nerves.

37. White Matter Myelinated nerve fibers.
Allows for communication btwn the brain and spinal cord or btwn different regions of the spinal cord.
White matter on each side of the cord is divided into columns or funiculi.
Typically, they are ascending or descending.
What does that mean?

38. Spinal Nerves
The 2 roots join to form a spinal nerve prior to exiting the vertebral column.
Roots are short and horizontal in the cervical and thoracic regions while they are longer and more horizontal in the sacral and lumbar regions.
Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a meningeal branch that reenters and innervates the meninges and associated blood vessels.

39. Each ramus is mixed.
Joined to the base of the ventral rami of spinal nerves in the thoracic region are the rami communicantes.
Dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs.