1. Spinal Cord – Part I
12b

2. Spinal Cord
CNS tissue is enclosed within the vertebral column from the foramen magnum to L1
Provides two-way communication to and from the brain
Protected by bone, meninges, and CSF
Epidural space – space between the vertebrae and the dural sheath (dura mater) filled with fat and a network of veins

3. Principal Parts Principal Parts 1. 42-45 cm in length; 2.5 cm wide
2. cervical enlargement - C4:T1 supply upper limbs
3. lumbar enlargement - T9:T12 supply lower limbs
4. conus medullaris - tapers off to end at L1-L2
5. filum terminale - pia mater anchors cord to coccyx
6. cauda equina - (horse tail) nerves below L2

4. Spinal Cord
Figure 12.28a

5. Things to NOTE about the Spinal Cord
1. Cord itself ends at L1-L2 vertebrae
2. Lower nerves dangle down in the cauda equina
3. There are 31 pairs of spinal nerves
4. spinal segment - gives rise to one spinal nerve
5. C1-C7 spinal nerves project ABOVE C1-C7 vertebrae
6. C8 spinal nerve projects below C7 vertebra
7. T1-S5 spinal nerves project BELOW T1-S5 vertebrae

6. Grey Matter areas vs. White Matter areas
1. grey matter - nerve cell bodies motor & interneurons
2. white matter - myelinated axons of motor & sensory

7. Cross-Sectional Anatomy of the Spinal Cord
Figure 12.30a

8. Regions in the Grey Matter - H shaped center
1. grey commissure - cross bar of the H
2. central canal - hole in the center
3. anterior (ventral) horns
4. posterior (dorsal) horns
5. lateral (intermediate) horns (T, L, S only)

9. Gray Matter and Spinal Roots
Figure 12.30b

10. Gray Matter: Organization
Dorsal half – sensory roots and ganglia
Ventral half – motor roots
Dorsal and ventral roots fuse laterally to form spinal nerves
Four zones are evident within the gray matter – somatic sensory (SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM)

11. Gray Matter: Organization
Figure 12.31

12. Spinal Nerves
13b

13. Spinal Nerves
Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head
They 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 (C0)

14. Spinal Nerves
Figure 13.6

15. Spinal Nerves: Roots
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 anterior horn and contain motor (efferent) fibers
Dorsal roots arise from sensory neurons in the dorsal root ganglion and contain sensory (afferent) fibers

16. Spinal Nerves: Roots
Figure 13.7a

17. Nerve Plexuses
All ventral rami except T2-T12 form interlacing nerve 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

18. Nerve Plexuses
Fibers travel to the periphery via several different routes
Each muscle receives a nerve supply from more than one spinal nerve
Damage to one spinal segment cannot completely paralyze a muscle

19. Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall
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, and abdominal wall

20. Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall
Figure 13.7b

21. 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

22. Cervical Plexus
Figure 13.8

23. Brachial Plexus
Formed by C5-C8 and T1 (C4 and T2 may also contribute to this plexus in some people)
It gives rise to the nerves that innervate the upper limb

24. Brachial Plexus There are four major branches of this plexus
Roots – five ventral rami (C5-T1)
Trunks – upper, middle, and lower, which form divisions
Divisions – anterior and posterior serve the front and back of the limb
Cords – lateral, medial, and posterior fiber bundles

25. Brachial Plexus
Figure 13.9a

26. Brachial Plexus: Nerves
Axillary – innervates the deltoid and teres minor
Musculocutaneous – sends fibers to the biceps brachii and brachialis
Median – branches to most of the flexor muscles of arm
Ulnar – supplies the flexor carpi ulnaris and part of the flexor digitorum profundus
Radial – innervates essentially all extensor muscles

27. Brachial Plexus: Distribution of Nerves
Figure 13.9c

28. Brachial Plexus: Nerves
Figure 13.9b

29. Lumbar Plexus
Arises from L1-L4 and innervates the thigh, abdominal wall, and related muscles
The major nerves are the femoral and the obturator

30. Lumbar Plexus
Figure 13.10

31. Sacral Plexus
Arises from L4-S4 and serves the buttock, lower limb, pelvic structures, and the related sacral areas
The major nerve is the sciatic, the longest and thickest nerve of the body
The sciatic is actually composed of two nerves: the tibial and the common fibular nerves

32. Sacral Plexus
Figure 13.11

33. Dermatomes
A dermatome is the area of skin innervated by the cutaneous branches of a single spinal nerve
All spinal nerves except C1 participate in dermatomes

34. Dermatomes
Figure 13.12

35. Spinal Cord – Part II
12b

36. White Matter in the Spinal Cord
Fibers run in three directions – ascending, descending, and transversely
Divided into three funiculi (columns) – posterior, lateral, and anterior
Each funiculus contains several fiber tracks
Fiber tract names reveal their origin and destination
Fiber tracts are composed of axons with similar functions

37. White Matter: Pathway Generalizations
Pathways decussate (cross to contralateral side of body)
Most consist of two or three neurons in the pathway
Most exhibit somatotopy (precise spatial relationships)
Pathways are paired (one on each side of the spinal cord or brain)

38. Ascending (Sensory) Tracts
Figure 12.32

39. Ascending Tracts TRACT FUNCTION
1. anterior (ventral) spinothalamic - touch and pressure to thalamus
2. lateral spinothalamic tract - pain & temperature to thalamus
3. fasciculus gracilis & cuneatus - touch, 2-pt. discrimination conscious proprioception, stereognosis, weight discrimination, vibration
4. posterior spinocerebellar - subconscious proprioception
5. anterior spinocerebellar - subconscious proprioception

40. Nonspecific Ascending Pathway
Nonspecific pathway for pain, temperature, and crude touch within the lateral spinothalamic tract
Figure 12.33b

41. Descending (Motor) Pathways
Motor pathways involve two neurons (upper motor neuron and lower motor neuron)

42. Descending (Motor) Tracts

43. Descending (Motor) Pathways
TRACTS FUNCTIONS
1. lateral & anterior corticospinal motor output from cortex motor to cells of ant. horn
2. rubrospinal motor from midbrain to anterior horn for precise movement
3. tectospinal motor from midbrain to anterior horn; movements in response to audiovisual/cutaneous stimuli
4. vestibulospinal motor from medulla to anterior horn; coordination/balance
5. lateral reticulospinal motor from medulla to anterior horn; inhibit extensor reflexes
6. medial reticulospinal motor from pons to anterior horn; facilitate extensor reflexes

44. The Direct (Pyramidal) Motor System
Direct pathways originate with the pyramidal neurons in the precentral gyri
Impulses are sent through the corticospinal tracts and synapse in the anterior horn
Stimulation of anterior horn neurons activates skeletal muscles
Parts of the direct pathway, called corticobulbar tracts, innervate cranial nerve nuclei
The direct pathway regulates fast and fine (skilled) movements

45. The Direct (Pyramidal) System
Figure 12.34a

46. Indirect (Extrapyramidal) Motor System
Includes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal system
This system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts
These motor pathways are complex and multisynaptic, and regulate:
Axial muscles that maintain balance and posture
Muscles controlling coarse movements of the proximal portions of limbs
Head, neck, and eye movement

47. Indirect (Extrapyramidal) System
Figure 12.34b

48. Extrapyramidal (Multineuronal) Pathways
Reticulospinal tracts – maintain balance
Rubrospinal tracts – control flexor muscles
Superior colliculi and tectospinal tracts mediate head movements

49. White Matter: Pathway Generalizations
Figure 12.32

50. Spinal Cord Trauma: Paralysis
Paralysis – loss of motor function
Flaccid paralysis – severe damage to the ventral root or anterior horn cells
Lower motor neurons are damaged and impulses do not reach muscles
There is no voluntary or involuntary control of muscles

51. Spinal Cord Trauma: Paralysis
Spastic paralysis – only upper motor neurons of the primary motor cortex are damaged
Spinal neurons remain intact and muscles are stimulated irregularly
There is no voluntary control of muscles

52. Spinal Cord Trauma: Transection
Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut
Paraplegia – transection between T1 and L1
Quadriplegia – transection in the cervical region

53. Poliomyelitis
Destruction of the anterior horn motor neurons by the poliovirus
Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexes
Vaccines are available and can prevent infection

54. Amyotrophic Lateral Sclerosis (ALS)
Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tract
Symptoms – loss of the ability to speak, swallow, and breathe
Death occurs within five years
Linked to malfunctioning genes for glutamate transporter and/or superoxide dismutase