spinal cord anatomy slidessssssssssssssssssssssssssssssssssssssssssss

spinal cord anatomy

1. Spinal Cord
TirgarS.
Tehran University of Medical Sciences

2. Functions
Sensory and motor innervationof
entire body inferior to the head
through the spinal nerves
Two-way conduction pathway
between the body and the brain
Major center for reflexes
40-50 cm long
1-1.5 cm diameter
Adult: L1-L2 upper 2/3
Fetal 3
rd
month: ends at coccyx
Birth: ends at L3
Runs through the vertebral canal of the vertebral column

6. CaudaEquina(“horse’s tail”): collection of nerve roots at inferior
end of vertebral canal
Cervical & Lumbar enlargement Bracial& Lumbosacral plexus
ConusMedullaris
FilumTerminale
Filumterminale

7. 31 pairs
Spinal nerves
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
8 cervical nerve
7 vertebra
1 coccygeal nerve
4 vertebra

8. Anatomical structure of Nerves
Nerve=bundleofneuronfibers(axon/dendrite)
Neuronfibersarebundledbyconnectivetissue

9. Protection
Subarachnoid mater
Bone
Meninges
CSF (cerebrospinal fluid)
3 meninges:
Dura mater (outer)
Arachnoid mater (middle)
Piamater (inner)
3 spaces:
Epidural: outside dura
Subdural: between dura&
arachnoid
Subarachnoid: deep to arachnoid

11. SpinaBifida
Congenital defect 1 baby out of 1000
Failure of vertebral arch to close covering spinal cord
Folic acid (VitB)

12. CSF (cerebrospinal fluid)
Central canal &
Subarachnoid space

13. LP (lumbar puncture)= spinal tap
Anesthetics are often injected into epidural space
Injection into correct space is vital; mistakes can be lethal
Tocollectasampleofcerebrospinalfluid(CSF)forbiochemical,
microbiological,andcytologicalanalysis
Veryrarelyasatreatment("therapeuticlumbarpuncture")torelieve
increasedintracranialpressure

14. S
pinal cord structure
“H” shaped on cross section
Central canal & Gray commissure
Anterior & posterior median fissure
Gray matter (Cell bodies)
White matter (Axons)
Dorsal horn
Ventral horn
Lateral horn (thoracic & superior lumbar)
Dorsal column
Ventral column
Lateral column

15. Dorsal (posterior)
white
gray
Ventral (anterior)
Central
canal
Gray matter:
Dorsal half of “H”: cell bodies of interneurons
Ventral half of “H”: cell bodies ofmotor neurons
White matter:
Ascending fibers: sensory information to brain
Descending fibers: motor information to spinal cord

16. Called “mixed” nerves
Ventral Root (anterior root):
Away from CNS
Efferent
Dorsal Root (Posterior root):
Toward CNS
Afferent
Dorsal Root ganglion:
Cell bodies of dorsal root
neurons
Spinal nerves

18. Ascendingpathways: sensory information from body up
to CNS
Dorsal column
Spinothalamictracts
Spinocerebellartracts
Descendingpathways: motor instructions from brain
Pyramidal (corticospinal) most important to know
All others (“extrapyramidal”)
White matter of the spinal cord
Most synapse two or three times along the way, e.g.
in brain stem, thalamus or other.
Most pathways cross (or decussate) at some point
(spinal cord or medulla).

20. Major ascending pathways
3 order neurons
Spinocerebellar:
Proprioception from
skeletal muscles to
cerebellum of same side
(don’t cross)
Dorsal column:
Discriminative touch
sensation through thalamus
to somatosensory cortex
(cross in medulla)
Spinothalamic:
Carries nondiscriminate
sensations (pain, temp,
pressure) through the
thalamus to the primary
somatosensory cortex
(cross in spinal cord before
ascending)

21. Descending Pathways
2 order neurons
Pyramidal tracts:
Lateral corticospinal–cross in
pyramids of medulla; voluntary
motor to limb muscles
Ventral (anterior) corticospinal–
cross at spinal cord; voluntary to
axial muscles
“Extrapyramidal” tracts:
One example

22. RexedLamina
The distribution of cells and fibers in the gray matter exhibits a pattern
of lamination
The cellular pattern of each lamina is composed of various sizes or
shapes of neurons (cytoarchitecture)
10 lamina

23. Autonomic reflexes
Smooth muscle regulation
Heart and blood pressure regulation
Regulation of glands
Digestive system regulation
Reflexes
Reflex: rapid, predictable, and involuntary
responses to stimuli
The entire reflex occurs without involving the brain
Monosynaptic / Polysynaptic
Somatic reflexes
Activation of skeletal muscles

24. The Reflex Arc
Reflex arc: direct route from a receptor, to a sensory neuron, to an
interneuron, to a motor neuron, to an effector

25. Stretch reflex
Knee jerk Ankle jerk

26. Muscle spindle
Containing 10 fibers:
Nuclear bag
Nuclear chain
I & II afferent axons
γ efferent axons
α efferent axons
contraction
contraction

27. Stretch reflex
19-24 mSec

28. Reverse stretch reflex
Golgi tendon organ

29. Withdrawal

30. Babinski reflex
Blushing reflex
Cough reflex
Sneeze reflex
Palmar grasp reflex
Scratch reflex

31. Plexuses
Sensory
receptors
of back
Dorsal ramus(Mix) Ventral ramus(Mix)
Spinal nerve
Plexus
Posterior Anterior

32. Plexuses
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus

33. Cervical Plexus
Cervical plexus
Ventral rami of first
4 cervical nerves
Skin & muscles of
head, neck and
shoulders
Phrenic nerve (Mix) Diaphragm

34. Brachial Plexus
Brachial plexus
5-8 cervical + 1Thoracic nerves
MusculocutaneousMedianUlnarRadial Axillary

35. Musculocutaneous n.
Innervate anterior of arm
Axillary n.
Circle sergical neck of
Humerus
Innervate deltoid

36. Ulnar n.
Without branches in arm/
Innervate forearm & hand
Median n.
Without branches in arm/
Innervate anterior of
forearm & hand
Radial n.
Innervate posterior of arm
& Forearm & hand

37. Median n. in hand
Ulnar n. in hand
Radial n. in hand

38. 12 Pairs
No plexus
Intercostal nerves in
costal groove
Thoracic spinal nerves

39. Lumbar Plexus
Lumbar plexus from ventral rami of first 4 lumbar nerves
(psoas muscle)
Femoral n. Obturatorn.

40. Femoral Saphenous
Innervate anterior of leg &
medial of calf
Obturator
Innervate medial of leg

41. Sacral Plexus
Sacral plexus from ventral rami of 4-5 lumbar & 1-4 sacral nerves
Lumbosacral trunk
Sciatic n. Pudendaln.

42. Sciatic
Largest nerve of the body
Innervate gluteal area &
posterior of leg
Common peronealn.
Common
peronealn.
Innervate
posterior
of calf
Medial
plantar n.
Lateral
plantar n.
Tibialn.
Innervate
some part of
calf

43. Pudendaln.
Gluteal area
Perinea

44. Coccygeal Plexus
Coccygeal plexus from ventral rami of 4-5 sacral & coccygeal nerves
Innervate skin of coccyx

45. Each spinal nerve receive
sensory input from a specific
area of skin called dermatome
Overlap at edges by 50 %
A total loss of sensation requires
anesthesia of 3 successive spinal
nerves
Dermatomes