Exam 1 Spinal Cord Flashcards
Spinal Cord- segmental levels cervical
8
Spinal Cord- segmental levels thoracic
12
Spinal Cord- segmental level lumbar
5
Spinal Cord- segmental level sacral
5
Spinal Cord- segmental level coccygeal
1
Where does the spinal cord end?
extend form foramen magnum to L1-L2 vertebra
What are the paired spinal nerves formed from?
a dorsal and ventral root
Dorsal root ganglion are composed of
sensory neuron cell bodies for spinal primary afferent sensory axons
What is the overall size of the spinal cord?
7-8mm dorsal-ventral and ~12mm lateral axis at largest segment
Where is the spinal cord located?
within the vertebral column
Where do the spinal nerves exit?
~C1-7 above similar # vertebra ~C8 below C7 vertebra ~T1-L5 below similar vertebra ~Sacral- in the sacral foramina ~coccygeal- below the sacrum
External features of the spinal cord
a number of longitudinal "furrows" on the surface ~Posterior or dorsal median sulcus ~Anterior or ventral median fissure ~Dorsolateral sulcus ~Ventrolateral sulcus
Posterior or dorsal median sulcus on the spinal cord
marking the dorsal surface
Anterior or ventral median fissure on the spinal cord
marking the ventral surfaces
Dorsolateral sulcus
entry point of dorsal root
Ventrolateral sulcus
exit for ventral root
Why is there a cervical enlargement in the spinal cord?
~gives rise to the brachial plexus
~innervating upper extremity, which has a high innervation density (that is a large number of neurons innervating a relatively small muscle mass)
~gives rise to the fine motor control muscles of the hand
Where is the cervical enlargement in the spinal cord?
C4-T1
Comparison of the innervation of the back musculature versus the innervation of hand musculature
~ low innervation density of the back musculature versus the high innervation density of hand musculature
~Smaller number of neurons in the ventral horn of the spinal cord segments which innervate a larger muscle mass in the trunk and proximal limbs.
~each neuron there innervates a large number of number of muscle fibers.
~low innervation density but a larger Motor Unit (# muscle fibers innervated by a single neuron by its single axon in the back and proximal limbs.
~larger number of neurons in the ventral horn of the spinal cord segments which innervate a smaller muscle mass in the distal limbs.
~each neuron innervates a large number of number of muscle fibers.
~high innervation density but a smaller Motor Units in the distal extremities.
~gives more power to the trunk and proximal limb muscles but more fine motor control to the distal limb muscles
Why is T2-L1 more narrow?
~these spinal segments innervate the trunk
Comparison of sensory density of skin on the back versus sensory density of skin on the hand
~there are few receptors cover large areas of skin of the back
~sensory density of skin of the distal extremities where there are a very large number of receptors in small areas of skin
~the back has a low sensory innervation density while the distal extremity has a very high innervation density
Where is the lumbosacral enlargement?
L5-S2
Why is there a lumbosacral enlargement?
~gives rise to lumbosacral plexus, which innervates lower extremity
~higher innervation but not as high as cervical enlargement
Conus medularis
the spinal cord tapers to form the medullaris (S3-Co1)
