functional organization of spinal cord

Question 1

Across which vertebrae does the spinal cord spine?

Answer 1

C1 to L1-L2

Question 2

Where is the safest place to do a lumbar puncture? Why?

Answer 2

L3-L4, reduced risk of damaging neural tissue

Question 3

What is the terminal point of the spinal cord called?

Answer 3

Conus medullaris

Question 4

What is the filum terminale?

Answer 4

connective tissue sheath extending posteriorly from the conus medullaris. it is continuous with the pia mater.

Two layers:

1. internum - upper 3/4
2. externum - lower 1/4, attaches to dorsal coccyx

Question 5

What are distinguishing features of each spinal cord segment on CT scan?

Answer 5

In cross section spinal cord:

• Cervical: oval shaped, lots of white matter
• Thoracic: has characteristic Clark’s nucleus and Interomediolateral cell columns
• Lumbar: large ratio of gray matter to white matter
• Sacral Spine cord has only small rim of white matter

Question 6

What do the white matter portions of the spinal cord contain?

Answer 6

Ascending sensory tracts and descending motor tracts

Question 7

what do propriospinal tracts do?

Answer 7

Stay within the spinal cord, linking segments of the spinal cord together

Question 8

Distal muscles are innervated by motor nuclei that are most lateral or medial in the spinal cord?

Answer 8

Lateral.

Proximal muscles have root nuclei in the medial part.

Question 9

What is motor pool?

Answer 9

All the particular motor neurons in the spinal cord that innervate a particular muscle

Question 10

Why antagonistic grouping of muscle pairs?

Answer 10

Muscles can only be stimulated to contract, thus need opposing muscle that can counter a movement, provide balance=pulling/pushing pairs.

Question 11

What is mechanoreception?

Answer 11

rapidly reported sensory information RE: length of muscle and extent of force

Question 12

what role does the muscle spindle play in relaying proprioceptive info?

Answer 12

contains fastest conducting fibres. detects muscle stretch and induces the muscle to relay information RE stretch and position

Question 13

What information do GTO (golgi tendon organ) relay about skeletal muscles

Answer 13

The Golgi Tendon organ lies in series with muscle fibre bundles, thus relay info re extent of force being applied through the tendon.

Question 14

What is the purpose of the Ib afferent neuron in the GTO

Answer 14

when the muscle generates force the sensory terminals of Ib afferent neuron are stretched, opens stretch sensitive ion channels causing depolarization –> sending signal to interneurons in spinal cord that project to cerebellum and motor cortex.

Sensory feedback from Ib produces spinal reflexes. (deep tendon reflexes)

Question 15

How is a deep tendon reflex generated?

Answer 15

1. tap the patellar tendon–>small stretch to the extensor muscle
2. Burst of neural activity–>spindle afferents go to spinal cord
3. Afferent excitatory fibre will stimulate extensor motor neuron and inhibit flexor motor neuron via inhibitory motor neuron
4. Efferent fibres from motor neuron pool excites muscle to extend

Spindles are the only sensory organ that feeds directly. mono-synaptically, to motor neurons.**

Question 16

how does the bilateral (cross-extensor) reflex work?

Answer 16

withdrawing one limb in response to threatening/noxious stimulus increases stimulation to the other supporting lumb

Question 17

what are complex multisegmental reflex actions?

Answer 17

When a noxious stimuli causes all the flexors in the limb to contract ( touch something hot and your whole arm jolts back)

Question 18

how does the length of lateral vs medial propriospinal tracts differ?

Answer 18

lateral tracts are shorter (one finger to the next), whereas medial tracts are long range connections.