9 - Functional Organisation of the Spinal Cord

Question 1

Functional roles of the spinal cord 1 2 3 4

Answer 1

1) Segmental reflexes, inter-segmental reflexes, pattern generators 2) Processing and transmission of somatosensory (tactile, nociceptive) information 3) Relay of descending motor commands 4) Relay of descending autonomic commands

Question 2

Is the spinal cord surrounded by meninges, CSF?

Answer 2

Yes

Question 3

Safest place to take a CSF sample

Answer 3

L3/L4 (lumbar puncture). Spinal cord has ended by this stage, only cauda equina.

Question 4

*Shapes of different spinal segments

Answer 4

White matter abundant in thoracic, less in sacral

Question 5

*Map of ascending and descending spinal tracts

Answer 5

Question 6

Name for neuronal linkages within spinal cord

Answer 6

Propriospinal

Question 7

Location of motor neurons in the spinal cord

Answer 7

Lie in clusters in the anterior horn

Question 8

Final common pathway for movement

Answer 8

Motor neurons

Question 9

Spatial organisation of motor neurons in the spinal cord

Answer 9

Medial motor neurons control proximal muscles. Lateral motor neurons control distal muscle

Question 10

Motor pool

Answer 10

All the motor neurons in the spinal cord that innervate a particular muscle. One neuron will innervate a collection of muscle fibres.

Question 11

Functional grouping of muscles (antagonism)

Answer 11

Muscles organised into antagonistic pairs

Question 12

Mechanoreception

Answer 12

Need rapid information about state of muscle contraction. Sensory apparatus within muscle that detects position, force (Golgi tendon organs, muscle spindles)

Question 13

Motor unit

Answer 13

Collection of muscle fibres innervated by a single motor neuron

Question 14

Development of muscle spindles

Answer 14

Sensory fibres that grow into muscle can induce normal muscle fibres to become muscle spindles.

Question 15

*Muscle spindle

Answer 15

Group I and II afferent axons wrap around intrafusal muscle fibres. Detect change in muscle length. Sensor is in parallel with muscle fibres.

Question 16

*Golgi tendon organ

Answer 16

Within capsule, Ib afferent neuron axon interdigitates with collagen tendrils of tendon. Sensor is in series with muscle fibres (sits in tendon). Detects amount of force transmitted through tendon.

Question 17

What is occurring in a tendon hammer test?

Answer 17

Monosynaptic stretch reflex. Muscle spindles are activated. Causes a reflexive muscle contraction

Question 18

Unusual aspect of synapse between muscle spindle afferent and motor neuron

Answer 18

Very efficient. Will cause muscle contraction from stimulation by one synapse. Hence monosynaptic reflex.

Question 19

*Organisation of spinal neurons in a monosynaptic stretch reflex

Answer 19

If extensor is elongating (EG is under load), sends spindle afferent to motor neuron to contract extensor, inhibitory signal to motor neuron innervating extensor muscle. This makes extensor elongate, which makes spindle afferent cause extensor contraction, flexor motor neuron is inhibited to compensate, etc etc etc

Question 20

Basic role of muscle spindles

Answer 20

Maintain muscle position under load.

Question 21

Basic function of Golgi tendon organ

Answer 21

Limit activity of muscle. NOT monosynaptic.

Question 22

*Organisation of neurons in a Golgi tendon reflex

Answer 22

Excessive force applied through tendon. Golgi afferent stimulates an inhibitory interneuron which inhibits motor neuron innervating muscle through which excessive force is being applied.

Question 23

*Cross-extensor reflex

Answer 23

If a limb is withdrawn from something noxious, then will fall if nothing else is done. Solution is achieved by signals stimulating spinal interneuronal circuits which make one limb move from noxious stimulus (stimulate flexors, inhibit extensors), while other limb compensates for balance (stimulates extensors, inhibits flexors).

Question 24

Propriospinal fibres

Answer 24

Interneurons within spinal cord that connect different spinal segments. Allow for complex reflexes such as cross-extensor reflex (where EG need to flex shoulder, elbow, hand, etc) Long propriospinal interconnections tend to be in the central spinal cord, short propriospinal interconnections tend to be lateral.

Question 25

Why are long propriospinal interconnections often in the middle of the spinal cord?

Answer 25

Neurons more medially control proximal muscles. Controlling posture involves a lot of proximal muscles along the whole length of the body.

Question 26

Interface between brain and spinal cord in terms of movement

Answer 26

Descending motor neurons from the brain synapse with neurons in the final common pathway of the spinal cord, modulate these circuits.