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Neuroscience > Lecture 16 - spinal circuits > Flashcards

Lecture 16 - spinal circuits Flashcards

1
Q

What type of arrangement is the motor system in?

A

hierarchical

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2
Q

What type of motoneurons control the wrists and hands?

A

dorsal lateral

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3
Q

What type of motoneurons control parts of the arms and shoulder?

A

ventral lateral

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4
Q

What type of motoneurons control the neck?

A

ventral medial

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5
Q

What are central pattern generators?

A

assemblies of neurons that produce a particular path of activity that control movements of limbs and walking

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6
Q

In development what develops first, middle and last?

A

CPGs first
sensory feedback second
descending inputs last

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7
Q

Describe the development of the spinal cord.

A
  • neuro stem cells organise in a straight line
  • they do this by diffusing down from the top of the body of one type of molecule, competing with others to form gradients across
  • this then determines which transcription factors they express
  • this instructs the cell what protein to make
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8
Q

What are the 4 different types of CPG neurons and what type are they?

A
  1. V0 - commissural
  2. V1 - inhibitory
  3. V2 - glutamatergic V2a and inhibitory V2b
  4. V3 - excitatory commissural
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9
Q

What is each of the CPG neurons axon projection in the embryonic spinal cord?

A

V0 = rostrally
V1 = rostrally and ipsilaterally
V2 = ipsilaterally and caudally
V3 = caudally

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10
Q

How could you alter the movement of an animal?

A
  • Different types of interneurons are specified by different transcription factors
  • Certain genes can be killed to alter movement by removing neurons (knock out)
  • If both the excitatory and inhibitory neurons are knocked out the animals can only do one type of movement
  • If only one neuron is knocked out, then the mice could die before birth
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11
Q

What does it mean when activity is happening on one side of the body?

A

inhibitory neurons are working on the other side of the body to inhibit it and then there is switchover

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12
Q

Describe the action of walking (spinal circuits).

A
  • involves activity within one side of the spinal cord changing
  • out of phase activity in phlexor and extensors so they act one after the other.
  • they inhibit the flexor motor neurons and at the same time inhibit the cells that are inhibiting the motor neurons from being active
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13
Q

Describe the stepping reflex in newborns.

A
  • disappears around 6 weeks
  • gradually replaced by voluntary walking behaviour
  • hierarchy not established
  • stepping driven by sensory feedback and CPGs - sets off local circuits in limbs
  • this disappears then re-emerges as corticospinal influence is established (descending control)
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14
Q

What are the two types of interneurons from the V1 family?

A
  1. renshaw cells
  2. Ia inhibitory interneurons
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15
Q

Describe renshaw cells.

A
  • recurrent inhibition
  • inhibits the activity of motoneurons to allow activity to go from one group of motoneurons to another
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16
Q

Describe what Ia inhibitory interneurons do.

A
  • send an axon to muscle spindles to detect stretching in muscles and they send a process in the spinal cord
  • they connect with the motor neuron that innervates the muscle that which the sensory neuron has derived its info.
  • also innervates Ia inhibitory interneurons that inhibit the other muscle group
17
Q

What are the 4 types of sensory fibres entering the CNS via the spinal cord?

A
  1. A alpha
  2. A beta and A delta
  3. A gamma
  4. C fibres
18
Q

What role do A alpha sensory fibres play?

A

type Ia from muscle spindle = monitor velocity of muscle stretch

type Ib from Golgi organ = monitor force of contraction

19
Q

What role do A beta and A delta sensory fibres play?

A

type 2 fibres from muscle spindle = monitor length of muscle and position in space

20
Q

What role do A gamma sensory fibres play?

A

touch, pain, heat and vibration

21
Q

What role do C fibres play?

A

pain, heat

22
Q

Describe the flexor reflex.

A
  • multi synaptic pathway
  • not as fast as the stretch reflex
  • c fibres are slow and their sensation arrives after the hand has been pulled away
23
Q

Describe the flexor and crossed extensor reflex.

A
  • requires more control than the flexor reflex
  • neurons sending information to the other side of the body to make sure that balance isn’t lost
  • for example if you stand on lego it make sure you only pick the leg that is in pain not both of them
24
Q

What are long propriospinal interneurons?

A

long propriospinal interneurons reciprocally connect the cervical and lumbar spinal cord and contribute to locomotor movement (rodents).

25
Q

Describe descending PINs.

A
  • form a complex bilateral system with excitatory and inhibitory components to mediate inter limb coordination and to relay info to CPG.
  • most originate from laminae VII-VIII and the deep dorsal horn.
  • vast majority of descending PINs are excitatory both on the ipsilateral or contralateral side, the small inhibitory population terminates ipsilaterally.
26
Q

Descrive ascending PINs.

A
  • form a powerful ipsilateral excitatory pathway from the rostral lumbar cord to motoneurons controlling proximal forelimb muscles.
  • originate mostly from the intermediate grey matter in the lumbar spinal cord and preferentially project ipsilaterally.
  • they project to the intermediate grey matter and the ventral horn throughout the length of the cervical spinal cord.
27
Q

Describe transcortical (slow) reflex pathways.

A
  • go by the cortex
  • info comes into the spinal cord
  • goes through white matter pathways to neurons in the medulla
  • goes into the brain cortex
  • gives us control over what we do in terms of reflexes (don’t have to remove hand from pain if we don’t want too)
28
Q

What represents ascending pathways carrying impulses to a subconscious level?

A

spinocerebellar tracts

29
Q

What are the 6 pathways into the spinal cord and their functions?

A
  1. lateral corticospinal tract - voluntary control of distal musculature
  2. anterior corticospinal tract - voluntary control of Proximal musculature
  3. reticulospinal tracts - regulate flexor reflexes and initiate patterned activity
  4. rubrospinal tract - excitation of flexor muscles
  5. tectospinal tract - orientation to visual stimuli
  6. vestibulospinal tract - balance

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