Basic Reflexes and Maintenance of Posture Flashcards

1
Q

Describe the different levels of integration in the CNS.

A

Cortical level - highest level of neural activity
Subcortical - primitive actions (securing food + water, reproduction)
Spinal cord - homeostasis, reflex actions, simplest level

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2
Q

Describe the typical reflex arc.

A

Sense organ - afferent neuron (via dorsal root) - control centre (spinal cord) - efferent neuron (via ventral root)

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3
Q

Describe the reflex arc of muscle stretch. (stretch reflex).

A
  • Depends on two variables: length and force
  • Intramuscular receptors (length sensed by muscle spindle and force sensed by golgi tendon organ)
  • Can be monosynaptic or more complicated
  • Integrated by spinal cord
  • Muscle contracts against the stretch
  • Smooths and dampens muscle movement
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4
Q

Describe how the body detects muscle stretch.

A

-Length transducer = muscle spindle (in parallel with muscle)
- Intrafusal fibres (lost most contractile proteins + wrapped in nerves)
- Afferent fibres from spindles = Type Ia (large, myelinated, fast-conducting)
- Type II fibres for tonic function of stretch reflex
- Gamma efferents for some contraction force (fusimotor system; efferents to dynamic nuclear bag, static nuclear bag, nuclear chain fibres; a + y co-activation; sets sensitivity of spindles; prevent spindle unloading; set baseline levels of alpha discharge and therefore muscle tone)
-Two main fibres in spindle
Sensing velocity (bag1 fibres, innervated by Type Ia nerves, fast-adapting to stimulus, phasic)
Sensing length (bag2 fibres, nuclear chain, innervated by slower-conducting Type II fibres, adapt slowly to stimulus, static response)

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5
Q

Describe how force of muscle contraction is detected.

A

Force transducer = golgi tendon organ

  • in series with muscle
  • embedded within tendons
  • fire in response to muscle contractile force - a lot of force needs to be put through muscle for tendon to stretch (collagenous fibres)
  • synapse via inhibitory neuron on a fibre
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6
Q

Describe the inverse stretch reflex.

A
  • reflex inhibition of alpha output to muscle
  • via an inhibitory interneuron, it reduces activity of motor neurons
  • regulates force so it can be constant (e.g. grip)
  • part of sophisticated control system sending info about force centrally
  • enable us to control muscle force finely as well as length
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7
Q

Give examples of some more complicated reflexes.

A
  • Crossed extensor reflex
  • Positive supporting reflex
  • Spinal righting reflex
    (all function w/o supraspinal input)
  • walking - central pattern generator in spine, alternate contraction of flexors + extensors
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8
Q

How is standing possible lol

A
  • Don’t need cortex
  • Proprioception, pressure sensors in soles of feet, visual input, vestibular input
  • Neck keeps head upright
  • Trunk keeps C of G over the feet
  • Leg muscle extensors active
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9
Q

What happens to reflexes in UMN lesions?

A

increase

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