Basic Reflexes and Maintenance of Posture Flashcards
Describe the different levels of integration in the CNS.
Cortical level - highest level of neural activity
Subcortical - primitive actions (securing food + water, reproduction)
Spinal cord - homeostasis, reflex actions, simplest level
Describe the typical reflex arc.
Sense organ - afferent neuron (via dorsal root) - control centre (spinal cord) - efferent neuron (via ventral root)
Describe the reflex arc of muscle stretch. (stretch reflex).
- 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
Describe how the body detects muscle stretch.
-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)
Describe how force of muscle contraction is detected.
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
Describe the inverse stretch reflex.
- 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
Give examples of some more complicated reflexes.
- 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
How is standing possible lol
- 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
What happens to reflexes in UMN lesions?
increase