Sensorimotor Integration Flashcards
What is the purpose of sensorimotor integration?
- Ensuring that movements are adaptive to behaviour
- Modulate motor response for environment/response to danger
What are the two types of signal which can modulate a reflex?
Proprioceptive - predictable (when you generate a movement you can predict what the feedback might be)
Extraceptive - non-predictable
What information do monosynaptic and polysynaptic relexes usually carry?
Monosynaptic - proprioceptive
Polysynaptic - sensory
What is:
a) cycle period
b) cycle frequency
c) burst duration
a) time cycles
b) cycles per second/certain time period
c) duration of time when ventral root is active
How may motor neurons modulate reflexes in tadpoles?
- During locomotion neurons are rythmically active and inactive
- During inhibition the membrane is clamped away from the spike threshold making reflex inputs less effective
How do sensory interneurons modulate reflexes in tadpoles?
- Excited by primary afferents which relay excitation to motor system
- They are inhibited during swimming in a rhythmic manner, specifically dlc’s (dorsolateral momisural interneurons) which relay information to the other side, preventing bending reflex according to motor phase
What has been shown with regards to entrainment in lampreys?
Through measurement of fictive swimming when tail was wagged artificially
- spinal cord entrains to rhythm of tail
- therefore must contain mechanoreceptors/proprioceptors
What are edge cells?
- Neurons with processes which abut to the outer edge of the spinal cord
- Responsible for entrainment
2 types: excitatory (glutamate- same side) and inhibitory (glycine - opposite side)
What benefits do edge cells provide?
In model: allowed lamprey to move through turbulent water
therefore: allow maintenance of goal directed movement
How is gaze controlled in tadpoles?
- Controlled by medial and lateral rectus muscles which move eyes in opposite direction to head
- CPG in spine produces “efference copy” to eye muscles
How is sensorimotor integration more complex in mammals?
Involves coordination of limbs, muscles, joints and skin which all give sensory feedback
What are muscle spindles?
Sense the length of muscles (Ia afferents)
What are golgi tendon organs?
Embeded within tendons, IB tendon neurosn monitor tension
Describe the monosynaptic stretch reflex
- Contraction of muscle when lengthened sensed by muscle spindle
- Ia afferents transmit this information to motor neurons to activate homonymous muscle and synergist muscle
- Ia inhibitory interneuron also activated which inhibits alpha motor neuron and therefore antagonist muscle
How can you infer the number of synapses in a reflex?
Delay in transmission - increased delay means more synapses
Describe the pain withdrawal reflex
- Noicireceptors project to the dorsal horn and produce widespread activation of limb flexors with inhibition of antagonistic extensors
- Coupled with crossed extensor reflex that ensures postural support (reverse activation/inhibiton on other limb)
- Stronger stimulus - stronger activation
What is the autogenic inhibition reflex?
- Golgi tendon organs Ib sensory afferents signal tension in the muscle
- Ib inhibitory interneurons provide negative feedback on minute changes in muscle tension to ensure that the muscle is not overexerted
How are reflexes activated during voluntary movements?
- Descending inputs exciting motor neurons send axon collaterals to Ia inhibitory interneurons, simplifying the system and so only one command is sent
- When co-contractions are required Ia interneurons can also be inhibited by descending inputs
At which 3 sites can spinal reflexes be modulated?
- alpha motorneurons
- interneurons in polysynaptic reflex circuits
- presynaptic terminals of afferent fibres
What is the role of PAD (primary afferent depolarisation) in presynaptic inhibition?
- PAD occurs during fictive locomotion and provides signal from CPG (efference copy) to sensory neurons, modifying release of neurotransmitter to phase movements
- During depolarisation transmitter released is reduced with smaller sensory spike produced (reduced Ca2+?)
- PAD may be modulate with Cl-
Describe the modulation of the monosynaptic (H) reflex?
- Decrease in H reflex related to increase in inhibitory GABA synapses resulting in an increased threshold and EPSPs
- Cerebellum and sensorimotor cortex are required however for long term changes
What are intrafusal and extrafusal fibres?
- Muscle spindles are intrafusal fibres which lie in parrallel to the force generating muscle extrafusal fibres
- Intrafusal fibres are innervated by gamma motorneurons
- Extrafusal fibres are innervated by alpha motorneurons
How is detection of muscle contraction regulated?
When a load is different to expected gamma motorneurons activate and contract intrafusal fibres thereby maintaining tension in the muscle spindle and responsiveness ar different lengths
What are the 3 main forms of sensory input during locomotion?
- Somatosensory
- Vestibular (balance)
- Visual
What are prioprioceptors and exteroreceptos?
proprioceptors - located in muscles and responsible for automatic stepping regulation
exteroreceptors - located on skin and adjust stepping to external stimuli
What are the two main phases of limbed locomotion and what are they controlled by?
Stance phase - controlled by extensors which bear the weight
Swing phase - controlled by flexors which lift limbs off the ground
What effect does the stretching of a cat hip have?
- Information regarding hip extension is detected via muscle spindles and transmitted via Ia afferents
- Stretching of hip flexor muscles inhibits extensor activity and facilitates the initiation of bursting in flexors
What role do the Golgi tendon organs play in the regulation of locomotion?
- Swing phase is initiated when force on extensor muscles is low (decrease in golgi tendon organ activity signals decrease in body load)
- If you stimulate Ib afferents from Golgi tendon organs at the right time you can prolong the stance phase
Give an example of a reflex reversal
Ib afferents usually produce inhibitory inputs on extensor motorneurons, however during locomotion this is reversed
What is the stumbling corrective reflex?
- Stimulus to dorsal paw during swing phase causes removal and elevation over object (activation of flexors and inhibition of extensors)
- However if stimulus occurs during stance phase the effect is the opposite
What is sensorimotor memory and what area is belived to be responsible?
- Cat which steps over object to feed for 10 minutes will step back over imagined object when it is removed
- Area S in parietal cortex is thought to be the source of motor memory
Describe the structure of the cerebellum
- Highly folded and compact with projections to deep cerebellum nuclei
- Purkinje neurons project to other brain areas and are inhibitory
- Climbing and mossy fibres provide important input
- Granule cells integrate information in the cerebellum
What is the role of the cerebellum?
- Control of fine motor commands and motor learning
- Efference copy of planned motor action is sent to the cerebellum, if feedback is different to what is expected this causes an error signal and Purkinje cells send signal to correct the movement
