Sensorimotor Integration

Question 1

What is the purpose of sensorimotor integration?

Answer 1

• Ensuring that movements are adaptive to behaviour

- Modulate motor response for environment/response to danger

Question 2

What are the two types of signal which can modulate a reflex?

Answer 2

Proprioceptive - predictable (when you generate a movement you can predict what the feedback might be)
Extraceptive - non-predictable

Question 3

What information do monosynaptic and polysynaptic relexes usually carry?

Answer 3

Monosynaptic - proprioceptive

Polysynaptic - sensory

Question 4

What is:

a) cycle period
b) cycle frequency
c) burst duration

Answer 4

a) time cycles
b) cycles per second/certain time period
c) duration of time when ventral root is active

Question 5

How may motor neurons modulate reflexes in tadpoles?

Answer 5

• During locomotion neurons are rythmically active and inactive
• During inhibition the membrane is clamped away from the spike threshold making reflex inputs less effective

Question 6

How do sensory interneurons modulate reflexes in tadpoles?

Answer 6

• 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

Question 7

What has been shown with regards to entrainment in lampreys?

Answer 7

Through measurement of fictive swimming when tail was wagged artificially

• spinal cord entrains to rhythm of tail
• therefore must contain mechanoreceptors/proprioceptors

Question 8

What are edge cells?

Answer 8

• 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)

Question 9

What benefits do edge cells provide?

Answer 9

In model: allowed lamprey to move through turbulent water

therefore: allow maintenance of goal directed movement

Question 10

How is gaze controlled in tadpoles?

Answer 10

• Controlled by medial and lateral rectus muscles which move eyes in opposite direction to head
• CPG in spine produces “efference copy” to eye muscles

Question 11

How is sensorimotor integration more complex in mammals?

Answer 11

Involves coordination of limbs, muscles, joints and skin which all give sensory feedback

Question 12

What are muscle spindles?

Answer 12

Sense the length of muscles (Ia afferents)

Question 13

What are golgi tendon organs?

Answer 13

Embeded within tendons, IB tendon neurosn monitor tension

Question 14

Describe the monosynaptic stretch reflex

Answer 14

• 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

Question 15

How can you infer the number of synapses in a reflex?

Answer 15

Delay in transmission - increased delay means more synapses

Question 16

Describe the pain withdrawal reflex

Answer 16

• 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

Question 17

What is the autogenic inhibition reflex?

Answer 17

• 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

Question 18

How are reflexes activated during voluntary movements?

Answer 18

• 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

Question 19

At which 3 sites can spinal reflexes be modulated?

Answer 19

• alpha motorneurons
• interneurons in polysynaptic reflex circuits
• presynaptic terminals of afferent fibres

Question 20

What is the role of PAD (primary afferent depolarisation) in presynaptic inhibition?

Answer 20

• 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-

Question 21

Describe the modulation of the monosynaptic (H) reflex?

Answer 21

• 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

Question 22

What are intrafusal and extrafusal fibres?

Answer 22

• 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

Question 23

How is detection of muscle contraction regulated?

Answer 23

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

Question 24

What are the 3 main forms of sensory input during locomotion?

Answer 24

• Somatosensory
• Vestibular (balance)
• Visual

Question 25

What are prioprioceptors and exteroreceptos?

Answer 25

proprioceptors - located in muscles and responsible for automatic stepping regulation exteroreceptors - located on skin and adjust stepping to external stimuli

Question 26

What are the two main phases of limbed locomotion and what are they controlled by?

Answer 26

Stance phase - controlled by extensors which bear the weight Swing phase - controlled by flexors which lift limbs off the ground

Question 27

What effect does the stretching of a cat hip have?

Answer 27

- 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

Question 28

What role do the Golgi tendon organs play in the regulation of locomotion?

Answer 28

- 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

Question 29

Give an example of a reflex reversal

Answer 29

Ib afferents usually produce inhibitory inputs on extensor motorneurons, however during locomotion this is reversed

Question 30

What is the stumbling corrective reflex?

Answer 30

- 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

Question 31

What is sensorimotor memory and what area is belived to be responsible?

Answer 31

- 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

Question 32

Describe the structure of the cerebellum

Answer 32

- 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

Question 33

What is the role of the cerebellum?

Answer 33

- 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