Peripheral Sensation and Reflexes

Question 1

Describe the various types of cutaneous receptor used to detect sensory modularity’s in the skin

Answer 1

FREE NERVE ENDINGS detect PAIN & TEMPERATURE
RUFFINI ENDINGS detect TOUCH
MEISSNER'S CORPUSCLES detect TOUCH
MERKELS DISCS detect TOUCH
PACINIAN CORPUSCLES detect TOUCH

Question 2

Describe the structure of muscle spindles and how they sense changes in the length/stretch of muscle

Answer 2

MUSCLE SPINDLES: Detect length/stretch of the muscle. A proprioceptive receptor. Formed from 8-10 intrafusal muscle fibres. Innervated by Ia sensory afferent fibres.
Signalling leads to modulation of muscle stretch my A gamma motor neurons to extrafusal muscle fibres.
Example: Flower-spray

Question 3

Describe Golgi/tendon organ

Answer 3

Detect tension/contraction within the muscle. Signal to the CNS by 1b afferent fibres.
Located between the junction of the muscle and tendon.
High threshold

Question 4

Describe the muscle spindle stretch reflex

Answer 4

• A monosynaptic reflex
  Muscle spindle –> 1a afferent –> CNS –> A gamma motor neuron –> muscle contracts and relieves stretch
  Example: KNEE JERK REFLEX (excitatory reflex)

Question 5

Describe the Golgi/tendon organ reflex (inverse myotactic reflex)

Answer 5

Muscle tension detected –> Golgi tendon organsignals via Ib afferent –> Inhibitory interneuron –> Inhibitory signals sent to the muscle via motor neuron
ALSO, excitatory interneuron acts to cause contraction of the antagonist muscle.

Question 6

Gamma motor neurones: Mechanism of adjusting sensitivity of muscle spindles

Answer 6

Innervate intrafusal muscle at either end of the muscle spindle.
Act to stretch the muscle spindle lowering the threshold for firing through the Ia afferent fibres. This adjusts the sensitivity of the spindle to the stretch reflex.