Spinal Reflexes Flashcards
What is the definition of a reflex
Reflexes are coordinated involuntary motor responses initiated by a stimuli applied to the peripheral receptors
Describe the stretch reflex
It is a sensorimotor loop evoked by tendon tap.
Abolished by cutting dorsal roots to the spinal cord thus the stretch reflex is not simply a mechanical response but involves a neural pathway
The stretch reflex muscle spindles:
1.muscle spindles are receptors that detect changes in the muscle length during contraction
2.stretch evokes an increase in spindle firing rate
3. In turn a motor neuron are activated in the spinal ventral horn leading to subsequent muscle contraction of the agonist and synergistic msuscles
What does the muscle spindle consist of
Consist of:
1.bundle of this fibres contained within a capsule
2.situated in parallel with main extrafusal muscle fibres but generate no force
3.wrapped around by a pair of sensory axons
What do muscle spindles detect
Detects length/stretch of muscle
And the rate of change (velocity)
What are intrafusal fibres
There are two main types:
Nuclear bag fibres enervated by type 1a afferents
Nuclear chain fibres and inverted by type 1a and type 2 afferents
What is reciprocal inhibition
Where antagonist muscles may interfere with the desired movement are suppressed by contraction of the agonist
What is lipped feel syndrome
Rare condition in which promoter neurons form cortex bifurcate to innervate both sides of the body
Moving one hand leads to mirror movement in the other hand
What is the purpose of the stretch reflex
1.stretch reflex operates in a negative feedback loop which prevents major disturbances to the regulation of a controlled variable, in this case muscle length
What is servo assistance
The stretch reflex may maintain accuracy of movement in the face of small deviations this is known as servo assistance
What is the Hoffman reflex
1.elicited by activation of type 1a sensory nerves and evokes a muscle contraction via monosynaptic spinal reflex that can be recorded using EMG
2
How is the Hoffman reflex condition
By associative learning tested on rats.
Rats were rewarded when a reflex amplitude exceeds a certain threshold and another group rewarded if was below a threshold
Shows that the neural pathway learnt is adaptable
Reflex adaptability: reversal of the Golgi tendon organ reflex
At rest the GTO input inhibits ongoing muscle activity via negative feedback
During locomotion GTO input increases extensor muscle activity to produce positive feedback which helps to produce sufficient force during the stance phase of locomotion
Reflex adaptability: gait phase dependant Golgi feedback
GTO reflex contributes to transition between stance and swing phase during walking
What are the long and cough reflexes mediated by
Pulmonary stretch receptors
