Lecture 13 - Somatosensory Evoked Reflexes Flashcards
Mono, di and polysnaptic
One, two or more synapses acting on a final neruon
Muscle spindle, stretch. Sends AP to alpha motor neuron for muscle contraction
Convergent and Divergent Pathway
Convergent pathway: many sensory neurons leading to one. Feed up into the brain
Divergent pathway: From one neuron going through multiple pathways
Feedback excitation and inhibition
Feedback excitation: positive feedback loop, increasing its own firing rate
Feedback inhibition: Renshaw cell, inhibits activity. Alpha motor neuron used
Rules of pathways and inhibition
Triangle = excitatory
Circle=inhibitory
1 neuron has one type of neurotransmitter it produces
Muscle stretch reflex
Muscle spindle stretch, tendon tap, causes contraction.
Single muscle spindle connects to a large number of motor neuron pool, this is called divergence. 1 neuron to many
Reciprocal inhibition
Tap stretches tendon, also stretches sensory receptors in leg extensor muscle
This leads to the contraction of the agonist muscle along with the inhibition of antagonist muscle
Sensory neuron excites spinal motor neurons and spinal interneurons. These interneurons inhibit motor neuron to flexor muscles
Reciprocal inhibition with synergist muscle
Synergest muscle supports direction of movement of agonist muscle
Ex: Leg is lifted up. Quad contracts (agonist) and inhibition is in hamstring (antagonist). Hamstring relaaxes without stretch. This leads to inhibition of flexion and excitation of extension
PAY DIRECTION TO MOVEMENT
Tonic excitatory input
Requires two sources of input, spindle isn’t enough.
One input is always muscle spindle, which if afferent.
The other input is cutaneous or brain signal. Cutaneous is skin touch which is sensory and sends info to spinal cord to synapse on to same alpha motor neuron as the spindle. This is of brain signal as well.
Cutaneous can attract tendon reflex.
Tonic excitatory input is another sensory in put (cutaneous or brain). In this cause the input is excitatory (facilitated)
With faciliatory tonic excitatory input, the same stimulation of muscle spindles is now enough to cross AP threshold
Cutaneous withdrawal reflexes
When the skin is stimulated by a sudden painful event of skins surface or even more subtle forms like stepping on stepping on tree root. Reflex is generated by nonireceptors (pain). This causes spinal loops to with drawl.
Cutaneous withdrawal reflexes are wired up such that appropriate muscle are activated to withdrawl limb
Sensory steering
The wiring sets up a mechanism whereby sensory input from the skin results in rapid reflexive steering “sensory steering”. This is from muscle spindles and GTO
Given position tell how nocireceptors, muscle spinal/GTO will react
EX: touch hot stove, bicep will contract
Polysynaptic reflexes
This type of flexability in reflex responses requires complex divergent synaptic connections from cutaneous afferents onto multiple muscles
Say you step on a nail…
Nocireceptors, withdraw from stimuli
The flexion-crossed-extension reflex circuity ensures that when you retract the injured leg, you also compensate and press down harder with your other leg to transfer your body weight and not fall over
Golgi Tendon Organ Autogenic inhibition relex
Activation of the Golgi Tendon (active force production) Organs results in a protective reflex, when force production gets too high, that shuts down the muscle to prevent ruptured tendons (autogenic inhibition)
Golgi Tendon shuts down tendon.
Recall that GTO’s become increasingly more active as we output greater force
Renshaw Cell
Manage upper firing rate of alpha motor neuron. Limits it by reducing amount of force out put. Causes inhibition by itself as it is activated by a small collateral branch of motor neuron (negative feedback loop)
