Reflexes

I've done a bit of physiology - but i wanted to check i've understood what i've done...

- knee-jerk reflex

- patella tendon tapped -> muscular spindles (strech receptors in muscle) are stretched -> nerve impulse generated -> monosynaptic pathway (i.e. only one sensory and one motor neurone involved) -> quadracepts contract

- a reciprocal stretch reflex causes the anatognistic muscle (the hamstrings) to relax -> "inhibitory" effect caused by relay neurone (thus 3 neurones involved in the reflex)

- tension in tendons increase when quads. contract -> detected by "golgi tendon organ" -> causes a inhibitory nerve impulse (and so has 3 neurones involved in the reflex) -> stops the contraction of muscle (otherwise tendon may break)

- i was told that the golgi tendon organ can act like feedback mechanism... in the case of the knee-jerk the golgi tendon organ act as a negative feedback (decrease muscular contraction in a reflex)... can anyone think of any instance where golgi tendon organ reflex have a positive feedback (i.e. would increase muscular contraction in a reflex)?

- also, what is the answer to "explain the role of descending supraspinal pathways in controlling reflex excitability?"...

cheers

Reply 1

Comp_Genius

this so-called monosynaptic reflex actually involves more than one neurones: many IA afferents (spindle receptors) innervate one motor neurone.

The descending pathway modulates reflexes (I haven't done this in detail yet, this is from my own reading) - if you have a upper motor neuron (UMN) lesion, then there is loss of inhibition from the brain - thus you get hyperreflexia.

Reply 2

Revenged

Photios

The descending pathway modulates reflexes (I haven't done this in detail yet, this is from my own reading)

ok, i guess this is something to do with brain function acting on reflexes...

e.g. if you flick your nose near your eye, you don't blink as the protective reflex is inhibited by higher brain function... but if someone else flicks your nose near your eye, you'll blink...