Spinal Reflexes

Question 1

What is a reflex?

Answer 1

rapid, involuntary response, yet stereotyped and co-ordinated response to a sensory stimulus

• usually involve muscle contraction but can involve granular responses (eg. sucking causes lactation)
• can be learned (pavlovian)

Question 2

What are somatic reflexes?

Answer 2

those in somatic nervous system, they are also called spinal reflexes since they involve spinal cord circuitary

Question 3

Spinal reflexes
spontaneous or not?
slow or fast?

Answer 3

require stimulation ( not spontaneous )  - need sensory input
are quick - suggests few synapses are involved
involuntary and automatic (often only aware once they've happened) = suggests little input from higher centres (even with spinal cord severed = reflexes still intact)
stereotyped - occur in same way each time - underlying circuitry very simple

Question 4

Patellar reflex -root?

why do we have it?

Answer 4

monosynaptic
sensory stimulus, dorsal root, direct synapse to motor neuron, to ventral root (spinal nerve)
(Motor neuron stimulates extensor muscle contraction)
= The Stretch(myotactic) reflex
- NOT a response to pain
- tap on knee stretches the thigh extensor muscle and associated tendon and sets in motion a process to ‘correct’ stretching = v important in maintaining body posture
(part of your proprioceptive system)

Question 5

Example of reflex when pouring drink;

Answer 5

1- sensory fibres= sense muscle stretch and send signals to spinal cord
2- Direct monosynaptic connection to motor neuron fires action potential which contracts bicep muscle
3- Simultaneously, a distinct connection to an inhibitory interneuron inhibits the firing of motor neurons connected to triceps = relaxing antagonistic muscle
= known as ‘Reciprocal Inhibition’

Question 6

What is a muscle spindle?
found?
innervated by?

Answer 6

detects muscle stretch = a sensory receptor

• it is a proprioceptor= sense organs that monitor the position and movement of the body
• found in most striated muscles (particularly abundant in muscles that involve fine motor control)
• innervated by: Ia sensory fibres - they provide feedback to motor neurons innervating the surrounding muscle (called alpha motor neurons) on the amount of stretch that is occuring
• • Muscle spindle has muscles!! - they are also innervated by axons from gamma motor neurons
• these stimulate the intrafusal (muscle) fibres to adjust the tension in the spindle, as the extrafusal (muscle) fibres contract= this is done so that the muscle spindle is never slack

Question 7

What is kinesthesia?

Answer 7

sense of your body moving in space

so, if proprioception goes, so does kineasthesia

Question 8

Golgi Tendon Organ
what is it?
how does it detect muscle tension?
negative feedback?

Answer 8

another kind of proprioceptor
it detects muscle tension via muscle contration (NOT muscle stretch, this is muscle spindles)
- activation of GTO sensory (Ib) afferents = activation of inhibitory interneurons, which in turn, inhibit alpha motor neurons that innervate the same muscle
Due to this = negative feedback - regulates the muscle tension and protects the muscle (and tendon) from damage
- regulates muscle contraction to regulate muscle length(similar to muscle spindle) but prevents muscle contracting too much
This and the stretch reflex= under control of higher centres

Question 9

Flexor (withdrawal) reflex

Answer 9

quick contraction of flexor muscles to withdraw a limb from an injurious stimulus eg. heat
- results from activation of nociceptive sensory receptors or nociceptors
- it is a polysynaptic reflex (despite speed of response) - activation of multiple excitatory interneurons sustains the reponse
= ‘parallel-after-discharge circuit’
eg input to output has 3 pathways with different number of synapses so the effect can occur quickly (via fewest synapses pathway) and then sustained

Question 10

Flexor (withdrawal) reflex II

Answer 10

inhibitory interneurons are also activated to relax exterior muscles ( reciprocal inhibition again )
-because rapid withdrawal of limb may cause imbalance = flexor reflexes often include a contralateral element–> this crossed extensor reflex provides postural support during limb withdrawal

Question 11

Simple reflexes may underlie repetitive behaviour

Answer 11

in individual limbs, extensors and flexors are alternatively active or inhibited as animal walks
-brain and spinal cord connection severed = coordination between legs still continues

Question 12

In simple organisms what is an important feature?

Answer 12

inhibition across the midline (brainstem inputs)