Spinal Reflexes Flashcards
What are the 4 basic functions of spinal reflexes?
- Restoration of muscle length after a stretch and adjustment of muscle tension.
- Maintenance of muslce tone for holding a limb in place when weight is placed upon it.
- Withdrawal of limb from painful stimulus.
- Maintenance of posture and balance.
Can reflexes be modified?
Yes - they are not fixed responses that occur exactly the same way every time
What are the 5 components of a spinal reflex?
- What is a homonymous muscle?
- Synergistic muscle?
- Antagonistic muscle?
- Contralateral muscle?
Flexors […] the angle of a joint and extensors […] the angle
Reduce; increase
Sensory fibers travel […] of the muscle spindle and motor fibers travel […] the muscle spindle
Out of
Into
- […] innervate the extrafusal muscle fibers and acivation of the neurons causes […].
- […] innervate the intrafusal muscle fibers to cause […] of the […]
- Alpha motor neurons; Contraction of the muscle
- Gamma motor neurons; contraction; ends of the fiber
What is the effect of intrafusal muscle fiber ends contracting?
Alters sensativity of muscle spindle so it can respond to range of muscle lengths
- What types of afferent gamma motor neurons innervate the intrafusal muscle fiber?
- What types of afferent gamma motor neurons innervate the golgi tendon organ?
- Type 1a, Type 2
- Type 1b
Types of cells that may be involved in a spinal reflex
What is a renshaw cell?
A neuron that is excited by an alpha motor neuron and then inhibits the neuron that excited it. Help shut down reflexes
What do muscle spindles detect?
What do golgi tendon organs detect?
Changes in length
Changes in tension
When talking about reflexes, the body is responding to a stimulus. Where can the receptors for that stimulus be located?
Skin, muscle spindle, golgi tendon organ
Inhibitory interneurons release […] as a neurotransmitter, whereas excitatory interneurons release […].
GABA
Glutamine
Describe what happens in the deep stretch reflex and why this is called reciprocal inhibition.
Is the stretch reflex mechanism unique to the patellar ligament or is this how all muscle stretch reflexes work?
All muscle stretch reflexes work in this manner
What spinal levels are tested by the following reflexes:
- Ankle
- Knee
- Brachioradialis
- Biceps
- Triceps
- S1
- L2 - L4
- C5 - C6
- C5 - C6
- C6 - C7
In addition to tapping tendons, stretch reflexes allow us to not drop things when additional weight is added (i.e. not drop a tray when someone places a pitcher of beer on it). Explain why this is.
What is the role of the golgi tendon organ in the stretch reflex?
The golgi tendon organ is activated by changes in tension of the stretched muscle. In order to protect our muscles from contracting too much, the golgi tendon organ is activated by muscle tension to turn off the reflex response. The golgi tendon organ sends an excitatory signal via afferent 1b fibers to the spinal cord (via DRG and dorsal horn) where it synapses on an inhibitory interneuron that then synapses on an alpha motor neuron to the homonymous muscle, signaling it to stop contracting. The afferent 1b is bifurcated, so it also synapses on an excitatory interneuron that activates an alpha motor neuron for the antagonistic muscle.
If a person has hyperreflexia and spasticity, what would that tell you clinically?
It would indicate possible damage to descending upper motor neurons
If a person has hyporeflexia, what does that tell you clinically?
That they may have damage to a lower motor neuron
Describe the reflex that results to withdraw your limb from a painful stimulus.
Similar to stretch reflex except there is an interneuron between both bifurcations of the sensory neuron, one that excites a flexor to remove the limb and one that inhibits an extensor.
When withdraw your foot from a painful stimulus, there is another reflex that occurs in the opposing leg to help you balance on that leg alone. Describe this reflex, called the crossed extensor reflex.
True or false: cranial nerves are lower motor neurons.
True
What is the role of the brain in reflexes?
The brain is not needed for reflexes to occur. However, it must not be forgotten that the afferent neurons do also still go up to the brain in the ascending sensory pathways. As such, the brain can mostly play a role modulating reflexes.
