W3 Spinal Reflex Postlab

alpha motor neurons

Synapse with muscle fibers and cause contraction

Alpha motor neurons are always

Excitatory(cause contraction)

reciprocal inhibition

When one muscle group is reflexively activated, opposing muscles are inhibited

importance of reciprocal inhibition

Prevents muscles from working against each other and allows for smooth muscle movement

Reciprocal inhibition occurs via

Inhibitory interneurons

Supraspinal descending inhibitory motor pathways

Prevent exaggerated reflexes by inhibiting spinal reflex neurons

Where do the signals in supraspinal descending inhibitory motor pathways originate

The brain

Jendrassik maneuver

Elicits exaggerated spinal reflex by decreasing inhibitory influences of descending pathways

What is the difference between an ipsilateral reflex and a contralateral reflex?

When a reflex action occurs on the same side of the body as the stimulus, it is considered an ipsilateral reflex

When the reflex action occurs on the opposite side of the body as the stimulus, it is considered a contralateral reflex

the stronger the percussion hammer taps on the patellar tendon, the greater the reflex contraction of quadriceps femoris. explain.

More stretch receptors are stimulated, causing greater activation of more motor neurons(leading to stronger contraction of quadriceps femoris)

The Jendrassik maneuver may exaggerate spinal reflexes such as the patellar reflex. Explain why using your data.

Jendrassik maneuver reduces inhibitory interneuron activity causing stronger reflexes. This was seen in the data as larger EMG amplitude was observed during Jendrassik maneuver

When a physician elicits the patellar reflex, what physiological activities are being examined? List at least 2.

Examines function of muscles and peripheral nerves

Explain the two pathways by which the Jendrassik maneuver facilitates alpha motor neuron output.

Pathway one: voluntary muscle contraction decreases activity of inhibitory interneurons, increasing activity in alpha motor neurons

Pathway two: voluntary muscle contraction increases excitatory inputs from supraspinal centers to spinal motor neurons. Increased excitatory inputs makes alpha motor neurons more responsive

How do voluntary reaction times of the involuntary reflex and voluntary activation of skeletal muscle compare?

Voluntary reaction times are much slower than involuntary reflexes

monosynaptic reflex

Reflex pathway with only one synapse between the sensory and motor neurons