The HEAT basketball team has called you up to join them team (due to injuries, t
ID: 40097 • Letter: T
Question
The HEAT basketball team has called you up to join them team (due to injuries, they are desperate). In order to be deemed fit to play, you must have a physical examination. During your physical, your reflexes are examined particularly your knee jerk reflex. Describe the actions that occur in your body to drive the monosynaptic reflex. What does the reflex entail, and what are the specific actions that take place to drive the muscle contraction? Make sure to include the specifics about the involvement of, and all steps including, Ca2+ and ATP in promoting the muscle contraction.
Explanation / Answer
The knee-jerk reflex is called that because it is a reflex most commonly tested by tapping on the patellar tendon and seeing if the leg kicks out, or jerks, in response.
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus . When a person accidentally touches a hot object, they automatically jerk their hand away without thinking. A reflex does not require any thought input.
The path taken by the nerve impulses in a reflex is called a reflex arc. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs.
When a reflex arc consists of only two neurons in an animal (one sensory neuron, and one motor neuron), it is defined as monosynaptic. Monosynaptic refers to the presence of a single chemical synapse. In the case of peripheral muscle reflexes (patellar reflex, achilles reflex), brief stimulation to the muscle spindle results in contraction of the agonist or effector muscle.
When the patellar tendon is tapped just below the knee, the patellar reflex is initiated and the lower leg kicks forward (via contraction of the quadriceps). The tap initiates an action potential in a specialized structure known as a muscle spindle located within the quadriceps.
This action potential travels to the spinal cord, via a sensory axon which chemically communicates by releasing glutamate onto a motor nerve. The result of this motor nerve activity is contraction of the quadriceps muscle, leading to extension of the lower leg at the knee.
The sensory input from the quadriceps also activates local interneurons that release the inhibitory neurotransmitter glycine onto motor neurons of antagonist muscle/s, blocking the innervation of these antagonistic (hamstring) muscles. The relaxation of the opposing muscle facilitates (by not opposing) the extension of the lower leg.
Phases of a muscle contraction
A muscle contraction in response to a single nerve action potential is called a twitch contraction.
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