MCAT- Muscle contraction and Reflexes

What determines the strength of a muscle contraction?

- The amount of overlap between actin and myosin

- increasing the actin-myosin overlap in a fiber increases the strength of contraction up to a point

What is the optimal contraction strength of a muscle?

- Occurs at mid-range fiber lengths with moderate amounts of overlap

Which type of muscle fibers have stronger contractions?

- Wider muscle fibers can have stronger contractions compared to thinner fibers because they contain more myofibrils

Which type of muscle fibers can perform more work?

- Linger muscle fibers can perform more work compared to shorter ones of the same diameter because longer fibers contract over a greater distance

What can increase contraction strength of a muscle?

- recruiting more motor units increases the number of fibers involved in a muscle contraction which increases contraction strength

What does contraction velocity increase?

- when contraction velocity increases, the power of the contraction increases

What controls muscle contractions?

- The movement of calcium ions into and out of the sarcoplasmic reticulum

- integral to the formation and breakdown of myosin- actin bridges

How is a muscle twitch propagated?

- A twitch is a result of a single contraction that comes from a sing action potential from a motor neuron

What is summation, and how does it relate to muscle contractions?

- summation occurs from repeated action potentials which leads to stronger muscle contractions

What is tetanus?

- Continuous muscle contraction without relaxation that is caused by continuous action potentials

What is a monosynaptic reflex arc?

A reflex which only involves two neurons and one synapse

- occurs when a sensory neuron transmits a message directly to a motor neuron in the spinal cord to elicit a repsonse

What is a knee-jerk reflex?

A reflex action that straightens the leg when the tendon below the knee cap is tapped.

- example of a monosynaptic reflex arc

What is a polysynaptic reflex arc?

- a reflex arc that has one or more interneurons in the spinal cord between the sensory neuron and the motor neuron cell body (also in spinal cord)

What is a withdrawal reflex?

An unconscious reaction to a painful stimulus. A sensory neuron synapses on inter neurons which synapse on motor neurons (more than one synapse occurs)

- example of a polysynaptic reflex are

- how is the brain involved in reflex responses?

- The brain is able to moderate reflex responses via connections to interneurons or motor neurons in the spinal cord