One motor neuron and all the muscle fibers it innervates.
What is the importance of the motor unit?
Important for the regulation of muscle contraction.
What does the motor axon do?
Area from cell body out to terminal lens to each fiber. Portion of neuron where AP is transmitted.
What are the components of the motor neuron?
• Soma - aka cell body; control center of the cell
• Axon hillock - where AP is initiated from cell body to muscle cell.
• Dendrites - extensions coming off the soma; the cell is innervated in neuron by the dendrite.
What covers the axon and what are its characteristics?
Axon covered with innervating sheath called myelin sheath which is a lipid based layer that allows the AP to be transmitted faster.
What does the Node of Ranvier do?
Along the axon there are small openings, Nodes of Ranvier, are openings in the insulated sheath where AP can move from one node to another.
What is Saltatory Conduction?
Propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials without needing to increase the diameter of an axon
What is a bouton and what is the importance of this area?
AKA terminal end of axon; is where signal from the nerve is transmitted across a gap, synapse, with signal then being picked up by muscle cell.
How does signal transduction work in the motor neuron?
Where it changes from an electrical signal to a chemical signal at the synapse and as muscle fiber picks up the signal it becomes electrical again.
What is the difference between precise and less precise muscles?
The control of a muscle depends on the number of muscle fibers within each motor unit. Muscles that function with great precision, like eye muscles, can have motor units with as few as one muscle fiber per motor neuron. Whereas in contrast, the quadriceps muscle group which moves the leg with less precision can have several hundreds fibers serve one motor neuron.
What neurotransmitter is released by the arrival of an AP, and where does it diffuse through? What does it excite?
Arrival of AP at nerve terminal causes release of neurotransmitter, acetylcholine, which diffuses across the neuromuscular junction, causing excitation of the sarcolemma.
What is the all-or-nothing principle?
All of the fibers in the motor unit contract and develop force at the same time. Stronger AP cannot produce a stronger contraction. This is known as the all-or-nothing principle of muscle.
Activation of the sarcolemma results in the release of what? And what does it cause?
Activation of the sarcolemma results in the release of Ca+ within fiber, and contraction proceeds.
What happens if a 2nd twitch comes from motor neuron before the fiber relaxes?
If a second twitch comes from the motor neuron before the fiber relaxes, force from the 2 twitches summates, and resulting force is greater than that produced by single twitches
The stimulus may be delivered at so high a frequency that the twitches begin to merge and eventually completely fuse, resulting in tetanus.
What is the fast-twitch muscle?
Develops force and also relaxes rapidly and thus has a shorter twitch time
What is the slow-twitch muscle?
Develop force and relax slowly and have a longer twitch time.
What is a Type I fiber and what type of people is it normally found in?
Slow twitch; distance athletes
Which Type of fiber is considered a hybrid and why?
Type IIb is a fast twitch, very powerful fiber where once you start training, they begin to disappear. Also considered to be a hybrid fiber.
Which type of fiber is found in highly fit people?