Lecture 12 Notes

Motor Unit

_______ consists of one motor neuron and all the skeletal muscle fibers it controls.

Neuromuscular Junction

The synapse between the axon terminal of a motor neuron and a skeletal muscle cell.

Excitation

The first phase of muscle contraction, where an action potential triggers the release of acetylcholine at the neuromuscular junction.

Excitation-Contraction Coupling

The process that links the electrical signals from the nerve to the mechanical contraction of muscle.

Contraction Cycle

The sequence of events that occur during muscle contraction, which includes crossbridge formation, power stroke, crossbridge detachment, and recovery stroke.

Sliding Filament Theory

The theory that explains muscle contraction as the sliding of actin over myosin filaments without changing their lengths.

Acetylcholine (ACh)

The neurotransmitter that is released at the neuromuscular junction to stimulate muscle contraction.

Calcium Ions (Ca²⁺)

Essential for muscle contraction; they bind to troponin, causing tropomyosin to move and expose active sites on actin.

Troponin

A protein on the actin filament that binds calcium and triggers muscle contraction when calcium is present.

Tropomyosin

A protein that blocks the active sites on actin filaments; it moves away when calcium binds to troponin.

Crossbridge

The formation between myosin heads and active sites on actin filaments during muscle contraction.

Power Stroke

The action that occurs when myosin heads pivot and pull actin filaments toward the M line of the sarcomere.

ATP (Adenosine Triphosphate)

The energy source required for muscle contraction; it binds to myosin heads for crossbridge detachment.

Spastic Paralysis

A condition where muscles contract uncontrollably due to issues with neurotransmitter regulation, like in the case of organophosphate poisoning.

Flaccid Paralysis

Loss of muscle tone leading to limp muscles due to failure of the acetylcholine release or receptor blockage.

Myofibril

The long, thread-like structures within muscle cells composed of overlapping actin and myosin filaments.

End Plate Potential

The graded potential that occurs at the motor end plate, resulting from the binding of acetylcholine.

Action Potential

A rapid change in membrane potential that is propagated along the muscle cell membrane, initiating contraction.

Z Line

The boundary of a sarcomere where actin filaments are anchored.

H Zone

The area within a sarcomere where only myosin filaments are present; it narrows during contraction.

Somatic Nervous System

The division of the nervous system responsible for controlling voluntary movements of skeletal muscles.

Acetylcholinesterase

An enzyme that breaks down acetylcholine in the synaptic cleft, stopping muscle stimulation.

Gated Sodium Channels

Ionic channels that open in response to membrane depolarization, allowing sodium to enter the muscle cell and initiate action potentials.

Gastric Nemesis

Referring to the gastrocnemius muscle, which has large motor units and is capable of generating significant force.