06.3C U6P1 (PART C) Stimulation & Contraction of Skeletal Muscle

Dendrites

Branch-like extensions of the neuron that detect signals from other neurons and conduct impulses toward the cell body

Cell body

The part of a neuron that contains the nucleus and produces the energy needed for the activity of the cell.

Axon

Long extension of a neuron that conducts impulses away from the cell body to the axon terminals

Axon terminals

Structures at the end of axons that secrete neurotransmitters when stimulated by the action potential

Neurotransmitter

Chemicals released by neurons that stimulate other neurons, muscles, or glands.

Resting Membrane (Neuron)

A state in neurons that results when sodium-potassium pumps found in the membrane actively move 3 sodium ions out of the cell and 2 potassium into the cell that polarizes the membrane so that there are more positive ions outside the cell than inside the cell

Stimulated Membrane (Neuron)

A state in neurons that results when a neurotransmitter like acetylcholine binds to a receptor on a sodium channel causing it to open

Stimulated Membrane (Muscle)

Depolarized Membrane (Neuron)

A state in neurons that results when sodium channels open allowing sodium to rush INTO the cell via facilitated diffusion that causes the membrane to become more positive on the inside than on the outside

Depolarized Membrane (Muscle)

A state in muscle cells that results when sodium channels open allowing sodium to rush INTO the cell via facilitated diffusion that causes the membrane to become more positive on the inside than on the outside

Propagation of an Action Potential (Neuron)

Occurs when sodium ions flood into a neuron triggering the opening of additional sodium channels along the membrane resulting in a more positive charge inside the cell than outside the cell

Propagation of an Action Potential (Muscle)

Occurs when sodium ions flood into the muscle fiber triggering the opening of additional sodium channels along the membrane resulting in a more positive charge inside the cell than outside the cell

Repolarized Membrane (Neuron)

A state in neurons that results when sodium channels close and potassium channels open allowing potassium to rush OUT of the cell via facilitated diffusion that causes the membrane to once again become more positive on the outside than the inside

Repolarized Membrane (Muscle)

A state in muscles that results when sodium channels close and potassium channels open allowing potassium to rush OUT of the cell via facilitated diffusion that causes the membrane to once again become more positive on the outside than the inside

Neuromuscular Junction

The synapse between a motor neuron and a skeletal muscle cell

Synapse

The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron

Acetylcholine

Neurotransmitter that diffuses across the neuromuscular junction and binds to receptors on the sarcolemma to produce an impulse along the muscle cell

Calcium ions

A type of ion that is responsible for initiating the release of neurotransmitters from synaptic vesicles and also helps to initiate muscle contractions

Acetylcholinesterase

An enzyme that breaks down acetylcholine which terminates the stimulation of the muscle

Actin

A thin globular protein that consists of two strands of proteins wound around each other (look like two strands of pearls)

Myosin

A thick globular protein with paddle-like extension that contains binding sites for actin and ATP

Troponin

A globular protein that is associated with tropomyosin as part of the thin filament of the sarcomere that covers the binding sites on actin; provides a binding site for calcium ions which cause tropomyosin to swivel and expose active sites on actin

Tropomyosin

A regulatory protein that, on a resting muscle fiber, covers binding sites along actin, preventing actin and myosin from interacting

Sliding Filament Theory of Muscle Contraction

A widely accepted theory that states that the cytoplasm of skeletal muscles have thousands of myofibrils that consist of thick and thin filament that slide past one when muscles contract

ATP (Muscle Contraction)

A compound composed of adenosine and three phosphate groups that supplies energy for many biochemical cellular processes like muscle contraction by undergoing enzymatic hydrolysis.

Cross bridge cycle

A series of four steps that results in the shortening of the sarcomere when the muscle is stimulate and ATP is present. Four steps include cross bridge formation (myosin head attaches to an actin myofilament , power stroke (myosin head pivots and pulls actin), cross bridge detachment (ATP binds to myosin), cocking of myosin head (hydrolysis of ATP)

Cross bridge formation

High-energy myosin head attaches to active site on the thin filament (actin)

Working (power) stroke

Myosin head pivots and pulls actin toward M line

Cross bridge detachment

ATP attaches to myosin head and the cross bridge detaches

"Cocking" of the myosin head

Energy from hydrolysis of ATP cocks the myosin head into the high-energy state