unit 3

agonist

the primary muscle responsible for producing a particular movement at a joint

antagonist

a muscle that opposes the action of the agonist, helping control or refine the movement

synergist

a muscle that assists the agonist in performing its actin

fixator

a muscle that stabilizes a joint or bone so taht the agonist can function effectively

origin

the fixed attachment point of a muscle, typically on the proximal or less mobile bone

insertion

the moveable attachment point of a muscle, usually on the distal or more mobile bone

lever system

a mechanical model describing how bones and muscles interact to create movement, with classes based on force, load, and fulcrum position

sarcomere

the functional unit of contraction in a muscle fiber, made up of overlapping thick and thin filaments

myofibril

bundles of protein filaments (myofilaments) inside muscle fibers, responsible for contraction

myosin

a motor protein that forms thick filaments; it binds to actin and pulls during contraction

actin

a structural protein forming thin filaments; it contains binding sites for myosin

troponin

a regulatory protein on thin filaments that binds calcium and initiates the movement of tropomyosin to expose actin’s binding sites

tropomyosin

a regulatory protein that blocks actin’s binding sites in relaxed muscle; it shifts when troponin binds calcium

sarcoplasmic reticulum (sr)

specialized smooth endoplasmic reticulum in muscle cells that stores and releases calcium ions, triggering contraction

t-tubules

invaginations of the sarcolemma that help spread the action potential deep into the muscle fiber

muscle tension

the force generated by muscle fibers during contraction, important in both movement and clinical assessment of functione

excitability

the ability of muscle cells to respond to a stimulus, typically from a neuron; essential for communication between nervous and muscular systems

neuron

a specialized cell that sends and receives electrical signals in the nervous system

neuroglia

supporting cells that protect, nourish, and insulate neurons; aka glial cells

central nervous system

the brain and spinal cord; processes information and makes decisions

peripheral nervous system

all the nerves outside the cns; connects the brain and spinal cord to the rest of the body

resting membrane potential

the electrical charge difference across a neuron’s membrane when it is not sending a signal

action potential

a fast electrical signal that travels along a neuron’s axon to communicate with other cells

voltage-gated ion channel

a protein in the neuron’s membrane that opens or closes in response to changes in voltage

synapse

the connection between two neurons (or a neuron and another cell) where signals are passed

neurotransmitter

a chemical messenger that carries a signal across a synapse to the next cell

myelin

a fatty covering around some axons that speeds up the movement of electrical signals