TOPIC 10

Flashcards covering key terms and definitions related to skeletal muscle, types of muscle, contraction mechanisms, and muscle physiology.

Skeletal Muscle Characteristics

• Large,

• multinucleated cells with voluntary control;

• looks striated due to sarcomeres.

Cardiac Muscle Characteristics

• Branched cells connected by gap junctions,

• involuntary control;

• also looks striated.

Smooth Muscle Characteristics

Small, spindle-shaped cells with involuntary control; not striated but contains contractile proteins.

Muscle Fiber

• A single muscle cell

• contains myofibrils of contractile proteins.

Sarcoplasmic Reticulum (SR)

Specialized smooth ER in muscle that stores large amounts of calcium.

Transverse Tubules (T-tubules)

• Tubes of cell membrane

• propagate action potential into the interior of the muscle fiber.

Cross-Bridge

Myosin head bound to actin during muscle contraction.

Excitation-Contraction Coupling

The process by which an action potential results in muscle contraction.

Acetylcholine (ACh)

A neurotransmitter released at the neuromuscular junction, facilitating muscle contraction.

Motor Unit

A motor neuron and all the muscle cells its axon terminals synapse with.

Passive Tension

The tension produced by a muscle when it returns to its resting length after shortening or stretching.

Active Tension

The tension produced by cross-bridge cycling during muscle contraction.

Fatigue

• Reduced tension in a muscle from repeated stimulation,

• leading to decreased shortening velocity

• slower relaxation.

Myasthenia Gravis

An autoimmune disease where antibodies destroy nicotinic ACh receptors on skeletal muscle cells.

Pacemaker Potential

depolarization to threshold in some smooth muscle cells.

Smooth Muscle Contraction Mechanism

Calcium binds to calmodulin, activating MLCK, which phosphorylates myosin allowing it to bind to actin.

Length-Tension Relationship

The influence of the resting length of a sarcomere on the amount of tension it can produce.

Twitch Contraction

• mechanical response of muscle to one action potential,

• consisting of latent,

• contraction,

• relaxation phases.

Concentric Contraction

where the muscle shortens while producing tension.

Eccentric Contraction

the muscle lengthens while producing tension.

Isometric Contraction

where tension changes but muscle length remains the same.

Glycolysis

A metabolic pathway that converts glucose into ATP, faster but with low yield.

Oxidative Phosphorylation

A metabolic process that uses oxygen to produce high ATP yield from fatty acids and amino acids.

Rigor Mortis

when myosin does not detach from actin due to lack of ATP, resulting in sustained contraction.

Neuromuscular Junction (NMJ)

The site where a motor neuron connects with a muscle fiber, enabling muscle contraction.

Synaptic Cleft

• narrow space between motor neuron and muscle fiber

• located the neuromuscular junction,

• neurotransmitters are released.

Acetylcholine Release

• being discharged from the motor neuron into the synaptic cleft

• triggering muscle contraction.

Nicotinic Acetylcholine Receptors

• located on the muscle cell membrane

• interact with acetylcholine,

• initiating muscle depolarization.

End Plate Potential (EPP)

• muscle fiber depolarization

• occurring at the neuromuscular junction

• result of Ach binding to its receptors.

Muscle Fiber Action Potential

The electrical impulse generated in the muscle fiber membrane following the end plate potential, leading to muscle contraction.

Cholinesterase

• An enzyme

• located in the synaptic cleft

• degrades acetylcholine,

• increasing the signal for muscle contraction.

Botulinum Toxin

A neurotoxin that obstructs the release of Ach at the neuromuscular junction, resulting in paralysis.

Curare

A toxin derived from plants that inhibits nicotinic acetylcholine receptors, causing muscle paralysis by blocking muscle fiber depolarization.

Single-Fiber Contraction

• an individual muscle fiber to a single action potential,

• characterized by a specific tension output.

Twitch

The mechanical response of a muscle fiber to a single action potential, consisting of latent, contraction, and relaxation phases.

Latent Period

The brief delay between the arrival of an action potential at the muscle fiber and the beginning of contraction.

Contraction Phase

• muscle tension increases as myosin heads bind to actin and the sarcomere shortens.

Relaxation Phase

The period following contraction when calcium is reabsorbed and the muscle fiber returns to its resting state.

Summation

• The increase in muscle tension

• occurs when a fiber is stimulated before it has completely relaxed from a previous contraction.

Tetanus

• A sustained muscle contraction

• from the rapid stimulation of a fiber,

• leading to maximum tension output.

Motor Unit Recruitment

The process of increasing the number of active motor units to enhance muscle tension output during contraction.