Muscle Physiology and Motor Unit Mechanics: A Comprehensive Quizlet

What is the term for the soma of a motor neuron?

The soma of a motor neuron is called a motor fiber.

What is a motor unit?

A motor unit is a single motor fiber and all the muscle fibers it innervates.

How are muscle fibers arranged in a motor unit?

The muscle fibers of a single motor unit are dispersed throughout a muscle.

What is the average number of muscle fibers innervated by each motor neuron?

On average, about 200 muscle fibers are innervated by each motor neuron.

What type of motor unit is found in eye movement muscles?

Small motor units with 3 to 6 muscle fibers per neuron are found in eye movement muscles.

What type of motor unit is found in the gastrocnemius?

Large motor units with about 1,000 muscle fibers per neuron are found in the gastrocnemius.

What is the NeuroMuscular Junction (NMJ)?

The NMJ is the synapse where a nerve fiber meets a muscle fiber.

What is a synaptic knob?

A synaptic knob is a swelling at the end of a nerve fiber that contains synaptic vesicles.

What neurotransmitter is released at the NMJ?

Acetylcholine (ACh) is released into the synaptic cleft.

What enzyme breaks down acetylcholine in the NMJ?

Acetylcholinesterase (AChE) breaks down ACh.

What is the resting membrane potential (RMP) of a muscle cell?

The resting membrane potential of a muscle cell is about -90 mV.

What occurs during depolarization of a muscle cell?

During depolarization, Na+ diffuses into the cell, making the inside positive.

What follows depolarization in muscle cells?

Repolarization follows, where K+ rushes out of the cell, turning the inside negative again.

What is the term for the wave of action potentials along a nerve fiber?

A nerve impulse or nerve signal.

What is excitation in muscle contraction?

Excitation is the process where action potentials in the nerve fiber lead to action potentials in the muscle fiber.

What triggers the release of ACh into the synaptic cleft?

Calcium ions (Ca2+) entering the synaptic knob trigger the release of ACh.

What is end-plate potential (EPP)?

EPP is the rapid fluctuation in membrane voltage at the motor end plate.

What is excitation-contraction coupling?

It refers to the events linking action potentials on the sarcolemma to activation of the myofilaments.

What role does calcium play in muscle contraction?

Calcium binds to troponin on thin filaments, exposing active sites for myosin binding.

What is the power stroke in muscle contraction?

The power stroke is when myosin releases ADP and phosphate, pulling the thin filament.

What happens when a muscle fiber relaxes?

A muscle fiber returns to its resting length after nerve signals stop and ACh is broken down.

What is the length-tension relationship in muscle fibers?

It describes how the amount of tension generated depends on the muscle's initial length.

What is the optimum resting length of a muscle?

The length at which a muscle can respond with the greatest force.

What happens to a muscle fiber when it is overly contracted?

The contraction is weak because thick filaments cannot contract farther than the Z discs.

What is the role of antagonist muscles in muscle relaxation?

Antagonist muscles help lengthen the muscle during relaxation.

What is the recovery stroke in muscle contraction?

The recovery stroke is when myosin hydrolyzes ATP and re-***** to attach to a new active site.

What is a myogram?

A chart of stimulation and muscle contraction recorded from a nerve-muscle preparation.

What is the minimum voltage necessary to generate an action potential called?

Threshold voltage.

What triggers the release of Ca2+ into the cytosol?

An action potential.

What is the quick cycle of contraction and relaxation called?

A twitch.

What is the delay between the onset of stimulus and twitch onset called?

Latent period.

What is the force generated before muscle shortening called?

Isometric tension.

What phase follows the latent period in a twitch?

Contraction phase.

What happens to muscle tension during the relaxation phase?

Muscle tension declines as Ca2+ levels fall.

What is the phenomenon called when higher voltages excite more nerve fibers?

Multiple motor unit (MMU) summation.

What is the staircase phenomenon in muscle twitches?

Treppe, where each twitch develops more tension than the previous one.

What is temporal summation?

When each new stimulus arrives before the previous twitch is over, generating higher tension.

What is the state of sustained fluttering contraction called?

Incomplete tetanus.

What is the term for a smooth, prolonged contraction?

Complete tetanus.

What is isotonic contraction?

Contraction with a change in length but no change in tension.

What type of contraction occurs without a change in muscle length?

Isometric contraction.

What is concentric contraction?

Muscle shortens as it maintains tension.

What is eccentric contraction?

Muscle lengthens as it maintains tension.

What are the two main sources of ATP synthesis in muscles?

Anaerobic fermentation and aerobic respiration.

What does anaerobic fermentation produce as a toxic end product?

Lactic acid.

What is the primary energy source for resting muscles?

Aerobic respiration of fatty acids.

What system provides energy for short bursts of intense activity?

Phosphagen system.

What enzyme transfers phosphate from one ADP to another to form ATP?

Myokinase.

What is creatine kinase's role in ATP production?

It donates phosphate from creatine phosphate (CP) to ADP to make ATP.

What is the glycogen-lactic acid system?

The pathway from glycogen to lactic acid that produces ATP for 30 to 40 seconds of maximum activity.

What happens to muscles as the phosphagen system is exhausted?

They shift into anaerobic fermentation for short-term energy.

What factors affect twitch strength?

Stimulation frequency, Ca2+ concentration, muscle stretch, temperature, pH, and muscle fatigue.

What is the primary energy source for prolonged exercise after 40 seconds?

Aerobic respiration

What is muscle fatigue?

The progressive weakness and loss of contractility resulting from prolonged use of the muscles.

What are some causes of muscle fatigue?

Accumulation of K+, ADP/Pi, decreased pH, fuel depletion, electrolyte loss, and CNS fatigue.

What type of muscle fibers are classified as slow oxidative (SO) fibers?

Red, type I fibers with abundant mitochondria, myoglobin, and blood capillaries.

What are characteristics of fast glycolytic (FG) fibers?

They are adapted for quick responses, rich in enzymes for anaerobic metabolism, and produce short twitches.

What distinguishes red muscles from white muscles?

Red muscles are composed mainly of slow oxidative fibers, while white muscles are composed mainly of fast glycolytic fibers.

What factors determine muscular strength?

Muscle size, fascicle arrangement, motor unit size, multiple motor unit summation, and the length-tension relationship.

What is hypertrophy in muscle growth?

The increase in muscle fiber size primarily due to the thickening of myofibrils.

How does endurance exercise affect muscle fibers?

It increases the number of mitochondria, glycogen stores, and blood capillary density in slow-twitch fibers.

What is cross-training?

A training method that incorporates elements of both resistance training and endurance training.

What are the characteristics of smooth muscle myocytes?

They are fusiform, have one nucleus, and lack striations.

What are varicosities in smooth muscle?

Beadlike swellings along autonomic nerve fibers that release neurotransmitters to stimulate smooth muscle.

What are the two functional types of smooth muscle?

Multiunit smooth muscle and single-unit (unitary) smooth muscle.

Where is multiunit smooth muscle found?

In large arteries, pulmonary air passages, piloerector muscles, and the iris.

What is the contraction mechanism in smooth muscle?

Contraction is triggered by Ca2+ from extracellular fluid and involves sliding of thin filaments over thick filaments.

How does smooth muscle differ from skeletal muscle in terms of ATP requirement?

Smooth muscle requires 10 to 300 times less ATP than skeletal muscle to maintain the same tension.

What happens to smooth muscle cells during contraction?

They pucker and twist, similar to wringing out a wet towel.

What is the role of the sarcoplasmic reticulum in smooth muscle?

It is scanty, and most Ca2+ for contraction comes from the extracellular fluid.

What is the significance of the length-tension relationship in muscle contraction?

A muscle resting at optimum length can contract more forcefully.

What is temporal summation in muscle contraction?

The increased strength of contraction due to rapid successive action potentials.

What is the effect of fatigue on muscle contraction strength?

Fatigued muscles contract more weakly.

What is the role of myofibrils in muscle hypertrophy?

Myofibrils grow thicker and can split longitudinally when they reach a certain size.

What adaptations occur in slow-twitch fibers with endurance training?

Increased mitochondria, glycogen, and capillary density.

What is the difference between hypertrophy and hyperplasia in muscle growth?

Hypertrophy refers to the increase in size of existing fibers, while hyperplasia refers to the increase in the number of fibers.

What is the primary function of smooth muscle?

To facilitate involuntary movements in various organ systems.

What is the role of gap junctions in single-unit smooth muscle?

They electrically couple myocytes, allowing them to contract as a unit.