Muscle Physiology Flashcards by Natalia Stando

How well did you know this?

Not at all

Perfectly

Describe the ultrastructure of a myofibril

● Made of two types of long protein filaments, arranged in parallel
-Myosin - thick filament
-Actin - thin filament
● Arranged in functional units called sarcomeres
-Ends – Z-line / disc
-Middle – M-line
-H zone – contains only myosin

How well did you know this?

Not at all

Perfectly

How well did you know this?

Not at all

Perfectly

Explain the banding pattern to be seen in myofibrils

● I-bands - light bands containing only thin actin filaments
● A-bands - dark bands containing thick myosin filaments (and some actin filaments)
-H zone contains only myosin
-Darkest region contains overlapping actin and myosin

How well did you know this?

Not at all

Perfectly

Explain sliding filament theory

How well did you know this?

Not at all

Perfectly

What happens during muscle relaxation?

Ca2+ actively transported back into the endoplasmic reticulum using energy from ATP
Tropomyosin moves back to block myosin binding site on actin again → no actinom

How well did you know this?

Not at all

Perfectly

What happens when a muscle is in a contracting state?

1.When Troponin binds to Ca2+ it moves the tropomyosin strand and unblocks the actin-binding site for the myosin head

How well did you know this?

Not at all

Perfectly

What is Excitation Contraction Coupling?

process that links a nerve signal to muscle contraction.

How well did you know this?

Not at all

Perfectly

Explain Excitation Contraction Coupling in steps

→ Excitation (Signal Arrival) –nerve sends an electrical signal (action potential) to the muscle.
→ Calcium Release –signal triggers the muscle cell to release calcium from a storage area (sarcoplasmic reticulum).
→ Contraction Begins –Calcium binds to special proteins (troponin), allowing muscle fibres to slide past each other and contract.
→ Relaxation –When the signal stops, calcium is pumped back, and the muscle relaxes.

How well did you know this?

Not at all

Perfectly

What is the T tubule function in Excitation Contraction coupling ?

Delivers action potential deep into the cell where sarcoplasmic reticulum is arranged on either side.

How well did you know this?

Not at all

Perfectly

Name the 4 types of skeletal muscle contractions

Isotonic, concentric, isometric and eccentric

How well did you know this?

Not at all

Perfectly

What is an isotonic contraction ?

Muscle contracts, shortens, and creates enough force to move load.

How well did you know this?

Not at all

Perfectly

What is a concentric contraction?

muscle shortens as contraction progresses. E.g. a bicep curl.

How well did you know this?

Not at all

Perfectly

What is an isometric contraction?

Muscle contracts but cannot shorten. Force cannot move the load.

How well did you know this?

Not at all

Perfectly

What is an eccentric contraction?

-muscle lengthens during contraction, e,g, walking downhill (braking action).
-Experimental evidence suggests eccentric contraction is more damaging – and causes late-onset pain and stiffness.

How well did you know this?

Not at all

Perfectly

What is phosphocreatine (quick ATP supply) ?

• Phosphocreatine rapidly regenerates ATP by donating a phosphate to ADP.
• The enzyme creatine kinase facilitates this reaction.
• When ATP is abundant, muscles store phosphocreatine for future use.

How well did you know this?

Not at all

Perfectly

What is limited during the early stages of exercise?

Oxygen

Oxygen availability is crucial for energy production in muscles.

How well did you know this?

Not at all

Perfectly

How is ATP produced during early exercise?

Via glycolysis (anaerobic metabolism)

Glycolysis does not require oxygen.

How well did you know this?

Not at all

Perfectly

What is the efficiency of glycolysis in terms of ATP production?

Produces only 2 ATP per glucose

This is considered inefficient compared to aerobic metabolism.

How well did you know this?

Not at all

Perfectly

What byproduct does glycolysis produce that leads to muscle fatigue?

Lactic acid

Accumulation of lactic acid can hinder muscle performance.

How well did you know this?

Not at all

Perfectly

What happens to blood supply to muscles as exercise continues?

Increases

Increased blood flow enhances oxygen delivery to muscles.

How well did you know this?

Not at all

Perfectly

What enables aerobic metabolism as exercise progresses?

Increased oxygen

Aerobic metabolism requires oxygen for efficient ATP production.

How well did you know this?

Not at all

Perfectly

How efficient is aerobic metabolism in ATP production?

Produces approximately 32 ATP per glucose

This is significantly more efficient than anaerobic metabolism.

How well did you know this?

Not at all

Perfectly

In the steady state, what fuels do muscles receive ATP from?

Glucose and fat metabolism

Both fuels are crucial for sustained energy during prolonged exercise.

How are glucose and fat supplied to the muscles for ATP production?

Via the bloodstream ## Footnote Nutrients are transported through blood to fuel muscle activity.

A motor neuron's stimulation of a skeletal muscle fiber is an "………. …. ………" phenomenon.

All or none

Factors contributing to force generation in muscle contraction:

→ Summation: Additive effect of repeated stimuli. → Recruitment: Number of motor units stimulated. → Length of muscle fiber: Sarcomere length determines tension.

What causes a brief muscle contraction (muscle twitch), followed by relaxation?

single electrical signal (action potential)

What is the duration of an action potential ?

1-3 milliseconds

What is the duration of a muscle twitch?

~100 milliseconds

What happens if another action potential arrives before the muscle relaxes?

-More calcium (Ca²⁺) is released inside muscle - Increases the force of contraction.

What do rapid, repeated action potentials prevent and result in?

- Prevent muscle relaxation between signals. - Result in a sustained contraction called “tetanus”

What happens in tetanus?

- Muscle force is much greater than in a single twitch. - Calcium builds up, maintaining continuous contraction.

What is tetanus essential for?

- Strong, controlled movements. - Nervous system regulation of muscle force via signal frequency.

What is a motor unit?

Group of muscle fibres innervated by the same motor neuron.

How many motor neurons innervate a muscle fibre?

A muscle fibre is innervated by only one motor neuron.

What type of fibre does a motor neuron innervate?

A motor neuron innervates one type of fibre.

What is required for precision in movement?

Fewer fibres supplied by one motor neuron.

Factors influencing strength:

→ Metabolic condition (fatigue). → Amount of load. → Recruitment of motor units. → Initial length of sarcomere.

What does the strength of contraction depend on?

The length of individual sarcomeres at the start ## Footnote This relationship is known as the length-tension relationship.

What is crucial for maximum cross-bridge formation and tension?

Optimum sarcomere length ## Footnote This is particularly important, unlike in cardiac muscle.

What happens when there is excessive overlap of filaments?

It interferes with crossbridge formation and tension ## Footnote This can lead to decreased muscle contraction efficiency.

Can cardiac muscle regenerate if damaged?

How does the cardiac muscle resemble skeletal muscle?

Due to striations (strips)

What are the key features of cardiac muscle fibres?

-Small in size. -Branched structure. -Single nucleus per cell.

What is the structural organisation of cardiac muscle?

Has a sarcomere structure, similar to skeletal muscle

What connects cardiac muscle cells and allows for the rapid spread of electrical signals?

Intercalated discs

What role do gap junctions play in cardiac muscle?

Help electrical signals pass easily between cells

Describe the contraction motion of the heart.

Heart contracts in a twisting motion, pushing blood from the apex to the top

What percentage of heart muscle cells are responsible for pumping blood?

99% ## Footnote The remaining 1% are pacemaker cells that generate electrical signals.

Does the heart require nerve input to beat?

No, it beats on its own ## Footnote However, nerves and drugs can influence heart rate.

What is a functional syncytium in the context of cardiac muscle?

Heart cells function as a functional syncytium, working together like a single unit for rhythmic contraction ## Footnote This allows for coordinated contraction of the heart muscle.

Which specialized cells control the automatic beating of the heart?

Pacemaker cells ## Footnote These cells include sinoatrial nodes and atrioventricular nodes.

What systems influence the heart rate?

Autonomic nervous system (sympathetic and parasympathetic) and medications ## Footnote The sympathetic nervous system increases heart rate, while the parasympathetic system decreases it.

What is the structure of a smooth muscle?

o Made of spindle-shaped (elongated, tapered) cells. o No striations (unlike skeletal and cardiac muscles). o Each cell has a single, centrally located nucleus

What is the function of smooth muscles?

o Involuntary control (works automatically without conscious effort). o Found in walls of hollow organs (e.g., intestines, blood vessels, bladder). o Regulates functions like digestion, blood flow, and respiration.

What’s the contraction like of a smooth muscle and what is it regulated by?

o Contracts slowly and steadily compared to skeletal muscle. o Controlled by the autonomic nervous system, hormones, and local factors

Can the smooth muscle regenerate and if so does it have a high regeneration capacity?

o High regeneration capacity, unlike cardiac and skeletal muscle. o Can repair and replace damaged cells efficiently.