Lecture 24. Muscle Physiology Flashcards
What is muscle tissue responsible for ?
Nearly all types of body movement
What do muscle cells consist of ?
Filaments of the proteins actins and myosin
What are the functions of the filaments of the proteins actin and myosin ?
Enable muscles to contract
What are the three types of muscle tissue ?
- Skeletal muscle
- Smooth muscle
- Cardiac muscle
What is skeletal muscle responsible for ?
Voluntary movement
What is smooth muscle responsible for ?
Involuntary body activities
What is cardiac muscle responsible for ?
Contraction of the heart
What does muscle contraction generate ?
Heat
What type of tissue is muscle ?
Electrically excitable tissue
What is muscle activity a response to ?
Input from nervous system
What does muscle cell contraction rely on ?
The interaction between thin actin filaments and thick myosin filaments
What does skeletal systems transform muscle contraction into ?
Locomotion
What does the skeleton provide ?
A rigid structure to which muscles attach
How are skeletal muscles attached ?
In antagonistic pairs
What are the actions of antagonistic pairs coordinated by ?
The nervous system
How do paired muscles work ?
Cooperatively
What is locomotion ?
Movement through space
How does skeletal muscle work ?
Moves bones and the body
How is skeletal muscle characterised ?
Hierarchy of smaller and smaller units
What does a skeletal muscle consist of ?
A bundle of long fibres, each a single cell, running along the length of the muscle
What is each muscle fiber ?
A bundle of smaller myofibrils arranged longitudinally
Why is skeletal muscle called striated muscle ?
Because the regular arrangement of myofilament creates a pattern of light and dark bands
What is the functional unit of a muscle called ?
A saromere
What is a sarcomere bordered by ?
Z lines
Where to thin filaments attach ?
Z lines
What is the sliding filament model of muscle contraction ?
Thin and thick filaments ratchet past each other longitudinally, powered by the myosin muscles
What is the structure of myosin ?
A long tail region and a globular head region
Where does the head of the myosin molecule bind to ?
An actin filament
What does the head of the myosin molecule binding to an actin filament form ?
A cross bridge
What does the head of the myosin molecule binding to an actin filament do ?
Pull the thin filament towards the centre of the sarcomere-the power stroke
What does muscle contraction require ?
Repeated cycles of binding and release - cross bridge cycling
What is muscle contraction dependent on ?
ATP
Why does muscle fatigue ?
Metabolic reasons: lack of substrate (ATP) or accumulation of metabolites that interere with contraction
What generates the ATP needed for muscle contraction ?
Glycolysis and aerobic respiration
What happens during intense muscle activity ?
02 becomes limiting and ATP is generated by lactic acid fermentation
Does cardiac muscle fatigue ?
No
What else is muscle contraction dependent on ?
Calcium
What binds to actin strands on thin filaments when a muscle fibre is at rest ?
The regulatory protein tropomyosin and the troponin complex
What prevents myosin and actin interacting ?
The regulatory protein tropomyosin and the troponin complex
What must happen for a muscle fibre to contract ?
Myosin binding sites must be exposed
When are myosin binding sites exposed ?
When calcium ions bind to troponin complex
When does contraction occur ?
When the concentration of calcium is high
When does muscle contraction stop ?
When the calcium ion concentration is low
What is the stimulus leading to muscle contraction of a muscle fibre ?
An action potential in a motor neuron that makes a synapse with the muscle fibre
What does the synaptic terminal of the motor neuron do ?
Releases the neurotransmitter acetylcholin
What is the function of acetylcholine in skeletal muscle contraction ?
Depolarises the muscle causing it to produce and end plate potential
Where do action potentials travel ?
To the interior of the muscle fibre along transverse tubules
What does the traveling of the action potential to the interior of muscle fibres do ?
Causes the sarcoplasmic reticulum to release calcium ions
Is the contraction of the whole muscle graded ?
Yes
How does the nervous system produce graded contractions ?
- Varying the number of fibres that contract
2. Varying the rate at which fibres are stimulated
What may each motor neuron synapse with ?
Multiple muscle fibres
What does a motor unit consist of ?
A single motor neuron and all the muscle fibres it controls
What is tetanus ?
Describes sustained muscle contraction, where a muscle doesn’t relax between contractions
What are some examples of disorders related to skeletal muscle ?
- Amyotrophic lateral sclerosis
- Myasthenia gravis
- Multiple sclerosis
- Duchenne muscular dystrophy
How is ALS caused ?
Interferes with the excitation of skeletal muscle fibers
What is myasthenia gravis ?
An autoimmune disease that attack acetylcholine receptors on muscle fibres
What is multiple sclerosis ?
Demyelinating disease
What does cardiac muscle consist of ?
Striated cells electrically connected by intercalated disks that contain gap junctions
What can cardiac muscle do ?
Generate action potentials without neural input
Do cardiac muscles have tetanic contraction ?
No
Where is smooth muscle found ?
Mainly in walls of hollow organs such as circulatory system, digestive and reproductive
What is slow in smooth muscle ?
Contractions - may be initiated by muscles themselves
What can contractions be caused by in smooth muscle ?
Stimulation from neurons in the autonomic nervous system
Why does smooth muscle lack striated ?
Actin and myosin are not regularly arrayed
How does calcium enter smooth muscle ?
They enter the cytosol through smooth muscle
What is muscle contraction regulated by in smooth muscle ?
Calcium ions
How would you build skeletal muscle ?
- Testosterone
2. Anabolic steroids
What is the building of muscle dependent on ?
Protein synthesis
What does lack of muscle lead to ?
Atrophy
What can the heart undergo in response to physiological stimulus ?
Changes in shape and mass
How does endurance training effect the heart ?
Increases the volume
How does resistance training effect the heart ?
Increase in mass
