Muscle Physiology Flashcards

Flashcards about muscle physiology

What is the primary function of all muscle?

Generate force or movement in response to a physiological stimulus.

Besides force generation, what are other functions of muscles?

Body movement, maintenance of posture, respiration, production of body heat, communication, constriction of organs and vessels, heart beat

What does the generation of force depend on in all muscle types?

Conversion of chemical energy (ATP)

Skeletal muscles are primarily voluntary and controlled by what?

Somatic motor neurons

What is a key characteristic of skeletal muscle cells?

Multinucleated

What alters cardiac muscle activity?

Spontaneous electrical activity, autonomic nervous system, hormones

What mechanical control does smooth muscle provide?

Digestive tract, urinary tract, reproductive tract, blood vessels, airways

What primarily regulates smooth muscle?

Autonomic control, spontaneous activity, hormones, paracrines, autocrines

What is the origin of a skeletal muscle?

Closest to the trunk or more stationary bone

What is the insertion of a skeletal muscle?

More distal or more mobile attachment

What are antagonistic muscle groups?

Flexor-extensor pairs

What does a flexor muscle do?

Brings bones together

What does an extensor muscle do?

Moves bones away

Approximately what percentage of total body weight is skeletal muscle?

40%

What percentage of daily energy expenditure is attributed to skeletal muscle?

15-60%

What is a muscle fiber equivalent to?

Muscle cell

What is the sarcolemma equivalent to?

Cell membrane

What is the sarcoplasm equivalent to?

Cytoplasm

What is the sarcoplasmic reticulum equivalent to?

Modified endoplasmic reticulum

What is a muscle fascicle?

Bundle of fibers

What is the cell membrane of a muscle fiber called?

Sarcolemma

What are myofibrils made of?

Thick (myosin) and thin (actin) filaments

What do striations correspond to?

Ordered arrays of thick and thin filaments within the myofibrils

How many myofibrils does a single muscle fiber contain?

1000+

What is the backbone of thin filaments?

F-Actin

What regulates the binding of myosin to actin?

Tropomyosin

What subunits comprise the troponin complex?

Troponin T (TnT), Troponin C (TnC), Troponin I (TnI)

What is the basic structure of thick filaments?

Two intertwined heavy chains

What are the two functions of the myosin head?

Binds actin and hydrolyzes ATP

What is Titin's role in muscle structure?

Stabilization and elastic recoil

What is Nebulin's role in muscle structure?

Regulates length of thin filaments

What is the function of the Z disk?

Attachment site for thin filaments

What is found in the I bands of the sarcomere?

Region occupied only by thin filaments

What area does the A band cover?

Encompasses entire length of the thick filament

What is the H zone?

Central region of A band, only thick filaments

What is the M line?

Attachment site for thick filaments

What is glucose stored as within the sarcoplasm?

Glycogen

What is skeletal muscle composed of?

Muscle fascicles, blood vessels, nerves, sarcoplasm, multiple nuclei, myofibrils, mitochondria, glycogen granules, Troponin, Actin, Tropomyosin, Myosin, Titin, Nebulin, Thin filaments

What is the force generated by a contracting skeletal muscle referred to as?

Muscle tension

Where does synaptic contact occur between a somatic motor neuron and muscle fiber?

Neuromuscular junction

What is the path of the alpha (lower) motor neuron?

Spinal cord to muscle

What is a neurodegenerative motor neuron disease?

Amyotrophic lateral sclerosis (ALS)

What are the three components of the neuromuscular junction?

Presynaptic motor neuron, synaptic cleft, postsynaptic membrane of the skeletal muscle fibre

What receptors are found on the muscle sarcolemma at the neuromuscular junction?

Nicotinic acetylcholine receptors

What type of channel is the nicotinic acetylcholine receptor?

Monovalent cation channel

What does Na+ entry through nACh generate?

Excitatory end-plate potential (EPP)

What enzyme breaks down acetylcholine in the synaptic cleft?

Acetylcholinesterase

What type of disorder is Myasthenia Gravis?

Autoimmune

What propagates action potentials from the sarcolemma to the interior of muscle fibers?

T-tubules

What is the process by which electrical excitation of the surface membrane triggers an increase of [Ca2+]i in muscle known as?

Excitation-contraction coupling

Where do T-tubules penetrate the muscle fiber?

A and I band junctions.

Briefly describe the initiation of muscle action potential

Somatic motor neuron releases ACh at neuromuscular junction, net entry of Na+ through ACh receptor-channel initiates a muscle action potential

What occurs when Ca2+ binds to troponin C?

Conformational change revealing binding site on actin

What occurs to allow Myosin to bind tightly to actin?

Elevated tropomyosin shifts allowing myosin to tightly bind actin

What triggers the power stroke?

Dissociation of Pi from myosin head

What theory explains how sarcomeres shorten during contraction?

Sliding filament theory

What MUST occur for contraction termination?

Muscle can be covered by tropomyosin

What action returns sarcomeres to initial resting position?

Elastic recoil of titin

What is the development of rigid muscle several hours after death called?

Rigor mortis

What causes Rigor Mortis Ca2+ leaks into?

Calcium leaks into sarcoplasm

What causes a slight delay between motor neuron AP and muscle fibre AP?

Synaptic Release