Physiology of Skeletal Muscle Flashcards
Muscles make up _______ % of the body.
45-50%
What is the purpose of contractions:
- accomplish movements
- Affect the pressure of cavities (uterus, bladder, intestine, gallbladder,
What are the three types of muscles?
- Skeletal
- Smooth
- Cardiac
How can the types of muscle be differentiated?
grossly, histologically, and by physiologic functions
What are some features of smooth muscle?
- fusiform cells
- One nucleus per cell
- Non-striated
- Involuntary
- Slow, wave-like contractions
What are some features of skeletal muscle?
- long cylindrical cells
- many nuclei per cell
- striated
- voluntary
- rapid contractions ( inter
- maintaining posture
What are some features of cardiac muscle?
- branching cells
- One/two nuclei per cell
- Striated
- Involuntary
- Medium-speed contractions
- Low electrical resistance
What are some functions of skeletal muscle?
- Produce movement
- maintain posture and body position
- Support Soft Tissues (external sphincter)
- Guard entrance/ exits
- Maintain body temperature (shivering)
- Store nutrient reserves (glycogen, lipids, proteins)
What are some functional properties of muscles?
- Irritability
- Conductivity
- Contractility
- Elasticity
- Rhythmicity
What are fasscicles?
Bundles of muscle fibers (myosin) that make up skeletal muscle
What is an epimysium?
Entire groups of fasciculi
What is perimysium
surrounds each fasciculus
What is endomysium?
each fiber within a fasciculus
The sarcolemma is the _____ of the muscle cell.
plasma membrane
There are 2 ‘m’s’ in both plasma membrane and sarcole’mm’a
What is the smallest functional unit of skeletal muscle?
The sarcomere
What does a myosin molecule consist of?
a tail, hinge, and heads
What active sites do myosin heads contain?
Actin
ATP
What does the M-line consist of?
myomesin and skelemin proteins
What is the function of the M-line?
- to stabilize the myosin filaments
- Theorized to aid in the transmission of force from sarcomere to cytoskeletal intermediate finalaments
What are thin filaments composed of?
- g-actin
- nebulin
- tropomyosin (blocks myosin binding site on actin)
- troponin (troponin T helps tropomyosin block site)
What are the 3 proteins of troponin, and what do they stand for and do?
Troponin T- tropomyosin
Troponin C- Calcium
Troponin I- inhibitor
What is the function of each polypeptide chain of troponin?
T- helps keep tropomyosin in place
C- switch for muscle contraction that kicks out tropomyosin and exposes myosin binding site
I- prevents Troponin C from coming close to T
What are the subcellular components of muscle?
- Outer cell membrane (sarcolemma)
- Mitochondria
- Golgi apparatus
- endoplasmic reticulum
- Peroxisomes
- Lysosomes
- Ribosomes
- Myofibrils (contractile organelles)
What 2 proteins in the cytoplasm generate the contracting force in muscles?
Actin and myosin
What are myofibrils?
elongated protein threads about 1-3μm in diameter in vertebrates
What are myofibrils composed of?
- dark A and light I bands, which are responsible for the striations
- thick and thin filaments
Which bands contain thick or thin filaments?
- Thick filaments- in the A band
- Thin filaments- in the I band and peripheral portions, but not the central H zone of the A band
What is the function of the Z line?
to anchor the thin filaments in the center of the I band
What is the function of the M line?
to anchor the thick filaments in the middle to the H zone
Where is the sarcomere?
the myofibril between the two Z lines
- smallest functional unit of skeletal muscle
What is the thick filament composed of and what are the different parts?
myosin
Head, hinge and tail
Light meromyosin forms the _______.
myosin tail
fireflies
Heavy myosin forms the ____.
myosin body
Double myosin forms the ______.
myosin head (contains actin-induced ATPase)
What is the thin filament composed of?
Actin
Tropomyosin
Troponin
What are actin monomers?
A spherical protein measuring about 11 nm in diameter.
Each thin filament contains about 340-380 actin monomers
What is Tropomyosin?
A rod-shaped molecule, about 42.3nm long,
lies in two grooves of the double standard actin filament
It aggregates end-to-end to produce two strands of tropomyosin running the entire length of the thin filament
What does each troponin polypeptide bind to/attach?
T- Attachess the troponin complex to tropomyosin
I- troponin-T and C, and actin the absence of calcium
C- Troponin-T and I, but not actin (has 4 affinity binding sites for Ca++ per molecule)
What is a synapse?
A non-protoplasmic connection between neurons
Which band(s) of the thick filaments shortens during muscle contraction?
The I-bands and the H-zone shortens. A-bands do not change their length.
What part of the muscle fiber is represented with the red square?
M line
What part of the muscle fiber is represented with the blue square?
I band
What part of the muscle fiber is represented with the black square?
H zone
What part of the muscle fiber is represented with the yellow squares?
Z disk
What part of the muscle fiber is represented with the green square?
A band
When sufficient calcium exits the smooth endoplasmic reticulum, which protein does it target?
In skeletal muscle
Troponin-C
What receptor does the neurotransmitter bind to when it is released?
Nicotinic receptor
What neurotransmitter is released at the neuromuscular junction?
Acetylcholine
What results in Acetylcholine binding to nicotinic receptors?
The sodium channel opens
What are the 3 stages of the muscle contraction process?
- Synaptic transmission at the neuromuscular junction
- Excitation-contraction coupling
- Ca2+ is released/signaled - Contraction-relazation cycle
- Muscle twitch (complete cycle) OR sliding filament theory
What makes up 1 motor end plate?
1 axon branch connected to 1 muscle fiber
A motor neuron comes from the ___ __ to the ____.
spinal cord; muscle
What are the steps in skeletal muscle contraction?
- Ca2+ is released from SR
- Ca2+ binds of troponin
- Free myosin head hydrolyses the ATP to initiate contraction
- Myosin binds to actin forming the cross bridge
- Myosin head pivots toward the center of the sarcomere (power stroke/ contraction proper)
- Myosin head binds to ATP and detaches from actin (relaxation)
What neurotransmitter is released at the neuromuscular junction?
acetylcholine
The net entry of what through the receptor channel initiates the muscle action potential? What happens to the membrane?
Na+
The membrane becomes polarized
What does acetylcholine act upon?
postsynaptic membrane receptor
What destroys acetylcholine after muscle contraction?
acetyl cholinesterase
What is a complete cycle of muscle contraction called?
A twitch
What is the receptor on the smooth endoplasmic reticulum (sarcoplasmic reticulum) that is attached to ion channels? What does it do?
Ryanodine receptor
It controls the opening and closing of the ion channels located on the SER membrane.
Does not happen until the complex is formed btw ryanodine & DHP receptor
What is the receptor located on the T-tubule and opens the RyR (Ryanodine receptor) in the SAR?
Dihydropyridine receptor (DHPR)
The action potential in the _______ alters the conformation of _______ receptor
T-tubule; DHP
What is the fastest energy-supporting system?
Creatine-phosphate system
is ATP required for relaxation?
yes
What are 3 specific sources of energy for muscle contraction?
- Creatine phosphate (fastest)
- Glycolytic lactic acid system (Glycolysis- it is anaerobic. 2nd fastest and produces lactic acid)
- Aerobic metabolism/oxidative phosphorylation (produces energy slowly, but in large amounts)
What is creatine made from?
The amino acids:
- arginine
- glycine
- methionine
Where is creatine created?
- liver
- kidney
- pancreas
Where is 95% of creatine stored?
In muscle cells
(5% in other cells)
What happens during resting muscle?
Fatty acids are catabolized. ATP is used to build ATP, CP, & glycogen
What happens during moderate activity?
Glucose and fatty acids are catabolized. ATP is used for contraction
What happens during peak activity?
ATP is produced through glycolysis, lactic acid is a by-product.
What metabolism is 95% of cell demand?
Aerobic metabolism
Why is lactate production necessary?
For ATP regeneration
What is oxygen debt?
Additional oxygen consumption after work
What controls the activity of Na+/K+ ATP during activity?
Insulin
Epinephrine
Norepinephrine
Thyroxine
What are the three types of twitching?
Red/slow
Red/fast
White/fast
What are the phases of a twitch?
Latent period- Short delay between milliseconds, action potential develops and travels along the sarcolemma and along T-tubules. No visible contraction.
Contraction period- Muscle tension increases, muscle contraction, muscle shortens, crosses bridge forms, power stroke developed, muscle tension peaks significantly
Relaxation period- Significant reversal, tension decrease, returns to ATP attaches to myosin, calcium is pumped back into cytoplasmic, detachment of cross bridge, muscle relaxes, tension returns to baseline.
What are the levels of fatigue classification?
Fatigable
Fatigue intermediate
Fatigue-resistant
Non-fatigable
What are the steps of the lactate shuttle?
- Conversion of glucose to glycogen & recycled to the muscle
- Hepatic glucose synthesis from lactate
- Muscle-generated lactate enters venous blood & passes to the liver
- Plasma glucose is converted to lactate by skeletal muscle
What is rigor mortis?
A loss of all energy compounds in the muscle.
What is activity-induced muscle injury?
A increase in H+ concentration and lactate concentration
What are the ways that skeletal muscle can be classified?
speed of contraction
metabolism of nutrients
myoglobin content
motor neurons innervating the muscle.
What is recruitment?
When the strength of stimulus that is applied to a muscle bundle is increased, the contractile response increases.
Skeletal muscle tone maintains some latent degree of ____ ____.
contractile tension
What is tetany?
A sustained muscle contraction
What are some causes of tetany?
- electrolyte imbalance (hypercalcemia, hypermagnesemia, hypokalemia)
- neuromuscular disorders (tetanospasmin)
- hyperventilation (alkalosis- body’s fluids become too alkaline)
What is unfused tetanus?
When muscle fibers do not completely relax before the next stimulus
What is fused tetanus?
When there is no relaxation of muscle fibers between stimuli
What is treppe or staircase effect?
When stimuli of equal strength are applied successively, a few seconds apart to a resting muscle, and progressively become stronger to a point of stagnation.
What is unfused tetanus?
When the muscle fibers do not completely relax before the next stimulus because
they are being stimulated at a fast rate;
however, there is a partial relaxation of the muscle fibers between the twitches
What is fused tetanus?
When there is no relaxation of the muscle fibers between stimuli and it occurs during a high rate of stimulation
- The strongest single unit twitch in contraction
What is the difference between spastic and flaccid paralysis?
- Spastic: connected to CNS
- Flaccid: disconnected from CNS
