ANP1105: TOPIC 2.3: PHYSIOLOGY OF MUSCLES.
220.127.116.11: In table form, compare + contrast skeletal, smooth and cardiac muscles.
Common features of Muscle Cells:
• Elongated cells = muscle fibers.
• Myo, Sarco= muscle.
• Muscle contraction depends on actin and myosin myofilaments.
COnly inrtscle Attach to & cWalls of hollow, visceral
contraction; neuraStriated, voluntainvoluntary,
increrate Ctires easily & mcontractions Skeletal: Physical acticvity, nuclei off to
Strong,ptable the side.
Smooth: actin and myosin are not orderly.
18.104.22.168: list and briefly describe 4 muscle functions as well as
4 functional characteristics.
• Generate movement: locomotion, manipulation, blood flow + pressue,
respiration, propelling of food, urine.
• Maintain posture: constantly working against gravity.
• Joint stabilization: shoulders, knees when moving parts of skeleton.
• Generation of heat: maintenance of body temperature.
Functional Characteristics of Muscle:
• Excitability (Irritability): ability to receive and respond to a stimulus.
• Contractility: ability to shorten forcibly when adequately stimulated.
• Extensibility: ability to be stretched or extended.
• Elasticity: ability to resume resting length after being stretched.
• Sarcolemma: plasma membrane of muscle.
22.214.171.124: describe the anatomy of skeletal muscle; define sarcolemma, sarcoplam,
myoglobin, myofibril, sarcoplasmic reticulum, ttubule, actin, myosin, A + I bands, A
disk, H zone and M line.
Anatomy of a Skeletal Muscle Fiber:
• Long cylindrical cell with many oval nuclei on the sides.
• Syncytium: have a lot of nuclei, divides instead of cell.
• Sarcoplasm has a lot of glycogen and myoglobin(oxygen carrier).
• Lots of myofibrils, extensive sarcoplasmic reticulum; T tubules.
• Each muscle fiber(cell) consists of parallel myofibrils.
• 3 connective tissue wrappings:
Endomysium: thin connective tissue wrapped around a single
Perimysium: When we bundle parallel muscle cells(fascicle) the
wrapping around it.
Epimysium: A bunch of fascicles, wrapping around it.
• Myofilaments(actin, myosin) arranged in a pattern forming sarcomeres. • Sarcomeres extend from one Z disc to the next Z; sarcomeres give this
muscle type the name “striated muscles”.
Actin: thin filaments Across I band and partly into A band.
Myosin: thick filaments Entire width of A band.
• Zones + Lines:
Z disc: anchors thin filaments + connects all myofibrils of a cell.
H zone: area with no thin filaments. (relaxed muscle)
M line: fine strands connecting adjacent thick filaments.
• Ultrastructure + molecular composition of myofilaments:
rod like tall + 2 globular heads.
Ends of heavy chains + 4 light chains = cross bridges.
Cross bridges are the business ends of the thick filaments because
it’s the part of the myosin part that can push and connect with the
actin and the actin filaments to slide.
Myosins arrayed so central part smooth + each end studded with
many myosin heads.
Myosin heads contain ATPase, heads have enzyme activity, the
heads can hydrolyze ATP.
• Perimysium: connective tissue surrounding a fascicle.
• Sarcomere: contractile unit of muscle.
• Fiber: a muscle cell.
• Endomysium: thin connective tissue investing each muscle cell.
• Sarcolemma: Plasma membrane of the muscle cell.
• Tendon: Cordlike extension of CT beyond muscle – attaches it to bone.
• Fascicle: A discrete bundle of muscle cells.
126.96.36.199: delineate the role of the Ttubule and sarcoplasmic reticulum system in
facilitating the synchronized contractile response of a sing skeletal muscle cell.
• Elaborate web of ER around each myofibril inside PM.
• Most SR tubules run longitudinally; pairs of terminal cisternae across AI
junctions. • ROLE: regulate intracellular Ca++ storage depot for Ca++ release it when
muscle stimulated to contract.
• A Bands: we have myosin and where we may not have actin moving in.
• I Bands: only actin.
• The sarcomere extends from one Z disc to the other Z disk.
• Terminal cisternae: hold calcium
• T tubule.
• As muscles depolarize, an action potential spreads down using the T
tubules into the depth of the muscle cells as oppose to only the plasma
• They had to develop this modification because the cells are so big to bring
the action potential throughout the large muscle cells.
• T tubules are extensions of the plasma membrane.
• Triad= 2 terminal cisternae + 1 t tubule.
When mucles move, the Z discs move closer together, sliding over myosin.
188.8.131.52: describe the sliding filament mechanism of skeletal muscle contraction,
indicating the roles of Ca+ and ATP in this process; your description should include an
indication of how muscle relaxation occurs.
Muscle fiber shortens because sarcomeres shorten because of the sliding;
filaments remain the same length.
Thin filaments slide over thick filaments:
• Relaxed: only slight overlap of thick and thin filaments.
• Contracted: thin filaments penetrate more deeply into A band – Z discs
pulled toward thick filaments.
Distance between Z discs reduced.
I bands shorten.
H zones disappear.
A bands move closer together, but stay the same length.
Actin slides over myosin.
How does sliding occur:
1) Stimulus to contract
2) Myosin cross bridges attach to actin
3) Detaches and attaches numerous times to pull thin filaments toward centre of
4) Muscle shortens as this process occurs in all sarcomeres.
• Cross bridge attachment to actin requires Ca+, to move troponin. Details on the Mechanism:
• Intracellular [Ca+] low: myosin binding sites on actin blocked by
• Ca+ influx: binds to troponin, causing shape change and brief detachment,
sites are exposed.
• Single power stroke of all cross bridges. 3035% shortening in a single
contractile response, it’s probably occurring very quickly. To stop it, the
sarcoplasmic has to take the calcium out.
• Rigor Mortis: when someone has stiff muscles. The muscles are stiff
because the calcium is staying out and ATP isn’t being made, so the cross
bridges can’t detach. Eventually the muscles will relax because everything
starts to degrade. Even the tissues itself because no O2 and no nutrient are
being sent to the muscle.
• The role of ATP is to allow detachment.
184.108.40.206: Describe the structural organization of a neuromuscular junction; justify the
latent period of excitationcontraction coupling.
Excitation contraction coupling: converts electrical message into muscular
Somatic NS is responsible for stimulating skeletal muscles.
Muscles under involuntary control Autonomic NS. Ach is the neurotransmitter.
• Neuromuscular Junction + Nerve Stimulus:
Skeletal muscles stimulated by motor neurons of somatic NS.
The motor end plate is the specialized motor area of a plasma membrane
that has the right chemically gated channels for K and Na.
Events at nerve muscle synapse identical to those in nervenerve synapse.
• Generation of an AP across sarcolemma:
Chemically gated channels: local depolarization, AP in all directions,
depolarization/repolarization with Na+, then K+ as for axon Na+/K+
pump to restore.
Once initiated, AP is unstoppable, all or none.
The contractile response takes longer; when the muscle contracts, means
you can keep firing action potentials to keep it moving.
• What is the latent period of excitation contraction coupling? What happens if
nerve impulse arrives at the NML at high frequency?
It is the stimulus of a neuron. Contraction of the muscle. (excitation)
The time taken for the depolarization to come out, the events that lead up
to the contraction. (latent period) 220.127.116.11: Define motor unit, describe the influences of wave summation and motor unit
summation on the contractile response of skeletal muscle, define tetanus in terms of
• Motor nerve (atleast 1/muscle).
• Hundreds of motor neuron axons.
• Each axon to many axonal terminals.
• Each axonal terminal to NMK of a single muscle fiber.
Avg. no muscle fibers/neuron= 150.
When neuron fires, all fibers contract.
• MOTOR UNIT: 1 motor neuron + all muscle fibers it supplies.
Graded Muscle Responses:
• 2 types:
1) Change speed of simulation.
2) Change # of motor units activated (bring more muscle cells to increase
the strength of muscle response).
Speed of stimulation: wave summation + tetanus: temporal.
• Rapid rate of stimuli: each contraction builds on the previous one.
• The AP refractory period is al