Muscle Physiology Flashcards
what are the properties of muscle
Excitability: capacity of muscle to respond to a stimulus
Contractility: ability of a muscle to shorten and generate pulling force
Extensibility: muscle can be stretched back to its original length
Elasticity: ability of muscle to recoil to original resting length after stretched
what are the types of muscle
smooth
skeletal
cardiac
Highlight some major features of skeletal muscle
-Attached to bones
-Makes up 40% of body weight
-Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
-Voluntary in action; controlled by somatic motor neurons
Highlight some major features of skeletal muscle
-Attached to bones
-Makes up 40% of body weight
-Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
-Voluntary in action; controlled by somatic motor neurons
highlight some major features of smooth muscle
-In the walls of hollow organs, blood vessels, eye, glands, uterus, skin
-Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow,
-In some locations, autorhythmic
-Controlled involuntarily by endocrine and autonomic nervous systems
highlight some major features of cardiac muscle
-Heart: major source of movement of blood
-Autorhythmic
-Controlled involuntarily by endocrine and autonomic nervous systems
describe the physiologic anatomy of a muscle
-Epimysium: Dense connective tissue that covers the entire muscle and separates it from surrounding tissues and organs
-Perimysium: Collagen and elastic fibres that cover a bundle of muscle fibers called a fascicle. It contains BV, nerves
-Endomysium: Loose connective tissue that covers the individual fibres. It also contains blood vessels and nerves, satellite cells
what are the notable feature of a skeletal muscle cell
-sarcolemma
-sarcoplasmic reticulum
-T-tubules and myofibrils
-sarcomeres
what be the sarcolemma
it forms a T system, with several transverse tubules that ru perpendicular to the myofibrils
what be the sarcoplasmic reticulum
It is a smooth E.R that runs longitudinally, surrounding each myofibril. It stores Ca in the muscle, when the muscle is stimulated, it releases the Ca, and after contraction, Ca pumps pump the calcium back in
Draw a sarcomere
check your book
Comment on myosin
A myosin molecule is shaped like a golf club, a single filament could have 300 myosin molecules.
A myosin molecule in itself consists of 2 heavy myosin molecules wound together to form a rod, and both myosin heads extending away laterally.
Myosin heads can:
-Bind to actin molecule to form cross bridges
-They are attached to the rod, by hinges that can bend and straighten during contraction
-They have ATPase activity(i.e they break down ATP for energy), the energy is used to bend the hinge portion in contraction and relaxation.
Comment on actin
Also known as the thin filament, they are composed of 3 major proteins:
-Fibrous (F) actin.
-Troponin.
-Tropomyosin.
Comment on F (fibrous) actin
2 strands of the F (fibrous actin) form a double helical structure, extending for the entire length of the myofilament, and attaches on both ends of the sarcomere.
They have G-actin monomers, which are myosin binding sites (where myosin heads attach to during muscular contraction).
comment on tropomyosin
An elongated protein that extends along the groove of the F actin. They cover the G actin monomer binding sites of the F actin when the muscle is not contracting.
comment on troponin
It acts as a lock to move the tropomyosin, it has 3 subunits:
-Tn-A: binds to actin
-Tn-T: Binding to tropomyosin
-Tn-C: binds to Ca.
what is the sliding filament theory
The sliding filament theory is used to explain the relationship between the thick and thin filament, (Actin and Myosin), as contraction proceeds.
-The thin filaments slide past the thick filaments, so that the actin and myosin overlap to a greater degree.
-When the muscle is in a state of relaxation, the filaments only overlap slightly, and once there is stimulation, overlapping begins again.
Draw a diagram to show the cylic process of sliding filament theory
check your book
what is rigor motis
Rigor mortis is a muscular condition that occurs after death. The muscles ATP BECOME DEPLETED AND THUS the muscle becomes stiff and unable to relax, as there is now a permanent attachement between the thin and thick filament.
draw the following sarcomeres
-relaxed
-partially contracting
-full contraction
check your book
what is a neuromusular junction
At its simplest, the neuromuscular junction is a type of synapse where neuronal signals from the brain or spinal cord interact with skeletal muscle fibers, causing them to contract.
What is the NT used in skeletal muscle
Acetylcholine only
How is acetylcholine synthesized
In the cholinergic neurons acetylcholine is synthesized from choline. This reaction is activated by cholineacetyltransferase.
As soon as acetylcholine is synthesized, it is stored within synaptic vesicles.
Outline the happenings at the neuromuscular junction during muscular contractions
👉nerve impulse (A.P) travels down the presynaptic axon of the neuron to it’s terminal bulb, the change in it’s membrane would open voltage gated calcium channels and allow calcium into the presynaptic bulb
👉An increase of calcium concentration in the bulb would make the synaptic vesicles that contain acetylcholine fuse with the axonal membrane, relaxing acetylcholine into the synaptic cleft
👉ACH binds to it’s receptor (cholinergic) on the postsynaptic terminal
👉 Acetylcholinesterase breaks ACH into choline and acetate, terminating the signal
👉choline is taken back (recycled) into the presynaptic membrane, and acetate diffuses out of the synaptic cleft.
What kind of receptors do ACH have in skeletal muscle
Cholinergic (nicotinic, i.e fast acting)
Outline the steps for skeletal muscle excitation -contraction coupling
👉Nerve impulse reaches myoneural junction
👉ACH is released from motor neuron
👉ACH binds to cholinergic neurons of the postsynaptic terminal activating sodium pumps and allowing sodium influx
👉Influx of sodium generates an A.P in sarcolemma
👉A.P travels down T tubule
👉S.R release calcium
👉Calcium binds with troponin to move the troponin-tropomyosin complex
👉Binding sites on actin are exposed
👉Myosin head binds to binding site on actin then a power stroke is created
👉ATP detatches the !yosin heads from the binding sites, and energize them for another contraction. Contraction ceases once ATP is diminished
Outline the steps of skeletal muscle relaxation
👉Calcium ions are pumped back to L tubules
👉calcium content of SR reduces
👉Calcium is released from troponin C
👉Thus, the myosin head detaches from F troponin, this is an active process that requires ATP
👉Muscle relaxes
Troponin A binds to
Actin
Troponin T binds to
Tropomyosin
Troponin C binds to
Calcium
What is a motor unit
It is a motor neuron and all the motor fibres innervated by it. Stimulation of that muscle fiber would cause contraction of all muscle fibres it supplies.
Muscles that control fine movement, e.g fingers and eyes are what kind of motor units
Small motor units
Muscles that are weight bearing e.g hips, are what kind of motor units
Large
What are the motor unit ratio of leg muscles
1:2000
What are the motor unit ratio for back muscles
1:100
What are the motor unit ratio for fingers
1:10
What are the motor unit ratio for eye
1:1
What are the types of contraction
Isometric
Isotonic
What is an isometric contraction
Tension in the muscle rises, but length remains constant. It produces no movement. E.g in sitting, standing
What is an isotonic contraction
Tension rises and length changes too. They are responsible for any movements
What is a twitch
It’s a single contraction-relaxation cycle in a skeletal muscle fiber. It is a muscle fibers response to a single AP
Draw a diagram to explain twitch
Check. The. Book.
What are the 3 phases of twitch
👉latent
👉contraction.
👉 relaxation
Latent phase of twitch?
In this phase, the stimulus for contraction is produced, i.e, the A.P that makes the cross bridge is produced here
Contraction phase of twitch
The beginning and end of a contraction are here, myosin heads slide along actin filaments
Relaxation phase of twitch
After peak tension is achieved, calcium ions are moved back to cisternae, troponin releases the tropomyosin, which slides back to cover the active sites, the myosin head releases the actin filaments back to resting position.
Comment on the energy usage of skeletal muscle
👉The backup energy source is phosphocreatinine. It has high energy phosphate bonds which are created by ATP and creatinine when the muscle is at rest. When the muscle becomes active, the high energy phosphate group is transferred to ADP, forming ATP to power the muscles. However this source is very limited.
👉In aerobic respiration muscles use compounds especially
-glucose
-glycogen
-fatty acids
To produce ATP, in presence of oxygen. Glucose is metabolized through glycolysis to yield pyruvate. Pyruvate enters the citric acid cycle also producing 36ATP/glucose
Fatty acids in the presence of oxygen would pass through oxidative phosphorylation to produce 36ATP/glucose.
👉In the case of inadequate oxygen, there is anaerobic respiration, which is a quicker source of energy, however it only produces a few ATP, (2ATP/glucose) and it causes accumulation of lactic acid, so it can only be used for a while before fatigue
What is muscle fatigue
A decline in a muscles ability to maintain force of contraction
Causes of muscle fatigue
👉build up lactic acid
👉decrease of oxygen
👉decrease of energy supply (glucose, glycogen, fatty acids)
👉decreased N.T at the synapse
Draw a graph to show fatigue
Check. The. Book.
Differentiate between red and white muscle
Check your book
What are the types of skeletal muscle fiber
Type I
Type II
What are type I skeletal muscle fiber
They are also called slow twitch fibers. They have small diameters, they are fatigue resistant and are thus are more common in marathon runners.
What are type II skeletal muscle fiber
Also called fast twitch fibers, they have large diameters, they are not fatigue resistant and are more common in sprinters
What is the effect of aerobic exercise in muscle
They are long, sustained exercises.
They:
👉Promote increased oxidative capacity of a muscle fiber
👉Increase blood supply
👉Increase mitochondria
🔥They are generally for improving endurance
What is the effect of high intensity, short burst exercise on skeletal muscle
👉 Increase glycolytic activity
👉Increase glycolytic enzyme synthesis
👉Increase synthesis of myofibrils (increase muscle size)
🔥They generally are for body building
What is summation
If a 2nd Stimulus is applied in the Latent phase or contraction period of the 1st, the 2 curves fuse to one. A Summation curve is wider and has a larger amplitude than a normal muscle twitch. As the twitches fuse, the resulting curve is larger than its precedent, due to calcium ion increase.
What is tetany
Tetanus is defined as the sustained contraction of muscle
due to repeated stimuli with high frequency. When the
multiple stimuli are applied at a higher frequency in such
a way that the successive stimuli fall during contraction
period of previous twitch, the muscle remains in state of
tetanus. It relaxes only after the stoppage of stimulus or
when the muscle is fatigued.
What are the types of tetanus, draw graphs
Incomplete: muscle relaxes partially
Complete: relaxation phase is eliminated
Check the book for the drawing
What are the functions of skeletal muscle
Produce movement
Maintain body posture, body position
Support soft tissue
Guard entrances and exits
Maintain body temperature
Facial expressions
What are muscle cramps
This is an involuntary tetanic contraction of Skeletal muscles. It is caused by the firing of A-Ps at abnormally high rates.
The cause of this is said to be electrolyte imbalances in the ECF Surrounding the muscle and nerves @ the neuromuscular junction. This causes an excessive AP firing in the motor neurons and muscle fibres.
What is myasthenia gravis
This is a collection of Neuromuscular fatigue disorders characterised by muscle cramps & weakness that worsens the more the muscle is used. It is more common in women than in men. Cause(s):
Destruction of the nicotinic Ach receptors on the post-synaptic terminal caused by antibodies of the bodies own immune system. The release of the Ach from the presynaptic is normal. But its magnitude is reduced due to decreased receptors for it.
What are the treatments for myasthenia gravis
👉Administer acetylcholinesterase inhibitors to increase the time that Ach is present in the Synaptic Cleft
👉Treatment with glucocorticoids to blunt immune response.
👉Removal of the thymus, to reduce production of antibodies.
👉Plasmapharesis: replacing the plasma of the blood (that contains the offending antibodies) (most effective)
What is Eaton Lambert syndrome
It is also an auto-immune disease, of the Neuromuscular function. The antibodies attack the calcium channels at the axon terminal. It therefore would cause insufficient release of Ach. It is characterised by fatigue’s weakness (esp. of muscles prox. to trunk).
Smooth muscle in comparison to skeletal muscle is:
👉Are Shorter 3 thinner
👉Have a single, centrally placed nucleus
👉Lack Striations: It doesn’t mean they don’t have myosin actin o! It only means that the filaments are thin randomly placed.
👉No T-tubuks
👉A poorly developed S-R.
What are the N.T in smooth muscle
Acetylcholine
Norepinephrine
Unlike skeletal muscle N.T that is only excitatory, smooth muscle N.T is
Inhibitory or Excitatory
They can also be stimulated by hormones e.g oxytocin
T- tubule for smooth muscle
Caveolae
Z disk for smooth muscle
Dense bodies
Are the intermediate filaments of smooth muscle non contractile
Yes
Types of smooth muscle
👉visceral or single unit smooth muscle
👉multiunit smooth muscle
What are the visceral smooth muscle
Here, only a few muscle fibers are innervated in each group, So the impulse Spreads through gap junctions, so that the muscle contracts as a single unit. The muscle is also auto rhythmic.
They are found in the walls of the hollow visceral organs Like Stomach, uterus, bladder, intestines.
The muscle fibers which are held by gap junctions into a single Sheet now have 2 layers:
👉Longitudinal layer: The outer layer is longitudinal along the length of the structure, contraction of this layer would make the structure dilate and Shorten
👉Circular layer: It’s the inner layer arranged circularly around the structure. Contraction of this layer makes the layer constrict and elongate
Both layers participate in peristalsis
Contraction of the outer longitudinal layer of visceral smooth muscle
The outer layer is longitudinal along the length of the structure,
contraction of this layer would make the structure dilate and Shorten
Contraction of inner circular layer of visceral smooth muscle
Contriction and elongation
Multiunit smooth muscle?
The cells here act as independent units. eg piloerector of skin, iris of the eye.
The fibers are poorly organised, scattered in the sarcoplasm. It requires stimulation from ANS
It is found in
→ Iris of the eyes
→ Piloerector
→ Blood vessels
→ Large airways of the lungs.
Similarities between smooth muscle and skeletal muscle contraction
Both contractile proteins need actin and myosin
Both are triggered by membrane impulses and the release of calcium ions; and
Both require ATP.
Differences between smooth muscle and skeletal muscle contraction
👉Actin has no troponin, the protein that binds to myosin in skeletal muscle. Rather smooth muscle has a calcium binding protein called calmodulin. This protein activates the actin and myosin crossbridge formation.
👉Most of the calcium required for contraction comes into the cell by diffusion from the extracellular fluid.
👉Smooth muscle is more resistant to fatigue and produces a slower, longer lasting contraction than skeletal muscle.
👉It is more energy efficient than skeletal muscle in that it can maintain a more forceful contraction for a longer period of time with the same amount of ATP.
Outline the steps of skeletal muscle contraction
👉Intracellular Ca2+ increase as calcium enters the cell and is released from the Sarcoplasmic reticulum.
👉Calcium binds to calmodulin.
👉[Calcium- calmodulin] activates myosin Light Kinase (MLCK)
👉MLCK phosphorylates light chains in my both heads and increases myosin ATPase activity.
👉The active Myosin Crossbridges glide along the actin to create muscle tension.
Outline the processes of smooth muscle relaxation
👉The free calcium in cytosol decreases when its pumped out from the cell or back into the S.R.
👉Ca2+ unbinds from calmodulin
👉Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity.
👉Less myosin ATPase means decreased muscle tension
Myogenic response of smooth muscle?
Smooth muscle is stimulated to contract when it is stretched. Smooth muscle is able to distend, or stretch, without great increases in tension or tightness. This allows hollow organs to be filled.
When the smooth muscle reaches its stretching capacity, it will contract and force the contents out
Such occurs in the intestines or urinary bladder.
What metabolism provides cardiac muscle with energy
Aerobic
Can cardiac muscle sustain oxygen debt
No
What is oxygen debt
a temporary oxygen shortage in the body tissues arising from exercise.
What is notable of a cardiac muscle S.R
Terminal cisternae have less calcium and
Strength of calcium depends on calcium from ecf and t-tubules
Why is there no tetany in cardiac muscle
The refractory period of cardiac muscle is dramatically longer than that of skeletal muscle. This prevents tetanus from occurring and ensures that each contraction is followed by enough time to allow the heart chamber to refill with blood before the next contraction.
What are the phases of cardiac muscle contraction
Plateau phase
Refractory period
Repolarization
What happens in plateau phase
The prolonged depolarization in cardiac muscle due to caletum from ECF. This prolonged phase prevents tetany or prolonged contractions that could interfere with the hearts pumping ability
What happens in refractory period of cardiac muscle
Due to the calcium influx, there is a prolonged refractory period for 250msec. It is So much longer than that of skeletal muscle (1-2msec). At this point the heart does not respond to any stimulation….
What happens in repolarization phase of cardiac muscle
calcium is pumped back into S.R and out of ECF Space
What is autorhythmicity of cardiac muscle
The ability of cardiac muscle to contract repeatedly and rhythmically without external Stimulation. This feature is due to PACEMAKER CELLS - Situated in the cardiac muscle that depolarize at regular intervals causing muscle excitation without Nervous System stimulation.
The impulses travel rapidly through the gap junctions in the intercalated discs, making the heart Contract as a single unit.
The Contractions of cardiac muscle:
→ Exhibit automaticity
→ Last Longer than skeletal muscle
→ Do not exhibit wave Summation.
What is the ALL OR NONE RESPONSE
The entire heart muscle contracts as a unit, or in syncytium
Two syncytium are in heart:
The atrial syncytium and the ventricular syncytium. They are almost completely separated from each other by fibrous tissue
Either both atria contact, or both do not contract at all
Either both ventricles contact, or both do not contract at all
Differentiate between skeletal, smooth and cardiac muscle
Check the book
