Muscle Physiology Flashcards
What is the outermost layer of connective tissue surrounding skeletal muscle? What kind of connective tissue is it?
The epimysium, dense irregular
What is the layer of connective tissue that surrounds each skeletal muscle fascicle called? What kind of connective tissue is it?
Perimysium; dense irregular
What is the deepest layer of connective tissue in skeletal muscle and what kind of tissue is it? What part of the muscle tissue does it surround?
The endomysium, made of areolar connective tissue, surrounds each individual muscle fiber
From the most macro to the most micro, what are the skeletal muscle organizational structures?
Muscle -> fascicles (10-100 cells) -> fibers (cells) -> myofibrils -> sarcomeres -> myofilaments (thin and thick)
Describe the two types of muscle attachments.
- Direct attachment - also called fleshy attachment, the epimysium is fused to the periosteum of a bone or perichondrium of cartilage.
- Indirect attachment - the muscle’s connective tissue wrappings extend beyond the muscle, either as a tendon or aponeurosis, and anchor to the connective tissue of the skeleton element or the fascia of other muscles
The triad lies over the Z-disc of a myofibril and consists of what structures?
Two terminal cisterns of the SR and one T tubule
Which type of muscle attachment is most common in the body and why?
Indirect attachments; durability and size - tendons can withstand the abrasions of rough, bony projections and their smaller size allows multiple tendons to pass over joints
What contractile protein do thick filaments contain? Thin filaments?
Thick filaments contain myosin and thin filaments contain actin
Myosin is composed of ____ polypeptide chains: ____ heavy chains and ____ light chains.
6; 2; 4
Tropomyosin provides structural benefits to the thin filament, including:
Surrounding the actin core to stiffen and stabilize it, blocking the myosin-binding site on actin when the muscle is relaxed
What molecule is found attached to tropomyosin on the thin filament? How many binding sites does it have and what are they meant to bind to?
Troponin; 3 binding sites, one for tropomyosin, one for actin, and one for calcium ions
What structural protein extends from the Z disc to the thick filament, forming its core before attaching to the M line?
Titin (elastic filament)
What stressor does titin help muscles resists?
Excessive stretching
What structural protein links thin filaments to integral proteins of the sarcolemma, aiding in stability? What disease is it associated with?
Dystrophin; Duchenne’s muscular dystrophy
What are the intermediate filaments that extend from the Z discs and connect each myofibril to the next throughout the width of the muscle cell made of?
Desmin
What molecule blocks myosin binding?
Tropomyosin
How many binding sites does actin have?
One - for myosin
How many binding sites does myosin have?
Two - for actin and ATP
What structural feature provides the muscle fiber with extensive surface area, allowing changes in the membrane potential to reach deep into the fiber?
The lumens of the T tubules are continuous with the extracellular space, allowing nerve impulses traveling along the sarcolemma to travel deep into the fiber
What structure is responsible for ensuring that every muscle fiber contracts at about the same time?
The T tubules
List the changes that occur in a sarcomere during sliding filament contraction.
The I bands (light bands) shorten as the thin filaments are pulled toward the M line and the area of overlap increases, the distance between Z discs shortens as the Z discs are pulled toward the M line, the H zone disappears, A bands move closer together because of the shortening I bands but their individual lengths do not change
Excitation begins at the ________________ _________.
Neuromuscular junction
What receptors does acetylcholine bind to on the muscle end plate?
Nicotinic cholinergic receptors
What step does muscle action potential end with?
The release of ionized calcium from the SR
What stage does calcium release (from the SR) initiate?
Contraction (cross-bridge cycling)
What feature gives the muscle end plate at the neuromuscular junction additional surface area?
Junctional folding of the sarcolemma
List the events that occur at the neuromuscular junction. (6 steps from initial action potential to termination)
- An action potential arrives at the axon terminal of the motor neuron
- Voltage-gated calcium channels open along the axon terminal membrane and calcium enters the terminal down its electrochemical gradient
- Calcium entry causes ACh to released by exocytosis
- ACh diffuses across the synaptic cleft and binds to receptors on the muscle end plate
- ACh binding opens ion channels that allow passage of sodium into the muscle fiber and potassium out of the fiber, producing a change in membrane potential (END PLATE POTENTIAL)
- ACh effects are terminated by its breakdown in the cleft by acetylcholinesterase
What is the end plate potential?
A change in membrane potential caused by the opening of sodium-potassium ion channels in the motor end plate
What are the four “big picture” steps of skeletal muscle contraction?
- Neuromuscular junction events
- Muscle fiber excitation (end plate potential propagation)
- Excitation-contraction coupling
- Cross bridge cycling
What is the final trigger for contraction and the internal messenger that links the action potential to contraction?
Ionic calcium
What are the three steps of action potential propagation?
- End plate potential is generated at the neuromuscular junction
- Depolarization of the sarcolemma opens voltage-gated sodium channels. Sodium enters by its concentration gradient. When a certain voltage is reached, an action potential is generated and spreads across the sarcolemma by opening more sodium channels.
- Refractory period (repolarization): the sarcolemma is restored to its initial polarized state due to potassium channels opening and allowing potassium ions to diffuse out of the muscle fiber
What is the autoimmune disease in which the immune system destroys ACh receptors?
Myasthenia gravis
List the steps of excitation-contraction coupling: (4 steps from AP propagation to cross bridge cycling)
- Action potential propagates along the sarcolemma and down the T tubules
- Voltage-sensitive tubule proteins within the T tubules change shape, activating calcium release channels in the terminal cisterns of the SR
- Calcium flows into the cytosol and binds troponin and removes the blocking action of tropomyosin
- Myosin binding to actin forms cross bridges and contraction and cross bridge cycling begins
Describe the steps of cross bridge cycling:
- Energized myosin head attaches to the actin filament, forming a cross bridge
- Myosin releases ADP and Pi, allowing it to pivot and bend, pulling the actin toward the M line
- A new ATP molecule attaches to myosin, weakening the link between myosin and actin. Myosin detaches.
- Myosin hydrolyzes ATP into ADP and Pi, which allows it to return to its pre-stroke high energy state. Returns to step 1.
What type of muscle contraction does not involve shortening of the muscle?
Isometric
What type of muscle contraction involves a change in length and movement of a load?
Isotonic
What type of isotonic contraction involves the shortening of a muscle?
Concentric (lifting a book)
What type of isotonic contraction involves lengthening of a muscle?
Eccentric contraction (lowering a book)
What is a motor unit?
One motor neuron and all of the muscle fibers that it supplies (could be four fibers to several hundred)
What is the term for a single muscle fiber’s response to a single action potential from a motor neuron?
Muscle twitch
What are the three phases of a muscle twitch?
- Latent period - excitation-contraction coupling
- Period of contraction - cross bridge formation
- Period of relaxation - calcium reentry into the SR
What are four factors that determine degree of muscle tension?
- Frequency of stimulation
- Muscle fiber diameter
- Motor unit size
- Motor unit recruitment
The activity of what enzyme affects contraction velocity?
ATPase speed (faster ATPase activity = increased velocity)
How does the method of forming ATP affect contraction velocity and duration?
Glycolytic fibers, which obtain energy solely from anaerobic respiration, make ATP quickly but run out fast. Aerobic respiration, performed by slow oxidative fibers, takes longer to form ATP and produces a lot, allowing for longer duration of muscle contraction.
Describe the creatine phosphate pathway of ATP production. How long does it provide energy for?
Creatine phosphate is an energy-rich molecule found in muscle tissue that directly restores ADP to ATP by transferring its phosphate group. Provides energy for about 15 seconds of contraction.
Describe the anaerobic pathway of ATP production. How long can it provide ATP for?
Glycogen stored in the muscle is broken down to glucose, which then undergoes glycolysis to produce 2 ATP and 2 pyruvic acid molecules. Pyruvic acid is converted to lactic acid and is released into the blood. The liver and kidneys break it down as waste. Can provide ATP for about 30-40 seconds of muscle contraction.
How does anaerobic metabolism compare to aerobic metabolism in terms of the speed and efficiency of ATP production?
Anaerobic respiration happens fast, about 2.5 times faster than aerobic, but only yields 2 ATP per glucose molecule. Aerobic respiration takes much longer but results in 32 ATP molecules per glucose.
Describe the aerobic respiration pathway.
Occurs in the mitochondria and requires oxygen. Breaks down pyruvic acid, fatty acids, and amino acids to produce ATP, CO2, and water. Yields 32 ATP per glucose. Carbon dioxide diffuses out of the muscle tissue and into the blood, to be removed by the lungs.
Which muscle fiber type has the largest diameter?
Fast glycolytic
Which muscle fiber type has the lowest glycogen reserves?
Slow oxidative
Which muscle fiber type has the lowest myoglobin?
Fast glycolytic fibers
Which muscle fiber type has the highest fatigue resistance? What is responsible for this?
Slow oxidative fibers; aerobic respiration
Which type of muscle fiber has the least amount of capillaries and mitochondria?
Fast glycolytic fibers
The prime mover muscle is also called the __________.
Agonist
Which muscles are synergists to the biceps brachii?
Brachioradialis and brachialis
Which muscle is the antagonist to the biceps brachii during arm flexion?
Triceps
In arm extension, which muscle is the agonist and which is the antagonist?
Triceps is the agonist, biceps the antagonist
What are 7 ways that muscles can be named?
- Location
- Location of attachments
- Shape
- Size
- Direction of fibers
- Number of origins
- Action
What type of lever would have the fulcrum between the effort and the load? Is this common in the body?
Class 1; not common
What type of lever would have the load in between the fulcrum and the effort? Is this common in the body?
Class 2; not common
What type of lever would have the effort between the fulcrum and the load? Is this common in the body?
Class 3; common
What is an example of a class 1 lever in the body?
The skull sitting on the cervical vertebrae: the front of the skull is the load, the vertebral column is the fulcrum, and the muscles attached to the base of the skull are performing the effort to keep the head upright.
What is an example of a class 2 lever in the body?
Plantar flexion of the foot: the toes are the fulcrum, the load is the weight of the body being lifted off the ground at the heel, and the muscles of the calf are providing the effort.
What is an example of a class 3 lever system in the body?
Arm flexion: the biceps provides the effort, the elbow is the fulcrum, and the hand carries the load. The effort is in the middle.
What type of movement would a muscle that crosses on the anterior side of a joint produce?
Flexion
What type of movement would a muscle that crosses on the posterior side of a joint produce?
Extension
What type of movement would a muscle that crosses on the lateral side of a joint produce?
Abduction
What type of movement would a joint that crosses on the medial side of a joint produce?
Adduction
What muscle shape has fascicles that are arranged in concentric rings? What is an other word for these muscles?
Circular; sphincters
What muscle shape has a broad origin with fascicles converging upon a single tendon of insertion? What is an example of this?
Convergent; Pectoralis major
What muscle shape has fascicles that run in the same direction as the long axis of the muscle and is often spindle-shaped? What’s another name for this type of muscle? What is an example of this type of muscle?
Parallel; fusiform; biceps brachii
What muscle type has short fascicles that attach obliquely to a central tendon that runs the length of the muscle? What three forms does this muscle type come in?
Pennate; unipennate, bipennate, and multipennate
What is an example of a unipennate muscle?
Extensor digitorum longus of the leg
What is an example of a bipennate muscle?
Rectus femoris
What is an example of a multipennate muscle?
Deltoid
Prime adductor of arm and medially rotates arm.
Pectoralis major
Pulls scapula forward and downward
Pectoralis minor
Rotates scapula laterally and upwards
Serratus anterior
Prime abductor of arm
Deltoid
Muscles of the ribs important for inspiration
External intercostals
Muscles of the ribs important for forced expiration
Internal intercostals
Flexes and rotates the lumbar region of the vertebral column and stabilizes pelvis.
Rectus abdominis
These two muscles flex the vertebral column and compress the abdominal wall
External and internal obliques
This deep muscle compresses the abdominal cavity
Transversus abdominis
This muscle stabilizes, elevates, retracts, and rotates the scapula.
Trapezius
This posterior muscle is the prime extensor and adductor of the arm and also medially rotates the arm.
Latissimus dorsi
These two muscles have their origins on the thoracic vertebral column and the inferior cervical vertebra, respectively, and help to stabilize the scapula.
Rhomboid major and Rhomboid minor
This muscle has its origin at the inferior edge of the scapula and is inserted at the medial side of the proximal end of the humerus. It extends, medially rotates, and adducts the arm.
Teres major
This muscle is inserted on the cervical vertebra from an origin on the upper medial edge of the scapula. It elevates and adducts the scapula.
Levator scapulae
What four muscles are involved in the rotator cuff?
Teres minor, supraspinatus, infraspinatus, and subscapularis
What is the name of the small muscle that spans from the olecranon to the distal/lateral end of the humerus? What does this muscle do?
Anconeus; weak extendor of the forearm
What muscles are involved in flexing the hands and fingers?
Flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, flexor carpi ulnaris, flexor carpi radialis, and palmaris longus
