Muscles Flashcards
Skeletal Muscle General Characteristics
Attached to bones and skin, covers the skeleton. Responsible for movement and maintenance of position. Is striated and is the most abundant. Voluntary, under conscious control. Very powerful cells, and longest cell type. Cells are multinucleated and have many mitochondria.
Smooth Muscle General Characteristics
Found in the walls of the visceral organs. Function is to control the movement of material. Nonstriated, smaller cells with pointed end and a belly. Under involuntary control. Innervation is rare unless it is to an entire mass.
Cardiac Muscle General Characteristics
Found in the heart. Striated, has intercalated discs. Involuntary and innervated as one mass.
Skeletal Muscle Cells
Called muscle fibers, and are long and stringy. Each one is served by one artery, one nerve, and one or more veins.
Endomysium
Fine areolar connective tissue surrounding each muscle fiber which insulates the cell.
Satellite cells
Scattered between the muscle cells and endomysium, they permit repair of damaged cells.
Fascicle
A bundle of muscle cells
Perimysium
A sheath of collagen that binds the fascicles
Epimysium
An overcoat of dense connective tissue that surrounds the whole muscle.
Indirect Attachment of Muscles
Tendons, cord-like structures, or aponeurosis, flat extensions, connect the muscles to bone. They are the most common, because they withstand friction better.
Fascicle Arrangement:
Parallel
The length of the fascicles runs parallel to the long axis of the muscle.
Fascicle Arrangement:
Convergent
The muscle has a broad origin where the fascicles lead to a single tendon called the insertion.
Fascicle Arrangement:
Pennate
The muscles look like a feather.
Fascicle Arrangement:
Unipennate
The muscles looks like half of a feather with a tendon as the shaft.
Fascicle Arrangement:
Bipennate
The muscle looks like a complete feather with a tendon as the shaft.
Fascicle Arrangement:
Multipennate
The muscle looks like 3 or more feathers attached at their bases.
Fascicle Arrangement:
Circular
Fascicles form a circle of muscle fibers, they form sphincter muscles.
Excitation (4 steps)
1) Vesicles in the nerve cells rupture and move to the terminal end of the nerve fiber releasing acetycholine.
2) The acetycholine diffuses across the cap and attaches to receptors on the scarcolemma.
3) There’s an influx of Na+ resulting in an inwards movement of Na+ and develops a local potential, an EPP.
4) Once the EPP reaches threshold, the Na+ channels open and Na+ flood in initiating the AP.
Excitation (4 steps)
1) Vesicles in the nerve cells rupture and move to the terminal end of the nerve fiber releasing acetycholine.
2) The acetycholine diffuses across the gap and attaches to receptors on the sarcolemma.
3) There’s an influx of Na+ resulting in an inwards movement of Na+ and develops a local potential, an EPP.
4) Once the EPP reaches threshold, the Na+ channels open and Na+ flood in initiating the AP.
Mechanism for Muscle Contraction
In order for the cell to contract, it must first be excited and an action potential must move across the membrane. For a skeletal muscle, the source is always the nervous system.
Calcium’s role in contraction
Calcium reacts with troponin and acts like a switch changing the shape of the troponin-tropomyosin complex. This uncovers the cross-bridge binding site on the thin filaments.
Mechanism of the Sliding of the Thin Filaments (4 Steps)
1) When the myosin of the cross-bridges attaches, it’s in the high energy configuration. As soon as it attaches to the binding site, it returns to the low energy configuration.
2) A new ATP attaches to the myosin head and causes it to detach from the binding site.
3) Now the ATP is hydrolyzed to ADP, releasing energy returning the myosin to the high energy configuration
4) The myosin head now binds to a new binding site and the process is now repeated.
Relaxation (3 steps)
1) Termination, the AP permits the sarcoplasmic reticulum to transport Ca2+ out of the myofibrils.
2) The loss of Ca2+ results in the reattachment of the troponin and tropomyosin complex to the binding sites and the breaking off of contact with the cross-bridges.
3) The end result is that the thin filaments are no longer attached to the thick filaments. They slide back to the resting, relaxed points because of the elastic elements.
Muscles in the absence of Calcium
No contraction will occur
Muscles in the absence of ATP
The cross-bridges lock onto the thin filaments, but no contraction. Rigor mortis
Muscle Twitch
A response of a single muscle cell to a single stimulus. 3 stages
1) Latent Period - the time it takes the AP to sweep over the muscle cell.
2) Contraction Period - the time the cell is actually shortening
3) Relaxation Period - the time the cell is lengthening
Summate
Because the contraction period is so much longer than the latent period, it’s possible to have a rapid series of stimuli and produce a rapid period of APs which result in waves so close together that the muscle never gets a chance to relax.
Tetanus
The APs are rapid enough that it ends up with a smooth, sustained contraction. These rapid series of impulses and various chemical reactions cause the muscle to warm, making the force of contraction greater, delivering more force than a single muscle twitch.
Treppe
A staircase pattern where the contraction strength of the muscle increases even though the stimulus does not increase. Due to calcium and enzymes.
Motor Unit
A motor neuron plus all the muscle cells that it innervates.
Muscles of Fine Control
Muscles, like those of the eye, which have many motor units but very few muscles cells per unit, 10-15 per unit.
Isometric Muscle Contraction
A muscle develops tension, but the muscle does not shorten. Muscles that maintain Position
Isotonic Muscle Contraction
A muscle develops tension, and shortens. Associated with movement.
Fast Glycolytic Fibers
Fibers that have a fast rate of contraction. they lack myoglobin, and are rich in glycogen. Depend on anaerobic glycolysis for energy. Most common in the body, and fatigue is rapid.
Slow Oxidative Fibers
Fibers with a slow rate of contraction. They do have myoglobin, are smaller, and rely on oxygen to make ATP. They have a slow rate of fatigue
Fast Oxidative Fibers
Fibers with an intermediate speed of contraction. They are large and pale due to low amounts of myoglobin. They have an extensive capillary network and are slower to fatigue.
Muscle Fatigue
When ATP use exceeds production. Weakness of heavily exercised muscles results in an accumulation of lactic acid.
Activity (Exercise)
The body needs a certain amount of activity or exercise for the well-being of the skeletal muscle.
Isometric Exercise
The muscle is placed under tension but not much movement happens. Ex: Weight lifting
Isotonic Exercise
Exercising the muscle over an extended period of time with a great amount of movement. The muscles increase their endurance, and all 3 types of fibers because more aerobic. Ex: Jogging, tennis, swimming.
Myasthenia Gravis
Weakness of the skeletal muscle. Loss of ACh receptor sites on the motor plate. Due to an autoimmune disease, the cells do not contract as often as they should. Can be treated with an anticholinesterase or with immunosuppressants.
Muscular Dystrophy
Degeneration of muscle cells which are usually replaced by fat. Atrophy sets in. Two forms, both genetic.
Duchenne
One type of muscular dystrophy which affects only males, usually in the early age. By adolescence they’re in a wheelchair. Due to a missing protein known as dystrophin, usually found in muscle fibers to internally support the sarcolemma. There is no cure, but can be treated with myoblasts injected into diseased cells.
Cramps
Painful, spasmodic contractions of muscles. An involuntary complete tetanus contraction.
Aging
Begins in the middle 20s and is a progressive loss of skeletal muscle cells usually replaced by fat. Results in loss of maximum strength by 50% between 20 and 80.
Mesoderm
Most all muscle tissue develops from embryonic muscle cells called myoblasts
Smooth Muscle
Cell Shape
Small, spindle shaped cells with one nucleus. Cells are arranged in sheets and can stretch more than skeletal muscle.
Smooth Muscle
Sarcoplasmic Reticulum
Poorly developed sarcoplasmic reticulum with missing t-tubules.
Smooth Muscle
Myofilaments
No striations. Do have thin and thick filaments but the proportion and organization is different. Have tropomyosin, but no troponin. No sarcomeres. Contain intermediate filaments and dense bodies forming a network to harness cross-bridge activity.
Single Unit Smooth Muscle
Most common type. The visceral muscle. It does not require innervation, but can be. It does not exhibit tetanus or summation. Found in the hollow organs.
Multiunit Smooth Muscle
Behaves more like skeletal muscle. It requires innervation, but the nerves come from the ANS. It can exhibit summation and tetanus. It’s organized into motor units and rarely have gap junctions. Found in the ciliary body and iris of the eye, walls of blood vessels, and arrector pilli.
Smooth and Skeletal Muscle Contraction Rate
Compared to skeletal muscle, smooth muscle shows a slower contraction and relaxation rate, but it has the ability to remain contracted for extended periods of time.
Hyperplasia
Certain smooth muscle cells are capable of dividing. Ed: the uterus during puberty.
Skeletal Muscles as organs
Are complex, composed of muscles, nerves, and connective tissue. Connected to the nervous system and have an extensive blood circulation. Make up about 35% of the body mass for women, 40% for men. Over 600 muscle types in the body.
Direct Muscle Attachment
Connective tissue envelope of the muscle is directly fused to the periosteum of the bone.
Tendons
Rope-like bundles of dense connective tissue, continuous with the envelope surrounding the muscle.
Aponeuroses
Sheet-like tendons
Action of Muscles
Muscles can exert their effect by pulling only, usually across a joint.
Antagonistic Groups
Since muscles can only pull across joints, there must be a muscle or set of muscles for every movement a joint is capable of performing. If there is a muscle(s) that moves a joint in one direction, there has to be a muscle(s) to move it in the other direction.
Primer Mover
Also known as an agonist. It is found within a group of muscles, it is the one muscle primarily responsible for the lead action
Synergists
The muscles that aid the prime mover.
Muscle Nomenclature:
Action
Named for the action the muscle does. Ex: Flexor digitorum, flexes the digits.
Muscle Nomenclature:
Location
Named for where the muscle can be found, the bone or region.
Muscle Nomenclature:
Number of heads
Named for how many heads the muscle has Ex: biceps or triceps.
Muscle Nomenclature:
Shape
Named for the shape of the muscle Ex: Deltoid is triangular shaped
Muscle Nomenclature:
Size
Named for the size of the muscle Ex: Gluteus maximus or minimus.
Muscle Nomenclature:
Direction of muscle fibers
Named for the direction the muscle fibers are moving in respect to the midline. Ex: Rectus has straight fibers, Obliques have angular fibers.
Origin
The muscle end attached to the stationary structure
Insertion
The muscle end attached to the moving structure.
Belly
The muscle between the origin and the insertion
Muscle Functions
Movement of bones or fluid. Maintenance of position. Generation of heat.
Functional Characteristics:
Excitability
The ability to receive and respond to a stimulus.
Functional Characteristics:
Contractility
The ability to shorten
Functional Characteristics:
Extensibility
The ability to be stretched
Functional Characteristics:
Elasticity
The ability to recoil to resting length.
Glycolysis
Ten chemical steps where glucose is converted into two pyruvic acid molecules. Happens in the cytoplasm, is anaerobic, and results in 2 ATP per glucose molecule and two NADHs.
Krebs Cycle
An aerobic pathway. The two pyruvic acid molecules are converted to acetyl CoA. This goes through the cycle being oxidized and decarboxylated. We end up with 8 NADH, 2 FADH2, and 2 ATP. This occurs in the mitochondria’s matrix.
E- transport chain
Aerobic, and occurs in the mitochondria’s membrane. Coenzymes deliver it to redox acceptors. P1 is added to ADP by oxidative phosphorylation. Hydrogen and O2 form the water, but the ETC doesn’t make ATP directly. It generated a proton gradient across the membrane, stores the energy and later adds the phosphate to the ADP.
Oxygen Debt
During peak exercise, the circulatory system may not have enough oxygen to supply the skeletal muscle. ATP is generated by converting pyruvic acid. However, this only lasts a short time, afterwards the body must metabolize the lactic acid, in the liver, and oxygen must be present. To pay off the oxygen debt, the body must increase O2 take in.
Energy for Contraction
A large amount of energy is needed to contract the muscle. The muscle itself stores very little ATP (4-6 sec), the remainder must be made.
Creatine Phosphate
A secondary source of energy. It is a high energy compound synthesized by ATP when the muscle is at rest. When all the ATP is used up, creatine phosphate donates a phosphate to ADP to become ATP.
Sarcoplasm
Cytoplasm of a muscle cell. Contains myoglobin, a protein used for O2 storage, and glycosome, granules of stored glycogen.
Sarcolemma
The plasma membrane of the muscle cell.
Sarcoplasmic Reticulum
Forms the endoplasmic reticulum tubules wrapped around the myofibril. Mainly regulates and stores calcium.
Myofibrils
Rod-like structures running parallel, extending the length of the cell. They make up about 80% of cell volume. The contractile elements of the cell, they exhibit striations and have repeating light and dark bands.
I Band
Actin, a thin filament, with a midline called the Z-Disk.
A Band
Myosin, the thick filaments, where thick and thin overlap. Has a light H-Zone with the M-line down the middle
H Zone
Has thick filaments only, no overlapping so it looks lighter.
M Line
Has proteins, stabilizes the position of the thick filament.
Z Line
Has proteins called “connectins”. They interconnect and anchor thin filaments to the next sarcomere.
Sarcomeres
Repeating subunits of myofibrils. The muscle part between two Z lines, the smallest contractile unit of the muscles.
Thin Filaments
Found across the I-band and partly into the A-band. Two long F-actin strands coiled around each other forming G-actin. Also composed of regulating proteins troponin and tropomyosin
Troponin - 3 polypeptides
1) TnI - binds to actin
2) TnT - binds to tropomyosin
3) TnC - bings to calcium
Thick Filaments
Have binding sites for ATP. Composed mainly of myosin with myosin heads called cross-bridges that will interact with the thin filaments.
Elastic Filaments
Extend from the Z-disc to the M-line
Transverse (T) Tubule
Filled with fluid, through which electrical impulses will travel, called Action Potentials which trigger the muscle contraction.
Cisternae
Storage areas for calcium, with the T-tubules they form a Triad.
Nerve Fiber
Does not actually touch the muscle sarcolemma, called the neuralmuscular cleft or synaptic gap. The section right beneath the nerve is called the motor plate.
Nerve Impulse
The AP moves from the nerve fiber, across the gap, to the motor plate and causes it to depolarize. The depolarization wave spreads across the rest of the sarcolemma.
