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What are the Universal Characteristics of Muscle?
- Responsiveness (excitability)
What is Responsiveness?
To chemical signals, stretch, and electrical changes across the plasma membrane
What is Conductivity?
Local electrical change triggers a wave of excitation that travels along the muscle fiber
What is Contractility?
The ability of muscles to shorten when stimulated
What is Extensibility?
It is the capability of being stretched between contractions
What is Elasticity?
The ability of muscle to returns to its original resting length after being stretched
What type of myofilaments are there in muscles?
What are Thick Filaments?
They are made of several hundred myosin molecules, they are shaped like a golf club. Two chains intertwined to form a shaftlike tail with Double globular heads. The heads are directed outward in a helical array around the bundle. One half the heads on the filament angle to the left and the other to the right. The zone which has no heads in the middle is called the bear zone.
What is the zone without any heads on the Thick filaments called?
The bare zone.
True or False: Thick Filaments have heads which face the same direction.
False half face right and the other left.
What are Thin Filaments made up of?
They are made up of Fibrous (F) actin, globular (G) actin, Tropomyosin, and Troponin.
What are Fibrous (F) actins?
They are two intertwined strands in a thin filament which has a string of globular (G) actin subunits each with an active site that can bind to head of myosin molecule
What are Tropomyosin molecules?
They are the string in the diagram which blocks 6-7 active sites on G actin subunits.
What is Troponin?
It is a small, calcium-binding protein on each tropomyosin molecule.
What are Elastic Filaments?
They are Titin (connectin): huge, springy protein. They flank each thick filament and anchor it to the Z disc. They help to stabilize the thick filaments and center it between the thin filaments. They also prevent overstretching.
What is an A band?
a dark; A stands for anisotropic. The part of A band where thick and thin filaments overlap is especially dark
What is an H band?
It is the middle of A band; thick filaments only
What is the M line?
It is the middle of H band
What is an I band?
It is the alternating lighter band; I stands for isotropic. The way the bands reflect polarized light
What is the Z disc?
It provides anchorage for thin filaments and elastic filaments. It also bisects I band.
What is a sarcomere?
It is the distance from Z disc to Z disc.
What is smooth muscle?
It is an involuntary muscle that can contract without nervous stimulation. It can also contract in response to chemical stimuli such as: Hormones, carbon dioxide, low pH, and oxygen deficiency. It can also contract in response to stretch.
How are smooth muscles in the stomach and intestines?
They are single-unit smooth muscle which have their own pacemaker cells that set off waves of contraction throughout the entire layer of muscle
What is a synapse?
It is the point where a nerve fiber meets its target cell
What is a Neuromuscular junction (NMJ)?
It is when the fibers target cell is a muscle fiber.
True or false: Each terminal branch of the nerve fiber within the NMJ forms separate synapse with the muscle fiber
How many muscle fibers does one nerve fiber stimulate within the NMJ?
One nerve fiber stimulates the muscle fiber at several points within the NMJ
What is a Synaptic knob?
It is the swollen end of nerve fiber. It also contains synaptic vesicles filled with acetylcholine (ACh)
What is a synaptic cleft?
It is a tiny gap between synaptic knob and muscle sarcolemma
What are Schwann cells?
Schwann cell envelops and isolates all of the NMJ from surrounding tissue fluid
What do synaptic vesicles do to release Ach?
Synaptic vesicles undergo exocytosis releasing ACh into synaptic cleft
How many ACh receptors are there?
50 million ACh receptorsproteins incorporated into muscle cell plasma membrane
What do junctional folds do?
Junctional folds of sarcolemma are beneath synaptic knob. They increase surface area holding ACh receptors.
What happens if there are no Ach receptors?
Lack of receptors leads to paralysis in disease myasthenia gravis
What is the Basal Lamina?
It is a thin layer of collagen and glycoprotein which separates Schwann cell and entire muscle cell from surrounding tissues. It contains acetylcholinesterase (AChE) that breaks down ACh after contraction causing relaxation
Describe and unstimulated resting cell.
There are more anions (negative ions) on the inside of the plasma membrane than on the outside. The plasma membrane is electrically polarized (charged). There are excess sodium ions (Na+) in the extracellular fluid (ECF). There are excess potassium ions (K+) in the intracellular fluid (ICF). Also in the ICF, there are anions such as proteins, nucleic acids, and phosphates that cannot penetrate the plasma membrane. These anions make the inside of the plasma membrane negatively charged by comparison to its outer surface.
Describe Stimulated (active) muscle fibers or nerve cells.
They have Ion gates open in the plasma membrane. This means that Na+ instantly diffuses down its concentration gradient into the cell. These cations override the negative charges in the ICF. Depolarization: inside of the plasma membrane becomes briefly positive. Immediately, Na+ gates close and K+ gates open. K+ rushes out of cell, repelled by the positive sodium charge and partly because of its concentration gradient. Loss of positive potassium ions turns the membrane negative again (repolarization).
Stimulated (active) muscle fiber or nerve cell (cont.)
- Action potential: quick up-and-down voltage shift from the negative RMP to a positive value, and back to the negative value again
- RMP is a stable voltage seen in a waiting muscle or nerve cell
- Action potential is a quickly fluctuating voltage seen in an active stimulated cell
- An action potential at one point on a plasma membrane causes another one to happen immediately in front of it, which triggers another one a little farther along and so forth
* Electrically excitable cells; slides 94-96
- * Muscle innervation; slides 111-112
- * Threshold, latent period and twitch; slides 134-136
- * Behavior of skeletal muscle fiber; slides 117-127
- * Circulatory system vs. cardiovascular system; slide 4
- * Function of circulatory system; slides 4-5
- * Erythrocyte homeostasis; slide 32
- * Erythrocyte death and disposal; slides 33-34
- * Erythrocyte production; slides 26-27
- * Leukocyte life cycle and leucopoiesis; 43-45
- * Platelet production; slide 71
- * Erythropoiesis
- * Valves; slide 22-23
- * Aneurysm; 117
- * Circulatory shock; 122
- * Myogenic shock; slide 124
- * TIAs; 126
- * Vasomotion control; slide 51
- * Skeletal muscle; slides 92-93
- * Fetal development; slides 99-103
- * ATP, slide 2
- * Arteries, veins, and capillaries; slide 4
- * Function of the respiratory system; slide 10
- * Organs of the respiratory system; slide 14
- * Cells of the alveolar; slides 55-57
- * Alveoli; slide 59