Muscle Flashcards
(29 cards)
When does contraction occur in skeletal muscle?
ONLY in response to synaptic excitation from motor neurons.
_______ _________ have long cylindrical cells, multinucleated, ~50 microns in diameter and can be up to several cm long.
Skeletal muscle.
________ ______ varies in properties from region to region, contain 1 or 2 nuclei and are interconnected electrically and mechanically.
Cardiac Muscle.
What does cardiac muscle contraction depend on?
NOT the synaptic excitation from neurons.
What does striated mean and what type of muscles does it describe, and what does it result from?
Striped. Skeletal and cardiac muscle. Result of the organization of contractile proteins into aligned structures termed sarcomeres.
__________ ________ cells have a single nuclease and are small at 2-5 microns wide and 20-200 microns long.
Smooth muscle cells.
What does smooth muscle contraction depend on?
Some require synaptic input, others do not. They are NOT striated.
What is EC Coupling?
Excitation-Contraction Coupling.
The physiological process of converting an electrical stimulus to a mechanical response.
What are the 4 differences in EC coupling in skeleton and cardiac muscle?
- Skeletal Ca entry is not required for contraction. For cardiac, it is.
- Skeletal has the slowly activating L-type current. Caridac has the rapidly activating L-type current.
- Alpha1s DHPR in skeletal vs. alpha1c DHPR in cardiac. (Type of receptor)
- RyR1 ryanodine receptor in skeletal muscle and RyR2 ryanodine receptor in cardiac.
Myofibril
Basic rod-like unit of a muscle. Muscles are composed of tubular cells called myocytes, also known as muscle fibers, and these cells in turn contain many chains of myofibrils.
T-Tubule
A T-tubule (or transverse tubule) is a deep invagination of the sarcolemma, which is the plasma membrane of skeletal muscle and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.
Sarcomere
The basic unit of a muscle. Muscles are composed of tubular muscle cells (myocytes or myofibers) Muscle cells are composed of tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands. Sarcomeres are composed of long, fibrous proteins that slide past each other when the muscles contract and relax.
Two of the important proteins are myosin, which forms the thick filament, and actin, which forms the thin filament.
SR/Sarcoplasmic Reticulum
A system of membrane-bound tubules that surrounds muscle fibrils, releasing calcium ions during contraction and absorbing them during relaxation.
What is the thick filament?
Myosin.
The globular head domain contains actin- and ATP-binding sites and is responsible for generating force.
Neck. Tail.
What is the thin Filament?
Actin.
Describe the relationship between myosin, actin and ATP.
Myosin is the motor, actin filaments are the tracks along which myosin moves, and ATP is the fuel that powers movement.
What is cross bridge cycling?
The actin-myosin bridge very rapidly dissociates due to ATP binding to myosin.
The free myosin bridge moves into position to attach to actin, during which ATP is hydrolyzed. The free myosin bridge along with its hydrolysis products rebinds to the actin filament.
The cross-bridge generates force, and actin displaces the reaction products (ADP and Pi) from the myosin cross-bridge. This is the rate-limiting step of contraction. The actin-myosin cross-bridge is now ready for the ATP binding of step 1.
Describe the relationship between troponin, tropomyosin and actin?
Ca goes up. Troponin binds. Tropomyosin moves. Myosin binds to Actin. Pulls towards the center of the sarcomere. If there is no ATP, it gets stuck in that position. (Rigor Mortis)
ATP binds, and re-cocks the myosin head.
What is the triad that causes Ca release from the SR.
DHPRs in t-tubles-SR juction.
What is the difference in cardiac-type EC coupling and skeletal coupling?
The entry of external calcium into the DHPRs in t-tubules-SR junction.
What needs to be present for the myosin-actin cycle to continue?
Ca-ATP.
What pumps Ca back into the SR? What are the effects?
Ca ATPase (SERCA), pumps Ca back into SR, lowering cytoplasmic Ca++ and tropomyosin again blocks the actin binding sites for myosin.
In Cardiac-Type EC coupling, depolarization activates __________ channels, external __________ enters and activates release from _______ via ________.
Calcium/Cav1.2 type, calcium, SR, RyR2.
In EC coupling in smooth muscle, what causes the generations of 2nd messenger? What are the second messengers.
NT causes generation of 2nd messenger IP3, which causes release of Ca via IP3 receptors in SR.
