Muscle Flashcards
Non-Muscle Contractile Cells- Myoepithelial cells- Myofibroblasts- Pericytes
- Flattened cells. Similar protein arrangement to that of smooth muscle. Part muscle part epithelium.- Part muscle part fibroblast. Secrete collagen particularly near to open wounds.- Dotted around capillaries. Act as stem cells and evidence suggests that they may play a part in altering capillary diameter.
Skeletal Muscle- Tissue formed from- Contains- Some characteristics
- Muscle cells and associated connective tissue- Blood vessels, nerves, lymphatics, connective tissue and specialised sense organs- Unbranched, striated, multinucleate - nuclei at periphery (sarcolemma) of cells
Skeletal Muscle Organisation- Fascicles- Epimysium, perimycium and endomycium- Sarcomeres and myofibrils- Striations
- Muscle fibres bundled into a group. Several of these in a muscle.- Surround the entire muscle, a single fascicle and a single muscle fibre respectively.- Sarcomeres are the contractile unit of the muscle fibre. Hundreds/thousands of these placed end to end to form myofibrils which are packed into the muscle like cigarettes- Not an actual structure. Formed by the meeting point of two sarcomeres at the Z lines.
The Motor Unit- What does it consist of?- More precise control achieved by?- Synapse
- The motor nerve and all of the fibres which it innervates- Reducing the number of fibres per nerve- Special kind of synapse called the motor end plate
The Neuromuscular Junction- Where are they found?- Motor end-plate- Acetlycholine
- Each fibre has a single neuromuscular junction- Motor axons terminate at these- Released when the action potentials arrive in the end-plate. Initiates an action potential in the sarcolemma.
Structures found in Skeletal Muscle- T-tubules- Sarcoplasmic reticulum- Triads
- Tubules which extend from the sarcolemma into the muscle cell. Effectively the outside of the cell. Release Ca2+ when reached by AP which allows ratchet of myosin across actin.- Specialised ER which has a high Ca2+ content. Branches of it lie on either side of each T tubule.- Each T-tubule associated with a sarcomere is flanked by segments of the sarcoplasmic reticulum. The three together are referred to as a triad.
Skeletal Muscle Fibre Types- Type I- Type IIA- Type IIB
- Relatively slow/weakly contracting fibres. Abundant mitochondria. Fatigue resistant. Depend on oxidative metabolism. Often called “red” fibres.- Intermediate between Type I and Type IIB. It is relatively uncommon.- Relatively fast contracting fibres. Depend on anaerobic metabolism. Relatively few mitochondria. Much easier to fatigue and produce relatively higher force. Often called “white” fibres.
Myotendinous Junction- What happens at the myotendinous junction?- How is the myotendinous junction set up?
- Collagen of tendon attaches to muscle fibres at this point.- Muscle fibre tightly anchored to tendon by complex interdigitations.
Skeletal Muscle Feedback- Intrafusal fibres- Extrafusal fibres
- Special fibres which detect the amount of stretch in the fibres of the muscle and feed it back to the CNS. Found inside spindle fibres.- Regular contractile muscle cells
Smooth Muscle Basics- Shape- Nucleus- Actin/myosin and focal densities
- Fibres are elongated, spindle shaped cells.- Single cigar-shaped nucleus near the centre of each cell.- Poorly organised compared to skeletal or cardiac muscle. They converge at focal densities on the peripheries of the cells.
Smooth Muscle Locations and Stimuli- Locations- Stimuli
- Often in walls of tubes. Gut, uterus, blood vessels, respiratory tract etc. Also found in iris of eye.- Typically gets signals for both contraction and relaxation. Smooth muscle usually contracts continually/rhythmically in the absence of additional signals. Stimuli can come from ANS and spread through muscle, or it can come from hormones.
Cardiac Muscle Basics- Forms- Fibres, striations and nuclei- Intercalated disks- Sarcoplasmic reticulum
- Major parts of heart chamber walls and origins of great vessels.- Shorter than in skeletal, and branch to form a complex network. Present but less prominent than in skeletal. Single (sometimes 2) nuclei near centre of fibres.- Areas where two cells meet. These have a huge junctional complex to maintain a very strong connection.- One branch per T-tubule. Forms a dyad rather than a triad.
Regeneration of Skeletal Muscle- Satellite cells
- Population of myoblasts or stem cells. Pressed against outside of muscle cell. When the fibre is damaged the satellite cell can proliferate to immediately replace the damaged cell.
