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31 Cards in this Set

  • Front
  • Back
What are muscles good for?
Movement, stabilization, posture, generating heat
What is so special about muscles?
They are contractile, excitable, extensible and elastic
What is skeletal muscle?
voluntary, striated muscle that you consciously control the movement of. Is found in all limbs and body walls. Parallel striated muscle cells (fibers) surrounded and held together by CT fibers, with capillary beds running parallel to fibers. Contract in response to acetylcholine. Striated appearance of this muscle is due to the arrangement of various myofilaments found within the contractile units (sacromeres) of the muscle.
What is cardiac muscle?
Involuntary, striated muscle, innervated by the autonomic nervous system. Found only in the walls of the heart.
What is smooth muscle?
Involuntary non-striated muscle. Innervated by the autonomic nervous system. Found in the walls of blood vessels and hollow internal organs.
Fascia
Fibrous CT (primarily collagen fibers) that surrounds and seperates muscles in the body
Tendon
A cord-like fascial extension at the end of muscle attaching it to the body by the intermingling of collagen fibers with those of the periosteum
Aponeurosis
Broad, sheet-like arrangement of fascia attaching muscle to muscle or bone
Sharpey's Fibers
Collagen fibers of the periosteum that insert into underlying bone. The collagen fibers of tendons blend with those of the periosteum which in turn blend with Sharpey's fibers, thus forming a contractile unit.
Explain a sacromere.
The smallest functional unit of a skeletal muscle cell, extending from z-line to z-line
Skeletal Muscle Cells
Long, multinucleated, cylindrical cells with peripheral nuclei. Each cell fiber contains a sarcoplasm(cytoplasm of muscle cells), Sarcolemma(plasma membrane + basal lamina of muscle cells), and Satellite cells(found between plasma membrane and basal lamina). Skeletal muscle cells are considered to be stem cells which give rise to form new myoblasts that fuse to form skeletal muscle cells
Sarcoplasmic Reticulum of Skeletal Muscle cells
The endoplasmic reticulum of muscle cells. Composed of two parts: terminal cisternae(swollen sacs that are connected by a smaller tubular system-sarcotubules).
T(transverse) tubules of skeletal muscle cells
Invaginations of muscle fiber cell membrane (sarcolemma) from the surface. They are found between the terminal cisternae of adjacent sarcomeres. Together the three structural units are referred to as a triad.
Myofibrils
Aggregations of myofilaments (actin and myosin) that occupy the bulk of the cytoplasm. It is these contractile units that provide the movement exhibited by a muscle when it contracts.
Calcium availability in skeletal muscle cells
Both the sarcoplasmic reticulum and T-tubule system penetrate the muscle cell and wrap around each myfibril. this ensures that calcium( supplied by sarcoplasmic reticulum) and depolarization wave (following cell membrane) are available for muscle contraction and that all the sarcomeres in each myofibril- no matter how deep they are within each fiber- recieve both.
Hierarchical Arrangment
Skeletal muscle is composed of bundles of fasiculi of muscle cells, surrounded by perimysium. Muscle fasciculi are composed of muscle cells(or fibers), each surrounded by its own endomysium. Muscle fiber/cell is composed of myofibrils contained within its sarcolemma of each cell. Myfibrils are made up of actin and myosin or myofilaments.
Skeletal Muscle Striations
Sacromere, I band(light) which are actin myofilaments only. A band (dark) which is actin and myosin and Z lines.
How Muscle Cells Contract I
The thinner actin (myo) filaments slide in over the thicker myosin (myo) filaments, pulling the Z lines behind them and thereby shorten the sarcomere.
How Muscle Cells Contract II
While each sarcomere shortens a miniscule amount, by multiplying that by millions(as sarcomeres are extremely numerous) the muscle contracts markedly.
Connective Tissue Arrangment
Septa: pass inward from the deep fascia of the limb to compartmentalize the muscles-generally into groups with a similar function and or innervation.
Epimysium, perimysium, endomysium
Epimysium-dense connective tissue surrounding entire muscle. Perimysium-surrounds bundles of fibers or fascicles. Pathway for blood vessels into muscle tissue. Endomysium-delicate, loose CT, investing each muscle fiber or cell
What controls contraction?
Each muscle cell makes contact with a nerve ending at the neuromuscular junction (or synapse) between the nerve ending and the muscle cell. The depression the synaptic knob sits on in the muscle fiber is the motor end plate.
Controlling contraction continued
One nerve ending and all the muscle cells it contacts is a motor unit or neuromotor unit. The ratio of nerve fibers to muscle cells delineates a delicate from a non-delicate muscle. Eye muscle: 1 neuron:3 muscle cells. Back muscle: 1 neuron: 100's of muscle cells. This generally defines the level of intricate control these muscles exert on the structures they move.
Cardiac Muscle
Found only in the myocardium (muscular wall) of the heart. Involuntary and striated, innervated by the ANS. Cardiac muscle cells are often referred to as cardiocytes. Small in size compared with skeletal muscle. Centrally located nucleus. Contain regularly arranged myofibrils (in sarcomeres) like skeletal muscle so exhibit the same banding. Incapable of division and have no satellite cells so no regeneration after injury. Cardiac muscle cells also branch and rejoin each other, the union facilitated by an intercalated disc.
Intercalated Disks
Specialized junctional connections between adjacent cardiocytes. Each disc is composed of two main structural elements: Desmosomes(myofibrils form a bridge between cells so all cells pull together when their sarcomeres contract. Gap Junctions which allow ions and molecules to move between cells providing communications between cells. Intercalated discs occur at Z lines of cardiac muscle sarcomere.
Smooth Muscle
Non-striated, involuntary muscle innervated by ANS. Cells are short, spindle-shaped and have a single central nucleus. No sarcomeres. Responds to norepinephrine and acetylcholine. Will contract in response to stretch of lumen it surrounds. Slower to contract than skeletal muscle and stays contracted much longer.
Arrangments of smooth muscle: multiunit
Multiunit smooth muscle are muscle fibers poorly organized and function as individual fibers not together as a syncytium. Found in walls of blood vessels and the iris of the eye. Typically contracts in response to nerve impulses and hormones.
Arrangments of smooth muscle: visceral (single unit)
Sheets of spindle shaped cells held together via gap junctions. Found in hollow organs (stomach, intestines, bladder and uterus). Normally arranged in 2 thick layers (outer longitudinally directed fibers, inner circularly directed fibers). Fibers are able to stimulate each other to contract.
Rhythmaticity
displayed by smooth muscle cells. Pattern of repeated contractions. Results from self exciting fibers which spread to adjacent cells. One example is peristalsis-slow contractile waves of gastrointestinal tract that results from fibers stimulating each other. Typical peristalsis moves food from the oral cavity down the esophagus to the stomach. Reverse peristalsis is vomiting.
Locations of smooth muscle
in walls of all blood vessels (except heart), walls of hollow organs, in organized layers in the walls of respiratory, circulatory, digestive, and reproductive tracts.
Smooth muscle cells
Are small, can exhibit gap junctions, have no t-tubules, exhibit poorly developed sarcoplasmic reticulum, are spindle-shaped with tapered ends. The single central nucleus can divide-therefore regeneration after injury possible or also hyperplasia(increase in cell number). Actin and myosin randomly arranged therefore no striations.