Term | Definition |
Types of muscle tissue | skeletal, cardiac, smooth |
Muscular system | includes only skeletal muscles |
Function of skeletal muscles | produce skeletal movement, maintain body position, support soft tissues, guard openings, maintain body temperature, store nutrient reserves |
Structures in skeletal muscle | muscle fibers, connective tissues, nerves, blood vessels |
Three layers of connective tissue within muscles | epimysium, perimysium, endomysium |
Epimysium | an exterior collagen layer connected to deep fascia; separates muscle from surrounding tissues |
Perimysium | connective tissue that surrounds fascicles; contains blood vessel and nerve supply to fascicles |
Fascicle | a bundle of muscle fibers |
Endomysium | connective tissue that surrounds individual muscle fibers, and contains capillaries and nerve fibers contacting muscle cells; also contains myosatellite cells that repair damage |
Myosatellite cell | a muscle stem cell |
Muscle attachment | connective tissue at the end of muscles made of the combined epimysium, perimysium, and endomysium that forms a connective tissue attachment to the bone matrix, either as a tendon or an aponeurosis |
Tendon | bundle of connective tissue that attaches muscle to bone matrix |
Aponeurosis | sheet of connective tissue that attaches muscle to bone matrix |
Function of nerves in the muscular system | connect muscles to the central nervous system, allowing voluntary control |
Nomenclature of skeletal muscles | a descriptive name followed by a location name |
Function of blood vessels in the muscular system | form an extensive vascular network that supplies nutrients and large amounts of oxygen, and carries away waste products |
Properties of skeletal muscle fibers | are very long; develop through fusion of myoblasts; contain hundreds of nuclei |
Myoblast | mesodermal stem cell that forms skeletal muscle cells |
Sarcolemma | cell membrane of a muscle fiber; maintains transmembrane potential to allow contractions |
Sarcoplasm | cytoplasm of a muscle fiber |
T tubule | transverse tubule; transmits action potential through the muscle fiber; allows entire fiber to contract simultaneously, and has same properties as the sarcolemma |
Myofibril | lengthwise subdivision within muscle fiber made up of myofilaments |
Myofilament | a protein filament responsible for muscle contractions |
Types of myofilaments | thin filaments made up of actin; thick filaments made up of myosin |
Sarcoplasmic reticulum | membranous structure surounding each myofibril that helps transmit action potential and forms terminal cisternae attached to the T tubule; similar structure to smooth endoplasmic reticulum |
Terminal cisterna | concentrates calcium ions via ion pumps, and releases them into sarcomeres to begin muscle contraction |
Triad | internal structure of a muscle fiber formed by one T tubule and two terminal cisternae |
Sarcomere | contractile unit of muscle that forms the structural unit of a myofibril, and forms visible patterns within the myofibril |
Muscle striations | a pattern of light (I band) and dark (A band) filaments within myofibrils |
A band | a dark, thick filament within the myofibril |
I band | a light, thin filament within the myofibril |
M line | the center of the A band, at the midline of the sarcomere |
Z line | the center of the I band, at the ends of the sarcomere |
Zone of overlap | the darkest area visible in the myofibril, where the A and I bands overlap |
H band | area around the M line that has thick filaments but no thin filaments |
Titin | a strand of protein that reaches from the tips of the thick filaments to the Z line, stabilizing the filaments |
Function of sarcomeres | contracts when calcium ions released by the sarcoplasmic reticulum cause the thin and thick filaments to interact |
Four proteins of thin filaments | F-actin, nebulin, tropomyosin, troponin |
Mnemonic for remembering thick and thin filaments | the "tin" in actin corresponds to the thIn filaments, which look lIght and form the I band; the A band looks dArk |
Types of fascicle organization | parallel, convergent, pennate |
Types of attachment sites for convergent muscles | tendon, aponeurosis, raphe |
Types of pennate muscles | unipennate (extensor digitorum), bipennate (rectus femoris), multipennate (deltoid) |
Sphincter | circular muscles that open and close to guard entrances of the body |
Orbicularis oris | the muscle that closes and opens the mouth |
Orbicularis oculis | the muscle that closes and opens the eye |
Lever | rigid, moving structure |
Fulcrum | fixed point |
Three functions of levers | changes direction of applied force, distance and speed of movement, effective strength of applied force |
First-class lever | fulcrum is in the center between the applied force and the resistance; for example, nodding yes |
Second-class lever | centers resistance between fulcrum and applied force, to move a large weight with a small force; for example, tiptoeing |
Third-class lever | centers applied force between resistance and fulcrum, to maximize speed and distance traveled; for example, flexion of the elbow |
Types of muscle functions | agonist, antagonist, synergist, fixator |
Agonist muscle | produces a particular movement |
Antagonist muscle | opposes movement of a particular agonist |
Synergist muscle | smaller muscle that assists a larger agonist |
Fixator muscle | stabilizes point of attachment of an agonist muscle |
Only two muscles without the word "muscle" in their correct names | platysma, diaphragm |
Platysma | flat muscle of the lower jaw |
Diaphragm | umbrella-shaped muscle that separates the thoracic and abdominal cavities |
Ways muscles are named | location in the body, origin and insertion, fascicle organization, relative position, structural characteristics, action |
Muscles of the eye | six extrinsic muscles (sclera), two intrinsic |
Six extrinsic muscles of the eye | superior rectus, medius rectus, inferior rectus, lateral rectus, superior oblique, inferior oblique |
Intrinsic muscles of the eye | ciliary, iris |
Ciliary muscle of the eye | controls the shape of the lens to focus vision |
Iris muscle | controls the size of the pupils |
Divisions of the muscular system | axial (60% of muscles), appendicular (40%) |
Six muscle groups of the head and neck | facial expression, extrinsic eye muscles, mastication, muscles of the tongue, muscles of the pharynx, anterior muscles of the neck |
Process of initiating contraction | Ca2+ ion binds to receptor on troponin molecule; troponin-tropomyosin complex changes, expressing the active site of F-actin |
Sliding filament theory | thin filaments slide along thick filaments toward the M line at the center of the sarcomere; width of the A zone stays the same, Z lines move closer together |
Five steps of the contraction cycle | exposure of active sites; formation of cross-bridges; pivoting of myosin heads; detachment of cross-bridges; reactivation of myosin |
Process of relaxation | Ca2+ concentrations fall; Ca2+ ions detach from troponin; active sites are re-covered by tropomyosin; tension gradually falls to resting levels; titin proteins recoil after stretching |
Neuromuscular junction | location of neural stimulation; action potential causes release of neurotransmitters into the synaptic cleft |
Action potential | electrical signal that travels along the nerve axon and ends at synaptic terminal |
Synaptic terminal | part of the neuron that releases acetylcholine into the synaptic cleft |
Acetylcholine | neurotransmitter that transmits action potential from a motor neuron to a muscle fiber by binding to membrane receptors on the sarcolemma, making it more permeable to sodium ions |
Synaptic cleft | gap between the synaptic terminal and motor end plate, where acetylcholine is released by the neuron and attaches to the motor end plate |
Motor end plate | portion of the sarcolemma that receives acetylcholine |
Cardiac muscle tissue | striated muscle tissue found only in the heart, notable for containing intercalated discs |
Intercalated discs | specialized contact points between cardiocytes made up of gap junctions and desmosomes that enhance molecular and electrical connections and conduct action potentials |
Smooth muscle tissue | nonstriated tissue with different functional characteristics from skeletal muscle; causes involuntary movement in the body, mainly in the cardiovascular (regulating blood pressure and flow), digestive (peristalsis, sphincters), and integumentary systems |
Muscles of the shoulders and upper limbs | position the pectoral girdle, flex and extend the shoulder and elbow, abduct and adduct the shoulder, and rotate the shoulder |
Muscles that position the pectoral girdle | trapezius, rhomboid, levator scapulae, serratus anterior, subclavius, pectoralis minor |
Muscles that abduct the shoulder | deltoid (agonist), supraspinatus (synergist) |
Muscle that adducts the shoulder | coracobrachialis |
Muscles that rotate the shoulder | subscapularis and teres major (medial), infraspinatus and teres minor (lateral) |
Muscle that extends the shoulder | latissimus dorsi |
Muscle that flexes the shoulder | pectoralis major |
Muscles of the rotator cuff | supraspinatus, subscapularis, infraspinatus, teres minor |
Muscles that flex the elbow | biceps brachii (agonist), brachialis and brachioradialis (synergists), triceps and anconeus (antagonists) |
Muscles that extend the elbow | triceps brachii (agonist), anconeus (synergist), biceps and brachioradialis (antagonists) |
Muscles that move the thigh | gluteal, lateral rotators, adductors, iliopsoas |
Gluteal muscles | gluteus maximus, gluteus medius and minimus, tensor fasciae latae |
Lateral rotators of the thigh | piriformis, obturator |
Adductors of the thigh | adductor magnus, adductor brevis, and adductor longus; pectineus, gracilis |
Hip flexors | psoas major, iliacus |
Extensors of the knee | four muscles of the quadriceps femoris |
Quadriceps femoris | vastus medialis, vastus intermedius, and vastus lateralis; rectus femoris |
Flexors of the knee | hamstring |
Hamstring muscles | biceps femoris, semitendinosus, semimembranosus |