MUSCLE TISSUE Muscle Contraction
I. TYPES OF MUSCLE A. Skeletal muscle-voluntary muscle, striated with light and dark bands, many nuclei. • Found in limbs, trunk of body, jaws, face, eyes etc.
B. Smooth muscle—involuntary, visceral muscle forms muscular layer of organs. Has one nucleus, contracts voluntarily. Rhythmic contractions. • Digestive tract, bladder, ducts, arteries and veins.
C. Cardiac muscle-involuntary, similar to skeletal-striated but controlled by the autonomic nervous system. Branched cells with central nuceli. Intercalated discs assure impulses travel between cells. • Heart muscle
II. Skeletal Muscle Components Muscle Fascicles Muscle Fibers (cells) Myofibrils Sarcomeres Myosin (thick) Actin (thin) Filaments
III. MICROSOPIC ANATOMY OF SKELETAL MUSCLE • Muscles contain fascicles that contain muscle fibers(cells). • Muscle fibers contain Myofibrils which contain sarcomeres. • Sarcomeres contain: • Actin-thin filaments • Myosin-thick filaments
IV. THE NEUROMUSCULAR JUNCTION A. Connects nerve cells called motor neuronswith muscle cells at a specialized region on the muscle called the motor end plate. B. Neurotransmitters-chemicals released by the nerve cell which stimulate muscles to contract. For muscle contraction acetylcholine (ACH) is used. C. Target of neurotransmitters is the sarcomere in the muscle.
V. CONTRACTION OF A MUSCLE FIBER A. Action potential-electrical signal from a motor neuron (nerve fiber) causes a change in the electrical charge of the membrane in the nerve cell (Na+ rushes in). B. A neurotransmitter (chemical that sends signals from the nervous system) called AChis released to signal the muscle fibers in the sarcoplasmic reticulum. C. Ca++ rushes in from surrounding sarcoplasmic reticulum. D. Ca++ binds to a molecule called troponin on actin which causes the shape to change. E. Cross bridges attach and detach on actin and myosin causing contraction of muscle. The muscle fiber shortens.
VI. MUSCLE CONTRACTION • Myogram-shows a pattern of muscle responses when electrically stimulated. • Simple twitch-response of a relaxed muscle to a stimulus. C. Latent period-pause between stimulation and contraction. D. Contraction period-onset of muscle shortening to peak of tension E. Relaxation period-muscle returns to normal length
F. Threshold stimulus-minimum stimulus needed for a muscle to contract. G. All or None Response-partial contraction does not happen, the muscle contracts when the threshold stimulus occurs. A stronger stimulus does not affect the contraction.
H. Summation-two or more stimuli delivered to a muscle before it has time to return to normal. I. Tetanus-the sum of stimuli eventually fuse to become sustained contractions. J. Fatigue-muscle can no longer contract it and returns to normal. SUMMATION TETANUS