Chapter 9

·       Know the 3 Muscle Tissue Types, locations and functions- skeletal, smooth, cardiac

-skeletal: attached to bones/ skin

            -voluntary, striated,  powerful

-smooth: found in walls of most hollow organs (except heart), usually in 2 layers (longitudinal & circular)

            -no striations, single nucleus, thick and thin arranged diagonally

·       Functions of muscles- stabilize joints, etc.

-movement of bones or fluids (blood, lymph)

-maintaining posture and body position

-stabilize joints

-heat generation (especially skeletal muscle

·       Microscopic muscle anatomy- connective tissue types, fascicles, etc.

-connective tissues: sheaths around skeletal muscle

            -epimysium: dense regular connective tissue surrounding entire muscle

            -perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers)

            -endomysium: fine areolar connective tissue surrounding each muscle fiber

-skeletal muscle fibers

            -sarcolemma: plasma membrane

            -sarcoplasma: cytoplasm

            -myofibrils: contractile elements; chains of sacromeres

·       Neuromuscular Junction anatomy AND physiology- understand how the AP from the somatic motor neuron leads to release of acetylcholine (Ach), then stimulates the sarcolemma. Know the details of all ions and neurotransmitters involved.

-release of ACh

1. action potential arrives at axon terminal of motor neuron

2. voltage gated calcium channels open and calcium enters axon terminal

3. calcium entry causes some synaptic vessels to release their contents (acetylcholine=ACh)

4. acetylcholine (a neuro transmitter) diffuses across the synaptic cleft and binds to receptors in the sarcolemma

5. ACh binding opens ion channels that allow simultaneous passage of Na+ (sodium) into the muscle fiber and K+ (potassium) out of the muscle fiber

6. ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase

-roles

            -calcium (Ca2+):

low Ca2+ concentrations: tropomyosin blocks active sites on actin, myosin heads cannot attach to actin, muscle fiber relaxes

high Ca2+ concentrations: Ca2+ binds to troponin, troponin changes shape and moves tropomyosin away from active sites, events of the cross bridge cycle occur, when nervous stimulation ceases, calcium is pumped back into the SR and contraction ends

·       Know the sarcomere anatomy (diagram) and physiology- thin and thick filaments, z-disc, A band, etc., how do they change during contraction?  

-thick filaments: run the entire length of an A band

-thin filaments: run the length of the I band and partway into the A band

-Z disc: coin shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another

-H zone: lighter midregion where filaments do not overlap

-M line: line of protein myomesin that holds adjacent thick filaments together

·       Know the components of the thick and thin filaments- actin, myosin, etc.  

-thick filaments: composed of the protein myosin; myosin heads form cross bridges with actin of thin filaments and binding sites for ATP

-thin filaments: composed of proteins actin, tropomyosin and troponin; actin has myosin binding sites

·       Excitation-Contraction Coupling- T-tubules, SR, sliding filament model (know details of function)

-transmission of Action Potential along the sarcolemma leads to sliding of the myofilaments

-latent period: time when E-C coupling events occur, time between AP initiation and the beginning of contraction

-action potential is propagated along the sarcolemma to the T tubules

-voltage sensitive proteins stimulate calcium release from SR

            -calcium is necessary for contraction

1. action potential is propagated along the sarcolemma and down the T tubules

2. calcium ions are released

3. calcium binds to troponin and removes the blocking action of tropomyosin

4. contraction begins

·       Aerobic vs. Anaerobic exercise- ATP production, etc.  ‘

-Aerobic: (endurance) increases muscle capillaries, # of mitochondria, myoglobin synthesis

-energy from glucose and acids, oxygen is required, produces 36 ATP per glucose, CO2&H2O

-Anaerobic: increases mitochondria, myofilaments, glycogen stores, and connective tissue

-energy from glucose, oxygen not required, produces 2 ATP per glucose, lactic acid

·       Factors influencing force of contraction- size, fiber recruitment, stimulation frequency, etc.

-# of muscle fibers stimulated, relative size of fibers, frequency of stimulation, length-tension relationship