Anatomy and Physiology: Muscular Systen

What are the types of muscle tissue?

• skeletal

• smooth

• cardiac

What are the characteristics of skeletal tissue?

• excitability: responds to stimuli

• conductivity: electrical charges run downthe axon

• Contractility: fosters movement

• extensibility: can stretch

• elasticity: can return to the original shape after stretching

What are the membranes that make up SKELETAL muscles?

• Epimysium (most superficial): continuous with tendons; covers entire muscles

• Perimysium (deep to epimysium): covers fascicle/ bundle of muscle cells

• endomysium (most deep): covers each individual muscle cell/fiber

What is the sarcolemma on a skeletal muscle?

plasma membrane for muscle fiber/cells

What are T-tubules on skeletal muscle fibers?

the tunnel/layer that is between the terminal cisternae

What is the sarcoplastmic reticulum (SR) on a skeletal muscle?

fishnetting around myofibril

What are terminal cisternae (part of the sarcoplasmic reticulum)?

bookend the T-tubules on the sarcoplasmic reticulum

How are muscles organized (smallest to biggest filaments)

myofilaments, myofibrils, muscle fibers/cells (endomysium), fascicles (perimysium), actual muscle (epimysium)

What are myofilments and what are the types?

Myofilaments are the smallest unit of a muscle cell.

• thick filaments: myosin

• thin filaments: actin

Parts of myosin/think head

• motorized head attached to lever arm

• fix tail attached to the main portion

Parts of the thin filament

• Tropomyosin: one strand that wraps around the strands of actin

• Troponin: small proteins that attach to the tropomyosin

• Actin: two strands wrapping around each other in a helical pattern

How does the thin filament work?

Troponin is attached to tropomyosin. Calcium binds to the troponin, and the tropomyosin gets pulled away from the myosin binding sites on the actin by the troponin. Wehn the myosin binding sides are available to the myosin heads, the heads attach and, since they have ADP +Pi attached to it, they have energy to move the head along the filament. The Pi and ADP detach which detaches the head from the actin.

What are the components of the sarcomere?

• Z line: attaches thin filaments

• A band: length of the thick filament (myosin)

• I band: has only thin filaments

• M(id) line: attaches thick filaments

• H zone: only thick filaments

What is muscular dystrophy?

• genetic

• Duchenne is the most common

• Dystrophin is faulty (helps thin filaments attach to sarcomere)

• Sarcolemma can tear

• no cure (often wheelchair bound)

What happens during rigor mortis to cause the stiffening?

For about 24 hours after death, Ca2+ is still in the cytosol (meaning the muscle is an the contracted position, because the myosin heads attach to the actin) and ATP isn’t available to release the myosin head from the actin. After about 24 hours, enzymes break down the muscle, which releases the myosin head and returns it to a relaxed state.

What is muscle tension?

force generated when the skeletal muscle is stimulated and contracts

What are the phases of muscle contraction?

1.) lag phase: electrical impulse travels down the sarcolemma and t-tubules

2.) Contraction period: tension increases, sarcomere shortens

3.) Relaxation period: muscle relaxes, returns to original length

How does intensity work for muscle contraction?

• the body just kinda figures out how many motor units to deploy depending on how big of a force is needed.

• max contraction is when ALL motor units are stimulated

What is meant by stimulus frequency?

How often the muscles are signaled to contract. An increase in the frequency of stimulations leads to an increase in muscle tension

• wave summation: additive strength of contraction by not letting the previous contraction to relax 100% before the next stimulus is deployed

• incomplete tetany: there are faster muscle twitches with higher increased tension than the wave summation frequencies.

• tetany: the frequency of the stimuli is so big, that there isn’t any relaxation period

• fatigue: follow quickly after tetany because muscles get tired after a while of working. Causes a drop in muscle tension

What are the three pathways of skeletal muscle metabolism?

• creatin phosphate

• glycolysis (anaerobic)

• aerobic phosphorylation

What is the process of creatin phosphate?

This happens during the first 10-15 seconds of muscle contraction. A phosphate is doated to ADP (from creatine phosphate) to get ATP. This energy is used to continue the muscle in the contracted position until glycolysis kicks in. Resting muscle builds up creatine phosphate.

What are the types of skeletal muscle fibers?

• Type I fibers: slow oxidative fibers

• Type IIa fibers: fast oxidative fibers

• Type IIx fibers: fast glycolytic fibers

What is the difference between slow and fast twitch fibers?

• slow twitch: endurance runners (Type I)

• fast twitch fibers: sprinters, anything that requires muscles to contract quickly (Type IIa and IIx)

What are characteristics of slow oxidative fibers?

• less powerful

• slower response time

• red in color

• high fatigue resistance

• found in trunk and lower limb

What are characteristics of fast oxidative fibers?

• more powerful contraction

• faster response time

• pink in color

• high fatigue resistance

• used in moderate activity

• found in lower limb

What are characteristics of fast glycolytic fibers?

• more powerful contraction

• fast reaction time

• white in color

• lower fatigue resistance

• used in short, intense activity

• found in upper limb