The Muscular System

• Movement
• Stability
• Control of body openings and passages
• heat production
• glycemic control

• Excitability (responsiveness)
• Conductivity
• contractility
• extensibility
• elasticity

• voluntary
• striated
• produces 85% heat
• usually connect to 1+bones

• involuntary
• striated
• found in heart
• very rich in myoglobin, glycogen and big mitochondria= very resistant to fatigue
• repair of damaged cardiac muscle primarily by fibrosis

• involuntary
• no striations
• found in walls of viscera and blood vessesl iris of eye, piloerectors of hair follicles

• cells of skeletal muscle
• surrounded by endomysium, bundled by perimysium, put together by epimysium, covered by fascia
• multiple nuclei, adjacent to sarcolemma

• cells of cardiac muscles
• aka myocytes
• usually one nucleus near middle of cell

• can refer to cells of either cardiac or smooth muscle
• in smooth muscle, contain only one nuclei
• z discs are absent

• muslce that produces most of the force during a particular joint action
• aka agonist

• muscle that aids the prime mover
• guide for prime mover

• opposes prime mover
• makes antagonistic pair with prime mover*

muscle that prevents a bone from moving

• intrinsic muscle has origin and insertion contained within a particular region
• extrinsic doesnt, ex. muscles that move fingers

fulcrum in the middle like seesaw (EFR)

Resistance in the middle (FRE)

effort applied between the fulcrum and resistance (FER)

plasma membrane of muscle fiber cell

• cytoplasm of myofiber
• occupied by myofibrils and myoglobin

smooth endoplasmic reticulum of myofibers

• thick filaments
• _myosin
• Thin filaments
• _{actin-> tropomyosin-> troponin}

• Elastic Filaments
• _{titin (anchor each thick filament to the z disc}

• myosin and actin
• because they do work of shortening the muscle fiber

becuase they act like a swetich to determine when the fiber can contract and when it cannot

Point of contact between nerve and muscle fiber

• a nerve signal arrives at the synaptic knob
• synaptic vesicles release ACh which diffuses xross synaptic cleft and binds to receptros on the sarcolemma of the muscle fiber, opens ion gates in sarcolemma and sodium and potassium movements throught hte membrane that electrically excite the msucle fiber
• self-propagating wave of excitation spreads down the length of the fiber and into the T tubules

• electrical events in T tubule lead to the opening of calcium gates in teh sarcoplasmic reticulum, sr releases calcium ions into the cytosol
• calcium ions bind to troponin molecules in the myofilaments
• myosin has been "waiting" in flexed position like elbow with atp bound to head, reaction straightens myosin head into extended "cocked"position

• myosin forms a link, or cross-bridge, with one of the active sites of actin, and releases the ADP and P
• mysoin flexes and tugs on thin filament (power stroke), myosin binds new ATP, lets go of thin filament and reckocks (recovery stroke)

• motor neuron stops firing and releasing ACh, muscle fiber no longer electrically excited
• sarcoplasmic reticulum reabsorbs calcium ions and stores them til next time muscle stimulated, troponin blocks active sites and prevents myosin-actin cross-bridges fro froming, muscle can no llonger maintain tension, relaxes

when muscle shrinks

spinal cord injuries or other injuries that sever nerve from muscle and cause muscle to shrink

lack of excercise

from aging

diseases of muscular tissue

collective term for several hereditary diseases in which skeletal muscles degenerate, lose strength, and are gradually replaced by fat and scar tissue which impede blood circulation and accelerates muscle degeneration

• most prevalent in women from 20-40
• autoimmune disease in which antibodies attack neuromuscular junctions and trigger destruction of ACh receptors
• fibers become lesss and less sensitive to ACh