Chapter 8 Muscular System

define the sliding filament model

*only occurs when the level of Ca 2+ is high enough and ATP is available Muscle action potential (impulse) travels along the sarcolemma & into the t-tubule system, Ca2+ release channels open, allow Ca2+ release channels open, allow ca2+ to escape into the sarcoplasm Ca2+ binds to troponin mole. in the thin filaments, cause the troponin to change shape (change in shape moves tropomyosin away from the myosin binding sites on actin) ONCE THE MYOSIN-BINDING SITES ARE UNCOVERED, CONTRACTION (repeating sequence of events that causes the filaments to slide) CYCLE BEGINS

What occurs in the sarcomere during muscle contraction? include changes in zone, bands, filaments

- myosin heads of the THICK filaments pull on the THING filaments, cause the THIN filaments to slide toward the center of the sarcomere - I bands and H zones become narrower & disappear altogether when muscle is max contracted - thin filaments slide past the thick filaments bc the myosin heads move like oars of a boat (pull on actin mole. of the thin filaments) - sarcomere shortens bc of increased overlap of THIN & THICK filaments, but lengths of filaments do not change!!! - sliding and shortening of sarcomeres = shortening of muscle fibers

Sliding filament theory of muscle contraction

1) ATP is hydrolyzed into ADP + P 2) The energized myosin heads bind to the myosin binding site on the actin & release the PHOSPHATE GROUP. cross bridges are formed (when myosin heads attatch to actin) 3) power stroke occurs- the myosin heads swivel toward the center of the sarcomere, pull the myofilaments towards the center of the sarcomere. ADP is released 4) New molecule of ATP attaches to the myosin heads and the myosin detaches from the actin

describe the neurological changes that occur at the neuromuscular junction prior to a muscle contraction

1) Acetylcholine (Ach) released from the synaptic end bulb of the motor neuron 2) Ach binds to receptors on the motor end plate, causing Na+ channels to open 3) Na+ diffuses into the cell cause ACTION POTENTIAL to occur along the sarcolemma & thru the t-tubules 4) Ach is rapidly broken by enzyme acetylcholinesterase

Muscle twitch 3 periods (in book)

1) latent period: occurs between application of the stimulus & the begin of contraction - muscle action potential sweeps over the sarcolemma & ca2+ released from the SARCOPLASMIC RETICULUM 2) contraction: rep power strokes occur, generate force of contraction 3) relaxation: power strokes stop bc level of CA2+ in the sarcoplasm is decreasing to the rest level

list the functions of skeletal muscles

1) movement 2) posture 3) heat production

list the microscopic parts of skeletal muscle

1) muscle fibers (aka cells) 2) myofibrils 3) myofilaments

what are the sequential events that occur during muscle fiber relaxation?

1) neurotransmitter Ach is rapidly broken down by the enzyme acHe; when nerve action potentials stop, release of ACh stops, & enzyme RAPID breaks down the ACh ALREADY PRESENT in the synaptic cleft ~ this ends the generation of muscle action potentials & the Ca2+ release channels in the sarcoplasmic reticulum membrane close~ 2) calcium ions are rapid transport from the sarcoplasm into SR; level of CA2+ in the sarcoplasm falls, TROPOMYOSIN slides back over the myosin-binding sites on actin; once the m-b sites are covered, thin filaments slip BACK to their relaxd postions

list the characteristics used to name muscles

1) size 2) location 3) # of attachments 4) shape 5) direction of muscle of fibers 6) action

smooth muscle & cardiac muscle differ from skeletal muscle in terms of contraction

Cardiac & smooth are involuntary (not under conscouis control of contractions)

prime mover

aka agonists main muscle of a particular movement

H zone

area of only thick (myosin) filaments

muscle fibers function

cell consist of sarcolemma (plasma membrane of muscle cell surrounds muscle fiber), sarcoplasmic reticulum (stores calcium), and sarcoplasm (cytoplasm/fluid filling the cell) muscle fibers give skeletal muscles striped/striated appearance

myofilaments function

chain of protein molecules found in the myofibrils of a striated muscle thick (myosin) or think (actin) striated muscle tissue: filaments arranged w/in myofibrils in sarcomeres (repeating polypeptide complexes)

myofibrils function

contain the proteins that produce the contraction # of myofibrils determines the diameter of a muscle fiber

tetanus

contractile activity: stimulation ceases or fatigue begins action potential: if muscle fiber is stimulated SO RAPID that it doesnt rest between stimuli, a maximal sustained contraction occurs

describe the parts of a sarcomere.

contractile unit of a muscle A band I band M line H zone

describe the basic structure of a skeletal muscle including the fibrous connective tissue layers that surround the fiber, fascicle & entire muscle

ea. skeletal muscle is a separate organ composed of cells (muscle fibers). Connective tissue (epimysium, perimysium, endomysium) surround muscle fibers and whole muscles myofibrils - muscle fiber - fasicle - whole muscle

synergist

help/enhance the movement of the prime mover

"all or none" law of muscle contraction

in any single nerve or muscle fiber, the response to a stimulus above threshold level is maximal and independent of the intensity of the stimulus

muscle fatigue

inability of a muscle to contract forecefully after prolonged acitivy

What causes rigor mortis?

lack of ATP (breathing stops) so prevents cross bridges to detach from actin state of rigidity

muscle twitch 3 periods in study guide

latent: when muscle stimulated and see slide of filaments (contraction) contraction: stop sliding relxation: fliaments slide back to original

I band

lighter, contains thin (ACTIN) filaments but NO THICK FILAMENTS

A band

middle area in the sarcomere where thick (MYOSIN) & thin (ACTIN) filaments are found

motor unit

motor neuron & all muscle fibers it innervates less ratio of muscle fibers to a single motor neuron = the better precision of control

How is the muscle contraction metabolically altered when oxygen levels are low?

muscle contraction when oxygen is LOW anaerobic glycolysis- without using oxygen

What is the ratio of motor neurons to muscle fiber in differing areas of the body?

muscles that control small/precise movements like the eyes: 10-20 mf per motor unit muscles that move powerful like biceps: 2000-3000 muscle fibers in some motor units

motor neurons

nerve cell that sends messages from the CNS to a muscle/gland

acetylcholine

neurotransmitter released by the motor neuron *responsible for muscle contraction*

origin

point of attachment on a fixed bone (stationary)

insertion

point of attachment on the bone that moves

myogram

record of a muscle contraction

Z disc

separate sarcomere from the next

sarcomere

single contractile unit of a muscle

M line

supporting proteins that hold the thick filaments together in the H zone holds myosin in place

neuromuscular junction (myoneural junction)

synapse between the muscle and motor neuron