lecture exam 4

chapters 10,11,12

3 types of muscle tissue

skeletal, cardiac and smooth

functions of muscle

body movement, maintenance of posture, protection and support, regulating elimination of materials and heat production

function of muscle

body movement (move bones, make facial expressions, speak, breathe, swallow)

function of muscle

maintenance of posture (stabilize joints, maintain body position)

function of muscle

protection and support (package internal organs and hold them in place)

function of muscle

regulating elimination of materials (circular sphincters control passage of material at orifices)

function of muscle

heat production (help maintain body temperatue)

characteristics of muscle tissue

excitability, conductivity, contractility, elasticity, extensibility

excitability

characteristic of muscle, ability to respond to a stimulus by changing electrical membrane potential

conductivity

characteristic of muscle, involves sending an electrical change down the length of the cell membrane

contractility

characteristic of muscle, exhibited when filaments slide past each other. enables muscle to cause movement

elasticity

characteristic of muscle, ability to return to original length following a lengthening or shortening

extensibility

characteristic of muscle, ability to be stretched

connective tissue components

epimysium, perimysium, and endomysium

epimysium

dense irregular connective tissue wrapping whole muscle

perimysium

dense irregular connective tissue wrapping fascicle. Houses many blood vessels and nerves

endomysium

areolar connective tissue wrapping individual muscle fiber. delicate layer for electrical insulation, capillary support, binding of neighboring cells

tendon

attachment of bone to bone, cordlike structure of dense regular connective tissue

aponeurosis

attachment of bone to bone, thin, flattened sheet of dense irregular connective tissue

deep fascia (muscular fascia)

in skeletal muscle

sheet of dense irregular connective tissue

located external to epimysium

separates different muscle while binding them together

superficial fascia

in skeletal muscle

subcutaneous tissue = hypodermis

blood vessels

skeletal muscle has extensive amounts

deliver oxygen and nutrients, removing waste products

tendon

epimysium+perimysium+endomysium

somatic neurons

inside skeletal muscle

axons of neurons branch, terminate at neuromuscular junctions

can allow for voluntary control of contraction

parts of the muscle cell (fiber)

sarcolemma, sarcoplasma, nuclei, sarcolemma, sarcoplasmic reticulum

sarcolemma

plasma membrane of a muscle cell

sarcoplasm

cytoplasm of the muscle cell

has typical organelles plus contractile proteins and other specializations

multiple nuclei

in the muscle cell

individual cells are multi nucleated

sarcolemma

has t-tubules that extend deep into the cell and wrap around the myofibrils

have voltage-gated ion channels that allow for conduction of electrical signals

whats inside the sarcoplasm

myofibrils and sarcoplasmic reticulum

myofibrils

hundred to thousands per muscle cell

bundles of myofilaments (contractile proteins)

sarcoplasmic reticulum

smooth endoplasmic reticulum of the muscle cell

terminal cisternae

blind sacs or sarcoplasmic reticulum

serve as reservoirs for calcium ions

combine in twos with central t-tubule to form triads

sarcoplasmic reticulum

has pumps that import Ca2+ inside

has channels that allow Ca+ to be released into surround sarcoplasm to trigger contraction

myofibrils

contain thick and thin filaments

thick filaments

consist of bundles of many myosin protein molecules

each myosin molecule has two heads and two intertwined tails

heads have actin binding site on thin filaments and ATPase site

thin filaments

consist mostly of two twisted strands of actin

each actin myosin has a myosin binding site to which myosin heads attach during contraction

troponin and tropomyosin are regulatory proteins

tropomysoin

twisted stringlike protein covering actin in a non contracting muscle

in thin filaments

tropopin

globular protein attached to tropomyosin

when Ca2+ binds to this, it pulls tropomyosin off actin allowing contraction

in thin filaments

sarcomeres

myofilaments arranged in repeating units

sarcomere

composed of overlapping thick and thin filaments

at both ends are Z discs

the position of thick and thin filaments give rise to alternating I-bands and A-bands

Z discs

at both ends of sarcomere

specialized proteins perpendicular to myofilaments, are anchors for thin filaments

I-bands

light-appearing regions that contain only thin filaments

bisected by Z-disc

A band

Dark appearing region that contains thick filaments and overlapping thin filaments

A band

represents the length of the myosin filaments

A band

makes up central region of sarcomere

H zone

central portion of A band

only thick filaments present; no thin filament overlap

M line

middle of H zone

attachment for thick filaments

sliding filament model

actin filaments slide over myosin to shorten sarcomeres

amount of overlap increases

acting and myosin do NOT change length

shortening sarcomeres responsible for skeletal muscle contraction

muscle fibers

have abundant mitochondria for ATP production

myoglobin

binds and stores oxygen for aerobic respiration

glycogen

is stored for when fuel is needed quickly

creatine phosphate

can quickly give up its phosphate group to help replenish ATP supply

motor unit

a motor neuron and all the muscle fibers it controls

fibers of this are dispersed throughout the muscle

small motor units

allow for precise control of force output

large motor units

allow for production of large amount of force

neuromuscular junction

how skeletal muscles are stimulated

neuromuscular junction

location where motor neuron innervates muscle

has synaptic knob, synaptic cleft, and motor end plate

synaptic knob

expanded tip of motor neuron axon

houses synaptic vesicles

has voltage gated Ca+ channels in membrane

synaptic vescicles

small sacs filled with neurotransmitter acetylcholine (ACh)

voltage gated Ca2+ channels in synaptic knob

Ca+ flows into the cell (down the concentration gradient) if these channels open

motor end plate

specialized region of sarcolemma with numerous folds

has many ACh receptors

ACh receptors

plasma membrane protein channels

opened by binding of ACh

allow Na+ entry and K+ exit

synaptic cleft

narrow fluid-filled space

separates synaptic knob from motor end plate

acetylcholinesterase resides here

acetylcholinesterase

enzyme that breaks down ACh molecules

resting membrane potential

fluid inside cell is negative compared to fluid outside of the cell

RMP of muscle cell

-90mV

set by leak channel and Na+/K+ pumps (voltage-gated channels are closed)

how are skeletal muscles stimualted

neuron excited muscle fiber

calcium enters synaptic knob

synaptic knob releases ACh

ACh diffuses across cleft, binds to receptors, excited fiber

what happens when calcium enters the synaptic knob

nerve signal travels down the axon, opens voltage-gated Ca2+ channels

Ca2+ diffuses into synaptic knob

Ca2+ binds to proteins on surface of synaptic vesicles

what happens when synaptic knob releases Ach

vesicles merge with cell membrane at synaptic knob: exocytosis

ACh molecules released into synaptic cleft

excitation-contraction coupling

stimulation of the fiber is coupled with the sliding filaments

coupling includes the end-plate potential (EPP), muscle action potential, and release of Ca2+ from the sarcoplasmic reticulum

first step of end-plate potential

ACh receptors are chemically gated channels that open when ACh binds to them

Na+ diffuses into the cell through the channels

cell membrane breifly becomes less negative at the end plate region

second step of end-plate potential

EPP lead to the openeing of voltage-gated ion channels and generation of action potentials in the adjacent region of the sarcolemma

action potentials propogate along the sarcolemma and t-tubules

third step of end plate potential

action potential opens voltage-gated Ca2+ channels of sarcoplasmic reticulum

Ca2+ diffuses out of cisternae into sarcoplasm

Ca2+ interacts with myofilaments triggering contraction

fourth step of end plate potential

when Ca2+ binds to troponin, it troponin, it triggers cross bridge cycling

troponin and tropomyosin move so actin is exposed

crossbridge cycling

1) crossbridge formation

2) power stroke

3) release of myosin head

4) reset myosin head

what happens during 1)crossbridge formation

myosin head attaches to exposed binding site on actin

what happens during 2)power stroke

myosin head pulls thin filament toward center of sarcomere

ADP and P are released

what happens during 3) release of myosin head

ATP binds to myosin head causing its release from actin

what happens during 4) reset myosin head

ATP split into ADP and P, by myosin ATPase

provides energy to reposition the myosin head

needs to be present in order for cross bride cycling to continue

Ca2+ and ATP

how do sarcomeres shorten

Z discs move closer together, narrowing or disappearance of H zone and I band

thick and thin filaments remain the same length but slide past each other