muscles Flashcards
smooth muscle
smooth texture, involuntary control, 5-10% of all muscle, function in hollow organs
cardiac muscle
striated appearance, involuntary control, miniscule percentage of all muscles, function in pumping blood
skeletal muscle
striated appearance, voluntary control, 40% of all muscle, function in movement and structural support; fibers run the entire length
functions of muscles
internal and external movement, maintaining posture, stabilizing the skeleton, and generating heat
characteristics of muscles
excitability: uneasy resting potential allows response to stimulus; contractility: use of ATP to forcibly shorten; extension and elasticity
myofibrils
parallel units within a fiber made of sarcomeres
sarcomere
a functional unit of a muscle that run z-disk to z-disk made up of actin and myosin
sarcolemma
surrounds the muscle layer
thin filaments
F actin: a double stranded helix of globular actin with myosin binding sites
tropomyosin: double stranded protein lying end to end on the actin spiral
troponin complex: Tnl binds to actin, TnT binds to tropomyosin, TnC binds to calcium ions
thick filaments
myosin protein made of a globular head and entwined tails which are held together by a light chain; head posses an actin binding site
Sarcoplasmic reticulum
modified endoplasmic reticulum made up of tubules and cisternae surrounding myofibrils; store calcium
sliding filament model
Z disks move towards each other upon contraction and sarcomeres get shorter
length tension relationship
relates the amount of actin myosin overlap to tension
cross bridge attachment
calcium moves tropomyosin allowing myosin heads to bind to the actin
power stroke
P in ATP is released triggering the slide of actin, ADP is released but myosin remains bound to the actin
cross bridge detachment
ATP binds to the head releasing the myosin from the actin
cocking myosin
ATPase cleaves providing energy for the conformational change of the head; ADP and P stay bound for the power stroke
twitch-timing of contraction
a latent period delays contraction
factors influencing muscle contraction
the number of muscle fibers contracting within a muscle, tension developed by each contracting fiber, frequency of stimulation, treppe effect, tension increases until reaching a plateau
muscle recruitment
relating the number of muscle fibers that are activated to the strength of the motor stimulus
Treppe effect
stimulation recurs every time the muscle reaches its relaxed state and tension increases each time due to excess calcium availability meaning the muscle becomes more effective the more it is used
muscle summation
the entry of another stimulus before a muscle is fully relaxed allowing the strength of the twitch to build on the last
tetanus
the maximum sustained contractile force a muscle can undergo; APs come so fast that no relaxation occurs
isotonic contraction
normal muscle function, enough force is generated to move the force acting against the muscle and muscle contraction occurs
isometric contraction
the muscles maximum contractile force is not enough to overcome the force pushing against it ex: pushing a wall
elastic properties of the muscle
allow for stretch to occur; when stretched actin and myosin overlap is minimized, as contraction occurs tension increases with overlap, contraction continues until the load is moved
load shortening relationship
muscles are more capable of meeting the demand of a light load quickly
force velocity curve
work increases with contraction until the load is too heavy to move
muscle fatigue
the physiological inability to contract due to lactic acid buildup from anaerobic metabolism
neuromuscular fatigue
ionic imbalance or acetylcholine deficit between the neuron and the muscle
central fatigue
muscles are willing and able but the spirit is not; due to signals from the CNS never reaching the muscle
smooth muscle structure
spindle shaped with a single nucleus, smaller than skeletal muscle, arranged in sheets rather than fibers, contain a third filament that acts as a connective filament, actin and myosin are arranged randomly
dense bodies
attachment points in smooth muscle that behave similarly to z disks
smooth muscle contraction
slow, sustained involuntary contraction in hollow organs; spontaneous depolarization due to being more permeable to calcium
substructure of smooth muscle
actin myosin and intermediate filaments, arranged diagonally, dense bodies act as z disks, no t tubules and an underdeveloped sarcoplasmic reticulum, gap junctions connect muscle cells into a single unit
smooth muscle mechanism of contraction
calcium interacts with the myosin light chain, caldesmon covers the actin binding site, calcium binds to calmodulin activating myosin kinase, kinase cleaves ATP cocking the myosin head, phosphorylated myosin forms cross bridges with actin
excitation contraction coupling
neurotransmitters released from varicosities lead to depolarization, calcium goes into cell from vesicles, calcium is released from the endoplasmic reticulum, the calcium calmodulin complex activates and unfolds myosin kinase which phosphorylates the myosin allowing coupling to occur
single unit smooth muscle
function as a sheet, connected via gap junctions, not all have varicosity function through myogenic activity, most common type of smooth muscle, found in the alimentary and urogenital canals
multi unit smooth muscle
each independent unit must receive a signal to activate due to few gap junctions, this allows for a graded response, neurogenic, every cell has a varicosity connecting to a neuron, found in air passages and blood vessels
special features of smooth muscle
different length tension relationship, single unit has stretch activation, efficient and fatigue resistant - latch mechanism slows the cross bridge cycle and minimizes the use of ATP allowing for continued tension and discontinued ATP use, hyperplasia
hyperplasia
enlargement of an organ or tissue caused by an increase in reproduction of cells
cardiac muscle
found in the middle layer of the heart, spiraled arrangement in all vertebrates, cardiac fibers create the atria and ventricles
direction of blood flow in a 4 chambered heart
right atrium > tricuspid valve > right ventricle > pulmonary ventricle > pulmonary artery > lungs > pulmonary vein > left atrium > bicuspid valve > left ventricle > aortic valve > aorta > tissues > venae cavae > right atrium
chordae tenidae
attachments inside the ventricle that prevent valves from inverting
intercalated disks
gap junctions in cardiac muscle allow rapid electrical connectivity and desmosomes hold fibers together
neurogenic pacemaker
open circulatory systems, rhythmic beat originates from the CNS and a cardiac ganglion with unstable resting potential
myogenic pacemaker
closed circulatory systems, rhythmic beat originates from heart muscles and myocytes with unstable resting potential, SA and AV nodes initiate contraction
sinoatrial (SA) node
natural pacemaker of the vertebrate heart located where the superior vena cavea meets the right atrium, activates the AV node signaling the bundle of hiss to squeeze the ventricles
ectopic foci
regions of the heart other than the SA node capable of initiating beats when higher order nodes fail
cardiac action potentials
myogenic pacemaker has a slow rise due to uneasy resting potential, muscle summation cannot occur due to a long action potential and refractory period
ECG
electrical measurements of the heart, high depolarization of ventricles in the QRS complex, depolarization from the SA node depolarizes atrial muscle and initiates AV node which depolarizes the bundle of his signaling the contraction of ventricles
lub dub of the heart
lub from the ventricular valves snapping shut, dub from the aortic and pulmonary valves snapping shut
sympathetic and parasympathetic control
the sympathetic nervous system automatically increases blood flow and the parasympathetic nervous system automatically inhibits it; parasympathetic control dominates at rest
cardiac output
heart rate x stroke volume; stroke volume increases with heart rate because of increases in pressure allowing more blood into the heart
heart size
a consistent proportion of body mass within a species, body mass is proportional to stroke volume, heart rate is more influential than stroke volume and is not dependent on heart mass
metabolic scope
the ability to increase cardiac output and oxygen consumption
intrinsic control
self regulating mechanisms that take advantage of the properties of the organ itself ex: contractile properties
extrinsic control
external signals used to regulate the function of the organ or system ex: input from hormonal or nervous systems
frank starling mechanism
increased filling pressure leads to increased stroke volume
