Exam 3 terms Flashcards
myology
the study of muscles
striations
Cross-banded appearance of muscle tissue under the microscope, indicating the presence of sarcomeres.
Fascicle
a bundle of myofibers
sarcolemma
plasma membrane of a muscle cell
sarcoplasm
cytoplasm of muscle cells
sarcoplasmic reticulum (SR)
smooth endoplasmic reticulum (ER)of muscle cells. SR is well-developed in skeletal muscle myofibers and is wrapped in a highly organized pattern around myofibrils
terminal cisternae
Repeated expanded sections of the SR that lie adjacent to T-tubules
transverse tubules (T-tubules)
are narrow membranous tunnels formed from and continuouswith the sarcolemma. Functionis to transmit action potentialsfrom surface to interior of myofibers
triad
one T-tubule + two adjacent terminal cisterns of SR
myofibril
Myofibrils are elongated strands of protein complexes found inside myofibers.
sarcomere
Myofibrils are organized into longitudinally repeated subunits called “sarcomeres”, which are composed of alternating light and dark zones.
I-Band
Light zonesare called I-Bands containing only thin myofilaments (one of the components of a sarcomere).
A-Band
Dark zonesare called A-Bandscontainingthick myofilaments and overlapping thin myofilaments (one of the components of a sarcomere)
Z-Disk
a dense line composed of -actinin that attaches the thin myofilaments of adjacent sarcomeres.
titin
performs two functionsin sarcomeres: 1)It helps hold the thick filaments in proper alignment, and 2)its elasticity helps return a stretched sarcomere to its original resting length.
H-Zone
area within the A-band where only thick filaments exist
Bare zone
middle portion of H-zone lacking myosin heads
M-line
a dark line in the middle of the bare zone that contains proteins that are critical for organization and alignment of the thick filaments
thick myofilaments
contain myosin and titin; consist of approximately 2500 myosin moleculeswith their tails wound together and myosin heads projecting outward toward surrounding thin filaments.
thin myofilaments
are made of proteins: Nebulin, F-Actin, Tropomyosin, & Troponin.
nebulin
a structural protein that lies alongside thin filaments and attaches the thin myofilamentsto the Z-disks.
F-Actin (filamentous actin)
is a filamentous polymer consisting of G-actin (globular actin) subunits arranged in twoF-actin strands that twist together to form a helix.
G-Actin
The “pearl” on the thin filament; each on contains a myosin binding site.
Tropomyosin
filamentous protein that lies in the groove between the F-actin strands. Each tropomyosin molecule spans seven G-actin subunits.
Troponin
a Ca2+-binding protein that binds at regular intervals along tropomyosin molecules
Neuromuscular junction (NMJ)
is the synapse where the nervous system communicates with skeletal muscles
synaptic cleft
Space between the end of the synaptic bulb and the sarcolemma of the myofiber. 20 to 30 nm (10-9meters)
motor endplate
A specialized region of the sarcolemma of the myofiber where the synaptic bulb of the alpha-motor neuron sits. This region of the sarcolemma is made up of a series of membrane folds containing a high density of nicotinic cholinergic receptors.
nicotinic receptor
Nicotinic receptorson the myofibers are ligand-gated Na+,K+channels that open when ACh binds to them, allowing Na+to flow into the myofiber and K+to flow out.
Dihydropyridine (DHP) receptor
In the triads, the T-tubules contain voltage-sensing dihydropyridine (DHP) receptors that are mechanically linked to Ca+2-release channels called ryanodine receptors (RyR) in the adjacent sarcoplasmic reticulum (SR).
Ryanodine receptor (RyR)
In the triads, the T-tubules contain voltage-sensing dihydropyridine (DHP) receptorsthat are mechanically linked to Ca+2-release channels calledryanodine receptors(RyR)in the adjacent sarcoplasmic reticulum (SR).
Acetylcholinesterase
an enzyme found in synaptic cleft, rapidly degrades ACh
Motor unit
consists of an -motor neuron and all of the myofibers (muscle cells) that it stimulates.
Twitch contraction
A brief response of a single motor unit. A twitch contraction is the muscle movement generated in response to a single AP moving down an -motor neuron and stimulating its myofibers.
myoglobin
is an O2-storage protein found in muscle cells. This protein contains an iron-containing heme group which gives slow-twitch muscle its red appearance.
slow-twitch muscle fibers
Red muscle; have slow contraction and relaxation but are very resistant to fatigue and small diameter
fast twitch/glycolytic fibers
White muscle; have a fast contraction and relaxation time but fatigue quickly and large diameter.
fast twitch/oxidative fibers
Pink muscle; have fast contraction and relaxation with intermediate fatigue level and diameter.
summation
is the process of adding together individualtwitch contractions to increase the overall strengthof muscle contraction
Multiple motor unit summation (recruitment)
occurs when multiple
motor units are stimulated to contract simultaneously in a muscle, thus increasing the overall strength of a muscle contraction
Wave (frequency) summation
frequency of an individual motor unit is increased so that the overall tension is greater
tetany or tetanus
“steady state of muscle contraction” wave summation results in sustained contraction
tetanus “lock jaw”
is pathological condition caused by Clostridium
tetani toxin.
motor nucleus
A given skeletal muscle is served by a group of motor neurons, whose cell bodies are grouped together in the spinal
cord (or brainstem) to form a motor nucleus. Found in the ventral horn of gray matter.
Fatigue
Decrease in work capacity of a muscle caused by work itself.
Rigor
is extreme fatigue that occurs when ATP is completely depleted in
a myofiber.
rigor mortis
Rigor mortis is the stiffening of a dead body that occurs a few hours after death of an animal. Body becomes stiff because ATP is not being produced by cells and Ca+2 leaks from SR
phasic smooth muscles
undergo periodic cycles of contraction and relaxation. So, the major function of phasic smooth muscle is to develop
force, shorten, and then relax similar to skeletal muscles
tonic smooth muscles
contract continuously (tonically) to maintain an organ’s dimensions against an imposed load or to keep a sphincter closed.
dense bodies
Actin myofilaments are attached to dense bodies, which serve a function
similar to Z-disks in skeletal muscles.
attachment plaques or membrane-dense areas
are dense bodies associated with inner surface of membranes of smooth muscle cells.
multi-unit smooth muscle
cells are NOT electrically connected by gap junctions. Each smooth muscle cell is individually stimulated at neuroeffector junctions by ANS motor neurons. (iris & ciliary body)
contact junctions
allow rapid and precise nervous system control of these smooth muscles. found in multi unit smooth muscle
single unit (unitary) smooth muscle
“Visceral type”- Found in walls of viscera (internal organs). 99% of all smooth muscle is this type.
diffuse junctions
(80 to 120 nm synaptic cleft). Diffuse junctions are slow to activate. found in unitary smooth muscles
calmodulin
a Ca2+ binding protein similar to troponin
myosin light chain kinase (MLCK)
Ca2+ calmodulin complex binds to and activates this that phosphorylates the myosin light chain called the regulatory chain, which is found associated with the myosin head.
macronutrient (fuel)
An organic compound (lipids, carbohydrates, and proteins) that can be broken down (degraded or catabolized) in the body to produce usable energy (e.g. ATP)
metabolism
the sum of all physical and chemical changes that take place within an organism
anabolism
(Biosynthesis) -all processes in which simpler substances are assembledinto more complex substances,usually requiring energy input
catabolism
(Degradation) -all processes in which complex substances are broken down into simpler substances, usually with the concomitant release of energy
Adenosine triphosphate (ATP)
ATP is “energy currency” ATP + H2O ADP + Pi+ ENERGY for work
ingestion
is to take into the body through the mouth.
digestion
Breakdown of food into smaller physical and chemical units that can be eventually be absorbed from the lumen of the GI tract into bloodstream.
mechanical digestion
Breakdown of food based on movements ofthe GI tract
chemical digestion
Breakdown of food based on enzyme-catalyzed hydrolysis reactions occurring in lumen of GI tract.