Chapter 11: Muscular Tissue
Properties of Cardiac Muscle
(1) It must contract with a regular rhythm; (2) it must function in sleep and wakefulness, without fail or need of conscious attention; (3) it must be highly resistant to fatigue; (4) the cardiomyocytes of a given heart chamber must contract in unison so that the chamber can effectively expel blood; (5) each contraction must last long enough to expel blood from the chamber.
A Bands
(dArk) Results from thick filaments lying side by side -Especially dark when thick and thin filaments OVERLAP
Process of Contraction/Sliding Filament Theory
10) Myosin head must have ATP molecule bound to it to initiate contraction. Myosin ATPase, an enzyme in the head, HYDROLYZES THIS ATP into ADP and Phosphate. This energy release "COCKS" the head into an extended, HIGH-ENEGY position -Head keeps ADP and Phoshate bound to it 11) COCKED myosin binds to an exposed ACTIVE SITE on the THIN FILAMENT, forming a CROSS-BRIDGE between the MYOSIN and ACTIN 12) Myosin releases the ADP and Phosphate and flexes into a BENT, LOW-ENERGY position, tugging the thin filament along with it (POWER STROKE) 13) Binding of a new ATP to myosin DESTABILIZES myosin-actin bond, BREAKING the CROSS-BRIDGE. -Myosin undergoes a RECOVERY STROKE; hydrolyzes new ATP, recocks, and attaches to a new active site farther down the thin filament, ready for another power stroke
PROCESS OF RELAXATION
14) Axon terminal stops releasing ACh 15) As the ACh separates from its receptor, AChE breaks it down into fragments that cannot stimulate the muscle -Axon terminal reabsorbs these fragments for recycling 16) Reabsorption of Calcium Ions by Sarcoplasmic Reticulum -Through ACTIVE TRANSPORT (ATP needed) 17) Loss of calcium ions from troponin 18) Tropomyosin moves back into position where it blocks the active sites of the actin filament. BOTH RELAXATION AND CONTRACTION REQUIRE ATP!!!
Aerobic Respiration is typically used when exercising longer than how many seconds?
40
Excitation-Contraction Coupling Process?
5) Action potentials propagated down T tubules and INTO the cell 6) Action potentials open VOLTAGE-GATED ion channels in the T Tubules AND saroplasmic reticulum; -CALCIUM DIFFUSES out of the SR, down its concentration gradient, and INTO the CYTOSOL! 7) Calcium binds to the troponin of the thin filaments 8)Troponin-tropomyosin complex changes shape and EXPOSES the ACTIVE SITES on the ACTIN FILAMENTS -MYOSIN HEAD binds to ACTIVE SITE on THIN FILAMENT
Within a sarcomere, the overlap of actin and myosin produce the _______ band?
A
M line
A dark, transverse protein complex that connects thick filaments in the middle of the H Band.
Electrical potential (Voltage)
A difference in electrical charge from 1 point to another
Synaptic Cleft
A narrow space between an axon terminal and the membrane of the postsynaptic cell, across which a neurotransmitter diffuses
Synaptic Vesicles
A spheroidal organelle in an axon terminal containing neurotransmitter, which are filled with acetylchonline (ACh)
Smooth Muscle Tone
A state of continual tonic contraction achieved by the skeletal cells by its fatigue resistance and latch-bridge mechanism of smooth muscle
Muscle Tone
A state of partial contraction of muscles -Makes muscles ideally ready for action -Maintained by CNS
Neuromuscular Junction (NMJ) OR Motor End Plate
A synapse between a nerve fiber and a muscle fiber
What do muscle contractions rely on?
ATP
Phosphagen system
ATP and CP; -Provide nearly all the energy used for SHORT BURSTS of INTENSE ACTIVITY
Autorhythmic
Ability to contract rhythmically and independently; the heart
How does muscle return to its resting length?
Achieved by some PULLING FORCE on the muscle and stretching it
Regulatory Proteins
Act like a switch determining when the fiber can contract, and when it cannot -Tropomyosin and Troponin
I Bands are composed primarily of WHICH protein?
Actin
Movement in Smooth muscle cell
Actin filaments attach to the intermediate filaments as well as directly to the dense bodies, so their movement (powered by myosin) is transferred to the sarcolemma and shortens the cell.
Long-Term Energy
Aerobic Respiration -Occurs after 40 seconds -Metabolizes glucose and fatty acids
Cardiac muscle relies mainly on what type of ATP Production?
Aerobic respiration
Immediate Energy (Short, intense exercise... 100m Dash)
Aerobic respiration using oxygen from MYOGLOBIN -Oxygen quickly depleted; catches up later (~40 sec) -Body borrows phosphate groups (Pi) from other muscles and transfers them to ADP 2 Enzymes control this: 1) Myokinase 2) Creatine Kinase
Striations
Alternating Light and Dark transverse bands, reflecting an overlapping arrangement of their internal contractile proteins
Dystrophin
An enormous protein that is located between the Sarcolemma and the outermost myofilaments -Leads to the fibrous endomysium surrounding the muscle fiber -When the thin filaments move, it pulls on the dystrophin, which pulls on the extracellular tissues leading to the tendon -Assists in movement of muscle fiber
Myosin light-chain kinase
An enzyme that adds a phosphate group to a small regulatory protein on the myosin head -Activated by calmodulin -This then activates myosin ATPase, enabling it to bind to actin and hydrolyze ATP (Power and Recovery strokes)
Acetylcholinesterase (AChE)
An enzyme that breaks down ACh after the ACh has stimulated the muscle cell
Short-Term Energy
Anaerobic fermentation is achieved -Production of lactate
Calmodulin
Associated with the myosin, it's where calcium binds (IDENTICAL TO TROPONIN) (Calcium Modulating Protein)
Example of internal/external/contraction phase
At first, internal tension would only stretch the rubber band. Then, as the rubber band became taut, external tension would lift the weight.
Somatic Motor Fibers
Axon of a somatic motor neuron
Somatic Motor Fibers and Muscle Fibers
Axons reach multiple muscle fibers; but each muscle fiber is supplied by ONLY 1 MOTOR NEURON
Z Disk (Z Line)
Bisects each Light I Band; Provides anchorage for the thin and elastic filaments
Tropomyosin
Blocks the active sites of 6 or 7 G actins and prevents myosin from binding to them -Prevents motion --Has Troponin
Cross-Bridge
Bond between myosin and actin
WHAT CAUSES CONTRACTION IN ALL MUSCLE CELLS??
CALCIUM IONS!!!!!!! Ca2+
MEMBRANE IS POLARIZED. What is more negative, cell interior or exterior?
CELL INTERIOR
Calsequestrin
Cal = Calcium; Sequestr = To Separate A protein in the sacroplasmic reticulum that binds calcium
What stimulates smooth muscle?
Calcium
Control of Contraction of Muscle Fibers
Calcium ions are released into sarcoplasm to activate contraction; calcium binds to troponin; troponin is bound to tropomyosin; and tropomyosin blocks the active sites of actin, so that myosin cannot bind to it when muscle is NOT stimulated
Aerobic respiration
Can be used to extract energy from other organic compounds besides glucose, including FATTY ACIDS
Cadiac Muscle Name?
Cardiomyocytes
Significance of DRYSTOPHIN??
Causes Motion of Cell?
Factors of Muscle Strength
1) Muscle Size -Greater size = more myosin-actin cross bridges; more tension can be generated 2)Fascicle Arrangement 3) Size of active motor units -Larger motor units produce stronger contractions THAN smaller ones 4) Multiple motor unit summation 5) Temporal Summation -Greater frequency of stimulation, the stronger the muscle contraction 6) Length-Tension Relationship -Muscle resting at optimum length is prepared to contract more forcefully than a muscle that's contracted/stretched 7) Fatigue -Rested muscles contract more strongly than fatigued ones
Excitation Process?
1) Nerve signal ARRIVES at the AXON TERMINAL, and opens VOLTAGE-GATED CALCIUM CHANNELS. -CALCIUM IONS ENTER TERMINAL 2) Calcium stimulates the synaptic vesicles to release acetylcholine (ACh) into the synaptic cleft 3) ACh diffuses across synaptic cleft and binds to receptors on the sarcolemma -Receptors are LIGAND-GATED Ion channels 4) 2 ACh molecules must bind to EACH receptor to open the channel. When it opens... -NA+ flows quickly INTO the cell -K+ flows OUT of cell -LEADS TO END-PLATE POTENTIAL (EPP) 5) Areas of sarcolemma next to end plate have voltage gated ion channels that open in response to EPP. -Some allow Na+ to enter cell; others allow K+ to leave ACTION POTENTIAL formed by movements of these ions
Reasons for fatigue in high-intensity, short-duration exercise
1) Potassium accumulation -Each action potential releases K+ from the sarcoplasm to the ECF --Results in Hyperpolarization ---Interferes w/ release of calcium from Sarcoplasmic reticulum 2) ADP/Pi Accumulation -ADP slows cross-bridge cycling mechanism of contraction -Pi inhibits calcium release from the SR
5 Components of Muscle Fiber?
1) Sarcolemma 2) Sarcoplasm 3) Myofibril (Made of Myofilaments) 4) Glycogen 5) Myoglobin
Twitch strength
DEPENDs ON STRENGTH OF STIMULUS; Greater stimulus, greater tension developed (More muscle cells excited) IF STIMULUS IS CONSTANT... TENSION INCREASES WITH... -Depends on stimulus FREQUENCY -Greater with better hydration -Greater with higher temps -Becomes weaker as muscle fatigues -Depends on how stretched the muscle was just before it was stimulated
Latent Period
Delay between the onset of stimulus and onset of twitch
Excess Post-exercise Oxygen Consumption (EPOC)
Difference between the elevated rate of oxygen consumption at the end of an exercise and the normal rate at rest
Terminal Cisterns
Dilated end sacs of the sacroplasmic reticulum
Internal Tension
Force generated that causes no shortening of the muscle; not seen on myogram
How does Smooth muscle cell get most of its calcium?
Has Sparse SR; therefore, its gets if from the EXTRACELLULAR FLUID THRU GATED CALCIUM CHANNELS IN THE SARCOLEMMA
Unlike skeletal and cardiac muscle, smooth muscle can..
Hypertropgy, mitotically divide and hyperplasia (Cell Division)
Striation Drawing
I A I H Z Z I = I Band A = A Band H = H Band Z = Z Disk
Advantage of having multiple motor units in each muscle cell?
Muscle fibers fatigue when subjected to continual stimulation; allows other motor units to take other and stimulate other cells , while the fatigued ones recover
White muscles
Muscles composed mainly of FG Fibers -Due to lack of myoglobin content
Red Muscles
Muscles composed mainly of SO Fibers -Due to abundant Myoglobin
Myoblast
Myo = Muscle; Blast = Make/Precursor Stem cells that fuse to produce a muscle fiber
Satellite Cells
Myoblasts that remain unspecialized between the muscle fiber endomysium. -Regenerate damaged skeletal muscle
Single-Unit (unitary) Smooth Muscle
Myocytes of this type of muscle are electrically coupled to each other by gap junctions -Nerve varicosities are not associated with a specific myocyte, but stimulate several of them at once when they release a neurotransmitter -Visceral Muscle --Found in Blood vessels, digestive, respiratory, and urinary tracts
Basal Lamina
Separates muscle fiber and nerve ending from surrounding connective tissue -Also passes through synaptic cleft and virtually fills it
Why do muscle fibers have many nuclei?
Several Stem Cells called Myoblasts FUSE TOGETHER to produce EACH MUSCLE FIBER, with each myoblast contributing 1 nucleus
How is skeletal muscle different from the other types of muscle?
Skeletal muscle has MULTIPLE NUCLEI
If a muscles nerve connections are severed, a muscle is...?
Paralyzed
Creatine Phosphate
Phosphate-storage molecule; donates it to creatine kinase
What special terms are given to the plasma membrane, cytoplasm, and smooth ER of a muscle cell?
Plasma Membrane: Sarcolemma Cytoplasm: Sarcoplasm Smooth ER: Sarcoplasmic Reticulum
Anaerobic Threshold (Lactate Threshold)
Point at which muscles transition to anaerobic fermentation to Generate ATP by GLYCOLYSIS -Increase in blood lactate
Excitation
Process in which action potentials in the nerve fiber lead to action potentials in the muscle fiber
Define responsiveness, conductivity, contractility, extensibility, and elasticity. State why each of these properties is necessary for muscle function.
Responsiveness: Refers to cell's ability to become excited; creates membrane potential upon being excited Conductivity: Muscle cells transmit impulse that excites them. Extensibility: Muscle cells ability to elongate Elasticity: Ability of muscles cell to return back to original size after extending/contracting
Striations:
Results from excessive concentration of myosin and actin
How to remember Sodium-Potassium Pump?
SALTY BANANA -Na+ on outside -K+ on inside
Triad
The T tubule and 2 cisterns associated with it
Myogram
The TIMING and STRENGTH of a muscle's CONTRACTION
Intercalated Discs
The branches that join cardiomyocytes together -Have ELECTRICAL GAP JUNCTIONS, allowing each cardiomyocyte to directly stimulate its neghbor and MECHANICAL JUNCTIONS that keep the cardiomyocytes from pulling apart when the heart contracts
Threshold
The minimum voltage necessary to generate an action potential in the muscle fiber
Connective tissues of endomysium, perimysium, and epimysium are CONTINUOUS with COLLAGEN FIBERS of TENDONS and those, in turn, with the COLLAGEN of the bone matrix
Thus, when a muscle fiber contracts, it pulls on those collagen fibers and typically moves a BONE
Why Junctional Folds?
To increase S.A. of ACh-sensitive membrane
Myokinase
Transfers Pi from one ADP to another, converting the latter to ATP that myosin can use
What happens when calcium ions bind to troponin?
Tropomyosin moves off the active site on actin; allowing myosin to bind to it and cause contraction
Transverse (T) Tubules
Tubular in-foldings of the sarcolemma that penetrate through the cell and emerge on the other side -Closely associated with 2 terminal cisterns running alongside it, 1 on each side
Complete (Fused) Tetannus
Twitches fuse into a single, nonfluctuating contraction -Doesn't happen in body; motor neurons don't fire that fast
Temporal Summation
Two stimuli arriving close together in time
Fine motor control requires which of the following?
Small motor units
Size Principle
Smaller, less powerful motor units with smaller, slower nerve fibers are activated first. If more power is needed, then larger motor units with larger, faster nerve fibers are SUBSEQUENTIALY activated
Excess of what ion in ICF?
K+
Resting membrane potential (RMP)
Electrical charge of cell -Negative value
Elastic Filament
-Run through core of each THICK Filament and anchors it to structures called the Z Disk at 1 end AND M line at the other -Stabilizes thick filament, centers it between thin filaments, and prevents over-stretching, recoils like a spring after a muscle is stretched Made of protein called TITIN
Purpose of AChE?
-Stops cell from contracting
Depolarization:
Electrical potential in cell becomes less negative -IE: Na+ rushing into cell
Latch-Bridge Mechanism
Enables the myosin to remain attached to the actin for a prolonged time WITHOUT consuming more ATP -What causes muscle cells to be very slow to relax
Myosin ATPase
Enzyme in the head of the myosin that HYDROLYZES ATP into ADP and phosphate
Excitation-Contraction Coupling
Events that link action potentials on the sarcolemma to ACTIVATION of the MYOFILAMENTS, thereby preparing them to CONTRACT
Small Motor Units are beneficial for?
When fine Control is needed -Usually supplied by small, relatively sensitive neurons -IE: Found in hand/eye
Large Motor units
When strength is more important than fine control -Muscle fibers innervated by LESS SENSITIVE neurons w/ larger cell bodies -IE: Found in calves of leg
Thin Filaments
-Composed primarily of 2 intertwined strands of a protein called Fibrous (F) Actin --Each F actin is like a bead necklace ---String of subunits called Globular (G) actin (Active site where myosin binds) -Consists of Protein called Tropomyosin
Thick Filaments
-Made of several hundred molecules of a protein called MYOSIN -15 nm in diameter -Bare Zone in middle of thick filament; no heads
Why EPOC occurs?
-O2 is needed to regenerate ATP aerobically -Make myoglobin -Dispose of lactate -B/c exercise raises body temp; consumes more oxygen
Modes of smooth muscle stimulation
1) Autonomic nerve fibers and neurotransmitters 2) Chemicals -Hormones, CO2, O2, low pH, oxytocin 3) Temperature -Cold induces contraction of smooth muscle 4) Stretch -Stomach and urinary bladder contract when stretched by food or urine 5) Autothythmicity: -Present in those found in stomach and intestines
2 Forms of isotonic contraction
1) Concentric Contraction 2) Eccentric Contraction
What happens when a nerve or muscle cell becomes stimulated?
1) Depolarization: Ion channels in plasma membrane open and Na+ instantly flows INTO the cell -Goes down its electrochemical gradient 2) Repolarization -When the electrical potential in the inside of the membrane becomes NEGATIVE again
Name and define the three layers of collagenous connective tissue in a skeletal muscle.
1) Endomysium: Fibrous connective tissue surrounding muscle fibers 2) Perimysium: Fibrous connective tissue surrounding groups os muscle fibers; creates fascicles 3) Epimysium: Connective tissue surrounding whole skeletal muscle
Functions of Muscle
1) Excitability (Responsiveness): -When stimulated by chemical signals, stretch, and other stimuli, muscle cells respond with ELECTRICAL CHANGES across the plasma membrane 2) Conductivity: -Stimulation of a muscle cell produces more than a local effect. Local electrical excitation sets off a wave of excitation that travels RAPIDLY from CELL TO CELL and initiates processes leading to contraction 3) Contractility: -Muscle cells SHORTEN (CONTRACT) substantially when stimulated. Allows them to pull on bones and other organs to create movement 4) Extensibility: -Ability of cells to be able to STRETCH AGAIN between contractions 5) Elasticity: - Ability of a STRETCHED STRUCTURE to return to its original dimensions when tension is released
4 Phases of muscle contraction and relaxation?
1) Excitation 2) Excitation-Coupling 3) Contraction 4) Relaxation
Fatigue from low intensity, long-duration exercise
1) Fuel depletion -Not enough glycogen and blood glucose 2) Electrolyte loss -Loss of electrolytes through sweating alters ion balance of ECF; enough to reduce muscle excitability 3) Central Fatigue -Exercising muscle generates ammonia, which is absorbed by the brain and inhibits motor neurons of the cerebrum
Myocyte Structure (Smooth Muscle Cell)
1) Fusiform 2)Endomysium, NO PERIMYSIUM, FASCICLES, or EPIMYSIUM 3) 1 nucleus 4) Scanty SR 5) NO T-TUBULES 6) No Striations, sarcomeres, or myofibrils 7) Dense bodies
Effects of Stimulus frequency on Muscle Tension
1) Temporal Summation 2) Wave Summation 3) Incomplete Tetanus
3 Types of Myofilaments?
1) Thick Filaments 2) Thin Filaments 3) Elastic Filaments
2 Types of Fast-Glycotic Fibers?
1) Type IIA 2) Type IIB -Described up above previously
Troponin
A calcium-binding protein found on tropomyosin
Titin
A huge springy protein
H Band
A lighter region within the middle of the A Brand; thin filaments don't reach here; Thick filaments linked to each other through the M line
Basal Lamina
A mat of collagen and glycoprotein
Myosin
A motor protein that constitutes the thick myofilaments of muscle, and has globular, mobile heads of ATPase that BIND to actin molecules; serves contractile functions in multiple cell types -Protein that looks like a golf club -2 chains intertwined to form a shaftlike tail, and a double globular head projecting from it an angle
Eccentric Contraction
A muscle lengthens as it maintains tension -Dropping Dumbbell -More prone to injury
Concentric Contraction
A muscle shortens as it maintains tensions Lifting dumbbell
Acetylcholine (ACh)
A neurotransmitter released by somatic motor fibers, composed of choline and an acetyl group
Myofilament:
A protein microfilament RESPONSIBLE for the CONTRACTION of a MUSCLE CELL; composed mainly of ACTIN or MYOSIN
Twitch
A quick cycle of contraction and relaxation
Action Potential
A rapid voltage change in which a plasma membrane briefly reverses electrical polarity; has a self-propagating effect that produces a traveling wave of excitation in nerve and muscle cells -Negative RMP, Positive RMP, Negative RMP
Type IIA Fiber (Intermediate Fibers)
Combine fast-twitch response with aerobic fatigue-resistant metabolism -Typically not in humans
Cross-Training
Combines endurance and resistance exercise
Resistance Exercise
Contraction of muscles against a load that RESISTS movement -Causes muscle fibers to enlarge
Isotonic Contraction
Contraction with a change in length -Muscle shortens and moves the load
Sarcoplasm
Cytoplasm of muscle fiber
How does neurotransmitter travel from neuron?
Exocytosis; Neurotransmitter functions as a chemical messenger from nerve cell to muscle cell
Sacroplasmic Reticulum (SR)
Forms a network around each myofibril
Pacemaker
Found in heart; rhythmically sets off waves of electrical excitation, which travels through the muscle and triggers the contraction of the heart chambers
Glycogen-Lactate System
Glycogen/glucose is metabolized to lactate -Generated a net yield of 2 ATP for each glucose consumed
Overall Contracting Effort
Muscle Shortens B/c its individual sarcomeres shorten and pull the Z discs closer to each other, and dystrophin and the linking proteins pull on the extracellular proteins of the muscle -As Z discs are pull closer (Sarcomere shortens), they pull on the sarcolemma to achieve overall shortening of the cell
Endurance (Aerobic) Exercise
Improves fatigue resistance of muscles by enhancing the use and delivery of oxygen -Jogging, swimming
Which type of contraction maintains joint stability and posture?
Isometric!
Junctional Folds
In-foldings within the sarcolemma
Fibrous (F) Actin
Intracellular protein that provides cytoskeletal support and interacts with myosin to cause cellular movement
When the muscle fiber is stimulated, what happens?
Ion gates in the SR membrane OPEN and Ca2+ floods into the cytosol to ACTIVATE CONTRACTION
Isometric Contraction
Iso = Same; metr = Length; ic = Pertaining to -Contraction without a change in length -PRELUDE TO MOVEMENT
Myofibrils
Long protein cords that MAINLY OCCUPIES the sacroplasm -1µm in diameter
Sliding Filament Theory
Mechanism of Contraction -Myofilaments don't become shorter during contraction; thin filament movement pulls Z discs behind them, causing EACH sarcomere as a WHOLE to shorten
Smooth muscle regenerates through...
Mitosis
Wave Summation:
One wave of contraction is added to another -Muscles only relaxes partially between stimuli
What is the difference between a myofilament and a myofibril?
Myofilaments make up myofibrils
List five proteins of the myofilaments and describe their physical arrangement.
Myosin: Makes up thick filaments; looks like golf club; motor protein Fibrous Actin (F) and Globular Actin (G): Makes up Thin Filament; G actin = subunits that consist of active site that binds MYOSIN; consists of Tropomyosin: Found on G actin; blocks active sites from myosin; prevents contraction Troponin: Calcium-binding protein; found on tropomyosin Titin = Spongy protein found in Elastic Filaments which run through core of each thick filament and anchor it to Z discs
ICF has what charge?
NEGATIVE
Smooth muscle
NO STRIATIONS, myocytes are small (Allows for fine control of tissues); Can remain contracted for a long time; FUSIFORM
Lactate has an affect on muscle fatigue
NO; removed very quickly
Excess of what ion in ECF?
Na+
Involuntary
Not under conscious control; NEVER attached to bones -Cardiac and smooth muscle tissue
Caveolae
Numerous little pockets found in the sarcolemma where a smooth muscle cell's calcium channels are concentrated
Creatine Kinase
Obtains Pi from a phosphate storage molecule, (Creatine Phosphate (CP)), and donates it to ADP to make ATP
Motor Unit
One motor neuron and all the muscle fibers innervated by it -Muscle fibers contract simultaneously
Nerve Fiber and excitation of muscle fiber
One nerve fiber stimulates the muscular fiber at SEVERAL points within the NMJ -Forearm and fingertips = Branching of Neuron; pressing fingertips into clay
Muscle Fibers (Myofiber):
One skeletal muscle cell -VERY LONG
Muscle Fatigue
Progressive weakness and loss of contractility that results from prolonged use of the muscles
Dense Bodies
Protein plaques that serve the purpose of the Z-discs
ACh receptors
Proteins found in a muscle fiber's membrane across from the axon terminal that bind to ACh
Contractile Proteins
Proteins that do the work of Shortening the Muscle Fiber -Myosin and actin
Myoglobin
Red oxygen-binding pigment that provides some of the oxygen needed for muscular activity -Stores Oxygen
What is longer; Contraction phase of Relaxation phase?
Relaxation phase
What muscle fiber makes up small motor units?
SO muscle fibers -Produce more precise movements
Sarcolemma
Sacro = Muscle/Flesh; Lemma = Husk Plasma membrane of a muscle fiber
How is the RMP maintained?
Sodium-Potassium pump -Ions going UP their GRADIENT
Glycogen:
Starchlike carbohydrate that provides ENERGY for the cell during HEIGHTENED levels of exercise
Describe a Cardiomyocyte
Striated, short, thick, 1 or 2 nuclei, NO PERIMYSIUM OR EPIMYSIUM, large T-Tubules (Admit more Ca2+ from ECF)
Globular (G) Actin
String of subunits of F Actin -Has an Active Site that can bind the HEAD OF A MYOSIN MOLECULE
Voluntary:
Subject to conscious control; we control our bones
Electrochemical Gradient
Substance traveling down its concentration gradient and charge gradient
Incomplete Tetanus
Sustained fluttering contraction -Results from high frequency stimuli
Significance of T Tubule and calcium release?
T Tubule SIGNALS the Terminal Cisternae WHEN to release these CALCIUM BURSTS
Explain movement of Filaments in sliding filament theory
THIN FILAMENT slides over the THICK FILAMENT
Contraction Phase
Tension developed that can move a resisting object, or load, such as a body or limb
External Tension
Tension developed that can move a resisting object, or load, such as a body or limb
Multiunit Smooth Muscle
Terminal branches of a nerve fiber synapse with individual myocytes to form a motor unit -Each varicosity is associated with a particular myocyte, and each myocyte responds independently of all the others—hence the name multiunit.
Why is the Transverse Tubule closely associated with the terminal cisterns?
The electrical excitation spreading down the T tubule must EXCITE the opening of calcium gates in the terminal cisterns
Explain why filament doesn't slide back into position after the POWER STROKE of the myosin?
The myosin heads don't all stroke at once but contract sequentially. -Some are bound to the thin filament making sure it doesn't go back into its original place, while the other half are extending forward to GRASP IT farther down
Maximum Oxygen Uptake (Vo2 max)
The point at which the rate of oxygen consumption reaches a plateau and increases no further with an added workload
Synapse
The point where a nerve fiber meets any target cell
Sarcomere
The portion of myofibril from one Z disc to the next; constituting ONE CONTRACTILE UNIT -Functional, contractile unit of muscle fiber -Thousands of them line up to form a myofibril
Recruitment OR Multiple Motor Unit (MMU) Summation
The process of bringing more motor units into play -Causes more muscle fibers to contract; develops greater tension
End-Plate Potential (EPP)
The rapid up-and-down fluctuation in voltage at the motor end plate -Caused by Na+ entering cell (Depolarization) and K+ leaving cell (re-polarization)
Electrophysiology
The study of the ELECTRICAL ACTIVITY of cells
Axon Terminal
The swollen tip at the distal end of an axon; the site of synaptic vesicles and neurotransmitter release
Length-Tension Relationship
The tension generated by a muscle, and therefore the FORCE of its contraction, depends on how stretched/contracted it was at the outset
Length/Diameter of Muscle cells
Usually 100 µm in diamter and 3 cm long
Skeletal Muscle (Multinucleate or not?) (Voluntary Vs. Involuntary) (Striated vs Un-Striated?)
Voluntary, striated muscle that's attached to 1 or more bones -Exhibits STRIATION -Multiple nuclei
Denervation Atrophy
Weakening of muscle that does not have a nerve.
Slow-Twitch Fibers, Type I Fibers, Slow Oxidative (SO), Red Fibers (B/c of High myoglobin content)
Well adapted for endurance and fatigue resistane -Due to Aerobic Respiration --Thus, they are surrounded by lots of blood vessels, rich in mitochondria, and have high concetration of myoglobin ---Thin (minimizes distance traveled by O2) ----Slow release of Ca2+ by Sarcoplasmic reticulum
Fast-Twitch Fibers, Fast Glycotic (FG), Type II Fibers, WHITE FIBERS (LACK OF MYOGLOBIN)
Well adapted for quick responses -Dependent upon anaerobic fermentation (Produces ATP more quickly) BUT less efficiently THAN AEROBIC RESPIRATION -Important in eye/hand muscles. -Sarcoplasmic reticulum releases Ca2+ fast -Myosin has quick ATP hydrolysis and cross-bridge cycling -Less myoglobin (WHITE FIBERS)
Power Stroke
When Myosin releases ADP and Phosphate and flexes into a bent, LOW-ENERGY position, TUGGING THE THIN FILAMENT ALONG WITH IT
Relaxation Phase
When the Ca2+ level in the cytoplasm falls, myosin releases the thin filaments and MUSCLE TENSION DECLINES
Contraction
When the muscle fiber develops TENSION and may shorten
Recovery Stroke
When the myosin hydrolyzes a new ATP, recocks, and attaches to a new active site farther down the thin filament
Relaxation
When the nerve fiber stops stimulating a muscle fiber, the muscle fiber relaxes and RETURNS to its RESTING LENGTH
Varicosities
When the nerve releases a flood of neurotransmitter into the tissue
