Unit IIIMuscular System Structure
and Physiology
Chapter 10
Muscle functionsProducing body motions
Walking, running, nodding, grasping, etc.
Stabilizing body positionsSustained contractions of neck hold head up
Storing & moving substances within body
GI tract, cardiac muscle
Generating heat (_______________)Exercise, shivering
4 Properties of muscle tissue
_________________ – respond to stimuli by producing electrical signals (AP)___________ – ability of muscle tissue to contract forcefully when stimulated by AP_____________ – stretch w/out being damaged ____________ – return to original length & shape after contraction or extension
Structure of skeletal muscle, fig 10.1
Each _______________________________composed of 100-1000s cells* muscle ______= muscle _____ = myofibers
Endomysium = CT surrounds each fiberB.V. & nerves penetrate into muscle
Perimysium = CT surrounds the fascicle_______= 10s-100s of cells (fibers) bundled together
Epimysium = CT surrounds many fascicles to bundle a whole muscle together as an organ
Structure of skeletal muscle (2)
All 3 layers of CT (endo, peri, epimysium)
protect and strengthenextend from deep fascia - dense irregular CT bind muscles w/ similar function
________ = fibrous membrane covering
Supporting & separating muscles
Submicroscopic skeletal muscle
_____________= muscle fiber’s plasma mem.Skeletal muscle fibers can have >100 nuclei just beneath the sarcolemma____________ = invaginations in sarcolemma
tunnel into center of fiber, filled w/ ECFassists in exciting entire muscle fiber during AP
_____________-cytoplasm within muscle fibercontains ___________________ ATPstuffed w/ myofibrils
Myofibrils – threadlike structurescontractile elements, extend entire length of muscleArranged in ___________- basic functional units
Striated appearance
Myofilaments - composed of contractile proteins
DO NOT extend whole length of fiber2 types:
______________________________________________
_____________- red, oxygen binding proteinonly in muscle fibersContributes oxygen for ATP synthesis
Mitochondria- many in skeletal muscle Myoglobin & sarcoplasm have ingredients for ATP production:
O2
Glucose
_____________________ (SR)- fluid-filled system of membranous sacs, similar to sER
in relaxed muscle stores Ca 2+ release of Ca 2+ causes muscle contraction
____________- appearance due to light I bands and dark A bands____________- small mesodermal cells
Embryonic: skeletal muscle fibers arise from fusion of 100 or more100’s of nuclei
Satellite cells- myoblasts persisting in mature skeletal muscle
capacity to fuse w/ one another or w/ damaged muscle fibers Regenerate functional muscle fibers
Motor neuron & its muscle fibers
Figure 10.11- neuromuscular junction (NMJ)__________________- motor neuron & all the muscle fibers it stimulates__________________- region of sarcolemma that includes Ach receptors
Near synaptic end bulbs
___________________ (NMJ)- a synapse between axon terminals of a motor neuron & sarcolemma of a muscle fiber
Graded potential________________ from membrane potential that makes the membrane more or less polarized (Na+ & Ca 2+ in, K+ out)occur in dendrites & cell body of the motor neuronif graded potential reaches the axon:voltage-gated ion channels openAP
All-or-none principleWhen ______________ voltage is reached voltage gated channels will open and an action potential occursDifferent neurons may have different thresholds BUT the point is:________________________________
Push over first domino, the rest fall
__________________- molecules within axon terminals
Released into synaptic cleft in response toNerve impulseChange in membrane potential
___________________- NT released at NMJ1000s of molecules in each synaptic vesicle
Acetylcholine receptor (AChR)- at each motor end plate 30-40 million
Transmembrane protein binds AChBinding opens ligand-gated ion channels
Acetylcholinesterase (AChE)- enzyme breaks down ACh, attached to ECM in synaptic cleft
ACh binding lasts only brieflyBreaks down excess not bound to receptor
Nerve elicits a muscle action potential:1.Release of ACh- diffuses across synaptic
cleft.2.Activation of AChR: binding opens gated
ion channels allowing flow of small cations (most importantly Na+)
3.Production of muscle AP: inflow of Na+ inside fiber + charged, changing membrane potential, trigger AP
4.Termination of ACh activity: effect of ACh binding lasts briefly (ACh rapidly broken down by AChE)
*NMJ usually located at midpoint of muscle fibers & propagate toward both ends
Excitation - depolarizationIncreased Ca 2+ concentration in cytosol initiates muscle contraction[Ca 2+] due to depolarization of muscle cell membrane = sarcolemma
AP from neuron ACh receptors opening Na+ channels on the sarcolemma which depolarizes the muscle- muscle AP travels along T tubules causing SR to release Ca 2+
Skeletal contraction & proteins
Myofibrils built from 3 types protein;________________ proteins- generate force
Actin and myosin
________________ proteins- switch on and offTroponin and tropomyosin
Both are part of the thin filament
________________ proteins- proper alignment, elasticity, extensibility, link myofibrils to sarcolemma and ECM
12: titan, myomesin, dystrophin
Sliding filament theory fig 10.7,8
Muscle contraction:______ heads attach & “walk” along _____Walking towards both ends of sarcomere
Thin filaments M lineThick filaments Z disc
Length of thick and thin NOT changing
Sarcomere shortening whole muscle fiber shortens shorten entire muscle
_______- motor protein (push and pull)found in all 3 types muscle300 molecules/thick filament______________- convert chemical energy in ATP to mechanical energy of motion & force productionShaped like 2 golf clubs twisted together
______- molecules join to form filament in form of helix
On each actin molecule is a myosin binding site for myosin head to attach
The contraction cycle, fig 10.8
Ca 2+ released from SRBinds troponin-tropomyosin complex & move it
In relaxed muscle, myosin binding sites are blocked by:
______________- Are held in place by: _______________
Contraction cycle can begin:ATP hydrolysisMyosin attaches actin, form crossbridgesPower stroke Detachment of myosin from actin
Contraction of skeletal muscle
Treadmill analogyMyosin moving draws Z discs together
neighboring sarcomeres pulled together
Skeletal muscle shortens, pulls CT & tendonsTension passes thru tendon, move boneFig. 10.11 to summarize contraction
Calcium’s role [Ca2+] in cytosol starts contraction
(decrease stops contraction)
Muscle fiber relaxed: [Ca2+] low, BUT huge amt of Ca2+ stored in SR.AP propogates along sarcolemma T tubules, ________________________ in SR membrane openCa2+ flows out into cytosol, combines with troponin to change its shape
Myosin binding sites are now free
Sources of energy Figure 10.12______________: powering contraction cycle, pumping Ca2+ to SR for relaxation (& other metabolic rxns)
Relaxed state- modest amount usedContracting- using at rapid paceAmt present only enough for a few seconds of contraction
If strenous activity more ATP made…
3 ways to produce ATP_____________________________
Unique to muscle fibersWhile relaxed, muscle making more ATP than neededExcess creatine phosphate – an energy rich molecule
Enzyme: creatine kinase (CK) catalyzes transfer of one phosphate of ATP to creatine creatine phosphate & ADPWhen contraction begins, ADP levels so CK transfers phosphate group from creatine phosphate back to ADP creating ATP (enough energy to last 15 sec)
______________________________________________________________
Cellular respiration & muscle
Anaerobic- ATP-producing rxns, without O2
Muscle activity but no creatine phosphate glucose is catabolized to generate ATPGlucose: blood muscle fibers, & glycogen breakdown within muscle
Glycolysis: 1 glucose (10 rxns) 2 pyruvate yields 2 ATP
Pyruvic acid enters mitochondria & enters series of O2 requiring rxns to produce large amt of ATP
If no O2, pyruvic acid lactic acid in cytosolLiver cells take lactic acid glucose
Aerobic cellular respiration- series of O2 requiring rxns in the mitochondria produce ATP
muscle activity longer than ½ minutePyruvic acid ATP, CO2, H2O, and heat
Slower than glycolysis BUT yields more: 1 glucose 36-38 ATP molecules.
F.a. molecule over 100 ATP moleculesOxygen comes from:
Diffuses into muscle from bloodReleased from myoglobin within muscle fibers
Motor unit recruitmentProcess of ____________________________
Typically different motor units in a whole muscle are NOT stimulated to contract in unison
Alternation delays muscle fatigueContraction of whole muscle can be sustained for long pds
One factor responsible for producing smooth movements rather than series of jerks
Recruitment causes small changes in muscle tension
Comparing isotonic & isometric
___________ contraction- iso= same, tonic= tension
Contraction where tension remains sameOccurs when constant load is moved thru the range of motions possible at a jointLifting a book off a table
_______________ contraction- iso = same, metric = measure
Contraction in which tension of the muscle increases but there is only minimal shortening so that no visible movement is produced Holding a book in an outstretched hand
Simple twitch figure 10.15__________________- brief contraction of all muscle fibers in motor unit due to a single AP in motor neuron
MyogramSkeletal muscle twitch= 20-200msec
_____________ period- brief delay between application of stimulus & beginning of contraction (@2msec)
Ca2+ being released from SR & filaments exert tension, elastic components stretch, shortening begins
_______________ period= 10-100msec_______________ period= 10-100msec
Active transport of Ca2+ back into SR
Duration of all periods depends on type of muscle fiber (see table 10.1)
Fast twitch (as in eye) – 10 msec for each contraction and relaxationSlow twitch (as in legs) – 100 msec for each contraction and relaxation
Repolarization happens…During the relaxation period Ca2+ is actively transported back to the SR
Refractory period= period of lost excitability
Characteristic of all muscle and nerve cellsDuration varies with muscle involved
Skeletal 5msecCardiac 300msec
___________ = minimum stimulus – the least amount of voltage required for contraction_________________ – the voltage at which maximal force is generated (increasing voltage will not increase force of contraction)
All motor units are stimulatedAll muscle fibers are contracting
Graded response (graded potential) – small deviation in the membrane potential that makes the membrane more polarized or less polarized
_______________________________-Maximal voltage applied to muscle in which all fibers in unit are stimulatedseries of shocks at max voltage causes separate twitcheseach twitch will stronger than the previous
Stimuli all at same intensity, cause muscle to contract more efficiently each time
May be warm-up effect, due to intracellular Ca2+ needed for contraction
Terms assoc. w/ frequency
Wave summation- (summation of contraction) strength of muscle contraction that results when muscle APs occur one after another in rapid succession
frequency = strength of contraction
Tetany- fused tetanus -hyperexcitability of neurons & muscle fibers
Sustained or fused contraction Continuous tonic muscular contractions – individual twitches not discernedMay be due to hypoparathyroidism
Muscle fatigueInability to mantain force of contraction after prolonged activityusually results from ∆ w/in muscle fiberMay feel tired, desire to cease activity
Central fatigue (CNS)Mechanism unknown, possibly protective
Suspect contributing factors:Inadequate release of Ca2+ from SRDepletion of creatine phosphate (ATP levels not much change)Insufficent oxygen, depletion of glycogen,build up of lactic acid and ADP, failure of AP to release Ach
Recovery oxygen uptakeFormerly called ___________________ – the added oxygen that is taken into body after exerciseRecovery: few minutes to several hours depending upon intensity of exerciseDepletions during exercise:
Convert lactic acid glycogen in liverResynthesize creatine phosphate & ATPReplace oxygen removed from myoglobin
Post exercise oxygen needs remain high: body temp chemical rxnsHeart & muscles still working hard ATP useTissue repair processes
Definitions:Tonus= Muscle tone - state of partial contraction
characteristic of normal musclemaintained at least in part by a continuous motor impulses originating from reflex, and serves to maintain body posture AKA muscle tone
______________- wasting away or decrease in size of a part due to a failure, abnormality of nutrition, or lack of use_______________- excessive enlargement or overgrowth of tissue without cell division
Cardiac muscle
Figure 20.9, table 10.2Only in heart
forms most of the heart wall
StriatedAction is involuntary
alternating contraction & relaxation cannot be consciously influenced.
beats due to pacemaker- ________________
Cardiac muscle (2)Requires constant O2, many mitochondriaHormones and neurotransmitters adjust heart rate by speeding or slowing the pacemaker_______________- thickening of sarcolemma connecting ends of fibers together
Gap junctions to communicate from cell to cell
Smooth muscle, fig 10.18, 19
In walls of hollow internal structures: b.v., airways, and most organs of abdominopelvic cavity, also in skin and attached to hair follicles.
Looks ____________________________Action is usually ___________, some also has autorhythmicity-built in or intrinsic rhythm.Regulated by neurons of autonomic NS and by endocrine hormonesCompared to other types of muscle cells:
Contraction usually slower, lasts longer Can stretch and shorten to greater extent
Muscle disorders & myopathies
Myopathy- signifies disease or disorder of skeletal muscle tissue.Neuromuscular diesase – problems at all 3 sites:
Somatic motor neuron, NMJ & muscle fibers
Myasthenia gravis – autoimmune disease, chronic, progressive damage to NMJ
AB bind and block AchR at motor end plates75% of patients have hyperplasia or tumors of thymus
Thymic abnormality may be the cause
1st affects eye swallowing, chewing, talkinglimbsDeath may result from paralysis of respirtory musclesAnticholinesterase drugs (inhibits AchE)
Muscular dystrophy- group of inherited muscle destroying diseases
Degeneration of skeletal muscle fibersDMD= Duchenne muscular dystrophy
Mutation on X chromosome strikes males almost exclusivelyDifficultly running, jumping, hoppingUnable to walk @12, resp or cardiac failure usually death between 20-30 yrsGene defect – protein dystrophin
Little or no dystrophin, sarcolemma tears during contractionGene therapy- inject myoblasts w/functional gene
_______________- painful, nonarticular rheumatic disorder
Usually ages 25-50, 15X more in femalesAffects fibrous CT components of muscle, tendons and ligamentsPain at tender points from gentle pressureFatigue, poor sleep, headaches, depression
______- sudden involuntary contraction of single muscle of large muscle group
__________- painful spasmodic contraction
______- spasmodic twitching made involuntarily by muscles that are usually under voluntary control
Eyelid, facial muscles
_____________- rhythmic, involuntary, purposeless contraction that produces quivering or shaking_____________-involuntary brief twitch of an entire motor unit that is visible under skin_________________- spontaneous contraction of since muscle fiber that is not visible but can be recorded
May signal destruction of motor neurons
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