Chapter 10: Muscular Tissue Flashcards
Describe the 3 types of muscle tissue
- Skeletal: striated and working in a voluntary manner
- Cardiac: strates but works involuntary
- Smooth muscle: non-striated and is involuntary
built-in rhythm of the heart contolled by a natural pacemaker is known as ___________
autorhymicity
What are the 4 key functions of muscular tissue?
Produce body movement
Stabolize body position
Store and move substances within body
Generating head
What adaptive function does shivering achieve?
It is the involuntary contractions of skeletal muscles that increase rate of heat production (thermogenesis)
What are the 4 special properties that allow muscular tissue to function and continue to homeostasis?
Electrical excitability – ability to response to stimuli by producing action potentials
Contractility – ability to contract forcefully when stimulated by action potentials
Extensibility – ability to stretch, within limits, without being damaged
Elasticity – ability to return to original length and shape after contraction or extension
Which 3 layers of connective tissue extend from the fascia (lining of body wall that surrounds muscles/organs) to protect and strengthen skeletal muscles?
Epimusium: outer layer, encircles entire muscle
Permysium: surrounds groups of 10-100+ muscle fibers separating them into bundles called fascilcles
Endomysium: penetrates inferior of each fascicle and separates individual muscle fibers from one another
All layers form a role like tendon that attaches a muscle to the peristeirum of a bone
When the connective tissue elements extend as a broad, flat sheet, it is called an _______
aponeurosis
The neurons that simulate skeletal muscles to contract are ________ motor neurons
somatic
Describe the following microscopic anatomic components of a skeletal muscle fibre:
Sarcolemma
Transverse tubules
Sarcoplasm
Sarcolemma: plasma membrane
Transverse tubules: tunnels into the centre of each muscle fibre where AP travel along
Sarcoplasm: cytoplasm of a muscle fibre that contains myoglobin that releases O2 needed for ATP production
Describe the following microscopic anatomic components of a skeletal muscle fibre:
Myofibrils
Sacroplasmic reticulum
Myofibrils: contractile organelles that make muscles appear striated
Sacroplasmic reticulum: fluid-filled salts that encircles each myofibril that have terminal cisterns that attach to T tubules to release Ca2+ and trigger muscle contraction
Define muscular hypertrophy
Muscle growth that occurs after birth by enlargement of existing muscle fibers due to increased production of myofibrils, mitochondria, SR, & organelles
occurs due to forceful muscular activity
Define muscular atrophy
decrease in individual muscle fibers as a result of progressive loss of myofibrils
Define fibrosis
replacement of fibers with scar
Thin vs. thick filaments
Thin filaments (8nm) are composed mostly of protein actin Thick filaments (16nm) are composed mostly of protein myosin
There are 2 thin filaments for every thick filament in the regions of overlap - both involved in the contractile process
The basic unit of a myofibril are filaments that are arranged in compartments called _____, which are separated from one another by _______
sarcomeres; z-discs (plate shaped proteins)
Describe the arrangement of filaments within a sarcomere:
A band
I band
H zone
M Line
A band: darker middle part of the sarcomere which extends the entire length of a thick filament (H zone is the centre of each A band)
I band: lighter, less dense area that contains the rest of the thin filaments and has a z-disc in the middle
I IS THIN AND H IS THICK
M line: middle of the sacromere that holds thick filaments together
What are the 3 types of proteins that constitute a myofibril?
Contractile
Regulatory
Structural
The two types of contractile proteins in muscles are:
Myosin (thick)
- myosin tail points toward M line and the tails of neighbouring myosin molecules run parallel
- myosin heads - 2 projections of each myosin molecule
Actin (thin): joint to form an actin filament that is twisted int a helix
- Each actin is a myosin-binding site where a myosin head can attach
Describe the 2 regulatory proteins
Tropomyosin: cover myoson-bdingin sites when muscle is relaxed
Tyoponin: binds with Ca2+ to move the topomyospin away from binding site
Describe tintin (structural protein)
Spands half a sarcomere in a relaxed muscle - stabilizes thick filaments; can stretch without harm; accounts for elasticity and extensibility
Describe the 4 steps of the contraction cycle
- Myosin heads hydroyze ATP and become reoriented and energized
- Myosin heads bind to actin, forming cross-bridges
- Myosin cross-bridges rotate toward centre of sarcomere (power stroke)
- As myosin heads bind to ATP, cross-bridges detach from actin
Describe exitaiton-contraction coupling
Ca2+ is stored in SR - as an AP propagates along the sarcolemma and into the T tubules, it causes Ca2+ release
Ca2+ combines with troponin, causing conformation change which moves tropmyposin away from myosin-bdinign sites on acting
Myosin heads bind to form cross-bridges and the contraction cycle begins
What is the length-tension relationship of muscle contraction?
The forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins
Maximum tensions occurs when the zone of overlap extends from edge of Hzone to one end of a thick filaments (too much or too little overlap decreases tension)
What are the steps of a muscle action potential?
- Release of ACh - Ca2+ flows inward stimulating ACh vesicles to undergo exocytosis and are released into the cleft
- Activation of ACh receptors: binds to motor end plate causing influx of cations
- Production of muscle action potential: increases membrane potential (makes it more positively changed) and triggers AP which travels along T tubules triggering Ca2+ release in the SR
- Termination of ACh: acetylcholinesterase (AChE) breaks fawn ACh
How do muscle fiebers produce ATP?
Creatine prophase
Anaerobic glycolysis
Aerobic respiration
Creatine phosphate: formed from ATP while muscle is relaxes, transfers a high-energy P group to ADP forming ATP during muscle contraction
Anaerobic glycolysis (no oxygen): breakdown of glycogen then glycolysis forms ATP and pyrutic acid
Aerobic respiration (oxygen): within mitochondria pyretic acid, faty acids, and amino acids, + oxygen produces ATP
Define muscle fatigue and central fatigue
Inability to maintain force of muscle contraction after prolonged activity
Central fatigue: the feeling of tiredness and desire to cease activity prior to muscle fatigue (CNS response)
Define oxygen debt/recovery oxygen uptake
added oxygen, over and above the resting oxygen consumption that is taken into the body after exercise
used to ‘payback’ metabolic conditions
Define motor unit
a somatic motor neuron plus all the skeletal fibers it simulates (150)
Whole muscles that control precise movements consists of many small motor neurons
What is a twitch contraction? What are the stages (as seen in myogram)?
the brief contraction of all muscle fibers in a motor unit in response to a single AP in its motor neuon
Latent period - ~2ms delay in which the AP sweeps over the sarcolemma and Ca2+ released from the SR
Contraction period - ~10-100ms in which Ca2+ binds to troponin, myosin-binding sites exposed, cross-bridges are formed and peak tension develops
Relaxation period – ~10-100ms, Ca2+ actively transported back into SR, myosin-binding sites covered, tension decreases
Refractory period: lost excitability
The length of the twitch contraction depends on the type of muscle fiber – some are fast-twitch and others are slow-twitch fibers
Describe how frequency of stimulation affects muscle tension
When a second stimulus occurs after the refractory period but before the muscle fiber is relazed, the second contraction will be stronger, a phenomenon called wave summation
Unfused (incomplete) tetanus: sustained but wavering contraction 20-30x/sex
Fused (complete) tetanus: contact contraction - twitches undetectable 80-100x/sec
The combination of the tautness of the elastic components and the partially contracted state of the filaments enables the force of another contraction to be greater than the one before
Define motor unit recruitment
process in which the number of active motor units increases
They have a staggered activity to delay muscle fatigue (weak ones are recruited first)
Muscle tone vs. flaccidity
Muscle tone: small amount of tautness or tension doe to weak, involuntary contractions, even at rest - this keeps muscles firm but is not strong enough to produce movement
Flaccidity: when motor neurons become damaged/cut, they become flaccid
Distinguish between isotonic and isometric contractions
Isotonic: tension developed in the muscle remains almost constant - 2 types:
1. Concentric: when tension is great enough to overcome resistance of an object, the muscle shortens (picking up a book)
- Eccentric: length of the muscle increases (lowering book)
Isometric: tension generated is not great enough to exeed the resistance of the object to be moved and the muscle does not change in length (holding a book steady with outstretched arm)
Contrast between the 3 totes of skeletal muscle fibers:
Slow oxidative (SO) Fast oxidative (FO) Fast glycolytic (FG)
Slow oxidative (SO): ATPase in the myosin head hydrozyxes ATP slowly- important for maintaining posture and aerobic endurance (aerobic respiration)
Fast oxidative (FO) ATPase in the myosin head hydrozyxes ATP quickly - importing for walking & sprinting (aerobic respiration and anaeronbic glycolysis)
Fast glycolytic (FG): hydrolyzes ATP rapidly, Fg fibers contract strongly and quickly (white) - important for intense movement of short duriaiton (anaerobic glycolysis)
How are cardiac muscle tissues different from skeletal muscles?
They have the same arrangement of actin and myosin and same bands but also have intercalated discs - thickenings of the sarcolemma that connects each ends of cardiac muscle fibre
They contain desmosomes which hold fibers together and gap junctions with allow APs to spread from one cardiac muscle to another
They have prolonged Ca2+ delivery and stay contacted longer
Describe the 2 types of smooth muscle tissue
Visceral
Multiunit
Visceral: most common and in tubular arrangements (auto-rhythmic, fibers connect via gap functions)
Multiunit: consist of individual diners, which with their own motor neurone terminal and a few gap functions (found in airways, arrestor pills muscles, eye)
What are the microscopic appearance & feature differences between skeletal, cardiac, and smooth muscles?
Skeletal: long cyndrical fibre with many peripherally located nuclei; unbranched; striated
Cardiac: branches cyndrical fibre with one centrally located nucleus, intercalated discs join neighbouring fibers
Smooth: fiber thickest in the middle, tapered at each end, and with one centrally positioned nucleus, not striated
Describe the microscopic anatomy of smooth muscles (filaments, dense bodies)
They are comprised of thin, thick, and intermediate filaments but are not arranged orderly as in striated muscles
They have no T-tubules but cave small invaginations called caveolae that contain Ca2+ for contraction
The thin filaments attach to dense bodies (similar to z-discs) and during contraction, sliding of thin and thick filaments generates tension
Describe the physiological features of smooth muscles
calmodulin
smooth muscle tone
stress relaxation response
calmodulin (regulatory proteins) bind to Ca2+ in cytosol and activated an enzyme myosin which allows for binding to actin for contraction
smooth muscle tone: prolonged ca2+ in cytosol provides muscle tone, a state of continued partial contraction
Stress relaxation response: smooth muscles initially contract when stretched developing increased tension which decreases in ~1 min which allow smooth muscles to undergo great changes will retaining ability to contract
Hypertrophy vs. hyperplasia
Hypertrophy: enlargement of texting cells (most common growth after birth)
Hyperplasia: increase in number of fibers
Define myasthenia gravis
An autoimmune disease that causes chronic, progressive damage of the NMJ - body binds and blocks ACh receptors, decreaseing the number of functional receptors at the motor end plates of sketal muscles
Define muscular dystrophy
a group of inherited muscle-destorying diseases that cuase progressive degermation of skeletal muscle fibers
Define abnormal muscle contractions:
Spasm Cramp Tic Tremor Fasciculation Fibrilation
Spasm: involuntary contraction of a single muscle in a large group of muscle
Cramp: painful spasmodic contraction
Tic: spasmodic twitching made involuntary by muscles that are ordinarily under voluntary control (eye twitch)
Tremor: rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement
Fasciculation – involuntary, brief twitch of an entire motor unit that is visible under the skin
Fibrillation – spontaneous contraction of a single muscle fiber that is not visible under the skin but can be recorded by an EMG
Smooth muscle fibers use troponin and tropomyosin for contraction
True or False
False - they use calmodulin and myosin light chain kinase (enzyme)
