Muscle Tissue Flashcards
What are the 4 characteristics of muscular tissue
- Excitable or irritable 2. Contractible 3. Extensible 4. Elastic
What are the main fxns of muscle tissue
- Create motion 2. Maintain posture/body position 3. Store substances using sphincters 4. Move substances via peristaltic contractions 5. Generate heat
Describe appearance of skeletal muscle
striated, multinucleated
Describe appearance of smooth muscle
no striations, 1 nucleus
Describe appearance of cardiac muscle
striated 1 nucleus
Rank the organizational structures of muscle from largest to smallest.
Muscle=>Fascicle=>Fiber=>Myofibril=>Sarcomeres=>Filaments
What is a muscle fiber
a single muscle cell
What is a fascicle
a bundle of muscle fibers
What is a myofibril
an organelle in a muscle fiber composed of filaments
What is a sarcomeres
arranged compartments of filaments inside a myofibril
What is a muscle filament
Fibrous protein molecules within myofibrils
What is the epimysium
connective tissue that surrounds the entire muscle
What is the perimysium
connective tissue that surrounds a fascicle
What is the endomysium
connective tissue that surrounds a fiber (cell)
How any many connections does a a muscle fiber have to a neuron.
1 fiber=1 neuron
Why are muscle fibers multinucleated
During embryonic development, myoblast fuse to form 1 fiber.
True or False muscle fibers mitotically active
False
Define sarcolemma
Plasma membrane of a muscle fiber (cell)
Define sarcoplasm
Cytoplasm of muscle fiber (cell)
Define T-tubules
Transverse tubules - open evaginations from the sarcolemma to the interior of the cell important for muscle action potentials
Define Sarcoplasmic reticulum
Smooth ER of a muscle fiber, stores calcium ions with Calsequestrin and releases them when stimulated
Calsequestrin
Ca binding protein in sarcoplasmic reticulum that allows Ca concentration in a relaxed muscle to be >10,000 x higher than the fiber cytoplasm
Define terminal cisterns
dilated regions of the sarcoplasmic reticulum that flank T tubules creating a triad.
What proteins compose the thin filament
- Actin=contractile protein, looks like string of pearl, as myosin binding sites
- Troponin and Tropomyosin=regulatory proteins, covers myosin binding sites in the abscence of Ca
What protein composes the thick filament
Myosin=contractile protein
- looks like golf club
- binds and hydrolyzes ATP
- binds reversibly to actin
What are the structural proteins associated with muscle filaments
- Titin= spans half sarcomere from Z disc to M line, spring like and helps sarcomere return to its resting length
- Myomesin= protein associated w/ the m line that binds myosin tails that face in opposite directions
- Dystrophin= links thin filaments to sarcolemma proteins, and transmits tensive forces
- Sarcolemmal proteins= integral proteins that attach to dystrophin
Define A band
dark zone, which comprises the length of the thick filaments and varying overlap of thin filaments
Define I band
Only thin filaments, of 2 adjacent sarcomeres
What is the Z disc of a sarcomere
Where adjacent sarcomeres connect, center of I band
What is the H zone
In the A band that only consist of thhick filaments
What is the M line or a sarcomere and what is it composed of
Midline of the sarcomere, composed of myomesin
Decscribe the route of an action potential from the the nerve to terminal cisterns.
- Action potential travels down somatic motor neuron
- When AP reaches synaptic end bulb of nueromuscuar junction at the axon terminals, acetylcholine is released from vesicles and crosses the synaptic cleft
- Acetylcholine receptors at the motor end plate of the nueromuscuar junction bind 2 acetylcholine molecules
- After binding 2 acetylcholine molecules ion channels in the sarcolemma open allowing Na to flow across the membrane causing AP in muscle fiber
- AP arrives at T tubule where Ca channels open in the terminal cisterns., allowing Ca to flow out of the sarcoplamic reticulum into the cytosol.
Once Ca is released from the sarcoplamic reticulum describe contraction at the sarcome level
(Sliding-filament theory).
- Ca released from sarcoplasmic reticulum binds to the tropin-tropomyosin complex causing it to move aside uncovering the myosin binding sites on actin
- Myosin hydrolyze ATP, energizing them and realigning them
- Myosin heads bind to actin, form cross bridge
- Power stroke, myosin-actin crossbridge rotates toawrds the center of the darcomere
- Myosin heads bind ATP and detaches from actin
Define Rigor Mortis and describe the cause
- Rigidity after death, that usually starts 3-4 hrs after death.
- Caused by Ca linking into cytosol, b/c cellmembranes are not maintained. This then causes filaments in the sarcomeres to bind and contract, but since ATP is no longer produced mysosin heads can not detach from actin
- disappears after ~24 hrs b/c proteolytic enzymes digest myosin-actin crossbridge
Define muscular hypertrophy
It is the increase in the diameter of muscel fibers
- Oragnelles increase in number
- in childhood growth of muscle is stimulated by homones
- in adulthood growth of muscle is caused by repative forceful activity
Define hyperplasia
The increase in the number of of cells, which increase the size of tissue/organ
Define atrophy
The decrease in the size of a cell/tissue/organ/body accompanied by diminished fxn.
What is myoglobin and what function does it have in the body.
Protein similar to hemoglobin (sructure and fxn) but only found in the muscle
-binds O2 and releases it during high levels of aerobic respiration
What are the roles of ATP during muscle contraction.
- need for Na-K pumps to maintain concentration gradients to produce AP’s
- Ca ion pumping necessary to terminate contraction
- Energize myosin head
True or False, ATP is produced faster than it is used.
False, ATP is produced and used at ~ the same rate
What are the ways ATP can be produced in the muscle.
- Creatine phosphate
- Glycolysis
- Aerobic respiration
Where is creatine made and what foods are it derived from
- Synthesized in the liver, kidneys and pancreas
- Derived from milk, red meat, and some fish
True or False, creatine supplementation decreases indogenious production
True
What are the 3 periods in a myogram and what happens in each.
- The latent period=> AP sweeps over the sarcolemma and Ca is released from sarcoplasmic reticulum
- The contraction period=> Ca binds to troponin-tropomyosin complex allowing for for mysoin-actin binding and contraction, peak tension is developed
- The relaxation period=> Ca is transported out of cytosol and is transported back into sarcoplasmic reticulum, myosin head detach and actin is covered, tension decreases.
What is wave summation
When a second stimulus occurs after the refactory period but before relaxation the second contraction will be stronger because mor Ca is released from the sarcoplasmic reticulum.
Describe motor unit recruitment
It is the process whereby the number of active number of motor units is increased according to need.
- the more neurons activated leads to more motor units which leads to greater muscle tension
- smallest/weakest recruited first, if needed larger/stroger motor units are recruited
How much longer does cardiac muscle contract when compared to skeletal muscle
10-15x
True or False smooth muscle cells are autorhythmic
True
How does smooth muscle produce ATP
Only through Glycolysis (anaerobic respiration)
What addition filaments (besides thick and thin) does smooth muscle have and what is its function.
- Contains intermediate filaments
- These fiaments connect to dense bodies (which are functionally similar to Z discs)
- During contraction the thick/thin filaments generate tension on interdiate filaments, which pulls on dense bodies and caused shortening of smooth muscle fiber
What are the 2 types of smooth muscles and how do you distinguish between them.
Distinguished by the number of fibers that comprise each motor unit.
- Single unit (visceral smooth muscle) => muscle fibers connect to one another by gap junctions and contract as a sinlgle unit
- Multi unit =>lack gap junctions and contract independently
What compounds are released into the blood stream when muscle is damaged.
- Myoglobin
- Creatine kinase
DOMS
Delayed onset muscle soreness=microscopic muscle damage after strenuous exercise
-occurs 12-48 hrs after exercise
Define muscle fatigue, and describe what can cause it
It is the inability of a muscle to maintain contraction after prolonged activity
-may be caused by: inadequate Ca release, depletion of creatine, insufficient O2, depletion of gylcogen, build up of lactic acid, build up of ADP, or insufficent acetylcholine
Define central fatigue
Feelings of tiredness and desire to cease activities caused by the brain, exact mech is unknown.
-maybe protective
Define muscle tone and describe why it is important
The small amount of tension or contraction that a muscle exhibits at rest, established by neurons in the brain and spinal cord
-imporatnt for posture, keeping pressure on digestive organs, maintaining BP
What does it mean when a muscle is flaccid
it is the state of limpness in which muscle tone is lost
-caused when muscle neuron supplying the motor unit is severed
Neuromusclar disease refers to problems that encompass what 3 sites.
- Somatic motor neuron
- Neuromuscluar junction
- muscle fibers
Describe Myasthenia gravis
an autoimmune dz attacks acetylcholine receptors at the neuromusclar junction that causes progressive weakness and loss of muscle function
Define spasm
- a sudden involuntary contraction of a single muscle
Define cramp
a painful spasmodic contraction
-caused by inadequate blood flow, overuse of muscle, dehydration, low levels of electrolytes
Define tic
an involuntary spasmodic twitching of muscle that are normally voluntary
Define tremor
involuntary rythmic purposeless contraction that produces quivering/shaking
Define fibrillation
a spontaneous contraction of a single muscle fiber that is note visible under skin but can be seen on electromyography
-may signal destruction of motor neurons
Define myopathy
a disease or disorder of skeletal muscle
Define muscle strain
forceful stretching or tearing of muscle fibers
Define myalgia
muscle pain
Define myoma
a tumor of muscle tissue
Define myositis
inflammation of muscle fibers
Define myotonia
slow relaxation or decreased ability to relax muscles after voluntary contraction
Myomalacia
pathological softening of muscle tissue
