10 Muscle Tissue Flashcards
How many muscles are there in the human body?
over 700
What are the 5 functions of skeletal muscle?
- move the body
2.maintain posture
3.protect and support
4.regulate elimination of materials (spinchters)
5.produce heat
What are the 5 characteristics of skeletal muscle?
- Excitability - respond to stimulus
- Conductivity - electrical signals connect cell membrane (stimulus) to interior of cell
- contractility - contractile proteins slide past one another
- extensibility - lengthening of the muscle cell
- elasticity - the ability of a muscle cell to return to its original length following shortening or lengthening
epimysium
dense irregular CT surrounding the whole skeletal muscle
perimysium
dense irregular CT surrounding each fascicle (bundle of muscle fibers
endomysium
areolar CT surrounding each muscle fiber
What is the cell membrane of a muscle cell called and why is it special?
sarcolemma
T(transverse)-tubules extend into muscle fiber’s sarcoplasmic reticulum so voltage gated Na+ and K+ channels in the sarcolemma extend into the cell interior, closely connected with sarcoplasmic reticulum
Myofibril
a bundle of myofilaments, enclosed in portions of the sarcoplasmic reticulum, each skeletal muscle fiber contains hundreds to thousands of myofibrils
sarcoplasmic reticulum
an internal membrane complex (similar to smooth ER), forms sleeves of membrane netting around myofibrils, at either end of sleeve are blind sacs called terminal cisternae which are closely associated with T-tubules (SR contains CA2+ pumps, calmodulin and calsequestrin)
Thick filaments
bundles of mysoin
each protein contains two strands with a globular head (point toward middle) and elongated intertwined tail (point toward end of filament,) the head contains actin and ATP binding sites, also ATPase site where ATP attches and is split
Thin filaments
bundles of actin
2 strands of actin protein twisted around each other to form a helical shape, G (globular)-actin is spherical and connects to form F (filamentous)-actin strands
associated regulatory proteins: tropomysin (short, thin twisted filament protein) and troponin (globular protein attached to tropomysin, contains Ca2+ binding site, covers myosin binding sites in non-contracting state)
A band
-the central region of a sarcomere that contains the entire thick filament
-appears dark under a microscope
-does not change length during a contraction
-thin filaments partially overlap the thick filament on each end of the band
H zone
-the central portion of the A band in a resting sarcomere
-does not have thin filament overlap
-during maximal muscle shortening this zone disappears when the thin filaments are pulled past thick filaments
M line
-thin transverse protein meshwork structure in the center of the H zone
-attachment site for thick filaments, keeps them aligned
Z discs
-at both ends of each sarcomere
-perpendicular to myofilaments and serve as anchors for the thin filaments
-appears zigzagged
I bands
-extend form both directions of a Z disk and are bisected by the z disk
-contain only thin filaments
-appear light under a microscope
-at maximal muscle contraction, thin filaments are pulled parallel along thick filaments and I bands disappear
synaptic knob
the expanded tip of an axon where it meets the sarcolemma
-cytosol houses synaptic vesicles filled with ACh (normally repelled from plasma membrane)
-Ca2+ pumps in plasma membrane establish a concentration gradient with Ca2+ outside of the cell
-when voltage-gated Ca2+ channels, also in plasma membrane, are opened Ca2+ flows down it’s concentration gradient, from interstitial fluid into the cell and triggers exocytosis of ACh from vesicles
neuromuscular junction, definition and 3 parts
The specific location, usually mid-region of the skeletal muscle fiber, where it is innervated my a motor neuron
-synaptic knob
-synaptic cleft (houses AChE)
-motor end plate (of sarcolemma with folds/indentations to increase surface area)
Describe a muscle fiber at rest
-the resting membrane potential of the sarcolemma is -90mV with more Na+ outside of the cell and K+ inside
-ACh receptors (chemically gated ion channels) within the motor end plate and the voltage gated Na+ channels and voltage gated K+ channels in the sarcolemma and T-tubules are closed
-Ca2+ ions are stored within the terminal cisternae of the sarcoplasmic reticulum
-contractile proteins of (myofilaments) within the sarcomeres are in their relaxed position
myoglobin
molecule unique to muscle tissue
reddish globular protein similar to hemoglobin
binds oxygen when muscle at rest
releases it during muscular contraction
provides additional oxygen to enhance aerobic cellular respiration
Three ways to generate ATP in skeletal muscle fiber
Immediate supply via phosphate transfer
Short-term supply via glycolysis (anaerobic energy production)
Long-term supply via aerobic cellular respiration
creatine phosphate
molecule unique to muscle tissue
provides fibers means of supplying ATP anaerobically
glycolysis
occurs in cytosol
does not require oxygen
glucose broken down into two pyruvate molecules
2 ATP released per glucose molecule
(pyruvate enters mitochondria for aerobic cellular respiration unless insufficient oxygen then converted to lactate)
aerobic cellular respiration
Long-term supply of ATP
Fuel includes pyruvate, fatty acids and amino acids
Occurs within mitochondria
Requires oxygen
Pyruvate oxidized to carbon dioxide
Energy used to generate ATP
30 net ATP produced
Oxygen debt
Amount of additional oxygen that must be inhaled following exercise
Needed to restore pre-exercise conditions
Additional oxygen required to
-replace oxygen on hemoglobin and myoglobin
-replenish glycogen
-replenish ATP and creatine phosphate in phosphagen system
-convert lactic acid back to glucose (in the liver)
Slow oxidative fibers (type I fibers)
contains slow ATPase
ATP supplied though aerobic cellular respiration
can contract long periods of time without fatigue
appear red due to large amounts of myoglobin
(high percentage in postural muscles)
Fast oxidative fibers (type II a fibers)
least numerous of types
contain fast ATPase
produce fast, powerful contraction
primarily aerobic respiration, but delivery of oxygen lower
Fast glycolytic fibers (type IIx, fast anaerobic fibers)
most common of types
contain fast ATPase
provide power and speed
ATP primarily anaerobic (glycolysis)
can contract only for short bursts
appear white due to lack of myoglobin
(high percentage in muscles of eye)
Periods of a muscle twitch
Latent period (period after stimulus before contraction begins, time needed to initiate tension in fiber)
Contraction period (begins as powerstrokes pull thin filaments, increasing muscle tension, shorter duration than relaxation period)
Relaxation period (begins with release of crossbridges, decreasing muscle tension)
Muscle Tension
Force generated when a skeletal muscle stimulated to contract
Recruitment
Increase in number of motor units with increasing stimulus
Helps explain how muscles can exert varying levels of force
treppe
An increase in twitch tension when stimuli occur 10–20 times per second
Voltage is the same for each stimulus and relaxation is complete for each twitch
Twitches get stronger due to
Insufficient time to remove all Ca2+ between twitches
Increased heat improves enzyme efficiency
wave summation
If stimulus frequency set at ~20 per/sec
Relaxation is not completed between twitches
Contractile forces add up to produce higher tensions
Incomplete tetany
If frequency is increased further
twitches partially fuse
Sustained contraction in body
Tetany
If frequency is increased further still (e.g., 40–50 per second)
without relaxation
leads to fatigue (decreased tension production)
resting muscle tone
Resting tension in a muscle
Generated by involuntary nervous stimulation of muscle
Some motor units stimulated randomly at any time
Change continuously so units not fatigued
Tension called the resting muscle tone
Do not generate enough tension for movement
Decreases during deep sleep
isometric contraction
Contraction of muscle and increased tension, but no movement
Muscle length the same
E.g., holding a weight while arm doesn’t move
Isotonic contraction
Muscle movement
Muscle length changes
E.g., swinging a tennis racket
concentric contraction
isontonic
muscle shortens as it contracts
e.g., in the biceps brachii when lifting a load
eccentric contraction
concentric
muscle lengthens as it contracts
e.g., in the biceps brachii when lowering a load
Hypertrophy
Increase in skeletal muscle size
Results from repetitive stimulation of fibers
Results in more mitochondria, larger glycogen reserves, increased ability to produce ATP, and more myofibrils that contain larger number of myofilaments
Hyperplasia
increase in the number of muscle fibers
may occur in a limited way with exercise
Atrophy
decreasing muscle fiber size
results from lack of exercise
can arise from temporary reduction in muscle use
e.g., individuals in a cast
causes decrease in muscle tone and power
initially reversible, but dead fibers not replaced
with extreme atrophy, loss of muscle function permanent
muscle replaced with connective tissue
Cardiac Muscle Tissue
Cardiac muscle cells
-arranged in thick bundles within heart wall
-Short, thick, branching cells
-one or two nuclei
-striated and contain sarcomeres
-have large numbers of mitochondria
-use aerobic respiration
-Intercalated discs-junctions joining cardiac cells, composed of desmosomes and gap junctions
-Autorhythmic pacemaker-responsible for repetitious, rhymic heartbeat,stimulates cardiac muscle cells, rate and force of heartbeat controlled by autonomic nervous system
Smooth Muscle Tissue -locations
Function by system,E.g., cardiovascular system,blood vessels regulating blood pressure and flow
Respiratory system, bronchioles controlling amount of air in alveoli
Digestive system, small and large intestines mixing and propelling materials
Urinary system, ureters propelling urine from kidney to bladder
Female reproductive system, uterus helping expel the baby
And others, e.g., iris of the eye
Smooth Muscle Tissue microscopic anatomy
Cell shape- Fusiform shaped,Central nucleus,Small (diameter up to 10 times smaller than skeletal muscle fiber, length thousands of times shorter)
Endomysium wrapping around cell
Cell characteristics:
-Involuntary control by autonomic nervous system
-Contracts in response to stretch
-Transverse tubules absent
-Sarcoplasmic reticulum sparse
-Source of Ca2+ outside cell or from sarcoplasmic reticulum
Smooth Muscle Tissue contraction
Contractile proteins actin and myosin oriented at oblique angles to longitudinal axis of cell, contraction causing a twisting motion
No sarcomeres or Z discs contribute to “smooth” appearance
Myofilaments have myosin heads along entire length can form additional crossbridges and can “latch on” to actin and remain attached without ATP
termed latchbridge mechanism
Have actin and tropomyosin, but no troponin
Calcium from outside of cell and activates myosin heads through a calcium-calmodulin complex
Controlling Smooth Muscle
Stimulated to contract by:
stretch
various hormones
decreased pH
lower oxygen concentration
increased carbon dioxide levels
certain drugs
pacemaker cells in GI tract
E.g., oxytocin
causing contraction of smooth muscle cells in uterus
