Chapter 9 - Muscles and Muscle Tissue Flashcards
What are the 3 types of tissues?
Skeletal, smooth, cardiac
Describe skeletal muscles (5).
skeletal muscle: organs that attach bones and skin
- fibers: longest and have striations (stripes)
- called voluntary muscle since can be controlled
- contract rapidly and get tired easily
-Key words: striations, voluntary, skeletal
Describe cardiac muscle (3).
- makes up most of heart wall
- contracts at steady rate because it is a pacemaker but heart increases rate
- Key words: cardiac, striated, involuntary
Describe Smooth Muscle.
- tissue: found in walls of hollow organs ex. stomach, bladder and airways
- Key words: visceral, nonstriated and involuntary
What are the 4 main characteristic all muscles share?
Excitability (responsiveness): ability to receive and respond to stimuli
Contractility: ability to shorten forcibly when stimulated
Extensibility: ability to be stretched
Elasticity: ability to recoil to resting length
What are the 4 functions of muscles?
- produce movement: responsible for all locomotion and manipulation ex. walking, digestion, pumping blood
- maintaining posture and body position
- stabilizing joints
- generate heat as they contract
What are the 2 types of attachments for muscles?
direct (fleshy) attachments: epimysium fused to periosteum of bone or perichondrium of cartilage
indirect attachments: connective tissue, epinysium, perimysium and endomysiumform complex at endof muscle
What are the things that make up skeletal muscle (4).
- nerves and blood supply
- connective tissue sheaths
- attachments
What does each muscle receive?
- nerve
- artery
- veins
What does consciously controlled skeletal muscles have?
They have nerves supplying every fiber.
What do contracting muscle fibers need and produce?
Need: large amounts of oxygen and nutrients
Produce: waste products
What are muscles fibers covered with and what does it support?
connective tissue (endomysium)
- supports cells and reinforces whole muscle
What is the difference between the sarcolemma and the sarcoplasm?
SL - muscle fiber plasma membrane
SP - muscle fiber cytoplasm
- Contains many glycosomes for glycogen storage, as well as myoglobin for oxygen storage
What are the different levels of the sheaths from external to internal?
Epimysium: dense irregular connective tissue surrounding entire muscle; may blend with fascia
Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers)
Endomysium: fine areolar connective tissue surrounding each muscle fiber
What are the structures within skeletal muscle cells?
- Myofibrils
- sarcoplasmic reticulum
- t tubules
What is a myofibril and how much of the muscle volume does it take up?
dense packed and rodlike elements
- a single muscle fiber contains 1000s
- 80%
What characteristics do myofibrils contain?
- striations
- sarcomeres
- myofilaments
- molecular composition of myofilaments (actin and myosin)
What is the difference between the A Band and the I band?
AB: dark region
- H zone: lighter region in middle of A band
- M line: line of protein (myomesin) that
bisects (divides in 2 lines) H zone
vertically
IB: lighter region
- Z disc (line): coin-shaped sheet of proteins on midline of light I band
Describe Sarcomeres.
- smallest contractile unit (functional unit) of muscle fiber
- contains A band with half of an I band at each end
- consists of area between Z discs - individual sarcomeres algin end to end along myofibril, like boxcars of train
What is a myofilament?
arrangement of actin and myosin
- actin: thin filament - extend across I band and partway in A band, anchored to Z disc
- myosin microfil: think filament - extends length of A band, connected to M line
Explain the composition of myosin.
contains two heavy and four light polypeptide chains
- heavy: intertwine to form myosin tail
- light: form globular head
- head links to thin filament to form cross bridging
- 2 heads are off set
What is the molecular composition of myofilaments (3 [5])?
Elastic fibers: made of protein titin
- holds thick filament in place; helps with recoil, resist over stretching
Dystrophin
- links thin filament to sarcolemma
Nebulin, myomesin and C protein: bind filament or sarcomeres together
- maintain alignment of sarcomere
Explain the composition of actin and their regulatory proteins.
polypeptide made of kidney shaped G-actin (globular) subunits
- G actin bears active sites for myosin head to attach during contractions
- G actin link together to form F actin (filamentous)
RP: tropomyosin and troponin
Explain the role of Sarcoplasmic reticulum.
SR: network of smooth endoplasmic reticulum tubules surrounding each myofibril
- run longitudinally
- terminal cisterns form perpendicular cross channels at the A-I band junction
- SR functions in regulation of intracellular Ca2+ levels
- stores and releases Ca2+
Explain the function of T tubules (6).
Formed by protrusion of sarcolemma deep into cell interior
- Increase muscle fiber’s surface area
- Lumen continuous with extracellular space
- Allow electrical transmissions to reach interior of each muscle fiber
- Tubules penetrate cell’s interior at each A–I band junction between terminal cisterns
Triad: area formed from terminal cistern of one sarcomere, T tubule, and terminal cistern of neighboring sarcomere
What are the triad relationship (5)?
T tubule contains integral membrane proteins into intermembrane space (between tubule and muscle fiber sarcolemma)
- T proteins act as voltage sensors that change shape
S R cistern membranes also have integral membrane proteins that protrude into intermembrane space
- S R integral proteins control opening of calcium channels in S R cisterns
- with impulses, T tubule proteins change shape, causing S R proteins to change shape, causing release of calcium into cytoplasm
Explain contractions in relation to muscle fibers (3).
activation of cross bridges to generate force
- occurs when forces exceeds forces opposing shortening
Sliding filament model of contraction: thin filaments slide past thick filaments (actin and myosin overlap) - don’t change shape
Which structures are involved in shortening of muscle fibers?
- I band shorten
- Z disc become closer
- H zones disappear
- A bands move closer to each other
Explain the location and function of axons in skeletal muscles.
stimulated by somatic motor neurons
- axons travel from CNS to skeletal muscle
- divides into branches to form neuromuscular junctions and motor end plate
How does AP cross from neuron to muscle cell?
Acetylcholine
Explain neuromuscular junction.
- motor neuron contacts the skeletal muscle
- consists of multiple axon terminal and the underlaying junctions folds of the sarcolemma
Explain end-plate potential.
- ACh released from motor neuron binds to ACh receptors on sarcolemma
- cause chemically gated ion channels (ligands) on sarcolemma to open
- Na+ diffuses in, interior of sarcolemma becomes less negative
What are the 3 steps of AP for skeletal muscles ?
- Generation of end plate potential
- Depolarization
- Repolarization
Explain depolarization.
- if end plate potential causes enough change, voltage-gated
- Na+ channels open
- AP spreads across sarcolemma from one voltage gated Na+ channel to the next
Explain repolarization.
Na+ voltage-gated channels close, and voltage-gated K+ channels open
K+ efflux out of cell rapidly brings cell back to initial resting membrane voltage
- refractory period: muscle fiber cannot be stimulated for a specific time, until repolarization is complete
What is special about AP in muscle fibers?
They don’t have a hyperpolarization period
Explain Excitation-contraction (E-C) coupling.
events that transmit AP along sarcolemma (excitation) are coupled to sliding of myofilaments (contraction)
- AP propagated into T tubules where it stimulates the release of Ca2+ from SR
What are the 4 steps of the cross bridge cycle?
1)Formation of cross bridging
2) the power stroke fueled by ADP and Pi
3) cross bridging detachments
4) returns back to pre stroke formation
explain what a muscle twitch is.
simplest contraction resulting from a muscle fiber’s response to a single action potential from motor neuron
What are the three phases of muscle twitch?
Latent: events of excitation-contraction coupling
- no muscle tension seen
Contractions: cross bride formation
- tension increase
Relaxation: Ca2+ reentry into SR
- tension declines
What are the 3 ways responses are graded by?
- changing frequency of stimulation
- changing strength of stimulation
- muscle response to change in stimulus frequency
- single stimulus results in single
contractile response
Draw and describe the 4 types of temporal summation.
- individual twitches
- temporal summation
- unfused tetanus
- fused tetanus
What is recruitments?
stimulus is sent to more muscle fibers, leading to more precise control
What are the 3 types of stimulus involved in recruitment?
Subthreshold: stimulus not strong enough, so no contractions seen
Threshold: stimulus is strong enough to cause first observable contraction
Maximal: strongest stimulus that increases maximum contractile force
- all motor units have been recruited
How does size effect recruitment?
- smaller fibers are recruited first then larger fibers (only for powerful contractions)
- some contract while others don’t to fight against fatigue
What are the 2 types of contractions and explain?
Isometric: no shortening; muscle tension increases but does not exceed load
Isotonic: muscle shortens because muscle tension exceeds load
- concentric contractions: muscle shortens and does work
- eccentric: muscle lengthens and generates force
What are the three mechanisms for regenerating ATP?
- direct phosphorylation of ADP by creatine phosphate (CP)
- anaerobic - glycolysis and lactate formation
- aerobic - glycolysis and aerobic respiration in mitochondria
What is the difference between short distance and prolonged duration exercise when it comes to ATP generation.
SD - uses ATP stored in muscles then ATP generated by creatine and ADP then glycogen
LD- generates ATP from other nutrients by aerobic pathway
Explain Muscle fatigue.
the inability to contract despite stimulation
causes:
Ionic imbalances
K, Na and Ca levels can change membrane potentials
- increased Pi from CP and ATP interfere with calcium release in SR
- decreased levels ATP means increased levels Mg which interferes with voltage sensitive T tubules
- decreased glycogen
What are the 4 things the force of muscle contractions depend on?
1) frequency of stimulation
2) number of muscle fibers stimulated (recruitment)
3) size of muscle fibers
4) degree of muscle stretch: if stretched to various lengths and maximally stimulated, the tension generated varies
Which stretch length percentage is optimal?
80% to 120%
How fast and long muscle fibers contract for is determined by …
- muscle fiber type
- load and recruitment
What are the muscle fiber characteristic for contractions?
speed: speed which myosin ATPases splits ATP - electrical activity of motor neurons
metabolic pathway for ATP synthsis
- oxidative fibers: use aerobic pathways
- glycolytic fibers: use anaerobic glycolysis
What are the 3 fibers types for contractile speed?
slow oxidative fibers: low-intensity, endurance activities
fast oxidative fibers: medium-intensity activates
fast glycolic fibers: short-term intense or powerful movements
What are the 2 layers of smooth tissue?
Longitudinal layer: fibers run parallel to long axis of organ
- contraction causes organ to shorten - more space
circular layer: fibers run around circumference of organ
- contraction causes less space
5 Characteristics of smooth muscles.
- are spindle-shaped
- have only 1 nucleus
- lack the coarse connective tissue sheaths found in skeletal muscles (only have endomysium)
- has varicosities (bulbous swellings) instead of neuromuscular junctions
- less elaborate SR and no T tubules
What is different between skeletal and smooth muscle when it comes to excitation-contraction coupling?
calcium doesn’t bind to troponin like it does in skeletal muscle
