Chapter 10 Vocab Flashcards
Muscle tissue types
- skeletal muscle
- cardiac muscle
- smooth muscle
Common properties of muscle tissue
- Excitability (responsiveness)
- Contractility (ability of cells to shorten)
- Extensibility (stretching)
- Elasticity (recoil)
Functions of skeletal muscle
- Producing movement
- Maintaining posture and body position
- Supporting soft tissues
- Guarding body entrances and exits
- Maintaining body temperature
- Storing nutrients
Skeletal muscles contain
- Skeletal muscle tissue (primarily)
- Connective tissues
- Blood vessels
- Nerves
Skeletal muscles have three layers of connective tissue
- Epimyseium
- Perimysium
- Endomysium
Epimysium
- Layer of collagen fibers that surrounds the muscle
- Connected to deep fascia
- Separates muscle from deep fascia
`Perimysium
Surrounds muscle fiber cells (fascicles)
Perimysium contains
- collagen fibers
- elastic fibers
- blood vessels
- nerves
Endomysium
Surrounds individual muscle cells (muscle fibers)
Endomysium contains
- capillary networks
- myosatellite cells (stem cells) that repair damage
- Nerve fibers
Collagen fibers of epimysium, perimysium and endomysium come together at ends of muscles to form
tendons (bundles) or aponeurosis (sheet)
Skeletal muscles have extensive vascular networks that
- deliver oxygen and nutrients
- remove metabolic wastes
Voluntary muscles
- Contract only when stimulated by central nervous system
- skeletal muscles are this
Skeletal muscle fibers…
- are enourmous compared to other cells
- contain hundereds of nuclei (multinucleated)
- develop by fusion of embryonic cells (myoblasts)
- also known as striated muscle cells due to striations
Sarcolemma
- plasma membrane of a muscle fiber
- surrounds the sarcoplasm (cytoplasm of a muscle fiber)
- A sudden change in membrane potential initiates a contraction
Transverse Tubules (T tubules)
- Tubes that extend from surface of muscle fiber deep into sarcoplasm
- Transmit action potentials from sarcolemma into cell interior
Sarcoplasmic Reticulum (SR)
- Tubular network surrounding each myofibril
- similar to smooth ER
- Forms chambers that attach to T tubules
- Specialized for storage and release of calcium ions
Terminal Cisternae
Chambers that attach to T tubules
Triad
two terminal cisternae plus a T tubule
Calsequestrin
Binds calcium so that more can come in
Myofibrils
- Lengthwise subdivions within a muscle fiber
- Responsible for muscle contraction
- made of bundles of protein filaments (myofilaments)
Myofilaments
Protein filaments that bundle up to make myofibril
Two types of myofilaments
Thin filaments: Composed of actin
Thick filaments: composed of myosin
Sarcomeres
- smallest functional units of a muscle fiber
- interaction between filaments produce contraction
A bands
Dark bands part of striated filament of sarcomere
I bands
light bands part of striated filament of sarcomere. Contains thin filaments but not thick filaments
M line
center of A band. Proteins stabilize positions of thick filaments
H bands
On either side of M line. Has thick filaments but no thin filaments
Zone of Overlap
Dark region where thin and thick filaments overlap
Z lines
Bissect I bands. Mark boundaries between adjacent sarcomeres
Titin
- Elastic protein
- Extends from tips of thick filaments to Z line
- keeps filaments in proper alignment
- Aids in restoring sarcomere length
Thin Filaments
Contain F-actin, nebulin, tropomyosin, and troponin proteins
Filamentous actin (F-Actin)
Twisted strand composed of two rows of globular G-actin molecules. Active sites on G-band bind to myosin
Nebulin
holds F-actin strand together
Tropomyosin
- Covers active sites on G-actin
- prevents actin-myosin interaction
Troponin
- Globular protein.
- Binds tropomyosin, G-actin, and Ca
Ca + Troponin
Releases Tropomyosin
Thick Filaments
- each contain about 300 myosin molecules
- core of titin recoils after stretching
Each myosin molecule consists of
Tail and head
Myosin tail
Binds to other myosin molecules
Myosin head
- made of two globular protein subunits
- Projects toward nearest thin filament
Sliding-filament theory steps
1) H bands and I bands narrow
2) Zone of overlap widen
3) Z lines move closer together
4) Width of A bands remains constant
- Thus thin filaments must slide towards center of sarcomere
Excitable membranes
- Found in skeletal muscle fibers and neurons
- Depolarization and repolarization events product action potentials
Action potentials
Electrical impulses
Skeletal muscle fibers contract due to
Stimulation by motor neurons
Neuromuscular junction (NMJ)
- Synapse between a neuron and a skeletal muscle fiber
- Axon terminal of motor neuron releases a neurotransmitter into synaptic cleft
- ACh binds to and opens a chemically gated Na channel on muscle fiber
Neurotransmitter of neuromuscular junction
Acetylecholine (ACh)
Mechanism for action potential
ACh binds to and opens chemically gated Na channel on muscle fiber. Na enters cell and depolarizes motor end plate
Synaptic cleft
Narrow space that separates axon terminal of neuron from opposing motor end plate
Excitation-Contraction coupling
- Action potential travels down T Tubules to triads
- Ca binds to troponin and changes its shape
- Troponin-tropomyosin complex changes position
- Contraction cycle is initiated
roponin-tropomyosin complex changes position
It exposes active sites on thin filaments
Contraction Cycle
1) Contraction cycle begins
2) Active-site exposure
3) Cross-bridge formation (myosin binds to actin)
4) Myosin head pivoting (power stroke)
5) Cross-bridge detachment
6) Myosin reactivation
Generations of muscle tension
- When muscle cells contract, they produce tension (pull)
- To produce movement, tension must overcome load (resistance)
- The entire muscle shortens at the same rate
Speed of shortening of muscles depends on
Cycling rate (number of power strokes per second)
Duration of a contraction depends on
- Duration of neural stimulus
- presence of free calcium ions in cytosol
- Availability of ATP
As Ca is pumped back into SR and Ca conc in cytosol falls
1) Ca detaches from troponin
2) Troponin returns to original position
3) Active sites are re-covered by tropomyosin and the contraction ends
Rigor mortis
-Fixed muscular contraction after death
Rigor mortis results when
- ATP runs out and ion pumps cease to function
- Calcium ions build up in cytosol
The amount of tension produced depends on the
- Number of power strokes performed
- Fiber’s resting length at time of stimulation
- Frequency of stimulation
Length-tension relationship
- Tension produced by a muscle fiber relates to the length of the sarcomeres
- Max tension produced when maximum number of cross bridges formed
Max tension occurs when
Zone of overlap is large
Frequency of stimulation
Single neural stimulation produces a single contraction, or twitch
Requirement of sustained muscular contraction
Requires many repeated stimuli
Myogram
Graph showing tension development in muscle fibers
Single twitch has three periods
Latent, contraction, relaxation
Latent period
Action potential moves across sarcolemma. SR releases Ca
Contraction phase
- Calcium ions bind to troponin and cross-bridges form
- tension builds to a peak
Relaxation phase
- Ca levels in cytosol fall
- Cross-bridges detach and tension decreases
Treppe
-Stair-step increase in tension
Treppe caused by
Repeated stimulation immediately after relaxation phase. Produces a series of contractions with increasing tension
Treppe typically seen in
Cardiac muscle and not skeletal muscle
Wave summation
-Increasing tension due to summation of twitches
Cause of wave summation
Repeated stiumulations before the end of relaxation period
Tetanus
Maximum tension
incomplete tetanus
- Muscle produces near-max tension
- Caused by rapid cycles of contraction and relaxation
Complete tetanus
- higher stimulation frequency eliminates relaxation phase
- Muscle is in continuous contraction
- All potential cross-bridges form
Tension produced by skeletal muscles
Depends on the number of stimulated muscle fibers
Motor unit
Motor neuron and all of the muscle fibers it controls.
- May contain few muscle fibers of thousands
- All contract at the same time (fibers)
Fasciculation
- Involuntary “muscle twitch”
- Unlike a true twitch, it involves more than one muscle fiber
Recruitment
- Increase in the number of active motor units
- produces smooth, steady increase in tension
Max tension in recruitment
achieved when all motor units reach complete tetanus
Sustained contractions in recruitments
- Produce less than max muscle tension
- motor units are allowed to rest in rotation
Muscle tone
- Normal tension and firmness of a muscle at rest
- Elevated muscle tone increases resting energy consumption
Without causing movement, motor units actively
- Stabilize positions of bones and joints
- Maintain balance and posture
Types of muscle contraction
Isotonic and isometric. Based on pattern of tension production
isotonic contraction
Skeletal muscle changes length
-resulting in motion
Isotonic concentric contraction
- muscle tension>load (resistance)
- Muscle shortens
-Isotonic eccentric contraction
-Muscle tension
Isometric contractions
- skeletal muscle develops tension that never exceeds the load
- Muscle does not change length
Load and speed of contraction
- are inversely related
- the heavier the load, the longer it takes for movement to begin
- Tension must exceed the load before shortening can occur
Elastic forces during muscle relaxation and return to resting length
- Tendons recoil after a contraction
- helps return muscle fibers to resting length
Opposing muscle contractions during muscle relaxation and return to resting length
-Opposing muscles return a muscle to resting length quickly
Gravity
Assists opposing muscles
ATP is the only energy source used
directly for muscle contraction
Contracting muscles use
alot of ATP
Muscle store enough ATP to
start contraction
More ATP must be generated to
sustain a contraction
At rest, Skeletal muscle fibers produce
more ATP than needed
ATP transfers energy to
Creatine
Creatine phosphate (CP)
Used to store energy and convert ADP to ATP
Creatine kinase
Catalyzes conversion of ADP to ATP using energy stored in CP
ATP is generated by
- Direct phosphorylation of ADP by CP
- Anaerobic metabolism (glycolysis)
- Aerobic metabolism (Citric acid cycle and electron transport chain)
Glycolysis main points
- Anaerobic process
- important energy source for peak muscular activity
- Breaks down glucose from glycogen stored in skeletal muscles
- produces two ATP per molecule of glucose
Aerobic metabolism
- Primary energy source of resting muscles
- breaks down fatty acids
Muscle metabolism
Skeletal muscle at rest metabolize fatty acids and store glycogen and CP
During moderate activity (muscle metabolism)
muscles generate ATP through aerobic breakdown of glucose, primarily
At peak activity, (muscle metabolism)
pyruvate produces via glycolysis is converted to lactate
Recovery period
The time required after exertion for muscle to return to normal
Lactate removal and recycling (Cori cycle)
- Lactate is transferred from muscles to the liver
- Liver converts lactate to pyruvate
- Most pyruvate molecules are converted to glucose
- Glucose is used to rebuilt glycogen reserves in muscle cells
Oxygen debt
also called excess postexercise oxygen consumption (EPOC)
After exercise or other exertion
- Body needs more oxygen than usual to normalize metabolic activities
- breathing rate and depth are increased
Heat production and loss
Active skeletal muscle release up to 85 percent of heat needed to maintain normal body temp
Several hormones increase metabolic activites in skeletal muscles
- Growth hormone
- testosterone
- thyroid hormones
- epinephrine
Force
the maximum amount of tension produced
Endurance
the amount of time an activity can be sustained
Force and endurance depend on
- types of muscle fibers
- Physical conditioning
Three types of skeletal muscle fibers
- Fast fibers
- slow fibers
- intermediate fibers
Fast fibers
- Majority of skeletal muscle fibers
- Contract very quickly
- large diameter
- large glycogen reserves
- few mitochondria
- produce strong contractions, but fatigue quickly
Slow fibers
- slow to contract and slow to fatigue
- small diameter
- numerous mitochondria
- High oxygen supply from extensive capillary network
- contain myoglobin (red pigment that binds oxygen)
Intermediate fibers
- Mid-sized
- little myoglobin
- slower to fatigue than fast fibers
White muscles
- mostly fast fibers
- pale
Red muscles
- mostly slow fibers
- dark
Most human muscles
contain a mixture of fiber types and are pink
Muscle hypertrophy
Muscle growth from heavy training
Hypertrophy causes increases in
- diameter of muscle fibers
- number of myofibrils
- number of mitochondria
- glycogen reserves
Muscle atrophy
Reduction of muscle size, tone, and power due to lack of activity
Changes in muscle tissue as we age
- Skeletal muscle fibers become smaller in diameter
- skeletal muscle fibers become less elastic
- Tolerance for exercise decreases
- Ability to recover from muscular injuries decreases
Fibrosis
Increase in fibrous connective tissue
Muscle fatigue
When muscle can no longer perform at a required level
Muscle fatigue correlated with
- Depletion of metabolic reserves
- damage to sarcolemma and sarcoplasmic reticulum
- decline in pH, which affects calcium ion binding and alters enzyme activities
- weariness due to low blood pH and pain
Anaerobic endurance
- uses fast fibers and stimulates hypertrophy
- improved by frequent, brief, and intensive workouts
Aerobic endurance
- supported by mitochondria
- does not stimulate muscle hypertrophy
- training involves sustained, low levels of activity
Improvements in aerobic endurance result from
- alterations in the characteristics of muscle fibers
- improvements in cardiovascular performance
Cardiac muscle cells
- found only in the heart
- have excitable membranes
- striated like skeletal muscle cells
Cardiac muscle cell characteristics
- small
- typically branched with single nucleus
- Have short, wide T tubles (no triads)
- have SR without terminal cisternae
- almost totally dependent on aerobic metabolism
- contact each other via interacalated discs
Intercalated discs
- Specialized connections
- Join sarcolemmas of adjacent cardiac muscle cells by gap junctions and desmosomes
Intercalated disc function
- Stabilizing positions of adjacent cells
- maintaining three-dimensional structure of tissue
- allowing ions to move from one cell to another
Automaticity (cardiac muscle)
Contraction without neural stimulation
controlled by pacemaker cells
Functional characteristics of cardiac muscle
- nervous system can alter pace and tension of contractions
- contractions last 10 times longer than those in skeletal muscle, and refractory periods are longer
- wave summation and tetanic contractions are prevented due to special properties of sarcolemma
Smooth muscle tissue exists in
- Integumentary system
- Cardiovascular and respiratory system
- Digestive and urinary systems
- reproductive system
Structural characteristics of smooth muscle
- long, slender, spindle-shaped cells
- single, central nucleus
- no T tubules, myofibrils, or sarcomeres
- Scattered thich filaments with many myosin heads
- thin filaments attached to dense bodies
- no tendons or aponeuroses
Smooth muscle functional characteristics
- Excitation-contraction coupling
- length-tension relationships
- control of contractions
- smooth muscle tone
Excitation-contraction coupling
- Free Ca in cytoplasms triggers contraction
- Ca binds calmodulin
Calmodulin
- Activated myosin light chain kinase
- allows myosin heads to attach to actin
Length-tension relationship
- Due to lack of sarcomeres, tension and resting length not directly related
- even a stretched smooth muscle can contract
Plasticity
the ability to function over a wide range of lengths
Mutliunit smooth muscle cells
- innervated in motor units
- each cell may be connected to more than one motor neuron
Visceral smooth muscle cells
- Not connected to motor neurons
- arranged in sheets or layers
- Rhythmic cycles of activity are controlled by pacesetter cells
Smooth muscle tone
- normal backgrond level of actvity
- can be decreased by neural, hormonal, or chemical factors
