Muscles and Muscles Tissue Part C Flashcards
Factors of Muscle Contraction
Force of contraction depends on number of cross bridges attached, which is affected by four factors:
Number of muscle fibers stimulated
(recruitment): the more motor units recruited, the greater the force.
Relative size of fibers
the bulkier the muscle, the more tension it can develop
Muscle cells can increase in size (hypertrophy) with regular exercise
Frequency of stimulation
the higher the frequency, the greater the force.
Stimuli are added together
Degree of muscle stretch
muscle fibers with sarcomeres that are 80–120% their normal resting length generate more force
If sarcomere is less than 80%
resting length, filaments overlap too much, and force decreases.
If sarcomere is greater than 120%
of resting length, filaments do not overlap enough so force decreases
How fast a muscle contracts and how long it can stay contracted is influenced by:
Muscle fiber type
Load
Recruitment
Muscle fiber type Classified according to two characteristics
Speed of contraction.
Oxidative fibers.
Glycolytic fibers
Speed of contraction
– slow or fast fibers
According to
Speed at which
myosin ATPases split ATP
According to pattern
Pattern of electrical activity of motor neurons
Metabolic pathways
used for ATP synthesis
Oxidative fibers
use aerobic pathways
Glycolytic fibers:
use anaerobic glycolysis
skeletal muscle fibers can be classified into three types:
Slow oxidative fibers, fast oxidative fibers, or fast glycolytic fibers
Most muscles contain
contain mixture of fiber types, resulting in a range of contractile speed and fatigue resistance
All fibers in one motor unit
are the same type
Genetics dictate
individual’s percentage of each
Muscle fiber type
Different muscle types are better suited for different jobs
Slow oxidative fibers example
: low-intensity, endurance activities
Example: maintaining posture
Fast oxidative fibers and example
medium-intensity activities
Example: sprinting or walking
Fast glycolytic fibers and example
short-term intense or powerful movements
Example: hitting a baseball
Load
muscles contract fastest when no load is added
The greater the load
the shorter the duration of contraction
The greater the load
the slower the contraction
Recruitment
the more motor units contracting, the faster and more prolonged the contraction
Aerobic (Endurance) Exercise
such as jogging, swimming, biking
leads to increased
Muscle capillaries
Number of mitochondria
Myoglobin synthesis
Results in
greater endurance strength, and resistance to fatigue
May convert fast
glycolytic fibers into fast oxidative fibers.
Resistance exercise (typically anaerobic),
such as weight lifting or isometric exercises
Leads to
Muscle hypertrophy.
Due primarily to increase in fiber size.
Increased mitochondria, myofilaments, glycogen stores, and connective tissue.
Increased muscle strength and size
Disuse atrophy
(degeneration and loss of mass).
Due to immobilization or loss of neural stimulation.
Can begin almost immediately.
Disuse atrophy
Muscle strength can decline 5% per day
Paralyzed muscles
may atrophy to one-fourth initial size
Fibrous connective tissue/ Rehabilitation
replaces lost muscle tissue.
Rehabilitation is impossible at this point.
Smooth Muscle location
Found in walls of most hollow organs.
Smooth Muscle found
Respiratory, digestive, urinary, reproductive, circulatory (except in smallest of blood vessels) except heart
Most smooth muscle
organized into sheets of tightly packed fibers
what are the two layer of sheet smooth muscles contains?
Longitudinal layer
Circular layer
Longitudinal layer
fibers run parallel to long axis of organ
Contraction causes organ to shorten
Circular layer
fibers run around circumference of organ
Contraction causes lumen of organ to constrict
Alternating contractions and relaxations of layer
layers mix and squeeze substances through lumen of hollow organs
Smooth muscle fibers and the size
fibers are spindle-shaped fibers.
thin and short
Smooth muscle
Only one nucleus, no striations
Smooth muscle lack of and contains of
connective tissue sheaths,
Contains endomysium only
Smooth muscle have
varicosities (bulbous swellings) of nerve fibers
Varicosities
store and release neurotransmitters into a wide synaptic cleft referred to as a diffuse junction
Innervated (smooth muscles)
by the autonomic nervous system.
Smooth muscle has less
elaborate SR
Smooth muscles have no
T tubules
SR of smooth muscle
less developed than in skeletal muscle
SR does store intracellular Ca2+, but most calcium used for contraction has extracellular origins
Sarcolemma(Smooth muscles)
contains pouchlike infoldings called caveolae
Caveolae
contain numerous Ca2+ channels that open to allow rapid influx of extracellular Ca2+
Smooth muscle fibers are usually electrically
connected via gap junctions whereas skeletal muscle fibers are electrically isolated
Gap junctions
are specialized cell connections that allow depolarization to spread from cell to cell
What does gap junction contains of and don’t contain of?
There are no striations and no sarcomeres, but they do contain overlapping thick and thin filaments
In smooth muscles thick filaments and ratio
are fewer and have myosin heads along entire length
Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2)
Thick filaments(smooth muscles)
have heads along entire length, making smooth muscle as powerful as skeletal muscle
Smooth muscle does not have(Proteins)
No troponin complex
Smooth muscle does have(proteins)
tropomyosin and Protein calmodulin binds Ca2+
Thick and thin filaments arranged diagonally
Myofilaments are spirally arranged, causing smooth muscle to contract in corkscrew manner
Intermediate filament–dense body network
Contain lattice-like arrangement of non contractile intermediate filaments that resist tension
Dense bodies:
proteins that anchor filaments to sarcolemma at regular intervals
Correspond to Z discs of skeletal muscle
During contraction of smooth muscle
areas of sarcolemma between dense bodies bulge outward
Make muscle cell look puffy
Mechanism of contraction
Slow, synchronized contractions.
Cells electrically coupled by gap junctions.
Mechanism of contraction(action potentials)
Action potentials transmitted from fiber to fiber
Some cells
are self-excitatory (depolarize without external stimuli)
Act as
pacemakers for sheets of muscle
Rate and intensity of contraction
may be modified by neural and chemical stimuli
Contraction in smooth muscle is similar to skeletal muscle contraction in following ways:
Actin and myosin interact by sliding filament mechanism
Contraction in smooth muscle is similar to skeletal muscle contraction in following ways:
Final trigger is increased intracellular Ca2+ level
Contraction in smooth muscle is similar to skeletal muscle contraction in following ways:
ATP energizes sliding process
Contraction in smooth muscle is similar to skeletal muscle contraction in following ways:
Contraction stops when Ca2+ is no longer available.
Some Ca2+ still obtained from SR, but mostly comes from extracellular space
Ca2+ binds
to calmodulin, not troponin
Activated calmodulin
activates myosin kinase (myosin light chain kinase)
Activated myosin kinase phosphorylates myosin head
activating it
Leads to crossbridge formation with actin
Relaxation requires:
Ca2+ detachment from calmodulin
Active transport of Ca2+ into SR and extracellularly
Dephosphorylation of myosin to inactive myosin
Energy efficiency of smooth muscle contraction
Slower to contract and relax but maintains contraction for prolonged periods with little energy cost.
Most smooth muscle maintain
moderate degree of contraction constantly without fatiguing
Referred to as smooth muscle tone
Makes ATP via
aerobic respiration pathways
Regulation of contraction
Controlled by nerves, hormones, or local chemical changes
Neural regulation
Neurotransmitter binding causes either graded (local) potential or action potential
Neural regulation(results)
Results in increases in Ca2+ concentration in sarcoplasm
Neural regulation(response)
depends on neurotransmitter released and type of receptor molecules
One neurotransmitter
can have a stimulatory effect on smooth muscle in one organ, but an inhibitory effect in a different organ.
Hormones and local chemicals
Some smooth muscle cells have no nerve supply
Depolarize
spontaneously or in response to chemical stimuli that bind to G protein–linked receptors
Chemical factors
can include hormones, high CO2, pH, low oxygen.
Some smooth muscles
respond to both neural and chemical stimuli
Response to stretch
Stress-relaxation response
Stress-relaxation response
responds to stretch only briefly, then adapts to new length
Stress-relaxation response functions
Retains ability to contract on demand
Enables organs such as stomach and bladder to temporarily store contents
Length and tension changes
Can contract when between half and twice its resting length
Allows organ to have huge volume changes without becoming flabby when relaxed
