Physiology: Functions, Properties and Receptors of the Muscles Flashcards
What percentage of body mass does muscle compose?
40%
How is the muscular system attatched to the skeletal system?
via tendons
What are the three types of muscle tissue?
- skeletal
- smooth
- cardiac
What is the function of skeletal muscle tissue?
- moves or stabilises the positions of the skeleton
- guards entrances and exits of the digestive tract, respiratory tract and urinary tracts,
- generates heat,
- protects internal organs,
What is the location of skeletal muscle tissue?
combined with connective tissues and nervous tissues in skeletal muscle.
Explain how skeletal muscle tissue cells look like.
muscle fibers:
- long
- cylindrical
- striated
- multinucleated
What is the function of cardiac muscle tissue?
- circulates blood,
- maintains blood (hydrostatic) pressure
Explain how cardiac myocytes look like.
- short
- cylindrical
- branched
- striated
- uninucleated
- intercalated disks
What is the function of smooth muscle tissue?
- moves food, urine, and reproductive tract secretions,
- controls diameters of respiratory passageways and blood vessels
Explain how smooth myocytes look like.
- short
- spindle shaped
- non striated
- uninucleated
What are intercallated disks?
gap junctions, cell junctions
Do skeletal muscle cells undergo cell division? What do they undergo?
no they do not. they only undergo hypertrophy and vertical growth due to increased cell and sarcomere numbers.
Are skeletal muscle cells contractions voluntary? What are they stimulated by?
yes, they are stimulated by electrical impulses.
What do intercallated disks allow for?
- the heart to contract in a wave-like pattern so that the heart can work as a pump.
- gap junctions: action potential to spread fast
Explain the contractions of the heart. Voluntary? What affects it?
- involuntary
- affected by the autonomic nervous system
How do smooth myocytes spread signals from one cell to another?
through cell junctions
Is the contractive force of smooth muscle regulated by variation in the number of cells contracting?
no! it cannot be regulated by a change in the number of contracting cells.
What are the functions of muscle?
- move the body
- control body posture
- support and protect
- contril orifices of the body
- generate peristaltic movements
- regulate blood flow
- participate in temperature regulation
Are cardiac muscle cells branched?
yes! very highly branched!
Explain the structure of skeletal muscle. (largest to smallest units)
muscle –> fascicle –> single muscle fiber (cell) –> myofibril
What are T-tubules?
narrow tubes which are continuous with the sarcolemma, and extend into the sarcoplasm (at right angles to the cell surface and filled with extracellular fluid)
What is the function of T-tubules?
to conduct electrical signals throughout the muscle tissue ensuring simountanous contractions.
What do electrical impulses trigger (which travel by T-tubules)?
muscle contraction
What do electrical impulses travel in (within muscle tissues)?
T-tubules
What is the T-tubule tightly bound to?
the sarcoplasmic reticulum
What is the sarcoplasmic reticulum? What does it form?
the sarcoplasmic reticulum forms a tubular network around each individual myofibril.
What does the SR contain in large amounts?
Ca2+ stores
What do t tubules form when they enlarge (in the SR)?
terminal cisternae
What are terminal cisternae?
enlarged t-tubules
What is a sarcomere?
the smallest contractile unit of a striated muscle
What two fillaments are sarcomeres made out of?
actin and myosin
What two bands (+ other names) does the sarcomere display? When does it display them?
two bands displayed under polarized light.
1) dark band= A band= anisotropic
2) light band= I band= isotropic
Isotropic vs anisotropic band.
isotropic is the light band,
anisotropic is the dark band.
Where is the A band located? What does it include?
located in the center fo a sacromere,
it includes:
- the M line,
- the H zone,
- the zone of overlap.
What is the A band? What does it do?
the central portion of each thick fillament. It stabilizes the positions of the thick fillaments.
Where is the H band located? What does it include?
lighter region on the other side of the M line,
it contains:
- thick fillaments only (myosin)
What is the zone of overlap? Explain the overlap.
thin + thick fillaments overlap.
1 thin - 3 thick
1 thick - 6 thin
- : is surrounded by
Explain the I band.
- contains thin fillaments
- extends from the A band of one sarcomere to the A band of the next sacromere
What are Z lines?
lines which mark the boundry between adjacent sarcomeres
- interconnect thin fillaments of adjacent sarcomeres
What extends from the tips of thick fillaments to attach to the Z line?
strands of the protein TINTIN
What is the function of tintin?
- helps keep the thick fillaments and thin fillaments in proper alignement
- helps the muscle fiber resist extreme stretching (which would disrupt the contraction mechanism)
What do thin fillaments contain?
actin
- tropomyosin strands
- troponin molecules
What three types of troponin molecules exist?
- TnT (attaches to tropomyosin)
- TnI (ihibitory portion which attaches to actin)
- TnC (binds to calcium ions)
What do thick fillaments contain?
myosin (pair of myosin subunits twisted around one another):
- long tail (bound to other myosin molecules)
- free head (consisting of 2 globular protein subunits)
What does the binding of myosin heads to actin form?
cross-bridges between the myofillaments
What does one sarcomere consist of?
- 2 Z lines
- 2 half I bands
- 1 A band
- tintin
- 1 M line
What happens as a muscle contracts? (what changes occur in the sarcomere?)
A band stays the same width,
Z lines move closer together,
I band shortens.
How much shorter is a sarcomere once contracted?
around 30% shorter
What is the sliding fillament theory?
theory which explains that thin fillaments slide alongside the thick fillaments.
What does the sliding theory explain? What doesnt it explain?
It explains what happens to a sarcomere during a contraction, yet it doesn’t explain the mechanism involved.
What are the synapses called between the somatic motor neurons and the skeletal muscle fibers? What type of synapses are they?
- excitory chemical synapses
NEUROMUSCULAR JUNCTIONS
What initiates a series of events leading to the contraction of a muscle?
the neuromuscular junction
What is the purpose of ATP in the contraction process?
- provide energy for the power stroke
- ATP binding (to myosin) breaks the crossbridge
- necessary for the pumping of Ca2+ from the cytosol back to the SR
How does muscle relaxation occur?
- SR begins to actively absorb Ca2+ from the sarcoplasm.
- tropinin returns to its original position
- tropomyosin covers the active sites once again.
- external forces must act on the contracted muscle fiber to stretch the myofibrils and sarcomeres to their original dimentions.
How are contracted sarcomeres relaxed?
external force which stretches it out.
How does smooth muscle contract?
a similar way, using actin and myosin however in a different pattern. Actin fillaments attach to dense bodies spread throughout the cell.
What are the steps involved in smooth muscle contraction?
1) depolarization of the membrane or hormone/neurotransmitter activation
2) L-type voltage gated calcium channels open
3) calcium-induced calcium release from the SR
4) increased intercellular calcium
5) calmodulin binds to calcium
6) myosin light chain kinase activation
7) phosphorylation of myosin light chain
8) increase of myosin ATPase activity
9) myosin-P binds actin
10) cross bridge cycling leads to muscle tone
smooth vs striated muscle
smooth:
- tonic contractions (last longer and consume less ATP)
- contractions are more resistant to fatigue
- tense and relax
- greater elastic properties
- actin fillaments lack troponin protein
- calmodulin binds calcium
What is in smooth muscle like troponin is in striated muscle?
calmodulin
What is isotonic contraction?
same force contraction
(tension remains constant even though the length of muscle changes)
What is isometric contraction?
same length
(tension of muscle peaks on stimulatio but the muscle does not shorten)
What do isometric contractions do?
- stabilize an animal’s vertebrae
- maitain an animal’s position
What types of movements are produced by isotonic contractions?
movements of:
- limbs
- fingers
- neck
- tail
Around how many ATP molecules does one thick fillament break down per second?
2500
What does a resting muscle break down to produce ATP?
fatty acids
How much ATP do skeletal muscles produce?
more than they need
What does ATP transfer energy to (in skeletal muscle)?
creatine
What do energy transfers to creatine create?
another high energy compound- creatine phosphate (CP)
What is a surplus of ATP used to create?
reserves of creatine phosphate and glycogen.
How does a resting skeletal muscle fibers creatine phosphate content compare to its ATP content?
six times as much creatine phophate as ATP
How much time does the 6x more creatine phosphate last in muscle contractions? What must be used later?
- lasts around 15 seconds
- muscle then must rely on other mechanisms to convert ADP to ATP
How can mitochondria meet the ATP demands of skeletal muscle?
through the aerobic metabolism of fatty acids and glucose.
What is the name of the acid which skeletal muscle depends on for ATP production? What is it provided by?
- pyruvic acid
- provided by glycolysis
What does pyruvic acid do?
breaks down glucose molecules obtained from glycogen in the muscle fiber
What process is most ATP provided to mitochondria by?
glycolysis
If there is a rise of pyruvic acid in the sarcoplasm, what is it converted into?
lactic acid
Under what conditions do how many molecules of glucose, make how many molecules of pyruvic acid, which are converted to how many molecules of what?
under anaerobic conditions
- 1 molecule of glucose
- 2 molecules of pyruvic acid
- lactic acid
What happens when a muscle fiber contracts?
conditions in the sarcoplasm are changed:
- energy reserves are consumed,
- heat is released,
- lactic acid is generated (if the contraction was at peak levels)
When is lactic acid generated?
when the contraction of muscles occured at peak level
What happens in the recovery period? How long does this process take?
- muscle fibers are returned to normal, preexertion levels,
- may take several hours
sustained activity at higher levels may take a week for full recover
What is the recovery period powered by? (what type of metabolism?)
ATP that aerobic metabolism generates.
How is ATP related to oxygen demand?
the more ATP required, the more oxygen is needed.
What is the name of the “amount of oxygen needed to restore normal, preexertion conditions”?
- oxygen debt
- excess oxygen consumption
What is excess oxygen consumption?
the amount of oxygen needed to restore normal, preexertion conditions
- created during muscle work
What is responsible for most of the additional oxygen consumption?
skeletal muscle fibers (which must restore creatine phosphate and glycogen concentrations.
What does normal muscle function require?
- substantial intercellular energy reserves
- a normal circulatory supply
- a normal blood oxygen concentration
What is muscle fatigue? How does it occur? When do the effects become more pronounced?
- strenuous and prolongued muscle activity results in muscle fatigue
- it is cumulative (the effects become more pronounces as more muscle fibers are affected).
What are some possible causes of muscle fatigue?
- changes at the neuromuscular junction
- the sarcoplasmic reticulum releases insufficient Ca2+ into the sarcoplasm
- there is a lack of energy (ATP) or energy reserves (glycogen) in the muscle cell, or the rising lactic acid level
What does resting muscle tone do?
stabilizes the position of bones and joints
What does hightened muscle tone do to the speed of voluntary contraction?
accelerates the recruitment process during cvoluntary contraction, as some of the muscle fibers are already stimulated.
Around how many muscle fibers does one skeletal muscle contain?
thousands
What are all muscle fibers controlled by?
a single motor neuron
What is a “motor unit”?
all muscle fibers + a single motor neuron
What is the strength of a muscle contraction determined by?
the size and number of motor units being stimulated
How to determine the size of a motor unit?
by the number of muscle fibers per motor neuron
What is meant by a “small” and “large” motor unit?
small- few muscle fibers per motor neuron
large- several thousand muscle fibers per motor unit
What are the two major types of skeletal muscle fibers? What factor is the division based on?
based on the contraction speed during a single twitch:
1) slow - red - type I
2) fast - white - type II
Compare the three types of muscles based on speed.
all skeletal muscle fibers are fast in comparison to cardiac and smooth muscle cells.
What does the percentage of fast and slow fibers in skeletal muscles depend on?
- species
- functions of the muscle
What do slow muscle fibers have?
- more mitochondria
- more myoglobin
- more extensive capillary supply
State the main properties of slow - red - type I fibers.
1) OXIDATIVE: more efficient at using oxygen to generate more ATP.
2) FATIGUE RESISTANT: fire more slowly, go on for a longer time
3) belong to SMALL MOTOR UNITS,
4) dominate in muscles which SUPPORT BODY STRUCTURE
also called “slow-twitch oxidative fibers”
State the main properties of fast- white - type II fibers.
1) power and SPEED for a SHORT DURATION
2) FATIGUE RAPIDLY: due to a build up of lactic acid and depletion of glycogen
3) GLYCOLYTIC/OXIDATIVE/INTERMEDIATE PROPERTIES
4) belong to LARGE MOTOR UNITS
5) dominate in muscles which BODY MOVEMENT (propulsive muscles)
also called “fast-twitch glycolytic fibers”
What are the different types of fast fibers?
- type IIa: oxidative fibers
- type IIb: glycolytic fibers (present in very small mammals, ike rodents)
- type IIx: intermediate properties (present in domestic mammals)
Which types of fibers dominate in propulsive muscles?
fast twitch - white - type II
What does muscle inactivity lead to?
muscle weakness and wasting
What does regular excersize do to muscle?
increase muscle size, strength and endurance
What does excersize result in?
stronger, more flexible muscles with greater resistance to fatigue.
What does training do?
- makes body metabolism more efficient
- improves digestion
- enhances neuromuscular coordination
- heart enlarges (more blood each pump)
- fat deposits are cleared from blood vessel walls,
- lungs become more efficient for gas exchange
What is the sense called which provides the nervous system with information about the position and movement of the body parts?
kinesthetic (musco-skeletal) sense
What does the kinesthetic sense allow animals to do?
move in a purpuseful, well coordinated manner.
What are the receptors of the muscles?
- muscle spindles (two types of stretch-sensitive nerve endings in the muscle)
- golgi tendon organs (stretch-sensitive receptors in nerve endings in the tendons)
What do muscle spindles detect?
muscle length and speed of shortening
spin: long + fast
What do golgi tendon organs do?
convery information to the nervous system about how much force the muscle is developing.
golgi, tendon = force
What happens if the muscle force becomes so large that the tendon is in danger of detatching?
1) the tendon reflex inhibits the muscle associated with the tendon
2) muscle relaxes
State the parts involved in the kinesthetic sense (the complex sense).
- muscle spindles
- golgi tendon organs
- receptors in joint capsules
- tactile nerve fibers from the skin surrounding the joints
What do the receptors in joint capsules and the tactile nerve fibers from the skin surrounding the joints do?
give information abount the angle and movement of the joints to the CNS.
What receptors do not adapt to constant stimulation?
proprioceptors
sensory receptor receiving stimuli from the body: position and movement.
Do receptors send out an impusle once or continuously to the CNS?
continuously
What is a muscle spindle?
an encapsulated group of several slender and specialised skeletal muscle fibers
Why are the muscle spindles called intrafusal muscle fibers?
because their capsule is spindle shaped
What are muscle fibers called that cause the physical shortening of the muscle? Where is the majority located?
extrafusal muscle fibers
- majority is located in a muscle belly
Describe the intrafusal muscle fibers. How do they look like? Length?
- short
- about 4-10mm
- functionally connected to both tendons through the connective tissue of the muscle
What does the polar region of the intrafusal muscle fiber do? What about the equatorial region?
polar region: contracts in response to a motor input to increase tension on the equitorial regions
equitorial region: contains the cell nuclei
What does the muscle spindle organ contain?
two types of intrafusal fibers attached to the caprule on the inside
How are the nuclei arranged in the muscle spindle organ?
either bag-like or chain-like
What does the sensory innervation consist of?
- group Ia fibers
- group II fibers
What do group Ia fibers do?
their endings wrap mainly around the equatorial zone of the bag fibers
What do group II fibers do?
their endings innerviate mainly the chain fibers
What happens when stetch or tension on the equatorial region of the fiber occurs?
group Ia and II fibers will fire action potentials
What happens once group Ia fibers and group II fibers fire action potentials?
the sensory input goes along into the spinal chord:
information is sent out to the cerebellum
What are the two types of gamma motor neurons?
1) gamma 1 (dynamic) endings
2) gamma 2 (static) endings
What are gamma 1 (dynamic) endings?
plate endings, innerviating mainly the polar ends of the bag fibers
What are gamma 2 (static) endings?
trail endings, end mainly on the chain fiber near the polar region
- contraction of the polar region of the muscle spindle,
- stretching,
- putting tentions on the equatorial region
What does stretching of the equatorial region lead to?
sensory Ia and II fibers fire
What happens when the sensory Ia and II fibers fire?
the resulting stimulation of alpha motor neurons in the ventral horn of the spinal chord causes skeletal muscle fibers to contract.
What do changes in muscle activity cause?
changes in the muscle spindle
What are the 5 steps of muscle contraction?
1) stretching of muscle stimulates muscle spindles
2) activation of sensory neuron
3) informatiom processing at motor neuron
4) activation of motor neuron
5) contraction of the muscle
6) shortening of the extrafusal muscle fibers causes the spindle to relax
How does a muscle relax?
the spindle reflex responds to a stretch on the muscle by contracting the extrafusal fibers, restoring the muscle to its original state before the stretch.
What do gamma motor neurons do? Why?
- act to modulate the length and the tention in the muslce spindle
- so that the information reported to the CNS can be controlled
What does the contraction of a muscle lead to?
the relaxing of the spindle so that little or no information goes into th CNS
What do gamma motor neurons do? (at the end)
reset the spindle sensitivity
The stimulation of gamma motor neurons increases what of the spindles?
increases the responsiveness of the spindles
What is the function of type Ia fibers?
report all information to the CNS
- report static information to the CNS
- report dynamic information to the CNS
What is the function of type II fibers?
report only static information
What type of information do type Ia and II fibers report?
Ia: static and dynamic information
II: static information only
What is the golgi tendon organ? How is it arranged? How does it look?
- arranged in series with the extrafusal muscle fibers
- sensory neurons have branched nerve endings intervowen between the collagen fibers of the tendon
- nerve endings are deformed when the muscle contracts and pulls on the tendon
What do the deformed nerve endings (when the muscle contracts and pulls on the tendon) of the GTO cause?
the depolarization of the nerve endings and nerve impulses conducted along the sensory nerve fibers.
What is the GTO extremely sensitive to?
tension of the tendon
Can one elicit a normal GTO response during a clinical examination?
it is very difficult
