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