L12. Muscles Part 2 Flashcards
Other names for a muscle cell is
Muscle fiber
Myofiber
What is the sacrolemma?
It is the plasma membrane of the muscle cell
What is the sarcoplasm?
Cytoplasm of the muscle cell ( myofiber/muscle fiber)
What is the sarcoplasmic reticulum
Smooth ER found in striated and smooth muscle fibers
Describe the skeletal muscle
- voluntary
- controlled by motor neurons
What is a motor unit
motor unit= motor neuron + the motor end plate+ all muscle fibers that motor neuron innervates
Can a motor neuron innervate more than one muscle fiber (cell)
Yes
What is the motor end plate?
- highly excitable
- specialized domain on the sarcolemma
- responsible for initiating the action potential across the myofibre causing muscle contraction
What is the neuromuscular junction?
junction between the axon terminal of he motor neuron and the motor end plate
Where are the acetocholyene receptors found?
on the sarcolemma
Memorize picture on L12 .4b
L12 .4b
Describe the excitation-contraction process
- neurotransmitter vesicles fuse with the pres-synaptic membrane
- acetocholine binds with the receptors on the sarcolemma
- action potential is generated down the sarcolemma into the T-tubules ( 2 SR cristae wedge the t-tubules)
- causes the release of Ca2+ from the SR
- the Ca2+ in the sacroplasm binds to troponin, shifts the tropomysoin to release myosin binding sites in the actin
- myosin binds to these sites, myosin pulls the actin filaments towards the center of the sacromere (ATP hydrolysis allows this process)
- end of the A.P the Ca2+ is returned to the SR via active transport
- troponin without Ca2+ shifts back to block the sites
What does botox do?
inhibits acetylcholine release by axon terminals
What clinical disease does botox cause?
botulism: causes muscle paralysis and respiratory failure
What is the Duschenne Becker Muscular Dystrophies
- mutation of the dystrophin gene on the X-chromosome
- muscle wasting
- mental retardation
What are the symptoms for Duschenne Becker
- limited fine movement
- breathing difficulties ( diaphragm muscle weak)
- scoliosis ( curve spine)
- thick low leg muscle
- muscle weakness affects the feet, hips, belly, shoulders and elbows.
What is the role of dystrophin
no dystrophin, no link between actin , sarcolemma and BM
What happens in DMD ( duchene muscular dystrophy)
the link between actin cytoskeleton and the basal filament is lost ( as no dystrophin links actin to sarcolemma which has dystroglycan complex linked to BM)
What is the protein missing in DMD?( duchene muscular dystrophy))
dystrophin
Why is there an enlarged calf muscle in duchene muscular dystrophy
macrophages and fats accumulate without the dystrophin. there is an increase in C.T and adipose tissues
(histology): what is different between DMD and normal cells
- disorganized sacromeres
- no dystrophin
- present of CT and adipocytes around muscle cells
What joins the cardiac muscle fibers?
intercalated disks
Features of the cardiac muscle
- found in heart
- forms thick layer (myocardium)
- intrinsic rhythmicity
- involuntary muscle (spontaneous contraction)
- short and branched striated fibers ( cardiac fibers/ cardiomyocytes)
- one nucleus / fiber
What is a cardiomyocyte?
short branched striated fibers (AKA cardiac fibers)
What are intercalated disks
- junctions between 2 cardiomyocytes ( cardiac fibers)
- steplike pattern
How many types of intercalated disks are there, what are they?
2 types
LAT: runs parallel to myofilaments
TR: transverse part, runs right angle to myofibers
what does the transverse part of the intercalated disk contain
- Zonular adherens: adhere actin myofilaments of the terminal sacromeres to the plasma membrane
- Desmosomes: binds fibers together to prevent their separation during contraction
what does the lateral part of the intercalated disk contain
Gap junctions : flow of info between fibers
What is in a diade of a cardiac fiber?
1 t-tubule with a junction towards 1 terminal SR cisternae
Characteristics of smooth muscle
- communicate solely by gap junctions
- no t-tubules
- involuntary
- non-striated fibers, spindle-shape, tapered
- found in GI tract, respiratory tract, blood vessels
- one nucleus per fiber
What is the role of smooth muscles in blood vessles?
control constriction and dilation
what is the tunica media made up of
smooth muscles + elastic tissues
Compare the tunica media in arteries and veins
arteries have a thicker tunica media
What muscles are involved in peristalsis
Longitudinal and circular ( both smooth)
what are circular muscles
muscle fibers that run around the circumference of the organ
What are longitudinal muscles
muscle fibers that run parallel to the long axis of the organ
What is peristalsis
Rhythmic contractions of the smooth muscles that propel food through the digestive tract
Name the 3 layers of muscles in the smooth muscle of the stomach ( pg 13 b)
longitudinal ,circular and oblique
What are the contractile units of a smooth muscle
myosin and actin filaments taht connect to the dense plaque on the sarcolemma and dense bodies in sacroplasm
Thin filaments in the smooth muscle are:
- obliquely arranged
- attached to dense plaques in sarcolemma
- attached to dense bodies in sarcoplasm
