muscular tissue Flashcards
Exhibit the greatest degree of contractility among cells in the body
Myocytes
- muscle cells or muscle fibers
- They are highly organized and work together in groups.
- These groups are held together by special substances to form muscle tissue (like the muscles in your arms, legs, and heart).
[Building blocks of muscle and responsible for movements]
Parts of myocyte
Sarcolemma – cell membrane
Sarcoplasm – cytoplasm
Sarcoplasmic reticulum – smooth ER
Sarcosomes – mitochondria
Types of muscle tissue
Ppt
Bundles of fibers
fascicles
What are the 3 parts of the skeletal muscle
Epimysium
- outermost layer, encloses whole bundle of fascicles of the muscle tissue
- dense irregular connective tissue
Perimysium
- middle layer,surrounds bundles of muscle fibers
- thin CT layers
Endomysium
- inert layer, enclose the muscle fiber
- reticular fibers with scattered fibroblast
A muscle is attached at either end by what tissue called tendon to a part of the skeletal system
Tendon
Tissue - dense regular CT
*attachment is referred to as: origin and insertion
Can move: body wall and muscles of the limbs
Cannot move: pharynx and upper part of the esophagus
How many myofibrils per muscle fiber
Roughly 5000 to 10 000
I bands vs A bands in myofibrils
Isotopic bands:
Light bands
Do not polarized light
Anisotropic bands:
Dark bands
Display birefringence in polarized light
Size of skeletal muscle cells and no. of nuclei
Length:
<10 to 35cm
Diameter:
10 to 100 um
No. of nuclei:
Oval shaped, longitudinal, hundreds and periphery located (near the outer surface)
Skeletal muscle cells origin
Fusion of myoblast (muscle cell precursor) during embryonic development
But some does not fuse and become myosatellite cells which act as a stem cells for muscle repair
*satellite cells can be found btwn sarcolemma and basal lamination of muscle cells
Overlapping structure between tendon and epimysium
Tendon region
Consist of repetitive small contractile units
Sarcomere
- basic unit of muscle contraction
- made up of bands and lines
A band (anisotropic band )
- M- line, mittelscheibe line
- H-zone, heller band
I band (isotropic band)
- Z-disc, zwischenscheibe
4 main proteins that made up the filaments
ATTM
Thick filament:
Myosin (274 myosin molecules)
+ 6 polypeptide chains (2 heavy and 4 light chain)
*myosin heads - act as tiny hands that grab and pull thin filament to create movement
Thin filament:
F-Actin (small building blocks)
- long chain of G-actin
Tropomyosin
- TnT (tropomysoin)
- TnC (Ca)
- TnI (inhibits myosin-actin interaction)
Troponin
*most abundant, 60% of total muscle protein:
actin and myosin
How muscle contractions happens
Ca will enter the muscle cells
TnC will bind with the Ca = tropomyosin to move and expose the myosin-binding site on actin
Myosin head attach to the actin
= pull the actin filament
= muscle contract
Needed before sliding filament theory proceeds
Nerve supply
What are the muscle fibers called where each branch of motor neutrons forms a junction with a muscle fibers
Neuromuscular junction or
Synapse
What are the 3 regions of the neuromuscular junction (synapse)
Presynaptic terminal:
End os the nerve cell that stores acetylcholine in vesicles
Synaptic cleft:
Space between presynaptic terminal & muscle fiber membrane
Postsynaptic Membrane:
Muscle fiber membrane that receives the signal
A somatic motor neuron l together with the muscle fibers it supplies
Motor unit
[motor unit is simply a nerve cell (motor neuron) and all the muscle fibers it controls. In other words, when the neuron sends a signal, it makes all its connected muscle fibers contract together.
What happens upon detection of nerve impulse
The acethylcholine in the vesicles will be released in the synaptic cleft via expcytosis
Then it will bind to the sarcolemma in the post synaptic membrane
After binding it, it will trigger
action potential in the muscle fiber
= start contraction
Briefly explain the sliding filament model
- Muscle contractions begins
A nerve impulse travel is in to the muscle via Txtubules - Calcium release
Impulse signals the sarcoplasmic reticulum to release Ca
E. Role
Bind to Troponin C which causes tropomyosin to move = exposes the myosin-binding site on actin Myosin head
- Sliding filament action
Myosin head attach to the exposed sites on actin
It then pulls the actin filament
= think and thin filament to slide past each other
When a muscle contracts, why does the sarcomere shorten
As the interaction of the actin and myosin molecules causes the thick and thin filaments to slide past each other
Cylindrical cells that are much shorter than skeletal muscle cells
Cardiac muscle cells
Fully contracted and fully relaxed
Fully contracted:
I band - smaller in diameter, thin filaments moved closer to the center so that the H zone disappear as the thick and think filaments overlap during contraction
Full relaxed:
All of it
Represent the interface between adjacent muscle cells
Intercalated discs (in cardia muscle)
- counterpart of Z disc
Modified cardiac muscle cells that are specialized to initiate and conduct electrical impulse
Purkinje fibers
- receive electrical impulse of the heart
- special heart muscle cells.
[This electrical impulse makes sure the heart beats in a coordinated way, so blood is pumped efficiently.]
True or false:
Myofilaments in the smooth muscles form sacromeres
False - do not
Why is the thick filaments in the smooth muscle cells are scattered all over the sarcoplasm
As there is lack of striations
Where does the thin filament in the smooth muscle cells are attached to
Dense bodies that contain proteins like a-actin
Involuntary contraction in the smooth muscle cells
Controlled by the body through autonomic nerves and neuromuscular junctions
- when it contracts, the whole cell folds rather than shortening in a straight line
Where are smooth muscle cells located
Organs
Especially in digestive tract, where smooth muscle helps move food along.
3 types of skeletal muscle fibers
Red muscle fibers (slow twitch)
- postural muscle
White muscle fibers (fast twitch)
- running muscle
Intermediate muscle fibers
What are the 2 groups of sensory receptors
Receptors
Proprioceptors
- include!simple nerve endings, neuromusclar spindles and golgi tendon organs
Referred to as striated because in routine LM preparations, they exhibit prominent alternating light and dark cross striations
Skeletal and cardiac muscle fibers
Tiny fibers inside the muscle cells that helps with contraction
Myofibrils
It has been shown by a high resolution microscopy to consist of a collection of thread-like structures
Sarcomere
- thread-like structures: filaments (myofilaments)
*around 1000 to 2000 araranges parallel to long axis
The junction of the A and I bands, whose lumens are continuous with the extracellular space are called
Transverse tubules (T-tubules)
A T-tubule and the pair of terminal cisternae associated with it are collectively referred to as
Triad
Embedded in the endomysium and perimysium
Neuromuscular spindles
- detected the degree and velocity of stretch applied to a muscle
It is a modified cardiac muscle cells. They are not contractile cells that are specialized to compromise the impulse conducting system of the heart which generated and probates the electrical impulse that initiates cardiac contraction
Purkinje fibers
Sensory neurons vs motor neurons
Sensory - carry info from body to spinal cord and brain
Motor - from brain and spinal cord to muscle
Ratio of thin to thick filaments in skeletal and smooth muscle cells
Skeletal 6:1
Smooth 15:1
Which muscle cells are incapable of cell division
Smooth muscle cells
- skeletal muscle cells is capable of some degree of regenrperation
At what age does the skeletal muscle cells progressively decrease in size and number
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