Types of Muscle Tissue Flashcards
What are the three types of muscle tissue?
Skeletal
Cardiac
Smooth
Which of the three types of muscles tissue are muscle fibers?
Skeletal and Smooth muscles are elongated which are muscles fibers.
Skeletal muscle (Voluntary muscles)
is packages into skeletal muscles and are organs that are attached to bones and skin and cover the bones
single, very long, multinucleate
Skeletal muscle fibers
the longest of all muscles and have striations (strips)
skeletal muscle(Voluntary muscles)
can be consciously controlled
Skeletal muscles
contract fast, tired easily and powerful or strong
What is the keyword for skeletal muscle?
skeletal, striated, and voluntary
Cardiac muscle tissue
Striated
found only in the heart. makeup bulks of the heart walls.
uni or binucleate
Cardiac muscle tissue(Involuntary)
cannot be controlled consciously.
Cardiac muscle tissue(contractions)
contract at steady rate due to heart’s own pacemaker(SA node).
NV can increases the rate.
What are the keywords for cardiac muscle?
cardiac, striated, and involuntary
Smooth muscle tissues
found in walls of hollow organs
Examples: stomach, urinary bladder, and airways.
Not striated.
single spindle-shaped and uninucleate.
Smooth muscle tissues (Involuntary)
cannot be controlled consciously.
What are the keywords for smooth muscle?
visceral, nonstriated and involuntary
Characteristics of Muscle Tissue
Excitability
Contractility
Extensibility
Elasticity
Excitability
(responsiveness): ability to receive and respond to stimuli
Contractility
ability to shorten forcibly when stimulated
Extensibility
ability to be stretched
Elasticity
ability to recoil to resting length
Four Important Function
Produce movement
Maintain posture and body position
Stabilize joints
Generate heat as they contract
Produce movement (examples)
Responsible for all locomotion and manipulation
Example: walking, digesting, pumping blood
Skeletal Muscle Anatomy
Skeletal muscle is an organ made up of different tissues with three features
What is the three features of skeletal muscle tissue?
Nerve and blood supply, connective tissue sheaths, and attachments
Nerve of skeletal muscle
Each muscle receives a nerve, artery, and vein.
Consciously controlled skeletal muscle has nerves supplying every fiber to control activity
Blood Supply of skeletal muscle
Contracting muscle fibers require huge amounts of oxygen and nutrients.
Also, need waste products removed quickly(Metabolic wastes)
Connective Tissue Sheaths
Muscles fibers and skeletal muscles are covered in connective tissue.
The function of the Connective tissues in the skeletal muscle?
Support cells and reinforce whole muscle which prevents the bulging muscles from nursing during exceptionally strong connections.
Sheaths from external to internal
Epimysium
Perimysium
Endomysium
Epimysium
dense irregular connective tissue surrounding entire muscle; may blend with fascia
Perimysium
fibrous connective tissue surrounding fascicles (groups of muscle fibers).
Endomysium
fine areolar connective tissue surrounding each muscle fiber
Attachments
Muscles span joints and attach to bones
What are the two-place muscles attach to bones
Insertion and origin
Insertion
attachment to the movable bone
Origin
attachment to the immovable or less movable bone
Attachments can be direct or indirect
Direct (fleshy): epimysium fused to the periosteum of bone or perichondrium of cartilage
Indirect: connective tissue wrappings extend beyond muscle as ropelike tendon or sheetlike aponeurosis. (more common)
Muscle Fiber Microanatomy
Skeletal muscle fibers are long, cylindrical cells that contain multiple nuclei
Sarcoplasm
muscle fiber cytoplasm
Contains many glycosomes for glycogen storage, as well as myoglobin for O2 storage
Modified organelles
Myofibrils
Sarcoplasmic reticulum
T tubules
Myofibrils
Densely packed, rodlike elements.
Single muscle fiber can contain 1000s.
Accounts for ~80% of muscle cell volume
Myofibril features
Striations
Sarcomeres
Myofilaments
Molecular composition of myofilaments
Striations(Myofibril features)
stripes formed from repeating series of dark and light bands along length of each myofibril
A bands
dark regions
H zone
lighter region in middle of dark A band
M line
line of protein (myomesin) that bisects H zone vertically
I bands
lighter regions
Z disc (line)
coin-shaped sheet of proteins on midline of light I band
Sarcomere
Smallest contractile unit (functional unit) of muscle fiber
Contains A band with half of an I band at each end
What does sarcomere consist of?
Consists area between Z discs
Individual Sarcomere
Individual sarcomeres align end to end along myofibril, like boxcars of train.
Myofilaments
Orderly arrangement of actin and myosin myofilaments within sarcomere.
Actin myofilaments
thin filaments.
Extend across I band and partway in A band.
Anchored to Z discs
Myosin myofilaments
thick filaments.
Extend length of A band.
Connected at M line.
Sarcomere cross
section shows hexagonal arrangement of one thick filament surrounded by six thin filaments
Molecular composition of myofilaments
Thick filaments
Thick filaments(Myosin myofilaments) are composed of?
composed of protein myosin that contains two heavy and four light polypeptide chains
Heavy chains of thick filaments.
intertwine to form myosin tail
Light chains of thick filaments?
form myosin globular head
What happens during contraction of the thick filaments?
During contraction, heads link thick and thin filaments together, forming cross-bridges.
Myosins are offset from each other, resulting in staggered array of heads at different points along thick filament
Thin filaments(Actin myofilaments)
composed of fibrous protein actin
Actin is
polypeptide made up of kidney-shaped G actin (globular) subunits
G actin
subunits bears active sites for myosin head attachment during contraction.
subunits link together to form long, fibrous F actin (filamentous)
F actin
Two strands twist together to form a thin filament
Tropomyosin and Troponin
regulatory proteins bound to actin.
Other proteins
help form the structure of the myofibril
Elastic filament
composed of protein titin
Holds thick filaments in place; helps recoil after stretch; resists excessive stretching
Dystrophin
Links thin filaments to proteins of sarcolemma
Nebulin, myomesin, and C proteins
proteins bind filaments or sarcomeres together.
Maintain alignment of sarcomere
Duchenne muscular dystrophy (DMD)
is most common and serious form of muscular dystrophies, muscle-destroying diseases that generally appear during childhood
How does someone get (DMD)
Inherited as a sex-linked recessive disease, so almost exclusively in males (1 in 3600 births).
At what age does DMD appears?
between 2 and 7 years old when boy becomes clumsy and falls frequently .
Disease progresses(DMD)
from extremities upward, finally affecting head, chest muscles, and cardiac muscle.
Treatment of DMD
With supportive care, people with DMD can live into 30s and beyond.
chest muscles, and cardiac muscle
Causes of DMV
defective gene for dystrophin, a protein that links thin filaments to extracellular matrix and helps stabilize sarcolemma
Sarcolemma of DMD patients tear easily, allowing entry of excess calcium which damages contractile fibers
defined Sarcoplasmic Reticulum
network of smooth endoplasmic reticulum tubules surrounding each myofibril.
Most run longitudinally
Sarcoplasmic Reticulum
Terminal cisterns form perpendicular cross channels at the A–I band junction
Sarcoplasmic Reticulum function
regulation of intracellular Ca2+ levels
Stores and releases Ca2+
T tubules
formed by protrusion of sarcolemma deep into cell interior
T tubules increase
muscle fiber’s surface area greatly
T tubules(Lumen)
continuous with extracellular space
What does T tubules allow?
electrical nerve transmissions to reach deep into interior of each muscle fiber
Tubules penetrate cell’s
interior at each A–I band junction between terminal cisterns
Triad
area formed from terminal cistern of one sarcomere, T tubule, and terminal cistern of neighboring sarcomere
Triad(Relationship)
T tubule contains integral membrane proteins that protrude into intermembrane space (space between tubule and muscle fiber sarcolemma)
Tubule proteins act as voltage sensors that change shape in response to an electrical current
Triad(Relationship) SR
cistern membranes also have integral membrane proteins that protrude into intermembrane space.
SR integral proteins control opening of calcium channels in SR cisterns
Triad(Relationship) electrical
When an electrical impulse passes by, T tubule proteins change shape, causing SR proteins to change shape, causing release of calcium into cytoplasm
Sliding Filament Model of Contraction
the activation of cross bridges to generate force
Shortening of Sliding Filament Mode
occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening
when does contraction ends?
ends when cross bridges become inactive(relax).
Relaxed state of Sliding Filament Mode
thin and thick filaments overlap only slightly at ends of A band
Sliding filament model of contraction
states that during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more.
Neither thick nor thin filaments change length, just overlap more
When nervous system stimulates muscle fiber
, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) process to begin
Cross bridge attachments
attachments form and break several times, each time pulling thin filaments a little closer toward center of sarcome in a ratcheting action.
Causes shortening of muscle fiber
Z discs (Sliding filament model of contraction )
are pulled toward M line
I bands (Sliding filament model of contraction)
shorten
Z discs (Sliding filament model of contraction)
become closer
H zones (Sliding filament model of contraction)
disappear
A bands (Sliding filament model of contraction)
move closer to each other.
Muscle Fiber Contraction
Decision to move is activated by brain, signal is transmitted down spinal cord to motor neurons which then activate muscle fibers
Neurons and muscle cells
excitable cells capable of action potentials.
Excitable cells are capable of changing resting membrane potential voltages.
AP crosses
from neuron to muscle cell via the neurotransmitter acetylcholine (ACh)
Ion Channels
Play the major role in changing of membrane potentials
What are the two classes of ion channels?
Chemically gated ion channels and Voltage-gated ion channels
Chemically gated ion channels and example
opened by chemical messengers such as neurotransmitters
Example: ACh receptors on muscle cells
Voltage-gated ion channels
open or close in response to voltage changes in membrane potential.
Anatomy of Motor Neurons
Skeletal muscles are stimulated by somatic motor neurons
Axons
(long, threadlike extensions of motor neurons) travel from central nervous system to skeletal muscle.
Each axon divides into many branches as it enters muscle
neuromuscular junction or motor end plate
Axon branches end on muscle fiber, forming.
Each muscle fiber has one neuromuscular junction with one motor neuron.
Axon terminal (end of axon)
Muscle fiber are separated by gel-filled space called synaptic cleft
synaptic vesicles
Stored within axon terminals are membrane-bound.
acetylcholine (ACh)
Synaptic vesicles contain neurotransmitter
Junctional folds
Infoldings of sarcolemma
contain millions of ACh receptors
NMJ
NMJ consists of axon terminals, synaptic cleft, and junctional folds
Four steps must occur for skeletal muscle to contract:
Events at neuromuscular junction
Muscle fiber excitation
Excitation-contraction coupling
Cross bridge cycling
First events at the Neuromuscular Junction
AP arrives at axon terminal
Seconds events at the Neuromuscular Junction
Voltage-gated calcium channels open, calcium enters motor neuron
Third events at the Neuromuscular Junction
Calcium entry causes release of ACh neurotransmitter into synpatic cleft
Fourth events at the Neuromuscular Junction
ACh diffuses across to ACh receptors (Na+ chemical gates) on sarcolemma
Fifths events at the Neuromuscular Junction
ACh binding to receptors, opens gates, allowing Na+ to enter resulting in end plate potential
Six events at the Neuromuscular Junction
Acetylcholinesterase degrades ACh.
Many toxins, drugs, and diseases
interfere with events at the neuromuscular junction.
Myasthenia gravis
disease characterized by drooping upper eyelids, difficulty swallowing and talking, and generalized muscle weakness
Myasthenia gravis involves shortage
Ach receptors because person’s ACh receptors are attacked by own antibodies
Suggests this
an autoimmune disease
Resting sarcolemma
is polarized, meaning a voltage exists across membrane.
Inside of cell is negative compared to outside.
Action potential
is caused by changes in electrical charges
Occurs in three steps
Generation of end plate potential
Depolarization
Repolarization
End plate potential
ACh released from motor neuron binds to ACh receptors on sarcolemma
End plate potential Causes
Causes chemically gated ion channels (ligands) on sarcolemma to open
Na+ diffuses into muscle fiber
End plate potential diffuses.
Some K+ diffuses outward, but not much
Because Na+ diffuses in, interior of sarcolemma becomes less negative (more positive)
Depolarization
Generation and propagation of an action potential (AP).
Excitation-contraction (E-C) coupling
events that transmit AP along sarcolemma (excitation) are coupled to sliding of myofilaments (contraction).
AP
is propagated along sarcolemma and down into T tubules, where voltage-sensitive proteins in tubules stimulate Ca2+ release from SR
AP
Ca2+ release leads to contraction
AP is brief
AP is brief and ends before contraction is seen
