Chapter 10 Flashcards
The three types of cells in muscle tissue are
- skeletal
- cardiac
- smooth
What function do all three muscle tissue types share in common?
generating a force called muscle tension
- create movement
- maintain posture
- stabilize joints
- generate heat
- regulate the flow of materials through hollow organs
other functions of muscle tissue
due to their length and appearance muscle cells are known as
fibers
- made up of long muscle cells arranged parallel to one another; some are quite long, extending nearly the entire length of the muscle
- they are multinucleated cells whose contractions arevoluntary (controlled by conscious thought)
skeletal muscle
- muscle cells are found only in the heart
- Each cell is short and highly branched, and has one to two nuclei
- Intercalated discs join adjacent cells; they contain gap junctions and desmosomes (modified tight junctions) that both unite the cells and permit them to coordinate contraction
- Contraction is involuntary, or not controlled by conscious thought
cardiac muscle
- muscle cells are long and flat with “spindle-shaped” pointed ends and a single centrally located nucleus
- muscle cells are found lining most hollow organs in the eye, skin, and some glandular ducts; their contractions are involuntary
smooth muscle cells
What makes smooth muscle cells different from skeletal and cardiac muscle tissues?
consists of nonstriated smooth muscle cells
What are the five properties of muscle cells?
- contractility
- excitability
- conductivity
- extensibility
- elasticity
the ability to contract where proteins in the cell draw closer together; this does not necessarily involve shortening of the cell
contractility
the ability of a cell to respond to a stimulus (chemical, mechanical stretch, or local electrical signals)
excitability
the ability of a cell to conduct electrical changes across the entire plasma membrane
conductivity
the ability of a cell that allows it to be stretched without being ruptured (up to 3 times their resting length without damage)
extensibility
the ability of a cell that allows it to return to its original length after it has been stretched
elasticity
or muscle cells, are described using specialized terminology
myocytes
the myocyte’s cytoplasm
sarcoplasm
the myocyte’s plasma membrane
sarcolemma
is modified endoplasmic reticulum that:
Forms a weblike network surrounding the myofibrils
Varies in structure in the three types of muscle tissue (discussed later)
sarcoplasmic reticulum
- cylindrical organelles found in each of the three muscle cell types
- made up of bundles of specialized proteins that allow for contraction
myofibrils
the most abundant organelle, are made up of mostly contractile proteins
myofibrils
surrounds the myofibrils and stores and releases calcium ions
The sarcoplasmic reticulum (SR)
- are deep inward extensions of sarcolemma that surround each myofibril
- form a tunnel-like network within the musclefiber, continuous with the exterior of the cell, and are therefore filled with extracellular fluid
Transverse tubules (T-tubules)
enlarged sections of SR found flanking each T-tubule
terminal cisternae
Two terminal cisternae and their corresponding T-tubule form
triad
made of hundreds to thousands of myofilaments, including contractile proteins, regulatory proteins, and structural proteins
myofibrils
generate tension
contractile proteins
dictate when a fiber may contract
regulatory proteins
maintain proper alignment and fiber stability
structural proteins
what are the three types of myofilaments?
- thick
- thin
- elastic
composed of bundles of the contractile protein myosin
thick filaments
composed of the proteins actin, tropomyosin, and troponin
thin filaments
composed of a single massive, spring-like structural protein called titin that stabilizes the myofibril structure and resists excessive stretching force
elastic filaments
a contractile protein that has active sites that bind with the myosin heads of thick filaments
actin
a long rope-like regulatory protein that twist around two strands of actin, covering active sites.
tropomyosin
a small globular regulatory protein that holds tropomyosin in place and assists with turning contractions on and off
troponin
- degenerative muscular disease occurring almost exclusively in boys
- Caused by a defective gene for the protein dystrophin, coded on X chromosome
Duchenne Muscular Dystrophy (DMD)
In the absence of normal dystrophin, the sarcolemma breaks down and the muscle fiber is destroyed and replaced with fatty and fibrous connective tissue
Duchenne Muscular Dystrophy (DMD)
Multiple muscle fibers (surrounded by extracellular matrix called the endomysium) form a
fascicle
Each fascicle is surrounded by a layer of connective tissue called the
perimysium
Bundles of fascicles make up a
skeletal muscle
a skeletal muscle is surrounded by
epimysium
The perimysium and epimysium come together at the end of the muscle to form
tendon
binds the muscle to its attaching structure (usually bone)
tendon
Skeletal muscles are enclosed by a layer of thick connective tissue called
fascia
where only thin filaments are found
light bands
where both thin and thick filamentsare found
dark bands
in light, mnemonic) is composed only of thin filaments
I bands
is a dark line in the middle of the A band made up of structural proteins that hold the thick filaments in place and serve as an anchoring point for elastic filaments
M line
contains the zone of overlap, the region where we find thick and thin filaments and where tension is generated during contraction
A bands
In the middle of the A band where only thick filaments exist is
H zone
is found in the middle of the I band and is composed of structural proteins that:
- Anchor the thin filaments in place and to one another
- Serve as attachment points for elastic filaments
- Attach myofibrils to one another across the entire diameter of the muscle fiber
Z disc
explains how tension is generated during muscle contraction
the sliding-filament mechanism
due to an unequal distribution of ions near the plasma membrane resulting in a polarized resting state
membrane potentials
When the barrier separating the ions is removed, they follow their gradients, creating a flow of electrical charges, and the potential energy becomes
kinetic energy
the electrical potential across the sarcolemma of a resting muscle fiber and it measures 85 mV, meaning the cytosol is 85 mV more negative than the extracellular fluid
the resting membrane potential
can then move through the sarcolemma using protein channels and carriers
sodium and potassium ions
how is the concentration gradient maintained?
the Na+/K+ pump
how many sodium ions and potassium ions does the pump move?
3 sodium ions out of the cell and 2 potassium ions into the cell
brief changes in the membrane potential of a cell from a resting negative value to a positive value, then back to its resting negative value
action potentials
open in response to the presence of a chemical
ligand-gated channels
open and close in response to changes in the membrane potential of the plasma membrane
voltage gated channels
begins when voltage-gated Na+ channels open, allowing Na+ to flow inward
depolarization
begins after Na+ channels have closed and voltage-gated K+ channels have opened, allowing K+ to diffuse out of the cell
repolarization
- the synapse where a single motor neuron communicates with many muscle fibers
- function is to transmit a signal, called a nerve impulse (an action potential), from the neuron to the sarcolemma of the muscle fiber
The neuromuscular junction
are chemicals that trigger changes in a target tissue when released, allowing for cell to cell communication
neurotransmitter
the space between axon terminal and muscle fiber, filled with collagen fibers and a gel that anchors the neuron in place
synaptic cleft
specialized region of the muscle fiber plasma membrane whose folded surface has many ligand-gated Na+ channels; ACh is the ligand that opens these gates, allowing Na+ to diffuse into the muscle cell
motor end plate
begins when an action potential signals the release of acetylcholine from the axon terminal into the synaptic cleft
excitation phase
the link between the stimulus and the contraction
excitation-contraction coupling
begins when Ca++ ions bind troponin, which pulls tropomyosin away from actin’s active site; the crossbridge cycle then begins
contraction phase
diffuses across the synaptic cleft where it can bind to ligand-gated channels found in the motor end plate of the muscle fiber sarcolemma
acetylcholine
Ligand-gated channels open when they bind acetylcholine which allows Na+ ions to enter the muscle fiber generating an
end plate potential
Motor neurons continue to fire action potentials as acetylcholine is rapidly degraded by the enzyme
acetylcholinesterase
The end plate potential is generated by the influx of _______ into the motor end plate.
sodium
Acetylcholine is released from the synaptic terminus in response to
An action potential arriving at the synaptic terminus
The term “synaptic cleft” refers to
The gap between the neuron and the muscle fiber
The sodium channels of the motor end plate are
ligand-gated channels
The end plate potential is
a local depolarization
leads to the opening of VOLTAGE-gated Na+ channels in the sarcolemma surrounding the motor end plate, which triggers an action potential
end-plate potential
The channels that open in the sarcolemma surrounding the motor endplate and generate an action potential are
voltage-gated channels
The term “propagate” when referring to an action potential means
spread
In order to trigger a muscle contraction, an action potential must reach the
triads
a triad consist of
Two terminal cisternae and a T-tubule
________ is released from the SR in response to arrival of an action potential
Ca2+
Covers actin active sites
tropomyosin
Troponin has three subunits. Which of the following does NOT bind to one of these subunits?
myosin
Action potential arrives at triad, calcium is released from the terminal cisternae, calcium binds to troponin, tropomyosin exposes the actin active sites
sequence of events that occur in preparation for contraction
begins when actin’s active site is exposed, initiating the crossbridge cycle
contraction phase
occurs when ADP + Pi are released from the myosin head
power stroke
Hydrolysis of ATP is responsible for
Recocking of the myosin heads
The binding of ATP to myosin is responsible for
Release of the myosin heads from the actin active sites
The release of ADP and Pi from myosin occurs during
the power stroke
The myosin heads return to their low-energy (relaxed) state during
the power stroke
Pulls the thin filaments toward the M lines
the power stroke
During muscle fiber relaxation, calcium channels in the SR close because
The resting membrane potential is restored
During muscle fiber relaxation
Calcium is pumped back into the SR
Acetylcholinesterase in the synaptic cleft degrades acetylcholine, allowing
Ligand-gated sodium channels to close
Sarcolemma repolarization during relaxation
Restores the resting membrane potential
Which aspect of muscle relaxation requires ATP?
Pumping calcium ions back into the SR
concentration in the cytosol is 5–6 times higher than ATP; it can immediately regenerate enough ATP for about 10 seconds of maximum muscle activity
creatine phosphate
