-
Axon terminal
when the end of and axon swells to form and axon terminal or synaptic bulb
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synaptic vesicles
- contain neurotransmitters, that trigger changes in the target cells of the neuron
- acetylcholine
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Synaptic Cleft
the narrow space between the axon terminal and the muscle fiber into which ACh is released
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Motor end Plate
is specialized region of the sarcolemma, who folded surface contains many receptors for ACh
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3 phases of the muscle contraction process
excitation phase, excitation-contraction coupling, contraction phase
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excitation phase
When the neuron excites the muscle
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stages of contraction from the intramuscular junction
- 1 an action potential arrives at the axon terminal
- 2 Synaptic vesicles release acetylcholine into the synaptic cleft
- 3 Acetylcholine binds to ligand-gated ion channels in the motor end plate
- 4 Ion channels open and sodium ions enter the muscle fiber
- 5 Entry of sodium ions depolarizes the sarcolemma locally, producing an end-plate potential
-
end-plate potential
This potential is simply a local depolarization in the area of the motor end plate
-
acetylcholinesterase
As soon as ACh is released from the synaptic vesicles, it is degraded and inactivated almost immediately by and enzyme in the synaptic cleft. For this reason the neuron must continue to fire action potentials and release new ACh in order to stimulate repeated end-plate potentials in the muscle fiber
-
botox
Block ACh from binding at the motor end plate
-
excitation-contraction coupling
In this phase, the end- plate potential leads to an action potential in the sarcolemma, which in turn triggers events that result in contraction
-
steps of excitation-contraction coupling
- 1 the end-plate potential stimulates an action potential
- 2 The action potential is propagated down the T-tubules
-
muscular system
The skeletal muscles
-
skeletal muscle
- striated
- long
- multinucleated
-
cardiac muscle
- Striated
- branched
- one or two nuclei
- have intercalated discs
- involuntary
-
smooth
- Nonstriated
- spindle shaped
- involuntary
-
Extensibility
Most cells rupture when stretched but muscle cells can stretch up to 3 times their original length
-
elasticity
Muscle cells can return to their original shape
-
Sarcoplasm
contains cytosol and all of the organelles in the muscle cell
-
composed of a phospholipid bilayer with multiple specialized integral and peripheral proteins
Sarcolemma
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inside of the sarcoplasm are small cylindrical organelles called _______ that help the muscle contract
myofibrils
-
how big is a myofibril
1/100 of a human hair
-
forms a web-like network around each myofibril
sarcoplasmic reticulum
-
Most abundant organelle in the sarcoplasm
myofibril
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a muscle fiber is surrounded by the
equivalent to the plasma membrane on a cell
Sarcolemma
-
The Sarcolemma creates inward extensions into the muscle called
T tubules
-
Two enlarged portions of the SR on either side of the T tubules is known as
Terminal Cisternae
-
terminal cisternae and the T tubule together are known as
Triad
-
Surrounds each muscle fiber
Endomysium
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a myofribril is composed of hundreds to thousands of protein bundles called ______
myofilaments
-
3 types of proteins and their function
- contractile- tension
- Regulatory- when contraction takes place
- Structural- hold myofilaments in their proper position (z discs)
-
tropomyosin and tropinin are known as _____ proteins
Regulatory
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actin is known as a __________ protein
Contractile
-
a structural protein that includes resisting excessive stretching and providing elasticity to the muscle fiber
titin
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multiple skeletal muscle fibers together with the surrounding endomysium form a ____
Fascicle
-
Each fascicle is surrounded by the
Perimysium
-
bundles of fascicles together make up a
Skeletal Muscle
-
the skeletal muscle is surrounded by the
epimysium
-
which band contains only thin filament
I band
-
Which band contains only thick filament and some of the thin filament from overlap
A band
-
middle zone is called
M line or H zone
-
what band are the z disc located in
The I band
-
The functional unit of contraction where muscle tension is produced
z disc to z disc
Sarcomere
-
the branch of physiology that studies electrical changes across plasma membranes
electrophysiology
-
Because the flow of ions across a gradient goes from potential to kinetic energy, we call the electrical gradient an
electrical potential
-
a difference in electrical ptential between two pints is called a
voltage
-
how much is a millivolt
1/1000 of a volt
-
the electrical potential across a plasma membrane
membrane potential
-
the electrical potential across the sarcolemma in a muscle fiber at rest is called the
Resting membrane potential
-
Why is the membrane considered to be polarized
Because of the charge on either side of the membrane
-
the most important active transport pump for Na and K is
Na/K ATPase pump
-
millions of these Na/K pumps work together to maintain concentration gradients that keep a resting potential, were do we find higher and lower concentration gradients
- low potassium and high sodium in the ECF
- High potassium and low sodium in the cytosol
-
a quick temporary change in the membrane potential in a single region of the plasma membrane
Action potential
-
what are the two types of gated channels
Ligand gated and voltage gated
-
open in response to the presence of certain chemicals called ligands
ligand gated channel
-
open and close in response to changes in the membrane potential across the plasma membrane
voltage gated channels
-
When Na flows in, the membrane potential becomes _______
- less negative
- (depolarization
-
when K leaves the cell the membrane potential becomes
- More negative again
- repolarization
-
returning the sarcolemma to restion potential of -85 mv will caus_______________
potassium ion channels to close
-
action potentials do not stay in one place; rather, they are conducted, or ________
Propogated
-
remember that that the t tubules are attached to the sarcolemma so that when the action potential affects the sarcolemma it also travels down the
T- tubules
-
a myosin head bound to an actin molecule is known as a
crossbridge
-
what cocks the myosin head
ATP Hydrolysis
-
for the average contraction, how many times will the myosin head preform the powerstroke
20-40
-
What are the two components of muscle relaxation
- ACh release stops and the remaining ACh in the synaptic cleft is broken down
- the calcium ion concentration in the cytosol returns to its resting level
-
a muscle that is unable to relax is said to be in a
Spasm
-
What are the three processes that regenerate ATP
- reactions in the cytosol that immediately add a phosphate group to ADP
- glycolytic catabolism
- oxidative catabolism
-
reaction in the cytosol that immediately add a phosphate group to ADP is known as
Creatine Phosphate reaction
-
What are the two potential sources of glucose for glycolysis
glucose that enters the fiber from the bloodstream and a storage form of glucose called glycogen
-
If oxygen is abundant ______ will enter the mitochondria for oxidative catabolism
pyruvate
-
If oxygen is not abundant, the pyruvate is converted into ____ molecules of the compound ______
two, lactic acid
-
about 20% of lactic acid is diffused into the bloodstream and converted to _____ in the liver
glucose
-
what pyruvate does not enter the bloodstream goes in to the mitochondria for
Oxidative or aerobic catablolism
-
similar to hemoglobin
the oxygen carrying protein in cytosol
myoglobin
-
the response of a muscle fiber to a single action potential in a motor neuron
-
latent period
The time it takes for an action potential to spread through the sarcolemma
-
an interval of about 5 ms during which the muscle cannot respond to another stimulus
Refractory period
-
have refractory periods as long as their contraction
Smooth and cardiac muscle
-
When repeated stimulation of a muscle fiber by a motor neuron results in twitches with progressively greater tension this is known as
Wave summation
-
when the muscle fiber can only partially relax between contraction
unfused tetanus
-
when the tension remains constant at a maximal level
fused Tetanus
-
the optimal tension level depends on the __________________
Length of the sarcomere prior to contraction
-
the _________ of the sarcomere is the length of the muscle fiber at which the most cross-bridges can form
optimal length
-
Muscle fibers with high myosin ATPase activity are called
Fast Twitch Fibers
-
Muscle fibers with low myosin ATPase activity are called
Slow twitch fibers
-
two main classes of skeletal fibers
Type I and Type II
-
-
a single motor neuron along with the muscle fibers it innervates
Motor Unit
-
as greater force is needed, more motor units are activated. This is known as a phenomenon called
Recruitment
-
During recruitment ______ units are recruited first followed by _______ motor units if more force is needed
slow, fast
-
the involuntary activation of motor units that creates a small degree of tension is known as
Muscle Tone
-
muscle tone serves important functions such as
Maintaining erect posture, stabilizing joints, generating heat and ensuring that the muscle is ready to respond if movement is initiated
-
if the tone in a skeletal muscle is abnormally low, this is generally known as a condition called
Hypotonia
-
a muscle with abnormally high tone is called
occurs during shivering
hypertonia
-
another way of saying that a muscle wil alter its structure to follow its function
principle of myoplasticity
-
These cells help repair injured skeletal muscle
Satellite cells
-
in response to physical inactivity, the diameter of the mucles fiber decreases due to loss of myofibrils
atrophy
-
During exercise, heat in the mody is generated and the body must dissipate this heat and return to pre-exercise temperature levels to maintain temperature homeostasis
Heat Dissipation
-
Propels materials through hollow organsof the digestive, urinary, and reproductive systems
Peristalsis
-
In smooth muscle cells, the actin filament are arranged obliquely in the sarcoplasm and are anchored to proteins called
Dense bodies
-
in smooth muscle cells there are more ______ filaments than _______fiaments
Thin, thick
-
in smooth muscle cells, thin filaments lack
troponin
-
3 ways smooth muscle is different than skeletal muscle (Structurally)
- Lacks motor end plates
- Teh sarcoplasmic reticulum is much less extensive
- T-tubules are absent
-
Some smooth muscle cells are able to depolarize and contract spontaneously, these cells are known as
Pacemaker cells
-
in smooth muscle, calcium ions bind to a protein called
Calmodulin
-
smooth muscle can contract up to _____ of its length while skeletal muscle can contract up to _______
-
during the _______ the muscle cell maintains tension while consuming very little ATP
Found in Sphincter that must remain close
latch state
-
_______ allows the heart to contract as a unit by attaching it physically and electrically
intercalated discs
-
cardiac muscle is run by a small population of ______ for contraction
Pacemaker cells
-
what is the resting potential of a muscle fiber
-85 mV
-
is caused by depletion of key metabolites, inadequacy of oxygen delivery to muscle fibers, accumulation of certain metabolites, and environmental conditions
Muscle fatigue
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