Quiz #1: Muscle (4) Flashcards
What are the three muscle tissue types?
- smooth muscle
- cardiac muscle
- skeletal muscle
What are the functions of skeletal muscles?
- maintains posture
- produces movement
- stabilizes joints
- protection and control of internal tissue structures/organs
- generates heat
What is the process within a muscle fiber of a muscle contraction?
- Z-discs attached to thin filament get pulled towards the M line
- whole sarcomere gets shorter
- A band does not change
- H zone/H band and I band shorten
What are Z-discs (Z-line)?
anchors the actin-rich thin filaments
What is the M line?
anchor point for myosin filaments during muscle contraction
What is the A-band?
region within a sarcomere of a muscle cell that contains thick myosin filaments and parts of thin actin filaments
What is the I band?
light band in skeletal muscle cells that contains thin actin filaments
What is the H zone?
a paler, less dense region of myosin filaments in the center of the A band of a sarcomere in striated muscle
What are the contraction steps for the sliding filament model?
- calcium release
- cross-bridge formation
- power stroke
- contraction stop
What are the five factors affecting force of contraction?
- size of muscle fiber
- number of active muscle fibers
- frequency of stimulation
- length of sarcomere
- velocity of muscle shortening
What is the force-frequency relationship between muscle force and electrical stimulus?
INCREASED muscle force increases the FREQUENCY of the electrical stimulus
same level of electrical stimulus just increases frequency
What is the length-tension relationship of the sarcomere?
- Ascending: as muscle is STRETCHED from short to long, force it will generate increases
- Plateau: force peaks
- Descending: as force decreases muscle is stretched FURTHER
If velocity of muscle shortening __________ (increases/decreases), the force will __________ (increase/decrease).
increases/decreases
OR
decreases/increase
What is isotonic contraction?
Same TENSION but changing LENGTH
Ex. holding weight and lifting it with arm from 90 degree –> 45 degree
What is isometric contraction?
Same LENGTH but changing TENSION
Ex. holding weight at 90 degree and NOT MOVING but just flexing muscle
True or false:
The force of muscle contraction is inversely proportional to the frequency of stimulation, but proportional to the velocity of muscle shortening.
FALSE
The force of muscle contraction is PROPORTIONAL to the frequency of stimulation, but INVERSELY PROPORTIONAL to the velocity of muscle shortening.
What is the energy sources for muscle contraction?
ATP
What are the skeletal muscle fiber types?
- Slow oxidative fiber
- Fast oxidative fiber
- Fast glycolytic fiber
Describe slow oxidative fiber.
- Type I
- Slow switch
- Small diameter
- Low contractile force
- Red
- Slow myosin ATPase activity
- Moderate Ca2+ pumping capacity
- High oxidative capacity
- Aerobic metabolism
- Low fatigue
- Ex. 1000 m running
Describe fast oxidative fibers.
- Type IIA
- Fast switch
- Large diameter
- High contractile force
- Red
- Fast myosin ATPase activity
- High Ca2+ pumping capacity
- Moderate oxidative capacity
- Mixed metabolism
- Moderate fatigue
- Ex. 400 m running
Describe fast glycolytic fiber.
- Type IIB
- Fast switch
- Large diameter
- Highest contractile force
- Red
- Fast myosin ATPase activity
- High Ca2+ pumping capacity
- Low oxidative capacity
- Anaerobic metabolism
- Fast fatigue
- Ex. 100 m running
What is the neuromuscular junction?
Where a motor nerve connects with a muscle
What are the three main parts of a neuromuscular joint?
- presynaptic membrane (axon terminal)
- postsynaptic membrane (membrane of skeletal muscle fiber aka motor end-plate)
- synaptic cleft (gap between the two)
The upper motor neuron is part of the __________ and activates a lower ______ neuron, which is located in the ____________
- cerebral cortex
- motor neuron
- anterior horn of the spinal cord
When the action potential reaches the axon terminal, it stimulates which channels and what does it do?
voltage-gated calcium channels in membrane
open
Ca2+ ions flow into lower motor neuronW
What does the extracellular calcium ions do once they enter the axon terminals?
Fuse to the cell membrane of the axon terminal
releases acetylcholine (synaptic vesicle contents) into the synaptic cleft
What happens after the acetylcholine is released into the synaptic cleft?
Diffuse quickly (short distance) to the motor end plate on the muscle fiber
What happens when the acetylcholine reaches the motor end plate on the muscle fiber?
TWO ACh molecules will bind to ONE ligand-gated ion channel: NICOTINIC RECEPTOR
binding causes them to open
Nicotinic receptors are selective for what type of ions?
Positively charged ions
What happens when the nicotinic receptors open up?
sodium ions rush into skeletal muscle fiber
some potassium ions will leak out of cell
OVERALL INCREASE IN POSITIVE CHARGE ON THE INSIDE OF MUSCLE FIBER/MEMBRANE
What is a one-word term for the increase in positive charge inside the membrane relative to outside the membrane?
depolarization
The local depolarization on the postsynaptic membrane is called a(n) _______________.
end plate potential
What is the resting potential of the cell membrane?
-100mV
What charge does the cell membrane’s resting potential rise up to after depolarization?
-60mV
Threshold for voltage gated SODIUM ion channels
When the threshold potential is reached, lots of _________________ channels open up and there is a huge influx of _________ ions into the muscle fiber.
- voltage gated sodium
- sodium
When the signal sent from the lower motor neuron stops, ___________ channels on the presynaptic membrane close and influx of __________ ions stops.
- voltage-gated calcium
- calcium
TRUE OR FALSE
Each skeletal muscle fiber has only one neuromuscular junction, so that means that each muscle cell is controlled by one lower motor neuron
TRUE
TRUE OR FALSE
the axon of a lower motor neuron does not branch and therefore can innervate only one muscle fiber
FALSE
the axon of a lower motor neuron SPLITS INTO MANY BRANCHES and EACH OF THESE BRANCHES CAN INNERVATE MULTIPLE ADJACENT MUSCLE FIBERS
A muscle that requires precision innervates more or less muscle fibers?
less
relatively small motor units
every lower motor neuron innervates only 10 to 15 muscle fibers
A muscle that does a large range of movements (not require precision) uses more or less muscle fibers?
more
can have up to 2000 muscle fibers within a single motor unit
What is a quick summary about the neuromuscular joint, its channels, and ion influx?
The neuromuscular junction is a site where a motor neuron meets a skeletal muscle fiber. It is where a nerve impulse is transmitted from a motor neuron to a muscle fiber. A neuromuscular junction is made up of a nerve terminal, which contains the neurotransmitter acetylcholine, and a muscle fiber, which has receptors for acetylcholine.
When an action potential reaches the nerve terminal, it causes the release of acetylcholine, which diffuses across the synapse and binds to receptors on the muscle fiber. This activates an ion channel, allowing ions to flow into the muscle fiber and causing it to depolarize. This depolarization triggers the release of calcium ions from intracellular stores, which initiates the contraction of the muscle.
What is hypertension?
when the pressure in your blood vessels is too high (140/90 mmHg or higher)
What is the relation between hypertension and a calcium channel blocker?
calcium channel antagonist block inward movement of calcium
How does a calcium channel antagonist block inward movement of calcium?
bind to L-type “long acting” voltage-gated calcium channels in heart, vascular smooth muscle, and pancreas
What are two major categories of calcium channel blockers?
- Non-dihydropyridines
- Dihydropyridines
Non-dihydropyridines have a greater effect on the ________.
heart
Dihydropyridines have an effect mainly on the ________.
blood vessels
What is botulinum toxin (botox)?
neurotoxic protein produced by bacterium: Clostridium botulinum + related species
What does botulinum toxin do?
prevents release of ACh at synaptic terminals of muscle cells, preventing an action potenial in sarcolemma from occurring
causes muscular paralysis
Why is botulism toxin useful?
efficacy in bruxism (teeth grinding), temporomandibular disorders, trigeminal neuropathic pain
What are neuromuscular blockers?
prevent acetylcholine from acting at neuromuscular junction, preventing the triggering of skeletal muscle contractions
What are the types of neuromuscular blockers?
- non-depolarizing
- depolarizing
What are non-depolarizing neuromuscular blockers?
bind to the same binding sites on the receptor as acetylcholine, but they don’t trigger the opening of ion channels
ANTAGONIST aka inhibit
What are depolarizing neuromuscular blockers?
stimulate the nicotinic receptors, opening up the ion channels
AGONIST - have affinity for and activate receptors
What are the two phases of depolarizing neuromuscular blockers?
Phase I: prolonged depolarization phase (temporary muscle contractions)
Phase II: repolarization and desensitization
What is Myasthenia gravis?
auto-immune disorder where body produces antibodies that most commonly target nicotinic acetylcholine receptors on surface of muscle cells
causes weakness in the body’s voluntary muscles
What is the mechanism of neostigmine and pyridostigmine?
mechanism of action: anticholinesterase agent
INHIBIT AChE –> raise the [ACh] in the neuromuscular junction –> prolong action of ACh
What is AChE?
Acetylcholinesterase (AChE), also known as acetylcholine hydrolase, is an enzyme that breaks down acetylcholine (ACh), a neurotransmitter, into acetic acid and choline
