Lectures 12-13 Flashcards by Valerie Solinap

What is a motor unit?

neuron + skeletal muscle (which has multiple muscle fibers)

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What will happen if the skeletal muscles have not been stimulated but a motor neuron?

muscle will undergo atrophy = loose muscle mass

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Why does the sarcolemma of the motor end-plate have a lot of receptors?

so it can increase the response to the neurotransmitter

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What are nicotinic acetylcholine (ACh) receptors?

ligand-gated channels that conduct sodium and potassium ions

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Which ion are nicotinic ACh receptors conduct more of?

sodium

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What is signal termination at the neuromuscular junction?

when ACh is broken down by acetylcholinesterase into choline and acetyl

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What does the variability of the ACh receptors allow?

toxins to bind to skeletal muscle receptors but not that which are involved in the ANS (somatic only)

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How many subunits are nicotinic ACh receptor made up of?

5 (same as GABA receptors)

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How many ACh molecules bind to nicotinic ACh receptors? What does this lead to?

two | net sodium influx = depolarization of muscle fiber

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What is cooperativity binding in reference to ACh binding to nicotinic ACh receptors?

one ACh binding to nicotinic ACh receptor increases the affinity of nicotinic ACh receptor for more ACh to bind to it

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What is the Hill coefficient for cooperativity?

≥ 2

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How does cooperativity binding occur?

first ligand binding to receptor = causes allosteric changes to the next binding site on receptor | allosteric changes must occur for subsequent ligand-binding

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What does cooperativity indicate about a ligand-receptor relationship?

there are at least 2 binding sites on the receptor

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What type of receptors are muscarinic ACh receptors?

G-protein coupled receptor

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What are the different types of muscarinic ACh receptors?

M1, M2, M3

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What happens when ACh binds to muscarinic ACh receptors?

activates second messengers &raquo_space;> signaling cascade &raquo_space;> increas calcium levels in sarcoplasm

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What are the 5 second messengers?

PIP2, IP3, DAG, PLC, AC

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What is the only gas neurotransmitter?

nitric oxide (NO)

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What are 2 other effects that can occur due to signaling cascade?

gene expression | opening of channels

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What is muscle fatigue?

reversible condition in which a muscle is no longer able to generate or sustain power input

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What is central fatigue?

originates from CNS | psychological fatigue

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What are the 3 characteristics explaining fatigue?

highly variable | complex mechanism | aerobic or anaerobic

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What is peripheral fatigue? What is it due to?

physiological fatigue originating at the muscle level | due to EC-coupling failure

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How can fatigue be protective?

muscle releases a compound due to too much exercise &raquo_space;> compound causes acid build-up = signals to the brain to stop sending impulses so acid build-up doesn’t worsen

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What type of classification is used to classify skeletal muscle?

based on the isoform of the myosin head

What are the 3 types of skeletal muscle?

slow twitch (type 1) | fast-twitch oxidative/glycolytic (type 2A) | fast-twitch glycolytic (2X)

What is myoglobin?

red protein in the skeletal muscles containing heme that oxygen binds to

What are fast-twitch movements used for?

fast-quick movements (ie: running)

What are slow-twitch movements used for?

posture and walking

How can a slow-twitch muscle fiber change into a fast-twitch muscle fiber (vice-versa)?

with training

What is tetanus?

when the summation of contractions are close to one another

What is the summation of contractions in skeletal muscles?

motor-neuron fires again before muscle has the chance to relax from previous twitch

What is a tetanus contraction?

sustained muscle contraction induced when motor neuron sends APs at a high rate

What is unfused tetanus?

motor neuron sends multiple stimulations but muscle relaxes slightly between stimuli

What is complete tetanus?

all muscles contracting, no relaxation phase | can break bones

What is the length and tension relationship of myosin and actin?

sweet-spot certain length of myosin-acton cross-bridges that allows muscles to perform the most and give the highest tension

What happens if there is not enough cross-bridges happening in the sarcomere?

no force generated = no tension

What is isometric contraction?

sarcomeres shorten = generates force but doesn't move load | elastic elements stretch to sustain load w/o moving = muscle stays same length

What is isotonic contraction?

(happens after isometric contraction) sarcomeres shorten more | elastic elements already stretched to capacity = muscle length shortens = creates enough force to move load

What allows isometric contractions?

elastic elements

What are proprioceptors?

sensory receptors in the skeletal muscles, joints, ligaments

What is the Golgi Tendon Organs (GTO)?

connects muscle and tendon

What are the 2 things the golgi tendon organ consist of?

sensory neurons | collagen fibers

Where are golgi tendon organs found?

on the tendon just before the muscle

What is the function of muscle spindles?

send information to CNS every time when muscles stretch

Where are the muscle spindles located?

buried on the surface within the muscle fibers

What are the 2 things that muscle spindles consist of?

gamma motor neurons | sensory neurons

What is special about the central region of the muscle spindle?

no myofibrils | innervated by sensory neurons

What type of reflex is the patellar tendon reflex (knee jerk)?

simple reflex

Why can the patellar tendon reflex still work when the brain is severed from the spinal cord?

reflex is purely integrated within the spinal cord = don't need brain to do this

What type of reflex is the crossed extensor reflex? Why?

complex | one side = connected to the directly affected limb, other side will provide balance = both sides of spinal cord involved | interneurons involved

What is the cardiovascular system?

series of tubes filled with fluid connected to a pump (heart)

What is the primary function of the cardiovascular system?

transport material = nutrients, water, gases enter>>>move throughout body>>>eliminate waste

What are the 2 blood vessels?

arteries | veins

What is the function of red blood cells?

transport and deliver oxygen | eliminate CO2

How many lobes are on each side of the lungs?

left = 2 | right = 3

What direction do veins go?

TO the heart

What direction do arteries go?

AWAY from heart (Aorta = Artery = Away)

What is the function of the connective tissue in the heart?

ensures one-way blood flow, prevents backflow = prevents deO2 blood from mixing with O2 blood

What is happening in the heart when you hear the "lub-dub" noise?

valves CLOSING

What is the function of check valves?

prevent backflow

What are the 3 factors that prevent back-flow of blood?

heart connective tissue | valves | pressure changes

What does "AV" stand for in AV valves? What are the 2 AV valves and where are they located?

atrioventricular valve | tricuspid (3 cusps) = Right side | bicuspid (2 cusps, mitral valve) = Left side

What is the function of semilunar valves? What are the 2 types?

ensures blood does not flow back into ventricles | pulmonary (to the lungs) and aortic (to the body)

What is pressure measured in?

mmHg

The closer the vasculature is to the aorta, the _____ the pressure. As you move away from the heart from the aorta, the pressure _______.

higher | decreases

What characteristic allows the aorta to withstand the high pressure?

thick walls of the aorta

What is aortic embolism?

when aorta explodes because the muscle fails

How thick are the walls of veins?

thinner than arteries, more flimsy, can collapse

Which vessel is blood supposed to be drawn from?

veins (deO2 blood)

What is the pericardium?

membranous fluid-filled sace that encases the heart

Why is it important that the heart functions as one unit?

the ANS only makes contact with one part of the heart

What are intercalated disks in cardiac muscle?

accumulation of gap junctions = allow electrical continuity from one fiber to another | contains desmosomes

What are desmosomes and its 3 functions?

type of junction | connects cardiac fibers together | ensures heart functions as one unit | allows material to flow through fibers

What is the sodium-calcium exchanger?

membrane transporter that pumps Ca2+ out of cell | secondary active anti-port (uses gradient, not ATP)

In cardiac muscle contraction, what does calcium bind to in order for contraction to occur?

troponin

What type of refractory period do cardiac muscles have and why?

absolute refractory period | contractions need to be fully completed in order to properly pump blood

How long is the absolute refractory period in cardiac muscles?

almost as long as the action potential itself | important for heart to go through full relaxation/contraction cycle to properly function

What are the 3 sets of delays in heart action potentials?

sodium channels need to open first | calcium channels open very late | opening of potassium channels is very slow (different isoform)