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Neuroscience and Muscle Physiology Flashcards
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Neuroscience and Muscle Physiology Flashcards
Neuroscience and Muscle Physiology Flashcards
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1
Question
What are the primary components of a nerve cell and their respective functions?
Answer
A nerve cell consists of the soma (cell body/nucleus), dendrites for receiving signals via receptors, an axon for transmitting signals, and an axon terminal (synapse) for releasing excitatory or inhibitory neurotransmitters.
2
Question
How is the resting membrane potential maintained in a nerve cell?
Answer
The resting membrane potential, typically around -70 mV, is maintained by the Na+/K+ ATPase pump, which actively expels 3 Na+ ions and imports 2 K+ ions, making the inside of the cell more negative than the outside.
3
Question
Describe the initial phase of an action potential when the threshold is reached.
Answer
When a nerve cell reaches the threshold potential of approximately -55 mV at the axon hillock, voltage-gated Na+ channels rapidly open, causing a swift influx of Na+ ions and depolarizing the cell.
4
Question
Explain how repolarization and subsequent hyperpolarization occur during an action potential.
Answer
At approximately +30 mV, voltage-gated Na+ channels inactivate, while voltage-gated K+ channels activate, leading to an efflux of K+ ions that repolarizes the cell. This is often followed by a temporary hyperpolarization before the Na+/K+ ATPase restores the resting potential.
5
Question
What factors influence the speed of action potential propagation along an axon?
Answer
The speed of action potential propagation is influenced by myelin, which reduces capacitance; temperature, with higher temperatures leading to faster impulses; and axon diameter, where a larger diameter results in lower resistance and faster impulses.
6
Question
What is the primary function of synapses in the nervous system?
Answer
Synapses primarily function to transmit signals from one nerve cell to another by releasing neurotransmitters from synaptic vesicles.
7
Question
How do AMPA receptors contribute to excitatory synaptic transmission?
Answer
AMPA receptors are ligand-gated ion channels that activate rapidly upon glutamate binding, allowing Na+ influx and K+ efflux, leading to short-lived excitation and rapid desensitization.
8
Question
What unique conditions are required for NMDA receptor activation, and what is their role in synaptic plasticity?
Answer
NMDA receptors require both ligand binding (glutamate and glycine/D-serine) and postsynaptic depolarization for activation. They allow Na+ and Ca2+ influx and K+ efflux, contributing to long-lasting excitation crucial for synaptic plasticity, including Long-Term Potentiation (LTP) and Long-Term Depression (LTD).
9
Question
How do GABA-A receptors mediate fast inhibitory synaptic transmission?
Answer
GABA-A receptors are ligand-gated ion channels that, when two GABA molecules bind, allow chloride ions to flow into the cell, causing hyperpolarization and a rapid, short-lived inhibition.
10
Question
Why is GABA excitatory in immature nerve cells but inhibitory in mature ones?
Answer
In mature nerve cells, the KCC2 pump maintains a low intracellular Cl- concentration, allowing Cl- to flow in and hyperpolarize the cell upon GABA-A activation. In immature cells, the NKCC1 transporter actively brings Cl- in, resulting in a high intracellular Cl- concentration, causing Cl- to flow out and depolarize the cell when the channel opens.
11
Question
What is the mechanism by which GABA-B receptors mediate slow, long-lasting inhibition?
Answer
GABA-B receptors are metabotropic, G-protein coupled receptors. Upon GABA binding, they activate a G-protein that leads to the opening of K+ channels. The subsequent efflux of K+ ions causes hyperpolarization, resulting in a slow, long-lasting inhibition.
12
Question
Describe the steps involved in neurotransmitter vesicle release at the presynaptic terminal.
Answer
Vesicle release begins with docking, where vesicles attach to the plasma membrane via SNARE proteins. This is followed by priming, where the proteins bind and pull the vesicle closer. When an action potential arrives, voltage-gated Ca2+ channels activate, Ca2+ flows in and binds to synaptotagmin, which then triggers SNARE proteins to fuse the vesicle with the membrane, releasing neurotransmitters via exocytosis.
13
Question
How does synaptic plasticity, specifically Long-Term Potentiation (LTP), strengthen a synapse?
Answer
In LTP, synapses are strengthened, for example, by increasing their size, the number of release sites, or the number of AMPA receptors. This process involves NMDA receptors allowing calcium influx into the postsynaptic cell, activating a cascade that leads to an increase in AMPA receptors on the membrane.
14
Question
What is Long-Term Depression (LTD), and how does it weaken a synapse?
Answer
LTD is the weakening of a synapse, occurring by making it smaller, reducing the number of release sites, or decreasing the number of AMPA receptors. Like LTP, it is mediated by NMDA receptors and calcium influx, but the resulting cascade leads to a decrease in AMPA receptors.
15
Question
What three factors, represented by n, p, and q, influence synaptic strength?
Answer
Synaptic strength is influenced by n (the number of release sites), p (the probability that an action potential leads to vesicle release), and q (the size of the postsynaptic response).
16
Question
Describe the initial steps of skeletal muscle contraction starting from a signal from the motor cortex.
Answer
Voluntary muscle contraction begins with a signal from the motor cortex, which travels down to the spinal cord. An alpha motor neuron then innervates several muscle fibers at a neuromuscular synapse, leading to an action potential and the release of acetylcholine (ACh).
17
Question
How does acetylcholine facilitate depolarization and action potential generation in a muscle fiber?
Answer
Acetylcholine binds to nicotinic receptors on the muscle fiber, causing an influx of Na+ and efflux of K+. This leads to depolarization of the muscle fiber, and once the threshold is reached, an action potential is triggered, which then propagates along the sarcolemma and into the T-tubules.
18
Question
Explain the role of T-tubules and sarcoplasmic reticulum (SR) in coupling excitation to contraction in skeletal muscle.
Answer
In the T-tubules, the action potential activates voltage-sensitive receptors that, in turn, activate ryanodine receptors on the sarcoplasmic reticulum (SR). This causes the release of calcium from the SR into the cytoplasm.
19
Question
How do calcium ions trigger muscle contraction at the myofilament level?
Answer
Calcium ions bind to Troponin C, causing a conformational change that moves tropomyosin away from the actin binding sites. This allows myosin heads to bind to actin, initiating the cross-bridge cycle and shortening the sarcomeres, leading to contraction.
20
Question
What mechanism ensures muscle relaxation after contraction ceases?
Answer
After the impulse ceases, calcium ions are actively pumped back into the sarcoplasmic reticulum by the SERCA pump, leading to the removal of calcium from Troponin C and subsequent muscle relaxation.
21
Question
How do summation and recruitment influence the force of muscle contraction?
Answer
Summation increases contraction force by increasing the frequency of action potentials, preventing calcium from being pumped away and allowing contractions to add up. Recruitment increases force by activating more motor units simultaneously, engaging type-I, then type-IIa, and finally type-IIx units as needed.
22
Question
Distinguish between peripheral fatigue and central fatigue in muscle activity.
Answer
Peripheral fatigue occurs within the muscle due to ATP breakdown and phosphate ion accumulation, inhibiting ryanodine receptors and reducing Ca2+ release. Central fatigue arises in the CNS, reducing action potential frequency and summation, decreasing contractile strength, potentially due to factors like lactate-induced pH drop activating pain receptors.
23
Question
Compare red (Type I) and white (Type IIa/IIx) striated skeletal muscle fibers.
Answer
Red (Type I) muscle fibers are slow-twitch, highly enduring, rich in mitochondria and capillaries, and primarily use aerobic metabolism. White (Type IIa/IIx) fibers are faster, more powerful, but fatigue quickly, have fewer mitochondria, and primarily use anaerobic metabolism.
24
Question
What are the key differences in activation and contraction between skeletal muscle, cardiac muscle, and smooth muscle?
Answer
Skeletal muscle is voluntary, activated by motor cortex via ACh, leading to RyR1 activation and Ca2+ release. Cardiac muscle is involuntary, activated by pacemakers via L-type Ca2+ channels, leading to RyR2 activation and Ca2+ release. Smooth muscle is involuntary, activated by the ANS via Ca2+ influx, which binds calmodulin, stimulating MLCK and phosphorylating myosin light chains.
25
Question
Despite their differences, what is the common fundamental outcome of activation and contraction in skeletal, cardiac, and smooth muscle?
Answer
In all three muscle types—skeletal, cardiac, and smooth—the ultimate result of activation and contraction is that myosin binds to actin, leading to the shortening of the muscle cell.
26
Question
What anatomical structures constitute the vestibular apparatus in the inner ear?
Answer
The vestibular apparatus, located in the inner ear within the temporal bone, consists of endolymph-filled structures, including otolith organs (utricle and saccule) that detect linear motion, and semicircular canals that detect rotational motion.
27
Question
How do utricle and saccule detect linear head movements?
Answer
The utricle and saccule contain maculae with hair cells that have stereocilia embedded in an otolith membrane topped with calcium carbonate crystals. Linear movement displaces these otoliths, bending the cilia towards the kinocilium, leading to K+ influx, depolarization, neurotransmitter release to the vestibular nerve, and action potentials.
28
Question
Explain how the semicircular canals sense rotational head movements.
Answer
Semicircular canals are filled with endolymph and have an ampulla containing a crista ampullaris with hair cells whose stereocilia are embedded in a gel-like cupula. Head rotation causes endolymph fluid movement, which exerts force on the cupula, bending the cilia towards the kinocilium, leading to K+ influx, depolarization, and action potentials in the vestibular nerve.
29
Question
Why is the bilateral arrangement of semicircular canals important for sensing rotational direction and speed?
Answer
Semicircular canals are arranged mirror-inverted in each ear. This means that depolarization in one ear during rotation is accompanied by hyperpolarization in the corresponding canal of the other ear, allowing the brain to precisely register both the direction and speed of rotation.
30
Question
Which brain regions receive vestibular signals, and what functions do they contribute to?
Answer
Vestibular signals are sent from the vestibular nerve to the brainstem, where four vestibular nuclei relay them to the cerebral cortex for spatial awareness, oculomotor nuclei for stable gaze and the vestibulo-ocular reflex (VOR), the spinal cord for balance control, and the vomiting center for nausea and vomiting reflexes.