Neurophysiology & Muscle Physiology — Study Materials Flashcards

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Neuron

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A neuron is the basic signaling cell of the nervous system composed of a soma, dendrites, and an axon that transmit electrical signals. Neurons process and relay information via action potentials and synaptic transmission.

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Dendrite

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A dendrite is a branched extension of the neuron that conducts incoming signals toward the soma. Dendrites increase the surface area for synaptic inputs.

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Axon hillock

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The axon hillock is the region connecting the soma to the axon and has the lowest threshold for action potential initiation due to many $Na^{+}$ channels. It is the usual site where graded potentials are integrated into a spike.

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Synapse

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A synapse is the junction between a presynaptic neuron's axon terminal and a postsynaptic cell, separated by a cleft ~30–50 nm wide. Neurotransmitters released into the cleft bind receptors and alter postsynaptic excitability.

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EPSP

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An excitatory postsynaptic potential (EPSP) is a depolarizing graded potential produced by neurotransmitter action that increases the likelihood of an action potential. Single EPSPs are small (~0.5–1 mV) and require summation to reach threshold.

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IPSP

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An inhibitory postsynaptic potential (IPSP) is a hyperpolarizing graded potential that decreases the probability of an action potential. IPSPs often result from opening $K^{+}$ or $Cl^{-}$ channels.

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Spatial summation

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Spatial summation occurs when multiple presynaptic neurons release neurotransmitter simultaneously at different locations on the postsynaptic neuron. The combined PSPs can add to reach threshold for an action potential.

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Temporal summation

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Temporal summation is the progressive build-up of postsynaptic potential from rapid successive discharge of the same presynaptic terminal. Rapid EPSPs can summate to bring the membrane to threshold.

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Acetylcholine

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Acetylcholine (ACh) is a neurotransmitter found at neuromuscular junctions and many CNS synapses, acting on nicotinic and muscarinic receptors. It is rapidly degraded in the synaptic cleft by acetylcholinesterase.

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GABA

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GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the brain that typically opens $Cl^{-}$ channels. Drugs that enhance GABA activity, like benzodiazepines, produce anxiolytic and sedative effects.

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Glutamate

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Glutamate is the primary excitatory neurotransmitter in brain and spinal cord, acting on AMPA, NMDA, and other receptors. Overactivation of glutamate receptors can lead to excitotoxicity in pathological states.

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Oligodendrocyte

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An oligodendrocyte is a CNS glial cell that forms myelin sheaths around multiple axons, increasing conduction velocity. Damage to oligodendrocytes underlies demyelinating diseases like multiple sclerosis.

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Schwann cell

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A Schwann cell myelinates a single axon segment in the PNS and can support axonal regeneration by forming a guidance tube. Schwann cells are essential for peripheral nerve repair.

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Motor unit

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A motor unit consists of one motor neuron and all the muscle fibers it innervates, and it is the basic unit of muscle contraction control. Recruitment of more motor units increases whole-muscle force in discrete steps.

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Sarcomere

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A sarcomere is the structural and functional unit of a myofibril, bounded by Z-lines and containing interdigitating actin (thin) and myosin (thick) filaments. Sarcomere shortening by sliding filaments produces muscle contraction.

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Troponin C

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Troponin C is the subunit of the troponin complex that binds $Ca^{2+}$, causing tropomyosin to move and expose myosin-binding sites on actin. This $Ca^{2+}$-triggered change initiates crossbridge cycling.

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T-tubules

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T-tubules are invaginations of the muscle cell membrane that transmit action potentials deep into the fiber to activate the sarcoplasmic reticulum. They ensure synchronous $Ca^{2+}$ release for uniform contraction.

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Sarcoplasmic reticulum

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The sarcoplasmic reticulum (SR) is a specialized ER in muscle cells that stores and releases $Ca^{2+}$ to trigger contraction and actively pumps it back to end contraction. The SR can maintain a very high $Ca^{2+}$ concentration relative to cytosol.

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Creatine phosphate

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Creatine phosphate donates a phosphate to ADP to rapidly regenerate ATP during the first seconds of intense muscle activity. The phosphagen system extends maximal power output for ~8–10 seconds.

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Anaerobic threshold

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The anaerobic threshold is the exercise intensity at which lactate begins to accumulate faster than it can be removed, indicating a shift toward greater anaerobic metabolism. It is a key predictor of endurance performance and can be raised with training.

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Smooth muscle

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Smooth muscle lacks striations and troponin; most $Ca^{2+}$ enters from the extracellular space and binds calmodulin to activate myosin light chain kinase. It can function as single-unit syncytia or multiunit independent cells.

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End plate potential

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End plate potentials are large graded depolarizations at the motor end plate produced by ACh opening ligand-gated channels, typically +50 to +70 mV. These potentials trigger action potentials in adjacent muscle membrane to initiate contraction.