Exam 2 terms Flashcards
Ion
Any atom that has an electrical charge, (Na+, K+, Cl-)
Cation
An ion with a positive charge
Anion
An ion with a negative charge
Electrolyte
Same as an ion
Principle of macroscopic electroneutrality
On a macroscopic level, each fluid compartment has the same concentration, expressed in mEq/L,
Neuronal pathways
groups of neurons that influence each others activity by communicating at neuronal synapses
Synapse
Act as switches that direct the flow of electrical signals within the nervous system.
Neuronal synapses
Are found between successive neurons in a neuronal pathway.
Neuromuscular junctions
Are found between somatic alpha-motor neurons and myofibers of skeletal muscles
Neuroeffector junctions
Are found between autonomic motor neurons and autonomic effectors including smooth muscle and glandular cells.
Effector
Cell or tissue that carries out the desired response (e.g. muscle contraction, glandular secretion).
Presynaptic neuron
Neuron that carries impulse into the synapse. This is the neuron whose synaptic knob is part of the synapse.
Postsynaptic neuron
Neuron that carries the impulse away from the synapse. This is the neuron whose dendrite, soma, and rarely axon is part of the synapse.
Chemical synapses
Two cells forming the synapse are separated by a physical space called the synaptic cleft.
Synaptic cleft
Narrow space ( about 20-30nm) that separates the presynaptic neuron from the postsynaptic neuron (or effector).
Neurotransmitters (NT)
Extracellular signal molecules (ESMs) released by neurons that diffuse across the synaptic cleft to stimulate or inhibit activity in a postsynaptic neuron or effector (muscle or gland).
Neurotransmitter receptor
Membrane proteins found on the postsynaptic neurons (or effectors) that bind a specific NT and generate a response in the postsynaptic cell.
Excitatory postsynaptic potential (EPSP)
Depolarizing graded potential that brings a postsynaptic neuron closer to the threshold for creating action potentials (APs).
Inhibitory postsynaptic potential (IPSP)
Hyperpolarizing graded potential that moves a postsynaptic neuron closer to the threshold for creating action potentials (APs).
Summation
The process of integrating the input from multiple synapses.
Spatial summation
Effect produced by the simultaneous release of NT from more than one (usually a large number) synaptic knobs on a single postsynaptic neuron.
Temporal summation
Effect produced by stimulation of NT release from the same presynaptic knob(s) in rapid succession on a postsynaptic neuron.
Facilitation
Occurs when the membrane potential of a postsynaptic neuron is held nearer to the threshold then normal but not yet above threshold.
Divergent pathways
When the signal entering into a neuronal pool excites a greater # of fibers leaving the pool. (“amplification” and “divergence into multiple tracts” are used)
Convergent pathways
Signals from multiple input fibers (or multiple axons terminals from a single input fiber) come together to excite a single output fiber. (spatial summation is used)
Efferent (motor) neurons
In neural reflex pathways, integrating centers respond to sensory inputs by sending output signals to effectors.
Somatic motor neurons
control skeletal contraction
Autonomic motor neurons
control involuntary effectors
Pupillary light reflex
pupil diameter changes due to contraction of smooth muscle within the iris (colored part of eye) to control the amount of light entering the eye.
Mydrasis
dilation of pupil (sympathetic division of ANS)
Miosis
Constriction of pupil (parasympathetic division of ANS)
Conductor
The name of the material when positive and negative ions can freely move through (water, copper wire).
Insulator
If oppositely charged ions are unable to move through the material separating them, this is the material.
Electrochemical potential
Form of PE (mV) created by the difference between the amounts of the electrical charge (in the form of ions) present at two points like the inner surface and outer surface of a membrane.
Diffusion Potentials of Membrane Equilibrium Potentials
The flow of ions down their concentration gradient creates an electrical imbalance. Eventually the chemical concentration gradient and the opposing electrical imbalance reach an equilibrium.
Resting Potential (V_rest)
When the membrane is “resting” (not actively conducting an electrical impulse) V_rest ranges from -60 to -90 mV in normal excitable cells. (meaning that the inside of the cells has more anions)
Graded potentials
Are a change in the membrane potential whose magnitude is proportional to the strength of the stimulus. They spread via electrotonic conduction and is decremental. Uses dendrites and the soma.
Action potentials (AP)
Are rapidly moving wave of electrical charge that moves along the membrane of an active excitable cell. They are uniform magnitude of +30mV and are nondecremental. Found in axons and sarcolemma of myofibrils.
Voltage-gated channels
Channels whose molecular conformation (opened or closed) responds to the changes in the electrical potential across the cell membrane.
Depolarization
Process of making membrane potential less negative.
Threshold stimulus
A stimulus strong enough to initiate an action potential by triggering opening of the activation gate of the voltage-gated Na+ channels. Stimulus must cause a change in the V_m > 10mV(to 30mV) to open the activation gate of the voltage-gated Na+ channel.
Subthreshold stimulus
A stimulus not strong enough to open the activation gate of the voltage gated Na+ channels and initiate an AP.
Repolarization
Process of regaining V_rest after depolarization.
Hyperpolarization
Undershooting of V_rest on repolarization due to excess K+ ions flowing out of the cell when the voltage-gated K+ channels are open. Contributes to the relative refractory period.
Refractory period
Brief space of time in which an excitable membrane is resistant to further stimulation.
Absolute refractory period
The short period during and immediately after depolarization where a neuron or myofiber will not respond to any stimulus, no matter how strong.
Relative refractory period
Period following absolute refractory period where a neuron or myofiber will only respond to a strong stimulus
Propagation
Is the spread of an action potential (impulse) along the membrane of an excitable cell (e.g. axon of a neuron of sarcolemma of a myofiber).
Continuous propagation
Is used in unmyelinated axons and muscle cells.
Saltatory propagation
Is used in myelinated axons
All-or-nothing principle
Once an action potential has been initiated, it will travel over the entire membrane of the cell if conditions are right (ALL), or not be created at all if the conditions are wrong (NOTHING; e.g. stimulus below threshold, refractory periods).
Myelinated neuron
Neuron whose axon is wrapped with myelin sheaths.
Myelin
A lipid that forms a sheath around an axon.
Nodes of Ranvier
The areas between the myelin sheath that the AP jumps on. By skipping the myelinated areas the AP conductance is 5 to 50-fold faster than in unmyelinated axons.