Nervous Tissue, the Action Potential and the Synapse: every key term you need (+ practice quiz)
25 flashcard terms for Anatomy & Physiology I Topic 8, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
The excitable signaling cell of the nervous system, typically amitotic and extremely long lived, with a high metabolic rate and an absolute requirement for oxygen and glucose. It receives, integrates and transmits electrical signals.
Neuron cell body
The region containing the nucleus and most organelles, the biosynthetic center of the cell. Clusters of these bodies are called nuclei within the central nervous system and ganglia outside it.
Dendrite
A short tapering branched process specialized to receive input. Dendrites carry graded signals toward the cell body, and the size of their branching tree sets how many contacts a neuron can receive.
Axon
The single long process that conducts the output signal away from the cell body. It begins at a cone-shaped hillock, may branch into collaterals, and ends in terminals that release chemical messengers.
Axon hillock and trigger zone
The junction between cell body and axon where graded potentials are summed and where the density of voltage-gated sodium channels is highest, making it the site at which an action potential is initiated.
Axonal transport
Motor-protein-driven movement of materials along microtubules within an axon. Forward transport carries organelles and vesicles outward, while reverse transport returns worn components and some viruses and toxins.
Multipolar neuron
A neuron with many dendrites and a single axon, the structural class comprising the vast majority of neurons in the body, including nearly all interneurons and motor neurons.
Sensory and motor neurons
The two functional classes defined by signal direction. Sensory neurons conduct impulses from receptors toward the central nervous system; motor neurons conduct commands away from it to muscles and glands.
Neuroglia
The nonexcitable supporting cells of nervous tissue, far outnumbering neurons. They insulate axons, control the chemical environment, provide immune defense, circulate cerebrospinal fluid and retain the ability to divide.
Astrocyte
The most abundant supporting cell of the central nervous system. Its processes brace neurons, help control the composition of interstitial fluid, take up excess transmitter and contribute to the blood brain barrier.
Oligodendrocyte
The central nervous system cell whose several flat processes wrap segments of nearby axons in insulating layers, so one cell can contribute sheath to a number of different axons at once.
Schwann cell
The peripheral counterpart that wraps itself repeatedly around a single segment of one axon to form its insulating sheath. It also guides and supports regrowth after a peripheral axon is severed.
Myelin sheath
The multilayered lipid wrapping around larger axons. Its high resistance and low capacitance prevent charge leakage, allowing the signal to travel far faster than an equivalent bare axon could manage.
Node of the myelin sheath
A short gap between adjacent insulating segments where the axon membrane is exposed and voltage-gated channels are concentrated. The impulse is regenerated only at these gaps.
Saltatory conduction
The rapid mode of impulse propagation along an insulated axon, in which current flows passively beneath each sheath segment and the signal is regenerated only at the exposed gaps, appearing to leap between them.
Resting membrane potential
The steady voltage of about seventy millivolts inside-negative maintained by a membrane far more permeable to potassium than to sodium, together with the pump that sustains both ion gradients.
Graded potential
A short-lived local change in membrane voltage whose size varies with stimulus strength and which weakens as it spreads. Summed graded potentials at the trigger zone determine whether an impulse fires.
Threshold
The critical membrane voltage at which sodium entry becomes self-reinforcing and outpaces potassium exit. Depolarization reaching this value inevitably produces a full action potential.
Action potential
The brief all-or-none reversal of membrane voltage that propagates without weakening along an axon. Its amplitude does not encode stimulus strength; frequency of firing does.
Depolarizing phase
The rising phase of the impulse, produced when voltage-gated sodium channels open rapidly and sodium rushes inward down its steep electrochemical gradient, driving the interior briefly positive.
Repolarizing phase
The falling phase, produced when sodium channels inactivate and slower voltage-gated potassium channels open, allowing potassium to leave and restoring the negative interior, often with a brief undershoot.
Absolute refractory period
The interval during which sodium channels are open or inactivated and no stimulus of any strength can trigger another impulse. It enforces one-way propagation and sets the ceiling on firing frequency.
Chemical synapse
A junction where an arriving impulse opens voltage-gated calcium channels in the terminal, calcium entry triggers vesicle fusion, and released transmitter diffuses across a narrow cleft to receptors on the target cell.
Excitatory and inhibitory postsynaptic potentials
The two graded responses to transmitter binding. Excitatory potentials depolarize the target toward threshold, usually by admitting sodium; inhibitory potentials hyperpolarize it, usually by admitting chloride or releasing potassium.
Temporal and spatial summation
The two ways graded inputs add at the trigger zone. Temporal summation combines rapid successive inputs from one terminal; spatial summation combines simultaneous inputs arriving from many different terminals.