![]() ![]() Dopamine – a CNS neurotransmitter, may be inhibitory or excitatory inhibitory – imp. Norepinephrine – in brain and ANS, has an excitatory, depolarizing effect on the postsynaptic membrane Dreaming, learning, emotions, sleeping, controls body temp. Is it possible to generate a second action potential during either refractory period If so, which one and how. A neuron will always send the same size action potential. This means that an action potential is either triggered, or it isn’t like flipping a switch. Define all or nothing principle The all-or-none law is the principle that the strength by which a nerve or muscle fiber responds to a stimulus is independent of the strength of the stimulus. Released at neuromuscular junctions At many synapses in CNS At all neuron-to-neuron synapses in PNS At all neuromuscular and neuroglandular junctions within the parasympathetic division of the ANS Action potentials work on an all-or-none basis. Define action potential a nerve impulse that travels along an axon away from a neuron's cell body. ![]() Myelinated axons allows the action potential to travel faster Action potential travels only along the nodes Node to node – skips the internodes Faster and uses less energyġ1 General Properties Electrical – the Presynaptic & Postsynaptic membranes are locked together at gap junctions, start action potential more quickly Located int CNS & PNS but very rare Few areas of the brain, the eye & ciliary ganglia of the PNS Chemical – Presynaptic & Postsynaptic membranes do not touch, most abundant type Several types of neurotransmittersġ2 Cholinergic Synapses Release Acetylcholine (Ach) Will open voltage-regulated sodium channels If less than -62 mV will produce a graded depolarization The action potential is independent of the relative strength of the depolarizing stimulus Like the pressure on the trigger of a gun: slight pressure gun does not fire, more pressure = gun firesĭepolarization to Threshold Activation of Sodium Channels & Rapid Depolarization (this is positive feedback) Inactivation of Sodium Channels & the Activation of Potassium Channels Return to Normal PermeabilityĪn action potential is propagated (moved) along an unmyelinated axon Action potential moves at the same speed along the entire length of the axon Moves at about 1 meter/second Similar to dominoes falling 1 Action Potential Action Potential The All-or-none PrincipleĢ All-or-None A threshold must be overcome (between -60 mV and - 55 mV) ![]()
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