Bio 168 Chapter 11 Part 3

Synapse

Junction mediating information transfer between neurons to other neurons or to effector cells

Presynaptic Neuron

Conducts impulses toward the synapse

Postsynaptic Neuron

Transmits impulses away from the synapse

Axodendritic Synapse

Between axon of one neuron and dendrite of another

Electrical Synapses

Neurons joined by gap junctions, less common than chemical synapses

Chemical Synapses

Specialized for release and reception of neurotransmitters

Synaptic Cleft

Fluid-filled space separating presynaptic and postsynaptic neurons

Neurotransmitter

Chemical released at synapse for communication between neurons

Graded potential types

excitatory- depolarizing

inhibitory- hyperpolarizing

EPSP

Excitatory postsynaptic potential causing net depolarization

IPSP

Inhibitory postsynaptic potential causing hyperpolarization

Temporal Summation

Rapid-fire transmission of impulses by one or more presynaptic neurons (machine gun fire)

Spatial Summation

Stimulation of postsynaptic neuron by multiple presynaptic terminals simultaneously (a firing squad)

Acetylcholine (Ach)

Neurotransmitter at neuromuscular junctions and some CNS neurons

Functional classification of neurotransmitters

Two classifications: excitatory and inhibitory

Excitatory neurotransmitters cause depolarizations

Inhibitory cause hyperpolarizations

Some have both excitatory and inhibitory effects

Determined by the receptor type of the postsynaptic neuron

Neurotransmitter actions

direct action and indirect action

Direct action of neurotransmitters

binds to channel-linked receptor and opens ion channels and promotes rapid responses

Indirect action of neurotransmitters

Neurotransmitter acts through intracellular second messengers, usually G-protein pathways

Broader, longer-lasting effects similar to hormones