SITES OF SYNAPTIC COMMUNICATION SYNAPSES Created by The North Carolina School of Science and Math.The North Carolina School of Science and Math Copyright North Carolina Department of Public Instruction.North Carolina Department of Public Instruction Created by The North Carolina School of Science and Math.The North Carolina School of Science and Math Copyright North Carolina Department of Public Instruction.North Carolina Department of Public Instruction

LEARNING OBJECTIVES Identify different types of synapses Describe the process of neurotransmitter release from chemical synapses Recall how neurotransmission can result in EPSCs and IPSCs in postsynaptic neurons Express how synaptic events can come together to propagate communication between brain cells

SYNAPSES Neurons communicate through synapses to other neurons to effector cells (like muscle cells) Pre and postsynaptic neurons Neuromuscular Junction presynaptic postsynaptic

TYPES OF SYNAPSES: MODE OF TRANSMISSION There are two general types of synapses Chemical These synapses release neurotransmitter Electrical These synapses create a direct electrical link between neurons Chemical Synapse Electrical Synapse

TYPES OF SYNAPSES: ANATOMICAL FEATURES Synapses have different anatomical locations Axodendritic: most prevalent synaptic site between the axon of one neuron and the dendrite of another Axosomatic: occur between the axon of one neuron and the cell body (soma) of another neuron.

SYNAPTIC CLEFT: INFORMATION TRANSFER

When an action potential travels down an axon, voltage sensitive calcium channels allow the entry of calcium

SYNAPTIC CLEFT: INFORMATION TRANSFER Calcium entry allows presynaptic vesicles, packed with neurotransmitter, to fuse with the presynpatic membrane This fusion event leads to the release of neurotransmitter into the synaptic cleft

SYNAPTIC CLEFT: INFORMATION TRANSFER Neurotransmitter then binds to receptors on the postsynaptic membrane

SYNAPTIC CLEFT: INFORMATION TRANSFER Ligand-gated ion channels allow for the influx of positively charged sodium ions

SYNAPTIC CLEFT: INFORMATION TRANSFER Neurotransmitter is degraded in the synaptic cleft and ligand-gated ion channels are inactivated

POSTSYNAPTIC POTENTIALS Neurotransmitter receptors mediate changes in postsynaptic membrane potential according to: The amount of neurotransmitter released The amount of time the neurotransmitter is bound to receptors The two types of postsynaptic potentials are: EPSP – excitatory postsynaptic potentials IPSP – inhibitory postsynaptic potentials

EXCITATORY POSTSYNAPTIC POTENTIAL (EPSP) Excitatory Postsynaptic Potential

INHIBITORY POSTSYNAPTIC POTENTIAL (IPSP) Inhibitory Postsynaptic Potential

SUMMATION Synaptic events can come together to trigger an action potential

SUMMARY There are many different types of synapses They can differ in their mode of transmission They can differ by anatomical location Axodendritic chemical synapses are the most abundant in the central nervous system Synaptic release of neurotransmitter at chemical synapses is a multi-step process Synaptic events can either make the postsynaptic cell more positive or more negative EPSC and IPSCs can come together to produce action potentials in postsynaptic neurons