PSY 241 Lecture 4

First to convincingly demonstrate that communication across the synapse occurs via chemical means

• Voltage-Gate Calcium Channels:
• Closed at RMP
• Open in response to voltage changes within the presynaptic terminal
• Only allow Calcium (Ca²⁺)

• Calcium (Ca²⁺) high concentrated on the OUTSIDE the presynaptic terminal
• There is a large INWARD driving force on Calcium
• Presence of enzymes needed for the synthesis of neurotransmitters
• Vesicles which store neurotransmitters

• 1. Neurotransmitter is synthesized and packaged into synaptic vesicles
• 2. Action potential arrive at presynaptic terminal and cause voltage-gated calcium (Ca2+) channels to open
• 3. Ca2+ ions enter cell
• 4. Ca2+ entry causes the synaptic vesicles to fuse with presynaptic membrane and release the neurotransmitter molecules into the synaptic cleft (EXOCYTOSIS)
• 5. Neurotransmitter molecules are carried across the synaptic cleft by diffusion and have their effects by interacting with postsynaptic receptors

• Action potential causes depolarization on postsynaptic side
• Sodium (Na+) ions responsible

• Harder to have action potential
• Chloride (Cl-) ions responsible

• Ionotropic: transmitter-gated ion channels
• Metabotropic: G-Protein coupled receptors

Any chemical that fits can activate that receptor

• Transmitter-gated ion channels
• Composed of 4 or 5 subunits that have a pore in the middle that open quickly by direct action of a neurotransmitter
• Allow passage of ions between the inside and outside of the cell
• There are multiple subtypes that can either have an excitatory or inhibitory effect on the postsynaptic neuron

membrane potentials that vary in magnitude and do not follow the all-or-none law like the action potentials

• Modulate neuronal activity
• Pain Signals
• Pain can be modulated by blocking action potential
• Tell brain you are receiving pain
• Modulatory pathway shuts down signals of experiencing pain

• Diffusion
• Enzymatic degradation
• Reuptake

Transmitter substance floats away from the synapse

The transmitter action is deactivated by an enzyme

The transmitter substance is returned to the presynaptic neuron

The axon synapses with a muscle

• Postsynaptic potetials (EPSPs and/or IPSPs) that are produced at different locations of the postsynaptic membrane of the neuron,
• Produced at the same time will be added together and produce a greater effect than each one by themselves and make it more likely to trigger an action potential

• Postsynaptic potentials (EPSPs and IPSPs) occur at different times.
• Single synapse may push the postsynaptic cell to threshold if many action potentials arrive in quick succession, thus the EPSPs overlap.

EPSPs and IPSPs can be added together as well and cancel each others postsynaptic effects.

• Open or close an ion channel in the membrane
• Alter the production of proteins
• Activate a gene in the nucleus via activation of transcription factors

Result of metabotropic receptors that initiate signals within the neuron

• Refers to changes in structure or biochemistry of synapses:
• Increase number of postsynaptic receptors
• Increase the size of the postsynaptic membrane
• Send signals to the presynaptic neuron to release more neurotransmitter
• Any change that alters how 2 neurons communicate

• Ionotropic:
• 4/5 units
• Contains intrinsic ion channel that opens in response to a NT
• No 2nd Messenger
• Fast
• Change in membrane potential
• There are subtypes

• Metabotropic:
• 1 subunit
• Contains G protein that becomes acctive in reponse to a NT
• 2nd messenger
• Slower
• Varies in effects (gene expression, open or close an ion channel)
• There are subtypes

Decrease in the release of neurotransmitters from the presynaptic membrane (despite the occurrence of an action potential) caused by the action of another neuron.

Enhanced release of neurotransmitters from the presynaptic membrane cause by the action of another neuron

Stimulation of autoreceptors by neurotransmitter that was released from the presynaptic neuron which causes a decrease in subsequent neurotransmitter release