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What is a synapse?
A functional association of a neuron with another neuron or effector organd.
What are the types of synapses?
Describe electrical synapses.
- Two neurons linked together by a gap junction.
- Functions: rapid communication, bidirectional communication, excitation and inhibition at the same synapse.
- Some are between neurons and gleal cells.
Describe chemical synapses.
- Neurotransmitter is released in response to an action potential arriving at axon terminal.
- Signal transduction occurs.
- Two types: Excitatory and inhibitory.
What are the components of a synapse?
- Axon terminal
- Synaptic vesicles with a neurontransmitter
- Voltage-gated calcium ion channel
- synaptic cleft
- Reuptake molecule.
Name and describe the three types of neuron to neuron synapses.
- Axondendritic: presynaptic neuron axon terminal forms synapse with a dendrite of postsynaptic neuron.
- Axosomatic: presynaptic neuron axon terminal forms synapse with the cell body of a postsynaptic neuron.
- Axonaxonic: presynaptic neuron axon terminal forms synapse with the postsynaptic neuron's axon terminal.
Describe communication across a synapse.
- 1. Action potential
- 2. Voltage-gated Ca2+ channels open
- 3. Calcium triggers exocytosis
- 4. Neurotransmitter difuses and binds to a receptor
- 5. Response in cell
What is synaptic delay and what is its cause?
- Delay between arrival of an action potential and change in postsynaptic membrane voltage.
- It is caused by changes in Ca2+ and realease in neurotransmitter.
What are the types of signal transductions at synapses?
- Channel-linked receptors: (ionotropic receptor) Fast and direct acting.
- G-protein linked receptors: (Metabolic receptors) Slow acting
What is postsynaptic potential?
A change in membrane potential in response to receptor-neurotransmitter binding.
How do EPSPs and IPSPs effect the membrane potential?
- EPSPs : bring membrane closer to threshold
- IPSPs : bring membrane further away from threshold
What is summation?
Adding effects of graded potentials.
List and describe the types of summation.
- Temporal : one synapse through time.
- Spatial : several synapses same time
Describe the synthesis of Acetylcholine.
- Takes place in axon terminal.
- Acetyl CoA + choline ---choline acetyl transferase---> acetylcholine + CoA
Describe the breakdown of Acetylcholine.
Acetylcholine ---acetylcholinesterase---> acetate + choline
What is a Cholinergic synapse?
A synapse utilizing acetylcholine.
What are the types of cholinergic receptors?
- Nicotinic (Ionotropic)
- Muscarinic (Metabotropic)
What are biogenic amines derived from?
What are Catecholamines derived from?
What are three examples?
- Dopamine, Norepinephrine, Epinephrine
What is serotonin derived from?
What is Histamine derived from?
What are three categories of Biogenic Amines?
What two enzymes degrade biogenic amines?
- Monoamine oxidase
Describe the synthesis and storage of Biogenic amines.
- They are synthesised in the cytosol of the axon terminal.
- They are then packaged into synaptic vesicles.
Describe the locations where catecholamines are released.
- Dopamine : CNS
- Norepinephrine : CNS & PNS
- Epinephrine : CNS
List and describe Alpha adrenergic receptors.
- Alpha1: Greatest affinity for norepinephrine. Uses pospholipase C-Ca2+ second messenger system.
- Alpha2: greatest affinity for norepinephrine.
How do all beta receptors produce their effects?
By stimulating the production of cyclic AMP second messenger system.
List and describe the three types of Beta adrenergic receptors.
- Beta1: greatest affinity for norephinephrine
- Beta2: greatest affinity for epinephrine
- Beta3: in adipose tissue, physiological significance not established.
Where is Serotonin released from and what is its function?
- The lower brainstem.
- Regulating sleep and emotions.
Where is Histamine released from and what is function.
- Alergic reaction
What are the amino acid neurotansmiters at excitatory synapses?
- Glutamate : Most common
What are the amino acid neurotransmiters at inhibitory synapses?
- GABA : Most common