SYNAPTIC PHYSIOLOGY Flashcards
A functional connection or junction between two nerve cells (neurons)
Synapse
What types of cells are involved in a synapse?
Neurons and other types of cells
Axon terminal synapses on the cell body (soma)
Axo-somatic Synapse
Axon terminal synapses on a dendrite
Axo-dendritic Synapse
The synapse between two axons
Axo-axonic Synapse
Synapse between two dendrites
Dendro-dentritic Synapse
- Blocked in its transmission
- Changed from a single impulse to a repetitive impulse
- Integrated with impulses of other neurons
How information is transmitted in the CNS mainly in the form of nerve action potentials
[Electrical/Chemical Synapse]
Low-resistance allows current flow directly & passively from one cell to another
Electrical Synapse
[Electrical/Chemical Synapse]
Fast and bidirectional
Electrical Synapse
[Electrical/Chemical Synapse]
Found mostly in Central Nervous System (CNS) and ciliary ganglia in eye muscles
Electrical Synapse
[Electrical/Chemical Synapse]
Unidirectional transmission
Chemical Synapse
[Electrical/Chemical Synapse]
Neurotransmitter binds to receptors on post-synaptic neurons altering their membrane potential
Chemical Synapse
[Neuroreceptors/Autoreceptors]
Receptors found on the presynaptic neuron
Autoreceptors
[Neuroreceptors/Autoreceptors]
Produce presynaptic inhibition
Autoreceptors
[Neuroreceptors/Autoreceptors]
Lessen the number of chemical messengers able to bind with the receptors in the post-synaptic neuron
Autoreceptors
[Neuroreceptors/Autoreceptors]
Chemical-gated ion channels in the membrane of the cell that is receiving the nerve impulse (post-synaptic neuron)
Neuroreceptors
Substance that mediates chemical signaling between neurons
Neurotransmitters
Production and storage of neurotransmitters
Vesicles at the axon terminal
2 Types of Neurotransmitter Receptors
- Ionotropic Receptors
- Metabotropic Receptors
What leads to the release of neurotransmitters?
Increase in intracellular Ca2+ levels
How is a neurotransmitter released from the axon terminal?
Via exocytosis
[Ionotropic/Metabotropic Receptors]
Ionic channels themselves
Ionotropic Receptors
[Ionotropic/Metabotropic Receptors]
Fast responses due to binding of ligand to receptors
Ionotropic Receptors
[Ionotropic/Metabotropic Receptors]
Act indirectly on separate ion channels through a G protein and/or second messenger
Metabotropic Receptors
[Ionotropic/Metabotropic Receptors]
Slower response due to the use of 2nd messengers to relay signal
Metabotropic Receptors
[Ionotropic/Metabotropic Receptors]
Biochemical events will happen before the expected result comes through
Metabotropic Receptors
2 Types of Post-synaptic Potentials
Excitatory Postsynaptic Potential (EPSP)
Inhibitory Postsynaptic Potential (IPSP)
[EPSP/IPSP]
Excitatory chemical synapses generate an EPSP, which brings the membrane potential closer to threshold
EPSP
[EPSP/IPSP]
Usual effect is to open non-selective Na+ and K+ channels
EPSP
[EPSP/IPSP]
Inhibitory chemical synapses generate IPSP, which makes the membrane potential more negative
IPSP
[EPSP/IPSP]
Open Cl- and K+ channels
IPSP
- Tetanus toxin
- Prevents vesicle fusion with membrane
- Causes increased muscle contraction
Clostridium tetani
- Causes muscle paralysis by inhibiting neurotransmitter release
- Bacili toxin (Botulism)
- Interferes with SNARE proteins at excitatory synapses that activate muscles
Clostridium botulinum
What are the therapeutic uses of low doses of botulinum toxin (Botox)?
Treating facial wrinkles, severe sweating, uncontrollable blinking, and misalignment of the eyes
What must be removed to terminate the signal in a chemical synapse?
Neurotransmitter
How is the removal of neurotransmitters accomplished in a chemical response?
Through diffusion of transmitter from the cleft, degregation of transmitter by enzymes, and reuptake into the pre-synaptic cells for reuse
The alteration of the efficacy of synaptic transmission by fine-tuning or changing a signal from EPSP to IPSP
Neuromodulation
Site of ACh production and enzyme involved
Presynaptic axon and Choline Acetyl Tranferase (CAT)
[Intrinsic/Extrinsic]
Both from one presynaptic neuron
Intrinsic
[Intrinsic/Extrinsic]
Two different synaptic neurons releasing neuropeptides
Extrinsic
What are the two types of receptors for neuromodulators?
Muscarinic and Nicotinic receptors
- Modify both the presynaptic and the postsynaptic cell’s responses to specific transmitters
- Tend to be associated with slower events
Neuromodulators
- Bring about changes in metabolic processes in neurons
- Can occur over minutes, hours or days
Neuromodulator receptors
What enzyme is responsible for the synthesis of acetylcholine?
Choline aceytl transferase (CAT)
- Released by cholinergic neurons are both found in CNS and PNS
- Acts at muscarinic (G-protein coupled) or nicotinic (ion channels) receptors
Acetylcholine
[Muscarinic/Nicotinic Receptors]
Mostly in the parasympathetic nervous system
Muscarinic Receptors (M1 to M5)
[Muscarinic/Nicotinic Receptors]
Found at neuromuscular junctions of skeletal muscles and both sympathetic and parasympathetic nervous systems
Nicotinic Receptors
It causes paralysis
a. Overstimulation
b. Desensitization
b. Desensitization
Causes uncontrolled muscle contractions
a. Overstimulation
b. Desensitization
a. Overstimulation
Sarin receptors
- Overstimulation
- Desensitization
What is the initial treatment for alleviating symptoms of Parkinson’s disease?
Drug L-Dopa
Neurons associated with the ACh system degenerate in people with this disease
Alzheimer’s disease
- Loss of dopamine-releasing neurons in the substantia nigra
- Not curative
Parkinson’s disease
An experimental treatment for Parkinson’s disease involving the surgical implantation of electrodes
Deep brain stimulation
A type of cell transplant used in experimental treatments for Parkinson’s disease
Fetal/stem cell transplants
Which biogenic amines are involved in Parkinson’s disease?
- Dopamine
- Norepinephrine
- Epinephrine
- Classical modulator with multiple effects
- Mainly excretory chemical inducing physical & mental arousal
- Mediates heart rate, bp, rate of glycogen
Norepinephrine and Epinephrine
Where is NE utilized as a neurotransmitter?
In the CNS and PNS
Where is Epi mainly utilized as a neurotransmitter?
Mainly in the PNS
What types of receptors are adrenergic receptors?
G protein coupled receptors
To what are adrenergic receptors generally linked?
Second messenger presetssignal transduction pathways
What is another name for Biogenic Amines?
5-hydroxytryptamine or 5-HT
Where are the majority of Biogenic Amines, specifically serotonin, found in the body?
Enterochromaffin cells in the gut (90%)
Besides the gut, where else are Biogenic Amines, specifically serotonin, found in the body?
Platelets and immune cells (8%)
Brain stem (1-2%)
Inhibits pain pathways in the spinal cord and higher regions of the nervous system and helps control mood
Serotonin
What is the major location of histamine in the CNS?
Hypothalamus
What type of actions is histamine commonly known for?
Paracrine actions
What is histamine involved in?
Allergic reactions, nerve sensitization, and acid production in the stomach
The primary neurotransmitter at 50% of the excitatory synapses in the CNS.
Glutamate
What is the cooperative activity of AMPA and NMDA receptors implicated in?
Long-term potentiation (LTP), a cellular process underlying learning and memory
What is excitotoxicity related to NMDA receptors?
Injury caused by excessively stimulating nearby neurons, leading to toxic levels of intracellular Ca2+
What is the main function of GABA neurons in the brain?
Dampen activity within neural circuits
What is the result of GABA binding to ionotropic receptors?
Increases Cl- flux into the cell, resulting in hyperpolarization of the postsynaptic membrane
What are some compounds that have additional binding sites on the GABA receptor?
Steroids, barbiturates, and benzodiazepines
How do benzodiazepine drugs like alprazolam affect the GABA receptor?
They increase Cl- flux through the GABA receptor, reducing anxiety, guarding against seizures, and inducing sleep
Which amino acid from inhibitory interneurons in the spinal cord and brainstem binds to ionotropic receptors on postsynaptic cells?
a. GABA
b. Glycine
b. Glycine
Causing convulsions and spastic contractions of skeletal muscles
Strychnine poisoning
Short chains of amino acids with peptide bonds are released by neurons and act on receptors throughout the CNS.
Neuropeptides
What are the mechanisms of action of neuropeptides?
They are released to terminals, acted upon by peptidases, and can work synergistically with classic neurotransmitters
What are neuropeptides known as endogenous opioids?
Enkephalins and endorphins
What are morphine and codeine primarily used for?
Pain relief, including anesthesia
What neuropeptide is released by afferent neurons involved in pain sensation?
Substance P
How are gases like nitric oxide released?
- Not released by exocytosis of presynaptic vesicles
- Produced by enzymes in axon terminals
What happens to nitric oxide once in the target cell?
Activates cGMP signaling pathways
What medical condition is associated with cGMP signaling pathways and nitric oxide?
Erectile dysfunction
Where is adenosine present?
In all pre-synaptic vesicles
What triggers the release of adenosine?
Ca2+ influx into the terminal
What kind of receptors does adenosine have?
Both presynaptic and postsynaptic receptors
Where can adenosine act as a transmitter?
At synapses in PNS and CNS
What is adenosine responsible for in small purines?
Sympathetic vasoconstriction
What is the function of Acetylcholine in the heart?
Inhibiting heart muscle, specifically through the vagus nerve
Neurotransmitters that INCREASE the likelihood of an action potential in the postsynaptic neuron.
Excitatory neurotransmitters
Neurotransmitters that DECREASE the likelihood of an action potential in the postsynaptic neuron.
Inhibitory neurotransmitters
- Released by neurons that originate in the substantia nigra
- Primarily inhibitory transmitter
Dopamine
What channels open when dopamine is released?
Na+ channels
What channels open when GABA is released?
Cl- channels
What happens when Na+ channels open in the neuron?
Na+ ions enter the cell
What happens when Cl- and K+ channels open in the neuron?
Cl- ions enter and K+ ions exit the cell
What happens to the charge inside the cell during depolarization?
It becomes less negative
What happens to the charge inside the cell during hyperpolarization?
It becomes more negative
A change in the membrane potential that makes it less negative, increasing the likelihood of an action potential.
Depolarization
