Introduction to Neurones, Excitatory and Inhibitory Neurotransmission in the CNS Flashcards
What is the role of the dendrite?
Receive inputs from other neurones and convey graded electrical signals passively to the soma
What is the role of the cell body (soma)?
Synthetic and metabolic centre. Integrates incoming electrical signals that are conducted passively to the axon hillock.
What is the role of the axon hillock and initial segment?
Site of initiation of the ‘all or none’ action potential
What is the role of the axon ?
Conducts output signals as action potentials to the presynaptic terminal. Mediates the transport of materials between the soma and presynaptic terminal and vice versa
What is the role of the synapse?
Point of chemical (usually) communication between neurones (or other cells)
Define unipolar, pseudo unipolar, bipolar and multipolar neurones?
Unipolar: one neurite
Pseudounipolar: one neurite that bifurcates ‘splits’
Bipolar: two neurites
Multipolar: three or more neurites
Where would you find a unipolar neurone?
Peripheral autonomic neurone
Where would you find a pseudo unipolar neurone?
Dorsal root ganglion
Where would you find a bipolar neurone?
Retinal bipolar neurone
Where would you find a multipolar neurone?
Lower motor neurone (LMN)
What are the four functional regions of a neurone?
Input
Integrative
Conductile
Output
What is overshoot?
When polarity is reveres to inside positive
Why do passive signals not spread far from their site of origin?
Due to current loss across the membrane accompanied by a reduced change in potential
How can the passive current spread and action potential velocity be increased?
Decrease ri (by increasing axon diameter) Increase rm (adding myelin)
What is saltatory conduction?
When action potential jumps from one node of ranvier to the next
What is found in the chemical synapse?
A matrix of fibrous extracellular protein
Describe the differentiators of pre-synaptic vs post-synaptic membranes?
Presynaptically- active zones around which vesicles cluster
Postsynaptically- the postsynaptic density containing neurotransmitter receptors
What are the three types of synapse?
Axodendritic
Axosomatic
Axoaxonic
Wha tis the commonest type of synapse?
Axodendritic
How can synapses be classified functionally?
Excitatory or inhibitory
What is the most frequent excitatory neurotransmitter?
Glutamate
What is the most frequent inhibitory neurotransmitter?
y-aminobutyric acid (GABA) or glycine
Describe the action of glutamate
Activates postsynaptic, cation selective, inotropic glutamate receptors generating a local, graded, excitatory (depolarising) response: the excitatory postsynaptic potential
Describe the action of GABA or glycine?
Activates postsynaptic, anion selective, inotropic, GABAa or glycine receptors, generating a local, graded inhibitory hyperpolarising response: the inhibitory postsynaptic potential
Which cation receptors are activated in excitatory synaptic transmission?
Na+ receptors
Which anion receptors are activated in excitatory inhibitory transmission?
Cl-
What types of synaptic integration are there?
Spatial and temporal integration
What is spatial summation?
Many inputs converge upon a neurone to determine its output
What is temporal summation?
A single input may modulate output by variation in action potential frequency of that output
What substances are released from synaptic vesicles?
Acetylcholine, amino acids and amines
What substances are released from secretory vesicles?
Peptides
What substances can mediate fast neurotransmission?
Glutamate, GABA, glycine, acetylcholine, 5-HT can activate inotropic ligand-gated ion channels (LGICs), which mediate fast transmission
What substances can mediate slow neurotransmission?
All but glycine can activate metabotropic G-protein-coupled receptors. these mediate relatively slow neurotransmission
What are the two modes of action of neurotransmitters on ion channels?
Direct or indirect
Describe direct gating?
done by inotropic receptors. The receptor is an integral component of the molecule that forms the channel it controls. Gating of channel is rapid
Describe indirect gating?
Mediated by activation of metabotropic receptors. receptor and the channel it controls are distinct. Gating of channel is slower (10ms)
Cholinergic synaptic transmission in autonomic ganglia display both ____ and ________ transmitter actions
Cholinergic synaptic transmission in autonomic ganglia display both direct and indirect transmitter actions
In autonomic ganglia fast EPSP is due to activation of ______ (________) ACh receptors. Channels conduct ___ and ___.
In autonomic ganglia fast EPSP is due to activation of nicotinic (ionotropic) ACh receptors. Channels conduct Na and K.
In autonomic ganglia slow EPSP is follows activation of ______ (________) ACh receptors. ACh closes a K channel (______)
In autonomic ganglia slow EPSP is follows activation of muscarinic (G protein-coupled) ACh receptors. ACh closes a K channel (M-type)
How does glutamate have an inhibitory effect?
Via its response at metabotropic glutamate receptors
What are the types of inotropic glutamate receptors?
non-NMDA (bind agonists kainate or AMPA- controlling a channel permeable to Na and K)
NMDA controls a channel permeable to Na, Ca, K
Non-NMDA inotropic receptors mediate _____ ________ ______ in the CNS whereas NMDA contributes a _____ ______ to the excitatory synaptic potential
Non-NMDA inotropic receptors mediate fast excitatory synaptic transmission in the CNS whereas NMDA contributes a slow component to the excitatory synaptic potential
What are phencyclidine and ketamine blockers of?
Selective blockers of NMDA operated channels
What is the role of metabotropic glutamate receptors?
To modulate neurotransmission- presynaptic inhibition of Ca2+ channels
