Neurophysiology and Neurosecretion Flashcards
Describe the anatomy of the neuron?
Cell body from which high branched nerve processes called dendrites and a single axon extend
What are dendrites covered by?
Dendritic spines
What does dendritic spines do?
form connections or synapses with dendritic spines of other neurons
Where does the Axon arise from?
Axon hillock
Describe an axon?
At its end an axon will branch forming telodendria
How is telodendria terminated?
By small swellings called presynaptic terminals or boutons
What does Presynaptic terminals contain?
Small vesicles
What does the Vesicles contain?
Chemical messengers or neurotransmitters
Describe the Process of Axonal transport?
neurotransmitters are synthesised in the nerve cell body and transported down the axon
What are the 3 major neuron types?
Multipolar, Unipolar and Bipolar
What is the Resting Membrane Potential?
is when the Inside of a nerve cell has negative potential in relation to the positive electrical potential contained in extracellular fluid
How is an Electrical gradient created?
Cells pump NA from interior to exterior fluid to swap NA for K, the high extracellular conc of NA and High intracellular conc of K causes this
What happens when the cell reaches RMP?
Cell becomes polarised
How does the Cell become polarised?
When K enters cell following electrical gradient but move out the cell along its own conc gradient and the forces are balanced
How can RMP value be calculated?
Nernst equation, average -70 to -90mV
What is the C0 and C1 (conc in and out of k) normally?
5mM and 140mM respectively
How can NA channels open in localised changes of RMP?
Through voltage gated channels
How can NA channels open in Neurotransmitter activation?
Ligand gated channels
How does the Cell become depolarised?
During an Action potential when NA channels open and NA enters cells
What are the small internal electric currents set up by the AP called?
Intrinsic/local currents
How does Intrinsic currents conduct AP?
Open voltage gated NA channels initiate another AP
What prevents the backflow of excitation?
The inactive/refractory period
How is a Inactivation period created?
Once voltage gated NA channels has opened and closed it goes through period of inactivation
How is conduction velocity enhanced?
Myelination of Axons
How is the myelin sheath formed?
Cells called Schwann cells
What does the myelin sheath do?
Wraps around axons to form 1mm sheath leaving short stretch of unmyelinated axon before next schwann cell
How does Myelin sheath function?
Increasing the conductivity of the axon which increases conductivity of intrinsic currents increasing conduction velocity
What do local anaesthetics target?
Voltage gated ion channels as have high affinity for NA ion channels in open state
What increases the effect of the local anaesthetic?
Exhibit use dependant block which creates more channels to open, maintains in inactivated state
What does maintenance in inactivated state mean?
Cell cant be re-stimulated
What is a synapse?
Junction between a neuron and target cell
Whar are the 2 types of Synapses?
Electrical and Chemical
How does Electrical Synapses work?
Transmission via pores (gap j), allows rapid communication between neurons found in smooth and cardiac muscle
What does the Chemical synape consist of?
Pre-synaptic membrane at pre-syn terminal of an axon and post-syn membrane
What seperates the pre- and post-synaptic membranes?
Synaptic cleft
How is a post-synaptic potential initiated?
AP in presyn activates release of neurotransmitter molecules into synaptic cleft that bind to specific receptors opening ligand gated channels
What happens if the post-syn potential is large enough?
Elicit an AP in the target neuron
What are 3 classical neurotransmitters?
AA, Monoamines, Purines
Give me an example of AA neurotransmitters?
Glutamate, Gabba, Glycine
Give me an example of Monoamine neurotransmitters?
ACh, Dopamin, NA, Adrenaline, Sertonin, Histamine
Give me an example of a Purine Neurotransmitter?
Adenosine, ATP
When fired where the does AP reach?
Synaptic bouton
What enters and opens the boutons?
Calcium channels open to release calcium
What protein is Calcium detected by?
Synaptotagmin
What does Synaptotagmin do?
Promotes formation of SNARE complex between snare proteins
What is the SNARE protein embedded in the vesicle membrane?
Protein Synaptobrevin
What are the SNARE proteins associated with pre-syn membrane?
Protein Synatacin and SNAP-25
How does a neurotransmitter release at an active zone?
Vesicle and pre-syn membranes fuse - then diffuse across synapse
How does a neurotransmitter get back into the neuron?
It binds to the receptor and is broken down and recycled back
Where do neuropeptides release?
From any location of the terminal membrane
What do neuropeptides require to be released?
High concentrations of calcium to increase cell firing rate
What is co-transmission?
More than 1 neuropeptide being released from single synapse
What is the control of neurosecretion mediated by?
Autoreceptors and heteroreceptors
What do Autoreceptors do?
Monitors self secretion
What does hetroreceptors do?
Transmission from other synapses
What do the receptors function as part of?
Localised negative feedback system
What are sub-threshold potentials?
Inhibitory postsyn (ISPS) or Excitatory postsyn (ESPS)
What are the 3 Mechanisms behind neurotransmitter inactivation?
Reuptake
Enzymes
Diffusion
How does Reuptake mechanism work?
Ion gradients with high affinities
How does Enzyme mechanism work?
AchE (acetate and choline) blocked by organophosphates
How can Diffusion mechanism work?
Route for peptides as they are large so have prolonged effects
