5.3 Neuronal Communication Flashcards
Define a sensory receptor
cells, tissues, organs that receive a stimuli and transduce them into electrical impulses
Define a pacinian corpuscle
Transduces mechanical pressure changes into electrical impulses
Describe the structure of a Pacinian Corpuscle
Sensory neurone ending wrapped by layers of lamellae (layers of connective tissue with Na+ ions in sol. between layers), with a myelinated sensory neurone leading out of it.
How does a stimulus activate a sensory receptor?
-RESTING POTENTIAL
- stimulus depolarises receptor cells with a GENERATOR POTENTIAL
- triggers depolarisation along neurones called an ACTION POTENTIAL
-depolarising effector -> response
-no more stimulus -> re-polarisation
What is a resting potential in a neurone
when the charge inside is more negative than outside the cell is at resting potential as it is polarised.
How is Pacinian Corpuscle depolarised?
-maintained at resting potential (more negative outside than inside) by Na+/K+ ion channels A.T ions in and out of cell (Na+ out, K+ in)
-stretch activated Na+ ion channels open and Na+ ions diffuse in, depolarising cell, becomes more positive inside than outside.
What are the key similarities between neurones? (5)
- contains dendrites that receive impulses
-cell body containing mitochondria and nucleus
-contain axons that send action potentials to other neurones
-most sensory and motor neurones are myelinated
-all contain voltage gated Na+ ion channels
What are the shapes of relay, sensory, and motor neurones
Sensory: unipolar
Motor: multipolar
Relay: multipolar
describe the myelination of relay, sensory, and motor neurones
Sensory & motor: myelinated
Relay: unmyelinated
Where are the sensory, motor, and relay neurones located?
Sensory: dorsal root ganglion
Motor & Relay: CNS
How is a stimulus generated?
- resting potential maintained by Na+/K+ ion channel A.T
-stimulus opens voltage gated Na+ ion channel, depolarises cell membrane
-local current activated Na+ ion channels further down eventual action potential generated- membrane fully depolarised
-As membrane further down depolarised, initial part re-polarised
-Na+ ion channels shut and some K+ ion channels also shut leading to the hyper polarisation of the cell
-Na+/K+ ion channels re-establish resting potential.
Describe positive and negative feedback in stimulus generalisation
Positive feedback:
opening of voltage gated Na+ ion channels leads to generation of local current which leads to opening of more Na+
Negative feedback: after depolarisation of the membrane, voltage-gated Na+ ion channels close and K+ is opened to re-polarise membrane
Describe the propagation of action potential in myelinated vs. non-myelinated neurones
Myelinated:
saltatory conduction is when…
-myelinated neurones only depolarise at nodes of ranvier
-long local currents cause action potentials to jump between nodes of ranvier
-this leads to a faster propagation of action potential
Non-myelinated:
-myelinated neurones depolarise across the whole axon
-short local currents only cause depolarisation of neighbouring part of axon
-longer propagation of action potential
What is a good way in describing the ‘feasibility?’ of action potential
All or nothing
(because the threshold has to be reached in order to generate an action potential)
Define a cholinergic synapse
A synapse that releases the neurotransmitter Acetyl choline (ACh) into the synaptic cleft.
(excitatory)
Define a GABA-ergic synapse
A synapse that releases the neurotransmitter GABA into the synaptic cleft
(inhibitory)
Describe the excitatory process that occurs at the cholinergic synapse
-Depolarisation reaches pre-synaptic membrane
-causes voltage-gated Ca2+ ion channels to open and Ca2+ to diffuse in
-Causes vesicles containing ACh to fuse to pre-S.M and release ACh into synaptic cleft
-ACh bind to comp. receptors on Na+ ion channels, allowing Na+ to diffuse into post-S.M
-This contributes to the generation of excitatory post-synaptic potential
-If enough EPSPs are formed, an action. potential will be generated
-An enzyme called acetylcholinesterase breaks ACh into ethanoic acid and choline
-Detach from receptor as no longer complimentary
-No more Na+ diffuse in
-Ethanoic acid and Choline diffuse back into pre-S.M where they are recombined using ATP to form ACh
Define what an excitatory post-synaptic potential is (EPSP)
The amount of depolarisation that occurs on the post-synaptic membrane caused by the release of ACh from one action potential arriving at an excitatory pre-synaptic membrane
Name the two types of summation
temporal and spatial
How does temporal summation lead to the generation of an action potential?
more than one action potential reaches the pre-synaptic membrane, releasing more neurotransmitter, leading to more EPSPs
How does spatial summation lead to the generation of an action potential?
action potentials arrive from different pathways, releasing more neurotransmitters, creating multiple EPSPs
Define an inhibitory post synaptic potential (IPSP)
The HYPERpolarisation of the post-S.M caused by the release of GABA by one action potential arriving at the inhibitory pre-S.M
What does GABA do?
binds to Cl- receptors on post-synaptic membrane causing Cl- to diffuse in and hyper polarise the post-S.M
why may different neurones have different amplitudes and durations?
Different type/number of
sodium/potassium pumps in neuron membrane
* Different type/number of potassium ion channels
* Different electrochemical gradients
* Different type/more voltage-gated sodium and potassium ion channels
