synapses Flashcards
What is synaptic transmission?
process of signal travelling from a neuron to a muscle.
Where does the process of action potential transmission occur?
-in the axon of the pre-synaptic neuron
Where does the process of synaptic transmission occur?
- occurs in the synaptic region- where information is transferred from the pre-synaptic neuron to the post synaptic neuron.
- A similar process occurs at the junction between a motor neuron and a muscle fibre.
What are the 2 alternatives to explain the process of synaptic transmission?
- Electrical - potential goes directly from one cell to next
- Chemical- chemical is released by presynaptic neuron.
What is the evidence for chemical synaptic transmission?
- Synaptic cleft- as its the section between the 2 neurones and if neurones are not touching each other then it cant be electrical
- Synaptic delay- there is a delay of 0.5-0.8msec which means that a chemical must be involved unlike an electrical signal which is fast
- Classic Otto Loewi experiment- 1 heart attached to a vagus nerve, whenn stimulating vagus nerve the heart would slow down. Then he attached 2 hearts with the vagus nerve and they both slow down. This could only happen from a chemical being released from a vagus nerve
What is the classic Otto Loewi experiment?
- Take heart with a vagus nerve attached to it
- kept heart alive in a perfusion chamber
- when stimulated vagus nerve -heart slowed down
- however when he connected the perfusion beaker to another perfusion beaker with a heart in it- when he stimulated the vagus nerve on the first heart the 1st and 2nd heart both slowed down
- shows synaptic transmission mediated by chemicals.
What are electical synapses?
- adjacent cells joined via gap junctions (membrane proteins of 2 cells fuse and make a channel) , thus ionic continunity between cells
- fast (transmission of a.p)
- Gap junctions are inflexible- can’t modify the A.P
What do gap junctions act as?
electrical synapses
What does it mean if the electrical synapse is inflexible?
you can transmitt action potential but cant modify action potential
Why are electrical synapses fast?
No neurotransmitter is released
action potential potential will go from neurone directly to the post synaptic neurone
Where are electrical synapse?
You have them in your heart and muscles of eye
What is the structure of a chemical synapse?
mitochondria
vesicles ( containing neurotransmitter)
synaptic cleft- 30-40nm wide
post synaptic receptors- for neurotransmitters to bind onto protein receptors
Why does the presynaptic area has lots of mitochondria?
its very energy intense
What are the inital stages of chemical synaptic transmission?
- the arrival of an action potential causes the influx of ca2+- when synaptic ending is depolarised
- this causes the vesicle to migrate towards the presynaptic membrane
- here it fuses with the meembrane and releases the neurotransmitter via exocytosis into synaptic cleft
- the transmitter diffuses down the concentration gradient across the synaptic cleft and binds to post synaptic receptors changing the shape of the protein and ion channels open and diffuse
What can a single post synaptic cell receive their synaptic input from?
from several thousand presynaptic neurons
What is motor endplate?
- junction between nerve cell and muscle cell
- a neuromuscular junction
What is the experiment of recording from 2 points on a muscle fibre following neural stimulation?
1, A motor neurone is stimulated
- 2 electrodes put on muscle cell
- action potential recorded on the muscle cell
-if you record a.p far away from synaptic region- normal looking a.p
if you record a.p close to motor endplate- you Geta. small positive bump- which is known as the endplate potential- which triggers a.p
What is an endplate?
when recording the action potential close to where the stimulus was, you have a positive bump
What did the drug curare do?
Used a drug curarae
It stopped action potential in muscle cells/skeletal- paraylsis/not able to move
Ended in endplate potential
What is an endplate potential?
when the action potential on a muscle fibre can be abolished by curare, revealing the endplate potential (triggering the action potential)
What is a neurotransmitter?
ACH