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Think it's about time we got this up and running again, don't you?
Here's my favourite bit of Unit 5 :D
A synapse, as we all know, is the small gap separating neurones.
The synapse is made up of the following:
- Pre-synaptic knob
- Post-synaptic knob
- Synaptic Cleft
An action potential can't travel across the synapse, so it has to be carried across by neurotransmitters.
Neurotransmitters are chemicals. They are stored in vesicles.
On the post-synaptic knob, there are chemical-gated ion channels in the membrane called neuroreceptors.
They have specific binding sites for the neurotransmitters.
Transmission Across The Synapse
1. At the end of the pre-synaptic knob, there are voltage-gated calcium channels. When an action potential arrives at the synapse, the channels open and there is an influx of calcium ions into the cell.
2. The calcium ions cause the vesicles containing the neurotransmitter chemicals to fuse with the cell membrane. The chemicals are then released by exocytosis. (Exocytosis is a cellular process where cells eject waste products or chemical transmitters (such as hormones) from the interior of the cell.)
3. The neurotransmitters then diffuse across the synaptic cleft.
4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane, causing the sodium channels to open. Sodium ions then flow into the cell.
5. The sodium ions cause the depolarisation of the membrane, and if the threshold is reached, the action potential will be fired.
6. The neurotransmitter is then broken down by a specific enzyme in the synaptic cleft. For example, the enzyme acetlycholinesterase breaks down the neurotransmitter acetylcholine. The breakdown products are absorbed by the pre-synaptic knob by endocytosis and used to re-synthesise more neurotransmitter.
:D Anyway that's enough from meee.
Got my info from www.biologymad.com
Muscle Contraction in short
1. action potential reaches muscle and goes across T-tubluals
2. This causes Calcium ions to diffuse into the scarcoplasm
3. Calcium binds to the molecule troponin in the actin fillimant
4. Troponin has a conformational change of shape causeing tropomyosin (which is attached to troponin) to reveal the actin-myosin bindng site
5. Myosin head binds to the site forming an actin-myosin cross bridge
6. Calcium also acivates ATPase which breaks ATP for energy
7. The energy released causes the Myosin head to move causeing th sarcomere to shorten
8. ATP is needed again to break the actin-myosin cross bridge
if there is still a stimulus the myosin head binds to another site and a new actin-myosin cross bridge is formed (no. 5)
9. Stimulation stops
10. Calcium leaves the binding site of troponin and is diffused via active transport back to the sarcoplasmic reticulum
11. As calcium has left the binding site of troponin, troponin goes back to its origional shape and tropomyosin once again blocks the actin-myosin binding site
12. The myosin head cant bind to the active site no more so the sarcomere goes back to its origional length
The End :)
Well Done Rob :D!
WOW u gud :o
Y U CRACKIN ON ABOUT KNOBS MAN I FIND DAT TINGZ OFFENSIVE
absolutely lurrv synapses