structure of the synapse
When an impulse arrives at a synaptic knob.
-causes calcium ion channels to open. (If no impulse, no reaction) -This results in calcium ions diffusing into it from the surrounding fluid. -The calcium ions cause some of the synaptic vesicles to move towards the presynaptic membrane •The vesicles fuse to the presynaptic membrane and discharge a neurotransmitter (acetylcholine) into the synaptic cleft. •The neurotransmitter (acetylcholine) diffuses across the cleft to the postsynaptic membrane •.The neurotransmitter binds to receptor sites on the sodium ion channel in the membrane of the postsynaptic neuron •This causes the sodium ion channels to open and sodium ions enter the post synaptic neuron diffusing rapidly along a concentration gradient. •The influx of sodium ions generates a new action potential in the postsynaptic neuron •Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid, which diffuses back across the synaptic cleft into the presynaptic neuron •Sodium ion channels close in the absence of acetylcholine in the receptor sites. •ATP released by mitochondria is used to recombine choline and ethanoic acid into acetylcholine.
The brain and central nervous system
-contain neurons that release acetylcholine. Here, the cholinergic synapse can influence a variety of processes. -Memory is an important process that these synapses are involved in. -Learning seems to strengthen the connection of these synapses, by making the postsynaptic, or recipient, cell more sensitive to acetylcholine -Alzheimer's disease is thought to cause memory problems by damaging cells that produce this neurotransmitter, thereby weakening synaptic connections
•It is believed that in Alzheimer's disease disrupts the neurotransmitters that cross the cholinergic synapses
...
Acetylcholine is made up of two parts:
1.Acetyl (ethanoic acid) 2.Choline
The structure of a neuromuscular junction.
1.Presynaptic terminal motor neuron 2.Postsynaptic muscle membrane (Sarcolemma) 3.Synaptic vesicle 4.Receptor 5.Mitochondria
•Stage 6
ATP released by the mitochondria is used to recombine choline and ethanoic acid into acetylcholine. This is stored in vesicles for future use.
•Stage 3
Acetylcholine diffuses across the synaptic cleft. It binds to specific receptor sites on the sodium ion channel in the postsynaptic neuron membrane.
•Stage 5
Acetylcholinesterase breaks down acetylcholine into choline and ethanoic acid. The removal of acetylcholine from the receptors cause sodium ion channels to close in the membrane of the postsynaptic neuron. The products diffuse back across the synaptic cleft into the presynaptic neuron
What happens at a cholinergic synapse? •Stage 1
An action potential arrives at presynaptic membrane. •Voltage gated calcium channels in the presynaptic membrane open. Calcium ions enter the presynaptic neuron
•Stage 2
Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane. The neurotransmitter acetylcholine is released into the synaptic cleft.
•Stage 4
Sodium channels open. •Sodium ions diffuse into the postsynaptic membrane causing depolarization. •This may initiate an action potential.
acetylcholine
The chemicals used to send messages are known as neurotransmitters, and one important type of neurotransmitter is __
synaptic cleft
The narrow gap that separates the presynaptic neuron from the postsynaptic cell.
Difference between ionotropic receptors and metabotropic receptors
While ionotropic receptors are typically ligand-gated ion channels, through which ions pass in response to a neurotransmitter, metabotropic receptors require G proteins and second messengers to indirectly modulate ionic activity in neurons.
A cholinergic synapse
a gap where a neuron that produces acetylcholine sends messages to other neurons, or to skeletal muscle cells.
Cholinergic synapse
a junction between two cells that employs acetylcholine as its transmitter substance.
Ionotropic receptors
acetylcholine released into the synapse, and open ion channels in the receiving cell's membrane.
Acetylcholine
enables muscle action, learning, and memory
Cholinergic synapse
essential to muscle movement any neuron sending messages to muscle does so through a cholingeric synapse
Synapse
junctions between cells that allow for the transmission of chemical messages.
Acetylcholine that is released opens ion channels in the _ causes it to contract.
muscle cell,
A post-synaptic neuron
neuron that receives the signal
sarcolema
post synaptic muscle membrane
Ionotropic receptors directly gate ion flow into cells, leading to either excitatory or inhibitory responses in _
postsynaptic neurons
The neuron that sends nerve impulses by releasing neurotransmitters via the axon terminal at the synapse is called a __
presynaptic neuron
Metabotropic receptors
receptors that are associated with signal proteins and G proteins After acetylcholine binds a receptor at a cholinergic synapse, another protein is activated. This protein, called a second messenger, can have a variety of effects on the cell. It may cause an ion channel to open, or it can induce changes in the cell itself.
At the end of the axon terminal;
releases acetylcholine and causes muscles to move
A cholinergic synapse
•These types of synapse are common in vertebrates. •They occur in the CNS and at neuromuscular junctions. •In cholinergic synapse the neurotransmitter is acetylcholine. Acetylcholine is made up of two parts: •1.Acetyl (ethanoic acid) 2.Choline the neurotransmitter is the acetylcholine
