WEEK8 - module 3. The Synapse

Electrical synapse -> fast but there are no control

Leak channel -> RMP
Voltage gated channel -> transmit AP
Chemically gated channel ->
EXCITATORY Na+ come in
INHIBITORY K+ release Cl- come in

Fire an action potential or not ->
Summation of all the signals decide

Memory
: if we keep firing the neuron and release NT, 
Post synaptic neuron develop and build more receptors
: a set of neural pathways that are firing inside the brain

 

 

Learning objective

What are the differences between fast and slow cell to cell communication?

It depends on the type of synapse. Chemical synapse is usually slower than the electrical synapse. They need to secrete vesicles to the post synaptic cell, on the otherhand, cells are binded with cell junctions (tight junctions) in electrical synapses so the signals can be transmitted rapidly.

 

-Electrical synapse is a type of gap junction. They are very fast but cannot be controlled. They are mostly located in brain. Chemical synapses convert electrical signals to chemical signals to transmit the signal to another neurons.

 

What is a synapse?

Synpase is the space between post and presynaptic cells. Presynaptic cells release neurotransmitters to postsynaptic cells, which receive them with the receptors in the membrane. 

 

What are the structural and functional differences between chemical and electrical synapses? 

Chemical synapses are structurally fall apart. They release vesicles containing neurotransmitter to communicate with the postsynaptic cells. They can control signaling with changing the amount of neurotransmitters and make the signals excitatory or inhibitatory. Their signallings are slower than electrical synapses.

Electrical synapses are structurally binded together with cell junctions. Electrical signal changes the membrane permeability to ions, which in turn generate a transmission of the signals to the post synaptic cells. They are faster than the chemical synapes but they don't have any controls, and they can only be excitatory.

 

What are chemically-gated ion channels? 

Chemically gated ion channels have chemical binding site. Those chemicals are called ligand which changes channels permeability to entering ions.

 

What factors affect the size of the graded/postsynaptic potential?

The frequency of stimulus determines the size of the potential. The more frequently the stimulus come, the more neurotransmitters are released in the presynaptic cell, which produces granded potential in the postsynaptic cells.

 

 

What are the differences between excitatory and inhibitory synapses?

EPSP refers to excitatory postsynaptic potential. The potential of the cell membrane is increased, which is depolarisation. Na+ influx generates EPSP.

IPSP refers to inbitatory postsynaptic potential. The potential of the cell membrane is decreased, which is hyperpolarisation. K+ efflux or the Cl- influx affects to IPSP. 

 

Understand neural integration and its control of neuronal firing. What are spatial and temporal summation?

Temporal summation is recieving multiple action potential from a single cell. Every 1-15 msec, action potential coming from same synapes are added to the neuron.

Spatial summation refers to recieving multiple inputs from all different synapse at the same time. Action potential coming from all different synapse are added to the neuron at the same time.

Understand that there are number of different sorts of neural circuits, and what (broadly) each is involved

 

Describe the detailed steps at at the neuromuscular junction, the neurotransmitter released and the function of acetylcholinesterase

1. Action potential arrives at the axon terminal of the presynaptic neuron. 

2. It opens the Ca2+ voltage gated channels and the Ca2+ enters into the neuron. 

3. Ca2+ stimulates snare proteins to release vesicles which are packed with neurotransmitters.

4. When neurotransmitters(Acetylcholine) are released to the synaptic cleft, receptors in the muscle bind those NT. 

5. After the potential is generated in the postsynaptic membrane, the neurotransmitters are reuptaken, degraded by the acetylcholinerase enzyme, or diffused. 

 

Removing the neurotransmitter after the signalling is important because it regulates the level of neurotransmitter in the synapse, controlling how long a signal will last. And it is important for muscle to work properly. It should be contract when the real signals come.   

 

Understand how the patellar reflex works

Patellar ligament is tapped and the sensory receptors (proprioceptors in the muscle spindle in the quadriceps muscle) send the signal to the spinal cord. The motor neuron is synapsed in the spinal cord with the sensory neuron and it contracts the quadriceps to extend the knee. At the same time interneuron is synapsed with the sensory neuron and send the signal to the antagonist muscle neuron which is hamstring to flex while the knee is extended.

 

Describe the details of how skeletal muscular function is affected by myasthenia gravis, curare, organophosphates and botulism

Myasthenia gravis:

Curare:

Organophosphate:

Botulism:

 

 

PPT

https://www.youtube.com/watch?v=L41TYxYUqqs 

For multi cellular organisms, there are two types of long distance communication, which is the nervous system and the endocrine system.

The nervous system is carried out by the connection, the synapse. There are chemical and electrical synapse.

 

 

 

 

SYNAPSE

*Where else in the body do we find gap junctions that allow for synchronized electrical activity of large numbers of cells? 

We can find gap junctions that are used for synchronised electrical activity in the heart. Cardiac muscle cells have intercalated discs, gap junctions, for their synchronous contractions. The gap junctions link the cells together and enable them to react to the electrical impulse rapidly and repeatedly in a group.

 

-Electrical synapse is a type of gap junction. They are very fast but cannot be controlled. They are mostly located in brain. Chemical synapses convert electrical signals to chemical signals to transmit the signal to another neurons.

 

 

 

 

 

 

 

 

 

 

SYNAPTIC FUNCTION

*Process of chemical synapse?

1) Action potential self propagates along the axon and reaches to the axon terminal

2) Voltage gated channel opens and Ca2+ enters to the axon terminal

3) Ca2+ stimulates the release of neurotransmitter in the form of vesicles, exocytosis

4) Neurotransmitters are released and bind to receptors in the postsynaptic membrane

5) Chemical gated channels (receptors) in the postsynaptic membrane binded with Ca2+ is opened and generate graded potential

6) Neurotransmitters can either be reuptaken, degraded by enzyme, and diffused away from the receptors

 

-Post synaptic membrane has only chemically activated channels , and instead of AP, graded potential (subthreshold potential) is generated.

 

*What is the name of the most common neuro transmitter?

Acetylcholine

 

*What determines how much neurotransmitter released affect the size of the graded potential?

Two factors are essential for the release of the neurotransmitter from the presynaptic terminal: (1) depolarization of the terminal and (2) the presence of calcium ions (Ca2+) in the extracellular fluid.

 

*How would the amount of neurotransmitter released affect the size of the graded potential?

Stronger stimuli makes more frequent action potential, and they stimulate to release more neurotransitter.  The increased release of neurotransmitter makes the size of graded potential bigger.

 

*Which neurotransmitter is being released and which post synaptic receptor is activated is also important?

*Why?

 

 

 

 

 

 

 

EPSP's and IPSP's

-Influx of Na+ makes depolarization/ efflux of K+ and influx of Cl- makes hyperpolarisation.

 

*What do temporal and spatial difference?

 

Temporal summation is recieving multiple action potential from a single cell. Every 1-15 msec, action potential coming from same synapes are added to the neuron.

Spatial summation refers to recieving multiple inputs from all different synapse at the same time. Action potential coming from all different synapse are added to the neuron at the same time.

 

 

 

 

 

 

 

CIRCUITS

*Wha is it called when a downstream signal interacts with the, in this case the cell, that produced it? 

*Explain the 'convergence, multiple sources' neural circuit in the example of when you are eating?

When we eat, we can see, smell, taste the food. We recieve signals from several receptors, such as optic sensory neurons, olfactory sensory neurons and taste cells. They all converge on to the one stronge response and send to our brain that percieve we eat. 

*Example of 'Divergence in same pathway' neural circuit in the body?

-Diverging circuit

EX) A single neuron in the brain can activate 100 or more motor neurons in the spinal cord and thousands of skeletal muscle fibres

-Converging circuit 

EX) Different sensory stimuli can elicit the same memory

-Reverberating circuit

EX) Involved in breathing, sleep-wake cycle, and repetitive motor activities such as walking

-Parallel after discharge circuit

EX) May be involved in exacting mental processes such as mathematical calculations

 

 

 

 

 

 

NEUROMUSCULAR JUNCTION & NEUROTRANSMITTER

*What would happen in the absence of Acetylcholinesterase?

The inhibition of the enzyme leads to accumulation of ACh in the synaptic cleft resulting in over-stimulation of nicotinic and muscarinic ACh receptors and impeded neurotransmission. The typical symptoms of acute poisoning are agitation, muscle weakness, muscle fasciculations, miosis, hypersalivation, sweating.

 

lose the control 

 

 

 

 

 

 

 

 

 

 

DISEASES AND POSIONS

*What cause the reduction in Acetylcholine receptors?

Myasthenia gravis causes the immune system to block or destroy acetylcholine receptors. Then, the muscles do not receive the neurotransmitter and cannot function normally. Specifically, without acetylcholine, muscles cannot contract. Symptoms of myasthenia gravis can range from mild to severe.

 

*Curare is used by indigenous South american people to ...*How was curare used in medicine in the past?

Curare, drug belonging to the alkaloid family of organic compounds, derivatives of which are used in modern medicine primarily as skeletal muscle relaxants, being administered concomitantly with general anesthesia for certain types of surgeries, particularly those of the chest and the abdomen.

 

*What affect of the nerve gases by incativating acetylcholinersterase?

 

*What does blown tins mean?

 

*What is the scientific name of the organism that produces the toxin?

Microbial toxins are toxins produced by micro-organisms, including bacteria, fungi, protozoa, dinoflagellates, and viruses. Many microbial toxins promote infection and disease by directly damaging host tissues and by disabling the immune system.

 

*How is the botulism is used in the beauty industry?

Botulinum toxin  produces paralysis by blocking presynaptic release of the neurotransmitter (acetylcholine) at the neuromuscular junction, with reversible chemical denervation of the muscle fibre, thereby inducing partial paralysis and atrophy. Botox injections are used to temporary smoothing of facial wrinkles and improving your appearance by preventing a muscle from moving 

 

Botulism toxin inhibit presynaptic neurons to release the neurotransmitter (AcH).

 

 

 

 

 

 

 

 

SELF PACED QUIZ

 

*What effects would contoxins(block voltage-gated calcium channels) have on synapse function?

Ca2+ stimulates the release of neurotransmitter in the axon terminal. If Ca2+ cannot flow in the axon by the blockage of the channel, the neurotransmitter cannot be released in the axon terminal. The post-synaptic neuron cannot generate action potential because they got nothing to bind to their receptors to generate the graded potential. 

As a result, muscle won't contract because they couldn't get any stimulus. 

*What do SNARE proteins control? What are v- and t- SNARES and how do they interact?

 

SNARE proteins are involved in exocytosis. v-SNARE refers to vesicle SNARE which attached to the vesicles which are containing the neurotransmitter. t-SNARE refers to target SNARE and it is on the membrane. v-SNARE and t-SNARE bind togther to help the vesicle fuse to the membrane and release neurotransmitter outside the membrane. The Ca2+ helps two SNARE proteins to bind together.

Electrical synapse  allows the rapid movement of ions between cells.

Unlike to the chemical synapse, which needs to release neurotransmitter and binding from the receptors, it passes signal without delay. It is located in the cardiac muscles in the gap juction, smooth muscle cells and some neurons, providing synchronised activiy.

However, all electrical synapse can only be excitatory and cannot generate IPSP. The signal from electrical synapse cannot be amplified or modified, which mean it is hard to control.

 

Myasthenia gravis is the immune system disease that has destroyed and blocked acetylcholine receptors.

If the muscle couldn't recieve acetylcholine, it cannot conract and function normally. 

Symptoms are droopy eyelids, blurred vision, slurred speech, and weakness in the arms and legs. Also Basic functions that many take for granted — like chewing, swallowing, and walking — may become difficult.

These acetylcholinesterase inhibitors increase the amount of acetylcholine available and so help muscle activation and contraction.

1) AP arrives to the axon terminal and the voltage gated Ca2+ channel is open.

2) Ca2+ flows inside the axon terminal and it stimulates the release of neurotransmitter.

3) Neurotransmitter is released with being packed in the vesicles, exocytosis

4) Neurotransmitter binds to the receptor in the postsynaptic neuron and the chemically gated channel generate graded potential.

5) Those graded potential generate action potential and it propagate along the axon and the signal is transmitted.

*Why acetylcholine esterase inhibitors make muscle tremor?

Acetylcholine is used as a signal to contract the muscle, by binding to the receptor in muscle fiber sarcolemma.

When the work is done, acetylcholine esterase degrade acethylcholine to stop the action and signaling. However when it is not removed, uncontrolled signal is keep sent to the muscle fiber, which can result in agitation, muscle weakness, muscle fasciculations, miosis, hypersalivation, sweating

IPSP, EPSP, thresholds

(a) The neuron recieve a signal from one single axon, and the size of stimulus couldn't reach the threshold and couldn't generate action potential. This signal is called subthreshold/ graded potential.

(b) The neuron recieve several stimulus from one single axon. The signals are sent to the neuron with the time gap and they are summated, as the time gap between signals decreases. The neuron is fired by reaching the threshold and action potential is generated. The membrane potential is increased,which is also known as excitatory postsynaptic potential. 

(c) The neuron recieve several stimulus from all different axons at the same time, which is called spatial summation. The membrane potential is increased and pass the threshold, which is called EPSP. 

(d) The neuron recieve inhibitory stimulus at the first time, which result in IPSP. Then the neuron is stimulated by the excitatory and inhibitory stimulus at the same time. Those two different signals are summated and compensated, and it couldn't reach the threshold. The action potential isn't generated.