Neural Signalling [incomplete]

central nervous system (CNS)

Made up of the brain and spinal cord, which receive sensory information from receptors around the body and interpret that information and can even initiate a response to it.

neurons

Cells that carry information in the form of electrical impulses.

sensory neurons

Carry information to the CNS.

motor neurons

Carry response information to muscles.

peripheral nerves?

Motor and sensory neurons together.

nerve

Many individual neurons grouped together into a single structure.

dendrites

Multiple, shorter fibers on the head of a neuron.

axon

Long, single fibers of a neuron. Conducts nerve impulses.

synaptic terminal buttons

At the end of the axon. Releases neurotransmitters.

action potential (aka nerve impulse)

Moves from the cell body towards the axon terminal buttons and are electrical in nature.

polarized

When a nerve is ready to send an impulse.

resting potential

When a nerve is polarized. It is created by the active transport of sodium and potassium ions across the cell membrane.

sodium-potassium pump

Active transport mechanism that transports three sodium ions out of the cell for every two potassium ions transported into the cell.

membrane potential

The potential difference in charge across a cell membrane that results from negatively charged organic ions permanently locate din the cytoplasm of the axon.

What does active transport need to function?

ATP.

Schwann cells

Make up the myelin sheaths on an axon, wrapping around the fibers and acting as insulators, resulting in no ion movement. They are spaced evenly along an axon with small gaps in between them.

nodes of Ranvier

The small gaps in the myelin sheath.

How do action potentials move down an axon if there is a myelin sheath?

Action potentials skip from one node of Ranvier to another as the impulse progresses along the axon towards the synaptic terminals.

What does the myelin sheath prevent?

Leakage through the membrane.

What does the myelin sheath act as?

An insulator.

Why is the myelin sheath advantageous?

The impulse travels much faster than when compared to travelling a non-myelinated fiber, because the in/out movement of ions only occurs at the nodes of Ranvier. Also, there is less energy, or ATP, expended because the sodium-potassium pump is only working at the nodes.

What relative size diameter has a faster transmission velocity?

Larger.

synapse

Junction between two neurons or where a neuron contacts a muscle cell.

neurotransmitter

A chemical released from the synaptic terminal buttons of the first neuron, resulting in a continuation of the impulse when it is received by the dendrites of the second neuron.

presynaptic neuron

Neuron that releases the neurotransmitter.

postsynaptic neuron

Neuron that receives the neurotransmitter.

synaptic cleft

The small gap between the presynaptic and postsynaptic neurons.

Why do two neurons always align when a synapse is formed?

So that the synaptic terminals are next to the dendrites of another neuron.

What are the nine steps of neurotransmitter transmission?

1. When an action potential reaches the area of the terminal buttons, it initiates the depolarization of the presynaptic membrane and the uptake of calcium ions (Ca²⁺) into the terminal buttons.

2. The Ca²⁺ ions act as a signal, activating a pathway that moves vesicles containing the neurotransmitter through the cell. The vesicles then fuse with the presynaptic membrane.

3. The neurotransmitter is released from the fused vesicles into the synaptic cleft.

4. The neurotransmitter binds with a protein receptor on the postsynapic neuron membrane.

5. This binding results in an ion channel opening, and sodium ions diffusing in through this channel.

6. This initiates the action potential to begin moving down the postsynaptic neuron, because it is now depolarized.

7. Any neurotransmitter that is bound to the protein receptor is released back into the synaptic cleft. They are then degraded by enzymes.

8. The ion channel in the postsynaptic membrane closes to sodium ions.

9. Neurotransmitter fragments diffuse back across the synaptic cleft to be reassembled in the terminal buttons of the presynaptic neuron.

What are the two types of neurons involved in neurotransmitter transmission?

Presynaptic and postsynaptic.

acetylcholine

A neurotransmitter found in synapses and neurotransmitter junctions.

neuromuscular junctions

Synapses between a neuron and a muscle cell.

acetylcholinesterase

An enzyme found in many synaptic clefts of muscles and nerves. It immediately breaks down acetylcholine into fragments so that the transmission of the action potential from the presynaptic membrane to the postsynaptic membrane occurs only once.

What happens when an impulse passes along a neuromuscular junction?

It contracts.

depolarization

When the axon becomes temporarily positive in relation to the outside due to the diffusion of sodium ions after an impulse travels through the neuron.

threshold potential

A minimum potential an action potential needs to be self-propagating, usually starting with the first receptor neuron that began the chain of events.

receptor neuron

A neuron that converts a physical stimulus of some kind into the first action potential.

"all-or-nothing" action of depolarization

If the minimum threshold for that type of receptor is reached, an action potential begins.

repolarization

When the inside of the axon becomes negatively charged relative to the outside.

What does the depolarized area of the axon initiate?

The next region of the axon to open up the voltage-gated channels for sodium and the action potential continues down the axon.

Are action potentials self-propagating?

Yes.

What is an example of where we can find receptor neurons?

Our retinas (in our eyes).

Is there such a thing as a strong or weak impulse?

No.

What causes the next area of the membrane to