C2.2 Neural Signalling

What is a neuron ?

Specialised cell that carry out electrical impulses

What is a sensory neuron?

They transmit nerve impulses from sense receptors to the central nervous system, they have nodes of ranvier to speed up signaling

What are interneurons

Located within the central nervous system they transmit nerve impulses between neurons

What are motor neurons?

Transmit nerve impulses from the central nervous system to an affector they have nodes of ranvier to speed up signaling

What are dentrites?

Short nerve fibers which receive nerve impulses from receptors, ot other neurons

What is a cell body?

Soma, contains the nucleus and most cytoplasm, determines if a signal coming from dendrite is to be passes on to the axon

What is the Axon?

Nerve signals (Action potential) travels down the axon to axon terminals

What is resting potential?

Electrical potential difference (voltage) of the cytoplasm of a neuron where it is not transmitting a nerve impulse

Why is resting potential negative?

High concentration of organic negative ions inside the neurons cytoplasm

Sodium ions are concentrated outside the cell while potassium and chlorine inside

How does the sodim potassium pump work?

It pumps 3 Na+ Ions out of the axon and 2 K+ ions in against their concentration gradients

This active transport is essential for maintaining membrane polarisation

What are the specific steps of the the sodim potassium pump?

1. 3Na+ Ions bind to the pump

2. ATP is hydrolysed releasing a phosphate group that attaches to the pump and causes it to change shape

3.Na+ is released outside the axon

4. 2K+ ions bind to the pump and the phosphate group is released

5. The pump returns to its original shape moving K+ inside the axon

6. This process repeats to maintain resting potential

What is the the sodim potassium pump an example of?

Exchange transporter as Na+ and K+ are transported in opposite directions

Why are nerve impulses electrical?

because it involves movement of + charged ions

What are synapses?

Synapses are junctions between neurons or a neuron an effector as muscles or glands, nerve impulses can easily pass from the presynaptic membrane to the postsynaptic membrane (one direction only)

What are chemical signaling

Neurotransmitters

What does the arrival of an action potential at an axon terminal indicate?

1. Voltage gated calcium channels open: Calcium ions (Ca2+) diffuse into the axon terminal

2. Movement of vesicles: The entry of the calcium ions into the axon terminal triggers the movement of vesicles containing neurotransmitters to the presynaptic membrane

3. Exocytosis: The vesicles fuse with the presynaptic membrane releasing the neurostransmitters into the synaptic cleft

What does the arrival of an action potential at the axon cause?

Depolarization of the presynaptic membrane

What is acytocholine?

Exist in many synapses, including neuromuscular junctions (synapses between axon terminals of motoneurons and muscle fibers)

How does acytocholine act?

Diffuses across the synaptic cleft, it binds to transmembrane acytocholine receptors on the postsynaptic membrane, which opens voltage dated sodium channels, Sodium ions flow into the neuron generating an excitatory postsynaptic action potential

What voltage of action potential must be reached to initiate action potencial?

-55mV, at this threshold voltage gated sodium channels open allowing Na+ ions to diffuse into the nerve fiber

What voltage is resting potential?

-70mV

At what voltage do voltage gated sodium channels close?

-30mV, voltage gated potassium channels open

What happens when voltage potassium channels open?

K+ ions move out of the cell, causing repolorization and reducing the potential difference, the potential may drop below resting potential causing hyperpolorization

What does the sodium potassium pump do?

Restores the resting potential by actively transporting Na+ out and K+ re-establishing the original ion balance

How does diffusion of sodium ions both inside and outside of an axon cause the threshold potential to be reached?

- During depolarization, there is an influx of sodium Na+ ions into a nerve fiber

- As sodium ions enter they spread out by diffusion within the axon creating local currents

- The diffusion of Na+ decreases the potential difference to the threshold potential in adjacent regions of the axon

-This triggers the opening of voltage-gated sodium channels, allowing the action potential to propagate along the nerve fibers

What are myelinated neurons?

have axons wrapped in myelin sheets formed by schwan cells

What are nodes of ranvier?

Gaps between myelin sheets

Where are ion pumps and channels

clustered at the nodes of renvier

Where does saltory conduction occur?

Myelinated neurons where acton potential jump from node to node, process is faster and more energy efficient that conduction in non-myelinated neurons

Where are sodium potassium pumps?

only active at the nodes of renvier reducing energy use

What are exogenous chemicals?

come from external sources and can interfere with synaptic transmission

What are Neonicotinoids?

Pestecides that bind irreversibly to acytocholine receptors in insects blocking synaptic transmission and causing paralysis and death, similar structure to acytocholine and nicotine

What is the effect of cocaine?

It prevents the uptake of dopamine by blocking dopamine transporters, this can lead to high dopamine levels in the synaptic cleft causing continued activation of the reward pathway producing euphoria

What are Excitatory neurotransmitters?

Increase the likelihood of action potential being generated and the posynaptic neuron

they open sodium channels allowing sodium ions to enter the neuron

What are inhibitory neurotransmitters?

Decrease likelihood of action potential being generated at the postsynaptic neuron, They bind to protein receptors that allow negative ions to ender the neuron, resulting in the neuron being hyperpolized. Potential difference is lower than resting potential of the neuron

What is summation?

The combined effect of signals in the cell body, the response follows an all or nothing principle, if threshold potential is reached=action potential is generated

If not, no action potential

What are Nociceptors?

have channels for positively charged ions, which open in response to a stimulus such as high temperature, acid, or certain chemicals such as capsaicin in chilli peppers.

What happens when nociceptor open when the nociceptor is stimulated?

Entry of positively charged ions causes the threshold potential to be reached and nerve impulses then pass through the neurons to the brain, where pain is perceived.