C2.2 Neural Signalling Flashcards
[C2.2.1] Annotate a neuron, including the main role of a neuron
Neurons help with internal communication by transmitting nerve impulses (electrical signal) through nerve fibres.
Dendrites: short and branched nerve fibres
Cell body: contains cytoplasm and nucleus
Axon: elongated nerve fibres
Myelin sheath and schwann cells
Node of ranvier
Axon terminal
[C2.2.2/ C2.2.3/ C2.2.8/ C2.2.9/ C2.2.10] Explain the stages of a neuron undergoing an action potential
- At resting potential, membrane potential is maintained at -70mV as the sodium potassium pumps maintain the inside of the neuron more negative than the outside (3 Na+ ions out, 2 K+ ions in by using ATP).
○ When a neuron transmits an impulse due to a detection of a stimuli, more sodium ions diffuse into the neuron through the pump until -55mV. This is the threshold potential, which result in an all-or-nothing response - if this threshold is not met, the nerve impulse does not continue.
○ Since there is an involvement of positively charged ions in nerve impulses, they are electrical.- If the threshold potential is met, voltage-gated sodium channels open, allowing Na+ ions to diffuse into the cell (down the concentration gradient), causing depolarisation of the neuron, where the membrane potential changes from negative to positive.
○ Depolarised part of the axon has different concentration of sodium ions compared to its neighbouring cells. Thus, sodium ions diffuse alongside of the axon that is still polarised. This movement of ions that lead to depolarisation allow action potential to be propagated along the nerve fibre in 1 direction. - When the voltage reaches +30mV, this results in the voltage-gated potassium channels to open, allowing K+ ions to diffuse out of the neuron (down the concentration gradient). This is repolarisation, where the membrane potential changes from positive to negative.
- Membrane potential becomes more negative than resting potential at hyperpolarisation. This is able to occur since the membrane is more permeable to K+ ions, allowing them to diffuse faster into the neuron.
- Refractory period is when the sodium potassium pump restore resting potential.
- If the threshold potential is met, voltage-gated sodium channels open, allowing Na+ ions to diffuse into the cell (down the concentration gradient), causing depolarisation of the neuron, where the membrane potential changes from negative to positive.
[C2.2.2/ C2.2.3/ C2.2.8/ C2.2.9/ C2.2.10] Describe how membrane potential can be measured and label the diagram
Membrane potential in neurons can be measured by placing electrodes on each side of the membrane. The potentials can be displayed using a oscilloscope like the diagram below, and can measure number of impulses per second.
Resting potential: -70mV
Threshold potential: -55mV
Depolarisation until +30mV
Repolarisation, then hyperpolarisation
Refractory period to return to resting potential
[C2.2.4] Describe the 2 factors that speed of nerve impulse depends on
- Diameter: if diameter increase, it reduces resistance, allowing faster nerve impulses
○ Ex. Giant axons in squid have large diameter, which allows impulses to be propagated rapidly- Myelination: if axon is myelinated, the axon is coasted with multiple layers of phospholipid that contain Schwann cells. The myelinated sheaths prevent ion movement, and the nodes are clustered with sodium potassium pumps and voltage-gated channels, allowing faster nerve impulses through saltatory conduction - impulses jump from 1 node of Ranvier to the next
[C2.2.5/ C2.2.6/ C2.2.7] Explain how the arrival of an action potential at a presynaptic neuron releases neurotransmitters in the synapse. Include a definition of a synapse.
Synapse is a junction between 2 cells in the nervous system. A signal can only pass in 1 direction across a synapse.
1. Action potential arrives at the end of the pre-synaptic neuron, allowing calcium ions to diffuse through the voltage-gated Ca2+ channels, and into the presynaptic neuron.
2. This influx of Ca2+ ions allow neurotransmitters to move towards the synaptic cleft.
3. Neurotransmitters are released into the cleft through exocytosis.
4. Neurotransmitters bind onto the transmembrane receptors on the post-synaptic neuron, allowing sodium ion channels to open. As Na+ ions diffuse into the post-synaptic neuron, this results in an increase in membrane potential of the post-synaptic neuron - excitatory synaptic potential.
5. Excitatory postsynaptic potential is strong enough to trigger an action potential.
6. Neurotransmitters are rapidly broken down or reabsorbed by the pre-synaptic neuron
[C2.2.5/ C2.2.6/ C2.2.7] Describe how acetylcholine is reabsorbed by the presynaptic neuron, and specify where they are released in
Acetylcholine - acetyl is broken down by acetylcholinesterase and choline is reabsorbed.
○ Many different neurotransmitters are used at synapses with different effects. For example, acetylcholine is used as the neurotransmitter in neuromuscular junctions (synapses between neurons and muscle fibres).
[C2.2.12] Define an exogenous chemcial and describe 2 examples
An exogenous chemical is the one that enters the body from an outside source through skin, lungs or it can be injected. Examples include:
1. Neonicotinoids as pesticides
○ Irreversibly binds onto acetylcholine receptors in synapses of insects since acetylcholinesterase cannot break it down
○ This prevents binding of acetylcholine to trigger action potential, leading to the death of insects
○ Advantage is that it is not very harmful for humans
2. Cocaine
○ Binds to dopamine reuptake transporters (membrane protein that pump dopamine back into pre-synaptic neuron)
○ Since cocaine blocks the transporters, dopamine builds up in the synaptic cleft and keeps post-synaptic neuron excited
[C2.2.13/ C2.2.14] Distinguish between excitatory and inhibitory neurotransmitters with examples
Inhibitory neurotransmitters bind to the post-synaptic membrane and result into the membrane potential to become more negative. This hyperpolarisation make it difficult for the post-synaptic neuron to reach threshold potential, hence inhibiting nerve impulses.
• Ex. GABA binds to its receptor and cause chloride channels to open, resulting in hyperpolarisation
Excitatory neurotransmitters, like acetylcholine, allow membrane potential to become more positive.
[C2.2.15] State what pain receptors detect, where they are located on the sensory neurons and how they convey impulse to the CNS
Pain receptors in skin detect stimuli like high temperatures, acids and certain chemicals like capsaicin in chili peppers. These receptors are the endings of sensory neurons which have channels that allow influx of positive ions to convey impulse to CNS if the threshold is met.
[C2.2.13/ C2.2.14] Describe summation
However, since there are more than 1 presynaptic neuron that forms synapses with the same post-synaptic neuron, multiple pre-synaptic neurons must release these neurotransmitter to trigger action potential. This is summation, and it can also combine effects of inhibitory and excitatory neurotransmitters. Depending on how much each neurotransmitters there are threshold potential can be reached.
[C2.2.16] Define emergent property with an example
Emergent property is caused by interactions between elements of a systems. An example of emergent property is consciousness as it emerges from the interaction of individual neurons in the brain.
