C2.2 Neural Signalling Flashcards
What are neurons?
Neurons are cells within the nervous system that carry electrical impulses along nerve fibers.
What is a resting potential?
The potential difference across a nerve cell membrane when it is not stimulated.
What is the approximated value of the resting potential?
-70mv
What are the factors that affect the value of the resting potential?
- Leakage of ions back across the membrane by simple diffusion (due to the permeability of the phospholipid bilayer to potassium.)
- Sodium-potassium pumps that alternate.
- Negatively charged proteins inside the nerve fibre.
Why are channel proteins closed?
To maintain the concentration of sodium and potassium ions.
What is an action potential?
The depolarisation and repolarisation of the electrical potential across a plasma membrane as a nerve impulse passes along a neuron.
What is an impulse?
The result of a change in the concentration of sodium (Na+) and potassium (K+) ions along the cell membrane.
Explain the process of generating an action potential (refer to the stages in the graph).
- A stimulus causes an electrical potential difference.
- An impulse reaches the threshold causing the
voltage-gated sodium ion channels to open. - Depolarization: sodium channels open, causing sodium ions to diffuse into the cell. The charge of the cell membrane becomes positive.
- Repolarization: after a certain concentration of sodium ions inside the cell is reached, sodium ion channels close and potassium ion channels open causing potassium ions to diffuse out of the cell. The charge of the cell membrane returns to negative, relative to the outside.
- Undershoot: After repolarization, the membrane does not completely return to resting potential as the concentration gradients of sodium and potassium ions haven’t been re-established. A few milliseconds are needed to actively pump Na+ out and K+ in, before there can then be another action potential.
Explain how leakage of ions across the membrane cause a resting potential.
- The pumped ions will leak back across the membrane by diffusion.
- The membrane is much more permeable to K+, causing it to leak faster than Na+
- Causes an imbalance of ions across the membrane.
What causes changes in the speed of nerve impulses?
- The diameter of nerve fibres: larger diameters enables impulses to be transmitted more quickly.
- Myelination increases the speed of impulses from enables nerve impulses to jump from one node of Ranvier to the next which speeds up transmission along the nerve fibre.
What are synapses?
Junctions or link points between neurons.
What does a synapse consist of?
- Pre-synaptic neuron
- Post-synaptic neuron
- Synaptic cleft
What are different types of synapses?
- between sensory receptor cells and neurons
- between neurons
- between neurons and effectors
How do impulses move? // How is an excitatory action potential generated?
- Nerve impulses are carried by neurotransmitters.
- When a nerve impulse arrives at the end of the presynaptic neuron, it becomes depolarized.
- Voltage-gated calcium ion channels on the membrane will open, causing calcium ions to diffuse inside the pre-synaptic neuron.
- This causes the synaptic vesicles containing neurotransmitters to move to the presynaptic membrane and fuse together.
- Via exocytosis, neurotransmitters diffuse across the synaptic gap and bind to the neuroreceptors on the postsynaptic membrane.
- Sodium channels of the receptors will open, allowing sodium ions to diffuse inside. This initiates an excitatory action potential, and the nerve impulse is propagated along the post-synaptic neuron.
How is an excitatory postsynaptic potential generated? (hint: acetylcholine)
- Acetylcholine is a common neurotransmitter used at many synapses such as the neuromuscular junction.
- In the presynaptic neuron, choline combines with an acetyl group which produces acetylcholine which is loaded into the vesicles and released into the synaptic gap during synaptic transmission.
- Acetylcholine diffuses across the synaptic cleft and reaches the
