Neurones (Unfinished)

Question	Answer
In the body, what detects stimuli?	Sensory Receptors
What are energy transducers?	Something that alters the energy input into a different energy output. Receptors are energy transducers as they convert a stimuli (eg, light or sound) into electrical energy.
What is the difference between the Central Nervous System and the Peripheral Nervous System.	The CNS is made up of the Brain and Spinal Cord, the PNS is made up of all the nerves and neurones.
What kind of sensory receptor detects physical force?	Mechanoreceptors, found in the skin
What kind of sensory receptor detects chemicals/smells/tastes?	Chemoreceptors, found in the nasal cavity, mouth and epiglottis.
What kind of sensory receptor detects changes in temperature?	Thermoreceptos found in the skin.
What kind of sensory receptor detects changes in light/light intensity?	Photoreceptors found in the cone cells in the eyes
What is the Pacinian Corpuscle?	A type of receptor that detects mechanical pressure. They're found deep within the skin, mainly in digits, feet and joints. It consists of a nerve ending in the centre with connective tissue bundling around it. When pressure is applies, the tissue depresses and triggers the nerve.
Why does applying pressure to the Pacinian Corpuscle trigger the nerve?	At rest, the nerve ending is polarised. Applying pressure makes it become depolarised as sodium is triggered to enter. This is because the receptors are stretch-mediated.
Using the Pacinian Corpuscle as an example, how does a nerve impulse start?	1. Pressure changes shape of the Corpuscle 2. Pressure causes stretch-mediated Na channels to open 3. Na enters the nerve end by diffusion, depolarising it, resulting in a generator potential. 4. If this passes the threshold potential, it will result in an action potential.
Why do we react to some stimuli but not to others?	If the stimulus is large, the generator potential (the more Na+ that moves in) will be greater so is more likely to pass the threshold potential and result in action potential. This is less likely with small stimuli.
What really is a nerve?	A nerve is a bundle of lots of motor and sensory neurones.
What are Myelin Sheaths?	Sheets of insulating fatty cells that cover the axon. They are produced by Schwann cells. Along the axon, there are gaps in Myelin Sheaths known as the Nodes of Ranvier.
What is the difference between dendrites and dendrons?	Dendrites are smaller branches, dendrons are one larger branch at the beginning of a neurone. Sensory Neurones have dendrons, motor neurones have dendrites.
What happens when a nerve is not transmitting an impulse?	There is a potential difference across it's membrane, known as a resting potential. At this point, the outside of the membrane is more positive than the inside of the neurone. It is polarised. The potential difference at rest is -70mV.
How is a resting potential brought about?	1. An active Na+/K+ pump actively pumps out three Na+ for two K+ to come in. 2. The sodium ions can't diffuse back into the neurone as their channels are closed. 3. Potassium ions can leave the neurone because K+ channels are open. (This causes more positive charges to build up outside of the neurone).
What changes this resting potential?	When stimulated, Na+ channels open. This allows Na+ to enter the neurone again which will change the charge inside the neurone.
How does an action potential occur?	1. The neurone starts off polarised, at a charge of -70mV 2. As sodium channels open, sodium enters and begins to depolarise the neurone 3. When the charge reaches -55mV, the threshold potential is reached and voltage gated sodium channels open, allowing more sodium in. 4. When the charge reaches +40mV, action potential moves across the neurone.
What happens after the action potential moves down the neurone?	The membrane is no longer permeable to Na+ but K+ instead. The K+ diffuses out, and repolarisation occurs, making the outside of the neurone more positive. There is a moment where too many K+ leave, known as hyperpolaraisation, but this fixes itself to resting potential again.
What is the refractory period?	The time it takes for the Na+ and the K+ to get into their right places to polarise the neurone. In this time, the neruone cannot be simulated again. This maintains that the impulses only travel in one direction and that there is a time for the neurone to recover.
What happens at the nodes of Ranvier?	Nerve impulses travel from one node of Ranvier to the other, being stimulated by action potentials at each node. This is called Saltatory Conduction, aka, 'jumping' conduction.

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Neurones (Unfinished)

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	Created by Emma Lloyd about 8 years ago