Nerves

Nerves

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Nerves:Neurones (sensory and motor)

Sensory receptor: a cell in which when a change occurs in the internal or external enviroment, producs a nerve impulse/ action potenisl. Receptors are TRANSDUCERS. (Change energy from one form to anoter..)

Sensory neuron: transmit nerver impulese, from a sensory receptor->CNS Brain or spinal cord. cell body at the side of the dendron.

Interneuron/ relay neuron: transmit nerve impuilses betweeb other neurones. Dendron: Carries action potenial from sensory receptor --> cell body.

Motor neurone: transmitts nerve impulsesfrom CNS-->an effector(muscle/gland) cell body at the end of the neurone.

Dendrites: Fibre of neurone which conducts the nerve impulses towards the cell body. xon: Fibre of neurone which conducts the nerve impulses the nerve impulses AWAY from the cell body. Cell body: part of the neuronecontaining nucleus and organelles. Myelinated Neurone: some axons asnd dendrites have schwann cells: wrapped around either the axon or dendron, producing mutiple layers, and increases the SA. speeds up transmission of nerve impulses. Gaps are nodes of ranvier.

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Motor and sensory neurone. :)

(http://content.answcdn.com/main/content/img/elsevier/dental/f0429-01.jpg)Motor: above. Sensory: Below.

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Nerve Impules

Nerve impulses: are produced by alteringthe permeability of the membrane. NA&K ions. The movememt of these ions through cahnnel proteins, in the axon membrane.

The resting potenial (polarisation) The resting potenial is the potenial difference/ voltage across the neurone cell membrane, whilst its at rest. (not cvonducting a impulse)

Na pumps into the membrane (ATP) 3NA OUT&2K IN the axon. This causes the membrane to be impermeable to NA. therefore they build up on the oustide, the axon. permeable to K which facillate diffuse from inside to the outside. Therfore this causes the outside axon being + to the inside. Membrane is polarised. Potenial difference is the RESTINJG POTENIAL. -70mv. NA volatge gated channels are closed. (http://www.fortunecity.com/greenfield/buzzard/387/newnakpump2.jpg)

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Action potenial: depolarisation

Mermbrane at resting potenial (-70mv) Stimmulus appiled which exceeds the theshold value- Opens volatges NA channels, Na move into, membrane depolarises. Inside becomes more positive compared to the outsidde. Potenial differnce is (+40mv) Voltage Na channels shut. Voltage gated K open. K moves out, and potenial dfiffernce becokmes neative. hyperpolarisationo membrance cant be depolarised. Resting potenial Restored!(http://media.wiley.com/assets/7/95/0-7645-5422-0_0704.jpg)

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Threshold potenial:

The action potenial can only occur if the threshild value has been exceeded. It hasd to be rather strong to trigger the openming of the NA channels.

If the threshod is not exceed the "ALL OR NOTHIUNG LAW" will occur. The action potenial is always the same strength. The intensity of a particular stimulus is distinguished by the frequency of teh action poptenial it initiates, & not the strength of them.

Greater no of receptors that pick up the stimulus, greater the strength of the stimulus.

Hyperpolarisation: overshoot which occurs because teh outward flow of K reaches equilibrium before the restring potenial.

Refactory period: for a millisecond repolarisation teh restijng potenial has not been restored. therefore impossible for another action potenial to occur. absolute refactory period. Important role: ensures that each wave of action potenials travels as a discrete impulse and travels in one direction only.

Relative refactory  period: an action potenial can be initiated but only if the stimulus is greater than usual. Means strong stimulus initaties more frequent impulses than a weak stimulus.

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Meylinated and Non meylinated:

Non meylinated:Just one section of the axon is used for the ap to occur. Local currents are set up: local currents have effects of opening NA Na moves in, diffuses across to the membrane of the next sectionm and an ap is initated. Impulses is a series of aps and eac ap initates the next. The alrger teh diameter the faster the rate ofg transmission.

Myelinated: Ions can only cross the membranes of myelinated axons at the nodea odf ranvier: Ap then jump from one node to the nexr. Saltatiry conduction: rate of transmission is faster than non myelinated. Myelinated neurones: tend to be smaller in diametre, myelin is fatty subtance which insulates the axon and prevemyts impulses in one neurone passion to another adjacent neurone.(http://faculty.washington.edu/chudler/axon.gif)

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Synapses:

A synapse if the junction between two neurones/ a neurone and effector. Impulses can cross viachemical neurotransmitter. Synapes are important: give the nervous system control over impulses. Therefore impulses can be stopped passed on to more than one neurone/ directed along certain pathways. Synapse the neurone is carried across the gap by a neurotransmitter which initates action potenial.

Action potenial at pre. Ca channesl open, ca moves in at pre. synapatic vesicles containg ach move towards the pre. Vesicles fuse with pre, ach releasawd from vesicles. Ach diffuses across the snaptoc celft. And biinds to sdpecific receptor proteins on the post. Na channels in post open, NA moves in, depolarise at the membrabne starts a new action potenial. The enzyme: acetyloinesrease breaks down ach andf it diffuses back inot the synaptic knob where iyt is then resynetsised into neurotransmitter.

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Comments

Hannah Nicholls

Fundamentally correct but the spelling is awful.

Susie Brater

ach- acetyl choline

ap- action potential

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