3:24 PM ooooo Sprint LTE 90% d21.depaul.edu Nerves Highly specialized cells spat

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3:24 PM ooooo Sprint LTE 90% d21.depaul.edu Nerves Highly specialized cells spatial specialization well regulated "energized" membrane voltage potential across membrane signals are generated by sending transient changes in voltage down the nerve cell membrane also communicates with other muscles or nerves by sending short-range chemical messengers Three main areas of nerve cell -cell body central portion of the cell which contains the nucleus and most of the synthesis, processing and packaging organelles (e.g. Golgi, ER) -dendrites large branched portion of membranes connected (usually on one side) to central portion which receives information -axon (ong cellular extension over which the voltage change [action potential] occurs) ong extensions of cell membranes connected on other side of central portion which transmit the signal to another site often ends in branches Nerves are really a set of integrated cells specialized for transmitting information rapidly from one site to to another rapid: signal can travel meters in milliseconds specific: signal can transmit information from one specific site on the body to another specific site (e.g. place the tip of a finger on hot surface. info goes to move hand) Axons can be very long (eg. giraffe neck) projections of single cells Nerve cells must be able to 1) conduct signals down their axons (done by transient voltage changes action potentials) 2) conduct signals from nerve to other nerve or muscle (chemicals neurotransmitters) Action Potentials The signals in nerve are transient changes in the electrical voltage across the cell membrane Resting potential inside of the membrane about -70 mV (inside more negative) relative to outside Nerve signals (action potentials) are transient change in the

Explanation / Answer

Nerves are highly specialised cells. They communicate with other nerves and muscles by chemical messengers. The nerve cell consists of three parts: cell body or soma, dendrites and axon. The cell body contains centralised nucleus and Nissl's granules. Dendrites are finger like projections that extend from cell body that receive impulse from synapse and conduct it to the cell body. The axons are large cylindrical strcutures that extend from the cell body. They are covered with myelin sheath. Nodes of Ranvier are the places in axons where myelin sheath is absent. Axons conduct nerve impulses from nerve cell body to synapse.

The resting membrane potential of nerve cell is -70 mV. Action potential is generated by the sequential flow of ions across the voltage gated ion channels. The action potential will open up sodium and potassium ion channels. The junction between axon and the nerve cell is called synapse and the space between them is called synaptic cleft. Neuromuscular junction, as the name implies is the junction between nerve and muscle.

When the action potential arrives at the presynaptic membrane, voltage gated calcium channels open up allowing inflow of calcium ions. These calcium ions causes exocytosis of neurotransmitter containing vesicles releasing the neurotransmitter acetylcholine in the synaptic cleft. Acetylcholine acts on acetylcholine receptors in the post synaptic membrane and results in depolarisation. The excess acetylcholine is hydrolysed by acetylcholine esterase enzyme and some are taken up back by the presynaptic membrane and few leave the synaptic cleft by diffusion.

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