Nervous System Essay

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Nervous and Endocrine System

• A neuron is a nerve cell specialized for conducting nerve signals over long distances • Dendrites receive impulses from the other neurons • The impulses are then passed on to the cell body which contains the nucleus • They are then transmitted to the axon, the axon terminal, and finally the synaptic knob • They also contain a neurolimma, which helps it repair itself if it’s injured • A white, fatty myelin sheath covers the axon, which is composed of Schwann cells • The spaces between each Schwann cells are called the Nodes of Ranvier, they allow the impulse to jump along the axon for faster transport

• There are 3 different kinds of neurons • Sensory neurons carry signals from sensory organs to the CNS • Motor neurons carry the signals from the CNS to the muscles • Signals travel through the CNS through interneuron’s

How do neurons produce electrical charges? Neurons produce electrical charges by altering the ion charge on either side of a neuron membrane. When a neuron is at rest, the Na+ ions are mostly found on the outside of the axon in the extracellular fluid. K+ ions are found on the inside in the intercellular fluid. The membrane is impermeable to Na+ so it stays on the outside. The membrane is slightly permeable to K+ ions so they can leak from the inside of the axon to the extracellular fluid. Therefore, there are slightly more positively charged ions on the outside of the cell than on the inside. Because of this, the resting membrane is polarized – the outside is more positive than the inside. -70mV • The voltage is always given from the perspective of the ICF • If the dendrite is stimulated strongly enough to reach threshold, and action potential/nerve impulse occurs • Once it is stimulated, the membrane becomes permeable to Na+ ions, causing them to rush into the ICF – the ICF becomes more positive on the inside than on the outside until it reaches an electrical potential of +30mV/+40mV – depolarized • In order for another impulse to be sent, it must go back to its normal state through repolarization. • The sodium channels close again and the positive ions are then actively transported back into the ECF • Once a particular point on the membrane has been depolarized, the impulse travels down the axon by conduction – an increase in sodium permeability causes increased permeability at an adjacent point • If the axon is covered in myelin, the Schwann cells prevent the entire axon from depolarizing – myelinated neurons are able to conduct impulses much faster than unmyelinated neurons • All action potentials reach a voltage of +30mV; anything that doesn’t reach threshold (-50mV) will fade out. This is called the all or nothing • More intense pain causes more impulses per second – instead of a larger action potential, there will be a greater frequency in depolarization

• An impulse will eventually reach a synapse – the space between the synaptic knob of a pre-synaptic neuron and the dendrite of a post synaptic neuron • Transmission is when an impulse is sent across a synapse – it begins when an axon potential arrives at the axon terminal • Calcium ions enter into the axon, stimulating the synaptic vesicles in the synaptic knob to release neurotransmitter molecules into the synapse • These diffuse across the synapse and bind with receptor sites on the postsynaptic dendrite, causing it to depolarize • All neurotransmitters are proteins produced by neurons – most common is acetylcholine • Hypersecretion of
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