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Transmission of Nerve Impulses. Anatomy & Physiology Chapter 9 (Sect. 5,6,7). Myelinated Axons “the need for speed!!!!”. Schwann cells – Cells that wrap around axons Myelin – lipid/protein molecule that makes up most of Schwann cells. Nodes of Ranvier – Gaps between Schwann cells.
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Transmission of Nerve Impulses Anatomy & Physiology Chapter 9 (Sect. 5,6,7)
Myelinated Axons “the need for speed!!!!” • Schwann cells – Cells that wrap around axons • Myelin – lipid/protein molecule that makes up most of Schwann cells. • Nodes of Ranvier – Gaps between Schwann cells. • Saltatory Impulse = propagation from Node to Node! • Speed of impulse is increased from 1 meter/sec to 100 meters/sec with Myelin!
Resting Potential – the neuron at REST • Sodium Ions (Na+)– are in high concentration OUTSIDE of neuron. • Potassium Ions (K+) – are in high concentration INSIDE of neuron. • This gives a charge of + outside and – inside = Polarized!!
Action Potential = the nerve IMPULSE • Sodium Gates – open up to let Na+ rush into cell. • This causes charge to change (depolarize) to + inside, - outside. • Change in charge signals next Sodium Gate to open.. . . . . . • Impulses moves (propagates) likes falling Dominoes!!
Returning to Resting Potential • Sodium/Potassium Pump – actively transports Na+ back out of cell and K+ back in the cell. • Pumps 3 Na+ out to 2 K+ in.
Threshold Potential –minimum stimuli required to send an impulse. • All-or-None Response – neuron will send impulse “fully” or not at all! • Refractory Period – time when neuron can NOT send impulse due to re-establishing resting potential. * Impulses can be sent at a rate of 100 per second!!! Impulses can reach speeds of up to 120 meters per second!!!
Synapse – Junction between 2 communicating neurons. • Synaptic cleft – gap between axon of one neuron and dendrite of the next. • Neurotransmitter – chemicals that carry impulse across the synaptic cleft.
There are 50 known neurotransmitters that act as. . . • Excitatory NTs= stimulates next neuron. • Inhibitory NTs= blocks or decreases action of next neuron. • After release – NTs can either be broken down by enzymes or re-absorbed by the axon.
