Nerve Impulses & The Eye Essay

781 WordsApr 13, 20124 Pages
Sensory nerve- carries electrical message from receptor to spine Sensory nerve- carries electrical message from receptor to spine Nerve Impulses Nerve Impulses Motor nerve- carries electrical message from spine to effector Relay nerve- connects sensory and motor nerves. Also relays message to the brain. Schwann cells- wrap around the axon of the long nerves, creating a thick layer of membrane, which insulates the nerve and allows for much faster conduction speed. The thick layer of membrane has gaps in it between adjacent Schwann cells; these are called Nodes of Ranvier. Motor nerve- carries electrical message from spine to effector Relay nerve- connects sensory and motor nerves. Also relays message to the brain. Schwann cells- wrap around the axon of the long nerves, creating a thick layer of membrane, which insulates the nerve and allows for much faster conduction speed. The thick layer of membrane has gaps in it between adjacent Schwann cells; these are called Nodes of Ranvier. Voltage-Gated K+ Channels open Voltage-Gated K+ Channels open Voltage-Gated Na+ Channels open Voltage-Gated Na+ Channels open A synapse is the junction between two nerves. * 1. The wave of depolarisation arrives at the synaptic knob. The membrane in the presynaptic neuron is depolarised to –50mv (threshold potential) and the voltage-gated Na+ channels open, letting Na+ into the cell. * 2. The membrane is depolarised to +30mV and voltage-gated K+ channels open. The membrane potential falls to –90mV and the cell goes into its refractory period, where the 3Na+/2K+-ATPase restored the ion concentrations. * 3. Unlike axons, presynaptic nerves also contain a Voltage-gated Ca2+ channel. As the presynapstic membrane depolarises these channels open and let Ca2+ into the cell. * 4. The Ca2+ causes vesicles in the presynaptic nerve to migrate and fuse

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