2State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that carry rapid electrical impulsesThe nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons which carry rapid electrical impulses.
4State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.Nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.
6Define resting potential and action potential (depolarization and repolarization). Resting potential: the electrical potential across the plasma membrane of a cell that is not conducting an impulse.Action potential: the reversal and restoration of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it (depolarization and repolarization).
7Explain how a nerve impulse passes along a non-myelinated axon Summary:Resting potential rises above threshold level.Voltage gated sodium channels open.Sodium ions flow into the cell, more sodium channels open.Inside of cell develops a net positive charge compared to the outside and results in depolarization.Voltage gated potassium channels open.Potassium ions flow out of the cell.Cell develops a net negative charge compared to the outside and results in repolarization.Concentration gradients restored by sodium-potassium pumps.Resting potential is restored.
8DetailedSodium is found in greater concentrations outside of the cell while potassium is found in greater concentrations inside the cell. Sodium-potassium pumps exist in the plasma membrane to maintain the the concentration gradients and the membrane potential. Nerve impulses have a domino effect. An action potential in one part of the neuron causes another action potential in the adjacent part and so on. This is due to the diffusion of sodium ions between the region of the action potential and the resting potential. It is the movement of sodium and potassium that reduce the resting potential.If the resting potential rises above the threshold level, voltage gated channels open. Voltage gated sodium channels open very fast so that sodium can diffuse into the cell down its concentration gradient. This reduces the membrane potential and results in more sodium channels opening. Sodium ions are positively charged and so the inside of the cell develops a net positive charge compared to the outside of the cell. This results in depolarization as the potential across the membrane is reversed.A short while after this, voltage gated potassium channels open and potassium ions flow out of the cell down the concentration gradient.
9Detailed cont’dSince potassium ions are positively charged, their diffusion out of the cell causes a net negative charge to develop again inside the cell compared to the outside. The potential across the membrane is restored. This is called repolarization.Finally, the concentration gradients of both ions are restored by the sodium-potassium pump. Sodium is pumped out of the cell while potassium is pumped in. The resting potential is restored and the neuron is ready to conduct another nerve impulse.
11Explain the principles of synaptic transmission Summary: Action potential reaches the end of a presynaptic neuron.Voltage gated calcium channels open.Calcium ions flow into the presynaptic neuron.Vesicles with neurotransmitters inside the presynaptic neuron fuse with the plasma membrane.Neurotransmitters diffuse in the synaptic cleft and bind to receptors on the postsynaptic neuron.The receptors are channels which open and let sodium ions into the postsynaptic neuron.The sodium ions cause the postsynaptic membrane to depolarize.This causes an action potential which passes down the postsynaptic neuron.Neurotransmitters in the synaptic cleft are degraded and the calcium ions are pumped back into the synaptic cleft.