Download and peripheral nerves, and is composed of cells called neurons that

Nerves, hormones and
homeostasis
State 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 impulses
• The nervous system consists of the central
nervous system (CNS) and peripheral
nerves, and is composed of cells called
neurons which carry rapid electrical
impulses.
Draw and label a diagram of a
motor neuron
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State 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.
Define 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).
Explain how a nerve impulse passes along a
non-myelinated axon
• Summary:
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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.
Detailed
• Sodium is found in greater concentrations outside of the cell while
potassium is found in greater concentrations inside the cell. Sodiumpotassium 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.
Detailed cont’d
• Since 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.
Visual Learner Version
• See youtube animation
Explain 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.
Visual Learner Version