Neurons and synapses

Topic 6.5

Essential idea: Neurons transmit the message, synapses modulate the message.


Introduction to the Nervous System

The nervous system consists of the central nervous system (CNS) and the peripheral nerves. It is composed of cells called neurons that can carry rapid electrical impulses. There are two types of neurons: sensory neurons which carry nerve impulses from sense organs to the central nervous system and motor neurons which carry nerve impulses from the central nervous system to effectors which produce the response. Within the CNS the impulses are carried by relay neurons. Figure 1 below illustrates a structure of the motor neuron.

Structure of the CNS

6.5.U1 Neurons transmit electrical impulses

Transmission of electrical impulse in a neuron

6.5.U2 The myelination of nerve fibers allows for saltatory conduction

Myelination and the myelin sheath

Myelination and the myelin sheath

Nerve fibers and saltatory conduction

Saltatory conduction in neurons

6.5.U3 Neurons pump sodium and potassium ions across their membranes to generate a resting potential

The different membrane pumps in a neuron

Creating resting membrane potential

Sodium pump and resting membrane potential

6.5.U4 An action potential consists of depolarization and repolarization of the neuron

How does depolarization and repolarization occur in the neuron?

Depolarization and repolarization of the neuron

6.5.U5 Nerve impulses are action potentials propagated along the axons of neurons

Movement of the action potential down the neuron

6.5.U6 Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential

Local currents and nerve impulses

6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells

Diagram of synapse

6.5.U8 When presynaptic neurons are depolarize the release of neurotransmitter into the synapse

synapses link nerve impulse across a synapse animation
neurotransmitter release into synapse

6.5.U9 A nerve impulse is only initiated if threshold potential is reached

nerve impulse link nerve impulse animation
Nerve impulse and threshold potential


6.5.A1 Secretion and reabsorption of acetylcholine by neurons at synapses

Synaptic transmission

6.5.A2 Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to                      the acetylcholine receptors

Neurotransmitter release into the synapse


6.5.S1 Analysis of oscilloscope traces showing resting potentials and action potentials

Oscilloscope tracing of resting and action potentials
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