The nervous system is composed of specialised cells called neurons that function to transmit electrical signals

Nerve impulses are action potentials propagated via axons

Synapses are the physical junctions between two neurons

Neurons have a difference in charge across their membranes due to the distribution of positively-charged ions (Na+ / K+)

Electrical signals are created by changing membrane polarity • Polarity of a neuron at rest is the resting potential (-70mV) • Polarity of a firing neuron is the action potential (+30mV)

Action potentials are ‘all or none’ and are only propagated if a certain threshold potential is reached (~ -55mV)

This enables saltatory conduction (⇧ transmission speed) • The action potential ‘hops’ between gaps in the myelin sheath (called nodes of Ranvier) for faster transmission

Dendrite

Soma (cell body)

axon

Myelin Sheath

Axon Terminal

Soma & Axon

Soma & Body Cell

Axon & Schwann

Axon terminal & Nucleus

Node of Ranvier & Nucleus

Axon & Nucleus

Soma & Axon Terminal

Node of Ranvier & Axon Terminal

Myelin Sheath & Nucleus

Myelin Sheath & Axon

Schwann cell & Myelin Sheath

Dendrite

Axon

Axon Terminal

Nucleus

Dendrite to Axon Terminal

Axon Terminal to Dendrite

Nerve impulses are action potentials propagated via axons • Action potentials are ‘all or none’ and are only propagated if a certain threshold potential is reached (~ -55mV)

In certain neurons, the axon is covered by a myelin sheath • This enables saltatory conduction (⇧ transmission speed) • The action potential ‘hops’ between gaps in the myelin sheath (called nodes of Ranvier) for faster transmission

Electrical signals are created by changing membrane polarity • Polarity of a neuron at rest is the resting potential (-70mV) • Polarity of a firing neuron is the action potential (+30mV)

Synapses are the physical junctions between two neurons • Electrical impulses cannot cross these physical gaps

l is maintained by a Na+/K+ pump • It exchange sodium ions (3 out) and potassium ions (2 in) so that the membrane potential becomes slightly negative

The opening of sodium channels causes a sodium influx • This creates a positive membrane potential (depolarisation) • Opening potassium channels causes a potassium efflux • This restores a negative membrane potential (repolarisation)

Depolarisation in axon terminals opens Ca2+ channels • Ca2+ influx causes vesicles containing neurotransmitters to release their contents into the synapse (via exocytosis)

Depolarisation in axon terminals opens Ca2+ channels • Ca2+ influx causes vesicles containing neurotransmitters to release their contents into the synapse (via exocytosis)

changes the resting membrane potential • The opening of sodium channels causes a sodium influx • This creates a positive membrane potential (depolarisation) • Opening potassium channels causes a potassium efflux • This restores a negative membrane potential (repolarisation)

Neurotransmitters bind receptors on post-synaptic cells and generate graded potentials (excitatory or inhibitory) • The summation of these graded potentials determines if the post-synaptic neuron (or effector cell) is activated

The ion distribution must be restored to original conditions before a neuron can fire again

Polarity of a neuron at rest is the resting potential (-70mV) • Polarity of a firing neuron is the action potential (+30mV)

The opening of sodium channels causes a sodium influx • This creates a positive membrane potential (depolarisation) • Opening potassium channels causes a potassium efflux • This restores a negative membrane potential (repolarisation)

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Synapses are the physical junctions between two neurons • Electrical impulses cannot cross these physical gaps

Nerve impulses are action potentials propagated via axons • Action potentials are ‘all or none’ and are only propagated if a certain threshold potential is reached (~ -55mV)

Acetylcholine is a neurotransmitter used in CNS and PNS • It is broken down in synapses by acetylcholinesterase • This prevents the overstimulation of the receptors

Neurons release neurotransmitters into the synapse cleft • Depolarisation in axon terminals opens Ca2+ channels

• Ca2+ influx causes vesicles containing neurotransmitters to release their contents into the synapse (via exocytosis)

Neurotransmitters bind receptors on post-synaptic cells and generate graded potentials (excitatory or inhibitory)

• The summation of these graded potentials determines if the post-synaptic neuron (or effector cell) is activated

• The summation of these graded potentials determines if the post-synaptic neuron (or effector cell) is activated

Neurotransmitters bind receptors on post-synaptic cells and generate graded potentials (excitatory or inhibitory)

Ca2+ influx causes vesicles containing neurotransmitters

Depolarisation in axon terminals opens Ca2+ channels

Depolarisation in axon terminals opens Ca2+ channels

Ca2+ influx causes vesicles containing neurotransmitters to release their contents into the synapse (via exocytosis)

Neurotransmitters bind receptors on post-synaptic cells and generate graded potentials (excitatory or inhibitory)

The summation of these graded potentials determines if the post-synaptic neuron (or effector cell) is activated

The summation of these graded potentials determines if the post-synaptic neuron (or effector cell) is activated

Neurotransmitters bind receptors on post-synaptic cells and generate graded potentials (excitatory or inhibitory)

Ca2+ influx causes vesicles containing neurotransmitters to release their contents into the synapse (via exocytosis)

Depolarisation in axon terminals opens Ca2+ channels

Acetylcholine is a neurotransmitter used in CNS and PNS • It is broken down in synapses by acetylcholinesterase • This prevents the overstimulation of the receptors

Neonicotinoid pesticides irreversibly bind to acetylcholine receptors and cannot be digested by acetylcholinesterase • Insects have higher levels of these types of receptors • This makes neonicotinoids highly effective pesticides

Neurotransmitters bind receptors on post-synaptic cells and generate graded potentials (excitatory or inhibitory

Depolarisation in axon terminals opens Ca2+ channels • Ca2+ influx causes vesicles containing neurotransmitters