Nervous System: Part 2

• The nervous system is discussed in Part 2 covering nerve impulses.

GDC Learning Outcomes

• Describe dental, oral, craniofacial, and general anatomy and their relevance to patient management.
• Describe relevant physiology and its application to patient management.

Nerve Impulses

• Nerve impulses are initiated by sensory nerve endings or an impulse from another nerve.
• Afferent nerve impulses run towards the brain and CNS, carrying sensory information.
• Efferent nerve impulses run from the brain and CNS, carrying motor information.
• Nerve impulses are also known as action potentials.
• In the axon, ion channels are voltage-gated.
• Depolarization at one axon segment triggers the opening of ion channels in the next segment.
• Action potential spreads along the axon as a wave of depolarization.

Process of Neural Impulse

• Resting neuron maintains a resting potential via Na+/K+ pumps.
• An excitatory stimulus opens sodium channels, leading to sodium ions entering the neuron.
• Subsequently, potassium channels open, facilitating potassium ions leaving the neuron.
• Charge restoration is achieved by the sodium-potassium pump restoring the original ion distribution.
• Nerve impulses travel down the neurone.
• Dendrites receive messages from other cells, the axon passes messages away to other neurons, muscles, and glands.
• The myelin sheath covers some axons, helping to speed neural impulses.

Synaptic Transmission

• Nerves are not physically joined or connected.
• Nerve impulses jump from one nerve to another at a synapse.
• The human brain contains approximately 1000 trillion synapses.
• Synaptic knobs contain synaptic vesicles with neurotransmitters, released into the synaptic cleft.

Neurotransmitter Journey

• Neurotransmitters are synthesized by nerve cell bodies.
• Actively transported along with the axons.
• Stored in synaptic vesicles.
• Released by exocytosis during action potential.
• Diffuse across the synaptic cleft.
• Act on specific receptor sites on the postsynaptic membrane.
• Action of them is short-lived.
• Inactivated by enzymes or taken back into the synaptic knob after action.

Local Anaesthetics & Neuralgia

• Local anesthetics block nerve transmission to pain centers by binding to and inhibiting sodium channels in nerve cell membranes.
• This obstructs nerve impulses near the injection site, without affecting awareness or sense perception elsewhere.
• Excessive nerve impulses can result in neuralgia, often trigeminal neuralgia.
• Herpes simplex virus lies dormant in the trigeminal ganglion; reactivation causes it to travel down the trigeminal nerve, resulting in cold sores.