Week 2 – Neurons (Behavioural & Cognitive Neuroscience, PSY224)

Neuron Anatomy

• Functional classes: sensory, motor, interneurons
• Key parts: dendrites, soma, axon, myelin sheath
• Myelin → insulation; saltatory conduction at Nodes of Ranvier
• CNS: oligodendrocytes wrap many axons; PNS: Schwann cells wrap one segment
• Multiple sclerosis = autoimmune attack on oligodendrocyte myelin ⇒ disrupted signalling

Glial Cells

• Oligodendrocytes & Schwann cells → myelination
• Astrocytes → regulate blood–brain barrier & local blood flow, buffer ions
• Microglia → immune defence, respond to injury/disease

Resting Membrane Potential

• Lipid bilayer blocks ions; selective channels control flow
• Outside: high \mathrm{Na}^+, \mathrm{Cl}^- Inside: high \mathrm{K}^+, \mathrm{A}^- (proteins)
• Driving forces: concentration & electrical gradients
• Typical -70\,\text{mV} resting potential

Ion Channels

• Ligand-gated: open when transmitter binds
• Voltage-gated: open/close at specific voltages; underpin action potentials

Postsynaptic Potentials & Summation

• EPSP = depolarising graded potential
• IPSP = hyperpolarising graded potential
• Spatial + temporal summation at axon hillock decide if threshold reached

Action Potentials

• Threshold ≈ -55\,\text{mV}
• Depolarisation: rapid \mathrm{Na}^+ influx
• Repolarisation: \mathrm{Na}^+ inactivate, \mathrm{K}^+ efflux
• Hyperpolarisation: prolonged \mathrm{K}^+ outflow
• Relative refractory: AP possible but needs larger EPSP
• \mathrm{Na}^+/\mathrm{K}^+ pump restores gradients ( 3 \mathrm{Na}^+ out / 2 \mathrm{K}^+ in, ATP-dependent)

Synaptic Transmission

• AP arrival opens voltage-gated \mathrm{Ca}^{2+} channels
• \mathrm{Ca}^{2+} influx → vesicle fusion & exocytosis
• Postsynaptic receptors: ionotropic (fast) or metabotropic via G-protein second messenger

Major Neurotransmitters

• Glutamate → chief excitatory
• GABA → chief inhibitory
• Dopamine → reward, motor control
• Norepinephrine → arousal, attention, heart rate
• Serotonin → mood, learning, memory
• Acetylcholine → neuromuscular junction; attention, arousal, motivation

Synapse Variations

• Axo-axonic, axo-somatic, axo-dendritic configurations
• Non-directed synapses: diffuse transmitter to nearby targets

Neuropharmacology Highlights

• GABA_{A} receptor modulators → anxiolytic
• Acetylcholinesterase inhibitors (e.g., galantamine) ↑ acetylcholine; used in Alzheimer’s