The Meninges are three protective membranes (from outside to inside): 1) Dura Mater (tough mother) = Outermost, thickest, fibrous layer. Attached to inner skull. Contains dural venous sinuses. 2) Arachnoid Mater (spider-like) = Middle layer, thin and weblike. The subarachnoid space between arachnoid and pia contains CSF. Arachnoid granulations reabsorb CSF. 3) Pia Mater (tender mother) = Innermost, delicate, directly covers brain surface. Meningitis = inflammation of meninges. Epidural haematoma = blood between skull and dura (arterial). Subdural haematoma = blood between dura and arachnoid (venous).

Neuroplasticity (Brain Plasticity) is the remarkable ability of the brain to reorganise its neural connections and functions throughout life. Types: Synaptic plasticity (Strengthening - LTP/Long-Term Potentiation - or weakening - LTD - of synapses - basis of learning and memory), Structural plasticity (Physical changes in synapses, dendrites, and brain areas), Functional plasticity (Brain areas take over functions of damaged regions), and Neurogenesis (New neurons born mainly in hippocampus and olfactory bulb in adults). Hebb's rule: Neurons that fire together, wire together. Clinical importance: Stroke rehabilitation - neighbouring brain areas take over function of damaged areas.

A Reflex Action is a rapid, automatic, involuntary response to a stimulus. It does not require conscious thought because it is processed in the spinal cord (not the brain). The pathway is called a reflex arc: Stimulus > Receptor > Afferent (sensory) neuron > Integration centre (spinal cord) > Efferent (motor) neuron > Effector (muscle/gland) > Response. Types: Monosynaptic reflex (e.g., knee-jerk/patellar reflex - only 1 synapse) and Polysynaptic reflex (e.g., withdrawal reflex from pain - multiple synapses and interneurons). Reflexes allow the body to respond faster than conscious thought.

Multiple Sclerosis (MS) is a chronic autoimmune demyelinating disease of the CNS where the immune system attacks the myelin sheath around axons, forming plaques/scleroses throughout the CNS. Features: Relapsing-Remitting MS (most common - 85%): Episodes of neurological deficits followed by recovery. Symptoms: Visual problems (optic neuritis - common first symptom), weakness, numbness, tingling, spasticity, bladder dysfunction, fatigue, cognitive impairment. Uhthoff's phenomenon: Symptoms worsen with heat. Diagnosis: MRI (white matter plaques), CSF (oligoclonal bands), Visual evoked potentials. Treatment: Interferon-beta, glatiramer, natalizumab, ocrelizumab.

Grey Matter vs White Matter: Grey Matter contains neuron cell bodies, dendrites, unmyelinated axons, synapses, and glial cells. Appears grey/pinkish (no myelin). In the brain: outer cortex and deep nuclei (basal ganglia, thalamus). In the spinal cord: central H-shape. Site of information processing. White Matter contains myelinated axon tracts (bundles of axons). Appears white (due to myelin). In the brain: deep to cortex. In the spinal cord: surrounds grey matter. Site of information transmission between regions. Key white matter tracts: Corpus callosum (connects hemispheres), Internal capsule (corticospinal tract), Optic radiation (visual pathway).

The Knee-jerk (Patellar) Reflex is the classic example of a monosynaptic stretch reflex: Tapping the patellar tendon stretches the quadriceps muscle. Muscle spindles detect the stretch. Sensory neuron carries signal to spinal cord (L3-L4). Directly synapses with the motor neuron (only ONE synapse - monosynaptic). Motor neuron signals quadriceps to contract causing knee extension. Used clinically to test the integrity of the L3-L4 spinal segment and the femoral nerve. Absent reflex = lower motor neuron lesion. Exaggerated reflex = upper motor neuron lesion.

An Action Potential is the electrical signal (nerve impulse) that travels along the axon. Sequence: 1) Resting potential - Membrane at -70 mV (inside negative - maintained by Na+/K+ pump). 2) Depolarisation - Stimulus causes Na+ channels to open - Na+ rushes IN - membrane reaches +30 to +40 mV. 3) Repolarisation - Na+ channels close - K+ channels open - K+ flows OUT - potential returns toward -70 mV. 4) Hyperpolarisation - Brief dip below -70 mV (refractory period). 5) Returns to resting potential. All-or-nothing principle: Action potential either fires fully or not at all. Refractory period prevents backward propagation.

The Somatic Nervous System (SNS) is the division of the PNS that controls voluntary movements of skeletal muscles (under conscious control) and carries sensory information (touch, pain, temperature, proprioception) from the body to the CNS. Components: Afferent (sensory) fibres (carry information FROM skin, muscles, joints TO CNS) and Efferent (motor) fibres (carry commands FROM CNS TO skeletal muscles). The neurotransmitter used at the neuromuscular junction is Acetylcholine (ACh). Somatic motor neurons are large, fast, myelinated (A-alpha) fibres.

Alzheimer's Disease is the most common cause of dementia (60-70% of all dementia cases). Pathology: Amyloid plaques (extracellular deposits of beta-amyloid peptide), Neurofibrillary tangles (intracellular accumulation of hyperphosphorylated tau protein), Loss of cholinergic neurons (especially in hippocampus and basal forebrain), and Brain atrophy. Features: Progressive memory loss (anterograde amnesia first), language problems, disorientation, personality changes. Risk factors: Age (>65), APOE-e4 gene, Down syndrome (trisomy 21). Treatment: Cholinesterase inhibitors (donepezil, rivastigmine), Memantine (NMDA antagonist).

The Autonomic Nervous System (ANS) is the division of the PNS that regulates involuntary body functions not under conscious control: Heart rate and blood pressure, Digestion and peristalsis, Breathing rate, Glandular secretions (sweat, saliva, hormones), and Pupil size and bladder control. Divided into: Sympathetic NS (fight or flight), Parasympathetic NS (rest and digest), and Enteric NS (gut nervous system - second brain). The ANS uses a two-neuron chain: preganglionic neuron (CNS) > ganglion > postganglionic neuron > effector organ.