The central nervous system (CNS) isn’t just a bundle of grey and white matter—it’s the command centre for sensation, movement, cognition, and survival. Understanding its architecture sets the stage for recognising how neurological damage unfolds in real patients.
Let’s take a tour through the cortex, subcortex, and brainstem—with just enough anatomical and functional depth to make it stick.
Functional vs Structural Anatomy: Why Names Aren’t Always Enough
Neuroanatomy isn’t just about knowing which gyrus is where—it’s about understanding what each area does, and what happens when it’s damaged.
🧩 Structural anatomy
This refers to the physical location or shape of regions:
- “Precentral gyrus” = part of the frontal lobe just in front of the central sulcus.
- “Hippocampus” = curled structure deep in the temporal lobe.
It helps you describe lesions on imaging or in surgical anatomy.
⚙️ Functional anatomy
Describes what happens there:
- “Primary motor cortex” = functional label for the strip in the precentral gyrus that controls voluntary movement.
- “Broca’s area” = region that coordinates motor aspects of speech—not defined purely by anatomical borders.
🧪 Why it matters:
- A stroke in the left inferior frontal gyrus is structurally precise—but functionally, we say it causes Broca’s aphasia.
- In neurodegenerative conditions, functional impairment may precede visible structural damage (e.g. memory loss in Alzheimer’s before hippocampal atrophy is obvious).
Let's look at some major regions in the brain and brainstem:
🧠 Cortex: The Crinkled Crown of Cognition
The cerebral cortex is the outermost layer of the brain, packed with billions of neurons and elaborate folds (gyri and sulci) that maximise surface area.
🧩 Structure:
- Divided into lobes: frontal, parietal, temporal, occipital (each with distinct roles).
- Organised somatotopically in areas like the motor and sensory homunculi.
- Grey matter here contains neuronal cell bodies; white matter underneath handles connections.
⚙️ Function:
- Frontal lobe: Executive function, speech production (Broca’s area), motor control.
- Parietal lobe: Somatosensory integration and spatial awareness.
- Temporal lobe: Auditory processing, memory encoding, language comprehension (Wernicke’s area).
- Occipital lobe: Visual processing.
🩺 Clinical hook:
- A lesion in the dominant inferior frontal gyrus → expressive aphasia.
- A stroke in the primary motor cortex → contralateral weakness.
- Seizure origin in the cortex often shows focal signs: jerking of a limb, sensory changes, or aura.
- Motor homunculus: left hemisphere controls right-sided motor function.
- Broca’s area (inferior frontal gyrus): expressive aphasia can occur if damaged.
- Teaches: Functional localisation, vascular territories, and lateralisation.
🧠 Clinical Vignette 1: The Cortex
Case: A 22-year-old student collapses during an exam, showing right facial droop and arm weakness. She’s confused but responsive.
Findings: Left middle cerebral artery infarct affecting the frontal and parietal cortices.
Discussion:
🧠 Subcortex: The Hidden Operators
Beneath the cortex lies a constellation of deep structures that refine movement, modulate emotion, and relay sensory data.
🧩 Anatomy Includes:
- Basal ganglia: Caudate, putamen, globus pallidus, subthalamic nucleus, substantia nigra.
- Thalamus: Relay centre between periphery and cortex.
- Hypothalamus: Master of autonomic and endocrine regulation.
- Limbic system: Emotion, memory, and instinct (hippocampus, amygdala, cingulate gyrus).
⚙️ Function:
- Basal ganglia: Initiation and inhibition of movement. Think of it as fine-tuning your motor signals before they go live.
- Thalamus: Every sensory modality (except olfaction) passes through here before reaching the cortex.
- Hypothalamus: Regulates hunger, thirst, temperature, circadian rhythms, and the pituitary.
- Limbic system: Processes emotions, stores memories, and influences behaviour
🩺 Clinical hook:
- Parkinson’s disease: Loss of dopaminergic input to basal ganglia → tremor, rigidity, bradykinesia.
- Thalamic stroke: Can cause sensory loss or pain syndromes on the contralateral side.
- Temporal lobe epilepsy: Often involves the hippocampus; seizures may start with déjà vu or emotional shifts.
- Basal ganglia: balance of excitation and inhibition disrupted.
- Highlights motor modulation, extrapyramidal system, and neurotransmitter pathways.
- Teaches: Classic subcortical syndromes and treatment targets.
🧠 Clinical Vignette 2: The Subcortex
Case: A 65-year-old man presents with slowed movements, reduced arm swing, and a resting tremor. His handwriting has become cramped and shaky.
Findings: Parkinson’s disease due to degeneration of dopaminergic neurons in the substantia nigra.
Discussion:
🧠 Brainstem: Vital Life Support
The brainstem connects the brain to the spinal cord, coordinating vital functions like breathing, heart rate, and consciousness.
🧩 Parts:
- Midbrain: Vision, hearing, motor control.
- Pons: Bridges cortex and cerebellum; critical for facial sensation and movement.
- Medulla oblongata: Regulates cardiac and respiratory rhythms, swallowing, and reflexes.
Also houses cranial nerve nuclei (III–XII) and reticular activating system (keeps you conscious and alert).
⚙️ Function:
- Relay station for ascending and descending tracts.
- Direct control of respiratory centres.
- Source of many primitive reflexes and core autonomic control.
🩺 Clinical hook:
- Locked-in syndrome: Infarction of ventral pons → complete paralysis except for vertical eye movements.
- Medullary stroke: May affect swallowing, voice, heart rate, or breathing.
- Cranial nerve palsies: Help localise lesions (e.g. unilateral CN VI palsy → pons lesion).
- Pons contains respiratory centres and cranial nerve nuclei.
- Autonomic disruption and coma risk due to reticular activating system damage.
- Teaches: Brainstem physiology and life-sustaining roles.
🧠 Clinical Vignette 3: The Brainstem
Case: A motorbike rider sustains head trauma and presents with pinpoint pupils, bradycardia, and respiratory irregularity. Cranial nerve testing shows bilateral CN VI palsy.
Findings: Pontine haemorrhage.
Discussion:
⚡Neuronal Directionality: Afferent vs Efferent Made Easy
Understanding how information travels within the nervous system lays the groundwork for everything that follows in neuro.
📩 Afferent pathways
- Think sensory input: These neurons carry signals toward the CNS.
- For example, when you touch a hot surface, thermoreceptors in your hand send afferent signals up through the spinal cord to the brain.
📤 Efferent pathways
- Think motor output: These neurons send signals away from the CNS to muscles or glands.
🧠Imagine the CNS as a command centre.
- Afferent = incoming mail (messages arriving).
- Efferent = outgoing orders (actions dispatched).
🔍 Clinical Relevance:
- In peripheral neuropathies, damage to afferent fibres results in numbness or altered sensation.
- Damage to efferent fibres causes weakness or paralysis.
It's especially vital when interpreting reflex arcs—for example, the patellar reflex relies on intact afferent input (from the stretch receptor) and efferent output (to the quadriceps).
📚 Wrapping Up
The cortex handles higher-order thinking and conscious perception. The subcortex integrates and regulates emotion, movement, and autonomic control. The brainstem keeps us alive and responsive to the world.
In practice, recognising which CNS region is affected gives us a roadmap to diagnosis—whether it’s decoding focal seizures, understanding the emotional fallout of limbic damage, or managing the consequences of a brainstem stroke.
- 📝 All posts on the nervous system →
- 📝 Structure and function of the CNS →
- 📝 Pathophysiology of seizures →
- 📝 Understanding seizure classification →
- 📝 Localisation of seizures →
- 📝 Neurotransmitters 101 →
- 📝 Consciousness and how we can lose it →
- 📝 Clinical cases in seizure localisation →
- 📝Principles of seizure management →
- 📝Neurotransmitters on drugs! →
- 📝A beginner's guide to EEG →
- 📝A beginner's guide to neuroimaging →
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