Source: Biology, Michigan State University
Difficulty: Introductory to Intermediate | Prerequisites: Basic cell biology and tissue types. Familiarity with neurons and nerve impulse transmission is helpful but not required.
The central nervous system (CNS) is the body's command centre: the brain and spinal cord working together to process sensory input, coordinate movement, and run higher-order thinking. This topic sits at the heart of any anatomy or neuroscience course and comes up repeatedly when you study neurological conditions, pharmacology, and clinical assessment. You should already be comfortable with basic cell biology (particularly neuron structure) and tissue types. If you can sketch a neuron and explain what an action potential does, you are ready for this material.
The CNS is made up of the brain and spinal cord. The brain develops from a simple neural tube into five distinct regions, each responsible for different functions, from voluntary movement and speech to sensory processing and homeostasis. Knowing which region does what is the foundation for understanding what goes wrong in strokes, traumatic injuries, and neurological disease.
Central nervous system (CNS)
The division of the nervous system consisting of the brain and spinal cord. Think of it as the main processing hub; everything else (peripheral nerves) reports to it.
Neural tube
The embryonic structure that gives rise to the entire CNS. In simple terms, it is the hollow tube of cells that folds shut early in development and eventually becomes the brain and spinal cord.
Prosencephalon (forebrain)
The most anterior of the three primary brain vesicles. It later splits into the telencephalon and diencephalon. Think of it as the precursor to the "thinking" parts of the brain.
Mesencephalon (midbrain)
The middle primary vesicle. Unlike the other two, it stays undivided as the brain matures. In simple terms, it is the relay and reflex centre sitting between the forebrain and hindbrain.
Rhombencephalon (hindbrain)
The most posterior primary vesicle, which splits into the metencephalon (pons and cerebellum) and myelencephalon (medulla oblongata). Think of it as the region that keeps you alive: breathing, heart rate, balance.
Telencephalon
The secondary vesicle that becomes the cerebral hemispheres. This is where higher cognition, voluntary movement, and sensory perception happen.
Diencephalon
The secondary vesicle that becomes the thalamus, hypothalamus, and epithalamus. In simple terms, it is the brain's relay switchboard and hormonal control centre.
Cerebral cortex
The thin outer layer of grey matter covering the cerebral hemispheres, responsible for conscious thought, sensation, and voluntary movement.
Gyri and sulci
Gyri are the raised folds on the brain's surface; sulci are the grooves between them. They increase the cortex's surface area so more neurons can fit without a larger skull.
Cerebrospinal fluid (CSF)
The clear fluid filling the ventricles and surrounding the brain and spinal cord. Think of it as a cushion and waste-removal system rolled into one.
Lateralisation
The tendency for certain cognitive functions to be handled predominantly by one hemisphere. In simple terms, your left hemisphere typically leads on language and logic, while the right leads on spatial awareness and creativity.
Broca's area
A region in the frontal lobe (usually left hemisphere) that directs the muscles used in speech production. Damage here means you understand language but struggle to produce fluent speech.
Primary motor cortex
The strip of cortex on the precentral gyrus that sends commands to skeletal muscles for voluntary movement.
Primary somatosensory cortex
The strip on the postcentral gyrus that receives touch, pressure, pain, and proprioceptive information from the body.
The entire CNS develops from the neural tube, which forms during early embryological development.
The anterior (head) end of the neural tube expands into three primary brain vesicles:
Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)
The three primary vesicles further differentiate into five secondary brain vesicles:
Prosencephalon splits into the telencephalon and the diencephalon.
Mesencephalon remains undivided.
Rhombencephalon splits into the metencephalon (becomes pons and cerebellum) and the myelencephalon (becomes medulla oblongata).
Week 5: Primary vesicles form and begin angling toward the future brain stem.
Week 13: Cerebral hemispheres grow posterolaterally, enclosing the diencephalon and rostral brain stem.
At birth: The brain shows adult-pattern convolutions (gyri and sulci), giving it the folded appearance that dramatically increases cortical surface area.
The largest part of the brain, divided into left and right hemispheres.
Each hemisphere contains four visible lobes, named after the skull bones above them:
Frontal lobe (front of the brain, behind the forehead)
Parietal lobe (top and upper back)
Temporal lobe (sides, near the ears)
Occipital lobe (back of the brain)
A fifth region, the insula, is buried deep beneath portions of the temporal, parietal, and frontal lobes and is not visible from the surface.
Sits between the cerebral hemispheres and the brain stem.
Key structures:
Thalamus: The main sensory relay station. Nearly all sensory information passes through the thalamus on its way to the cortex.
Hypothalamus: Controls homeostasis, body temperature, hunger, thirst, sleep cycles, and links the nervous system to the endocrine system via the pituitary gland.
Epithalamus: Includes the pineal gland, which secretes melatonin and helps regulate the sleep-wake cycle.
Retina: Developmentally part of the diencephalon and part of the visual system.
Connects the cerebrum to the spinal cord and houses vital autonomic centres.
Three subdivisions, from superior to inferior:
Midbrain (mesencephalon): Visual and auditory reflex centres.
Pons: Relay station between the cerebrum and cerebellum; helps regulate breathing.
Medulla oblongata: Controls heart rate, blood pressure, breathing rhythm, swallowing, and vomiting.
Sits posterior to the pons and medulla, beneath the occipital lobes.
Coordinates voluntary movements, balance, posture, and motor learning.
Does not initiate movement; it fine-tunes commands coming from the motor cortex.
Primary motor cortex: Located in the precentral gyrus of the frontal lobe. Sends direct commands to skeletal muscles for precise, voluntary movements. The body is mapped onto this strip (motor homunculus), with areas controlling fine movements (hands, face) taking up disproportionately large regions.
Premotor cortex: Sits just anterior to the primary motor cortex. Plans and coordinates learned, patterned movements such as playing an instrument or typing.
Broca's area: Found in the frontal lobe, usually in the left hemisphere. Directs the muscles of the lips, tongue, and larynx for speech production. Damage produces Broca's aphasia: the person knows what they want to say but cannot form fluent speech.
Frontal eye field: Controls voluntary scanning eye movements, such as tracking a moving object.
Primary somatosensory cortex: Located in the postcentral gyrus (just behind the central sulcus). Receives sensory information from the skin, muscles, and joint proprioceptors. Like the motor cortex, it has its own body map (sensory homunculus).
Somatosensory association cortex: Integrates multiple sensory inputs so you can recognise an object's size, texture, and spatial relationship without looking at it.
Primary visual (striate) cortex: Located in the occipital lobe. Receives raw visual data from the retinas via the thalamus.
Visual association area: Surrounds the primary visual cortex. Interprets visual stimuli: colour, form, movement, and object recognition. Damage here does not cause blindness, but the person cannot make sense of what they see.
The two hemispheres are not equal partners for every task. This division of labour is called lateralisation.
Left hemisphere (in most right-handed people): dominant for language, mathematical reasoning, and logical analysis.
Right hemisphere: dominant for visual-spatial processing, face recognition, intuition, and creative/artistic tasks.
Both hemispheres communicate through the corpus callosum, a thick bundle of nerve fibres.
These regions integrate inputs from multiple sensory and motor areas and are responsible for the most complex brain functions.
Three key association areas:
Anterior association area (prefrontal cortex): Executive functions, planning, personality, judgement, abstract reasoning.
Posterior association area: Integrates visual, auditory, and somatosensory data to build a unified perception of the environment.
Limbic association area: Emotion, memory formation, and motivation.
Damage to specific brain regions produces predictable deficits:
Primary motor cortex damage: Paralysis on the contralateral (opposite) side of the body.
Visual association area damage: The person can see but cannot interpret what they are seeing (visual agnosia), with no actual blindness.
The brain contains a network of fluid-filled chambers called ventricles, lined by ependymal cells and filled with cerebrospinal fluid (CSF).
Main components:
Lateral ventricles (one in each hemisphere)
Third ventricle (in the diencephalon)
Fourth ventricle (between the pons/medulla and the cerebellum)
These are connected by narrow passages (foramina and the cerebral aqueduct).
CSF cushions the brain, delivers nutrients, and removes metabolic waste.
Understanding which brain region does what is essential in clinical settings. A neurologist examining a stroke patient uses knowledge of cortical maps to predict which functions are lost based on the location of the lesion. Surgeons planning tumour removal rely on the same maps to avoid damaging critical areas such as Broca's area or the primary motor cortex.
Students often think the cerebellum initiates voluntary movement. It does not. The cerebellum fine-tunes and coordinates movements that the motor cortex initiates.
Students often confuse Broca's area with Wernicke's area. Broca's area (frontal lobe) controls speech production; Wernicke's area (temporal lobe) handles speech comprehension. Damage to Broca's produces broken, effortful speech. Damage to Wernicke's produces fluent but nonsensical speech.
Students often assume lateralisation means one hemisphere does nothing during a "left-brain" or "right-brain" task. Both hemispheres are always active; lateralisation means one takes the lead for a given function, not that the other switches off.
Students often think "grey matter" and "white matter" are located in the same arrangement everywhere. In the cerebral cortex, grey matter is on the outside; in the spinal cord, it is on the inside. The arrangement flips.
⚠️ Know the three primary vesicles and their five secondary derivatives cold. This is a classic short-answer or matching question.
⚠️ Be able to match each cerebral lobe to its primary function (frontal = motor and executive, parietal = somatosensory, occipital = vision, temporal = auditory and memory).
⚠️ The precentral gyrus (motor) and postcentral gyrus (sensory) are separated by the central sulcus. Exams love asking which is which.
⚠️ Understand contralateral control: the left motor cortex controls the right side of the body and vice versa. This comes up in every stroke or lesion scenario.
⚠️ CSF production, flow pathway through the ventricles, and the role of ependymal cells are frequently tested in both anatomy and physiology exams.
True or False: The mesencephalon divides into two secondary vesicles during development. (False: it remains undivided.)
Fill in the blank: The ______ gyrus contains the primary motor cortex, while the ______ gyrus contains the primary somatosensory cortex. (Precentral; postcentral.)
True or False: Damage to the visual association area causes complete blindness. (False: the person can still see, but cannot interpret the visual information.)
Fill in the blank: The fluid that fills the brain's ventricles is called ______. (Cerebrospinal fluid / CSF.)
True or False: The cerebellum initiates voluntary movement. (False: it coordinates and fine-tunes movement initiated by the motor cortex.)
Q: Name the three primary brain vesicles and state which secondary vesicles each one produces.
A: Prosencephalon (forebrain) produces the telencephalon and diencephalon. Mesencephalon (midbrain) remains undivided. Rhombencephalon (hindbrain) produces the metencephalon and myelencephalon.
Q: A patient suffers a stroke affecting the left precentral gyrus. What deficit would you expect, and on which side of the body?
A: Paralysis or weakness of voluntary muscles on the right (contralateral) side of the body, because the primary motor cortex is in the precentral gyrus and motor control is contralateral.
Q: Distinguish between Broca's area and the primary motor cortex in terms of location and function.
A: Both are in the frontal lobe, but Broca's area specifically controls the muscles used for speech production (usually left hemisphere only), while the primary motor cortex (precentral gyrus) controls skilled voluntary movements across the entire body.
Q: What is the role of the thalamus, and why is it sometimes called the brain's "relay station"?
A: The thalamus receives nearly all incoming sensory information (except smell) and routes it to the appropriate area of the cerebral cortex for processing. It acts as a gateway, filtering and directing signals.
Q: Describe the path of CSF through the ventricular system.
A: CSF is produced (mainly by choroid plexuses) in the lateral ventricles, flows through the interventricular foramina into the third ventricle, passes through the cerebral aqueduct into the fourth ventricle, and then circulates into the subarachnoid space around the brain and spinal cord.
Q: A patient can see objects clearly but cannot recognise faces or identify what the objects are. Which area is most likely damaged?
A: The visual association area. The primary visual cortex is intact (the patient can see), but the association area that interprets form and meaning is compromised.
This material connects directly to peripheral nervous system (PNS) topics, since the PNS is the other half of the nervous system and carries signals to and from the CNS. Understanding brain regions here sets you up for studying cranial nerves, spinal nerves, and reflex arcs.
The embryonic development section ties into broader developmental biology and embryology content. Neural tube defects (spina bifida, anencephaly) are clinically important conditions covered in pathology courses that rely on understanding how the neural tube forms.
The functional cortical areas are foundational for neurological assessment and clinical neuroscience. Courses on stroke, traumatic brain injury, neuropharmacology, and neuropsychology all build on the structure-function relationships covered here.
CNS, central nervous system, brain anatomy, spinal cord, neural tube, brain vesicles, prosencephalon, mesencephalon, rhombencephalon, telencephalon, diencephalon, metencephalon, myelencephalon, cerebral hemispheres, frontal lobe, parietal lobe, temporal lobe, occipital lobe, insula, thalamus, hypothalamus, epithalamus, brain stem, midbrain, pons, medulla oblongata, cerebellum, cerebral cortex, gyri, sulci, precentral gyrus, postcentral gyrus, primary motor cortex, premotor cortex, Broca's area, frontal eye field, primary somatosensory cortex, somatosensory association cortex, primary visual cortex, striate cortex, visual association area, lateralisation, lateralization, multimodal association areas, prefrontal cortex, limbic association area, ventricular system, ventricles, cerebrospinal fluid, CSF, ependymal cells, contralateral control, motor homunculus, sensory homunculus, neural tube defects, cortical lobes, brain development, embryonic brain