Brain: forebrain, midbrain, hindbrain, meninges and CSF
The brain has three parts: forebrain, midbrain and hindbrain. It is protected by the skull, three meninges and cerebrospinal fluid.
Parts of the brain and their jobs
| Region | Part | Main job |
|---|---|---|
| Forebrain | Cerebrum: two cerebral hemispheres joined by the corpus callosum | Thinking, memory, intelligence, speech, senses and voluntary actions |
| Forebrain | Thalamus | Relay centre: passes sensory and motor messages to and from the cerebrum |
| Forebrain | Hypothalamus | Controls body temperature, hunger, thirst, sleep and emotions; controls the pituitary gland |
| Midbrain | Corpora quadrigemina (four round bodies) | Reflexes of sight and hearing, e.g. turning the head towards a sudden sound |
| Hindbrain | Cerebellum | Keeps balance and posture; makes voluntary movements smooth |
| Hindbrain | Pons | Relays messages between parts of the brain; helps control breathing |
| Hindbrain | Medulla oblongata | Controls heartbeat, breathing, blood pressure, swallowing, coughing, sneezing and vomiting |
The cerebrum in more detail
The cerebrum is the largest part of the brain. A deep groove divides it into right and left cerebral hemispheres. A thick band of nerve fibres, the corpus callosum, joins the two halves. The right hemisphere controls the left side of the body, and the left controls the right. The outer layer, the cerebral cortex, is grey matter (cell bodies). It has ridges called gyri and grooves called sulci, which give more room for neurons. Inside is white matter (myelinated fibres).
Protection: meninges and cerebrospinal fluid
- The brain lies inside the bony cranium (skull).
- Three membranes called meninges cover the brain and the spinal cord.
- Duramater: the tough outer layer, just under the skull.
- Arachnoid membrane: the thin, web-like middle layer.
- Piamater: the delicate inner layer that sticks to the brain and carries blood vessels.
- Cerebrospinal fluid (CSF) fills the space between the arachnoid and piamater, the ventricles (cavities) of the brain and the central canal of the spinal cord.
- CSF acts as a shock absorber, keeps the brain moist, carries nutrients, removes wastes and keeps the pressure steady.
Cerebrum vs cerebellum
The medulla oblongata, not the cerebrum, keeps the heart beating and the lungs breathing.
How to draw the L.S. of the human brain
- 1Draw a large dome with wavy folds on top. Label cerebrum, gyri and sulci.
- 2Draw a curved band under the middle of the dome. Label corpus callosum.
- 3Below the band, draw an oval. Label thalamus. Just under it, label hypothalamus, with the pituitary gland hanging from it.
- 4Behind the thalamus, draw a short stalk with small round bumps. Label midbrain (corpora quadrigemina).
- 5At the back, under the cerebrum, draw a small rounded part with leaf-like lines. Label cerebellum.
- 6In front of the cerebellum, draw a rounded bulge. Label pons. Below it, draw a tapering stalk. Label medulla oblongata and spinal cord.
- 7Mark the three regions with brackets: forebrain, midbrain, hindbrain.
Always wear a helmet on a two-wheeler: the skull, meninges and CSF cannot protect the brain in a hard crash. Alcohol upsets the cerebellum, so a drunk person cannot walk straight or ride safely.
2 marks: “Name the three meninges that cover the brain.” Duramater (outer), arachnoid membrane (middle) and piamater (inner).
2 marks: “Mention any two functions of cerebrospinal fluid.” Acts as a shock absorber; keeps the brain moist; carries nutrients and removes wastes (any two).
7 marks: “Draw the L.S. of the human brain and describe the functions of the forebrain, midbrain and hindbrain.” Labelled diagram; forebrain: cerebrum, thalamus, hypothalamus with jobs; midbrain: corpora quadrigemina, reflexes of sight and hearing; hindbrain: cerebellum, pons, medulla with jobs; protection by meninges and CSF.
Meninges from outside in: Dura, Arachnoid, Pia, or 'Don't Annoy Pia'.