Brain: MDCAT Biology notes
Brain MDCAT notes: meninges, forebrain, midbrain and hindbrain, cerebrum, thalamus, hypothalamus, limbic system, cerebellum, pons, medulla, spinal cord.
Protection: meninges
The brain and spinal cord are covered by three meninges. From outside in, they are:
- Dura mater: tough and outermost.
- Arachnoid mater: the middle layer.
- Pia mater: thin and innermost, lying on the nervous tissue.
Cerebrospinal fluid circulates in the space under the arachnoid.
Divisions of the brain
| Division | Parts |
|---|---|
| Forebrain | Cerebrum, thalamus, hypothalamus, limbic system (including the hippocampus and amygdala), olfactory bulbs |
| Midbrain | Relay centres for visual and auditory reflexes, such as the reflexes of the eyes |
| Hindbrain | Medulla oblongata, pons, cerebellum |
The brain stem is the midbrain, pons and medulla oblongata. The reticular formation is a network of neurons running through the brain stem (midbrain and hindbrain). It filters sensory input and keeps the brain alert.
Forebrain
Cerebrum
The cerebrum is the largest part of the brain. It is split into left and right hemispheres, joined by the corpus callosum, a thick band of axons. The outer cerebral cortex is grey matter, made of neuron cell bodies (somas). The inner cerebral medulla is white matter, made of myelinated axons. The cerebrum handles thinking, reasoning, problem solving (such as a mathematician working out an equation), language, voluntary movement and interpreting sensations. The olfactory bulbs lie at the anterior end of the hemispheres.
Thalamus
The thalamus is the main relay centre. It receives sensory input from the eyes, ears, skin and internal organs and passes it to the cerebrum.
Hypothalamus
The hypothalamus regulates hunger, thirst, water balance, body temperature and sleep, and it controls the pituitary gland. It does not store long-term memories.
Limbic system
The limbic system is made up of the hypothalamus, amygdala and hippocampus. It produces basic, primitive emotions and drives.
- Amygdala: emotions such as love, hate, fear and rage.
- Hippocampus: forming long-term memory and memory storage.
Hindbrain
- Cerebellum: the second-largest part of the brain. It coordinates skeletal muscles and makes movements smooth and accurate. It maintains posture, balance and equilibrium, and it stores motor memory for learned movements. It is well developed in birds because flight needs fine coordination.
- Pons: a bridge between the brain parts. It helps the medulla regulate breathing and controls the transition between sleep and wakefulness.
- Medulla oblongata: controls breathing, heart rate and blood pressure. It contains the central chemoreceptors that monitor blood $\mathrm{CO_2}$. It controls the reflexes of vomiting, coughing, sneezing and swallowing.
Spinal cord
The spinal cord is part of the central nervous system. It is about 40–50 cm long and is protected by the vertebral column and the three meninges. In the spinal cord the pattern is reversed: grey matter is on the inside (in a butterfly shape) and white matter is on the outside.
Common MDCAT traps
- The arachnoid is the middle meninx. Dura is outer and pia is inner.
- The corpus callosum joins the hemispheres. The corpus luteum is in the ovary.
- The medulla is part of the hindbrain, and the brain stem does not include the cerebellum.
- Balance and posture belong to the cerebellum. Breathing belongs to the medulla.
- Eye reflexes are handled by the midbrain, not the limbic system.
Quick revision
- The thalamus relays sensory input to the cerebrum.
- The amygdala controls emotions; the hippocampus controls long-term memory.
- Grey matter is made of neuron cell bodies.
- The medulla controls the vomiting, coughing and sneezing reflexes.
- The spinal cord has three meninges.