Question

The given diagram is an external view of the human brain. Study the same and answer the question that follows: Mention the collective term for the membranes covering the brain.

Answer 1

Brain is the central information processing organ. It acts as the command-and-control system. Brain is protected by cranial meninges (membranous) followed by a bony cavity called a skull or cranium. Brain is divided into three parts- forebrain, midbrain and hindbrain.

Complete answer:
- Cranial Meninges: It refers to the membranous coverings of the brain and spinal cord. These coverings have the major function of providing a supportive framework for the cerebral and cranial vasculature. It is of three types:
- Durometer: It is the outermost covering. It is thick, strong and elastic in nature.
- Arachnoid: It is the middle layer which is thin and delicate.
- Pia Mater: It is the innermost membrane, and is thin and transparent.
The space between dura mater and arachnoid is the subdural space and the space between arachnoid and pia mater is the sub arachnoid space.
The subarachnoid space is filled with CSF (Cerebral Spinal Fluid), which acts as a shock absorber.
The middle membrane, Arachnoid, is one of the mammalian characteristic features.

The labelled structure in given diagram:
- Cerebrum: It is the part of the forebrain, which is made of two cerebral hemispheres, and forms the major part of the brain. The two hemispheres are connected by a tract of nerve fibers called the corpus callosum, which is the longest commissure and is also a mammalian character. Cerebrum performs function in intelligence, memory, reasoning, will power and other voluntary movements.
- Cerebellum: It is the part of the hindbrain. Cerebellum has a very convoluted surface which provides additional space for many more neurons. The white matter projects outwards and forms a branched tree-like structure called “Arbor Vitae'', the Tree of Life. The main function of cerebellum is body balance.
- Spinal Cord: It is the extension of medulla. In the center of the spinal cord there is a neural canal filled with neurocoele/CSF, that runs along with the complete cord. The cord ends with a thread-like, non-nervous part called ‘filum terminale’. The spinal cord forms the bridge between the brain and organs of the body and is involved in providing the relay path for impulses coming from the brain. Another important function is the regulation of reflex action.

The collective term for the membranes covering the brain is called cranial meninges. The parts labelled are: A-Cerebrum, B- Cerebellum, and C-Spinal cord.

Note: The other parts of brain are:
- Fore Brain: It has cerebrum, olfactory lobe, and diencephalon.
- MidBrain: divided into corpora quadrigemina and crura cerebri.
- HindBrain: It has cerebellum, pons varolii and medulla oblongata.
The neurons form grey matter (due to Nissl’s granules present in the cell body) and white matter (due to axons). The brain has inner part as white matter and outer part as grey matter, while it is opposite in spinal cord i.e., the inner part has the grey matter ang outer part has the white matter.