Question

Among thalamus, hypothalamus, cerebral cortex, cerebral medulla, cerebellar cortex, cerebellar medulla, pons and medulla, which are composed of grey matter and which are with white matter? Support our answer with the reason.

Answer 1

The central nervous system (CNS) comprises two parts namely: The brain and the spinal cord. The central nervous system consists of bones and the meninges. It comprises a fluid named as the Cerebrospinal fluid. This fluid protects the CNS from any injury. While the brain is protected by the skull of bones, which is the biggest organ of the human body.

Complete answer:
Brain forms the major part of the central nervous system present above the spinal cord and weighs about 3 pounds. The brain is mainly composed of white matter and grey matter which are situated in two different membranes. White matter is differentiated from gray matter because the white matter comprises very limited cell bodies and a large number of myelinated axons while gray matter comprises various cell bodies and very limited myelinated axons.
Thalamus, Hypothalamus, cerebral medulla pons and medulla are made of the white matter because these parts of the brain are coated with myelinated cells called myelinated sheath and because of the presence of myelin, they appear to be white in colour as myelin is white.
Cerebral cortex, cerebellar cortex and cerebellar medulla are composed of the gray matter because in these parts of the brain, unmyelinated neurons are present and inside these neurons, capillaries of blood are present and due to the absence of myelin, they appear gray in colour.

Note: Hypothalamus is made up of gray matter fibres according to the structural point of view. But, it is also composed of white matter fibres as it is covered by myelinated nerve fibres. The output fibre tract of the thalamus is called optic radiations and these radiations project to the central observable cortex.