The Central Nervous System (CNS) is the collective name for the brain and the spinal cord. It contrasts with the Peripheral Nervous System which passes nerve signals between the CNS and rest of the body.

The CNS contains billions of nerve cells called neurons, which do all the processing and communication, and trillions of suport cells, called glial cells, which assist its functioning, repair damage and isolate it from the rest of the body. There are two different types of region in the CNS called grey matter and white matter. Grey matter is where all the processing is done and white matter is responsible for communicating between regions of grey matter and between the grey matter and the reset of the body.

In multiple sclerosis (MS), neurons get stripped of their insulating material (myelin) in patches of damage called lesions or plaques. These lesions predominantly affect the white matter (about 95%) but a few lesions are found in grey matter (about 5%).
 

Central Nervous System areas and % frequency of MS lesions over whole course of disease

Anatomical CNS Site	Function	% frequency of MS lesions
Cerebral Cortex	Memory, perceptual awareness, "thinking", language and consciousness	22.0
Subcortical White Matter	Communication between CNS areas	45.8
Central White Matter	Communication between CNS areas	86.3
Frontal Lobe	Reasoning, planning, parts of speech and movement (motor cortex), emotions, and problem-solving.	45.8
Parietal Lobe	Perception of stimuli related to touch, pressure, temperature and pain.	35.7
Occipital Lobe	Vision.	10.1
Periventricular	The areas close to the ventricles
IIIrd	Communication between CNS areas	11.1
IVth	Communication between CNS areas	53.8
Lateral	Communication between CNS areas	77.7
Corpus Callosum	Connects the right and left hemispheres of the brain	55.6
Hippocampus	Memory	21.6
Caudate Nucleus	Processing of somatosensory, auditory and visual information	9.5
Thalamus	Processing of olfactory (taste and smell) information	15.9
Putamen	Processing of somatosensory, auditory and visual information	9.5
Globus Pallidus	Coordinating movement	12.7
Internal Capsule		25.4
Fornix	Fibre tract that connects the parts of the brain involved emotional and other behaviours	4.9
Hypothalamus	Brain structure that monitors internal body environment and attempts to maintain balance of these systems. Controls the pituitary gland.	6.5
Insula/Claustrum		15.4
Tectum		47.1
Tegmentum		47.1
Periaqueductal		55.9
MidBrain	Nerve pathway of cerebral hemispheres. Coordination, Auditory and Visual reflex centres. Cranial nerves III and IV.
Red Nucleus	"	29.4
Substantia Nigra	"	29.4
Basis Pedunculi	"	35.3
Pons	Respiratory centre, cranial nerves V, VI, VII and VIII.
Tegmentum	"	53.8
Decussation	"	53.8
Medulla	Crossing of motor tracts. Cardiac and respiratory centres, control of the blood vessel walls, centres for cough, gag, swallow, and vomit. Cranial Nerves IX, X, XI and XII.
Dorsal	"	30.4
Reticular	"	35.9
Olives	"	23.9
Pyramids	"	13.0
Cerebellum	Coordination and control of voluntary movement.
Brachium Pontis	"	48.1
Inferior Cerebellar      Peduncle	"	34.5
Cortex	"	1.0
Dentate Nucleus	"	2.0
Digital White Matter	"	7.8
Central White Matter	"	30.4
Optic Nerve	Transmission of visual information from the eye to the brain	55.0
Optic Chiasm	The area where visual information crosses to the opposite hemisphere	35.0
Spinal Cord	Transmission of information between the central nervous system and the body
Lateral Column	"	50.8
Ventral Column	"	18.5
Grey Matter	"	3.4
Cord Thoracic, post, column	"
Lateral Column	"	27.1
Ventral Column	"	10.2
Grey Matter	"	3.4
Cord Lumbar, post, column	"
Lateral Column	"	8.5
Ventral Column	"	8.5
Grey Matter	"	1.7

Central Nervous System Links:
Brain Facts and Figures
Neuroscience for Kids

MS Glossary
All About Multiple Sclerosis