All sensory receptors can be classified by their structure and by the type of stimulus that they detect. Structurally, there are 3 classes of sensory receptors: free nerve endings, encapsulated nerve endings, and specialized cells. Free nerve endings are simply free dendrites at the end of a neuron that extend into a tissue. Pain, heat, and cold are all sensed through free nerve endings. An encapsulated nerve ending is a free nerve ending wrapped in a round capsule of connective tissue. When the capsule is deformed by touch or pressure, the neuron is stimulated to send signals to the CNS. Specialized cells detect stimuli from the 5 special senses: vision, hearing, balance, smell, and taste. Each of the special senses has its own unique sensory cells—such as rods and cones in the retina to detect light for the sense of vision.
Like the brain, the spinal cord is covered by the meninges and contains both gray matter and white matter. The interior of the spinal cord consists of neurons contained within an H-shaped region of the spinal cord. This region is composed of gray matter. The gray matter region is surrounded by white matter containing axons insulated with a special covering called myelin . Myelin functions as an electrical insulator that helps axons to conduct nerve impulses more efficiently. Axons of the spinal cord carry signals both away from and toward the brain along descending and ascending tracts.
The common symptoms of PACNS are: confusion, headache and personality change. Other symptoms noted are: seizures, bleeding in the head, coma and vision loss . Occasionally patients can develop symptoms similar to stroke, which can involve a wide range of neurological symptoms, such as mobility and balance problems, speech difficulties, memory loss, hearing loss, cognitive problems, difficulties controlling arms and legs, fatigue, and bladder and bowel incontinence. Usually symptoms appear over several months but can occur quickly. Some forms of CNS vasculitis can closely mimic multiple sclerosis.