Nervous System

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Genetic Disorders

2.17   Our genes (the hereditary materials in cells) carry instructions for the development of the brain. These instructions are extremely complex and so errors occasionally occur. Errors in the instructional material can lead to serious defects, like mental retardness in the structure and functioning of the brain.

 Concussion

2.18   When the head receives a violent blow – such as from a fall – the brain is jarred. The force of the blow hitting the skull interferes with normal brain function and is called a concussion. If the force is mild, loss of consciousness may occur but will usually last only a few seconds. However, if the force is intense, loss of consciousness may be prolonged and damage may be extensive. It is common for a person to experience confusion or even amnesia following a concussion. Although the damage may not be obvious from the outside, concussions can be very dangerous.

The Spinal Cord

2.19   The spinal cord is a cable of nerve tissue that extends from the base of the brain to just below the level of the ribs. In adults, it is about the thickness of the little finger. The spinal cord is surrounded by the spinal column (backbone), which protects it. Thirty-one pairs of spinal nerves connect the spinal chord with the rest of the body. The spinal nerves are composed of millions of both sensory neurons and motor neurons. These neurons transfer millions of messages or impulses between the body and the brain.

2.20   Spinal Cord Injuries – Spinal cord injuries are relatively common. About 45 percent of all spinal cord injuries are incurred in motor-vehicle accidents. Injuries to the spinal cord can alter or prevent communication between the brain and the body. If the injury is serious enough, paralysis can occur. In general, the higher up on the spinal cord the injury is, the more severe the damage will be. Damage to the spinal cord in the neck can result in paralysis from the neck down, while injuries lower on the spinal chord may produce paralysis only in the legs.

 Reflexes

2.21   Reflexes are involuntary responses to stimuli and are not controlled by the brain. Reflex movements take only a split second to occur. For example, when a person touches a hot stove, a nerve impulse travels through a sensory neuron in the person’s hand to the spinal chord. There, it is transferred first to an association neuron and then to a motor neuron traveling quickly back to the hand. In a split second, the withdrawal reflex pulls the hand away from the stove. If this message had to go through the brain, the response time would be longer increasing the possibility of injury.

Sensory Receptors and Sense Organs

2.22   Your senses are the window through which you view the world around you. They allow you to interpret changes in your internal and external environment. One day you may feel well; the next day you may have a headache. Your senses are what provide this information to the brain, which in turn, interprets it. Not everyone interprets information in the same way chord