Nervous system

The nervous system gathers, analyses, stores, and transmits information. It controls vital body functions and interacts with the outside world. There are two parts: the central nervous system, which comprises the brain and spinal cord, and the peripheral nervous system, which is made up of nerves that branch from the brain and spinal cord to all areas of the body. Signals, in the form of tiny electrical impulses, are transmitted through the nervous system from the brain to the rest of the body and vice versa. The brain controls almost all activities – both conscious activities, such as movement, and unconscious functions, such as maintaining body temperature. It also receives information from the nerves about the environment and the condition of other parts of the body. For example, the nerves leading from the eyes register visual information and nerves beneath the surface of the skin transmit sensations such as pain. In addition, the brain is capable of complex processes such as learning, memory, thought, and emotion, and can instruct the body to act on the basis of these processes.

Structure and function of the brain

The brain is the most complex organ in the body. It has more than 100 billion nerve cells and billions of pathways. The largest part of the brain is the cerebrum. It is divided into two halves (hemispheres), which are connected by a bundle of nerve fibres called the corpus callosum. brainThe outer layer (cerebral cortex) consists of tissue called grey matter, which generates and processes nerve signals. The inner layer consists of white matter, which transmits the signals. The cerebrum controls conscious thought and movement and interprets sensory information; different parts govern specific activities such as speech and vision. A structure at the base of the brain called the cerebellum controls balance, coordination, and posture. The brain is connected to the spinal cord by the brainstem, which controls vital functions such as respiration. Just above the brainstem is the hypothalamus, which links the nervous system and the endocrine system and helps to regulate body temperature, sleep, and sexual behaviour. The brain is protected by the skull and by membranes called meninges. Clear cerebrospinal fluid cushions the brain and spinal cord from injury.

Organization of the nervous system

nervous-systemThe central nervous system, comprising the brain and spinal cord, processes and coordinates nerve signals. The spinal cord forms the link between the brain and the rest of the body. Motor pathways, which carry messages from the brain, descend through the spinal cord, while sensory pathways from the skin and other sensory organs ascend through the spinal cord carrying messages to the brain. A network of peripheral nerves reaches all parts of the body. Each nerve is formed from hundreds of nerve fibres, which project from nerve cells, grouped in bundles. Thirty-one pairs of nerves branch off the spinal cord. These divide into smaller and smaller nerves throughout the torso and the limbs.

spinal-cardStructure of the spinal cord

The spinal cord is made up of grey matter, which contains nerve cells and supporting cells, and white matter, which contains nerve fibres. The cord is enclosed by protective membranes called meninges.

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