The Nervous System and the Brain
The nervous system is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body. It is essentially the body’s electrical wiring. Structurally, the nervous system has two components: the central nervous system and the peripheral nervous system which includes the nerves that extend from the brain and the spinal cord. The brain of an average-sized adult weighs about three pounds, yet the amount of information it contains is amazing!
Parts of Brain
The brain lies within the skull and is shaped like a mushroom. The brain consists of four principal parts:
- The cerebrum—the large, upper part of the brain—orchestrates memory, thoughts and learned behaviour. The cerebrum’s surface is called the cerebral cortex, and is convoluted—patterned with intricate twists.
- The cerebellum—the underneath part of the brain—coordinates voluntary muscle action and balance.
- The brainstem—the distal part of the brain that is made up of the midbrain, pons, and medulla oblongata—connects to the spinal cord and controls involuntary activities.
The cerebrum is divided into two hemispheres, or halves, which are connected by a communication bridge called the corpus callosum. Each hemisphere controls the actions of the opposite side of the body.
- The diencephalon—the fore brain stem. It includes the thalamus and hypothalamus. The thalamus is where sensory and other impulses go and coalesce.
The hypothalamus is a smaller part of the diencephalon
Other parts of the brain include the midbrain and the pons:
- the midbrain provides conduction pathways to and from higher and lower centers
- the pons acts as a pathway to higher structures; it contains conduction pathways between the medulla and higher brain centres
In human brains and some animal brains, there are certain specific skills that are controlled by each hemisphere. In human brains, the left hemisphere controls temporal (time) judging skills, rhythm processing, mathematics skills and both spoken and written language skills. The right hemisphere controls pattern-matching, hand-eye coordination, facial recognition, non-speech-sound processing, and music skills. Logic or artistic ability can be on either side, depending on which skills a person is strongest in.
Experiments and research have been done which demonstrate where certain thought activities take place. The split-brain phenomenon is an indicator of which skills are located in each hemisphere. Split-brain patients have had their corpus callosum severed, usually to cure epileptic seizures. This means that the two hemispheres can no longer communicate with each other. Research on split-brain patients has shown that what the right hemisphere knows can only be communicated non-linguistically—without using written or spoken language. However, what the left hemisphere knows can be expressed using language, indicating that language skills are contained in the left hemisphere.
- Nerve cells, called neurons, are the communications cells of the nervous system. Hair-like tentacles (dendrites), which extend from the cell body, are the neuron’s receivers.
- The axon, a tail-like structure on the cell body, is the neuron’s transmitter.
- The synapseis the connection point between two neurons or a neuron and a muscle or gland cell.
Our skin has pain receptors, both mechanoreceptors that that allow us to feel pressure and touch, and thermoreceptors that allow us to feel heat and cold. With all of our senses, an electrochemical signal is passed between neurons and travels through the nerves, spinal cord, and brain.
The branch of medicine that studies and treats the nervous system is called neurology, and doctors who practice in this field of medicine are called neurologists. Once