Nervous System

The nervous system is made of two parts viz. Central Nervous System (CNS) and the Peripheral Nervous System (PNS). CNS is made of Brain {cerebrum, brainstem and cerebellum} and spinal cord. The PNS is made of nerves and neural ganglia. Further, the meninges {three membranes that envelop the brain and spinal cord) are also a part of the nervous system.

Cells of the Nervous System

The main cells of the nervous system are neurons. In addition to neurons, the nervous system is also made up of glial cells. Neurons are cells that have the function of receiving and transmitting neural impulses. Glial cells support, feed and electrically insulate the neurons. One common example of Glial cells are the so called “Schwann cells” that produce the myelin sheath of the peripheral nervous system.

Neuron

The neuron is the functional unit of the nervous system with 3 parts viz. Dendrite, Cell Body and Axon. Dendrites receive information from another cell and transmit the message to the cell body.  The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells. The axon conducts messages away from the cell body.

There are three types of the Neurons viz. Sensory, Motor and Inter. Sensory neurons carry messages from sensory receptors to the central nervous system. Motor neurons transmit messages from the central nervous system to the muscles. Inter neurons are found only in the central nervous system where they connect neuron to neuron.

Some axons are wrapped in a myelin sheath by specialized glial cells known as Schwann cells. The gap between Schwann cells is known as the Node of Ranvier, and serves as points along the neuron for generating a signal.

Synapses

Synapses are the structures that transmit a neural impulse between two neurons. When the electric impulse arrives, the presynaptic membrane of the axon releases neurotransmitters that bind to the postsynaptic receptors of the dendrites of the next cell. The activated state of these receptors alters the permeability of the dendritic membrane and the electric depolarization moves along the plasma membrane of the neuron to its axon.

Brain

The brain is made up of three main sections: the forebrain, the midbrain, and the hindbrain.

Forebrain

The forebrain is the largest and most complex part of the brain. It consists of the cerebrum and some other structures beneath it. The cerebrum contains the information that essentially makes us who we are: our intelligence, memory, speech, ability to feel etc.  Specific areas of the cerebrum are in charge of processing these different types of information. These are called lobes, and there are four of them: the frontal, parietal, temporal, and occipital lobes.

The cerebrum has right and left halves, called hemispheres, which are connected in the middle by a band of nerve fibers (corpus collosum) that enables the two sides to communicate.

The left side is considered the logical, analytical, objective side. The right side is thought to be more intuitive, creative, and subjective.

The outer layer of the cerebrum is called the cortex (also known as “gray matter”).  Information collected by the five senses comes into the brain from the spinal cord to the cortex. This information is then directed to other parts of the nervous system for further processing.

• In the inner part of the forebrain sits the thalamus, hypothalamus, and pituitary gland.
• The thalamus carries messages from the sensory organs like the eyes, ears, nose, and fingers to the cortex.
• The hypothalamus controls the pulse, thirst, appetite, sleep patterns, and other processes in our bodies that happen automatically.
• It also controls the pituitary gland, which makes the hormones that control our growth, metabolism, digestion, sexual maturity, and response to stress.

The Midbrain

The midbrain, located underneath the middle of the forebrain, acts as a master coordinator for all the messages going in and out of the brain to the spinal cord.

The Hindbrain

The hindbrain sits underneath the back end of the cerebrum, and it consists of the cerebellum, pons, and medulla.

The cerebellum — also called the “little brain” because it looks like a small version of the cerebrum — is responsible for balance, movement, and coordination.

The pons and the medulla, along with the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates all of the brain’s messages.

It also controls many of the body’s automatic functions, like breathing, heart rate, blood pressure, swallowing, digestion, and blinking.

Spinal cord

The spinal cord is a long bundle of nerve tissue about 18 inches long and ¾ inch thick. It extends from the lower part of the brain down through spine. Along the way, various nerves branch out to the entire body. These are called the peripheral nervous system. Both the brain and the spinal cord are protected by bone: the brain by the bones of the skull, and the spinal cord by a set of ring-shaped bones called vertebrae. They’re both cushioned by layers of membranes called meninges as well as a special fluid called cerebrospinal fluid.