By Dr Ananya Mandal, MD
The nervous system is formed of two parts that are integrally linked with each other. The brain and the nervous system has multiple functions that are vital for normal functioning of the body.
Transmission of nerve impulses
A nerve impulse is essentially an electrical stimulus that travels over the cell's membrane. It passes through the axons and dendrites of the neurons. It travels via the dendrites from the skin and then reaches the cell body, axon, axon terminals and the Synapse of the neuron.
The Synapse is the junction between two neurons where the impulse moves from one to the other. At the synapse neurotransmitters are present. These are chemical transmitters of messengers that transmit the impulse. They include Acetylcholine and Noradrenaline.
The impulse continues to the next dendrite, in a chain reaction till it reaches the brain that in turn instructs the skeletal muscles to work.
The Reflex Arc
These reflexes are automatic, involuntary responses. They may or may not involve the brain for example blinking does not involve the brain. The Reflex arc is the main functional unit of the nervous system that helps a person react to a stimulus.
Functions of different parts of the nervous system
Different parts of the nervous system have different functions. They can be outlined as follows.
Functions of the brain
The brain is made up of several parts. Each part has a certain function:
Thought , voluntary movement , language, reasoning and perception are the major functions of the cerebral cortex.
Cortex literally means "bark" (of a tree) in latin and is so termed because it is a sheet of tissue that makes up the outer layer of the brain.
The thickness of the cerebral cortex is between 2 to 6 mm. The right and left sides of the cerebral cortex are connected by a thick band of nerve fibers called the "corpus callosum."
The cortex has numerous grooves and bumps to increase its surface area. A bump or bulge on the cortex is called a gyrus (the plural of the word gyrus is "gyri") and a groove is called a sulcus (the plural of the word sulcus is "sulci").
The major functions of the cerebellum are maintenance of movement, balance and posture. The word "cerebellum" comes from the Latin word for "little brain." It is divided into two parts or hemispheres and has a cortex that covers the hemispheres.
The hypothalamus regulates the body temperatures, emotions and hunger, thirst and controls the circadian rhythms.
This pea sized organ is in control of body temperature. It acts like a "thermostat" by sensing changes in body temperature and sends out signals to adjust the temperature.
Brain stem or Medulla oblongata
This area is vital for life as it controls breathing, heart rate and blood pressure. The brain stem comprises of the medulla, pons, tectum, reticular formation and tegmentum.
Works by integrating sensory information and motor information. The thalamus receives sensory information and relays this information to the cerebral cortex.
The cerebral cortex also sends information to the thalamus which then transmits this information to other areas of the brain and spinal cord.
This part of the brain includes amygdala, the hippocampus, mammillary bodies and cingulate gyrus. These help in controlling the emotional response. The hippocampus is also important for learning and memory.
This part works in maintaining balance and movements. It includes structures like the globus pallidus, caudate nucleus, subthalamic nucleus, putamen and substantia nigra.
This part of the brain has sites controlling vision, hearing, eye movement and general body movement. The structures that are part of the midbrain are superior and inferior colliculi and red nucleus.
Functions of the Cerebrospinal nervous system
This system has 12 pairs of cranial nerves. These are attached to the brain and have specific functions. Each cranial nerve leaves the skull through an opening at its base.
The nerves and their functions include:
- Olfactory – for smell
- Optic - Sight
- Oculomotor - Movement of the eyeball, lens, and pupils
- Trochlear – Movement of the Superior oblique muscle of the eye
- rigeminal – Innervates the eyes, cheeks and the jaw areas and controls chewing
- Abducens - Moves the eye outward
- Facial - Controls muscles of the face, scalp, ears; controls salivary glands; receives taste sensation from the anterior two-thirds of the tongue
- Acoustic – Hearing and maintenance of balance
- Glossopharyngeal – Taste sensation from the back of the tongue and throat
- Vagus – Innervates the chest and abdominal organs
- Spinal Accessory - movement of head and shoulders
- Hypoglossal - Controls muscles of tongue
Functions of the Autonomic nervous system
The autonomic nervous system is divided into sympathetic and parasympathetic nervous systems. These two systems have opposite effects on the same set of organs.
The sympathetic nervous system is important during an emergency and is associated with “fight or flight reaction”. The energy is directed away from digestion, there is dilation of pupils, increased heart rate, increased perspiration and salivation, increased breathing etc.
The parasympathetic nervous system is associated with a relaxed state. The pupils contract, energy is diverted for digestion of food, heart rate slows etc.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)