Nervous System...the role and the functioning - Part 1

A system whose purpose is to control every function in the body. Without the nervous system, your muscles and other organs would be completely inactive. Your heart would not beat, blood would not circulate, and muscles would not contract. In a few words, we could classify the nervous system as the ruler of the body.

Because the nervous and muscular systems are so closely linked, to the point of being symbiotic, they are collectively called the neuromuscular system. Nerve related to nerves and Muscular related to muscles. So the connection between them is understood.

The roles of the Nervous System

Sensory: There is a vast array of sensory nerves spread throughout the body that constantly collect information such as temperature, the level of CO2 in your blood, the degree of distension of the stomach, the weight of the object you are trying to lift or the uphill of the hill where are you running.

Analysis: The information collected from myriad sensors around your body must be interpreted and analyzed to generate the appropriate response. While some responses are voluntary, many are automatic or involuntary, known as reflexes.

Output: Finally, after the input information has been collected and analyzed, the response or output is initiated, e.g. increased breathing rate due to increased CO2 levels or sweating at a higher or lower body temperature.

The main parts of the nervous system are two:

• The central nervous system or CNS.

• The peripheral nervous system or PNS.

The Central Nervous System

The central nervous system comprises the brain and spinal cord and is responsible for all conscious and unconscious decision-making.

The brain consists of two hemispheres, the cerebrum and the cerebellum, and many other parts, all of which have specialized functions. For example, the main job of the cerebellum is to control muscle actions and store memories.

The spinal cord controls reflex reactions and provides the means to connect the brain to the nerves that supply the rest of the body. It consists of cervical, thoracic, lumbar and sacral segments named after the part of the spine through which they pass.

The Peripheral Nervous System

The peripheral nervous system is the name used to describe all nerve branches outside the central nervous system. It transmits information to and from the central nervous system and is divided into motor and sensory nerves, also called neurons.

Motor neurons transmit impulses from the central nervous system to organs, glands and muscles. These impulses will cause the muscles to contract and the organs and glands to do their particular jobs. Motor nerves exit the anterior or front part of the spinal cord and essentially "flow away" from the central nervous system.

Instead, sensory neurons, attached to the posterior aspect of the spinal cord, flow to the central nervous system relaying information such as limb position, core temperature, texture, taste, and smell.

Information constantly flows to and from the central nervous system through sensory and motor neurons. Both motor and sensory neurons play an essential role in muscle contractions.

The structure of Neurons

The primary cellular unit of the nervous system is the nerve cell or neuron. Neurons are designed to transmit information quickly in response to changes inside and outside the body. They differ in size and shape depending on their function and location within the nervous system, but all neurons have different characteristic components, which we will see in detail.

• The cell body maintains the cell's metabolic activities and contains the nucleus.

• The Axon transmits the information away from the cell body and is coated with a myelin sheath for protection.

• Dendrites are located in the cell body and are the ones that receive the information or, at the end of the Axon, pass information to the next neuron.

• The myelin sheath is a protective covering that surrounds fibres called axons. The primary function of myelin is to protect and insulate these axons and to enhance the transmission of their electrical impulses.

• Neurotransmitters are chemical substances released from the presynaptic neuron into the synaptic cleft, where they can act on the corresponding receptors found on the postsynaptic neuron. Neurotransmitters are produced by the neurons themselves with the help of enzymes. Neurotransmitters are divided into two categories: excitatory and inhibitory. Excitatory messages stimulate brain function, while inhibitory messages reduce chemical reactions.

Afferent Neuron

Neurons, which carry sensory stimuli to the central nervous system, are referred to as afferent neurons. Afferent neurons convert external stimuli into internal electrical impulses.

The nerve impulse travels along afferent nerve fibres in the central nervous system. Afferent neurons collect information from sensory perceptions such as light, smell, taste, touch, and hearing from the eye, nose, tongue, skin, and ear.

The sensory signals of light are collected in the eye's retina, and these nerve impulses are carried to the brain by the afferent neurons of the eye.

Different odours stimulate afferent neurons in the nose, sending nerve impulses to the brain. The taste buds on the tongue gather sensory information about different tastes, and the nerve impulses are carried to the brain by the afferent nerves of the tongue.

The skin and nerve signals detect mechanical stimuli such as touch, pressure, stretch and temperature are sent to the brain by afferent neurons.

Different wavelengths stimulate the afferent neurons of the ear within the sensory region for each animal, and nerve impulses are transmitted to the brain.

All sensory signals are processed in the brain, and the brain coordinates the relevant organs for a specific response.

Efferent Neuron

Neurons that carry motor impulses away from the central nervous system are called efferent neurons. Efferent neurons carry information from the central nervous system to the control organs, facilitating muscle contraction and secretion of substances from glands. The cell body of the efferent neuron is connected by a single long axon, which forms neuromuscular connections with the control organs.

Similarities Between Afferent and Efferent Neurons

Afferent = Sensory Neurons

Efferent = Motor Neurons

• Afferent and Efferent neurons belong to the peripheral nervous system.

• Both neurons help the brain coordinate sensory stimuli with their responses.

• Both neurons consist of a cell body, dendrons and dendrites.

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