The nervous system is a highly sophisticated element of an animal that organises its actions and sensory information by conveying signals to and from different sections of its body, according to the classical doctrine of biology. The nervous system detects changes in the environment that affect the body and then works in unison with the endocrine system to respond. Around 550 to 600 million years ago, nerve tissue initially appeared in wormlike invertebrates. However, findings about the existence and usage of electrical impulses in plants have cast doubt on this fundamental notion in recent decades.
Some scientists have advocated that a plant nervous system exists and that a scientific field called plant neurobiology be established as a result of their results. This proposition has sparked a debate in the scientific community between those who believe we should discuss plant nervous systems and those who oppose it. Due to the inflexibility of both sides’ stances in the scientific dispute, a solution has been proposed, which involves redefining the nervous system using just physiological criteria and eliminating phylogeny criteria.
The central nervous system (CNS) and the peripheral nervous system (PNS) are the two primary elements of the nervous system in vertebrates (PNS). The brain and spinal cord make up the central nervous system. Nerves, which are enclosed bundles of long fibres or axons that connect the CNS to every other portion of the body, make up the majority of the PNS. Motor nerves, also known as efferent nerves, send signals from the brain, whereas sensory nerves, also known as afferent nerves, transmit information from the body to the CNS. Spinal nerves are a type of mixed nerve that has two functions. The somatic, autonomic, and enteric nervous systems are the three subsystems of the PNS. Voluntary movement is mediated by somatic nerves. The sympathetic and parasympathetic nervous systems are subsets of the autonomic nervous system.
In emergencies, the sympathetic nervous system is triggered to mobilise energy, whereas when organisms are relaxed, the parasympathetic nervous system is active. The gastrointestinal system is controlled by the enteric nervous system. Both the autonomic and enteric nervous systems work without our knowledge. The nerves that escape the cranium are referred to as cranial nerves, whereas those that exit the spinal cord are referred to as spinal nerves.
The presence of a unique type of cell called a neuron, sometimes known as a “nerve cell,” defines the nervous system at the cellular level. Neurons have unique features that allow them to convey signals to neighbouring cells quickly and precisely. They provide these signals in the form of electrochemical impulses that travel along thin fibres called axons and can be directly communicated to nearby cells via electrical synapses or cause neurotransmitters to be produced via chemical synapses. When a cell gets a synaptic signal from a neuron, it can be stimulated, inhibited, or modified in some way. Neural pathways, neural circuits, and bigger networks formed by the connections between neurons can generate an organism’s experience of the world and control its behaviour. Other specialised cells called glial cells (or simply glia) offer structural and metabolic support to neurons in the nervous system.
Nervous systems can be found in most multicellular species, but their complexity varies substantially. Sponge, placozoans, and mesozoans, which have relatively simple body designs, are the only multicellular organisms without a nervous system. A diffuse nerve net makes up the neural systems of radially symmetric creatures such as ctenophores (comb jellies) and cnidarians (which include anemones, hydras, corals, and jellyfish). Except for a few types of worms, all other animal species have a nervous system that includes a brain, a central cord (or two cords running in parallel), and nerves radiating from the brain and central cord. The nervous system can be as small as a few hundred cells in worms to as large as 300 billion cells in African elephants.
The central nervous system’s job is to send and receive messages from one cell to another, or from one portion of the body to another. Genetic flaws, physical damage from trauma or toxicity, infection, or just senesence can all cause nervous system dysfunction. Neurology is a medical speciality that investigates nervous system problems and works for ways to prevent or treat them. The most prevalent problem in the peripheral nervous system is nerve conduction failure, which can be caused by a variety of factors, including diabetic neuropathy and demyelinating illnesses like multiple sclerosis and amyotrophic lateral sclerosis. Neuroscience is a branch of science concerned with the investigation of the nervous system.