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The 'nervous system' of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. Prominent parts of a nervous system include neurons and nerves, which are used in coordination. All parts of the nervous system are made of nervous tissue. The classification of the nervous system is mostly similar in humans as in other vertebrates.

Contents

Humans

Central nervous system

Peripheral nervous system

By direction

By function

Vertebrates

Worms

Arthropoda

See also

External links

Humans

The nervous system of humans is often divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord.

Central nervous system

The central nervous system (CNS) represents the largest part of the nervous system, including the brain and the spinal cord. Together with the peripheral nervous system, it has a fundamental role in the control of behavior. The CNS is contained within the dorsal cavity, with the brain within the cranial subcavity, and the spinal cord in the spinal cavity. The CNS is covered by the meninges. The brain is also protected by the skull, and the spinal cord is also protected by the vertebrae.

Central nervous system	Brain	Prosencephalon	Telencephalon	Rhinencephalon, Amygdala, Hippocampus, Neocortex, Lateral ventricles
			Diencephalon	Epithalamus, Thalamus, Hypothalamus, Subthalamus, Pituitary gland, Pineal gland, Third ventricle
		Brain stem	Mesencephalon	Tectum, Cerebral peduncle, Pretectum, Mesencephalic duct
			Rhombencephalon	Metencephalon	Pons, Cerebellum,
				Myelencephalon	Medulla oblongata
	Spinal cord

Peripheral nervous system

The PNS consists of all other nerves and neurons that do not lie within the CNS. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS. The peripheral nervous system can be further classified either by direction of neurons and by function.

By direction

There are three types of directions of the neurones:

★ Sensory system by sensory neurons, which carry impulses from a receptor to the CNS

★ Efferent system by motor neurons, which carry impulses from the CNS to an effector

★ Relay system by relay neurons, which transmit impulses between the sensory and motor neurones. However, there are relay neurons in the CNS as well.
The junction between two neurones is called a synapse. There is a very narrow gap between the neurones - the synaptic cleft.

By function

By function, the peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system.
The somatic nervous system is responsible for coordinating the body's movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control.
The autonomic nervous system is then split into the sympathetic division, parasympathetic division, and enteric division. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and genitourinary systems. The role of the enteric nervous system is to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon.

Peripheral nervous system	by direction	sensory system
		efferent system
	By function	Somatic
		Autonomic	Sympathetic
			Parasympathetic
			Enteric

Vertebrates

The nervous system of all vertebrate animals, is often divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord.

Worms

Planaria, a type of flatworm, have dual nerve cords running along the length of the body and merging at the tail and the mouth. These nerve cords are connected by transverse nerves like the rungs of a ladder. These transverse nerves help coordinate the two sides of the animal. Two large ganglia at the head end function similar to a simple brain. Photoreceptors on the animal's eyespots provide sensory information on light and dark.
The nervous system of the roundworm ''Caenorhabditis elegans'' has been mapped out to the cellular level. Every neuron and its cellular lineage has been recorded and most, if not all, of the neural connections are known. In this species, the nervous system is sexually dimorphic; the nervous systems of the two sexes, males and hermaphrodites, have different numbers of neurons and groups of neurons that perform sex-specific functions. In ''C. elegans'', males have exactly 383 neurons, while hermaphrodites have exactly 302 neurons [1]

Arthropoda

Arthropods, such as insects and crustaceans, have a nervous system made up of a series of ganglia, connected by a ventral nerve cord made up of two parallel connectives running along the length of the belly [2]. Typically, each body segment has one ganglion on each side, though some ganglia are fused to form the brain and other large ganglia [3].
The head segment contains the brain, also known as the supraesophageal ganglion. In the insect nervous system, the brain is anatomically divided into the protocerebrum, deutocerebrum, and tritocerebrum. Immediately behind the brain is the subesophageal ganglion, which is composed of three pairs of fused ganglia. It controls the mouthparts, the salivary glands and certain muscles.
Many arthropods have well-developed sensory organs, including compound eyes for vision and antennae for olfaction and pheromone sensation. The sensory information from these organs is processed by the brain.

See also

★ Major systems of the human body

★ Neural network

★ Neuroendocrinology

★ Neuroscience

★ Neurotoxin

★ Neural ensemble

★ Somatic sensation

External links

★ Neuroscience for Kids

★
Reference:

★ Kimball's Biology Pages, CNS

★ Kimball's Biology Pages, PNS