Nervous system
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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 participants in a nervous system include neurons and nerves, which play roles in such coordination. All parts of the nervous system are made of nervous tissue.
Worms
Planarian, a type of flatworm, have dual nerve cords running along the length of the body and merging at the tail. 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 darkness.
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 bugs 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 controls the mouthparts.
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.
Mollusca
Most molluscs, such as snails and bivalves, have several groups of intercommunicating neurons called ganglia. The nervous system of the sea hare Aplysia has been extensively used in neuroscience experiments because of its simplicity and ability to learn simple associations.
The cephalopods, such as squid and octopuses, have relatively complex brains. These animals also have complex eyes. As in all invertebrates, the axons in cephalopods lack myelin, the insulator that allows fast saltatory conduction of action potentials in vertebrates. To achieve a high enough conduction velocity to control muscles in distal tentacles, axons in the cephalopods must have a very wide diameter in the larger species of cephalopods. For this reason, the squid giant axons were used by neuroscientists to work out the basic properties of the action potential.
Vertebrates
| Peripheral | Somatic | |
| Autonomic | Sympathetic | |
| Parasympathetic | ||
| Enteric | ||
| Central | ||
The nervous system of 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. 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 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 cancer.
Parts of the Nervous System
There are three essential parts of the nervous system. These include the brain, the spine, and the nerves. The brain has three main parts that interact with the nervous system: the cerebrum, the cerebellum, and the medulla. Examples of the cerebrum's tasks include high-order thinking and learning, while the cerebellum manages learned automatic bodily functions, including walking, jumping, and running. The medulla processes simple body functions, such as breathing and digestion
The spine is the area where reflexes are made. Split-second decisions do not go back to the brain and then back to the organ or body part. This would take too long and the nerve impulse would arrive too late to prevent the stimulus from becoming reality. For instance, if a ball was thrown at an individual's head, the reflex to move out of the way would come from the spine, not the brain, increasing reaction time. The spine is also the "highway" which passes orders from the brain to motor nerves.
There are four kinds of nerves: motor, sensory, afferentnerves, and interneurons. Messages carried in all nerve types travel in only one direction.
See also
- Major systems of the human body
- Neural network
- Neuroendocrinology
- Neuroscience
- Neurotoxin
- Neural ensemble
- Somatic sensation
External links
Reference:
| Human organ systems |
|---|
| Cardiovascular system | Digestive system | Endocrine system | Immune system | Integumentary system | Lymphatic system | Muscular system | Nervous system | Skeletal system | Reproductive system | Respiratory system | Urinary system |
| Nervous system, receptors: somatosensory system |
|---|
| Medial lemniscus: Touch/mechanoreceptors: Pacinian corpuscles - Meissner's corpuscles - Merkel's discs - Ruffini endings - Free nerve endings - Hair cells - Baroreceptor Proprioception: Golgi organ - Muscle spindle (Intrafusal muscle fiber) Spinothalamic tract: Pain: Nociceptors Temperature: Thermoreceptors |
Neural development/Neurulation - Neurula - Neural folds - Neural groove - Neural tube - Neural crest - Neuromere (Rhombomere) - Notochord - Neural plate
Eye development - Optic vesicles - Optic stalk - Optic cup - Auditory vesicle - Auditory pit
Neurons (gray matter): soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine)
types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
Afferent nerve/Sensory nerve/Sensory neuron (GSA, GVA, Type Ia sensory fiber), Efferent nerve/Motor nerve/Motor neuron (GSE, GVE, Alpha motor neuron, Gamma motoneurons, Upper motor neuron, Lower motor neuron), Interneuron (Renshaw)
Synapses: neuropil, boutons, synaptic vesicle, neuromuscular junction, electrical synapse
Sensory receptors: Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor, Hair cell, Taste bud
Glial cells: astrocyte, ependymal cells, microglia, radial glia
Myelination (white matter): Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
closely related Connective tissue: epineurium, perineurium, endoneurium, nerve fascicle, meninges
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