Difference Between Central and Peripheral Nervous System | Definition, Components, Function
CNS vs PNS. CNS is the Central Nervous System that functions in order to coordinate each and every activity taking place in all the parts of the. Sensory (Afferent). – convey impulses from sensory receptors to. CNS. – Afferent Consists of. – brain. – spinal cord. Spinal Cord. • Links brain and PNS. Here is a chart showing different divisions of the nervous system. The first is the central nervous system (CNS), which is the control center for The peripheral nervous system (PNS) is subdivided into several smaller units.
A network of neurons that uses its internal structure to generate temporally structured output, without requiring a corresponding temporally structured stimulus, is called a central pattern generator.Peripheral Nervous System: Crash Course A&P #12
Internal pattern generation operates on a wide range of time scales, from milliseconds to hours or longer. One of the most important types of temporal pattern is circadian rhythmicity —that is, rhythmicity with a period of approximately 24 hours.
All animals that have been studied show circadian fluctuations in neural activity, which control circadian alternations in behavior such as the sleep-wake cycle. Experimental studies dating from the s have shown that circadian rhythms are generated by a "genetic clock" consisting of a special set of genes whose expression level rises and falls over the course of the day.
Animals as diverse as insects and vertebrates share a similar genetic clock system. The circadian clock is influenced by light but continues to operate even when light levels are held constant and no other external time-of-day cues are available.
The clock genes are expressed in many parts of the nervous system as well as many peripheral organs, but in mammals, all of these "tissue clocks" are kept in synchrony by signals that emanate from a master timekeeper in a tiny part of the brain called the suprachiasmatic nucleus. Mirror neurons A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another.
Such neurons have been directly observed in primate species. Some researchers also speculate that mirror systems may simulate observed actions, and thus contribute to theory of mind skills,   while others relate mirror neurons to language abilities.
Difference between CNS and PNS
Development of the nervous system In vertebrates, landmarks of embryonic neural development include the birth and differentiation of neurons from stem cell precursors, the migration of immature neurons from their birthplaces in the embryo to their final positions, outgrowth of axons from neurons and guidance of the motile growth cone through the embryo towards postsynaptic partners, the generation of synapses between these axons and their postsynaptic partners, and finally the lifelong changes in synapses which are thought to underlie learning and memory.
The gastrula has the shape of a disk with three layers of cells, an inner layer called the endodermwhich gives rise to the lining of most internal organs, a middle layer called the mesodermwhich gives rise to the bones and muscles, and an outer layer called the ectodermwhich gives rise to the skin and nervous system. The inner portion of the neural plate along the midline is destined to become the central nervous system CNSthe outer portion the peripheral nervous system PNS.
As development proceeds, a fold called the neural groove appears along the midline. This fold deepens, and then closes up at the top.
At this point the future CNS appears as a cylindrical structure called the neural tubewhereas the future PNS appears as two strips of tissue called the neural crestrunning lengthwise above the neural tube. The sequence of stages from neural plate to neural tube and neural crest is known as neurulation.
In the early 20th century, a set of famous experiments by Hans Spemann and Hilde Mangold showed that the formation of nervous tissue is "induced" by signals from a group of mesodermal cells called the organizer region.
Induction of neural tissue requires inhibition of the gene for a so-called bone morphogenetic proteinor BMP. Specifically the protein BMP4 appears to be involved. Two proteins called Noggin and Chordinboth secreted by the mesoderm, are capable of inhibiting BMP4 and thereby inducing ectoderm to turn into neural tissue.
It appears that a similar molecular mechanism is involved for widely disparate types of animals, including arthropods as well as vertebrates.
In some animals, however, another type of molecule called Fibroblast Growth Factor or FGF may also play an important role in induction.
Induction of neural tissues causes formation of neural precursor cells, called neuroblasts. A GMC divides once, to give rise to either a pair of neurons or a pair of glial cells. In all, a neuroblast is capable of generating an indefinite number of neurons or glia.
As shown in a study, one factor common to all bilateral organisms including humans is a family of secreted signaling molecules called neurotrophins which regulate the growth and survival of neurons.
DNT1 shares structural similarity with all known neurotrophins and is a key factor in the fate of neurons in Drosophila. Because neurotrophins have now been identified in both vertebrate and invertebrates, this evidence suggests that neurotrophins were present in an ancestor common to bilateral organisms and may represent a common mechanism for nervous system formation. Psychiatry Layers protecting the brain and spinal cord.
Brain CNS and PNS
The central nervous system is protected by major physical and chemical barriers. Physically, the brain and spinal cord are surrounded by tough meningeal membranes, and enclosed in the bones of the skull and vertebral columnwhich combine to form a strong physical shield. Chemically, the brain and spinal cord are isolated by the blood—brain barrierwhich prevents most types of chemicals from moving from the bloodstream into the interior of the CNS.
Although nerves tend to lie deep under the skin except in a few places such as the ulnar nerve near the elbow joint, they are still relatively exposed to physical damage, which can cause pain, loss of sensation, or loss of muscle control. Damage to nerves can also be caused by swelling or bruises at places where a nerve passes through a tight bony channel, as happens in carpal tunnel syndrome.
If a nerve is completely transected, it will often regeneratebut for long nerves this process may take months to complete. Many cases have no cause that can be identified, and are referred to as idiopathic. It is also possible for nerves to lose function temporarily, resulting in numbness as stiffness—common causes include mechanical pressure, a drop in temperature, or chemical interactions with local anesthetic drugs such as lidocaine.
A stegosaurus dinosaur weighed approximately 1, kg but had a brain that weighed only approximately 70 grams 0. Therefore, the brain was only 0. In contrast, an adult human weighs approximately 70 kg and has a brain that weighs approximately 1. This makes the brain to body ratio of the human times greater than that of the stegosaurus. Peripheral Nervous System The peripheral nervous system is divided into two major parts: Somatic Nervous System The somatic nervous system consists of peripheral nerve fibers that send sensory information to the central nervous system AND motor nerve fibers that project to skeletal muscle.
The picture on the left shows the somatic motor system. The cell body is located in either the brain or spinal cord and projects directly to a skeletal muscle.
Difference between CNS and PNS
Autonomic Nervous System The autonomic nervous system is divided into three parts: The autonomic nervous system controls smooth muscle of the viscera internal organs and glands. This picture shows the general organization of the autonomic nervous system. The preganglionic neuron is located in either the brain or the spinal cord. This preganglionic neuron projects to an autonomic ganglion.
Peripheral nervous system
The postganglionic neuron then projects to the target organ. Notice that the somatic nervous system has only one neuron between the central nervous system and the target organ while the autonomic nervous system uses two neurons.
The enteric nervous system is a third division of the autonomic nervous system that you do not hear much about.