- published: 23 Mar 2015
- views: 345120
The central nervous system (CNS) is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except radially symmetric animals such as sponges and jellyfish. It contains the majority of the nervous system and consists of the brain and the spinal cord. Some classifications also include the retina and the cranial nerves in the CNS. 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 in the cranial cavity and the spinal cord in the spinal cavity. In vertebrates, the brain is protected by the skull, while the spinal cord is protected by the vertebrae, and both are enclosed in the meninges.
During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens and the ridges on either side of the groove (the neural folds) become elevated, and ultimately meet, transforming the groove into a closed tube, the ectodermal wall of which forms the rudiment of the nervous system. This tube initially differentiates into three vesicles (pockets): the prosencephalon at the front, the mesencephalon, and, between the mesencephalon and the spinal cord, the rhombencephalon. (By six weeks in the human embryo) the prosencephalon then divides further into the telencephalon and diencephalon; and the rhombencephalon divides into the metencephalon and myelencephalon.
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous system of vertebrates (such as humans) contains the brain, spinal cord, and retina. The peripheral nervous system consists of sensory neurons, clusters of neurons called ganglia, and nerves connecting them to each other and to the central nervous system. These regions are all interconnected by means of complex neural pathways. The enteric nervous system, a subsystem of the peripheral nervous system, has the capacity, even when severed from the rest of the nervous system through its primary connection by the vagus nerve, to function independently in controlling the gastrointestinal system.
Neurons send signals to other cells as electrochemical waves travelling along thin fibers called axons, which cause chemicals called neurotransmitters to be released at junctions called synapses. A cell that receives a synaptic signal may be excited, inhibited, or otherwise modulated. Sensory neurons are activated by physical stimuli impinging on them, and send signals that inform the central nervous system of the state of the body and the external environment. Motor neurons, situated either in the central nervous system or in peripheral ganglia, connect the nervous system to muscles or other effector organs. Central neurons, which in vertebrates greatly outnumber the other types, make all of their input and output connections with other neurons. The interactions of all these types of neurons form neural circuits that generate an organism's perception of the world and determine its behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia), which provide structural and metabolic support.
Comfort? Sofa chair pacifying words
A touch on the shoulder to tell me that you'd heard
Understanding to attention just in case you heard it wrong
A fear of contradiction cos your feeling can't belong
To this given situation that no-one can take away
A smile, a nervous glance, "Well I'll be back some other day"
But you really had to go and left this atmosphere behind
So now it's back to circumstance, solutions hard to find
As I turn the burning embers of a past that recently
I'd found harder to remember than I thought was good for me
But once confirmed the truth had pulled that 'recently' to shreds
Now the obvious lies bleeding and the future holds my breath
Shall I turn the page and start again?
Or throw the book away
Shall I tell you of these feelings?
Or find something new to say?
It's the act of making choices
Asking questions, hearing voices
Mixing pain and self-resentment
With a knowledge that contentment
Is a process of selection
Cos in every situation
There are good and bad directions you can go
You can wallow in the fantasy
Regenerating memories
Or use the open scenery
Impulse flow more easily
If all the good things disappear for what seems like eternity
Remember you created them by being what you'll always be
Receiving input, giving back what makes you tick in time
Natural instinctive tack running up the spine
Use your central nervous system
To help make up your mind
Looking out with indecision
Wastes a lot of time
If it feels good take the risk
And here I am talking like this
And saying 'you' instead of 'me'...
Experience is globally perceived as being basically
A common sense capacity to understand the variety of influence upon the way we are
Having gone so far