By: sAlvatore borgognone, adrian drobenko and billy dunn
Introduction to the Nervous System
It is out processing system, keeping us in contact with the outside world. It tells us that we exist, and along with muscles it allows us to move and react to stimuli. Our consciousness resides in our nervous systems, as do our thoughts and emotions.
In short, the roles of the nervous system are: responsibility for coordination of movement, response to environmental stimuli, intelligence, self-awareness, thought, emotion.
The nervous system is composed of nerve cells called neurons, which are specialized to carry nerve impulses.
Nervous system has two major divisions: (the division is arbitrary and the two systems are connected to one another)
- Central Nervous System: (CNS) - includes spinal cord and brain. In the "center" of the body. - Peripheral Nervous System: (PNS) - the rest of the nervous system: PNS is further divided into the: 1. Somatic Nervous System (connects to skeletal muscle) 2. Autonomic Nervous System (connects to smooth, involuntary muscles).
The Autonomic Nervous System is further divided into the
1. Sympathetic Nervous System (usually causes effects associated with emergency situations) 2. Parasympathetic Nervous System (promotes activities associated with a normal state).
All neurons have three parts:
1) Dentrite(s) -conduct nerve impulses towards the 2) Cell body and 3) Axon(s) which conducts nerve impulses away from the cell body.
Dentrites and axons are sometimes called fibers. Most long fibers are covered by a myelin sheath which has spaces in it called nodes of ranvier that expose the axon. The sheath is secreted by schwann cells, each of which has a nucleus.
There are three types of neurons:
Sensory Neuron (afferent neuron) - takes a message from a sense organ to CNS. It has a long dendrite and a short axon.
Motor Neuron (efferent neuron) - takes message away from CNS to a muscle fiber or gland. It has short dendrites and a long axon.
Interneuron (association neuron or connector neuron) - completely contained within CNS. Conveys messages between parts of the system. Dendrites and axons may be long or short.
Altogether, the nervous system is the chief controlling and coordinating system of the body. It controls and regulates all voluntary and involuntary activities of human body. There are three characteristic properties of nervous system of human body:Sensitivity, Conductivity and Responsiveness.
Functions of the nervous system:
CONTROL OF ALL BODY FUNCTIONS: The nervous system is the master system of human body. It controls the activity of all other systems in such a way that all the systems collectively make a human being or organism. Without a controlling system, there is no concept of life because in such case there will be no coordination between different body functions and they will all act separately. The nervous system not only controls the voluntary functions of organisms that are directed by will, but it also controls those functions that are below the level of consciousness, or involuntary functions. Control of a function means that the intensity of that function can be increase or decreased according to the demands of an organism.
COORDINATION OF DIFFERENT BODY ORGANS: Nervous system not only produces coordination between different systems, but also between different organs of a system. To form an organ system, role of the component organs must also be coordinated. So a nervous system is not only important for formation of an organism by different organ systems, but also for formation of a system by different organs of an organism.