I. The nervous system has three functions; sensory input, integration, and motor output.
1.Sensory input is the conduction of signals from sensory receptors. Sensory receptors are structures that detect changes in the external and internal environment due to stimuli. They detect stimuli such as light, heat, pressure, and chemicals.
2.Integration is the responsibility of the central nervous system, brain and spinal cord. It includes interpretation and determining the appropriate response i.e. motor output.
3.Motor output is the conduction of signals from the processing center to effector cell that carry out the body's response. Nerves that conduct in this way are grouped together in the peripheral nervous system.
The nervous system of the human being is responsible for sending, receiving, and processing nerve impulses throughout the body. All the organs and muscles inside your body rely upon these nerve impulses to function. It could be considered as the master control unit inside your body. Sense organs provide the nervous system with information about the environment by means of such senses as sight, hearing, smell, taste, tough, pressure, and pain. Nerves are connected throughout the whole body to the brain. They carry the information throughout the body in the form of electrochemical signals called impulses. These impulses travel from the brain and spinal cord to the nerves located throughout the body. For example, if we touch something, impulses travel through the nerve network to the brain at a rate of 350 feet per second. It is largely made up of specialized cells called neurons. Each of these neurons has a cell body, or cyton, which contains the nucleus and organelles. It takes the corporation of three systems to carry out the mission of the nervous system. They are the central, the peripheral, and the autonomic nervous systems.
At any given moment, millions of bits of "information" from the sight and hearing enter your nervous system and must be analyzed to determine an appropriate response. About 99.9 per cent is discarded as "unimportant" at the moment. While all this is going on, all of the other senses are active, too, bombarding the nervous system and demanding a response. At the same time the body's many organs and functions must be tirelessly monitored, directed and unified. This is all accomplished by the integration of the body's three nervous systems. The following is a description of each.
The central nervous system has the responsibility for issuing nerve impulses and analyzing sensory data. The central nervous system (CNS) is composed of the brain and spinal cord. Impulses originating in the brain are sent to various parts of the body via the spinal cord. The brain is protected and encased by the bones of the skull, while the spinal cord is protected and encased by the 24 individual and movable bones of the spine called the vertebrae. The spinal cord is a direct downward continuation of the brain stem that starts at the upper border of the uppermost vertebra and ends at the lower border of the first lumbar vertebrae. In the average adult human, the brain weighs 1.3 to 1.4 kg. (about 3 pounds). The brain contains about 100 billion nerve cells (neurons) and trillions of "support cells" called glia. The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 gm. The vertebral column, the collection of bones (back bone) that houses the spinal cord, is about 70 cm long. So the spinal cord is much shorter than the vertebral column.
The peripheral nervous system is responsible for carrying these nerve impulses to and from the body? The Peripheral Nervous System connects the Central Nervous System with all the tissues of the body. Thirty-one pairs of spinal nerves exit the spine and form a very complex network of nerves reaching out to every part of the body. Messages or signals are thus relayed from the tissues of the body back to the brain and vice versa.
The autonomic nervous system is composed of the sympathetic and parasympathetic systems and is responsible for regulating and coordinating the functions of vital structures in the body. The Autonomic Nervous System includes all the nerve cells, or neurons, located outside the spinal cord and the brain stem. The ANS itself is divided into two separate entities: the Sympathetic and the Parasympathetic divisions. The Sympathetic division sends impulses that speed up or enhance (as in running) whereas the parasympathetic slows down (digestion). These two systems combined regulate the majority of the body's involuntary functions. Examples of involuntary control are the heart rate, respiration, blood circulation and digestion.
Neurons---> nerve cell
cell body---> contains nucleus, controls cell activity
dendrites---> carries messages to the cell body
axon---> carries messages away from the cell body
Types of neurons:
sensory neurons
interneurons
motor neurons
receptor cells---> recieve information from the environment
sensory neurons---> messages travel from the receptor cells through the sensory neurons to the spinal cord and brain
interneurons---> connect sensory neurons to the motor neurons
motor neurons---> messages travel from the brain and spinal cord through motor neurons to the muscles and glands
effector cells---> cells stimulated by the motor neurons
Nerve Impulse:
-is the pathway of a message from receptor to effector
-are chemical/electrical charges
-travel at 120 meters per second
-once a nerve impulse is fired it is fired completely
Synapse:
-a small gap between nerve dendrites and nerve axon terminals
-a chemical message is sent across the gap to the next neuron.
Functioning of neurons
Action potentials are electrical impulses that travel the length of neurons
1. Membrane resting potential - all cells have this
2. Action Potential
A propagating action potential travels along the axon driven by diffusion of charge down the axon. Action potentials only travel one way in our nervous system - domino effect
A positive charge attracts a negative charge, and vice verse. However, positive charges repel each other, and negative charges repel each other. This forms the foundation for electrical forces. Positively charged ions would tend to move from areas of a positive charge to areas of a negative charge.
Ions move from areas of higher concentration to areas of lower concentration. This forms the foundation for diffusional forces. Sodium ions, for example, would tend to move from areas of their high concentration to areas of their low concentration. Potassium ions would tend to move from areas of their high concentration to areas of their low concentration.
Electrical charge (electrical potential) is the result of excess ions on one side of the membrane.
Summary of ion movements in action potential
1) stimulus depolarizes membrane
2) at threshold, Na channels open and Na diffuses into cell through voltage-gated channels
3) leads to greater depolarization and generation of an action potential
4) Na channels close, more K channels open and K diffuses out of cell
5) repolarization (some hyperpolarization)
6) ion pumps reestablish resting ion concentrations
Bottom line - know that it is ions that are the basis for the action potential. The potential
difference in charges and ion concentrations is what provides the POTENTIAL to do work -
and it is the channels that are selectively opened that controls when the work will be done.