THE NERVOUS SYSTEM
GENERAL FUNCTIONS
The regulatory and coordinating activities of the nervous system arenecessary for the
human body to function normally. The nervoussystem allows for this in the following ways:
1. Maintaining homeostasis. The trillions of cells in the human body do not function
independently of each other but mustwork together to maintain homeostasis.
For example, heart cellsmust contract at a rate that ensures adequate delivery of blood
toall tissues of the body. The nervous system can stimulate orinhibit these activities to
help maintain homeostasis.
2. Receiving sensory input. Sensory receptors monitor numerousexternal and internal
stimuli. We are aware of sensations fromsome stimuli, such as sight, hearing, taste,
smell, touch, pain, bodyposition, and temperature. Other stimuli, such as blood pH,
bloodgases, and blood pressure, are processed at an unconscious level.
3. Integrating information. The brain and spinal cord are the majororgans for processing
sensory input and initiating responses.The input may produce an immediate response,
be stored asmemory, or be ignored.
4. Controlling muscles and glands. Skeletal muscles normallycontract only when stimulated
by the nervous system; thus,the nervous system controls the major movements of the
bodyby controlling skeletal muscle. Some smooth muscle, such asthat in the walls of
blood vessels, contracts only when stimulatedby the nervous system or by
hormones.Cardiac muscle and some smooth muscle, such as that in thewall of the
stomach, contract autorhythmically—that is, no external stimulation is necessary for
each contraction event.Although the nervous system does not initiate contraction
inthese muscles, it can cause the contractions to occur morerapidly or more slowly.
Finally, the nervous system controlsthe secretions from many glands, including sweat
glands, salivaryglands, and glands of the digestive system.
5. Establishing and maintaining mental activity. The brain is thecenter of mental activities,
including consciousness, thinking,memory, and emotions.
CELLS OF THE NERVOUS SYSTEM
Glial Cells
There are about 1 trillion glial cells in the brain
- 50 x more than there are neurons
Glial cells have perform important functions including:
GENERAL FUNCTIONS
The regulatory and coordinating activities of the nervous system arenecessary for the
human body to function normally. The nervoussystem allows for this in the following ways:
1. Maintaining homeostasis. The trillions of cells in the human body do not function
independently of each other but mustwork together to maintain homeostasis.
For example, heart cellsmust contract at a rate that ensures adequate delivery of blood
toall tissues of the body. The nervous system can stimulate orinhibit these activities to
help maintain homeostasis.
2. Receiving sensory input. Sensory receptors monitor numerousexternal and internal
stimuli. We are aware of sensations fromsome stimuli, such as sight, hearing, taste,
smell, touch, pain, bodyposition, and temperature. Other stimuli, such as blood pH,
bloodgases, and blood pressure, are processed at an unconscious level.
3. Integrating information. The brain and spinal cord are the majororgans for processing
sensory input and initiating responses.The input may produce an immediate response,
be stored asmemory, or be ignored.
4. Controlling muscles and glands. Skeletal muscles normallycontract only when stimulated
by the nervous system; thus,the nervous system controls the major movements of the
bodyby controlling skeletal muscle. Some smooth muscle, such asthat in the walls of
blood vessels, contracts only when stimulatedby the nervous system or by
hormones.Cardiac muscle and some smooth muscle, such as that in thewall of the
stomach, contract autorhythmically—that is, no external stimulation is necessary for
each contraction event.Although the nervous system does not initiate contraction
inthese muscles, it can cause the contractions to occur morerapidly or more slowly.
Finally, the nervous system controlsthe secretions from many glands, including sweat
glands, salivaryglands, and glands of the digestive system.
5. Establishing and maintaining mental activity. The brain is thecenter of mental activities,
including consciousness, thinking,memory, and emotions.
CELLS OF THE NERVOUS SYSTEM
Glial Cells
There are about 1 trillion glial cells in the brain
- 50 x more than there are neurons
Glial cells have perform important functions including:
