# Science: An Elementary Teacher’s Guide/The Human Body: Brain and Nervous System
## Nervous System

The nervous system is a system in the body which sends signals around the body. It lets people and animals respond to what is around them. The central nervous system is the brain, the spinal cord, and nerves. It is present in most animals. It is there to coordinate movement, to process the input of the senses, and to make the animals act a certain way. It is made up of neurons and cells called glia, among other things. Glial cells keep the neurons safe and healthy.
The structure of the system includes the brain and spinal cord, which together are called the central nervous system.[2] The brain has billions of nerve cells to help think, walk, and breathe. The nervous system can react in 1/100 of a second to a stimulus, like a pain signal.
Functionally, the nervous system has two main subdivisions: the somatic, or voluntary, component; and the autonomic, or involuntary, component. The autonomic nervous system regulates certain body processes, such as blood pressure and the rate of breathing, that work without conscious effort. The somatic system consists of nerves that connect the brain and spinal cord with muscles and sensory receptors in the skin. -
The anatomy of nervous systems can be sub-divided as follows

## Central nervous System

The central nervous system (CNS) is the largest part of the nervous system. It is made up of the brain and the spinal cord.
Together with the peripheral nervous system, it has an important role in the control of behaviour. The CNS is protected by bone in the dorsal cavity: the brain in the cranial subcavity, and the spinal cord in the spinal cavity.
The brain is one of the body's most complex organs. It is the organ which controls our thoughts, our decisions, our other organ's functions, and our movements. All parts of the brain work together, but the brain can be divided functionally into three parts:Function The brain does the thinking, learning, and feeling for the body. For humans, it is the source of consciousness.The brain also controls basic autonomic body actions, like breathing, digestion, heartbeat, that happen automatically. These activities, and much else, are governed by unconscious functions of the brain and nervous system. All the information about the world gathered by our senses is sent through nerves into the brain, allowing us to see, hear, smell, taste and feel things. The brain processes this information, and we experience it as pictures, sounds, and so on. The brain also uses nerves to tell the body what to do, for example by telling muscles to move or our heart to beat faster. The forebrain: most developed and largest part of the brain, consisting mostly the cerebrum. The cerebrum is involved in most intellectual activities such as: storing memories, being able to plan, and allowing you to to think and imagine.
The midbrain: uppermost part of the brain stem, which controls some reflexes, involuntary actions, and eye movement.
The hindbrain: contains the cerebellum*, upper part of spinal cord, the brain stem, the pons, and the medulla. The cerebrum is divided in half by a deep fissure going through it's center. These two halves are called hemispheres. One of the very odd things about the brain is that signals from the brain to the body or body to brain cross over on their way to the brain or vice-versa. Meaning that our right hemisphere controls our left side and our left hemisphere controls our right side. Reasons for this phenomenon are currently unknown. The brain weighs on average 1,500 grams (3 pounds). It makes up approximately 2% of the whole body's weight. Commonly divided into 4 lobes: Frontal lobes: The frontal lobes are the area of the brain which controls our emotions and personality. It is the part of brain involved in higher functions, such as the following: motor functions, problem solving, spontaneity, memory, language, initiation, judgement, impulse control, social behavior, and sexual behavior. The frontal lobes are divided into two lobes: the right and left lobe. The two lobes are asymmetrical The left lobe is concerned with controlling language related movement, and the right frontal lobe is concerned with non-verbal abilities. Some scientists argue this is not necessarily true, and both lobes are engaged with all behaviors Parietal lobes:- The parietal lobe’s function is aiding a person by recognizing objects and understanding spatial relationships (spatial relationships are to compare yourself to the objects around you). It is also the part of the brain which interprets pain and touch.
It can be divided into two parts: one that is involved with sensation and perception and the other is involved with integrating sensory input. The first function analyses sensory information to make a single perception (also known as cognition). The second function transforms the world into a spatial coordinate system to represent our world.
Temporal Lobe:- The temporal lobe is located on the sides of the brain and they are involved in a variety of functions such as: memory, speech, and sense of smell. The temporal lobes are located underneath the frontal lobe and the parietal lobe. It is responsible for receiving information from the ears and retrieving memories associated to sound or music. The temporal lobes are also a crucial part of the brain in forming and retrieving memories.
Occitipal Lobe:- The occipital lobe is located in the back part of the brain and is concerned with vision. When you are looking at a page with picture or words, the occipital lobe process the image that is being seen and matches that information with ones already stored in the memory. If the occipital lobes are damaged, it may cause blindness.
The spinal cord is a bundle of nerves that go to and from the brain. It is enclosed in and protected by the bony vertebral column. The main function of the spinal cord is transmission of neural inputs between the periphery and the brain.
Spinal cord segments[change | change source] Humans have 31 left-right pairs of spinal nerves, each roughly corresponding to a segment of the vertebral column. The spinal nerve emerges from the spinal column through an opening between adjacent vertebrae. Outside the vertebral column, the nerve divides into branches.
The nerves for incoming sensory information are bundled separately from nerves for outgoing motor instructions for muscles. The system serves the autonomic nervous system as well as the motor activities which we control consciously.
The spinal cord is a continuous extension from the brain, but it is divided for discussion into five regions based on the vertebrae surrounding the cord. In between the vertebrae there are paired spinal nerves (part of the peripheral nervous system) that exit on each side and serve distinct regions.There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves.
* The Cervical Spinal Cord passes through the seven cervical vertebrae, commonly referred to as C1-C7. This is the topmost portion of the Spinal Cord, where the brain connects to the Spinal Cord, and the neck connects to the back. Even though there are only 7 cervical vertebrae, there are 8 cervical spinal nerves: C1 passes between the first cervical vertebrae and the bottom of the skull; C1-C7 spinal nerves exit just above the respective vertebrae, but C8 is just below C7. After that spinal nerves are named for the vertebrae that is just above them. Damage to the spinal cord in the cervical region results in quadriplegia. If the damage happens above C3 the person will be unable to breathe and will either die or, if lucky, be a respirator-dependent quadriplegic. The cervical region has the greatest range of motion, making it also the most vulnerable.
* The Thoracic Spinal Cord consists of the middle of the Spinal Cord, surrounded by twelve vertebrae (numbered T1-T12). There are spinal nerves exiting laterally beneath each of these. Damage to the thoracic spinal cord can result in paraplegia, with less use of the trunk, abdomen, shoulders and arms the higher the damage occurred. The thoracic vertebrae have the least range of motion.
* The Lumbar Spinal Cord is surrounded by the five lumbar vertebrae numbered L1-L5. this is the lower region of the Spinal Cord, where your vertebrae have wide range of motion. Spinal nerves from this region include the sciatic nerve, which travels down the leg. Although nerves extend further, the spinal cord itself ends between L1 and L2, so for spinal taps or epidurals the needle is typically inserted between L2 and L3.
The Sacral Spinal region contains nerve roots which exit foramina (passages) between the five fused sacral vertebrae. These nerves supply parts of the hip, thigh, and down to the foot as well as genitals, bladder, and parts of the lower digestive system.
The coccygeal Region consists mainly of small fused vertebrae attached to the base of the sacrum, with a single nerve that just supplies the skin directly over the coccyx.

## Peripheral Nervous System

The Peripheral nervous system, or PNS, is part of the nervous system, and consists of the nerves and neurons that are outside the central nervous system (the brain and spinal cord) and serve the limbs and organs, for example.
The PNS is not protected by bone like the central nervous system. Therefore it is exposed to toxins and mechanical injuries. The peripheral nervous system is divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS). But the enteric nervous system (ENS) can be seen as a third branch of its own and not as part of the autonomic nervous system.
The SNS coordinates your body's movement, receiving external stimuli, and regulates everything under conscious control. The ANS controls all automatic actions. That means that it controls all reflexes and actions during sleep. The ENS controls the gastrointestinal system.

## Automatic Nervous System

The autonomic nervous system (ANS) controls the conditions inside the body. It is sometimes called the 'visceral nervous system' or 'involuntary nervous system'. The ANS is part of the peripheral nervous system.
ANS controls all automatic actions. That means that it controls all reflexes and actions during sleep.
Most of its activities are done without the person having conscious control over them. The person usually cannot feel what the ANS is doing. However, some of the ANS's activities some work together with the conscious mind, like with breathing.
The ANS controls many different things, like heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, the discharge of urine, and erection.
There are two different sections within the ANS:
The sympathetic nervous system, which causes the body to become more active as in the "fight or flight" response. The parasympathetic nervous system, which is mostly involved in "rest and digest".
Many organs are controlled primarily by either the Sympathetic or the parasympathetic division. Sometimes the two divisions have opposite effects on the same organ. The Autonomic nervous system controls internal body processes such as the following:
* Blood pressure
* Heart and Breathing rates
* Digestion
* Body temperature
* Metabolism
* Urination
* The balance of water and electrolytes
* The production of body fluids

## Sympathetic Nervous System

The Sympathetic nervous system is part of the autonomic nervous system. It becomes more active when you are stressed. It is a part of the "fight or flight" response. The sympathetic nervous system can increase heart rate; make bronchial passages wider; decrease motility (movement) of the large intestine; make blood vessels narrower; increase peristalsis in the esophagus; cause pupil dilation, piloerection (goose bumps) and perspiration (sweating); and raise blood pressure.

## Parasympathetic Nervous System

The parasympathetic nervous system (PNS or PSNS) is part of the autonomic nervous system. It does the opposite things of the sympathetic nervous system, the other part of the autonomic nervous system. This way, the parasympathetic and sympathetic nervous systems balance each other's effects. The sympathetic nervous system helps a person "fight or flight" when they are in danger. When the danger is gone, the parasympathetic nervous system lets the person "rest and digest," "feed and breed."
The parasympathetic nervous system has many different effects. It affects every part of the body, including:[1]
The heart: The heart relaxes and beats slower. This makes the heart rate and blood pressure lower. The lungs: Breathing slows down. The bronchi (the tubes that bring air to the lungs) also get narrower. The eyes: The pupils get smaller. The digestive system: Extra blood is sent to the stomach and intestines. The stomach and intestines also work faster. This helps the person digest the food in their stomach. The blood vessels: The blood vessels in the parts of the body that are far away from the heart, lungs, and brain get wider. (This is called vasodilation.) This helps make the blood pressure lower. It also makes the skin warmer, and can cause a man to have an erection. Because of these effects, the parasympathetic nervous system always has to balance with the sympathetic nervous system. For example, if only the parasympathetic nervous system was working, a person's heart rate and breathing would keep getting lower and lower. Eventually the person would stop breathing or their heart would stop beating.[1]
However, in a healthy person, the brain realizes when the parasympathetic nervous system's effects are getting too strong. For example, the brain may realize that the person is breathing too slowly, or that their heart rate is too low. The brain reacts by making the sympathetic nervous system kick in. Because the sympathetic nervous system has the opposite effects, it will make the person breathe faster and raise their heart rate. These two systems have to balance each other constantly for a person to stay healthy.
The parasympathetic nervous system is controlled mostly by the vagus nerve.[2] This is an important nerve that comes from the brain and goes all the way down to the bottom of the spinal cord. The vagus nerve sends out chemical messengers called neurotransmitters - mostly one called acetylcholine.[2] This chemical causes changes in many different parts of the body.

## Somatic Nervous System

The somatic nervous system (SNS) is part of the peripheral nervous system.[1] It controls various muscles and the sensory input from external stimuli
The SNS controls voluntary body movements by skeletal muscles. Its outgoing (efferent) nerves stimulate muscle contraction. Its incoming (afferent) nerves relay sensation from the skin, and sense organs to the central nervous system. This includes touch, hearing, and sight.
The SNS does not, however, control reflex arcs.

## Sense of Sight

Eyes are the organs that provide the sense of sight are delicate instruments resting in protective sockets at the front of the skull. Front of the eyeball is constantly bathed with a watery liquid referred to as tears it comes from tear glands. The eyelids are small windshield wipers spread this fluid over the eyeballs with a frequent blinking action it keeps the eyeballs clean and moist. The liquid contains chemicals that kill harmful bacteria that may be present. The tear gland are stimulated either by emotion or by a speck of dust or other foreign particle in the eye to produce more liquid than can be drained off.

## Functions of the Eye

The eye is like a video camera that is supplying the brain with pictures of everything that is in front of it. The outside of the eyeball is a white except for a transparent window at the front the cornea. Behind the thin clear covering is the iris is the colored part of the eye that opens and closes like a diaphragm camera. Behind the iris is a convex lens and the opening in the center of iris is called pupil. Light passes through the lens which bends the light and focuses it onto the back of the eyeball. The lining of the back of the eyeball is the retina is filled with light sensitive nerve endings that are connected to the optic nerve it carries the impulses to the brain and it converts these impulses to images and we experience sigh. The retina contains cones that respond to color and objects in bright light and the rods respond to objects in dim light but they do not respond to color it explains why the things we see in dim light appear only in shades of black and white.

## Sense of Hearing

The significance of the auditory canal must not be overlooked because in a distance of about 2.5 centimeters there are myriads of hairs and about 4,000 wax glands that protect the inner parts from intrusion by dust and insects. The wax also protects against infection and should not be removed with toothpicks or other instruments. The process of hearing really takes place inside the head. The outer ear the body auditory apparatus includes structures within the middle ear and inner ear. The middle ear consists of the eardrum and three small bones called hammer and stirrup. The hammer is connected to the inside of the eardrum and sound waves cause the eardrum to vibrate the hammer vibrates also.