1. The Nervous system
Chapter: 16 Lesson:1

3. Health concepts
The nervous system is the body’s communications network and control center.
Your brain is a complex, computer like organ at the core of your nervous system that continuously receives, processes, and gives information.
The brain plays a key role in the development of speech and language, two distinctly human characteristics.

4. Structure of the nervous system
There are two main divisions of the nervous system, the Central Nervous System(CNS) and the Peripheral Nervous System(PNS).
PNS gathers information from inside and outside your body.
CNS receives and analyzes this information and initiates responses.
PNS then picks up and carries the response signals.
Information is transmitted throughout your body by means of electrical charges (impulses) that travel at speeds up to 248 mph!
The messengers and receivers of these transmissions are neurons, or nerve cells.

5. Functions of neurons
There are three main types of neurons: sensory neurons, motor neurons, and interneurons.
Sensory neurons carry signals from sense receptors into the CNS.
Motor Neurons carry signals from the CNS to muscles or glands.
Interneurons form all the electrical connections within the CNS itself.

6. 3 important parts of neuron
Nucleus – the control center of the cell.
Axon – Acts as an exit, allowing impulses to move away from the cell body.
Dendrite – Acts as an entrance, allowing impulses toward the cell body.

7. The central nervous system
In one way or another, every body function involves the CNS.
The CNS is made up of two main parts: the spinal cord and the brain.

8. The spinal cord
The spinal cord is a cylinder of nerve tissue about 18 inches long and about as thick as your index finger.
It is a downward extension of the brain.
The spinal cord runs down the central canal in the spine and is protected by the vertebrae, the bones that make up your spine.
It’s also protected by cerebrospinal fluid that acts like a shock absorber and by three layers of connective membranes called the spinal meninges.

9. The BrAIN
The brain is the largest most complex part of the nervous system.
Your brain helps you receive and process messages to think, remember, and reason-and coordinates your muscular movement.
Your brain is involved in your emotions and everything you sense.
The brain weighs about 3 pounds, and contains almost 100 billion neurons.
At birth the brain weighs about 1 pound, and reaches full size by age 6 (maturity – 25).
Although the brain makes up only 2 percent of your total body weight, it uses more than 20 percent of the oxygen you inhale. Without oxygen, the brain can last for only four or five minutes before suffering serious and irreversible damage.
The brain is protected by eight cranial bones that form the skull and three layers of membranes called cranial meninges. Cerebrospinal fluid between the meninges cushions the brain from injury.

10. 3 subdivisions of the brain
Cerebrum – largest, most complex part of the brain. It is the site of most conscious and intelligent activities.
Divided into two halves or hemispheres: right & left. The right half controls the muscular activity and receives sensory input from the left side of the body. The left half controls the muscular activity and receives sensory input from the right side of the body.
Right: hemisphere is concerned with imagination and visual thinking – artistic activities, and emotional responses.
Left: hemisphere is concerned with language, logic, math, analysis, and critical thinking.
Each hemisphere has 4 lobes – named for the bone in the skull that protects it:
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe

11. Cerebellum
2nd largest part of the brain. It is concerned mainly with maintaining posture, balance, and coordinating skeletal muscle movements.

12. The brain Stem
A 3 inch long stalk of nerve cells and fibers that connect the spinal cord to the rest of the brain. The activities of the brain stem are not under conscious control.
The brain stem consists of the three main parts:
Medulla oblongata
Pons
Midbrain

13. The peripheral nervous system
Peripheral means “located away from center.”
The peripheral nervous system (PNS) consists of nerves that fan out from the CNS to the muscles, skin, internal organs, and glands.
The PNS is composed of two subdivisions:
Autonomic Nervous System – responsible for controlling involuntary functions of the body such as sweating, digestion, and heart rate. Consists of two parts:
Sympathetic Nervous System – prepares the body for “fight or flight.” Responds to the body’s needs during increased activities or emergencies. Examples: increased heart rate, respiration, sweating, saliva, etc.
Parasympathetic Nervous System – opposes the actions of the sympathetic system by slowing body functions. Examples: slows heart rate, respiration, sweating, etc.
Somatic Nervous System – includes cranial and spinal nerves that transmit impulses from CNS to skeletal muscles. This involves voluntary responses – responses under your control.

15. Reflex Action
Reflex – a spontaneous response of the body to a stimulus. It occurs automatically without conscious thought or effort.
Knee (patellar reflex)
Touching something hot