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The two parts of the nervous system are:
THE CENTRAL NERVOUS SYSTEM- made up of your brain and spinal cord.
THE PERIPHERAL NERVOUS SYSTEM- made up of the nerves that carry messages to and from the CNS and other parts of your body

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2. Nerve Cells, Neurones and the Myelin sheath 

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2. Nerve Cells, Neurones and the Myelin sheath 

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Motor neurones- nerve cells that carry messages from the CNS to effectors.
Sensory neurones- nerve cells that carry messages from cells in the sense organs to the CNS.
Relay neurones- carry messages from one part of the CNS to another.

The nervous system is made up of trillions of nerve cells or neurones. Neurones carry electrical messages called nerve impulses from one part of your body to another at a very high speed. These nerve impulses can only travel in one direction. In your body, the neurones are bundled together to form nerves. neurones are covered with an insulating layer called a myelin sheath. the myelin sheath electrically insulates the neurones from each other and increases the speed of the nerve impulse .

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Synapse- The space between two neurones. At the synapse, the electrical signal of the nerve is converted into a chemical signal and then back into an electrical signal.

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The brain controls and regulates body functions. Without it you cannot survive. The right and left sides of the brain control the opposite sides of the body.

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Cerebrum: The cerebrum is the part of the brain responsible for emotion, memory, decision making and individual thought. Without your cerebrum, you could not think or make decisions.
Cerebellum: The cerebellum is the area of the brain involved in actions such as walking and writing. It processes actions involving motor skills, coordination and muscle action. Without your cerebellum, you could not walk.
Medulla: The medulla oblongata, or brain stem, controls unconscious actions, vital systems and organ function. Without your medulla, you could not survive.

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6. The somatic nervous system (the senses!)

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6. The somatic nervous system (the senses!)

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The somatic nervous system collects information about our surrounding through sensory organs such as eyes, ears, tongue, nose and skin. It also coordinates movement of the body.
Eye - Only about one-sixth of eye is visible. Most of it is protected within the skull. The pupil is an opening that allows light to pass through the lens and int your eye. Vision is when messages are sent from the photoreceptors via the optic nerve to the brain for interpretation.
Ears - The ear not only senses sound, but also helps you to keep your balance. In your inner ear are fluid-filled semicircular canals. Nerves in the semicircular canals of the inner ear responds to gravity and help you maintain your balance.
Tongue/Nose - The chemoreceptors for taste and smell work together. Tastebuds are arranged in groups to form a taste pore. Chemicals fix to the taste receptors and stimulate sensory nerves. Message sent to the brain give the sensation to the brain.
Skin - The skin has many receptors and provides you with a lot of information about your surroundings, such as touch, pain and temperature. One of the ways that your body protects itself from the outside world is by being very sensitive to touch.

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Receptors are special organs or tissues that have nerve endings that detect changes in the environment. There are four types of receptors and they are:
1. Mechanoreceptors: sensitive to stimuli; touch. Also make you aware of muscles being stretched.
2. Photoreceptors: are sensitive to light.
3. Thermoreceptors: respond to changes in temperature.
4. Chemoreceptors: sensitive to chemicals such as those found in food.

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The sympathetic nervous system and makes it work more efficiently. It's the system that prepares the body for emergencies by making you more alert and preparing your body for action.
The sympathetic nervous system does this by
-diverts blood away from the skin and digestive tract
-stopping peristalsis, muscular action that mixes food in the intestines
-blood flow to muscles and lungs are increased, as much as up to 120%
-opens the bronchioles, which lets more air into your lungs, increasing oxygen that is sent to muscles.
-heart rate speeds up, increasing blood flow to body
-relaxes muscles in eye to allow pupils to dilate, the lens also flattens out and it results in better distance vision
-blood flow to and from heart is increased

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The parasympathetic nervous system slows everything down and is the system in control while you sleep.
- It increases the blood flow to digestive track
- It stimulates the salivary glands and increases the rate of peristalsis, in support of digestion
- Reduces diameter of bronchioles when there is a reduced need for oxygen
- Controls heart beat
- Contracts the muscles of the eye and reduces the diameter of the pupil to allow close vision

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The sense organs, for example, skin, senses anything harmful to your body (E.g. hot flame). The message from the skin travels along the sensory neurone, the relay neurone where the information is processed in the central nervous system, and the motor neurone reaching the effector. The effector responds to the stimulus by activating muscle contraction, and moving part of your body away from harm.

The reason this response is so fast - nearly instantaneous - is because the message does not travel up the spinal cord to the brain, and instead passes through a relay neurone. This means the process of sending a message up the spinal cord to the brain, then having the brain formulate a response and send it back down the spinal cord is skipped, meaning the reflex is very fast as only a few neurones are involved. Shortly after the reflex action a message is sent to the brain, and only then can it register pain.

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Cornea

Bends light into the lens. Lies in front of the iris. Is clear.

Aqueous humour

Lies between the cornea and the lens. It is a clear, watery fluid produced by the ciliary body to lubricate the lens and cornea.

Lens

A flexible structure that enables light to be focused on the retina.

Ciliary body

The lens is connected to the ciliary body. Muscles in the ciliary body change the shape of the lens.

Optic nerve

Carries the electrical signals from the retina to the brain.

Sclera

White of the eye.

Pupil

An opening in the iris that determines the amount of light entering the eye.

Iris
The coloured part of the eye — it contains the dilator muscles and sphincter muscle as part of its structure.

Retina

The cells on the retina called cone and rod cells absorb light rays and turn them into electrical signals.

Vitreous humour

Clear fluid between the lens and retina.

Choroid

Has a rich blood supply and nourishes the retina.

Blind Spot
Blind spot, small portion of the visual field of each eye that corresponds to the position of the optic disk within the retina There are no photoreceptors in the optic disk, and, therefore, there is no image detection in this area.

Fovea
Responsible for sharp central vision.

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The lenses within the human eye focus on objects at different distances by changing focal length. The ability of the lenses to change shape is called accommodation. When the muscles attached to the lens contract, the lenses stretch and become quite flat and are able to focus on objects in the distance. When the muscles relax the lens becomes fatter and are able to bend light more. This allows close objects to become focused. As we age our lenses harden making accommodation more difficult.
If light is not focused to a point at the retina, then a person will not see a clear image. This commonly leads to short sightedness (myopia) or long sightedness (hyperopia). Concave lenses are used to correct short sightedness which is when people can only focus on close objects.
Convex lens is used to correct long sightedness which is when people can only focus on distant objects.
Bifocal or graded lenses may be used if a person has more than one type of vision problem. This allows people to be able to see short and distant objects through one pair of glasses.
Some treatment options, such as laser surgery, reshape the surface of a patients cornea to alter how it focuses light.

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Bacteria:
bacteria are microscopic, unicellular organisms.
- Thousands of different bacteria have been discovered
- Bacteria are decomposers which makes them an important part of of the natural environment
- Bacteria can be good and bad, some bacteria like the ones in sheep stomach that help with digestion while things like pathogenic bacteria that can cause serious illness such as tetanus and whooping cough.

Antibiotics:
- antibiotic is a substance that kills bacteria or prevents the growth of bacteria
- The first successful antibiotic was penicillin developed in the late 1940s
- before antibiotics your own body would have to fight off infection

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Ways pathogens can enter the body are:
-food and water. This causes food poisoning and cholera
Some symptoms are vomiting, diahorrea, loss of appetite, mild fever, nausea and headaches.
-breathing in. This causes flu, pneumonia and tuberculosis
Some symptoms are coughing, sore throat, runny nose, muscle aches, headaches and fatigue.
-cuts and wounds. This causes tetanus and blood poisoning
Some symptoms are difficulty swallowing, irritatability, stiffness of muscles and uncontrollable jaw spasms.
-sexual contact. This causes gonorrhoea and syphilis
Some symptoms are burning while urinating, burning in throat and swollen glands in throat.
-other contact. This causes Anthrax and leprosy
Some symptoms are nausea, shortness of breath, coughing up blood and painful swallowing.

Pathogens entering a cut/wound.

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Your bodies first line of defences purpose is to prevent pathogens from entering the body. It is a barrier to stop pathogens from entering the body in the first place.

There are 6 ways that your body does this:

Skin: protects your internal organs from harmful chemicals

Tears/saliva: washes away dust and harmful substances from openings in your body, like your mouth. 💧

Nose: the hairs in your nose filter the air. Any chemicals that get through are released by coughing or sneezing. 👃🏻

Stomach acid: kills unwanted bacteria

Vomiting: gets ride of undesirable things in the stomach

Diarrhoea: gets rid of pathogens that pass the stomach💩

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WHAT IS IT?
An inflammatory response the second line of defence. It is a defence mechanism that combats injury or disease.
WHEN DOES IT OCCUR?
Inflammation occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause. The damaged cells release chemicals including histamine, bradykinin, and prostaglandins.
WHAT HAPPENS?
Typically causes the affected area to swell to isolate the area and become hot. Redness, pain and tenderness are associated symptoms of inflammation.
WHY DO THE SYMPTOMS HAPPEN?

The tissues in the area are red and warm, as a result of the large amount of blood reaching the site.

The tissues in the area are swollen, again due to the increased amount of blood and proteins that are present.

The area is painful, due the expansion of tissues, causing mechanical pressure on nerve cells, and also due to the presence of pain mediators

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The lymphatic system is the last line of defense which consists of a series of vessels and capillaries that carry fluid from around your cells back to your heart. In areas of the lymphatic system, swellings or nodes – lymph nodes – are present.

The main roles of this system include managing the fluid levels in the body, filtering out bacteria, and housing types of white blood cells.

Lymph nodes contain a large of different types of white blood cells, called lymphocytes* and macrophages. The function of these is to destroy pathogens and to help protect the body in the future.

*a white blood cell that makes antibodies and is found in lymph nodes.

Lymph is filtered through the spleen, thymus and lymph nodes before being emptied into the blood.

Summary:
• Lymph is filtered in the lymph nodes. Trapped pathogens are consumed by white blood cells

• The spleen removes pathogens and foreign proteins from the lymph fluid

• The lymphatic system carries lymphocytes and macrophages that destroy foreign proteins and manufacture antibodies.

The lymphatic system diagram:

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Vaccines are like a training course for the immune system. They prepare the body to fight disease without exposing it to disease symptoms. When foreign invaders such as bacteria or viruses enter the body, immune cells called lymphocytes respond by producing antibodies, which are protein molecules.