+ Nervous System The nervous system, the brain, the eye and neurons

+ The Nervous System Your nervous system is made up of your brain, spinal cord, and neurons that connect your whole body. The function of the nervous system is to help you perceive and react to the world around you. It coordinates the action of your whole body. It also controls vital involuntary processes like breathing, eating, and your heart beating. It helps you speak, read, think, and be creative.

+ Parts of the Nervous System There are two main parts of the nervous system. Central Nervous System (CNS) Peripheral Nervous System (PNS)

+ CNS The central nervous system is made up of your brain and your spinal cord. Its job is to coordinate all of your body’s activities.

+ PNS The peripheral nervous system is made up of all the nerves that carry messages to and from the CNS. It is separated into 2 divisions: The Somatic Nervous System The Autonomic Nervous System

+ PNS: Somatic Nervous System The somatic nervous system: relays information between your skin, the CNS, and your muscles. It is voluntary, which means you control it. This is how you move your body where you want it to go.

+ PNS: Autonomic Nervous System The autonomic nervous system controls your involuntary reactions. It is also divided into 2 parts: Sympathetic Nervous System: controls your internal functions during times of stress, “fight or flight” Parasympathetic Nervous System: controls your internal functions during times of relaxation, “rest and digest”

+ The Brain The brain is the control center of the entire nervous system. White matter in the brain are parts that have more fat, which help speed up nerve impulses. Gray matter does not have that fat, called myelin. It has 3 main parts, and several smaller parts you need to know.

+ The brain: Cerebrum The cerebrum makes up the majority of your brain. It controls conscious activities, intelligence, memory, language, movement and the senses.

+ The brain: Cerebellum The cerebellum is located at the back of your brain. It controls your balance, posture, and coordination.

+ The brain: Brain Stem The brain stem is where the brain connects to the spinal cord. It controls involuntary activities and relays messages to and from the brain.

+ Other brain parts Medulla oblongata: in the brain stem, controls breathing and heart rate Pons: in the brain stem, helps the brain communicate Hypothalamus: releases and controls hormones and glands Pituitary gland: main gland that makes hormones Thalamus: regulates sleep and alertness Hippocampus: controls memory Corpus Callosum: made of white matter, helps the brain communicate

+ Neurons Neurons are the basic units of structure and function of the nervous system. They are also called nerve cells.

+ Neurons Parts of a neuron: Dendrites: branchlike extensions of the neuron that receive impulses and carry them towards the cell body Axon: an extension of the neuron that carries impulses away from the cell body and towards other neurons, muscles, or glands

+ 3 types of neurons There are three types of neurons: 1. Sensory neurons carry impulses from the body to the spinal cord and brain 2. Interneurons are found within the brain and spinal cord and relay messages. 3. Motor neurons carry the response impulses away from the brain and spinal cord to muscles and glands

+ Relaying an impulse 1. You are exposed to a stimulus. 2. Sensory neurons send the message to the brain. 3. Interneurons in the brain help translate the message. 4. Motor neurons send a message back to the muscles. 5. The muscles are activated and respond to the stimulus.

+ Connections between neurons Neurons don’t touch each other, there are gaps between them called synapses. Chemicals called neurotransmitters travel across the synapses to help neurons communicate. Serotonin: contributes to feelings of well-being or happiness, not enough can cause depression Dopamine: coordinates movement, not enough can be caused by Parkinson’s disease Epinephrine: regulates heartbeat, blood pressure, and the size or your airways, can be given to people having an allergic reaction

+ Eyes Eyes have receptors in them that respond to light energy. The optic nerve is a large nerve (bundle of neurons) that connects the back of the eye to the brain. The brain interprets this information, which allows you to see.

+ Parts of the Eye The retina is at the back of the eye, it senses the difference between light and dark. It has rod cells (used to see black/white or in dim light) and cone cells (used to see color and in bright light) Cornea: transparent front part of the eye, helps you focus Sclera: white of the eye, protects the eye Lens: helps you see objects far away Iris: colored part of the eye, controls the size of the pupil

+ Parts of the Eye Pupil: the black part in the middle, where light enters the eye Vitreous humor: clear gel that makes up the bulk of the eyeball Aqueous humor: clear fluid between the lens and the cornea in the front of the eye

+ Diseases and Disorders Multiple sclerosis (MS): myelin around the neurons is damaged, communication slows, body stops responding Depression: lower levels of serotonin in the brain Shingles: caused by the chicken pox virus, damages nerve ends and causes pain Alzheimer’s Disease: build up of protein in the brain, causing memory loss and loss of body functions Parkinson’s Disease: cells can’t make dopamine, body stops responding, brain stops all processes

+ Diseases/Disorders Nearsightedness/myopia: light does not focus at the back of the eye (retina) but in front of it instead Cataracts: eye lens becomes cloudy