The Nervous System

Communication Center Central Nervous System (CNS): system of nerves, the spinal cord, and the brain that receives signals from environment and sends out responses to those signals Neurons: nerve cell; 3 sections – Dendrites: fan like branches that receive impulses – Cell body: main area of cell – Axon: long extension that sends impulses on to other neurons or body cells

Regions of the Brain 3 main sections: 1)Cerebrum- main area of the brain; divided into two hemispheres; where language, memory, intelligence, personality, muscle movement come from 2)Cerebellum- back of your brain; controls balance, senses, and coordination 3)Brain stem- connection between brain and spinal cord

Types of Neurons Sensory neurons: receive signals from the environment and send impulses to the spinal cord and brain Relay neurons: nerves that make up the brain and spinal cord; process impulses and send response impulses to motor neurons Motor neurons: react to impulses from brain and spinal cord; activate glands, muscles, etc..

They Mighty Reflex I throw a ball at you. What nerves first take in the input? – Sensory nerves in eyes The input to the brain quickly calculates distance, speed, angle, etc… to conclude if the ball will hit him. What nerve cells to this? – Relay neurons What is your reaction? What caused this? – Muscles move body away from ball; Motor neurons If input is strong enough, you don’t even need his brain!

They Mighty Reflex Where are relay neurons located? – Brain AND Spinal Cord Reflex action: – When input is significantly higher/lower than normal, spinal cord sends response before brain even gets input – Cuts only fractions of a second off but can save your life Reflex arc: – Sensory impulse travels to relays in spine, set point comparison causes response on effector neurons Explains why we can feel temp, pressure, etc… BEFORE we feel pain (Brain is too slow)

The Senses

The 5 Major Senses Smell Taste Touch Hearing Sight How our brain/body takes in stimulus from the environment How we learn about the world

Smell Breathing air through your nose pulls in particulate matter (chemicals floating in the air) Breathing air through your nose pulls in particulate matter (chemicals floating in the air) Olfactory: Olfactory: – collection of receptors in top of the nose – Chemicals bind to receptors, and signals are sent to the brain – Brain interprets good and bad smells based on what chemicals are detected Why have a sense of smell? Why have a sense of smell?

Good Smells vs. Bad Smells Things smell good because they are good for the body or the mind: Meat- smell of fats and proteins Flowers- smell triggers release of hormones that relax us Fruits- smell of sugars and vitamins Things smell bad because they might kill us: Waste material- contain bacteria; no useful material Rotten Food- contain bacteria; bad for digestion

Taste Smell and taste are strongly linked Taste buds: - receptors for each of the 5 tastes: salty, sweet, sour, bitter, umami - Chemical reacts with receptor and signals are sent to the brain Why do things taste good? Why do they taste bad?

Hearing Sound travels as waves through media (air, water, etc…) Eardrum: – Vibrates to changing pressure from sound waves – Vibrations travel through the body’s smallest bones (Malleus, Incus, and Stapes) Cochlea: – Vibrations from travel into fluid – Fluid activates hire-like receptors which send impulses to the brain – Ear as a hair for different frequencies

Hearing (Balance) Cochlea as 3 semicircular canals filled with fluid and motion receptors (hair-like) Movement in the fluid triggers impulses that tell the brain direction and orientation Small Ca+ stones inside also push down on the hairs Why? -Feel which way is up/down

Touch A collection of different receptors: – Temperature – Pressure – Pain Different parts of the body have higher concentration of touch sensors – Eyelids, fingers, feet, tongue, etc… Some receptors fire faster than others: – You can feel the texture of an object before its temperature

Sight Sight is detecting the photons of light bouncing of objects – 80% of all you know comes from sight Conjunctiva: protective layer; cleaned by tears Cornea: transparent cover over eye Pupil: opening into the eye Iris: colored membrane that changes size due to light intensity Lens: focuses the light to clear the image; made of clear cells Retina: special part of the eye that reacts to photons Images passing through the lens are flipped and our brain learns to flip them back

Light Level and Depth Iris muscles  muscles change diameter to iris – Low light  make wider pupil (dilated) Need more light – Bright light  make narrower pupil (constricted) Need less light; may damage receptors in eyes Two eyes = two sets of information – Brain compares sets to produce 3D image (depth perception)

Seeing Colors To see clearly, light must be focused on the fovea – Center point on the back of the retina; has most receptors Rod cells: detect low levels of light (black and white) Cone cells: detect high levels of light (color) S- detect blue light M- detect green light L- detect red light Overlapping signals from cones create the other colors

Extra Senses Echolocation: use sound waves to find objects Infrared vision: can see heat of an object UV vision: see UV signals Electroreception: can sense electric fields Magnetoreception: can sense magnetic fields