The Nervous System

1. The Nervous System

2. 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

3. Basic Structure of Information • What are the parts of a negative feedback system? • Stimuli information about environment • Receptor something that can sense stimuli (input) • Integrator thinking part; uses set point • Also called coordinator • Effector sends the response to the stimuli (output) • What does the nervous system run on? • SAME THING! • Stimuli comes in through receptor • Input moves on to integrator • Integrator activates effector • Effector causes response

4. Regions of the Brain • 3 main sections: • Cerebrum- main area of the brain; divided into two hemispheres; where language, memory, intelligence, personality, muscle movement come from • Cerebellum- back of your brain; controls balance, senses, and coordination • Brain stem- connection between brain and spinal cord • Medulla oblongata- controls involuntary activities • Midbrain- responds to signals and sends them to regions of the brain • Hypothalamus- connection between nervous and endocrine system

5. Layers of the Nervous System • Peripheral Nervous System (PNS):nerves that carry messages to and from the CNS • Two system in the PNS: 1) Somatic Nervous System: - 12 nerves in the brain - 31 nerves in the spine - send information for all voluntary movement Reflex: automatic response to set stimuli so to quickly minimize damage - pulling back when burned

6. Layers of the Nervous System 2) Autonomic Nervous System: - send impulses to organs in the body - control involuntary movements Two systems in the ANS: • Sympathetic Nervous System: - controls organs during times of stress - release of epinephrine • Parasympathetic Nervous System: - controls organs during times at rest

7. Layers of the Nervous System

8. Types of Neurons • Sensory neurons: receive signals from the environment and send impulses to the spinal cord and brain • Interneurons: 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..

9. 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? • Intermediate neurons • What is your reaction? What caused this? • Muscles move body away from ball; Motor neurons (effector neurons) • If input is strong enough, you don’t even need his brain!

10. They Mighty Reflex • Where are intermediate neurons located? • Brain AND Spinal Cord • Reflex action: • When input is significantly higher/lower than set point, 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 intermediates in spine, set point comparison causes response on effector neurons • Explains why we can feel temp, text, etc… BEFORE we feel pain (Brain is too slow)

11. How Neurons Send Impulses • Ion channels allow the inward flow of K+ and limit the flow of Na+ • Concentration difference between Na+/K+ is made greater by Na+/K+ Pump • Membrane is polarized: • Inside has negative charge • Outside has positive charge • About -70mV difference (resting potential) • Impulse is sent as swift of K+ and Na+ across the membrane change the polarity of the cell (action potential)

12. Na+/K+ Pump • Concentration gradient of Na+ and K+ most be large so the flow of ions is fast • Na+/K+ Pump uses ATP to pull in K+ and push out Na+ 1 ATP= 2 K+ in; 3 Na+ out • Also helps to repolarize membrane after impulse

13. All About Speed! • Signals can “jump” down axon by traveling to pockets between myelin sheaths • Myelin sheaths increase signal transmission • Heavily myelinated nerves have a white color • Inner areas of the brain • Spinal cord nerves • Regular nerves have gray color • Outer areas of the brain • Body nerves

14. Neuron to Neuron Signals • Nerve cells don’t touch; signal “wave” has to be passed from cell to cell • Synapse: small space (10-20 nm) between neurons • Neurotransmitter: chemical signals that travel from axon of one neuron to the dendrite of the next neuron; triggered by Ca+ channels

15. Nerves and Muscles • Antagonistic Muscles • System of paired muscles that allow all our complex movement • Contraction of Bicep • Bicep muscles fibers shorten (contract) while triceps muscle fibers relax • Tendons pulls lower arm • Ligaments allow elbow joint to end • Triceps and Biceps are antagonsitic pairs • If one contracts the other must relax

16. The Senses

17. 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

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

19. 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

20. 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?

21. 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

22. 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

23. 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

24. Sight • Sight is detecting the photons of light bouncing of objects • 80% of all you know comes from sight • Conjunctiva: protective layer; cleaned by lysosome filled 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

25. Light Level and Depth • Iris muscles circular and radial muscles change diameter to iris • Low light radial contract to make wide pupil (dilated) • Need more light • Bright light circular contract to make narrow 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)

26. 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

27. Accommodation • Focusing the eye so objects at different distances are clear • Lens elastic clear fluid sac that changes shape with ciliary muscles • Distant objects: • Ciliary relax • Pressure in eye pulls lens into a thin elliptical (oval) shape • Light focused on fovea • Near objects: • Ciliary contract • Lens pulled into thick spherical shape • Light focused on fovea • Optic nerve main nerve that send images to the brain • Creates a blind spot cause no receptors there

28. 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