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Why Do Animals Need a Nervous System? • Because the world is always coming at you! Many animals have nervous tissue, but mammals have the most organized and efficient nervous system. Nervous System • Central nervous system – brain & spinal chord • Peripheral nervous system – nerves from senses – nerves to muscles cerebrum cerebellum spinal cord cervical nerves thoracic nerves lumbar nerves femoral nerve sciatic nerve tibial nerve Nerve Cells • Neuron – building blocks of the nervous system – sends signals so your body can respond to the environment Labeling A Nerve Cell 1. Cell Body 2. Nucleus 3. Dendrites 9. Terminal branch 4. Axon 7. Node of Ranvier 5. Schwann cell nucleus 6. Schwann cell 10. Synaptic knobs 8. Myelin Sheath . Fun Facts about Nerve Cells • Most specialized cell in animals • Longest cell – blue whale neuron • 10-30 meters – giraffe axon • 5 meters – human neuron • 1-2 meters Nervous system allows for 1 millisecond response time Myelin Coating • Axon coated with insulation made of myelin cells – controls speed of signal • signal hops from node to node myelin coating Multiple Sclerosis immune system (T cells) attacks myelin coating loss of signal Synapse • Junction between nerve cells – Can be electrical or chemical Each axon may have synapses with up to 1000 other neurons Synapse • A chemical synapse involves release of a neurotransmitter. • Neurotransmitters are removed from a synapse by enzymes, or they are reabsorbed from the presynaptic neuron. • This is where drugs effect the system. Reflexes • Now that we know about neurons…how do they work in the system as a whole? • They work by reflexes, or automatic response Sensory Neuron - RECEPTORS • Sensory Neuron neurons activated by sensory input (vision, touch, hearing, etc.), which send external stimuli to the central nervous system • A receptor is a structure which receives something Interneuron • A neuron that forms a connection between other neurons. • These neurons receive signals in the brain and spinal cord. Motor Neuron - EFFECTORS • Neurons that receive signals from the brain to perform motor functions. – Movement – Twitch – Run/Walk/Etc • The effectors are the organs which respond to the signals sensory neuron (from senses) interneuron (brain & spinal cord) motor neuron (to muscle) Simplest Nerve Circuit • Reflex, or automatic response rapid response automated signal only goes to spinal cord no higher level processing advantage essential actions don’t need to think or make decisions about blinking balance pupil dilation startle Testing Your Reflexes - Video Nerve Potential • Nerve cells use IONS to function. Nerve Potential • Membrane Potential – difference in electrical charge (caused by ions) across cell membrane. • How many ions on each side? • Action Potential – causes a nerve impulse – uses ions • Resting Potential – membrane potential of a neuron at rest, neuron not working – but can when needed (all or none response). Human Brain Primitive Brain • The “lower brain” – medulla oblongata – pons – cerebellum • Functions – basic body functions • breathing, heart, digestion, swallowing, vomiting People in – homeostasis – coordination of movement “vegetative” states only use their primitive brain. Higher Brain • Cerebrum – 2 hemispheres – left = right side of body – right = left side of body • The right side of your brain perceives and controls the left side of your body • Left side of brain perceives and controls right side of your body Higher Brain • Corpus callosum – connection between 2 hemispheres – When your corpus callosum is severed, you can use each half of the brain independently These two sides work together. It’s difficult to use only one side of the brain. For example: Have your right hand tap your head while your left hand rubs your stomach Division of Brain Function • Left hemisphere – “logic side” – language, math, logic operations, vision & hearing details – fine motor control • Right hemisphere – “creative side” – pattern recognition, spatial relationships, non-verbal ideas, emotions, multi-tasking Activity – Left or Right Test • Clockwise = Right Dominant • Counter-Clockwise = Left Dominant • Lets take a Paper Test to see if this is TRUE… Cerebrum Specialization • Regions specialized for different functions • Lobes parietal frontal – frontal • speech, control of emotions – temporal • smell, hearing – occipital • vision – parietal • speech, taste reading temporal occipital Limbic System Controls basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory Memory Loss and Amnesia is due to Limbic System Damage Speaking of Memory…. • Do you really pay attention? How much stuff do you miss when you think you’re observing carefully… The Ear • Your ears convert sound waves into electrical signals that are interpreted by your brain • The cochlea is the auditory portion of the inner ear. It is shaped like a snail shell. • Bones of the ear: – Anvil – Hammer – Stirrup The Eye • Eyes enable us to see in color and to distinguish fine details and movement. • The retina is the lining on back inner surface of the eye – consists of photoreceptors. • The optic nerve exits the back of the eye and connects in the brain to the thalamus. It contains many neurons that process visual information. • – Rods - respond to dim light and black and white shading. – Cones- respond to bright light and enables the sight of the colors. The Eye Lens Cornea Iris Pupil The Tongue