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The Nervous System and The Brain Neuroscience and Behavior Modules 3 & 4 Early Theories - Phrenology - Bumps on the skull tell us nothing about the brain’s underlying functions - Some assumptions were true…different parts of the brain DO control different parts of behavior The Nervous System An electrochemical communication system that enables us to think, feel and act How do we study the Nervous System? Clinical Observation – Direct clinical observation of patients with brain damage or disease - Ex. Phineas Gage http://www.youtube.com/watch?v=kc213mMSsjY Invasive Techniques – Since 1850, experimenters have opened the skull and “invaded” the brain while the patient is still alive Brain Tissue can be stimulated with electricity, chemicals, heat or cold. In addition, it can be lesioned, or destroyed in place Brain Tissue can also be ablated, or removed with a vacuum or scalpel. It can also be transected, meaning isolated or cut. Neuroimaging Techniques EEG – Electroencephalogram – Detects electrical currents in the brain making possible early evaluation of issues Neuroimaging Techniques cont’d PET Scan – Positron Emission Tomography – Patient is injected with a safe dose of radioactive sugar. Brain cells that are particularly active will consume more (or perhaps none) of the substance. The brain activity is measured by an imaging computer Neuroimaging Techniques cont’d CAT Scan – Computerized Axial Tomography – A narrow X-ray beam is aimed through the patient’s head & hits a detector on the other side. Brain tissue has different densities, and blocks the beam to different degrees. The computer then constructs a picture that reveals damaged or dead tissue. http://en.wikipedia.org/wiki/File:64_slice_scanner.JPG Neuroimaging Techniques cont’d MRI – Magnetic Resonance Imaging – Safer than a CAT Scan because there are no X-Rays. The nuclei at the center of atoms have their own resonant frequencies. If they are perturbed, the bounce around, and return to their normal position. The MRI disturbs the atoms of the brain, and the computer assembles a detailed picture that may reveal tumors, tissue degeneration, clots and leaks, etc. http://videos.howstuffworks.com/tlc/29321-understanding-brain-mri-video.htm Neurons and their Messages Neural Pathways – Information travels in the Nervous System through three types of neurons Sensory or Afferent Neurons (Inward) – Sends information from the body’s tissues and sensory organs inward to the spinal cord and brain for information Neurons and their Messages cont’d Interneurons – This processing involves a second class of neurons of the brain and spinal cord (CNS). Motor or Efferent Neurons – Sends instructions to the body’s tissues and extremities Mnemonic Device – SAME http://www.youtube.com/watch?v=wK3VUQTRIBg&NR=1&safety_mode=tr ue&persist_safety_mode=1&safe=active The easiest example is the simple reflex – Ex. Touching a hot stove http://www.youtube.com/watch?v=1OYKegnG8Lo&NR=1 Nervous system vid 1:00 http://www.youtube.com/watch?v=iBnGeDzTYD4&feature=related&safety_mode=tru e&persist_safety_mode=1&safe=active Generating a Neural Impulse Each neuron consists of a cell body (Soma) and one or more branching fibers. The fibers are of two types: Dendrites – Receive information from sensory receptors, or other neurons Axons – Pass information along to other neurons ***Dendrites – Short; Axons – Long *** Neurons and their messages Generating a Neural Impulse – cont’d A layer of fatty cells called the Myelin Sheath insulates and speeds up their impulses When does a neuron fire? When the neuron is stimulated by pressure, heat, light or chemical messages from adjacent neurons. This impulse is called the action potential. Action Potential is a brief electrical charge that travels down the neuron like a spark down a fuse. The signals trigger an impulse if the stimulus exceeds a minimum intensity called the Threshold – See handout on Action Potential Generating a Neural Impulse – cont’d Increasing the stimulus above the threshold will not increase the intensity of the impulse. The neuron’s reaction is an “All or None Response” – Like firing a gun – either it fires, or it doesn’t ***Reaction Time Experiment*** http://www.bbc.co.uk/science/humanbody/sleep/sheep/ How do you know the difference between getting touched with a feather, or getting hit with a punch? More neurons can fire, and fire more often Generating a Neural Impulse – cont’d There are tiny gaps, less than a millionth of an inch wide. This junction is called the… Synapse If the neurons don’t touch, how does one neuron pass information to the next? Through chemical messengers called neurotransmitters For a second, the neurotransmitter unlocks tiny gates like a “Lock and Key” system - http://www.youtube.com/watch?v=90cj4NX87Yk Generating a neural impulse – cont’d One of the best understood neurotransmitters is Acetylcholine (ACh) Acetylcholine is the neurotransmitter at every junction between a motor neuron and a muscle. When ACh is released to the muscle cells, the muscle contracts. If ACh is blocked, muscles cannot contract. Ex. Curare – Poison that occupies and blocks ACh receptor sites leaving the neurotransmitter unable to affect the muscles – result is paralysis. Monkey http://www.youtube.com/watch?v=0P-FuwMDq5s&feature=related Generating a neural impulse – cont’d Ex. Botulin – Poison that causes paralysis by blocking the release of ACh http://www.youtube.com/watch?v=OX2ECc1lNFc ***Opposite – Venom of a Black Widow Spider *** - Causes a flood of Ach which leads to muscle contractions and convulsions Endorphins – “Morphine Within” – Natural opiate-like neurotransmitter linked to pain control and pleasure. Most commonly released during exercise (“Runner’s high”) If endorphins lessen pain, and boost mood, why not simply take morphine? – Handout of common neurotransmitters – “Must Know 5” http://www.youtube.com/watch?v=TjrBdKXgYFY Divisions of the Nervous System Neurons function through several sub-systems – The Central Nervous System (CNS) includes all the neurons in the brain and spinal cord The Peripheral (On the outside) Nervous System (PNS) – Links the CNS with the body’s sense receptors, muscles and glands The PNS has two components: The Somatic Nervous System and the Autonomic Nervous System Divisions of the Nervous System – cont’d The Somatic transmits sensory input (touch and taste for example) to the CNS from the outside world and directs motor or muscle output, such as our voluntary movements The Autonomic influences glands and the muscles of our internal organs. Usually operates on its own – “Autonomously” – Activities such as heartbeat, digestion, glandular activity, etc. The Autonomic Nervous System also has subcomponents The Nervous System Peripheral Nervous System Somatic Nervous System Central Nervous System Autonomic Nervous System Brain Sympathetic Nervous System Parasympathetic Nervous System Spinal Cord Divisions of the Nervous System – cont’d The Sympathetic Nervous System – Arouses us for defensive action. It accelerates your heartbeat, slows digestion, raises your blood sugar, and cools you with perspiration. When the stress is over, your Parasympathetic Nervous System produces the opposite effects and calms you down http://www.youtube.com/watch?v=8PWH 745MMMY The Brain