Signals Traveling in Neurons
Two opposing ideas about the nervous system
* Reticular theory ( the nervous system consisted of a large network of fused nerve cells) * Neuron theory ( the nervous system consisted of distinct elements or cells * Discovery of staining led to the acceptance of neuron theory. Staining is a chemical technique that caused nerve cells to become colored so they stood out from surrounding tissue * A way of electricity is transmitted in groups of neurons, such as the optic nerve. Basic Structure of the brain
* Cerebral cortex- A 2mm thick layer that covers the surface of the brain and contains the machinery for creating perception, as well as language, memory, and thinking. * A basic principle of cortical function is modular organization – specific functions are served by specific areas of the cortex * Primary receiving areas- the first areas in the cerebral cortex to receive the signals initiated by each sense’s receptors.- occipital love( vision),, temporal lobe (hearing), parietal lobe (skin senses, eg: touch, temperature, and pain. * The frontal lobe receives signals from all of the sense, and plays an important role in perceptions that involve the coordination of information received through two or more senses.
Structure of neurons
* The cell body- it contains mechanisms to keep the cell alive * Dendrites branch out from the cell body to receive electrical signals from other neurons * Axon/nerve fiber is filled with fluid that conducts electrical signals * Some neurons have long axons; others have short axons or none at all * Receptors- which are specialized to respond to environmental stimuli such as pressure for touch, all receptors look different but they all have something in common. Part of each receptors, indicated by the star, reacts to environmental stimuli and triggers the generation of electrical signals, which eventually are transmitted to neurons with axons.
Recording electrical signals in neurons
* A nerve (eg: optic nerve) carries signals out the back of the eye, consists of the axons (or nerve fibers) of many neurons. * When the nerve fiber is at rest, the oscilloscope records a difference in potential of -70mV. This value which stays the same as long as there are no signals in the neurons, called the resting potential. In the other words the inside of the neuron is 70 mv negative compared to the outside and remains that way as long as the neuron is at rest * When the neuron’s receptor is stimulated so that a signal is transmitted down the axon. * As the signal passes the recording electrode, the charge inside the axon rises to +40 mV compared to outside. AS the signal continues past the electrode, the charge inside the fiber reverses course and starts becoming negative again, until it returns to the resting level. * This signal is called the action potential, lasts about 1 millisecond.
Chemical Basis of Action Potentials
* Electrical signals in neurons are created by and conducted through liquid * Neurons are surrounded by a solution rich in ions, molecules that carry an electrical charge * Ions are created when molecules gain or lose electrons, as happens when compounds are dissolved in water. * For example, adding table salt (NaCl) to water creates positively charged sodium ions (Na+) and negative charged chlorine ions (Cl-). * The solution outside the axon of a neuron is rich in positively charged sodium (Na+) ions, whereas the solution inside the axon is rich in positively charged potassium (K+)ions * The changes of mV are caused by the flow of sodium ions and potassium ions across the cell membrane * First sodium flows into the fiber, then potassium flows out, and this sequence of sodium-in and potassium-out continues as the action potential travels down the axon * The flow of sodium and potassium is translated into a change of the charge inside the axon. The upward phase of...
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