Your neurons carry messages in the form of electrical signals called nerve impulses. To create a nerve impulse, your neurons have to be excited. Stimuli such as light, sound or pressure all excite your neurons, but in most cases, chemicals released by other neurons will trigger a nerve impulse.
Although you have millions of neurons that are densely packed within your nervous system, they never actually touch. So when a nerve impulse reaches the end of one neuron, a neurotransmitter chemical is released. It diffuses from this neuron across a junction and excites the next neuron. Over half of all the nerve cells in your nervous system do not transmit any impulses.
Learn How Neurons Communicate. Nuts and Bolts: The Neuron. Wellcome Trust. Electrifying the Brain. Interact with the Brain. Then, if you sense that this information is important enough to remember permanently, it's passed inward to other regions of the brain such as the hippocampus and amygdala for long-term storage and retrieval.
As these messages travel through the brain, they too create pathways that serve as the basis of memory. Different parts of the cerebrum move different body parts. The left side of the brain controls the movements of the right side of the body, and the right side of the brain controls the movements of the left side of the body. When you press your car's accelerator with your right foot, for example, it's the left side of your brain that sends the message allowing you to do it. Basic body functions.
A part of the peripheral nervous system called the autonomic nervous system controls many of the body processes you almost never need to think about, like breathing, digestion, sweating, and shivering.
The autonomic nervous system has two parts: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system prepares the body for sudden stress, like if you witness a robbery.
When something frightening happens, the sympathetic nervous system makes the heart beat faster so that it sends blood quickly to the different body parts that might need it. It also causes the adrenal glands at the top of the kidneys to release adrenaline, a hormone that helps give extra power to the muscles for a quick getaway. This process is known as the body's "fight or flight" response.
The parasympathetic nervous system does the opposite: It prepares the body for rest. It also helps the digestive tract move along so our bodies can efficiently take in nutrients from the food we eat. Sight probably tells us more about the world than any other sense. Light entering the eye forms an upside-down image on the retina. The retina transforms the light into nerve signals for the brain. The brain then turns the image right-side up and tells you what you're seeing.
Every sound you hear is the result of sound waves entering your ears and making your eardrums vibrate. These vibrations then move along the tiny bones of the middle ear and turn into nerve signals. The cortex then processes these signals, telling you what you're hearing.
The tongue contains small groups of sensory cells called taste buds that react to chemicals in foods. Taste buds react to sweet, sour, salty, bitter, and savory. The taste buds send messages to the areas in the cortex responsible for processing taste.
Olfactory cells in the mucous membranes lining each nostril react to chemicals you breathe in and send messages along specific nerves to the brain. Dendrites are tree-like extensions at the beginning of a neuron that help increase the surface area of the cell body. These tiny protrusions receive information from other neurons and transmit electrical stimulation to the soma. Dendrites are also covered with synapses. Most neurons possess these branch-like extensions that extend outward away from the cell body.
These dendrites then receive chemical signals from other neurons, which are then converted into electrical impulses that are transmitted toward the cell body. Some neurons have very small, short dendrites, while other cells possess very long ones. The neurons of the central nervous systems have very long and complex dendrites that then receive signals from as many as a thousand other neurons.
If the electrical impulses transmitted inward toward the cell body are large enough, they will generate an action potential. This results in the signal being transmitted down the axon. The soma, or cell body, is where the signals from the dendrites are joined and passed on. The soma and the nucleus do not play an active role in the transmission of the neural signal.
Instead, these two structures serve to maintain the cell and keep the neuron functional. Think of the cell body as a small factory that fuels the neuron. The soma produces the proteins that the other parts of the neuron, including the dendrites, axons, and synapses, need to function properly.
The support structures of the cell include mitochondria, which provide energy for the cell, and the Golgi apparatus, which packages products created by the cell and dispatches them to various locations inside and outside the cell. The axon hillock is located at the end of the soma and controls the firing of the neuron. If the total strength of the signal exceeds the threshold limit of the axon hillock, the structure will fire a signal known as an action potential down the axon.
The axon hillock acts as something of a manager, summing the total inhibitory and excitatory signals. If the sum of these signals exceeds a certain threshold, the action potential will be triggered and an electrical signal will then be transmitted down the axon away from the cell body.
This action potential is caused by changes in ion channels which are affected by changes in polarization. When a signal is received by the cell, it causes sodium ions to enter the cell and reduce the polarization. If the axon hillock is depolarized to a certain threshold, an action potential will fire and transmit the electrical signal down the axon to the synapses.
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