Gatekeepers of Your Gut Health
This is the exciting thing is. Okay, now speed up your heart. In addition to the brain and spinal cord, principal organs of the nervous system include the following:. Acetylcholine Ach and noradrenialin, also called norepinephrine, are 2 of the main neurotransmitters. Whether you're crossing the country or the globe, we make it easy to access world-class care at Johns Hopkins. They carry information between sensory and motor neurons.
What is the nervous system?
The same impulse is sent regardless of strength. The sensitivity to mild or severe pain depends on the number of neurons stimulated as well as the frequency of their stimulation. When the threshold is reached the axon or dendrite changes. The inside, at the point of the stimulation, becomes positive and the outside becomes negative. This creates unlike charges along the length of the neuron and the impulse travels along the neuron. This is called the action potential. Once the impulse moves along, the area behind the impulse is changed back to its normal negative resting state.
Below is a cross-section of an axon, with an action potential AP moving from left to right. The AP has not yet reached point 4; the membrane there is still at rest. At point 3, positive sodium ions are moving in from the adjacent region, depolarising the region; the sodium channels are about to open. Point 2 is at the peak of the AP; the sodium channels are open and ions are flowing into the axon.
The AP has passed by point 1; the sodium channels are inactivated, and the membrane is hyperpolarized. Refractory Period — While the ions are moving in and out of each region of the neuron, there is a brief period during which the neuron is unable to have another action potential.
This delay is called the refractory period. The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. The action potential is an explosion of electrical activity that is created by a depolarising current.
This means that some event a stimulus causes the resting potential to move toward 0 mV. When the depolarisation reaches about mV a neuron will fire an action potential.
This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire. Also, when the threshold level is reached, an action potential of a fixed sized will always fire…for any given neuron, the size of the action potential is always the same.
There are no big or small action potentials in one nerve cell — all action potentials are the same size. Neural impulse — takes the same path all the time — it is a process of conducting information from a stimulus by the dendrite of one neuron and carrying it through the axon and on to the next neuron.
The way it selects is easy — it has pores that are only so big. So, only very small ions can fit through. Outside the neuron, the ions are mostly positively charged. In this state with mostly negative charge inside and positive charge on the outside the neuron is said to be Polarized.
The charge inside the neuron then rises to approx. This only occurs for a brief moment, but it is enough to create a domino effect. This can occur fast enough to allow up to 1, action potentials per second.
Then the charge inside the neuron drops to about mv refractory period before restoring itself to normal. The speed depends on whether a myelin sheath is present or not. If there is no myelin sheath then the impulse travels all along the axon or dendrite. This acts to slow down the impulse. If there is a myelin sheath then the impulse charges can only move in and out at the nodes of Ranvier. These impulses move more rapidly than the non-myelinated neurons.
Also, the larger the diameter of the axon or dendrite the faster the impulse. There is no in between. Once the threshold is reached, there is no going back, the neural impulse will begin and will go through the complete cycle.
If the threshold is reached, an action potential will occur. After sensory neurons carry impulses most eventually reach the brain. The brain acts to interpret, sort, and process the incoming impulses and then decide on a response. The brain s grey matter is composed of cell bodies and synapses. The white matter is made of nerve fibres axons and dendrites. There are about 12, million neurons that form the brain.
The space between the inner 2 membranes is filled with a liquid called cerebrospinal fluid. There is a total of about mL of this liquid in the CNS. It protects the CNS by acting as a shock absorber.
Inflammation of the meninges causes a sometimes-serious condition called meningitis. Refer to your text for a description of viral and bacterial meningitis. The right hemisphere controls the left side of the body while the left hemisphere controls the right side of the body. The outer part of the cerebrum is grey and called the cerebral cortex.
It is divided into 4 lobes. Each lobe controls specific functions:. Notice that there are many infolds of the cerebral cortex. This gives it a larger surface area. This allows for more interconnections between different parts of the brain and for more efficiency.
The inner part of the cerebrum is white matter. It is made of millions of nerve fibres. These nerve fibres connect different areas of the cerebral cortex as well as the 2 sides of the brain.
Acts as a sorting centre for the brain. It relays incoming impulses to the relevant part of the brain. The spinal cord is a long, fragile tubelike structure that begins at the end of the brain stem and continues down almost to the bottom of the spine spinal column. The spinal cord consists of nerves that carry both incoming and outgoing messages between the brain and the rest of the body.
It is also the centre for reflexes, such as the knee jerk reflex. Like the brain, the spinal cord is covered by three layers of tissue called meninges. The spinal cord and meninges are contained in the spinal canal, which runs through the centre of the spine.
In most adults, the spine is composed of 26 vertebrae, which are the individual bones of the back. Just as the skull protects the brain, vertebrae protect the spinal cord. The vertebrae are separated by disks made of cartilage, which act as cushions, reducing the forces generated by movements such as walking and jumping. Like the brain, the spinal cord consists of grey and white matter. The butterfly-shaped centre of the cord consists of grey matter. The grey matter contains dendrites and cell bodies.
The front or ventral root contain motor nerves, which transmit information from the brain or spinal cord to muscles, stimulating movement. The back or dorsal root contain sensory nerves, which transmit sensory information from other parts of the body through the spinal cord to the brain. The surrounding white matter contains columns of axons that carry sensory information to the brain from the rest of the body ascending tracts and columns that carry impulses from the brain to the muscles descending tracts.
There are a total of 31 pairs of spinal nerves. These carry impulses to and from the spinal cord. A reflex is the simplest, quickest form of activity in the nervous system. The information contained in this website is for general information and educational purposes only. It does not constitute medical advice.
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