Altered mood and impulsive behavior Auditory hallucinations Depression[ edit ] Depression is the most common major mental illness and is characterized by both emotional and physical symptoms. Symptoms of depression are: The cause of depression and its symptoms are a mystery but we do understand that it is an illness associated with biochemical changes in the brain. A lot of research goes on to explain that it is associated with a lack of amines serotonin and norephinephrine.
The membrane is said to be polarized. The potential difference across the membrane at rest is called the resting potential and is approximately mV in neurons. The negative sign indicates that the inside of the cell is negative with respect to the outside.
The establishment of this potential difference involves several factors, most importantly the transport of ions across the cell membrane and the selective permeability of the membrane to these ions.
The active transport of potassium and sodium ions into and out of the cell, respectively, is accomplished by a number of sodium-potassium pumps scattered across the cell membrane.
Each pump transports two atoms of potassium into the cell for every three atoms of sodium pumped out. This establishes a particular distribution of positively charged ions across the cell membrane, with more sodium present outside the cell than inside, and more potassium inside the cell than outside.
The natural tendency of sodium and potassium is to diffuse across their electrochemical gradients to attempt to reach their respective equilibrium potentials, with sodium diffusing into the cell and potassium diffusing out.
However, the resting cell membrane is approximately times more permeable to potassium than to sodium, so that more potassium diffuses out of the cell than sodium diffuses in. As a result, the dominant outward leak of potassium ions produces a hyperpolarizing current that establishes the cell's resting potential of roughly mV.
Like the resting potential, action potentials depend upon the permeability of the cell membrane to sodium and potassium.
Saltatory Conduction, thus, is an effective alternative to large-diameter axons and allows rapid action potential through small axons. A myelinated frog axon 10 µm in diameter conducts action potential at the same speed as an unmyelinated µm squid axon. Within most solid materials a current arise from the flow of electrons, which is called electronic conduction. In all conductors, semiconductors, and many insulated materials only electronic conduction exists, and the electrical conductivity is strongly dependant on the number of electrons available to participate to the conduction process. Saltatory Condunction refers to the conduction of nerve impulses along myelinated fibres. These impulses 'jump' along the nerve fibre from each 'node of ranvier*' effectively skipping parts of the axon and thus travelling faster down th.
This is known as the action potential, and in this condition the membrane is said to be depolarised. See depolarization This depolarisation occurs because channels in the axon membrane change shape, and hence open or close, depending on the voltage across the membrane. They are therefore called voltage-gated ion channels.
The sequence of events is described below.
At resting potential some potassium voltage-gated channels are open but the sodium voltage-gated channels are closed. The energy of the stimulus causes the sodium voltage-gated channels in the neuron cell surface membrane to open and therefore sodium ions diffuse in through the channels along their electrochemical gradient.
Being positively charged, they begin a reversal in the potential difference across the membrane. As sodium ions enter, so more sodium channels open, causing an even greater influx of sodium ions. This is an example of positive feedback.
While this occurs, the voltage gates on the potassium channels begin to open. With some potassium voltage-gated channels now open, the electrical gradient that was preventing further outward movement of potassium ions is now reversed, causing more potassium channels to open.
This means that yet more potassium ions diffuse out, causing repolarisation of the neuron.
The outward movement of these potassium ions causes the temporary overshoot of the electrical gradient, with the inside of the neuron being more negative relative to the outside than usual.
This is called hyperpolarisation hyperpolarization. The gates on the potassium channels now close and the activities of the sodium-potassium pumps cause sodium ions to be pumped out and potassium ions in, once again.
The resting potential of mV is re-established and the neuron is said to be repolarised.
Action potentials are triggered when an initial depolarization reaches threshold. This threshold potential varies, but generally is about 15 millivolts above the cell's resting membrane potential, occurring when the inward sodium current exceeds the outward potassium current.
The net influx of positive charges carried by sodium ions depolarizes the membrane potential, leading to the further opening of voltage-gated sodium channels. These channels support greater inward current causing further depolarization, creating a positive-feedback cycle that drives the membrane potential to a very depolarized level.
The action potential threshold can be shifted by changing the balance between sodium and potassium currents. For example, if some of the sodium channels are in an inactivated state, then a given level of depolarization will open fewer sodium channels and a greater depolarization will be needed to trigger an action potential.
This is the basis for the refractory period see Refractory period. Action potentials are largely dictated by the interplay between sodium and potassium ions although there are minor contributions from other ions such as calcium and chlorideand are often modeled using hypothetical cells containing only two transmembrane ion channels a voltage-gated sodium channel and a non-voltage-gated potassium channel.
It represents the peak current through channels at a given voltage before any inactivation has taken place i. The most positive voltages in this plot are only attainable by the cell through artificial means - i. The green arrow indicates the resting potential of the cell and also the value of the equilibrium potential for potassium Ek.
Thus, any perturbation of the membrane potential around a positive slope crossing will tend to return the voltage to that crossing value.
In this two-ion system, ENa is the natural limit of membrane potential beyond which a cell cannot pass. Current values illustrated in this graph that exceed ENa are measured by artificially pushing the cell's voltage past its natural limit. Note however, that ENa could only be reached if the potassium current were absent.
The blue arrow indicates the maximum voltage that the peak of the action potential can approach. This is the actual natural maximum membrane potential that this cell can reach.
It cannot reach ENa because of the counteracting influence of the potassium current.The term saltatory conduction refers to conduction of a nerve impulse along a _____ and is faster due to nodes if Renvier? myelinated axon Myelinated fibers conduct impulses faster than _____ fibers?
anterograde conduction transmission of a cardiac impulse in the normal direction, from the sinus node to the ventricles, particularly forward conduction through the atrioventricular node.
Diagrammatic view of the conducting system of the heart, showing anterograde conduction of the cardiac impulse. The Action Potential C. George Boeree. The word potential refers to the fact that there is a potential for change here.
We use the same term to refer to a battery that is just sitting there, not connected to anything: It, too, has a resting potential. This is called saltatory conduction, from the Latin word for "jump" (also seen in.
The term central nervous system refers to the: A) autonomic and peripheral nervous systems B) brain, spinal cord, and cranial nerves Which one of the following describes saltatory conduction: A) occurs only if the myelin sheath is continuous The substance that is released at axonal endings to propagate a nervous impulse is called: A) an.
The term saltatory conduction refers to conduction of a nerve impulse along a _____ and is faster due to nodes if Renvier? myelinated axon Myelinated fibers conduct impulses faster than _____ fibers?
Within most solid materials a current arise from the flow of electrons, which is called electronic conduction.
In all conductors, semiconductors, and many insulated materials only electronic conduction exists, and the electrical conductivity is strongly dependant on the number of electrons available to participate to the conduction process.