Task 1

Task 1

·         Researchers at the University of Pennsylvania School of Medicine have discovered the mechanism that facilitates how two ion channels collaborate in the control of electrical signals in the brain ·         The channels were anchored by a third protein at key locations on the nerve cell surface, allowing them to work together to set the timing and pattern of nerve impulses. ·         this channel partnership mechanism is present in all vertebrates, but is lacking in invertebrates ·         The elucidation should aid effort  to develop new treatment for epileptic seizures, pain, and abnormal muscle movements. ·         Electrical impulses in neurons are created when these ions are allowed to return to their original locations by passing rapidly through channels in nerve cells' outer membranes.

·         They are two ion channel collaborate in the control of electrical signal in the brain. ·         There are protein channel and carrier protein. ·         Vertebrate have both CNS and spinal cord but in invertebrate only PNS present. ·

·         What are two channel involved? ·         What is the third protein and how it works together and set the timing and pattern of nerve impuls? ·         How nervous system functions in invertebrate without CNS? ·         How can we explain two ion channels collaborate in the control of electrical signals in the brain? ·         What is the relationship between potassium and sodium channels in neurotrans-mission?

·         Refer to lecture notes ·         Reference book ·         Search internets

1. what are two channels involved

         Potassium channel and sodium channel, cells pump extra potassium into their interiors, and pump extra sodium out to the surrounding fluid. Electrical impulses in neurons are created when these ions are allowed to return to their original locations by passing rapidly through channels in nerve cells' outer membranes. Nerve cells possess wire-like extensions, called axons, which initiate these impulses and carry them from one cell to the next.

2. What is the third protein and how it works together and set the timing and pattern of nerve impulse?

            The third protein is ankyrin-G because in a study by Penn's Edward Cooper, MD, PhD, Assistant Professor of Neurology, and colleagues, and the research team was able to identify a molecular motif that allows both channel types to link to a protein called ankyrin-G. The function of Ankyrin-G, in turn, it binds tightly to the nerve cell's cytoskeleton, ensuring the channels' stabilization at the initial segment. The chemical motif identified in the potassium channels was nearly identical to that previously discovered in sodium channels, revealing that the potassium and sodium channels link to the ankyrin-G protein in a similar manner.

            "The ankyrin-G-interaction with potassium and sodium channels establishes a unique domain of the cell for initiating the nerve impulse and for boosting the impulse across the nodes of Ranvier," states Cooper.

            Sodium and potassium are salt molecules (or ions) found throughout the body. Cells pump extra potassium into their interiors, and pump extra sodium out to the surrounding fluid. Electrical impulses in neurons are created when these ions are allowed to return to their original locations by passing rapidly through channels in nerve cells' outer membranes. Nerve cells possess wire-like extensions, called axons, which initiate these impulses and carry them from one cell to the next.

            The efficient and speedy passage of nerve impulses along axons is aided by the presence of an insulating cover, known as myelin, which maintains the electrical activity along the entire length of the axon. The nerve impulse is able to skip across the unmyelinated regions of the axon at the nodes of Ranvier, with the help of sodium and potassium channels.

            Cooper had explain that Myelination and the coupling of axonal sodium and potassium channels are fundamental improvements in the nervous system, and these changes are probably necessary for the vertebrate 'life-style'. He also said that people can only be large and fast-moving if you have a nerve impulse mechanism that is both rapid and highly reliable.

3.  How nervous system functions in invertebrate without CNS?

Invertebrates is an animal which do not have a backbone. The spinal cord and brain make up the CNS. Cnidarians, Nematoda, Annelida,

However, nervous system do evolve from sponges to higher invertebrates which are annelids, arthropods and some mollusks

Sponges are the only animals without neurons

In Cnidarians (sea anemones, corals, jellyfish, freshwater Hydra), there is a simplest existing nervous system which is known as nerve net. Nerve net extends throughout the body and controls simple movements of the body wall and tentacles. E.g: In jellies the net primarily commands the body wall to slowly contract and expand for swimming and the tentacles to move through the water

In a swimming cnidarians or medusae, their radial symmetry is often associated with a nerve ring and some of these animal have certain neurons condensed into simple ganglia/ ganglion.

The beginnings of a true CNS is only find when we progress from cnidarians to bilaterally symmetric animals such as platyhelminthes (flatworms, tapeworms and so on)

Complex ganglionic nervous system are characteristic of higher invertebrates which include annelids, arthropods and some mollusks

4. How can we explain two ion channels collaborate in the control of electrical signals in the brain?

An action potential are generated by a special types of voltage- activated ion channels, which is embedded in cell’s plasma membrane. There are two types of voltage- activated ion channels which are voltage- gated Na+ and voltage- gated K+.

The voltage- gated Na+ channel has two gates: an activation gate and inactivation gate. The voltage- gated K+ channel only has one gate, which can be either open or closed.

Both K+ and Na+ channels are closed. When Na+ channel open, Na+ rush into the cell. Interior of the cell become more positive. Hence, an action potential is generated. This is known as depolarizing phase. In repolarizing phase, Na+ channel closed, K+ channel open. K+ leave the cell and inside the cell become more negative. At undershoot/ hyperpolarization, Na= channel closed but K+ channel remain open because of their slow moving gate, K+ keep flowing out of the cell.

5. What is the relationship between potassium and sodium channels in neurotrans-mission?

1	The inside of the cell is slightly negatively charged (resting membrane potential of -70 to -80 mV).
2	A disturbance (mechanical, electrical, or sometimes chemical) causes a few sodium channels in a small portion of the membrane to open.
3	Sodium ions enter the cell through the open sodium channels. The positive charge that they carry makes the inside of the cell slightly less negative (depolarizes the cell).
4	When the depolarization reaches a certain threshold value, many more sodium channels in that area open. More sodium flows in and triggers an action potential. The inflow of sodium ions reverses the membrane potential in that area (making it positive inside and negative outside the electrical potential goes to about +40 mV inside)
5	When the electrical potential reaches +40 mV inside (about 1 millisecond later), the sodium channels shut down and let no more sodium ions inside (sodium inactivation).
6	The developing positive membrane potential causes potassium channels to open.
7	Potassium ions leave the cell through the open potassium channels. The outward movement of positive potassium ions makes the inside of the membrane more negative and returns the membrane toward the resting membrane potential (repolarizes the cell).
8	When the membrane potential returns to the resting value, the potassium channels shut down and potassium ions can no longer leave the cell.
9	The membrane potential slightly overshoots the resting potential, which is corrected by the sodium-potassium pump, which restores the normal ion balance across the membrane and returns the membrane potential to its resting level.
10	The membrane potential slightly overshoots the resting potential, which is corrected by the sodium-potassium pump, which restores the normal ion balance across the membrane and returns the membrane potential to its resting level.
11	Now, this sequence of events occurs in a local area of the membrane. But these changes get passed on to the next area of membrane, then to the next area, and so on down the entire length of the axon. Thus, the action potential (nerve impulse or nerve signal) gets transmitted (propagated) down the nerve cell.­