Impulse Transmission PDF

Impulse Transmission  Impulse Transmission ① Potential Resting : Neurons have which is the electrical difference...

Impulse Transmission  Impulse Transmission ① Potential Resting : Neurons have which is the electrical difference a resting potential , charge across their membrane when they are not transmitting impulse. This is typically around - 70 millivolts (MV) ② Stimulus : When receives to exceed certain threshold , a neuron a stimulus strong enough a it triggers an action potential. This can be due to various factors , such as sensory input or chemical signals from other neurons. ③ Depolarisation : The action potential begins with depolarisation , where sodium (Nat) Channels sodium ions to rush into the This influx of positive open , allowing neuron. ions cause the inside of the neuron to become more positive compared to the outside. ④ Action Potential : If the depolarisation reaches the threshold level , an action potential is generated. This all meaning that the threshold is reached the is an or nothing response , once , action potential will occur fully. ⑤ Propagation : The action potential travels down the axon of the neuron. This occurs through a process called saltatory condition in myelinated neurons , where the impulse jumps from one node of Ranvier to the next , speeding up transmission. ⑥ Repolarisation : After the peak of the action potential potassium /K+) channels open , , allowing potassium ions to flow out of the neuron. This causes repolarisation , restoring the inside the negative charge neuron. & Hyperpolarisation : Sometimes , the membrane potential becomes even more negative than the resting potential as hyperpolarisation. This occurs due to prolonged opening - a phase known , of potassium channels. ⑧ Return to Resting Potential : The eventually the action of the neuron returns to its resting potential through sodium-potassium pump , which actively transports sodium out3 potassium back into the neuron. ⑨ Synaptic Transmission : Once the action potential reaches the axon terminals it the of , triggers release neurotransmitters into the synaptic cleft. These channels cross the gap to bind to receptors on the next neuron , continuing the transmission of the impulse. Action Potential - Dendrites Neuron & - Receive information body processes interes the information Axon carries information along & Axon Terminal - long distances from one part of Transmits the information to the neuron to another the next cell in the chain. ·a Nee :ot j Nerves can be very long as they often need to transmit information over long distances. Dendrites are the part of the nerve that receives incoming signals T W. Based on the Stimulation the neuron must &&&& strength of the incoming , decide whether to pass that signal along or not. If the stimulation is strong enough , the signal is transmitted along the entire of the potential. length axon in a phenomenon called an action  Potassium M sodium Nat Transmission of a neuronal signal is chloride dependent on the movement ot ions , or charged particles. Various ions, including sodium , potassium Chloride , are unequally distributed between the inside 3 the outside of the Cell. The presence 3 movement of these ions is important when a neuron is at rest B also when a neuron fires. RESTING m som The concentration of sodium MM must ions is higher outside of the cell than inside. The relative concentration of ⑭ potassium ⑭ potassium ions is the opposite with , ⑭ more ions inside the cell than outside ⑭ This ionic separation occurs right at the cell membrane B creates a chemical gradient across the membrane. Because ions are charged particles , It rest there are more positively charged ions outside the cell relative to the inside. This creates a difference in charge across the membrane Electrical gradient = Together with the chemical gradient Electrochemical Gradient. = + The difference in total charge inside outside of the cell = O The membrane potential -e m Sodiuma A rest when, being transmitted no , a signals are neuronal MM must membrane has a resting potential of aprox minus TO. millivolts potassiumTOmV ⑭ + + + + ++ + While the inside of the cell has a net negative charge the outside of the Cell has a net positive the line up at the membrane. charge , charges --------- The bulk solution on either side is electrically neutral. The res-membrane potential is the point where the cell achieved electrochemical Hing has equilibrium m. This means that the concentration gradient the electro gradient for each ion is equal 3 opposite. lons cannot more across the membrane at will. They need a protein embedded in the membrane to facilitate their movement. Mostions the membrane structure called channel cross through a an ion Sodium Potassium ion Channel lon channel Mechanica, g · their concentration Some through channels gradient. ion channels are always open but many by passive diffusion along , require signal to tell them to open or close.  Voltage gated channels only open when the membrane potential reaches a certain value Ligand-gated ion channels are trigged to open when they are bound by a specific molecule Mechanically-gated ion channels open in response to physical forces , such as changes in length or changes in pressuree. Most ion channels are selectively permeable meaning , that they only allow one ord small subset of ions to pass , through. Voltage gated ion channels - typically only allow a single ion to cross the membrane when they open. Therefore, Separate channels for each ion is needed · e. g. Voltage gated sodium Channels & Voltage gated potassium channels. As ions more through a channel 3 across from one side of the cell membrane to another they , cause the membrane potential of the cell to away from. move its resting potential If the resulting change in membrane potential is small-graded potential + 40 sizes /- which can very in be either + are transient a typically do not result A from the opening of the VG channels. O When ion channels open Ba graded a potential occurs, the neuron moves quickly - - 55 to rest its membrane values. This is done potential resting by the use of to e (mV) Sodium Potassium pump which uses , the energy generated by ATP hydrolysis , to actively transportions across the membrane against their concentration gradient. Sodium is transported to the outside of the cell where its concentration higher B potassium - is is transported back into the cell , where its concentration is higher. - One cycle of this pump transports three sodium ions outside the cell 3 brings two potassium ions Inside the cell.  This unbalanced charge transfer contributes to the separation of charge across the membrane also to the ionic concentrations & we see at rest , restoring the chemical electrical gradients to their levels. resting Maintaining these ionic balance 40 % of the brain's total in neurons use. is important as this process can account for 20 % to energy Only when the resting membrane potential Bion distributions maintained at precise are levels , will the neuron be poised B ready to fire an action potential. When the outside stimulation large enough to bring the membrane potential in the neuron is body up from -70mV to the threshold voltage of -55mV or higher this triggers an action , potential at the axon hillock , which then travels down the axon. Voltage-gated sodium channels have three states closed Binactivated. # open - , Over Shoot ↑ & O I Depolarisation g 55 78 - - Threshold At rest the Sodium channel , is closed. mV) Once the cell membrane reaches the threshold voltage , the channel changes to an open position 3 sodium rushes into the cell because of the electrochemical gradient. As positive sodium ions enter the cell the membrane potential becomes less , negative more positive as it approches OmV = Depolarisation Eventially the Voltage gradient goes beyond O up to a positive 30mV Overshoot = , As the membrane potential becomes positive, the Sodium channel Inactivation gate shuts , making the Channel inactivated. flow of sodium ions into the cell - Stopping. The change in membrane potential also opens the voltage-gated potassium channels they , open B close slowly Due to the potassium-electrochemical gradient K+ ions flow out of the cell. , , making it less positive 3 eventually negative Repolarisation. =  As the potassium channels are more ReprisationStor slow to close , for a breif period , the membrane potential is hyperpolarised. = More negative then the resting potential. During hyperpolarisation the potassium channel closes. Throughout all this the sodium-potassium pump is still working. The chemical gradients pump restores the by putting the sodiumB potassium back in place B re-establishes the potential gradient by moving more sodium ions out then potassium in, This returns the membrane potential back to its resting potential.