Introduction to Information Processing PDF

1 ‫ان كنت غير قادر علي االشتراك في الكورس فبرجاء التواصل معي علي الواتس اب او علي الحساب‬ ‫الشخصي و سيتم قبولك في الكورس مجانا ً في الحال و سوف اكون سعيد و راضي بذلك ‪...‬لكن هذا‬ ‫ال يتيح لك استخدام او تصوير او طباعة هذا العمل بعيدا ً عني و بدون اذني ‪...‬فبذلك يتم نشر العمل‬ ‫لمن لم يسهر علي تنف...

1 ‫ان كنت غير قادر علي االشتراك في الكورس فبرجاء التواصل معي علي الواتس اب او علي الحساب‬ ‫الشخصي و سيتم قبولك في الكورس مجانا ً في الحال و سوف اكون سعيد و راضي بذلك ‪...‬لكن هذا‬ ‫ال يتيح لك استخدام او تصوير او طباعة هذا العمل بعيدا ً عني و بدون اذني ‪...‬فبذلك يتم نشر العمل‬ ‫لمن لم يسهر علي تنفيذه ليتم اخراجه بهذه الصورة لك ‪...‬فلن اسامح امام هللا كل من شارك في نشر‬ ‫العمل و كل من ساعد علي ذلك وهللا علي ما اقول شهيد‬ ‫‪Made By: Dr. Samuel George‬‬ ‫‪2‬‬ 3  Introduction to Information Processing Information processing by a nervous system occurs in three stages: sensory input, integration, and motor output CNS PNS neurons that carry out integration are organized in central neurons that carry information into and out of the CNS nervous system (CNS) When bundled together, such neurons form nerves. Includes brain and Spinal cord o Stages of information processing: 1. Sensory neurons transmit information from eyes and other sensors that detect external stimuli (light, sound, touch, heat, smell, and taste) or internal conditions (such as blood pressure, blood carbon dioxide level, and muscle tension). 2. This information is sent to processing centers in the brain or ganglia. 3. Neurons in the brain or ganglia integrate (analyze and interpret) the sensory input. 4. The vast majority of neurons in the brain are interneurons, which form the local circuits connecting neurons in the brain. 5. Motor output relies on neurons that extend out of the processing centers and trigger muscle or gland activity. For example, motor neurons transmit signals to muscle cells, causing them to contract. 4  Neuron structure and Function Structure Its Function cell body (Soma) In which Most of a neuron’s organelles, including its nucleus, are located dendrites Together with the cell body, the dendrites receive signals from other neurons. Axon Extension that transmits signals to other cells axon hillock The cone-shaped base of an axon where signals that travel down the axon are generated. Synapse The junction at which the axon transmits information to another cells Synaptic terminal The part of each axon branch that forms synapses At most synapses, these chemical messengers pass information from the transmitting neuron to the neurotransmitters receiving cell. 5 N.B: 1. In describing a synapse presynaptic cell Postsynaptic cell. transmitting neuron the neuron, muscle, or gland cell that receives the signal 2. The neurons of vertebrates and most invertebrates require supporting cells called glial cells, or glia to: - nourish neurons - insulate the axons of neurons - Regulate the extracellular fluid surrounding neurons. - Overall, glia outnumber neurons in the mammalian brain 10- to 50-fold. The resting potential of a neuron - Ions are unequally distributed between the interior of cells and the fluid that surrounds them. - As a result, the inside of a cell is negatively charged relative to the outside. - This charge difference, or voltage, is called the membrane potential. - The resting membrane potential is typically between -60 and -80 mv Formation of resting Potential Potassium ions (K+) and sodium ions (Na+) play an essential role in the formation of the resting potential. Each type of ion has a concentration gradient across the plasma membrane of a neuron 6  The concentration of K+ is highest inside the cell (InK), while the concentration of Na+ is highest outside.)‫(برص‬ These Na+ and K+ gradients are maintained by sodium-potassium pumps in the plasma membrane. These ion pumps use the energy of ATP hydrolysis to: →Actively transport three Na+ ions out of the cell for every two K+ ions it transports into the cell Although this pumping generates a net export of positive charge, the resulting voltage difference is only a few millivolts. Why, then, is there a voltage difference of 60–80 mV in a resting neuron? → the answer lies in ion movement through Ion channels Ion channels: pores formed by specialized proteins that span the membrane which allow ions to diffuse back and forth across the membrane. 7  Diffusion of K+ through open potassium channels is critical for formation of the resting potential. The K+ concentration is 140 mM inside the cell, but only 5 mM outside. ↓ The chemical concentration gradient thus favors a net outflow of K+. ↓ Furthermore, a resting neuron has many open potassium channels ↓ Because Na+ and other ions can’t readily cross the membrane, K+ outflow leads to a net negative charge inside the cell. ↓ This buildup of negative charge within the neuron is the major source of the membrane potential. What stops the buildup of negative charge? The excess negative charges inside the cell ↓ Exert an attractive force opposes the flow of additional positively charged potassium ions out of the cell. The separation of charge (voltage) thus results in an electrical gradient that counterbalances the chemical concentration gradient of K+. 8  Action potentials are the signals conducted by axons - Changes in the membrane potential occur because neurons contain: gated ion channels, ion channels that open or close in response to stimuli. - The opening or closing of gated ion channels alters the membrane’s permeability to particular ions, which in turn alters the membrane potential. Hyperpolarization and Depolarization o what happens when gated potassium channels that are closed in a resting neuron are stimulated to open.? Opening these potassium channels ↓ increases the membrane’s permeability to K+. ↓ Net diffusion of K+ out of the neuron increases ↓ shifting the membrane potential more negative. ↓ This increase in the magnitude of the membrane potential, called a hyperpolarization, makes the inside of the membrane more negative. In a resting neuron, hyperpolarization results from any stimulus that 1. increases the outflow of positive ions 2. or increase the inflow of negative ions. 9 o what happens when gated Sodium channels that are closed in a resting neuron are stimulated to open? If a stimulus causes the gated sodium channels in a resting neuron to open ↓ the membrane’s permeability to Na+ increases. ↓ Na+ diffuses into the cell along its concentration gradient ↓ causing a depolarization as the membrane potential shifts More positive depolarization →A reduction in the magnitude of the membrane potential. (The inside of the membrane less negative). Depolarization Hyperpolarization - Increased Membrane permeability to Na+ - Increased Membrane permeability to K+ - Influx of Na+ → makes inside of the membrane more - Efflux of K+ →makes inside of the membrane more positive (Less negative) negative (Less positive) Graded Potentials and Action Potentials Graded potential Action potential - induce a small electrical current that leaks out of the - massive change in membrane voltage due to a neuron as it flows along the membrane. depolarization that shifts the membrane potential - decay with distance from their source sufficiently. - have a constant magnitude. - Can regenerate in adjacent regions of the membrane. - Can spread along axons, well suited for transmitting a signal over long distances. 10 Graded Potential: Shift in membrane potential in response to Depolarization or Hyperpolarization and has a magnitude that varies with the strength of the stimulus Beginning of Action Potential o Action potentials arise because some of the ion channels in neurons are voltage-gated ion channels: If a depolarization opens voltage-gated sodium channels→ the resulting flow of Na+ into the neuron results in further depolarization. ↓ Because the sodium channels are voltage gated→ an increased depolarization causes more sodium channels to open. ↓ The result is a process of positive feedback that triggers a very rapid opening of all voltage-gated sodium channels and the marked change in membrane potential that defines an action potential. - Action potentials occur whenever a depolarization increases membrane voltage to a particular value, called threshold. (-55 mV) Voltage-gated ion channels: ion channels which open or close when the membrane potential passes a particular level. The threshold: The membrane voltage of about -55 mV at which all the sodium gated ion channels open. - Once the threshold is reached→ the action potential has a magnitude that is independent of the strength of the triggering stimulus→ (All or none law) All or none law: - Action potential will not be generated, unless the stimulus makes the membrane potential reaches the threshold to stimulate the nerve with a maximal strength, i.e., the sufficient stimulus produces maximum response. - Any increase in the stimulus strength→ will not increase the response strength. 11  Generation of Action potential o When the membrane of the axon is at the resting potential, most voltage-gated sodium channels and voltage gated potassium channels are closed. When a stimulus depolarizes the membrane, some gated sodium channels open ↓ allowing more Na+ to diffuse into the cell. ↓ The Na+ inflow causes further depolarization, which opens more gated sodium channels, allowing more Na+ to diffuse into the cell. ↓ Once threshold is crossed, opening all Na+ voltage gated channels rapidly make membrane potential highly more positive.(rising phase) ↓ o Two events prevent the membrane potential from becoming more positive: 1. Voltage-gated sodium channels inactivate soon after opening, preventing Na+ inflow. 2. most voltage-gated potassium channels open, causing a rapid outflow of K+. ↓ Both events quickly bring the membrane potential back more negative (falling phase). ↓ In the final phase of an action potential, called the undershoot, the membrane’s permeability to K+ is higher than at rest, so the membrane potential is more negative than it is at the resting potential. ↓ The gated potassium channels eventually close, and the membrane potential returns to the resting potential. 12 13  1- The absolute refractory period: It is the period, during which the excitability is completely abolished = zero ↓ thus, no stimulus can excite the nerve fiber whatever its strength may be. o The absolute refractory period coincides with depolarization and early part of repolarization: 1. the ascending limb of the action potential upper 2. the first 1/3 of the descending limb. o Causes of the absolute refractory period: 1. During depolarization → the sodium channels are fully activated and cannot be activated more. 2. During repolarization→ the sodium channels are inactivated by the closure of Inactivation gates → so no sodium influx and no action potential can occur. 2- The relative refractory period: It is the period, during which the excitability is only partially recovered (>0and