General Biophysics Lecture 1 and 2 PDF

General Biophysics Lecture 1 and 2 Prepared by Associate professor. Mohamed M. Fathy, PhD, Biophysics Department , Cairo University. What is Biophysics!!  Biophysics is an interdisciplinary science that employs and develops theories and methods of the physics to discover and solve the...

General Biophysics Lecture 1 and 2 Prepared by Associate professor. Mohamed M. Fathy, PhD, Biophysics Department , Cairo University. What is Biophysics!!  Biophysics is an interdisciplinary science that employs and develops theories and methods of the physics to discover and solve the problems of the biological systems.  The active fields of research in Biophysics :  Bio-equivalent materials  Electrophysiology  Radiotherapy and medical imaging  Electricity within the body  The electricity generated inside the body serves for the control and operation of nerves, muscles, and organs.  The action of the brain is electrically.  The information is transmitted as electrical signals along various nerves.  The forces of muscles are caused by the attraction and repulsion of electrical charges. The Nervous System and the Neuron  The nervous system can be divided into two parts:  Central nervous system (brain and the spinal cord)  Peripheral nervous system 1. Sensory somatic nervous system (peripheral nerves)  Sensory nerves (afferent nerves) which transmit sensory information to the brain.  Motor nerves (efferent nerves) which transmit information from the brain or spinal cord to the appropriate muscles or organ.  The Nervous System and the Neuron 2. Autonomic nervous system  Controls various internal organs such as the heart, intestines, and glands.  The control of the autonomic nervous system is essentially involuntary.  The Nervous System and the Neuron  Neuron : The basic structural unit of the nervous system.  Neuron specialized for the reception, interpretation and transmission of nerve signal.  Cell body : receives electrical signal from other neurons through synapses  Strong nerve signal transmitted along the Axon to muscles, glands, or other neurons Electrical Potential of Nerves  Why is there potential difference around the membrane??  Across the membrane of every neuron is an electrical potential difference due to the presence of more negative ions on the inside of the membrane than on the outside.  Electrical Potential of Nerves  The electrical potential difference across the neuron membrane Is about -70 to -90 mV. The neuron membrane is said to be polarized.  This potential difference called Resting membrane potential of the neuron.  A model of the resting potential  To build this model we assume that : membrane separates a concentrated solution of K+ (potassium ions)& M− (massive negative proteins)from one that is less concentrated.  The membrane is assumed to permit K+ to pass through it but does not permit the passage of the M−  A model of the resting potential  K+ ions diffuse across the membrane, and the net transfer takes place from the high concentration region (cytosol, inside the cell ) to the low concentration region.  Excess of positive charge in extracellular and an excess of negative charge in cytosol. A model of the resting potential  These charges form layers (dipole layer) around the membrane to produce an electrical force that retards the flow of K+ ions from cytosol to extracellular.  A model of the resting potential  Equilibrium produced when the K+ ion movement due to diffusion is balanced by the ion movement due to the electrical force from the dipole layer.  Resting potential of a nerve exists because the membrane is impermeable to the large negative protein while it is permeable to the small ions. Electrical Potential of Nerves  The equilibrium membrane potential for any ion (X )can be calculated from Nernst equation.  where R is the gas constant, T the temperature (in degrees Kelvin), z the valence of the ion, F the Faraday constant, and [X]o and [X]i are the concentrations of the ion outside and inside of the cell.  Electrical Potential of Nerves  At room temperature (25°C, 298K ), RT/F equal 25 mV ,(Kelvin = Celsius + 273), the Nernst equation can also be written as:  Example, If the out side and in side concentrations of K+ ion are 20,400 g/l, respectively. find the equilibrium membrane potential of K+, given that RT/F is 25 mV. How the signal transmitted through neuron!!  When the neuron is stimulated, a large momentary change in the resting potential occurs at the point of stimulation, called the Action potential.  The stimulation may be physical (heat, cold, light, sound) or chemical stimuli (odors).  If the stimulation of about 20 mV across the membrane is needed to initiate the action potential. How the signal transmitted through neuron!!  At stimulation, the membrane walls become porous to Na+ ions which pass through the membrane causing it to depolarize.  The inside goes positive to about 50 mV. How the signal transmitted through neuron!!  The positive current flow stimulates the regions to the right so that depolarization takes place and the potential change propagates.  Meanwhile the point of original stimulation has recovered (repolarized) because K+ ions have moved out to restore the resting potential.