General Biophysics Lecture 6 PDF

GENERAL BIOPHYSICS LECTURE 6  Measurement of the velocity of action potential in motor nerves  Stimuli are applied at two locations, and the time (t) from stimulus to recording the nerve signal is measured.  This time is required for nerve signal to travel dista...

GENERAL BIOPHYSICS LECTURE 6  Measurement of the velocity of action potential in motor nerves  Stimuli are applied at two locations, and the time (t) from stimulus to recording the nerve signal is measured.  This time is required for nerve signal to travel distance (x) between the stimulus and recording point.  Measurement of the velocity of action potential in motor nerves  The velocity of the action potential is this distance divided by this time.  (velocity = distance x (cm)/time (s)).  Measurement of the velocity of action potential in motor nerves  To calculate the conduction velocity between point 1 and 2.  The distance between these points is 0.25 m.  The time required for the nerve signal to travel this distance ( from point 1 to point 2) is (4ms).  Therefore the nerve conduction velocity v = x/t = 0.25 m/0.004 s = 62.5 m/s.  Measurement of the conduction velocity for sensory nerves  Stimulus is applied at one site and recording electrodes are placed at several locations that are known distances from the point of stimulation  Measurement of the conduction velocity for sensory nerves  The conduction velocity from electrode 1 to electrode 2.  The distance is 0.25 m and the time required to travel this distance is 4.3 ms.  The conduction velocity is 0.25 m/4.3 x 10-3 s = 58 m/s.  The conduction velocity from electrode 2 to electrode 3 is 0.20 m/4 x 10-3 s = 50 m/s.  Measurement of the conduction velocity for sensory nerves  Many times nerve damage results in a decreased conduction velocity.  Typical velocities are 40 to 60 m/sec; a velocity below 10 m/sec would indicate a problem.  Electrical Signals from the Heart – The Electrocardiogram (ECG):  The heart is considered as a double pump with four chambers.  The two upper chambers, the left and right atria, are synchronized to contract simultaneously.  The right atrium receives blood from the body and pumps it to the right ventricle.  right ventricle pumps the blood to lungs. The blood then flows into the left atrium.  Electrical Signals from the Heart – The Electrocardiogram (ECG):  The contraction of the left atrium moves the blood to the left ventricle, which contracts and pumps it into the general circulation.  Electrical Signals from the Heart – The Electrocardiogram (ECG):  - Sinoatrial (SA) node,or the pacemaker:  It is special cells located in the right atrium.  The SA node fires at regular intervals about 72 times per minute.  The electrical signal from the SA node initiates the depolarization of the nerves and muscles of atria, causing the atria to contract and pump blood into the ventricles.  Electrical Signals from the Heart – The Electrocardiogram (ECG):  Atrioventricular (AV) node  It initiates the depolarization of the right and left ventricles  as the electrical signal passes from the atria, causing them to contract and force blood into the pulmonary and general circulations.  The ventricle nerves and muscles then repolarize and the sequence begins again. Electrical Signals from the Heart – The Electrocardiogram (ECG):  The nodes of the heart can be regarded as sources of electricity.  diagnostic information is obtained by measuring the electrical potentials generated by the heart using surface electrodes.  The record of the heart's potentials on the skin is called the electrocardiogram (ECG).  Electrical Signals from the Heart – The Electrocardiogram (ECG):  The major electrical events of the normal heart cycle  (1) The atrial depolarization and contraction, P wave  (2) the ventricular depolarization, QRS complex  (3) the ventricular contraction occurs between S and T  (4) the ventricular repolarization, T wave. Electrical Signals from the Heart – The Electrocardiogram (ECG):  If the normal SA node signal is not conducted into the ventricle.  then a pulse from the AV node will control the heartbeat at a frequency of 30 to 50 beats/min  which is much lower than normal (70 to 80 beats/min).  While a heart block like this could make a patient a semi-invalid, an implanted pacemaker could enable him to live a reasonably normal life.