Adv Phys Lab

bullfrog heart

• the atrial hump is smaller and has thinner walls because it only pumps to the ventricles and does not need high force. the ventricular hump is larger because it pumps to the body and needs thicker walls to provide force

• silver wires used to stimulate the muscles were not needed in this experiment because the heart is autorhythmic and needs to input

dissection steps

• remove ventral surface

• expose the heart, cut the ligament and the tissue around the heart

• hook the apex of the heart, lift to set up the apparatus

[remember: keep heart moist, fill in data sheet]

experiment - normal heart rate without stimulation

baseline heart rate: 48.19 beats/minute

experiment - acetylcholine

acetylcholine stimulation

• decreases heart rate, slows down firing of SA node

• released by parasympathetic nervous system (rest/digest) and increases membrane permeability to potassium. the concentration is higher inside the cell, so more potassium will leave and hyperpolarize the cell to generate action potential (slowing down the heart)

• in skeletal muscle, Ach causes contractions, but does not the same in the heart. This is because the skeletal muscle has different receptors. Both receptors can receive Ach, but they do no elicit the same response.

experiment - atropine effect

atropine effect

• increases heart rate, blocks parasympathetic nervous system

• acts on SA and AV nodes to speed up conduction

experiment - epinephrine stimulation

epinephrine stimulation

• increases heart rate, stimulates heart to beat faster

• enhances contractility

• alters the permeability of the membrane to calcium ions (higher permeability, more calcium inside cell, more crossbridges, stronger contraction)

experiment - temp change (cold vs hot)

temp change

• cold: slows heart rate

  • dive reflex (parasympathetic activating rest/digest)

  • metabolic reactions are slowed, SA node slows down pacemaker cells

• heat: increases heart rate

  • blood vessels dilate and blood flow increases while the body tries to cool down

  • metabolism increases, proteins may denature

experiment - refractory period

• the refractory period of the heart allows for a compensatory pause (pause in the beat of the heart with external stimulation)

• acts like a reset mechanism to get the heart back on track

• ventricle contracts early after being stimulated, in refractory period so the SA node cannot stimulate them again (heart pauses), heart beats normally when the SA node fires again

• refractory period is determined by open calcium channels that maintain depolarization and keep sodium channels from opening until potassium hyperpolarizes the cell

experiment - heart to tetanus?

• cardiac muscle has a long refractory period, meaning that a high frequency of stimuli cannot cause mechanical summation or tetanus (which is important because the heart needs to be able to contract and relax to pump blood)

• heart rate and muscle tension will still increase, but no tetanus

experiment - heart block, degree stages

• the AV node becomes damaged when pressure is applied to the ventricle, so the signal is altered between the atria and ventricles

mechanical activity of the frog heart

control, epinephrine, and acetylcholine

mechanical activity of the frog heart - refractory period

refractory period - skeletal vs cardiac

heart stimulus, tetanus attempt

autonomic nervous system's control over the heart. The heart rate "reset" or slowing after the stimulus suggests a parasympathetic (vagal) response, where the body briefly slows the heart in response to a sudden input before returning to homeostasis

• cannot go into tetanus because the refractory period is long, but can “skip” a beat if a stimulus is sent right at the end of the period

electrical stimulation of the heart

• AP spreads through heart via gap junctions

• SA node

• AV node

• Bundle of His

  • left and right bundles

• Purkinje fibers

heart block degrees

• 1st degree: delay between atrial and ventricular contractions

• 2nd degree: multiple atrial contractions paired with ventricular contractions

• 3rd/complete: no ventricular contractions

heart block comparison

key points of frog heart lab

• mechanical activity recorded, not electrical

• substances modulate heart activity, but the activity of the heart is auto-rhythmic

• heart block is due to disruption in the electrical transmission of the heart

• refractory period of the action potential in the heart is very long, thus the heart cannot fatigue

• euthanasia produced by KCl

  • disrupts the electrical balance by introducing more potassium outside the cell (destroying/balancing the gradient)

  • when the muscles depolarize, the high potassium outside the cell stops it from repolarizing/hyperpolarizing, resulting in cardiac arrest

  • heart stops pumping, blood flow stops, tissues lose oxygen (hypoxia)

Human Heart Function and Cardiovascular Physiology

electrical events

• P wave, QRS complex, T wave

mechanical events

• pressure: EDV, ESV

• sound

• volume: DP, SP