Electrical Activity of the Heart/Cardiac Action Potential Block 1

2 Parts of the Cardiovascular System

• Heart: acts as a pump

• Blood vessels: set of tubes connected to the pump

2 Parts of the Circulatory System

• Pulmonary circulation: the right side of the heart pumps blood to the pulmonary circulation and the left side of the heart receives blood from the pulmonary circulation

• Systemic circulation- the left side of the heart pumps blood to the systemic circulation and the right side of the heart receives blood from the systemic circulation

arterioles

these blood vessels are surrounded by smooth muscle. Contraction of the SM changes diameter of the blood vessel which affect blood pressure

these blood vessels are the site of nutrient and waste exchange

capillaries

systemic circulation contains a # of capillary beds arranged :parallel are found where?

most beds are arranged this way

just not kidneys and liver

capillary beds arranged in series are found where?

in the liver and kidneys

capillaries are found within______um of most cells in the body

50

this is important since O2 moves from blood into the interstitial compartment via diffusion

the veins contains how much of the blood? how about the arteries and arterioles?

vein- 64% (low P)
arteries and arterioles- 16% (high P)

Cardiovascular system: transports what INTO the body

-nutrients and water
-oxygen

Cardiovascular system: transports what OUT of the body

-CO2
-metabolic wastes
-heat

Cardiovascular system: transports what within the body

-hormones
-immune cells
-Abs
-clotting proteins
-stored nutrients

what generates the pulsitile pressure of the heart

the pulsitile property of the heart originates in specialized cells in the heart capable of generating periodic action potentials. These periodic APs spread throughout the heart, causing periodic contraction of the heart. This periodic contraction generates periodic, pulsitile pressure

a pulse of pressure is defined as

the difference between the highest pressure developed in a beat and the lowest pressure

the pressure pulse is largest in

the heart

before the heart contracts, the pressure is

close to zero

as the heart (left ventricle) ejects blood the pressure reaches

its maximum at about 120 mm Hg

by the time the pressure pulse reaches the the arterioles and the capillaries the pressure pule is

close to 0

this does NOT mean that the pressure in the arterioles and the capilarries is 0, but that there is no fluctuation in pressure from 1 heartbeat to the next. This insures a continuous flow of blood through the capillaries

the pressure in the veins and on the right side of the heart is what? then what would the pressure difference at the max pressure between the left side of the heart and right side of the heart be?

close to zero

so about 120 mm Hg

the biggest difference between the pressures in the pulmonary vs systemic

just lower in the pulmonary circulation

at resting heart rate what ANS exerts a stronger influence?

P-ANS

thus, severing P-ANS nerves to the heart will increase resting HR to a greater extent that severing sympathethic nerves would decrease HR

P-ANS control of the heart involves what NTs and what receptors?

ACh and M2

S-ANS control of the heart involves what NTs and what receptors?

NE; beta-1 (cardiomyocytes) and alpha-1 (smooth muscle)

the P-ANS innervates what of the heart?

only nodal regions of the heart

the heart's pump strength is controlled by what branch of the ANS?

S-ANS

There is some P-ANS control of ATRIAL muscles, but bc most of blood is pumped from heart as a result of ventricular contraction, there is little P-ANS effect on the strength of contraction of the ventricles

this is a collection of pacemaker cells near the right atrium

sino-atrial (SA) node

Electrical Activity in the Heart Pathway

SA node-->atrial muscle contracting--> AV node--> Bundle of His (AV bundle--conducting)--> Bundle Branches (Left/Right--conduction)--> Purkinje Fibers (conducting)--> Ventricular Muscle (contracting)

3 basic types of cells in the heart

-pacemaker
-conducting cells
-contracting cells

pacemaker cells

cells that set the automatic rhythm of the heart and allow it to beat contiunously throughout a lifetime. These cells are found in the SA and AV node.

These cells are electrically connected via gap junction--fire APs on their own

conducting cells

conduct the electrical signal (AP) from 1 part of the heart to another. These cells are found in the bundle His, the bundle branches and the Purkinje fiber networks

where are conducting cells found?

-bundle of His
-bundle branches
-Purkinje fiber network

contracting cells

generate P w/in the heart and pump blood out of the heart. These cells make up most of the cells in the walls of the atria and the ventricle. Contracting cells are called myocytes and make up about 75% of the total volume of the heart

contracting cells are aka? and make up what % of volume of heart?

myocytes; 75%

what are the 2 main types of action potentials in the heart?

-pacemaker AP
-AP in conducting and contracting cells

nodal/pacemaker APs

found in the SA and AV nodes. This type of AP is autorhythmic: these cells generate the same AP periodically for long periods of time

conducting/contracting APs

AP found in myocytes and conducting cells such as bundle of His, bundle branches, purkinje fibers

these cells either contract in response to an AP or conduct the AP to neighboring cells

the nernst potential for Na+ in the heart

+70

the Nernst potential for K+ in the heart

-94

the Nernst potential for Ca2+ in the heart

+132

the 5 phases of an AP in conducting and contracting cells

Phase 0- Upstroke
Phase 1- Initial (or early) repolarization
Phase 2- Plateau
Phase 3- (final) repolarization
Phase 4- Resting Membrane Potential

Phase 0: Upstroke (Conducing and Contracting Heart Cells AP)

cells repolarizes as a result of the spread of an AP from a neighboring cell.
-this depolarization opens FAST voltage-gated Na+ channels.
-this leads to further depolarization which opens up more voltage-gated Na+ channels

Phase 1: Initial (or early) repolarization (Conducting and Contracting Heart Cells AP)

-cell hyperpolarizes slightly
-this is due to the opening of voltage-gated type I K+ channels and inactivation of voltage-gated Na+ channels

Why does Phase 1- Early repolarization occur in conducting and contracting cells

due to the opening of voltage-gated K+ channels and inactivation of voltage-gated Na+ channels

What type of K+ channel opens up in early repolarization (Conducting and Contracting Heart Cells AP)

type I

Phase 2: Plateau (Conducting and Contracting Heart Cells AP)

-the cell remains at 0 mV (due to the opening of type II K+ channel and voltage gated Ca2+ channels)
-Since both channels are open, the membrane potential is somewhere in between the Nernst potential for K+ and Ca2+ (near 0mV)

why does the cell remain around 0 mV during phase 2: plateau (Conducting and Contracting Heart Cells AP)

due to the opening of type II K+ channel and voltage gated Ca2+ channels--the membrane potential in the middle for the Nernst for both

what type of K+ channel is open in Phase 2: plateau (Conducting and Contracting Heart Cells AP)

type II

type I inactivates in the beginning of phase 2

Phase 3: repolarization (Conducting and Contracting Heart Cells AP)

towards the end of phase 2 and during this phase (3), the voltage-gated Ca2+ channels inactivate and the voltage-gated K+ channels dominate so the membrane potential hyperpolarizes towards the Nernst potential for K+ (-94 mV)

in phase 3 (Conducting and Contracting Heart Cells AP) , why does repolarization occur

the voltage-gated Ca2+ channels inactivate and the voltage-gated K+ channels dominate so the membrane potential hyperpolarizes towards the Nernst potential for K+ (-94 mV)

Phase 4:resting membrane potential (Conducting and Contracting Heart Cells AP)

-the membrane potential when there is no AP
-it is negative and is due to K+ channels which are open at any membrane potential (leak channels)

all 4 types of voltage-gated channels in the conducting/contracting AP (2K+, 1Na+,1Ca2+) are what type of channels in terms of voltage

depolarization activated channels

order of opening of channels in the conducting/contracting AP

voltage-gated Na+ channel--> type I voltage-gated K+ channel--> voltage-gated Ca2+ channel--> type II voltage-gated K+ channel

in phase 0 (conducting/contracting AP) which channels are open, inactive, closed and what dominates

open: Na+ (dominates), K+-type I, Ca2+, K+-type II

in phase 1 (conducting/contracting AP) which channels are open, inactive, closed and what dominates

open: K+-type I (dominates), Ca2+, K+-type II
inactive: Na+

in phase 2 beginning which channels are open, inactive, closed and what dominates

open: K+-type II, Ca2+ (both dominate)
inactive: Na+, K+-type I

in phase 2 (conducting/contracting AP) towards the end which channels are open, inactive, closed and what dominates

open: K+-type II (dominates)
inactive: Ca2+

in phase 3 (conducting/contracting AP) which channels are open, inactive, closed and what dominates

open: K+-type II (dominates)
inactive: Ca2+, Na+, K+-type I

in phase 4 (conducting/contracting AP) towards the end which channels are open, inactive, closed and what dominates

all 4 are closed. only channel open are K+ leak channels

of the 4 channels in the AP in conducting/contracting heart cells which does not inactivate

K+-type 2 goes from closed to open to closed

Pacemaker Action Potential is made up of what phases

4) Slow depolarization
0) Upstroke
3) Repolarization