PHYSIO UNIT 4 PART 1

Now remember the electrical conduction pathway of the heart

Begins at Sinoatrial Node (SA node) * In pacemaker (autorhythmic) cells that are modulated by the ANS -Spreads to adjacent conducting and contractile cells through ... * Gap junctions ** Located in intercalated disks l Ions move through openings that connect the cytosol of two adjacent cells ** Ion movement = change in charge = spreading of action potential from one cell to the next ** In CONTRACTILE CELLS, influx of cations from adjacent cells causes opening of Na+ channels (See Figure 14.10) and initiation of action potentials - Action potentials spread quickly so all cells contract almost simultaneously * First in the atria, then in the ventricles

FEEDBACK LOOP PRACTICE: ANS modulation of ventricular contractility

Can you incorporate this information into a feedback loop if the stimulus is decreased blood pressure? -What about increased blood pressure? -What about if CO2 levels increase or decrease? -Is the control of contractility antagonistic or tonic? tonic

FEEDBACK LOOP PRACTICE: ANS control of heart rate

Can you incorporate this information into a feedback loop if the stimulus is decreased blood pressure? -What about increased blood pressure? -What about if CO2 levels increase or decrease? -Is the control of heart rate antagonistic or tonic?

These blood vessels are where gas and nutrient exchange occurs in body tissues.

Capillaries

Factors that affect blood pressure #3 = Cardiac Output

Cardiac Output is the total amount (volume) of blood pumped by the left ventricle in one minute (See Fig 14.23) - Two sub-factors affect this ... * Heart Rate (HR) - the number of heart beats per minute * Stroke Volume (SV) - the volume of blood pumped by one ventricle during a contraction * Cardiac Output = HR x SV

How is venous return accomplished?

For body parts above the heart, it's gravity! But for body parts below the heart ... -Muscle Pump: Skeletal muscles squeeze on veins with 1- way valves to aid in venous return *blood flows from tissues through veins, skeletal muscles contract, increased pressure opens valve, blood flows to heart **as you exercise the activity of the muscle pump goes up -Respiratory Pump: Pressure changes in thoracic cavity during ventilation aid in venous return *inhalation increases blood flow into thoracic veins *exhalation increases blood flow into heart and abdominal veins -The efficiency of both pumps increases by activating the sympathetic nervous system

In the SA Node diagram above, the part of the action potential marked with the "4" gets a special name to denote how it automatically climbs towards threshold. What is that special name?

Pacemaker potential

Action potential and twitch duration

Refractory period -Note in Figure 14.12a, that a twitch of a contractile cell must be complete before the next action potential can be generated, so these cells CANNOT achieve a state of TETANUS (maximum tension) like skeletal muscle cells (see Figure 14.12d) - This refractory period ensures that an entire chamber (composed of MANY interconnected contractile cells) will relax fully before being cued to contract again. That ensures an efficient pumping action of the heart, despite how vigorously it is being stimulated!! Wow, what a great insurance policy!

At the peak of the depolarization of an autorhythmic cell, the channels in the previous question close, and these channels open, resulting in the repolarization phase marked with a "3" in the left diagram above. Make sure to choose a type of channel from the list, not an ion.

Slow K+ channels

When contractile cells receive a depolarization from an adjacent conducting or contractile cell, they immediately depolarize (stage marked "0" above) through the opening of these channels. Make sure to choose a type of channel from the list, not an ion.

Voltage gated Na+ channels

.In the SA Node diagram above, these channels are open in abundance at the stage marked "0". No wonder there is a big depolarization, eh? Make sure to choose a type of channel from the list, not an ion.

Voltage-gated Ca2+ channels

Rhythmic electrical activity coordinates heart pumping and filling

What's happening in the heart (in terms of depolarization or repolarization) when the: - P wave occurs? atria depolarize - QRS complex occurs? ventricles depolarize - T wave occurs? ventricles repolarize - What event (systole or diastole) occurs just after each of these electrical signals? systole

The vessel labeled "F" in the above diagram is the ______. It is the initial conduit for all oxygenated blood to pass to the entire body.

aorta

This general category of vessels conducts blood away from the heart.

arteries

These blood vessels are the primary site of vasoconstriction and vasodilation because they contain large amounts of smooth muscle.

arterioles

The electrocardiogram (ECG) measures the electrical signals coming from the heart as it passes through the cycle described in the preceding questions. Look at the ECG trace in the demonstration. The P wave represents ________, also called atrial systole.

atrial depolarization

The signal then passes through a very short pathway along the septum of the heart before branching. This pathway is called the ______ in the demo on the CD, but also called the bundle of His in our textbook.

atrioventricular bundle

When the signal reaches a second node in the base of the right atrium, it is delayed for a short time. This node is called the ______.

atrioventricular node

The valve labeled "G" is generally called a _______. Don't worry about left or right on this one. These one-way valves connect the top chambers of heart to the bottom ones.

atrioventricular valve

portal system

blood goes out one capillary bed and back to the heart -3 exceptions: 1. hepatic portal system: blood will move through a capillary bed that surrounds the digestive tract and doesn't go directly back to the heart, but through a portal vein and into a capillary bed in the liver before going to the heart 2. kidneys: blood goes through glomerulus, then through a second cap bed surrounding the main tubules of the nephron (peritubular capillaries) 3. brain: goes through cap bed in hypothalamus, through portal vein, through cap bed in anterior pituitary gland

When the signal then splits down the septum separating the ventricles, it is called left and right ______.

bundle branches

These specific myocardial cells make up ~1% of the heart, and mostly lack thick and thin filaments. Rather they are specialized for passing electrical signals around the heart.

conducting (autorhythmic) cells

These specific myocardial cells make up ~99% of the heart, are striated muscle, and have thick and thin filaments organized into sarcomeres.

contractile cells

Within the junctions mentioned in the previous question, the cells are physically tethered by these strong connections that allow force created in one cell to be transferred to the adjacent cell.

desmosomes

In the final pathway of this circuit, the electrical signal reaches the apex of the heart and then moves up its left and right lateral edges. This part of the pathway is called the ______.

purkinje fibers

The compartment labeled "A" in the above diagram is the _____. It receives venous (deoxygenated) blood from the body.

right atrium

The compartment labeled "B" in the above diagram is the _____. It contracts to send blood to the lungs for gas exchange.

right ventricle

The valve labeled "H" is generally called a _______. Don't worry about left or right on this one. These one way valves prevent back-flow of blood from adjacent vessels when the bottom chambers relax.

semilunar valve

The electrical conduction pathway through the heart begins at this node in the system. It is also called the natural pacemaker of the heart.

sinoatrial node

After the channels mentioned in the previous question close, the cell will rapidly repolarize (phase "3" in the diagram above). This change in membrane potential is due to the opening of what kind of channels? Make sure to choose a type of channel from the list, not an ion.

slow K+ channels

if Co2 levels increase

stroke volume increases to increase heart rate and vice versa

The circuit of the cardiovascular system that conducts oxygenated blood from the heart to body tissues, and returns deoxygenated blood back to the heart is called the _______.

systemic circuit

The electrocardiogram (ECG or EKG)

the ECG tracks the movement of electrical activity through the heart -This pattern of waves and segments is NOT a single action potential - It is an amalgamation of all action potentials during one cardiac cycle - The ECG is an extremely useful measure for diagnosing heart dysfunction

This general category of vessels returns blood to the heart.

veins

In the ECG trace, the QRS complex represents this phase of the heart cycle, also called ventricular systole).

ventricular depolarization

In the ECG trace, the T wave represents this phase of the heart cycle. The heart is at rest (also called diastole) during this point in the cycle.

ventricular repolarization

These blood vessels receive deoxygenated blood from the vessels named in the previous question.

venules

After this brief repolarization, the plateau phase (marked "2" above) ensues, and this flattening of the action potential is due to what kind of channels opening. Make sure to choose a type of channel from the list, not an ion. The ion that moves in from the interstitial fluid will lead to power strokes in the contractile cell and sarcomere shortening. See Figure 14.9 for more on this, and we will talk about it in lecture.

voltage gated Ca+ channels

The vessel labeled "E" in the above diagram is the ______. It is the initial conduit for deoxygenated blood to pass to the lungs.

pulmonary artery

The circuit of the cardiovascular system that conducts deoxygenated blood from the heart to the lungs, and returns oxygenated blood back to the heart is called the _______.

pulmonary circuit

Fluid flows down a pressure gradient 2

- Blood pressure is highest at or near its source (the heart) * Decreases as it progresses - Note the dramatic drop in pressure by the time blood gets to the capillaries * Allows for slower movement for transfer of gases, waste & nutrients * Capillaries are also very delicate - The heart is responsible for getting blood TO tissues, not for bringing blood back to it * Other mechanisms for this

Review of heart anatomy

- From where does each side of the heart receive blood? Right side = systemic circuit, Left side= pulmonary circuit * Is that blood oxygenated or deoxygenated? Right= deoxygenated, Left= oxygenated - Where does each side of the heart send blood? Right= pulmonary circuit, Left= systemic circuit

Concept check: Essential CVS terminology

- Let's define these terms before going on. Compare the terms in a row from left to right: *Systole: contraction phase of cardiac cycle (atrial and ventricular systole) *Diastole: relaxation phase of cardiac cycle (atrial and ventricular diastole), also when chambers fill w blood *Cardiac Cycle: time from end of one heartbeat to the end of the next, all actions the heart will go through during one heart beat, can be visualized with the electrocardiogram *Heart Rate: number of cardiac cycles (aka heart beats) in one minute *Stroke Volume: volume of blood pumped by left ventricle per contraction *Cardiac Output: volume of blood pumped by left ventricle per minute, CO= HR * SV **avg CO at rest is 5 L/min -above 3 variables are interrelated to eachother *End-Diastolic Volume: max volume of blood held by ventricles at end of diastole *goes up w exercise, heart accommodates more blood coming back to it *End-Systolic Volume: amount of blood left over in the heart ventricles after systole (contraction) *goes down w exercise *Venous Return: volume of blood returning to the heart w any given moment *goes up w exercise *Total Peripheral Resistance: opposition to blood flow, mostly created by diameter of arterioles, helps to regulate amount of blood that flows to a given organ *Vasoconstriction: when smooth muscle cells contract and lumen diameter decreases *Vasodilation: when smooth muscle cells relax and lumen diameter increases

The CVS is a closed system

- The heart MUST move the blood through the vessels * Frank-Starling Law > The heart MUST pump all blood that returns to it and its force of contraction is determined by how much blood is returning to it (venous return) *venous return will increase during exercise bc blood pressure increases during exercise, leads to increased force of contraction - Two circuits 1. Pulmonary Circuit - From Right side of heart to lungs - Blood picks up O2 and drops off CO2 - Back to Left side of heart 2. Systemic Circuit - From Left side of heart to all body cells - Blood drops off O2 and picks up CO2 and other metabolic wastes - Moves hormones, neurohormones, stored nutrients (e.g., glucose, triglycerides, etc.), and immunoglobulins around the body - Back to Right side of heart

Sub-factors that affect Total Peripheral Resistance

- Vessel diameter (the most important factor for this class), controlled by smooth muscle cells and autonomic nervous system * Diameter or radius of the lumen that blood has to pass through **Vasoconstriction increases resistance and decreases blood flow **Vasodilation decreases resistance and increases blood flow - Blood viscosity * Thickness of blood ** Increased thickness leads to increased resistance ** More water/plasma, decreases thickness and decreases resistance -Vessel length *The longer the vessel, the greater the resistance -How long would it take for each of these 3 factors to change? * Which can change immediately with the correct stimulus? vessel diameter *Which can change within many minutes to less than an hour? blood viscosity *Which would require days or weeks to show change? vessel length

OK, the remaining questions will target the right diagram. They sure look cool, huh? First off, what is their resting membrane potential (phase marked "4" in above diagram)?

-90mV

Action potential in contractile cells

-Action potential of a cardiac contractile cell *Notice the difference in resting membrane potential from other excitable cells like neurons * Notice the plateau region (point labeled 2) ** Yeah, that's important * Notice there is no hyperpolarization *Notice how much longer this action potential lasts relative to a neuron -image: *resting membrane potential is -90mV *no threshold -sodium channels open at 4, cause depolarization, and inactivate at 1 *double gated channels w activation gate and inactivation gate -fast potassium channels from 1-2, cause little repolarization effect -L type calcium channels open *positive ions are effluxing from K channels and positive ions influxing from L type calcium channels > no net change that's why it flattens out -both channels close at shoulder -slow K channels cause repolarization and close at the bottom

Components of the CVS

-Blood is composed of ... * Formed elements (cells, platelets): erythrocytes or leukocytes or thrombocytes for example * Plasma: water, proteins, ions, etc. -The heart is the pump -The vasculature (blood vessels) distributes blood to all body cells -blood leaves the heart through this order: * Arteries, arterioles, capillaries, venules, veins - What are the structural and functional differences between these vessels?

contractile cells

-Contractile cells, especially those of the left ventricle, are the Effector for modulating Stroke Volume - Compared to skeletal muscle, myocardial contractile cells are ... * Smaller and have a single nucleus * Connected by intercalated disks that contain ... **Desmosomes - provide strength and transfer of force between cells **Gap junctions - allow transfer of action potentials between cells -Sarcoplasmic reticulum is smaller * Ca2+ also enters cell from interstitial fluid - Lots more mitochondria * Occupy 1/3 of cell volume. WHY? they need a lot of energy (ATP) to pump the heart 24/7

Factors that affect blood pressure #1 = Total Blood Volume

-If the volume of blood stays constant... *As the network of blood vessels increases (during development), the pressure inside that network will decrease * As the network of blood vessels decreases, the pressure inside that network will increase - If the network of blood vessels stays constant ... * As blood volume increases (over-hydration), the pressure inside the network will increase * As blood volume decreases (dehydration), the pressure inside the network will decrease - Can the network of blood vessels change? The volume of blood? -Total Blood Volume is managed by the kidneys -in reference to image: -3 factors that affect blood pressure: total peripheral resistance, cardiac output, total blood volume

Blood pressure is typically measured hydrostatically

-Pressure of a fluid against the walls of a closed container is called hydrostatic pressure *hydrostatic pressure is measured as systolic pressure over diastolic pressure **systolic is max pressure in that artery, diastolic is the minimum pressure -normal resting bp in an adult should be about 120mmHg/80mmHg - Blood pressure is a form of hydrostatic pressure * It is the pressure applied against blood vessel walls when we temporarily occlude it with a sphygmomanometer and cuff -Hydraulic blood pressure can also be measured as blood is in motion * A more invasive procedures where a canula is inserted into an artery * Usually reserved for lengthy surgeries and intensive care units * Allows for blood pressure to be monitored continuously

Concept check: Factors that affect blood pressure

-Pull out your Factors that Affect Blood Pressure Worksheet and figure out how each of these conditions will affect overall blood pressure: * Decreased total blood volume (dehydration)? decreased blood pressure * Increased total blood volume (over-hydration or water intoxication)? increased blood pressure * Vasoconstriction? increases total peripheral resistance which increases blood pressure * Vasodilatation? decreases total peripheral resistance which decreases blood pressure * What about an increase or decrease in heart rate? increased heart rate increases cardiac output which increases blood pressure and vice versa * What about an increase or decrease in stroke volume (ventricular contractility)? increased stroke volume increases cardiac output which increases blood pressure and vice versa

Steps of the Electrical Conduction Pathway

-Sinoatrial node * The lead pacemaker * Its rate of depolarization (modulated by the autonomic nervous system) determines how fast the action potentials zip through the remaining components of this circuit -Intra-atrial & internodal pathways - Atrioventricular (AV) node *At this point the atria contract - Bundle of His (or AV bundle) - R & L bundle branches - Purkinje fibers * At this point, the ventricles contract

worksheet

-TBV= total blood volume

Fluid flows down a pressure gradient

-There must be a pressure gradient for fluid to flow from one place to another * If there is no pressure gradient, then there will be no flow -The difference in pressure between two points on a vessel determines the magnitude of the flow (volume per unit time) * Which vessel in image has the greater flow? top - One-way valves prevent backflow if pressure builds up on other end

Factors that affect blood pressure #2 = Total Peripheral Resistance

-Total Peripheral Resistance (TPR) = opposition to the flow of blood through vessels due to friction (mostly due to resistance at the arterioles, blood cells lose their kinetic energy when they rub against eachother and vessel walls) *Blood cells lose kinetic energy when they rub against each other and vessel walls * TPR is directly related to pressure in a blood vessel ** What does that tell you about the relationship between these two variables? HINT: We've talked about direct and indirect relationships before in Lab 6 (the relationship between EMG and skeletal muscle force) -So, if TPR in the CVS increases, what will happen to blood pressure? -exercise increases blood pressure bc most arterioles will constrict, less arterioles will dilate

Differences between vessels

-What are some important differences in structure between the different types of blood vessels? - What do these structural differences indicate about functional differences? -arteries: closest to heart, have to withstand most pressure, thickest walls, have elastic tissue that allows them to stretch, have fibrous tissue that allows them to be strong -arterioles: endothelial cells wrapped w smooth muscle cells, more numerous in body than arteries, controlled by autonomic nervous system, one of the primary regulators of blood pressure -capillaries: made of endothelial cells, leaky; used for exchange in lungs or body tissues of oxygen/nutrients/CO2/wastes, funnel into venules -venules: fibrous tissue and endothelial cells -veins: fibrous and elastic tissues that allow strength and flexibility, near surface of skin

Concept check: The function of contractile cells

-Where does the signal to depolarize come from? - What ion depolarizes a contractile cell? -Which ion(s) is/are responsible for the plateau phase? -Which ion repolarizes the cells? -What is calcium-induced calcium release? -Where have we seen this before? *Aka: calcium-stimulated calcium release -What are the sources of calcium for a myocardial cell? - How is calcium used during contraction? - How is Ca2+ transported during relaxation? * Back into the SR? Symport, antiport, uniport? Energy requirements? * Out of the cell? Symport, antiport, uniport? Energy requirements?

The heart's pacemaker

Conducting cells (especially those at the sinoatrial (SA) node) set the heart rate. They are the Effector for modulating heart rate. * Depolarize rhythmically on their own * Electrical signal spreads quickly from conducting cell to contracting cell * How does the signal spread from cell to cell? -If the heart is removed from body, it will continue to self- depolarize and contract (as long as it can make ATP) -What if heart rate needs to increase or decrease? * The autonomic nervous system will change the function of SA node conducting cells - What would be the sympathetic neurocrines and receptor? Neurocrines: norepinephrine and epinephrine Receptors: either= beta 1 **norepinephrine: released from sympathetic postganglionic neurons **epinephrine: released from chromafin cells of the adrenal medulla - What about parasympathetic? Acetylcholine onto muscarinic receptors

Conducting cells and contractile cells have different action potentials

Conducting cells at the SA node spontaneously generate action potentials. -Those action potentials then spread to neighboring conducting or contractile cells through gap junctions. -This enables all the cells of a given chamber to function as one and contract virtually simultaneously!

Two types of myocardial cells

Conducting or autorhythmic cells -Aka: pacemaker cells * Make up only 1% of myocardial cells **make up the electrical conduction pathway - Very few contractile proteins * Not designed to generate force - Designed to self-depolarize * What does that mean? they will generate the action potential and filter them into contractile cells via channels * How could that possibly happen? all cells of the heart are connected by gap junctions so they can work like a collective Contractile cells - Most cells in the heart (99%) - Designed to contract, generate force, and pump blood - Contain an abundance of contractile proteins arranged into sarcomeres * As seen in skeletal muscle

Factors that cause graded contraction of cardiac muscle cells

Force can be graded similar to smooth muscle, but unlike the "all or none" contraction of a skeletal muscle cell - How can the contraction force vary? * It comes down to how much Ca2+ enters a contractile cell from the interstitial space **What might affect Ca2+ levels outside these cells? ** What might limit entry into the cell? -Sarcomere length (overlap of thick and thin filaments) ALSO affects force of contraction * Similar to the length-tension relationship we saw with skeletal muscle * According to the Frank-Starling Law - the heart must pump all the blood that returns to it AND its force of contraction is determined by how much blood is arriving to it (venous return) at any given moment **More venous return > increased stretch of the heart chambers and contractile cells> better alignment of thick and thin filaments > increased force of contraction ** Less less venous return > leads to the opposite conditions and effect on contractile force

Excitation-contraction coupling

How is the process different from a skeletal muscle? Ca transported back into SR, contraction and relaxation - How is it similar to smooth muscle? Ca induced Ca release, Ca transported back into SR 1. action potential from neighboring cell, either conducting or contractile -travels on sarcolemma, down transverse tubules 2. L type Ca2+ channels sense depolarization and open -calcium influxes 3. Ca that influxes from extracellular fluid will trigger more Ca release from sarcoplasmic reticulum through ryanodine channels 4. calcium rains down on thick and thin filaments, they contract same as in a skeletal muscle -calcium that was binding to troponin needs to be returned back to the sarcoplasmic reticulum using primary active transport carrier proteins for the next contraction 9. Na Ca exchangers, carrier protein doing secondary active to put calcium back in extracellular fluid, 10. sodium potassium pumps use primary active transport to put Na back in extracellular fluid

In the SA Node figure above, these channels are open at the stage marked "4".

IF channels

When the membrane potential reaches +20 mV (stage marked "1" above), channels for this ION open and close very quickly, causing a very brief repolarization

K+

Concept check: Know your cardiovascular system!

Make a process map with these terms. Begin at the right atrium. ¨ Bicuspid valve ¨ Left atrium ¨ Pulmonary semilunar valve ¨ Right atrium ¨ Right ventricle ¨ Tricuspid valve ¨ Aorta ¨ Aortic semilunar valve ¨ Superior and inferior vena cava ¨ Left ventricle ¨ Pulmonary circuit ¨ Systemic circuit

The channels in the previous question got their name due to their "funny" behavior of allowing both Na+ and K+ ions to pass through. However, these channels are MORE permeable to one of these ions, and that's what leads to the net depolarization seen in stage "4" of the SA Node diagram. Which ION are these channels more permeable to?

Na+

how the heart pumps

The entire heart pumps rhythmically -All on its own! * No innervation needed for the heart to beat at its baseline rhythm * Changes in baseline heart rate DO require input from the sympathetic and parasympathetic nervous system -Conducting cells of the SA node depolarize automatically *The secret is in the structure of these cells, especially their ion channels -Conducting cells then depolarize the contractile cells (cardiac muscle cells) through gap junctions, and badda-bing, you've got yourself a pumping organ called the heart!

Antagonistic control of heart rate at the SA node

The sinoatrial (SA) node is a cluster of conducting cells that determines heart rate (it is the Effector for modulating heart rate) -Sympathetic stimulation of the SA node conducting cells (norepinephrine released onto β1 receptors) or epinephrine from adrenal medulla can arrive via the blood and leads to an increase in heart rate -Parasympathetic stimulation of the SA node conducting cells (acetylcholine released onto muscarinic receptors) leads to a decrease in heart rate

Concept check: ANS modulation of heart rate

Which branch increases HR? sympathetic -What are the signal molecules? norepinephine (neurotransmitter), epinephrine (neurohormone) -What kind of receptor(s)? beta-1 adrenergic receptors, when signal mols bind, pacemaker potential goes faster * Effect on the cell' s pacemaker potential? goes faster ** Faster or slower in getting to threshold? faster - Manipulating channels for which ion(s) would accomplish this? If channels and first set of Ca channels - Increased/decreased influx or efflux? increase Na influx, increase Ca influx *more action potentials fired over unit time > more heart beats per min. -Which branch decreases HR? parasympathetic *What is the neurotransmitter? always acetylcholine * What kind of receptor? muscarinic receptors * Effect on the cell' s pacemaker potential? slow down * Faster or slower in getting to threshold? slower -Manipulating channels for which ion(s) would accomplish this? first set of Ca channels and K channels - Increased/decreased influx or efflux? decreases Ca influx, increases K efflux *increased K efflux creates hyperpolarization, decreased Ca influx lengthens the process of reaching the pacemaker potential, slows heart rate

Action potentials in autorhythmic cells

from image: A: the action potential in a conducting cell looks like an action potential in a neuron except its longer in time, takes about 150-200milliseconds to complete *another diff is that the resting membrane potential is -60mV and the threshold is -40mV C: * these cells are autorhythmic; as soon as the cell returns to -60mV, If channels (I= current, f= funny) open. **these channels are called funny current channels bc they were the first observed that allow Na influx and K efflux, allow more Na influx and less K efflux, leads to net depolarization when open *If channels close, the first set of Ca channels open, threshold is reached, K channels begin to open *second set of Ca channels open, depolarization, and close at the peak *K channels open fully when Ca channels close, repolarization phase *K channels close, If channels open *process repeats The pacemaker potential makes these cells "autorhythmic" - Where is the heart's lead pacemaker? - How does it become activated? - What causes each change in membrane potential within these cells? Steps of a autorhythmic cell action potential - Initial slow depolarization; Na+ influx and K+ efflux through If channels - Near threshold, "some" Ca2+ channels open * Speeds membrane potential towards threshold - What happens at threshold? - What kind of ion channel will repolarize the membrane?

These components of the junctions mentioned in Question 9 allow cardiac muscle cells to be electrically connected. These direct conduits between myocardial cells allow waves of depolarization of to pass rapidly between cells, causing them to contract almost simultaneously.

gap junctions

blood pressure go up when you exercise because

glucose, triglycerides, oxygen, lipids, etc. is needed in larger quantities for working muscles -delivers more nutrients like oxygen -pick up waste products like carbon dioxide

EXAM PREP: Compare and contrast the action potentials you've learned about

important

OK, enough with that figure above. Let's talk more about the myocardial cells. Cardiac muscle cells are held together, end-to-end, at complex junctions called ________ that consist of interdigitated membranes.

intercalated disks

The signal then moves through this pathway which spreads it throughout both atria

internodal pathway

The compartment labeled "C" in the above diagram is the _____. It receives oxygenated blood from the lungs.

left atrium

The compartment labeled "D" in the above diagram is the _____. It contracts to send blood to the entire body.

left ventricle

units of pressure

mmHg