READ ME / 1: Origin and conduction of cardiac impulses

Question 1

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Question 2

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Question 3

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Question 4

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Question 5

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Break a leg 👍

Question 6

What is the function of the heart?

Answer 6

Muscle pump - contracts to push blood through the circulation

Question 7

The pumping of the heart is controlled by electrical impulses.

Where in the body are they generated?

Answer 7

Within the heart

Question 8

What is autorhythmicity?

Answer 8

The heart generates its own electrical impulses - doesn’t require anything else to beat

Question 9

The heart can beat without any external stimuli - what is this called?

Answer 9

Autorhythmicity

Question 10

Which chamber of the heart do electrical impulses start in?

What is the specific area called?

Which type of cell is found in this area?

Answer 10

Right atrium

Sino-atrial node (SA node)

Pacemaker cells

Question 11

What do pacemaker cells initiate and where are they found?

Answer 11

Heartbeat

Found in SA node of right atrium

Question 12

Where is the sino-atrial node (SA node) found?

Answer 12

Right atrium

Question 13

Which great vessel of the heart is the SA node closely related to?

Answer 13

Superior vena cava (SVC)

Question 14

The SA node normally determines the heart’s ___.

Answer 14

rate

Question 15

A heart controlled by the SA node is said to be in which type of rhythm?

Answer 15

Sinus rhythm

Question 16

What is the arrow pointing to?

Answer 16

Sino-atrial node (SA node)

Question 17

What is the membrane potential of a cell?

Answer 17

Difference in ion concentrations inside and outside the cell, generating an electrical current

Question 18

Pacemaker cells in the SA node (have / don’t have) a stable membrane potential.

Answer 18

don’t have a stable membrane potential

Question 19

What are the two changes in membrane potential seen in SA node cells?

Answer 19

1. Spontaneous pacemaker potential - slowly increases towards threshold
2. Action potential - rapid change in potential which occurs when the threshold is reached

Question 20

What happens after the threshold potential of SA node cells is reached?

Answer 20

Action potential - generation of a nerve impulse

Question 21

Name A and B.

Answer 21

A - pacemaker potential

B - action potential

Question 22

Is the action potential of an SA nodal cell a depolarisation, hyperpolarisation or repolarisation?

Answer 22

Depolarisation

(Hyperpolarisation - going from negative to even more negative

Repolarisation - going from positive back to negative

Depolarisation - going from negative to positive)

Question 23

The pacemaker potential is caused by three changes in ion concentration - what are they?

Answer 23

1) Decrease in K⁺ efflux (less potassium OUT)
2) Na^{+<strong> </strong>}and K⁺ influx (sodium and potassium IN)
3) Transient Ca²⁺ influx (calcium IN through T-type channels)

Question 24

During spontaneous pacemaker potential, sodium and potassium ions enter the cell causing slow depolarisation - what is this called?

Answer 24

Funny current

Question 25

During the **spontaneous** **pacemaker potential**, **calcium** ions enter the cell through which type of channel?

Answer 25

**T-type** **Ca²⁺** **channels**

Question 26

During the pacemaker **action** potential, what causes the rising phase (i.e the **depolarisation**) and which channel is responsible?

Answer 26

**Ca²**⁺ **influx** caused by the **activation** of **L-type calcium channels** (Remember the T-type channels are involved in the spontaneous part only)

Question 27

Two events cause the **falling phase** (i.e the **repolarisation**) of a pacemaker action potential - what are these and which channels are responsible?

Answer 27

1) **Inactivation** of **L-type Ca**⁺⁺ **channels** - no more calcium IN 2) **Activation of K**⁺ **channels** - causes **K**+ **efflux** - more potassium OUT

Question 28

There are two kinds of calcium channel - what are they called and which processes are they responsible for?

Answer 28

**T-type** - involved in **spontaneous pacemaker potential** **L-type** - involved in **pacemaker action potential**

Question 29

Where is the **atrioventricular node (AV node)** found?

Answer 29

**Base of the right atrium** At the wall between the right and left atrium, also called the **inter-atrial septum**

Question 30

How are **action potentials** carried from the **SA node** to the **AV node**?

Answer 30

**Conduction between cells** via **Gap junctions**

Question 31

What **structures** allow action potentials to travel **between** cells?

Answer 31

**Gap junctions**

Question 32

Which node is found at the base of the right atrium?

Answer 32

**AV node**

Question 33

Which node is found in the upper right atrium?

Answer 33

**SA node**

Question 34

The AV node is the **only** point of electrical contact between which two heart structures?

Answer 34

**Atria** **Ventricles**

Question 35

Does the **AV node** transmit electrical impulses immediately?

Answer 35

**No - there's a delay** Vital so that the heart contracts rhythmically

Question 36

**\_\_\_ systole** precedes **\_\_\_ systole** due to delayed conduction in the AV node. (systole = contraction of muscle and ejection of blood)

Answer 36

**Atrial systole** precedes **Ventricular systole**

Question 37

Through which structure do action potentials travel across the **interventricular septum**?

Answer 37

**Bundle of His**

Question 38

Name the **sequence of structures** along which an action potential travels before reaching the terminal nerves of the heart (and include the name of them!)

Answer 38

**SA node** **AV node** **Bundle of His** **Right and left bundle branches** Terminal nerves = **Purkinje fibres**

Question 39

The **Bundle of His** and **Purkinje fibres** allow ___ spread of action potential to the ventricles.

Answer 39

**rapid**

Question 40

How do action potentials travel **through** the ventricular muscle of the heart?

Answer 40

Cell-to-cell conduction via **g****ap junctions**

Question 41

Apart from pacemaker cells, a different type of cardiac cell generate action potentials - what are they called?

Answer 41

**Cardiac myocytes** i.e the main bulk of cardiac muscle

Question 42

The **resting membrane potential of cardiac myocytes** remains at \_\_mV until the cell is excited.

Answer 42

**-90mV** Remember **membrane potential of potassium is -90**, **membrane potential of sodium is +60** Cell is always trying to get rid of sodium via sodium-potassium pump, so resting membrane potential is usually CLOSER to potassium's (i.e really negative)

Question 43

What causes the **rising phase** of action potential (i.e depolarisation) in **cardiac myocytes**?

Answer 43

**Fast Na⁺ influx**

Question 44

After depolarisation, the **membrane potential** of **cardiac myocytes** has changed from -\_\_mV to +\_\_mV.

Answer 44

- 90mV to +20mV i. e potassium's potential to sodium's potential (because a ton of sodium has just entered the cell)

Question 45

What happens in **Phase 0** of the action potential in cardiac myocytes?

Answer 45

**Fast Na⁺ influx** causing **depolarisation**

Question 46

This graph shows the membrane potential of ventricular muscle during an action potential - describe what happens to cause the numbered phases shown on the graph.

Answer 46

**Phase 0:** fast influx of Na⁺ **Phase 1:** closure of Na⁺ channels and transient efflux of K⁺ **Phase 2:** mainly Ca⁺⁺ influx through L-type channels **Phase 3**: closure of Ca⁺⁺ channels and K⁺ efflux **Phase 4:** resting membrane potential

Question 47

In cardiac myocytes, the membrane potential is maintained near the peak of action potential for a few hundred milliseconds - what is this phase called?

Answer 47

**Plateau phase**

Question 48

The **plateau phase** is a unique characteristic of which cell's action potential?

Answer 48

**Cardiac myocytes**

Question 49

What causes the **plateau phase** of action potentials in **cardiac myocytes**? Which Phase of the action potential does it line up with?

Answer 49

**Influx of Ca²⁺** through **L-type** **channels** ## Footnote **Phase 2**

Question 50

What causes the **falling phase** of **action potential** (i.e the **repolarisation**) in **cardiac myocytes**?

Answer 50

(Closure of L-type Ca²⁺ channels) **K⁺ efflux**

Question 51

**Heart rate** is mainly influenced by the _____ nervous system.

Answer 51

**autonomic** (Autonomic nervous system supplies the MOTOR aspect of the internal organs and is split into the **sympathetic** and **parasympathetic** arms, lots more of this throughout the year so dw)

Question 52

Which kind of autonomic nervous stimulation **increases heart rate?**

Answer 52

**Sympathetic stimulation** | (think "fight or flight")

Question 53

**Sympathetic** stimulation **(increases / decreases)** heart rate.

Answer 53

**increases**

Question 54

Which kind of autonomic nervous stimulation **decreases** heart rate?

Answer 54

**Parasympathetic**

Question 55

**Parasympathetic** stimulation **(increases / decreases)** heart rate.

Answer 55

decreases

Question 56

Which **cranial nerve** gives the **parasympathetic** supply to the heart?

Answer 56

**CN X** | (Vagus nerve)

Question 57

The **vagus nerve (CN X)** exerts a continuous influence on which **node** of the heart?

Answer 57

**SA node**

Question 58

The **vagal tone** slows the heart rate from around 100bpm to its normal **resting** heart rate of \_\_bpm.

Answer 58

**70 bpm**

Question 59

What is the normal range for **resting heart rate?**

Answer 59

**60 - 100 bpm**

Question 60

When a patient's heart rate is found to be **\< 60 bpm** they are said to be...

Answer 60

**bradycardic**

Question 61

When a patient's heart rate is found to be **\> 100 bpm** they are said to be...

Answer 61

**tachycardic**

Question 62

What are two effects of **vagal stimulation** on heart excitation?

Answer 62

1) **Slows** heart rate 2) **Increases AV nodal delay**

Question 63

What is the **post-synaptic parasympathetic neurotransmitter** for the heart? Which **receptor** does it act on?

Answer 63

**Acetylcholine** **M2** muscarinic receptor

Question 64

Which **drug** is used to treat patients with **extreme bradycardia** and why is it effective?

Answer 64

**Atropine** Competitive inhibitor of acetylcholine, reducing vagal bradycardia

Question 65

**Vagal stimulation** decreases the **frequency** of action potentials - why?

Answer 65

It causes the pacemaker cell to **hyperpolarise**, so it takes **longer** to reach the same **threshold** **potential** to trigger an action potential

Question 66

Vagal stimulation **reduces** the heart rate, so it is said to have a ___ **chronotropic effect** on the heart.

Answer 66

**negative**

Question 67

Which parts of the heart are supplied by **sympathetic nerves?**

Answer 67

**AV node** **SA node** *(to increase heart rate)* **Myocardium** *(to increase force of contraction)*

Question 68

What are the **three** effects of **sympathetic stimulation** on the heart?

Answer 68

1) **Increases heart rate** 2) **Decreases AV nodal delay** (so the opposite of parasympathetic stimulation) 3) **Increases force of contraction** (note that parasympathetics have NO EFFECT on contractility)

Question 69

What is the **post-synaptic sympathetic neurotransmitter** for the heart? Which **receptor** does it act on?

Answer 69

**Noradrenaline** **ß1** adrenoceptors

Question 70

Sympathetic stimulation **increases** the **frequency** of action potentials - why?

Answer 70

Pacemaker cell **depolarises,** so it reaches **threshold potential** quicker, so more action potentials occur and heart rate increases

Question 71

What is an **electrocardiogram (ECG)**?

Answer 71

"A record of depolarisation and repolarisation cycles of cardiac muscle obtained from the skin surface" Graph of heart's electrical activity which can be used to diagnose disease

Question 72

\_\_\_ **tone** dominates under **resting** conditions.

Answer 72

**Vagal** to keep the heart rate between 60 - 100 bpm

Question 73

As it **increases heart rate**, **sympathetic** stimulation has a ___ **chronotropic** effect on the heart.

Answer 73

**positive**