Lecture2-The heart

Induction of Ca2+ Release From SR

- AP along sarcolemma conducted down Ttubules • Depolarization opens DHPR • Ca2+ enters cell from extracellular fluid 1- In heart, [Ca2+] causes RyR to open, allowing release of Ca2+ from SR » "Ca2+ induced Ca2+ release" 2- In skeletal muscle, change in DHPR shape causes RyR to open, allowing release of Ca2+ from SR » "Depolarization induced Ca2+ release"

Action Potentials- APs along sarcolemma signal contration

- APs along sarcolemma signal contraction • Na+ enters cell when Na+ channels open - Depolarization • Voltage-gated Ca2+ channel open - Increase in cytoplasmic [Ca2+] • Na+ channels close • K+ leave cell when K+ channels open - Repolarization • Reestablishment of ion gradients by Na+/K+ ATPase and Ca2+ ATPase - image import

Ca2+ Channels and Transporters

- Action potential travels along sarcomere causing the DHPR to open; - so calcium ions enters cells; image import

Initial Cause of Depolarization

- Myogenic ("beginning in the muscle") • Spontaneous - For example, vertebrate heart • Pacemaker cells - Cells that depolarize fastest - Unstable resting membrane potential - Neurogenic ("beginning in the nerve") • Excited by neurotransmitters from motor nerves - For example, vertebrate skeletal muscle • Can have multiple (tonic) or single (twitch) innervation sites

Phases of a typical action potential in excitable cells

- Sodium ions enters cell when sodium ions channels open (at -50mV depolarizing graded potential and also threshold potential); calcium ions increases in cytoplasm (at around -10mV depolarization phase of action potential); Potassium ions leave the cells when potassium channels open ( repolarisaiton phase of action potential); the shape of the stimulus goes under the threshold potential and the resting membrane potential (at around -90mv after-hyperpolarization); notes: potassium channels close before repolarization; -image import

Depolarization Induced Ca2+ Release

- This is when change in the DHPR causes RyR to change; -causing calcium ions to release; Figure 5.29 - image import

T-Tubules and SR (sarcoplasmic reticulum

- when the muscle is stimulated, calcium ions are released from its store inside the sarcoplasmic reticulum, into the sarcoplasm; -Inginations of the plasma membrane (Sarcolemma) of the muscle fibres are T or transverse tubules; - The SR is smaller and less elaborate, and stores less calcium ions

Action Potentials

-APs along sarcolemma signal contraction • Na+ enters cell when Na+ channels open - Depolarization • Voltage-gated Ca2+ channel open - Increase in cytoplasmic [Ca2+] • Na+ channels close • K+ leave cell when K+ channels open - Repolarization • Reestablishment of ion gradients by Na+/K+ ATPase and Ca2+ ATPase -import image

Electrochemical gradients

-for important ions ina typical cell, resting voltage is -81 mV image import

What is Ca2+ Induced Ca2+ Release?

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An image showing .... Action potentials in various parts of the heart

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Sinoatrial node

..The impulse of contraction of the heart originates in the sino atrial node (SA node) situated in the right atruim close to the point of entry of the vena cava. SA node consists of a small number of diffusely oriented cardiac fibres, possessing few myofibrils, and a few nerve endings from the autonomic nervous system.It is also known as the pace maker of the heart. Image import .

Auto-rhythmicity

.The automatic rhythmicity of the heart is its ability to contract spontaneously and at a regular rate. ...

What is the major difference between SA and And SA node vs AV node Part 1; location, length and shape or outline

1) Sinoatrial node is located in superior lateral wall opening of superior vena cava. AV node is present in the posterior septal wall of right of right atrium near the atrium near the opening of coronary sinus. 2) SA is longer.; while AVIt is shorter. 3)SA node is ellipsoid flattened; while AV It is half oval in outline

what is the steps of Skeletal muscle being depolarized

1) action potential travels through the T or transverse tubuel; 2) change in DHPR 3) this causes RyR to change 4) increased calcium released, which is called depolarisation; image import

what is the pathway of action potential in the heart and the skeleton muscle?

1) in the heart: calcium ions increases; then the RyR is ..... 2) But in the skeleton muscles cells: The DHPR channels are opened; then the RyR -image import

What is Ca2+ Induced and Ca2+ Release?

1. ATP travel through T-tubules 2. Depolarisation causes DPHR to open 3. Calcium ions enters from extracellular 4. In heart, calcium ions from Extracellular that entered cells causes RyR to open 5. This allows release of calcium ion from SR- sarcoplasmic reticulum - This is called calcium induced and calcium released Import image

What is the major difference between SA and And SA node vs AV node Part 2; cardiac impulse, pathway of impulse; and what influences of each

4) SA It generates the cardiac impulse, while AV relays and intensifies the cardiac impulse. 5) SA node transmits impulse directly to the two atria; while AV, Atrioventricular node carries the impulse to the two ventricles through AV bundle, its branches and terminal strands. 6) The SA node is influenced by autonomic nervous system, while the AV is influenced by SA node.

What is the major difference between SA and And SA node vs AV node Part 3; function; and autorythmic fibres

7) SA node acts as pacemaker.; but the AV node functions as pacesetter. 8) Function: Autorhythmic fibres initiate cardiac action potentials, which set basic pace for heart rate and conduct throughout both atria.; but the AV Receives action potentials from SA node and passes them to atrioventricular(AV) bundle

Action potentials

An action potential is the neurons ways of transporting electrical signals from one cell to the next; -This is a picture of a neuron, where you have dendrites in one end, and the axon terminal in the other end -import image

atrioventricular nodes

Atrioventricular Node or AV node: It is compact half oval mass of myogenic fibres which lies in the posterior septal wall of right atrium near the opening of coronary sinus. It receives impulse from SA node and transmits it to ventricles. Direct transmission of impulse from SA node to ventricles is not possible due to the absence of continuity of muscles between atria and ventricles and the presence of fibrous connective tissue of atrioventricular septum. Transmission from SA node stimulates AV node to generate fresh impulse for ventricles. Therefore, AV node is also called pacesette...

.what is repolarisation in neuroscience?..

In neurrepolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive

What is Pacemaker action potential

In the pacemaking cells of the heart (e.g., the sinoatrial node), the pacemaker potential (also called the pacemaker current) is the slow, positive increase in voltage across the cell's membrane (the membrane potential) that occurs between the end of one action potential and the beginning of the next action potential.

Cardiac muscle

Individual cells ◦ joined by specialized anchoring junctions called intercalated discs Impor image

The heart

Learning objectives • Explain the terms: myogenic, pacemaker and nonpacemaker/work cell, automaticity. • Contrast cardiac action potentials with those found in nerve and skeletal muscle cells • Draw typical action potentials from pacemaker (e.g. SA node) and nonpacemaker/work cells (ventricular cells). • State the reasons for, and the significance of the refractory period.

Cardiac muscle

Muscle cells

What is Skeletal muscle cells

Muscle cells Skeletal muscle cells ◦ Large multinucleate cells called fibres, ◦ ranging from a few millimetres to ten centimetres in length and 50µm to 100µm in diameter

what is refractionary period

Refractory period in excitable cells mean: Inability of the cell to respond to any stimulus ( abolishing of excitability ) during a period of time. / Can you expand on refraction onIn skeletal muscle cells?/ , refractory period is quite short (1-2 ms ) , it usually coincides with the depolarization phase of the action potential . Comparing to the contraction phase duration ( about 50 ms ) and the relaxation phase duration (about 50 ms too) the refractory period of the skeletal muscle is quite short. This mean that the muscle could be re-excited while it contracts , and to start a new contraction before the previous one proceed

- Excitation of Vertebrate Striated Muscle

Skeletal muscle and cardiac muscle differ in mechanism of excitation and excitation and contraction (EC) coupling - Differences include • Initial cause of depolarization • Time course of the change in membrane potential (action potential) • Propagation of the action potential along the sarcolemma • Cellular origins of Ca2+

Electrical conductance through the heart

The cardiac conduction system comprises of the: Sinoatrial (SA) node Atrioventricular (AV) node Bundle of His Bundle branches Purkinje fibres Contractions in the heart begin when electrical impulses are sent from the SA node (also known as the natural pacemaker) which is located in the right atrium. The impulse from the SA node causes the atria to contract, pushing blood through the open valves into the ventricles. The electric signal arrives at the AV node which is located between the two atria. From here it travels through the bundle of His, divides into the left and right bundle branches and through the Purkinje fibres. This causes the ventricles to contract. Both ventricles do not contract at precisely the same time, the left ventricle contracts slightly before the right. When the ventricles contract blood from the right ventricle is pumped through the pulmonary valves and onto the lungs, blood from the left ventricle is pumped through the aortic valves and onto the rest of the body. After contraction the ventricles relax, and wait for the next electric impulse. The atria fill with blood and an impulse from the SA node starts the cycle over again. The electrical impulses caused by the heart's activity can be observed on a graph called an electrocardiogram (ECG), this is a good way to monitor the heart's cardiac conduction system and is especially used to detect any abnormalities. -import image

why and how does the cell membrane reach the threshold potential and finer the next action potential?

The increase in membrane potential is what causes the cell membrane, which typically maintains a resting membrane potential of -70 mV,[1] to reach the threshold potential and consequently fire the next action potential; Image import

what is the resisting potential of non-pacemaker close very negative during phase4?

The resting membrane potential is very negative during phase 4 (about -90 mV) because potassium channels are open (K+ conductance [gK+] and K+ currents [IK1] are high). As shown in the figure, phase 4 is associated with K+ currents, in which positive potassium ions are leaving the cell and thereby making the membrane potential more negative inside. At the same time, fast sodium channels and (L-type) slow calcium channels are closed.

What is Tetanus of the skeletal muscle?

This mean that the muscle could be re-excited while it contracts , and to start a new contraction before the previous one proceed , and this event is the reason for the physiological tetanus of the skeletal muscle ( repetitive contraction )

what is the true resting membrane potential of the non-pacemaker cells?

Unlike pacemaker cells found in nodal tissue within the heart, non-pacemaker cells have a true resting membrane potential (phase 4) that remains near the equilibrium potential for K+ (EK).

Time Course of Depolarization Phase 0?

When these cells are rapidly depolarized to a threshold voltage of about -70 mV (e.g., by an action potential in an adjacent cell), there is a rapid depolarization (phase 0) that is caused by a transient increase in fast Na+-channel conductance (gNa+) through fast sodium channels. This increases the inward directed, depolarizing Na+ currents (INa) that are responsible for the generation of these "fast-response" action potentials (see above figure). At the same time sodium channels open, gK+ and outward directed K+ currents fall as potassium channels close. These two conductance changes move the membrane potential away from EK (which is negative) and closer toward the equilibrium potential for sodium (ENa), which is positive. - image imoport

Cardiac muscle action potential

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Excitation-contraction coupling

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Time Course of Depolarization

image import Figure 5.24 Prolonged Effective Refractory period

Comparison of cardiac and skeletal striated muscle

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Electrocardiogram (ECG)

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Muscle contraction depends upon intracellular calcium

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What is Intercalated disks?

import image Figure 3.2 Need to be able to label iGap Junction in detail

Automaticity

the pacemaker potential is what drives the self-generated rhythmic firing (automaticity ) of pacemaker cells Import image

Sarcoplasmic reticulum

the sarcoplasmic reticulum is a specialized type of smooth ER (endoplasmic reticulum); - this regulates the calcium ion concentration in the cytoplasm of striated muscle cells

Howy many types of Muscle cells are they?

they are two: cardiac and skeletal muscle cells Import image

Non pacemaker (ventricular tissue) action potential

ventricular action potentialAtrial myocytes, ventricular myocytes and Purkinje cells are examples of non-pacemaker action potentials in the heart. Because these action potentials undergo very rapid depolarization, they are sometimes referred to as "fast response" action potentials.

Cardiac muscle cells

◦ Individual cells ◦ joined by specialized anchoring junctions called intercalated discs

Skeletal muscle cells

◦ Large multinucleate cells called fibres, ◦ ranging from a few millimetres to ten centimetres in length and 50µm to 100µm in diameter