HUBS1403 Lecture 34: Lecture 34- Cardiac and Smooth Muscle

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grayhippopotamus876

8 Jun 2018

School

University of Newcastle

Department

Human Biosciences

Course

HUBS1403

Professor

karen mate

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Cardiac and Smooth

Introduction to the heart

• Heart is a double pump

• Blood has to first fill the chamber (ventricle) before it can be pumped from it

Both sides (pumps) have to be co-ordinated in pumping action - achieved by coordinated electrical

signalling

Cardiac Muscle Features

Skeletal muscles were large cells, tendon to tendon driven by AP

Cardiac muscle cells are different:

• 20uM diameter and 50-100uM long

• They are mononucleated and joined by intercalated discs - cope with rigors of contraction

• Cells do not multiply so they have to last a lifetime - heart damage is serious

o It had been found that prenatal babies in the womb can repair their heart cells

• Cardiac has length tension relationship but smooth must be different

Cardiac Muscle Activity

Unlike skeletal muscle, contraction is initiated by pacemaker cells

Light muscle - in atrium because of its staging point

Strong muscle - In ventricle because they must push blood through the body

Left ventricle - more muscled because body has more resistance than lungs

• Unlike skeletal muscle, cardiac AP is triggered by pacemaker cells

• AP signal for contraction initiated in the SA node and is conducted through the heart by

specialised muscle cells called purkinje cells

• Conducting system. These are specialised muscle cells (purkinje) that behave more like

neurons and have very little contractile purposes

• Every single cell has the ability to beat - they only beat in synchrony because they are together

o They receive signals from other cells and SA node to coordinate the beating

• SA node beats at about 60bpm - if it gets damaged:

o AV node will continue to beat at 40bpm -if it then gets damaged:

o Ventricular cells continue to beat at 20bpm

o So all the cells will continue to beat - not at an ideal rate though

• Atria first then ventricles

• Pacemaker is the SA node in the right atrium that initial contraction style of heart

• They are pacemakers because they are the fastest cycle time, ventricle cells can beat

spontaneously but slower (every cells has beating properties)

Hierarchy of peacemaking:

• SA node resents clock in ventricle - refractory period

• Ectopic (out of place) contractions - when ventricle cells beat to fast

Aps in SA Node Pacemaker Cells

• Na channel for upstroke - always open

• K channel for downstroke

Similar to the neuronal AP but with some key difference

1. AP is very slow compared to neurons (different types of K channels)

2. PD does not rest like a neuron, is climbs (depolarises) spontaneously

Depolarisation is due to Na current and due to Na Ca exchanger which increases pace making during

exercise

• Leads to 75bpm for rest

• 45bpm for trained athletes

Autonomic Inputs Modulate Pacemaker Activity

parasympathetic input slows pacemaker activity

• What is working most of the time when at rest

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Parasympathetic neurons use Ach to open K channels. Slows and extends hyperpolarisation of

membrane. Longer to get to threshold

Sympathetic input accelerates pacemaker activity

Sympathetic neurons release adrenaline which acts on receptors that lead to opening of Na

channels, this causes the opposite effect

Also ca2+ release from SR which has a clock cycle

Thus, neural inputs do not initiate cardiac contractions, but they can modulate them

• Each AP sets off a heart contraction

More Na - reach threshold earlier - more Aps - increase in HR

Neural inputs alter the rate of pacemaking in the SA node

• Threshold at -40mV in all panels

• Other line at -60mV

Active Process: HR without neuronal input is about 100bpm

Pacemaker Aps spread via gap junctions

Another difference between skeletal and cardiac muscle cells are their size:

• Cardiac cells are 20um diameter and 100um long

• They are joined at intercalated discs by 2 structures

o Desmosomes hold together - withstands rigors

o Gap junctions (large diameter channels;) give an electrical connection by allowing ions to

flow

• Transmission of signal occurs from cell to cell through gap junctions - unique to cardiac muscle

AP in non-pacemaker cardiac muscle fibres

• Occurs in ventricle

• Ions that underlie AP here are quite like in a neuron - but much slower

o Voltage gated K channels - take a while to open - but bring AP back down again

• There is a refractory period (important!)- Na channels are paralysed until the

hyperpolarisation finishes

• This helps the heart not to have summation of contractions - regular beat

Timing of contractions in cardiac vs skeletal muscle

• Aps of "ordinary" cardiac muscle cells differ from both pacemaker and skeletal muscle Aps

• Key difference between cardiac and skeletal muscle AP is the duration of AP relative to

contraction, and thus the refractory period - prevents tetanus in cardiac muscle

Skeletal muscle: Contraction can happen during refraction

Cardiac Muscle: Contractions must be after refraction

Note: resting PD more negative than in pacemaker cells --- slower

• The timing of muscle contraction is very different in cardiac and skeletal muscles

• This is in contrast to skeletal muscle where summation occurs, contraction after refraction

• Duration of AP is much longer in cardiac - due to slower K channels

o Skeletal AP is more like a neuron

• Hence Abs refractory period and relative refractory period is much longer

o Cardiac muscle can't have another beat during contraction

o This gives time for the blood to flow

• When AP is too long the refractory period interferes with the next excitation

• When AP is too short tissue can excite again before the next heart beat (reentrant)

Structural Features of Cardiac Muscle Cells

• Smaller than skeletal muscle cells (max 20 x 100um)

• Single nucleus

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Document Summary

Introduction to the heart: heart is a double pump, blood has to first fill the chamber (ventricle) before it can be pumped from it. Both sides (pumps) have to be co-ordinated in pumping action - achieved by coordinated electrical signalling. Skeletal muscles were large cells, tendon to tendon driven by ap. 20um diameter and 50-100um long: they are mononucleated and joined by intercalated discs - cope with rigors of contraction, cells do not multiply so they have to last a lifetime - heart damage is serious. It had been found that prenatal babies in the womb can repair their heart cells: cardiac has length tension relationship but smooth must be different. Unlike skeletal muscle, contraction is initiated by pacemaker cells. Light muscle - in atrium because of its staging point. Strong muscle - in ventricle because they must push blood through the body.

Related Questions

Question 1. Increased peripheral edema could be caused by:

a. blocked lymph vessels

b. decreased capillary blood pressure

c. increased concentration of albumin in the blood

d. slowed heart rate

Question 2. The pulse pressure of a healthy student is most likely to be:

a. 5 mm Hg

b. 30 mm Hg

c. 95 mm Hg

d. 120 mm Hg

Question 3. beta-blockers inhibit the activity of beta-adrenergic receptors and change the function of the heart by:

a. increasing heart rate and increasing contractility

b. increasing heart rate and decreasing contractility

c. decreasing heart rate and increasing contractility

d. decreasing heart rate and decreasing contractility

Question 4. In cardiac pacemaker cells, the L-type calcium channels:

a. open during diastole

b. close when the membrane potential rises above threshold

c. are located in the cell membrane

d. pump Ca2+ ions into the sarcoplasmic reticulum

Question 5. Dr. Campbell used an elliptical trainer for 40 minutes at the gym. Although the workload remained constant, Dr. Campbellâs heart-rate rose to 150 beats per minute during the first 5 minutes, stayed at that level for the next 25 minutes and then started to rise. It was 180 beats per minute at the end of the exercise period.

What was the time interval between QRS complexes when Dr. Campbellâs heart rate was 180 beats per minute?

a. 3.3 ms

b. 33 ms

c. 333 ms

d. 3333 ms

Question 6. In the question 5 above, Dr. Campbellâs heart rate is most likely to have risen during the last 10 minutes of exercise because his:

a. lungs were becoming congested

b. atrial cells were fatigued

c. extracellular Ca2+ concentration had increased

d. hematocrit increased due to sweating

Question 7. A Physiology student is sitting still in a cold igloo. After 30 minutes, she stands up, walks slowly around the igloo, and suddenly starts to shiver.

The student preserved their core temperature while they were sitting by:

a. depressing their Frank-Starling mechanism

b. decreasing the extracellular Ca2+ concentration

c. relaxing smooth muscles in their peripheral circulation

d. increasing the resistance of arterioles in their arms and legs

Question 8. In the question 7 above, the student started to shiver soon after walking because:

a. their atria started to fibrillate

b. their ventricles started to fibrillate

c. blood moved to the periphery, became cold, and chilled the core when it returned to the chest

d. the ATP concentration in their skeletal muscles had dropped to zero

Please use the following scenario for answering the questions 9 and 10.

A newly discovered drug binds to myosin molecules in cardiac muscle (and nowhere else) and increases the probability that myosin molecules in ventricular cells will bind to actin filaments when the intracellular Ca2+ concentration rises. The drug is being tested as a potential therapy for patients with heart failure.

Question 9. This drug might help people who have low cardiac output by:

a. increasing peripheral resistance

b. increasing the force developed by ventricular cells

c. increasing the isovolumic contraction time

d. increasing heart rate

Question 10. The increased binding of cardiac myosin molecules to actin might prevent the drug from being a useful treatment by:

a. slowing ventricular relaxation

b. decreasing the duration of systole

c. decreasing resistance of capillaries

d. slowing heart rate

crimsoncrab890

1)What type of cell allows the immune system to respond morequickly if the same antigen is encountered a second time?

A)leukocytes

B)memory cells

C)macrophages

D)neutrophils

E)natual killer cells

2)why is the heart divided funtionally into two separate pumpsthat work in series?

A)because arteries carry blood away from the pump and veinsbring blood back to the pump

B)because blood decreases in pressure as it travels throughcirculation

C)because vessles in the vasculature keep blood moving in onedirection'

D)because there are four chambers to the heart

E)none of the above-the heart contracts in unison and is notdivided into two pumps

3)which of the following statements is correct?

A)Na+,K+, Ca2+ and Cl- are all more concentrated in theEXTRACELLULAR fluid

B)Na+, K+, Ca2+ and Cl- are all more concentrated in theEXTRACELLULAR fluid

C)Na+, Ca2+, and Cl- are all more concentrated in theEXTRACELLULAR fluid

D)K+, ca2+ are more concentrated in the EXTRACELLULAR fluid

E)K+, Ca2+ are more concentrated in the EXTRACELLULAR fluid

3)During skeletal muscle contraction:

A)the width of the H-zone decreases

B)the actin heads bind to myosin chain

C)ATP hydrolysis requires Ca2+ as a cofactor

D)tropomyosin changes conformation when Ca2+ binds

E)all of the above occur during skeletal muscle contraction

4)The rapid depolarization phase of myocardial contratile cellaction potential is due to the movement of which ion(s)?

A)Ca2+ flows into the cytosol

B)K+ flow out of the cytosol

C)Na+ flow into the cytosol

D)Ca2+ flow out of the cytosol

E)K+ flow into the cytosol

5)You are a physiology graduate student asked to study theeffect of ion permeability on the initiation of action potentials.You have isolated a cell with resting membrane potential of -70mVand have determined that the cell's threshold voltage is -55mV. Youthen change the cell to make it less permeable to K+ ions(Eions=-90mV)

With all ther condition staying the same, has cell's restingmembrane potential been DEPOLARIZED or HYPERPOLARIZED; and will thecell require a greater or smaller stimulus to reach threshold?

A)hyperpolarize; smaller

B)depolarize;greater

C)hyperpolarize;greater

D)depolarized; smaller

E)none of the above answers are possibe

6)Skeletal muscle cells are UNUSUAL in that they :

A)lack smooth endoplasmic reticulum

B)have no mitochondria

C)depend entirley on anaerobic respiration

D)have MULTIPLE nuclei

E)none of the baove are found in the skeletal muscle cells

7)What is the name for the autonomic nervous system synapses atthe neuroeffector?

A)electrical synapses

B)axon viscosities

C)bidirectional synapses

D)axon varicosities

E)light bulb synapse

8)Which cytokines are involvedin making cells resistant toviruses?

A)colony-stimulating actors

B)interferons

C)erythrpoietin

D)major histocompatibility complex

E)none of the above can make a cell resistant to a virus

9)If a person switiches from normal breathing to more shallowbreathing, whcih statement is true

A)tidal volume decreases

B)alveolar PO2 decreases

C)alveolar ventilation decreases

D)"a" and "b"

E)"a", "b', and "c"

10)Which scenerio supports hyperpolarization of pre-synapticcell?

A)allowing Cl- ions into the cell

B)allowing K+ ions to leave the cell

C)allowing Ca2+ ions into the cell

D)"a" and "b"

E)"a", "b", and "c"

11)The gap junctions in cardia muscle are part of specializedcell junctions that are localized to the__________.

A)transverse tubules

B)intercalated discs

C)Interdigitated fingers

D)desmosomes

E)high-end shppoinf malls

12)What role does myosin light chain kinase (MLCK) play insmooth muscle cell contraction?

A)dephosphorylates myosin

B)phosphorylates actin

C)phosphoylates myosin

D)dephosphorylates actin

E)both "a" and "c"Given that your forearm is 30cm long and yourbiceps inserts 2 cm away from your elbow joint, how much force mustyour biceps exert to hold up a 10kg weight?

A)0.67kg

B)6.0kg

C)20kg

d)150kg

e)600kg

erinbadger748

Select 30 medical terms from the articles.

Complete the table in this document, like the Summary Tables in your textbook.

In the first column list the medical term.

In the second column, list any prefixes and define them.

In the third column, list the root and define it.

In the fourth column, list any suffixes and define them.

In the fifth column list the exact definition of the term.

NOTE: You many not use any medical terms that appear in any of the summary tables in your textbook.

Make sure to include references to the articles your terms come from.

1: Facelift Anatomy

With age, characteristic changes occur in the central third of the face. ^[¹^] A youthful midface is characterized by prominent cheeks and a smooth transition between the lower eyelid and cheek. Structural, soft tissue, and skin changes develop as wrinkles and creases, progressive ptosis, and general atrophy of the structures.

Pessa confirmed the changes seen in the bony structures of the face, and these include a downward migration of cephalometric points. ^[²^] The downward migration manifests as a change in soft tissue volume. The effects of gravity and repeated animation of the face also directly affect the soft tissue that overlies the mimetic musculature.

The results of magnetic resonance imaging (MRI) evaluations have helped to determine that the mimetic muscles themselves remain intact; however, the attachment to the overlying soft tissue and skin changes. The repeated action of smiling results in deepening of the nasolabial fold at the point at which the superficial musculoaponeurotic system (SMAS) inserts into the dermis.

2: Pancreas Anatomy

Embryology

The pancreas develops as 2 buds (outpouchings) of endoderm from the primitive duodenum at the junction of the foregut and the midgut. A small ventral bud (pouch) forms the lower (inferior) part of the head and the uncinate process of pancreas, whereas a large dorsal bud (pouch) forms the upper (0) part of the head as well as the body and tail of the pancreas. The ventral bud rotates behind the duodenum dorsally from right to left and fuses with the dorsal bud, and the duct of the distal part (body and tail) of the dorsal bud unites with the duct of the ventral bud to form the main pancreatic duct (of Wirsung). Because the common bile duct (CBD) also arises from the ventral bud, it forms a common channel with the main pancreatic duct. The remaining proximal part (head) of the duct of the dorsal bud remains as the accessory pancreatic duct (of Santorini).

3: Conduction System of the Heart

The conducting system of the heart consists of cardiac muscle cells and conducting fibers (not nervous tissue) that are specialized for initiating impulses and conducting them rapidly through the heart (see the image below). They initiate the normal cardiac cycle and coordinate the contractions of cardiac chambers. Both atria contract together, as do the ventricles, but atrial contraction occurs first.

The conducting system provides the heart its automatic rhythmic beat. For the heart to pump efficiently and the systemic and pulmonary circulations to operate in synchrony, the events in the cardiac cycle must be coordinated.

4:Spleen Anatomy

Overview

The spleen is an organ shaped like a shoe that lies relative to the 9th and 11th ribs and is located in the left hypochondrium and partly in the epigastrium. Thus, the spleen is situated between the fundus of the stomach and the diaphragm. The spleen is very vascular and reddish purple in color; its size and weight vary. A healthy spleen is not palpable.

Development

The spleen develops in the cephalic part of dorsal mesogastrium (from its left layer; during the sixth week of intrauterine life) into a number of nodules that fuse and form a lobulated spleen. Notching of the superior border of the adult spleen is evidence of its multiple origin (see the image below)

5:Lung Anatomy

Development

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HUBS1403 Lecture 34: Lecture 34- Cardiac and Smooth Muscle

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