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Introduction to Physiology and Parmacology > Muscle, Skin and Epithelia > Flashcards

Muscle, Skin and Epithelia Flashcards

1
Q

What are the 4 things Skeletal Muscle is responsible for ?

A

Voluntary movement of bones that underpins locomotion

Control of inspiration by contraction of diaphragm

Skeletal-muscle pump – help with venous return to the heart

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2
Q

What is the general structure of Skeletal Muscle ?

A

Multiple myofibrils make up muscle cells. Myofibrils can be broken down into sarcomere. Actin and myosin filaments make up the sarcomere.
The sarcomeres aligns with eachother
Ends of sarcomeres are Z line, middle of sarcomere is the M line.

During muscle contraction A band stays the same and I band will shorten.

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3
Q

What does skeletal muscle look like ?

A

Striated in appearance

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4
Q

What are T-Tubules ?

A

T tubules are an extension of the sarcolemma which passes deep through the muscle fibres

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5
Q

What is the Sarcoplasmic Reticulum ?

A

Sarcoplasmic reticulum is the specialsed form of the endoplasmic reticulum.

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6
Q

What is the difference between slow versus fast muscle fibres?

A

Slow fibers are half the diameter of fast fibers take longer to contract after nerve stimulation

Fast fibers take 10msec or less to contract

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7
Q

What are the symptoms of Botulinum toxins?

A

1st symptoms: dry mouth, double vision
2nd symptoms: gastrointestinal (diarrhea, vomiting)
3rd symptoms: paralysis of limbs, respiratory muscles

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8
Q

What are the steps in cross-bridge formation and contraction of the sarcomere ?

A
  1. Binding of ATP to myosin head. Myosin head dissociates from the actin, separating the actin and myosin fibres.
  2. Gives a conformational change in the myosin molecule. ADP and phosphate. Head moves forward.
  3. The head is extended so can interact with other molecules further down the chain
  4. Cross bridge formation (weak). Phosphate is released.
  5. ADP is then released.
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9
Q

What is Botulinum toxin ?

A

Common cause of food poisoning

Causes muscle weakness and paralysis

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10
Q

What is Aerobic exercise?

A

Typically is a sustained, low level exercise (jogging, distance swimming)

Stimulation of slow fibers

Conversion IIx into IIa

When you respire with oxygen

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11
Q

What is the clinical use of botulinum toxin ?

A

Treatment of strabismus (cross eyedness) by injection into peri-ocular muscles

Blepharospasm (uncontrolled eyelid movements)

Cosmetic treatments (Botox: Toxin A)

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12
Q

What is Anaerobic exercise ?

A

Typically is a brief, intense exercise (weight lifting, 50-yard dash)

Stimulation of fast fibers

No change in the number of muscle fibers

Enlargement of myofibril size by addition of new myofilaments. This causes increased diameter of muscle fiber: hypertrophy

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13
Q

How is ATP made and recycled ?

A

ATP TO ADP + Phosphate + Energy

ADP + PCr to ATP + Creatine catalysed by creatine kinase

ADP + ADP to ATP + AMP catalysed by adenylate kinase

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14
Q

What does a build up of ADP, AMP and Phsopjaye stimulate ?

A

They will stimulate metabolic pathways involved in energy productions

Creatine is recycled into P-creatine in mitochondria at rest.

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15
Q

What are the advantages and disadvantages of Anaerobic/Glycolytic metabolism ?

A

Advantage: produces ATP in the absence of O2
-
Disadvantage: ATP yield is low and toxic products are generated.

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16
Q

What is the aerobic phase (oxidative) of energy release?

A

As tissue oxygen delivery increases, energy production via oxidative phosphorylation is stimulated.

Process more efficient - 30 ATP molecules per glucose molecule

Glucose is sourced from blood, and breakdown of glycogen stored in the liver.

Lactate is converted back into pyruvate, this feeds oxidative phosphorylation.
Type IIx fibers release lactate into circulation – can enter other skeletal muscle cells or utilized by liver.

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17
Q

What is the anaerobic phase (non oxidative) of energy release?

A

Anaerobic metabolism using glycolysis.

Muscle fibres store glycogen about 300-400g.

Substrates enter glycolysis at two points

Glycogenolysis of glycogen produces Glucose-1-Phosphate

Glucose-1-Phosphate converted to Glucose-6-Phosphate – enters glycolysis at reaction 2

Uptake of Glucose from blood by GLUT4.

Glucose enters glycolysis pathway.

Pyruvate produced.
Pyruvate is converted to lactic acid/lactate.

Process is very inefficient (2 ATP molecules per glucose) compared to oxidative phosphorylation.
H+ from lactic acid lowers cell pH and leads to muscle fatigue

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18
Q

What is muscle fatigue ?

A

Inability to maintain a desired power output.

Decline in force and velocity of muscle shortening.

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19
Q

What is the difference between high-free and low-freq fatigue ?

A

High-Frequency Fatigue – alteration in cell Na/K balance. Particularly relevant to type II fibres.

Low-Frequency Fatigue – Reduced release of Ca2+ from sarcoplasmic reticulum – more apparent at low frequency stimulation – type 1 fibres

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20
Q

What is ATP depletion ?

A

Intense stimulation can cause large drops in ATP near sites of cross-bridge formation and ATPases.

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21
Q

Describe the structure of Cardiac Muscle

A

Cardio myocytes are also striated like skeletal muscle

The myocytes are shorter are more branched. Join together at the intercalated disk.

Electrical coupling between adjacent myocytes at the intercalated disk by means of the gap junctions.

22
Q

How do Action Potentials work in Cardiac muscle?

A

Action potential initiated in the pacemaker cells of the Sino-Atrial node and propagates between cells via the gap junctions

23
Q

What is Smooth Muscle involved in ?

A

Involved in mechanical control of organ systems – eg digestive, urinary and reproductive system. Also control of blood vessel and airway diameter.

24
Q

What are the 2 classes of Smooth Muscle ?

A

Multiunit

Unitary

25
Q

What is the structure of Smooth Muscle?

A

Non-striated. Multiple actin fibers join at spots known as dense bodies and thick filaments intersperse around the thin filaments.

26
Q

What are the two effects of activating L-type Ca2+ channels in the T-tubule membrane when increasing intracellular Ca+ in skeletal muscle

A
  1. Leads to opening of the L-type Ca2+ channel and influx of calcium into the cell.
  2. Causes a mechanical tethering between the L-type Ca2+ channels in the T-tubule and Ca2+ release channels (also known as ryanodine receptors) in the SR membrane.

The Ca2+ release channels in the SR open and Ca2+ moves into the cytoplasm.

27
Q

What does the removal of calcium do ?

A

Terminates muscle contraction

28
Q

How is Calcium removed from cytoplasm during muscle contraction ?

A
  1. Across the cell membrane by means of the Plasma Membrane Calcium ATPase (PMCA) or the electrogenic Sodium/Calcium exchanger (NCX).
  2. Back into the SR via the sarco/endoplasmic reticulum calcium ATPase.
29
Q

What is the mechanism of contraction in Smooth Muscle ?

A

NO TROPONIN IN SMOOTH MUSCLE. Two other proteins Calponin and Caldesmon tonically inhibit interaction between actin and myosin

Instead stimulation of contraction involves stimulation of calmodulin by Ca2+

Downstream effects:

Activation of myosin light chain kinase - phosphorylates MLC.

Removes inhibitory effects of Calponin and Caldesmon facilitating crossbridge formation and contraction.

To stop contraction need to de-phosphorylate MLC which involves myosin light chain phosphatase (MLCP)

30
Q

What are the downstream effects of smooth muscle contraction ?

A

Downstream effects:

Activation of myosin light chain kinase - phosphorylates MLC.

Removes inhibitory effects of Calponin and Caldesmon facilitating crossbridge formation and contraction.

To stop contraction need to de-phosphorylate MLC which involves myosin light chain phosphatase (MLCP)

31
Q

What is the role of Calcium and Troponin in Skeletal

and Cardiac Muscle in cross-bridge formation ?

A

Low calcium levels means tropomyosin will block further myosin-actin interactions.

If there is a lot of Calcium a conformational change will occur to move tropomyosin so myosin can bind to actin.

32
Q

What is the role of Calcium and Troponin in Skeletal

and Cardiac Muscle in cross-bridge formation ?

A

Calcium

33
Q

List a few features of smooth muscle

A

Smooth muscle lacks T-tubles and Triad/Dyad structures.

Instead shallow invaginations – caveolae

Peripheral SR – encircles the caveolae
Central SR – runs through the cell

34
Q

How is calcium removed from the cytoplasm to terminate muscle contraction ?

A

a2+ removed from the cytoplasm

  1. Across the cell membrane by means of the Plasma Membrane Calcium ATPase (PMCA) or the electrogenic Sodium/Calcium exchanger (NCX).
  2. Back in to the SR via the sarco/endoplasmic reticulum calcium ATPase.
35
Q

What are the 2 effects of depolarisation activating L-type Calcium channels in the T-tubule membrane ?

A
  1. Leads to opening of the L-type Ca2+ channel and influx of calcium into the cell.
  2. Causes a mechanical tethering between the L-type Ca2+ channels in the T-tubule and Ca2+ release channels (also known as ryanodine receptors) in the SR membrane.

The Ca2+ release channels in the SR open and Ca2+ moves into the cytoplasm.

36
Q

What are the 2 main types of epithelia?

A

Simple – single layer of cell (lung)

Stratified – many layers of cells (skin)

37
Q

What germ layers do epithelia develop from ?

A

Mesoderm - lining of cardiovascular system
Ectoderm - epidermis
Endoderm - GI lining

38
Q

what are the 2 non-main types of epithelia ?

A

Pseudo-stratified (upper respiratory tract)

Transitional (urothelium)

39
Q

What is is Simple Squamous ?

A

Simple squamous - Appearance of thin scales and facilitates rapid passage of molecules (alveoli)

40
Q

What is Simple Cuboidal epithelia ?

A

Simple cuboidal epithelia - Secretion and absorption of molecules requiring active transport (kidney tubules)

41
Q

What is Simple Columnar epithelia ?

A

Simple columnar epithelia - With or without cilia/microvilli
Absorption and secretion of molecules using active transport
Majority of GI tract
Ciliated surfaces line fallopian tubes to move egg, and parts of respiratory system to remove particulate matter (small intestine)

42
Q

What is Transitional epithelia ?

A

Transitional epithelia - allows change in shape distension without damaging the epithelial lining. Cells are round when relaxed.

43
Q

What is Pseudostratified columnar epithelia ?

A

Pseudostratified columnar epithelia - All in touch with basement membrane
Some do not reach the apical surface
Cilliated or uncilliated
Cliliated cells can be interspersed with goblet cells

44
Q

What is stratified squamous epithelia ?

A

Startified squamous epithelia - Most common type of stratified epithelium, areas of high abrasion. Apical cells appear squamous, basal appear cuboidal. (Skin upper layers keratinised)

45
Q

What is stratified columnar epithelia ?

A

Stratified columnar epithelia - Rare, found in conjunctiva, pharynx, anus, male urethra and embryo. Allows tissue to stretch and contract

46
Q

What are the different types of glands and what do they excrete?

A

Exocrine glands secrete with ducts

Endocrine gland secretes without ducts.

Mucus glands secrete mucus

Serous glands secrete protein

47
Q

How is polarity useful for epithelia cells ?

A

Polarity – apical surface to external environment, specialisation on basal, lateral or apical surfaces related to function

Polarity determines specialisations

48
Q

What sort of basement membrane do all epithelia have ?

A

Basal Lamina

Reticular lamina are fibres that anchor the basal lamina to underlying connective tissue (collagen/elastin)

49
Q

What does cell adhesion and communication do for epithelia cells ?

A

Lateral communication through gap junctions of water, ions and small molecules

Cell-matrix attachments bond epithelial tissue to connective tissue beneath

Strong adhesion between cells

Stress-bearing cytoskeletons linked from cell to cell by adhesive junctions

Adhering junctions form belt around the cell linked to bundles of actin filaments

Myosin filaments can pull on the actin to contract the cell (NB development)

50
Q

How long does it take the epithelium of the intestine, interfollicular epidermis and the lung to renew ?

A

epithelium of the intestine completely self-renews within ∼5 days
interfollicular epidermis takes ∼4 weeks to renew
lung epithelium can take as long as 6 months to be replaced.

Introduction to Physiology and Parmacology (7 decks)

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