Exam 3

Question 1

Describe briefly the steps of a contraction cycle

Answer 1

Calcium binds to troponin causing a conformational change which moves tropomyosin off of the myosin binding site

1) Myosin head hydrolized ATP and becoms energized and oriented.
2) Myosin head binds to actin forming a cross-bridge
3) Myosin head pivots, pulling the thin filaments past the thick filament toward center of the sarcomere
4) As myosin head binds ATP the cross-bridge detaches from actin

Question 2

When does the muscle fiber start to relax?

Answer 2

As Ca++ ion is pumped back to sarcoplasmic reticulum, Ca++ is no longer bound to troponin causing tropomyosin molecules to block the myosin binding site on actin. This prevents the interaction between actin and myosin head and muscles start to relax.

Question 3

What is a sarcomere

Answer 3

Sarcomere is the contractile unit in myofibril defined by the part of a myofibril between two consecutive Z-disc.

Question 4

What are the functions of actin

Answer 4

Contractile protein that is the main component af thin filament; each actin molecule has a myosin binding site where myosin head of thick filament binds during muscle contraction

Question 5

What are the functions of myosin

Answer 5

Contractile protein that makes up thick filement; molecules consists of a tail and two myosin heads which bind to myosin-binding sites on actin molecules of thin filament during muscle contraction

Question 6

What are the functions of titin

Answer 6

Structural protein that connects Z-discs to M-line of sarcomere thereby helping to stabilize thick filament position, can strech and then spring back unharmed and thus accounts for much of the elastcity and extensibility of myofibrils

Question 7

How does the protein dystrophin help in the contraction of muscle fibers?

Answer 7

Dystrophin is a rod-shaped protein that connects the ends of myofibrils (from Z-disc) to a protein complex containing dystroglycan in sarcolemma (plasma membrane). Dystroglycan provides attachment to extracellular matrix protein laminin and is essential for transmitting individual myofibril-generated force to connective tissue.

Question 8

What disease condition can result from a mutation in the dystrophin gene resulting in defective protein synthesis?

Answer 8

Duchenne muscular dystrophy can result from a mutation in the dystrophin gene
-Weakness of muscular mass

Question 9

What is the effect of calcium entry in the synaptic end bulbs following an action potential?

Answer 9

Calcium entry in the synaptic end bulbs causes exocytosis of Ach containing synaptic vesicles in the synaptic cleft
See figur 10.9

Question 10

Give examples of two molecules that block the transmission at the neuromuscular junction by separate mechanisms.

Answer 10

Molecules blocking synaptic transmission:

• Botulinum toxin
• Curare

Question 11

Weightlifter Jamal has been practicing many hours a day and his muscles have gotten noticeably bigger. He tells you that his muscle cells are “multiplying like crazy and making him get stronger and stronger.” Do you believe his explanation? Why or why not

Answer 11

No, because mature skeletal muscle fibers generally does not undergo mitosis

Question 12

What is the muscle hypertrophy

Answer 12

Hypertrophy (Increase in the muscle mass): (a) increase in actin and myosin filaments in each myofibril and (b) splitting of myofibril. Hypertrophy occurs to a much greater extent when the muscle is loaded during the contractile process. The enzyme systems that provide energy (especially enzymes for glycolysis) also increases

Question 13

What is muscle hyperplasia

Answer 13

Hyperplasia (increase in the number of muscle fibers): Very rarely, under intense condition skeletal muscle fibers are observed to divide.
Find in the smooth muscle

Question 14

What is atrophy

Answer 14

Atrophy: Muscle mass decreases over time; here the degradation of the contractile proteins is more rapid than the rate of replacement.

Question 15

Write any three differences observed between the structures of skeletal and cardiac muscle tissue.

Answer 15

Major difference from skeletal muscle:

• Single nucleus
• Intercalated discs (gap junctions and desmosomes)
• Functions as a syncytium
• Autorhythmic
• Prolonged duration of action potential (200-300 ms as -opposed to 1-2 ms in skeletal muscles

Question 16

Why cardiac muscle fibers have a more prolonged action potential compared to skeletal muscle fibers?

Answer 16

Why duration of action potential is cardiac muscles is much longer:

• Opening of slow Ca++ channel follows the opening of fast Na+ channels
• Inhibition of Ca++ dependent K+ channel prevents outwards K+ flux.

Question 17

Smooth muscle fibers lack striations; does this suggest that smooth muscle cells lack actin and myosin filaments?

Answer 17

Even striations are absent, actin and myosin are highly organized in smooth muscle.

Question 18

How the smooth muscle tissue is classified based on their innervation pattern?

Answer 18

Dense bodies (made of a-actinin) and intermediate filaments (desmin/vimentin) form a three-dimensional lattice in the cytoplasm where dense bodies act as nodes of filament attachment
Actin fibers originate from the dense bodies and myosin filaments intercalate in between them.

Smooth muscle are in the blood vessel

Question 19

Even though smooth muscles are much slower than skeletal muscles in initiating a contractile response, several properties of smooth muscles could be physiologically advantageous. Mention any two such advantages.

Answer 19

• Less energy spent than skeletal muscles to contract (10 – 300 times less)
• maximum force of contraction (4-6 kg/cm2 ) could be higher than skeletal muscle (3-4 kg/cm2 in)
• Can maintain tonic contraction for long time with minimal use of energy
• Smooth muscle can shorten and stretch to a greater extent (e.g. urinary bladder, stomach)

Question 20

What are the main structural divisions of the pituitary gland?

Answer 20

Two (three) parts:

• Anterior pituitary (adenohypophysis)
• Posterior pituitary (neurohypophysis)
• Pars intermedia (Intermediate part); rudimentary in human

Question 21

What are the hormones secreted from anterior pituiraty?

Answer 21

Hormones secreted from anterior pituitary:

• Somatotropes (acidophilic cells, 30-40% of anterior pituitary cells): secretes human growth hormone (hGH).
• Corticotropes (20% of anterior pituitary cells): adrenocorticotropic hormone (ACTH)
• Thyrotropes: thyroid-stimulating hormone (TSH)
• Gonadotropes: gonadotropic hormones, which include luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
• Lactotropes: prolactin (PRL)

Question 22

What are the hormones secreted from posterior pituiraty?

Answer 22

Hormones secreted from posteriorr pituitary:

• Antidiuretic hormone (ADH, vasopressin) primarily from supraoptic nuclei neurons
• Oxytocin from paraventricular nuclei neurons.

Question 23

Briefly explain how the homeostasis of the hormonal secretion is maintained by hypothalamus, anterior pituitary and a target endocrine organ using the example of thyroid hormone.

Answer 23

See picture

Question 24

Name the hormones secreted from the pancrea

Answer 24

• Insulin

- glucagon

Question 25

What are the main functions of the hormone insulin?

Answer 25

Functions of insulin:

• Lowers blood glucose level: Enhanced glucose transport in cells (GLUT4 transporter – especially abundant in liver and skeletal muscle), glycogenesis; decrease glycogenolysis, gluconeogenesis
• Enhanced fat and protein synthesis
• Enhanced growth – synergistic effect with human growth hormone.

Question 26

Name three physiological stimuli for insulin secretion.

Answer 26

Insulin secretion is stimulated by,

• Increased blood glucose concentration
• Amino acids arginine and leucine
• Parasympathetic (vagus nerve) stimulation

Question 27

. How type I diabetes mellitus differs from type II diabetes mellitus?

Answer 27

Diabetes mellitus type I: Viral infection or autoimmune disease causing destruction of insulin producing b-cells

Diabetes mellitus type II: Resistance to metabolic effects of insulin; adult onset diabetes, associated with obesity and diet.

Question 28

Enumerate the main functions of the thyroxine hormone

Answer 28

Functions of Thyroid Hormones:

• Stimulate synthesis of Na+/K+ ATPase
• Increase basal metabolic rate (can be 60-100% higher than normal at high level of hormonal stimulation)
• Mitochondrial growth and division
• Increase body temperature (calorigenic effect)
• Stimulate protein synthesis
• Increase the use of glucose and fatty acids for ATP production
• Stimulate lipolysis
• Enhance some actions of epinephrine (e.g. lipolysis)
• Regulate development and growth of nervous tissue and bones

Question 29

What symptoms will you make you suspect that a patient might be suffering from a high level of thyroxine hormone in the blood?

Answer 29

Symptoms: (1) Intolerance to heat and increased sweating, (2) mild to extreme weight loss (sometimes as much as 100 pounds), (3) varying degrees of diarrhea, (4) muscle weakness, (5) extreme fatigue but inability to sleep, and (6) tremor of the hands, (7) exophthalmos (eyes appear protruding)

Question 30

Name two common causes for hyperthyroidism (increased thyroxine concentration in blood).

Answer 30

Hyperthyroidism:
-Cause: Due to antibodies mimicking TSH function (thyroid stimulating antibody, TSI) or an hormone-secreting tumor in the thyroid gland.

Question 31

What change will you expect in the plasma TSH (thyroid stimulating hormone) level in these conditions? Give reasons.

Answer 31

Very low level of TSH is expected in hyperthyroidism due to negative feedback inhibition by a high level of T3 and T4

Question 32

Rigor mortis

Answer 32

When you die and your muscle stay controlled -> because have no ATP

Question 33

Why binding of acetylcholine molecules to their receptor in the motor endplate causes depolarization of the membrane?

Answer 33

Sodium is pumped into muscle cell, making it less negative.

So the muscle cell is negative but sodium makes it less negative

Question 34

Slow oxidative fiber
Fast glycolytic fiber
Fast-oxidative-glycolytic fiber

Answer 34

Slow oxidative fiber

• many mitochondria
• Myosin head activity is slow
• Aerobic respiration

Fast glycolytic fiber

• few mitochondria
• Myosin head activity is fast
• anerobic glycolysis

Fast-oxidative-glycolytic fiber

• many mitochondria
• both anerobic glycolysis and aerobic respiration

Question 35

. Briefly describe the three categories of levers based on the position of their fulcrum.
. Give an example of each type of lever system formed by muscles and bones.
State whether the levers in the examples work at a mechanical advantage, disadvantage or both.

Answer 35

First class lever - both
-Posterior neck muscle

Second class laver - mechanical advantage
-Calf muscle

Third class lever - disadvantage
-Elbow joint

Question 36

What are the two main categories of hormones based on their solubility?

Answer 36

Lipid soluble hormones

• Steroids
• Thyroid hormones
• Gasesous small molecules

Water soluble hormones
-Amines
Peptides and proteins
Eicosanoids

Question 37

Briefly describe how they differ in terms of their transport in the blood and interaction with target cells?

Answer 37

Water soluble need a second messenger protein

and can not just go into the cell, need a receptor on the putside of the cell

Question 38

Which of these two categories of hormones amplifies the response by activation of signaling cascades?

Answer 38

Water soluble hormones - cascades of signal event

Question 39

hypothryroidism

Answer 39

Low level of thyroid hormones -> TSH and TRH is high -> fat

Autoimmune disease - Myxedema

Question 40

Name two hormones secreted from the posterior pituitary

Answer 40

(a) Antidiuretic hormone (ADH, vasopressin) is primarily synthesized by supraoptic nuclei neurons and (b) oxytocin by paraventricular nuclei neurons of hypothalamus. The hormones are transported by the axons of these neurons and secreted from posterior pituitary.

Question 41

Function of oxytocon

Answer 41

Function of Oxytocin:

(a) Stimulates contraction of uterine smooth muscle cells during childbirth
(b) Contracts myoepithelial cells in mammary gland for milk ejection
(c) Helps to form interpersonal bond and affection (often referred to as “love hormone”)

Question 42

Function of ADH

Answer 42

Function of ADH: The hormone primarily acts on kindneys, skin, and blood vessels to help restore homeostasis by increasing blood volume/pressure.
Kidneys: increases water retention by facilitating water reabsorption from kidney tubules
Skin: reduces the amount of sweat
Blood vessels: vasoconstriction, which increases the blood pressure

Question 43

Where these hormones are synthesized and what stimulates their secretion?

Answer 43

Stimulus for oxytocin release:
Stretching of cervix by baby’s head during childbirth
Mother nursing her baby
Sexual activity

Stimulus for ADH secretion: (a) High blood osmotic pressure (detected by hypothalamus), (b) a decrease in blood volume (commonly occurs after dehydration or blood loss).

Question 44

How their chemical structure differs from the hormones secreted from the anterior pituitary?

Answer 44

Oxytocin and ADH are short peptide while anterior pituitary hormones are either protein or glycoprotein.