Muscle Physiology

Question 1

Characteristics of Thick filaments

Answer 1

Present in A bands
Conatin myosin

Question 2

Characteristics of Thin filamentsr

Answer 2

anchored at Z lines
present in the I bands
contain actin tropomyosin and troponin

Question 3

What is Troponin?

Answer 3

A regulatory protein permitting cross-bridge formation
complex of 3 globular proteins
T - attaches troponin to tropomyosin
I - inhibits interaction of myosin and actin
C - Calcium binding protein allowing interaction with acin and myosin

Question 4

Charateristics of T-tubules

Answer 4

Carry depolarization of sarcolemma membrane to cell interior
located at junctions of I and A bands
volatge sensitive protein- dihydropyridine receptor

Question 5

Characteristics of sarcoplasmic reticulum

Answer 5

site of storage and release of Ca2+
possess terminal cisternae that make contact with T tubules
Ca2+ pump
Ca2+ bound to calsequesterin
Ca2+ released via Ryanodine receptor channel

Question 6

Describe contraction coupling in skeletal muscles

Answer 6

Action potential received by T-tubules
T tubules pass to SR
Ca2+ released via ryanodine receptors
Ca2+ binds to Troponin C
Tropomyosin moved
ATP binds to MYOSIN and actin is disengaged
ATP—-> ADP
Mysoin attaces to a new site on actin (moves towards psoitive)
ADP released
When intracellular Ca2+ levels fall, contarction stops. Tropomyosin returned.

Question 7

What are the types of smooth muscle?

Answer 7

Multiunit - iris, ciliary muscleof lens, vas deferens
Unitary (single unit)- ballder, G.I. tract, uterus, ureter
Vascular smooth muscle

Question 8

Describe contraction coupling in smooth muscles

Answer 8

depolarization/ hormones/ neurotransmitters cause gated (voltage/ligand) Ca2+ gates to open
intracellualr Ca2+ levels increase
Ca2+ binds to calmodulin (CaM)
CaM activate myosin light chain kinase
Myosin phosphorylated and binds to actin

Question 9

What are signalling pathways in the types of muscle?

Answer 9

Skeletal- T tubules
Smooth- Caveolae
Cardiac muscle - T tubule

Question 10

What is the Triads area?

Answer 10

1 t tubule and 2 terminal cisternae

Question 11

Define a power stroke

Answer 11

This is the pivoting of the myosin head where energy is released in the form of ADP +P. The sarcomere is shortened by about 1%

Question 12

Where is energy used in muscle contraction?

Answer 12

Most is used in the power stroke
Small amounts used to pump Ca2+, Na+ and K+

Question 13

What are the sources of energy to facilitate contraction?

Answer 13

Phosphocreatine (Anaerobic metabolism)
Glycolysis (Anaerobic metabolism)
Oxidative (Aerobic) metabolism

Question 14

Where does calcium come from for contraction in the different types of muscles?

Answer 14

Skeletal- ONLY sarcoplasmic reticulum
Smooth- MOSTLY extracellular fluid, some SR
Cardiac- MOSTLY extracellular fluid, some SR

Question 15

What is the difference between Isometric contraction and Isotonic contraction?

Answer 15

Isometric- maintenace of constant muscle length by a contracted muscle as it is unable to move the load
Isotonic - Maintenace of constant tension as it moves a load

Question 16

What are the catergories of myopathies? Give examples

Answer 16

Genetic : mitochondrial disease, muscular dystrophy, storage myopathy
Non-genetic : Myasthenia Gravis, Lambert-Eaton, Drug disorder

Question 17

What are causes of myopathies?

Answer 17

Injury/overuse
Genetics
Some cancers
Inflammation
Nerve death that affects muscles (Huntingtons and parkinsons)

Question 18

What are cramps?

Answer 18

Sudden Invluntary contraction os muscles
mostly occur in leg muscles
Sudden sharp severe pain
Labour
excercise
health conditions

Question 19

What is spascity?

Answer 19

Condition where certain muscles are continuously contracted
Muscle hypertonia, stifness or tightness
Usually caused by damage to part of brain or spinal cord
Can be seen with cerebral palsy and multiple sclerosis

Question 20

What is a common cause of muscular dystrophy?

Answer 20

Dystrophin gene mutation
Beckers - reduced dystrophin
Duschenns - absence of dystrophin

Question 21

What is McArdle’s syndrome and example of?

Answer 21

Myophosphorylase deficiency
Metabolic myopathy
A rare group of hereditary muscle disorders caused by faulty genes leading to defectice muscles.

Question 22

What is clinical myotnia?

Answer 22

Prolonged muscle relaxtion after voluntary contraction
Abnormal chromosomal genes —-> abnormal Na+ or Cl- channels
improved with excercise

Question 23

What are the types of clinical myotonia?

Answer 23

Congenital myotonia - severe muscle stifness
Becker’s - temporary attacks of msucle weakness
Thomsen’s

Question 24

Describe Famlial periodic paralysis

Answer 24

Rare autosomal dominant condition
Sudden epsisodes of paralysis
Hypokalemic
Hyperkalemic
Thyrotoxic
Ander - Tawil syndrome