11) Muscle Tissue

Question 1

What is myoglobin?

Answer 1

A red protein, similar to one subunit of haemoglobin - provides O2 to working striated muscles
Has a higher affinity to O2 than Hb

Question 2

Does myoglobin or haemoglobin bind more strongly to O2?

Answer 2

Myoglobin - so O2 is not taken away from respiring muscle cells during exercise

Question 3

What is the outer membrane of a muscle cell called?

Answer 3

Sarcolemma

Question 4

What is the cytoplasm of a muscle cell called?

Answer 4

Sarcoplasm

Question 5

What is the mitochondrion called in a muscle cell?

Answer 5

Sarcosome

Question 6

What is a sarcomere

Answer 6

The most basic contractile unit in striated muscle

Question 7

What is the Sarcoplasmic reticulum?

Answer 7

The smooth endoplasmic reticulum of a muscle cell

Question 8

What are the 3 types of muscle contraction speeds?

Answer 8

Slow, intermediate, fast

Question 9

what colours are the 3 muscle fibre types?

Answer 9

Slow - red
Intermediate - red to pink
Fast - white

Question 10

What 2 factors/molecules affect continued muscle contraction?

Answer 10

Ca2+ ions
Amount of ATP

Question 11

How does nucleus placement differ between cardiac, smooth and skeletal muscle?

Answer 11

Nucleus positioned centrally in cardiac and smooth muscle cells.
Nucleus positioned on the edge of the cell in skeletal muscle

Question 12

Name some unique structural features of cardiac muscle cells.

Answer 12

• Intercalated disks (for electrical and mechanical coupling with adjacent cells)
• branching

Question 13

Where is ANP released?

Answer 13

Released by atria

Question 14

Where is BNP released?

Answer 14

Released by ventricles

Question 15

What do ANP and BNP do?

Answer 15

Act to decrease blood pressure during heart failure

Question 16

What is hypertrophy?

Answer 16

Enlargement of individual cells

Question 17

What is hyperplasia?

Answer 17

Multiplication of cells

Question 18

What is atrophy?

Answer 18

Decrease in size of individual cells

Question 19

Where are the pacemaker cells located?

Answer 19

Right atrium of heart

Question 20

What are purkinje fibres?

Answer 20

Large cells found in the ventricle walls of the heart which propagate an electrical signal rapidly to allow the ventricles to contract synchronously.
They have abundant glycogen, sparse myofibrils and extensive gap junction sites

Question 21

Where do purkinje fibres transmit action potentials from?

Answer 21

The atrioventricular node

Question 22

Give some similarities between cardiac and skeletal muscle.

Answer 22

• striated
• similar contraction mechanisms

Question 23

Give some ways in which cardiac muscle differs to skeletal muscle.

Answer 23

• nuclei in cardiac muscle are central (sometimes 2 per cell)
• sarcomere not so well developed
• reduced number of T-tubules associated with sarcoplasmic reticulum
• only one contractile cell type - cardiomyocyte
• cardiomyocytes communicate through gap junctions (intercalated disk)

Question 24

Describe smooth muscle

Answer 24

Spindle shaped with single, central, large nucleus

Question 25

Compare and contrast smooth muscle to other muscle types.

Answer 25

- Can stretch - Not striated - No sarcomeres - No T-tubules - Capable of being stretched substantially - Contraction still relies on actin-myosin interactions - Contraction is slower, more sustained and requires less ATP - May remain contracted for hours or days - Respond to numerous stimuli (nerve signals, hormones, drugs, blood gases) - Form sheets, bundles or layers containing many cells - Each cell has numerous pinocytic caveolae

Question 26

Can skeletal muscle repair itself?

Answer 26

Skeletal muscle cells cannot divide, they generate by mitotic activity of satellite cells

Question 27

Can cardiac muscle repair itself?

Answer 27

Generally considered incapable of regeneration. However new research suggests 1% division. Fibroblasts invade after damage and lay down scar tissue

Question 28

Can smooth muscle repair itself?

Answer 28

Can retain their mitotic activity and form new muscle cells

Question 29

What effect does the sympathetic nervous system have on the heart?

Answer 29

Increases HR

Question 30

What effect does the parasympathetic nervous system have on the heart?

Answer 30

Decreases HR

Question 31

What are the differences between cardiac and smooth muscle?

Answer 31

- No sarcomeres in smooth muscle - Specialised cells/routs for electrical conduction in cardiac muscle - No troponins in smooth muscle

Question 32

Describe events leading to contraction of skeletal muscle

Answer 32

Nerve impulse along motor neuron axon arrives at neuromuscular junction. Impulse prompts release of Ach into synaptic cleft causing local depolarisation of sarcolemma. Voltage-gated Na+ channels open and Na+ ions enter cell

Question 33

What is the role of ionic calcium in contraction?

Answer 33

Ca2+ binds to TnC of troponin. Conformational change moves tropomyosin away from actin’s binding sites. This allows myosin heads to bind actin and contraction begins. Tropomyosin sits in cleft of G-actin ‘spheres’

Question 34

What is Ptosis?

Answer 34

The drooping of upper eyelid which can occur in one or both eyes

Question 35

What is atrophy and hypertrophy in terms of muscle remodelling

Answer 35

Destruction > replacement = atrophy Replacement > destruction = hypertrophy

Question 36

Describe duchene. Muscular dystrophy.

Answer 36

- Most common muscular dystrophy. Inherited through X-linked recessive pattern. - Mutation in the dystrophin gene. Absence of dystrophin allows: - excess calcium to enter muscle cell - calcium taken up by mitochondria, along with water - mitochondria burst. Muscle cells burst - keratins kinase and myoglobin levels are extremely high in the blood. - Multiple skeletal muscle related symptoms and signs - Muscle cells replaced by adipose tissue

Question 37

Describe the pathophysiology of myasthenia gravis

Answer 37

- autoimmune disease - antibodies directed against Ach receptor - 30% reduction in receptor number sufficient for symptoms - endplate ‘invaginations’ in synaptic clefts reduced - reduced synaptic transmission - intermittent muscle weakness

Question 38

What proteins are present in the blood in high quantities over a number of days after a heart attack?

Answer 38

Troponin I&T If these are present in the blood, this is an indication of a heart attack having happened.

Question 39

What is the effect of organophosphate (a type of pesticide) poisoning?

Answer 39

Inhibits the normal function of Ach esterase Ach activity at the neuromuscular junction is potentiated