Histology

Question 1

How many nerves is each fibre of skeletal muscle innervated by?

Answer 1

1,however one neuron innervates multiple muscle fibres (motor unit)

Question 2

What structures helps with proprioception (length and tension)

Answer 2

Muscle spindles and golgi tendon organs

Question 3

What does the basal ganglia help with?

Answer 3

Maintaining tone and posture

Question 4

What are primary muscle diseases called?

Answer 4

Myopathies

Question 5

Why does muscle have to be fresh-frozen not fixed with aldehyde?

Answer 5

So enzymes are active (need to thaw so reactions occur again and can see the products of reaction via dyes) - oxidative enzyme activity

Question 6

What are the 2 broad types of muscle fibres?

Answer 6

Slow twitch (type 1, oxidative, fatigue resistant - stain red)
Fast twitch (fatigue rapidly. 2 A = glycolytic and oxidative 2B = relies on glycolysis - stain white)

Question 7

Motor unit

Answer 7

A lower motor neuron and the fibres it innervates. All fibres innervated by this neuron will be either fast or slow twitch.

Size of motor unit varies between muscles - smaller units when more dexterity and co-ordination is needed. eg many small motor units in hand.

Question 8

Denervation and Reinnervation

Answer 8

Loss of innervation causes fibre atrophy.
Adjacent motor units will attend to reinnervate the fibres by collateral sprouting.
This creates larger motor unit and fibres may switch to become other type of fibre (eg fast becomes slow twitch fibre)

Question 9

Basic unit of contraction is called a

Answer 9

Sarcomere

Question 10

Sarcomere consists of

Answer 10

Thick (myosin) and thin (actin) filaments.
Actin attached to z disc (edges of sarcomere), myosin in middle of sarcomere in A-band, darker. Where only actin is lighter in I-band.

Several proteins at the z-line (a-actinin, titin, nebulin, desmin)

Question 11

Sliding filament theory

Answer 11

Energy required from hydrolysis ATP to ADP for movement of myosin head

Power stroked releases ADP.

Shortening due to filaments sliding, not actin or myosin changing length.

Initiated by increased cytosolic Ca2+

Question 12

How can you test for muscle damage?

Answer 12

When muscle fibres damaged, creatine kinase is released. Increased levels of CK = damage

Question 13

What does creatine kinase (CK) help do?

Answer 13

Replenish creatine phosphate, a short term energy store.

Question 14

Where do you get all your mitochondrial DNA from?

Answer 14

Mother

Question 15

What is heteroplasmy?

Answer 15

Different organs and cells contain different amounts of the mutated DNA in their mitochondria.

Question 16

Genetic dysfunction of mitochondria

Answer 16

Complex 4 produces brown staining which obscures the complex 2 staining.
Diagnostic marker of mitochondrial pathology.

Question 17

Mechanism to deal with strain on cell membrane in sarcomere

Answer 17

extracellular protein joins to intracellular membrane l(inked to sarcoglycans), inside of membrane protein called dystophin joins it all to actin.

Question 18

Dystrophin

Answer 18

Links actin to transmembrane complex for stability.
Is x-linked as gene for it is on Xp21.
Mutations can cause the protein not to be formed or to be too short.
Women can carry disease. Few women, may manifest disease due to lyonization.

Question 19

Neuromuscular transmission

Answer 19

Nerve impulse down axon, causes pre-synaptic vesicle containing ACh to be released into cleft.

ACh bind to receptor.
Cation entry results in depolarisation, endplate potential.

An action potential travels across muscle cell membrane into T-tubule system.

Calcium released from sarcoplasmic reticulum leading to activation of contraction.

Question 20

Disorders of neuromuscular transmission

Answer 20

Not enough ACh receptors due to anti-AChR antibodies, causes variable weakness, fast to fatigue = Myasthenia gravis.

Acetyl cholinesterase inhibitors can improve muscle function

Question 21

Myelinated sheath

Answer 21

Schwann cells responsible for myelin sheath (insulator) in PNS.
One cell responsible for one segment of myelin.

Nodes of Ranvier lie between myelin segments, where depolarisation of membrane occurs. Conduction much faster as skips over the insulating myelin sheath.

Myelination allows saltatory conduction.

Question 22

Types of peripheral neuropathies

Answer 22

Neuronopathies = damage to motor or sensory neurons

Axonopathies = damage to axons

Demyelination = selective damage to myelin sheaths

Question 23

Axonal degeneration / regeneration

Answer 23

Injury to axon, globules of myelin and axon debris form, initially within Schwann cell.
Axonal sprouts form from proximal part of damaged axon and grow along columns of proliferating Schwann cells.
Regenerated axons can remyelinate.

Question 24

Demyelination

Answer 24

Injury to Schwann cell in PNS. Remyelination results in thinner sheath. Slower conduction.