Skeletal and Cardiac Muscle

Question 1

What are the 3 muscle tissue types?

Answer 1

+ Skeletal
+ Smooth
+ Cardiac

Question 2

What is skeletal muscle also known as?

Answer 2

Voluntary muscle; striated muscle

Question 3

What are the 5 characteristics of skeletal muscle cells/fibres?

Answer 3

1. Multinucleated
2. Contains many mitochondria
3. Transverse (T) tubules
4. Myofibrils and sarcomeres
5. Specific names for some of the intracellular structures

Question 4

In a skeletal muscle cell/fibre, what is the sarcolemma?

Answer 4

Plasma membrane

Question 5

In a skeletal muscle cell/fibre, what is the sarcoplasm?

Answer 5

Cytoplasm

Question 6

In a skeletal muscle cell/fibre, what is the sarcoplasmic reticulum?

Answer 6

Smooth ER

Question 7

What are features of skeletal muscle?

Answer 7

+ Voluntary, striated
+ Attached to bone
+ Under voluntary control
+ Involved in interaction of the body with external environment

Question 8

What are myofibrils?

Answer 8

The structures that give skeletal (and cardiac muscle) their characteristic striated appearance

Question 9

What are striations a result of?

Answer 9

The orderly arrangements of thick and thin filaments

Question 10

What are the structural features of cardiac muscle?

Answer 10

+ Striations
+ Muscle fibres
+ Intercalated discs
+ Nucleus

Question 11

What are features of cardiac muscle?

Answer 11

+ Structurally like skeletal muscle

+ Functionally like smooth muscle

+ Activity dependent upon:

• intrinsic properties
• hormones
• ANS

Question 12

How many nuclei do cardiac muscle cells have?

Answer 12

One to two nuclei, centrally located

Question 13

What mechanism does cardiac muscle use to contract?

Answer 13

The sliding filament mechanism, as it is striated

Question 14

Cardiac muscle is made up of branching cells with what other structures?

Answer 14

INTERCALATED DISCS with desmosomes and GAP JUNCTIONS

Question 15

What are gap junctions critical to in cardiac muscle?

Answer 15

The heart’s ability to be electrically coupled

Question 16

What ability do nodal cells have?

Answer 16

The ability to stimulate their own actions potentials - called automaticity or auto-rhythmicity

Question 17

What is the absolute refractory period of cardiac muscle (cells)?

Answer 17

250ms

Question 18

What is the purpose of a refractory period?

Answer 18

Prevents tetanic contractions which would interfere with the heart’s ability to pump

Question 19

What is the structural relevance of intercalated discs in cardiac muscle?

Answer 19

Provides a mechanical connection between adjacent cardiac muscle cells

Question 20

What is the functional relevance of intercalated discs in cardiac muscle?

Answer 20

Provides an electrical connection between adjacent cardiac muscle cells

Question 21

What are features of gap junctions?

Answer 21

+ Constructed from a hexagonal array of protein subunits - connexins

+ Sites of low electrical resistance between cells

+ Act as communicating channels - connexon

Question 22

What is the diameter of the central pore in a gap junction?

Answer 22

1.5 nm

Question 23

What size of molecules can pass through the central pore in a gap junction?

Answer 23

Small molecules (<500 MW) pass through

Question 24

How does skeletal muscle become activated?

Answer 24

Neurons from the primary motor cortex in the brain synapse on the motor neuron, which projects to the periphery and activates the skeletal muscle

Question 25

Where is the motor neuron located?

Answer 25

In the grey matter of the ventral horn

Question 26

What makes up a motor unit?

Answer 26

Axon and muscle fibres

Question 27

What is a motor unit defined as?

Answer 27

The motor neuron and the skeletal muscle fibres it innervates

Question 28

What is the link between motor neurons and muscle fibres?

Answer 28

One motor neuron innervates many muscle fibres, but one muscle fibre is innervated by only one motor neuron

Question 29

What is the only mechanism by which action potentials are initiated in skeletal muscle?

Answer 29

By stimulation of the nerve fibres to a skeletal muscle

Question 30

What are motor neurons also known as?

Answer 30

Somatic efferent neurons

Question 31

What are some physical features of axons of motor neurons?

Answer 31

+ Myelinated | + Largest-diameter axons in the body

Question 32

Axons of motor neurons propagate action potentials at high velocities - what does this then allow?

Answer 32

Signals from the CNS to travel to skeletal muscle fibres with minimal delay

Question 33

What do axon terminals of a motor neuron contain?

Answer 33

Vesicles similar to the vesicles found at synaptic junctions between two neurons

Question 34

What do the vesicles found at the axon terminals contain?

Answer 34

Neurotransmitter - acetylcholine (ACh)

Question 35

What region is known as the motor end plate?

Answer 35

The region of muscle fibre plasma membrane that lies directly under the terminal portion of the axon

Question 36

What is the neuromuscular junction?

Answer 36

The junction of an axon terminal with the motor end plate

Question 37

Once ACh is released into the synaptic cleft, where does it go?

Answer 37

Ach is rapidly degraded enzymatically by the action of acetylcholinesterase

Question 38

What is the role of the nicotinic cholinergic receptor?

Answer 38

It binds (to) two ACh molecules, opening a nonspecific monovalent cation channel

Question 39

What does the open nonspecific monovalent cation channel allow to pass?

Answer 39

Na+ and K+

Question 40

What happens to acetylcholine (ACh)?

Answer 40

1. Combines with nicotinic receptors OR 2. Metabolised by acetylcholinesterase (AChE)

Question 41

What do action potentials arriving at the axon terminal do?

Answer 41

Open gated Ca2+ channels

Question 42

What is myasthenia gravis?

Answer 42

An autoimmune disease that causes muscle weakness that increases during periods of activity and improves after periods of rest

Question 43

What actions are especially susceptible in myasthenia gravis?

Answer 43

``` + Eye and eyelid movement + Facial expression + Chewing + Talking + Swallowing + respiration ```

Question 44

How can myasthenia gravis affect the respiratory muscles?

Answer 44

Can cause paralysis of them

Question 45

What is the result of the production of auto-antibodies?

Answer 45

+ Most commonly directed against NACh receptors + Some impair the ability of ACh to bind to receptors + Some lead to the destruction of receptors

Question 46

What are some different types of muscle myopathies?

Answer 46

``` + Myositis + Muscular dystrophy + Myasthenia + Myotonia + Channelopathy + Metabolic myopathies ```

Question 47

What is myositis?

Answer 47

Inflammation

Question 48

What is muscular dystrophy?

Answer 48

Inherited disorders with progressive weakness

Question 49

What is myasthenia?

Answer 49

Fatiguable weakness (worse on exercise)

Question 50

What is myotonia?

Answer 50

Sustained contraction/slow relaxation

Question 51

What is channelopathy?

Answer 51

Ion channel disorders

Question 52

What are metabolic myopathies?

Answer 52

Metabolic/enzyme defects