Topic 2 - Nerve and Muscle

Question 1

In the CNS white matter contains large numbers of nerve cell bodies.

Answer 1

False

The white matter contains large numbers of myelinated nerve fibers. The gray matter contains large numbers of nerve cell bodies.

Question 2

In the CNS the myelin of axons is formed by oligodendrocytes.

Answer 2

True

Question 3

In the CNS the end-feet of astrocytes cover the capillaries of the brain.

Answer 3

True

The end-feet of the astrocytes form part of the blood-brain barrier that isolates the extracellular fluid around the neurons from changes in the composition of the blood.

Question 4

In the CNS the extracellular fluid surrounding nerve cells is insulated from changes in the composition of the plasma.

Answer 4

True

The end-feet of the astrocytes form part of the blood-brain barrier that isolates the extracellular fluid around the neurons from changes in the composition of the blood.

Question 5

The axons of peripheral nerves are protected by three layers of connective tissue.

Answer 5

True

Peripheral axons are protected by the epineurium, the perineurium, and the endoneurium.

Question 6

The axons of peripheral nerves are always associated with Schwann cells.

Answer 6

True

All peripheral axons are associated with Schwann cells.

Question 7

The axons of peripheral nerves are always covered by a layer of myelin.

Answer 7

False

All peripheral axons are associated with Schwann cells but only the larger fibers are covered by layers of myelin.

Question 8

The axons of peripheral nerves only conduct action potentials from the CNS to a target organ.

Answer 8

False

Efferent (motor) fibers convey action potentials from the CNS to target organs while afferent (sensory) fibers convey action potentials from sense organs and other receptors to the CNS.

Question 9

The action potential of a single nerve fibre is caused by a large change in the permeability of the membrane to sodium.

Answer 9

True

Question 10

The action potential of a single nerve fibre is terminated when the sodium channels have inactivated.

Answer 10

True

Question 11

The action potential of a single nerve fibre can summate with an earlier action potential.

Answer 11

False

Action potentials don’t summate.

Question 12

The action potential of a single nerve fibre becomes larger as the stimulus is increased above threshold.

Answer 12

False

Once the stimulus intensity has reached threshold, an action potential is elicited but the amplitude of the action potential does not increase further with increasing stimulus strength. The action potential is all or none. When one action potential has passed along an axon the nerve passes through its refractory period and a second action potential cannot occur until the membrane regains its excitability.

Question 13

The velocity of action potential propagation is faster size for size in myelinated axons than in unmyelinated axons.

Answer 13

True

Question 14

The velocity of action potential propagation is faster the larger the diameter of the nerve fiber.

Answer 14

True

Question 15

The velocity of action potential propagation is independent of the thickness of the myelin.

Answer 15

False

Myelin thickness and internodal distance increase with increasing fiber diameter. Thus large myelinated nerve fibers conduct faster than small myelinated (or unmyelinated) fibers.

Question 16

The velocity of action potential propagation will fall if an axon loses its myelin sheath (demyelination).

Answer 16

True

If the myelin sheath is lost, saltatory conduction cannot occur and the speed of conduction falls dramatically.

Question 17

During an epsp the membrane potential of the post-synaptic neuron always depolarizes.

Answer 17

True

Question 18

Unlike action potentials, epsps can summate to produce larger depolarizations of the postsynaptic membrane.

Answer 18

True

Question 19

The effects of a synaptic transmitter are always terminated by enzymatic destruction.

Answer 19

False

The actions of synaptic transmitters are terminated by enzymatic destruction, uptake, or diffusion away from the synaptic region.

Question 20

Both epsps and ipsps can result from activation of second-messenger systems.

Answer 20

True

Question 21

During an ipsp the postsynaptic membrane hyper-polarizes.

Answer 21

True

Ipsps hyperpolarize the membrane potential and this makes the postsynaptic cell less excitable.

Question 22

Ipsps alter the threshold for action potential generation.

Answer 22

False

Ipsps hyperpolarize the membrane potential and this makes the postsynaptic cell less excitable. They do not alter the threshold for action potential generation. The release of a synaptic transmitter in response to a nerve impulse occurs by exocytosis and this is triggered by the entry of calcium into the nerve terminal.

Question 23

Both excitatory and inhibitory synaptic transmission is triggered by an influx of calcium into the presynaptic nerve terminal.

Answer 23

True

The release of a synaptic transmitter in response to a nerve impulse occurs by exocytosis and this is triggered by the entry of calcium into the nerve terminal.

Question 24

Excitation of a motor nerve fiber leads to the contraction of all the muscle fibers innervated by its branches.

Answer 24

True

A motor nerve together with the muscle fibers it innervates is called a motor unit.

Question 25

The epp is the result of a summation of many mepps.

Answer 25

True

Question 26

The epp is the result of an increase in the permeability of the junctional membrane to chloride.

Answer 26

False

The end-plate potential is the result of an increase the permeability of the junctional membrane to sodium and potassium leading to depolarisation.

Question 27

At the neuromuscular junction the cholinergic receptors are muscarinic.

Answer 27

True

The junctional receptors are nicotinic cholinergic receptors and these receptors can be blocked by curare.

Question 28

Endplate potentials can be prolonged by drugs that inhibit acetylcholinesterase.

Answer 28

True

If acetylcholinesterase is inhibited, the acetylcholine released by the motor nerve endings is not destroyed and can continue to stimulate the nicotinic receptors. Very prolonged action of acetylcholine ultimately leads to depolarization of the muscle and block of neuromuscular transmission.

Question 29

All muscle cells contain actin and myosin.

Answer 29

True

Skeletal muscle is striated.

Question 30

Skeletal muscle has the same structure as cardiac muscle.

Answer 30

False

Skeletal and cardiac muscle are both striated but the organization of each differs considerably.

Question 31

In skeletal and cardiac muscle, actin is the major protein of the thin filaments.

Answer 31

True

Question 32

The myofibrils of skeletal muscle are surrounded by the sarcoplasmic reticulum.

Answer 32

True

Question 33

Skeletal muscle has a system of T tubules while smooth muscle does not.

Answer 33

True

Skeletal muscle fibers are large multinucleated cells with a well-developed T system. Unlike cardiac muscle, individual fibers are not coupled via gap junctions.

Question 34

The sarcoplasmic reticulum acts as a store of Ca2+ for the contractile process.

Answer 34

True

Question 35

Ca2+ entry across the plasma membrane is important in sustaining the contraction of cardiac muscle.

Answer 35

True

Question 36

A muscle will relax when intracellular Ca2+ is raised.

Answer 36

False

Muscles relax when Ca2+ is pumped out of the sarcoplasm (i.e. when intracellular Ca2+ falls).

Question 37

A rise in intracellular Ca2+ allows actin to interact with myosin.

Answer 37

True

Question 38

In skeletal muscle a motor unit consists of a single motor neuron and the muscle fibers it innervates.

Answer 38

True

Question 39

In skeletal muscle the action potential propagates from the neuromuscular junction to both ends of the muscle fiber.

Answer 39

True

Question 40

In skeletal muscle the muscle action potential is an essential step in excitation-contraction coupling.

Answer 40

True

Question 41

In skeletal muscle the muscle fibers are electrically coupled so that one nerve fiber can control the activity of several muscle fibers.

Answer 41

False

Skeletal muscle fibers act independently of each other, unlike cardiac and smooth muscle cells which are linked by gap junctions.

Question 42

In skeletal muscle the energy for muscle contraction comes from the hydrolysis of ATP.

Answer 42

True

Question 43

In skeletal muscle the muscle can contract by more than two-thirds of its resting length.

Answer 43

False

Skeletal muscle contracts by about one-fifth of its resting length.

Question 44

Neurones may be myelinated by microglia.

Answer 44

False

Question 45

Neurones secrete NTs from their nerve terminals in response to action potentials.

Answer 45

True

Question 46

Neurones are the most abundant cell type in the brain.

Answer 46

False

Question 47

Neurones often contain swellings at the nerve endings known as synaptic battons.

Answer 47

False

Question 48

Neurones conduct information following sub-threshold signal detection.

Answer 48

False

Question 49

Compound action potentials increase in amplitude as the stimulus strength is increased.

Answer 49

True

This is due to the presence of multiple axons with varying thresholds.

Question 50

ONE action potential takes in the order of 1-2 seconds to be observed.

Answer 50

False

Question 51

Generation of an action potential decreases the Na+ conductance.

Answer 51

False

Question 52

Action potentials induce nerve conductance velocities that are solely determined by axon diameter.

Answer 52

False

Question 53

Action potentials can be propagated by sub threshold stimuli eliciting active voltage changes

Answer 53

False

Question 54

During skeletal muscle contraction the A and I bands do not change length.

Answer 54

False

Question 55

During skeletal muscle contraction cross bridges are formed between actin and myosin.

Answer 55

True

Question 56

During skeletal muscle contraction minimal tension can be generated when the muscle is close to its normal resting length.

Answer 56

False

Question 57

During skeletal muscle contraction the myofilaments change length.

Answer 57

False

Question 58

During skeletal muscle contraction calcium is released from the T tubule.

Answer 58

False