Nerve Cell A&P Pt.3

Question 1

What diameter axons propagate nerve impulses faster: Larger diameter or smaller diameter?

Answer 1

Larger.

Question 2

What are the 3 categories of nerve fiber diameters?

Answer 2

1. A fibers.
2. B fibers.
3. C fibers.

Question 3

How wide are A fibers?

Answer 3

5-20 um.

Question 4

Are A fibers myelinated or unmyelinated?

Answer 4

Myelinated.

Question 5

What type of refractory period do A fibers have?

Answer 5

Brief absolute refractory periods.

Question 6

How quickly do A fibers conduct nerve impulses?

Answer 6

12-130 m/sec. .

Question 7

What types of sensory neuron axons contain A fibers?

Answer 7

Those associated with touch, pressure, joint position, and some thermal sensations (rapid temperature change).

Question 8

What type of motor neuron axons contain A fibers?

Answer 8

Those that conduct impulses to skeletal muscle.

Question 9

How wide are B fibers?

Answer 9

2-3 um.

Question 10

Are B fibers myelinated or unmyelinated?

Answer 10

Myelinated.

Question 11

How rapidly do B fibers conduct nerve impulses?

Answer 11

~15 m/sec. .

Question 12

What type of refractory period do B fibers have?

Answer 12

Absolute refractory periods that are longer than in A fiber.

Question 13

What types of sensory neuron axons contain B fibers?

Answer 13

Those sending nerve impulses from the viscera to the brain and spinal cord.

Question 14

What types of motor neuron axons contain A fibers?

Answer 14

All autonomic ones that extend from the brain and spinal cord to autonomic ganglia.

Question 15

How wide are C fibers?

Answer 15

0.5-1.5 um.

Question 16

Are C fibers myelinated or unmyelinated?

Answer 16

Unmyelinated.

Question 17

How rapidly are nerve impulses conducted in C fibers?

Answer 17

0.5-2 m/sec. .

Question 18

What type of refractory period do C fibers have?

Answer 18

Absolute refractory period, longest of the three fiber types.

Question 19

What types of sensory neuron axons contain C fibers?

Answer 19

Those associated with pain, touch, pressure, temperature from skin (gradual temperature change), and pain impulses from viscera.

Question 20

What types of motor neuron axons contain A fibers?

Answer 20

Autonomic ones that extend from the autonomic ganglia to the glands, heart, and smooth muscle.

Question 21

What are 3 motor functions of B and C fibers?

Answer 21

1. Pupil constriction and dilation.
2. Heartrate decrease and increase
3. Urinary bladder contraction and relaxation.

Question 22

What is the pre-synaptic neuron?

Answer 22

The neuron sending the signal.

Question 23

What is the post-synaptic neuron?

Answer 23

The neuron receiving the signal.

Question 24

What does the term axodendritic refer to?

Answer 24

The movement or communication of something from the axon of one neuron to the dendrite of another neuron.

Question 25

What does the term axosomatic refer to?

Answer 25

The movement or communication of something from the axon of one neuron to the soma of another neuron.

Question 26

What does the term axoaxonic mean?

Answer 26

The movement or communication of something from the axon of one neuron to the axon of another neuron.

Question 27

What are the 2 types of synapse?

Answer 27

1. Chemical. 2. Electrical.

Question 28

Which synapse is faster: chemical synapse or electrical synapse?

Answer 28

Electrical synapse.

Question 29

How are signals communicated through an electrical synapse?

Answer 29

Gap junctions.

Question 30

What 3 kinds of tissues utilize electrical synapses?

Answer 30

1. Visceral smooth muscle. 2. Cardiac muscle. 3. Embryo.

Question 31

What feature of an electrical synapse allows for its use in the heart?

Answer 31

Synchronized messaging, allowing the heart to beat as one unit.

Question 32

What is the synaptic cleft?

Answer 32

The space between the pre- and post-synaptic neurons that allows for indirect communication.

Question 33

What is the synaptic cleft filled with?

Answer 33

Interstitial fluid.

Question 34

What does the nerve impulse in the presynaptic neuron cause to occur when it reaches the dendrites and telodendria?

Answer 34

It causes the release of neurotransmitters.

Question 35

What happens after the binding of the neurotransmitters to the post-synaptic neuron?

Answer 35

A postsynaptic signal (a type of graded potential) is produced.

Question 36

What do the neurotransmitters do once released?

Answer 36

They diffuse through the synaptic cleft and bind to receptors on the plasma membrane of the postsynaptic neuron.

Question 37

What do presynaptic cells covert electrical signals into?

Answer 37

Chemical signals.

Question 38

What do postsynaptic cells convert electrical signals into?

Answer 38

Chemical signals.

Question 39

When the nerve impulse reaches the synaptic end bulb of the pre-synaptic axon, what voltage-gated channels are opened?

Answer 39

Ca2+ by depolarization.

Question 40

Which direction does Ca2+ flow through the open voltage-gated Ca2+ channels?

Answer 40

Into the cell membrane.

Question 41

What does the change in membrane potential in the synaptic end bulb trigger?

Answer 41

The exocytosis of synaptic vesicles.

Question 42

What do the vesicles merge with to release the neurotransmitters into the synaptic cleft?

Answer 42

Plasma membrane.

Question 43

What specific type of channels do the neurotransmitters bind to on the postsynaptic plasma membrane?

Answer 43

Ligand-gated channels.

Question 44

What does the binding to ligand-gated channels allow for the influx of?

Answer 44

Na+, K+, or Cl-.

Question 45

What does the influx of ions cause to form?

Answer 45

A postsynaptic potential.

Question 46

What occurs when enough Na+ has entered the cell membrane?

Answer 46

Depolarization has reached the threshold, triggering an AP.

Question 47

What are the 2 potentials that neurotransmitters could induce in the post-synaptic cell?

Answer 47

1. Excitatory. 2. Inhibitory.

Question 48

What induces excitatory potential or excitatory post synaptic potentials (EPSP)?

Answer 48

Depolarization.

Question 49

What ion(s) causes EPSP?

Answer 49

Na+ moving through open cation channels.

Question 50

What induces inhibitory potential or inhibitory post synaptic potentials (IPSP)?

Answer 50

Hyperpolarization.

Question 51

What ion(s) causes IPSP?

Answer 51

Cl- moving through open anion channels and some K+.

Question 52

What are the 3 ways neurotransmitters are removed?

Answer 52

1. Diffusion. 2. Enzymatic degradation. 3. Uptake by cells.

Question 53

How does diffusion remove neurotransmitters?

Answer 53

They diffuse away from the synaptic cleft, likely into the post-synaptic cell.

Question 54

How does enzymatic degradation remove neurotransmitters?

Answer 54

Enzymes breakdown the neurotransmitters in the synaptic cleft. ex: Acetylcholinesterase

Question 55

How does uptake by cells remove neurotransmitters?

Answer 55

The neurotransmitters are moved back to the presynaptic neuron for reuse in a process called reuptake. ex: Norepinephrine.

Question 56

How many synapses does the typical CNS neuron receive input from?

Answer 56

1-10K.

Question 57

What is summation?

Answer 57

The process of integrating neuron inputs that occurs in the trigger zone.

Question 58

In EPSPs, what is the correlation between the level of summation and the chance of the threshold being achieved?

Answer 58

Positive.

Question 59

What are the 2 types of summation?

Answer 59

1. Spatial. 2. Temporal.

Question 60

What is spatial summation?

Answer 60

When a build-up of neurotransmitters in several presynaptic end bulbs are simultaneously released.

Question 61

What is temporal summation?

Answer 61

When a build-up of neurotransmitters is released by one presynaptic end bulb 2+ times in rapid succession.

Question 62

Can spatial and temporal summation occur at the same time?

Answer 62

Yes.

Question 63

Are postsynaptic neurons only connected to one presynaptic neuron?

Answer 63

No, they are connected to multiple neurons that are potentially releasing conflicting neurotransmitters.

Question 64

What ultimately determines the effect of neurotransmitters on the postsynaptic neuron?

Answer 64

The sum of all the excitatory and inhibitory neurotransmitters.

Question 65

What is required for a EPSP to occur?

Answer 65

The total excitatory potential must be greater than the total inhibitory potential, but less than the threshold.

Question 66

What is required for a nerve impulse to occur?

Answer 66

The total excitatory potential must be greater than the total inhibitory potential and the threshold must be reached.

Question 67

What is required for an IPSP to occur?

Answer 67

The total inhibitory potential must be greater than the total excitatory potential.

Question 68

What 3 things occur as a result of IPSP achievement?

Answer 68

1. Membrane hyperpolarization. 2. Inhibition of postsynaptic neuron. 3. Inability to generate nerve impulses.

Question 69

What are Renshaw cells?

Answer 69

Inhibitory neurons in the spinal cord that prevent excess skeletal muscle contraction.

Question 70

How do Renshaw cells complete their function?

Answer 70

They release glycine at inhibitory synapses with somatic motor neurons.

Question 71

What does strychnine poison bind to?

Answer 71

Glycine receptors.

Question 72

What does strychnine poison cause to occur?

Answer 72

The excitation/inhibition balance in the CNS to be disturbed by allowing for uninhibited generation of nerve impulses by motor neurons.

Question 73

What do skeletal muscles look like in an individual that has ingested strychnine?

Answer 73

Fully contracted and unable to relax.