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MCAT: Biology > Chapter 4: The Nervous System > Flashcards

Chapter 4: The Nervous System Flashcards

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1
Q

Where is the nucleus of a neuron located?

A

In the cell body (soma)

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2
Q

Where are the endoplasmic reticulum and the ribosomes of a neuron contained?

A

In the cell body (soma)

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3
Q

What is myelin produced by in the central nervous system?

A

Oligodendrocytes

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4
Q

What is myelin produced by in the peripheral nervous system?

A

Schwann cells

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5
Q

What carries neural signals away from the soma? What carries them towards the soma?

A
  • Axons carry away

- Dendrites carry towards

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6
Q

What are the nodes of Ranvier critical for?

A

Rapid signal transduction

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7
Q

What are the three components of a synapse?

A
  • Nerve terminal
  • Synaptic cleft
  • Postsynaptic membrane
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8
Q

The cell bodies of neurons of the same type are clustered together into ________.

A

ganglia

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9
Q

The cell bodies of neurons in the same tract are grouped into ________.

A

nuclei

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10
Q

What are tracts?

A
  • In the central nervous system, axons may be bundled together to form tracts
  • Only carry one type of information
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11
Q

Neurons are supported by other cells, what are they called?

A

Glial cells or neuroglia

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12
Q

What is the function of astrocytes?

A

Nourish neurons and form the blood-brain barrier

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13
Q

What is the function of the blood-brain barrier?

A

Controls the transmission of solutes from the bloodstream into nervous tissue

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14
Q

What is the function of ependymal cells?

A

Line the ventricles of the brain and produce cerebrospinal fluid

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15
Q

What is the function of cerebrospinal fluid?

A

Physically supports the brain and serves as a shock absorber

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16
Q

What is the function of microglia?

A

Phagocytic cells that ingest and break down waste products and pathogens in the central nervous system

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17
Q

What is the function of an axon?

A

Transmits an electrical signal (action potential) from the soma to the synaptic knob

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18
Q

What is the function of the axon hillock?

A

Integrates excitatory and inhibitory signals from the dendrites and fires an action potential if the excitatory signals are strong enough to reach the threshold

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19
Q

What is the function of dendrites?

A

Receive incoming signals and carry them to the soma

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20
Q

What is the function of the myelin sheath?

A

Acts as insulation around the axon and speeds conduction

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21
Q

What is the function of the synaptic bouton? Where is it?

A
  • At the end of the axon

- Releases neurotransmitters

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22
Q

How does electrical communication occur?

A

Via ion exchange and the generation of membrane potentials down the length of the axon

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23
Q

How does chemical communication occur?

A

Via neurotransmitter release from the pre-synaptic cell and the binding of these neurotransmitters to the post-synaptic cell

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24
Q

What are Nodes of Ranvier?

A

Exposed areas of myelinated axons that permit saltatory conduction

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25
Q

What is the difference between a nerve and a tract?

A

A nerve may carry multiple types of information, a tract may only carry one

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26
Q

What is the resting membrane potential? How does the inside of the neuron compare to the outside?

A
  • -70 mV

- The inside of the neuron is relatively negative compared to the outside

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27
Q

How do neurons maintain a negative internal environment? (2)

A
  • Selective permeability

- Na+/K+ ATPase

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28
Q

How many ions does the Na+/K+ ATPase move? What does it require?

A
  • Moves 3 Na+ ions out of the cell for every 2 K+ ions moved into the cell
  • Requires 1 ATP
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29
Q

How do the concentrations of Na+ and K+ inside the neuron compare to outside?

A
  • Inside: high K+, low Na+

- Outside: low K+, high Na+

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30
Q

Why is ATP required in the Na+/K+ ATPase? What kind of transport is this?

A
  • Because the ions are moving against their gradients

- Primary active transport

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31
Q

What does excitatory input cause?

A

Depolarization, which raises the membrane potential

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32
Q

What does inhibitory input cause?

A

Hyperpolarization, which lowers the membrane potential

33
Q

What is the threshold value?

A

Usually in the range of -55 to -40 mV

34
Q

What is temporal summation?

A

Multiple signals are integrated during a relatively short period of time

35
Q

What is spatial summation?

A
  • The additive effects are based on the number and location of the incoming signals
  • Signals firing directly on the soma > signals on the dendrites
36
Q

What happens if the neuron is brought to threshold?

A
  • Voltage-gated sodium channels open in the membrane
  • The Na+ wants to go into the cell because it is more negative inside and has a lower Na+ concentration
  • Increase of the resting membrane potential (depolarization)
37
Q

What inactivates sodium channels?

A

When Vm approaches +35 mV

38
Q

How can sodium channels be deinactivated?

A

By bringing the membrane potential near the resting potential, the inactivation of the sodium channels will be reversed, and will be closed

39
Q

What are the three states of sodium channels?

A
  • Closed (before cell reaches threshold, and after inactivation is reversed)
  • Open (threshold to approximately +35 mV)
  • Inactive (+35 mV to resting potential)
40
Q

How does the depolarization of the cell by sodium influence the voltage-gated potassium channels?

A
  • Triggers the potassium channels to open

- Positively charged potassium is driven out of the cell

41
Q

What happens when the potassium channels are open?

A

Restoration of the negative membrane potential (repolarization)

42
Q

What is the function of hyperpolarization?

A

Makes the neuron refractory to further action potentials

43
Q

What is the absolute refractory period?

A

No amount of stimulation can cause another action potential to occur

44
Q

What is the relative refractory period?

A

There must be greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than its resting value

45
Q

What happens when the action potential has fired in one segment of axon, allowing it to become momentarily refractory?

A

Information can only flow in one direction

46
Q

How does an increased length of the axon influence the speed of an action potential?

A

Results in higher resistance and slower conduction

47
Q

How do greater cross-sectional areas influence the speed of an action potential?

A

Allow for faster propagation due to decreased resistance

48
Q

Is the effect of length more significant to the effect of cross-sectional areas?

A

Cross-sectional areas are more significant

49
Q

The membrane is only permeable to ion movement at ___________

A

the nodes of Ranvier

50
Q

What does increased intensity of a stimulus result in?

A
  • Does NOT result in an increased potential difference of the action potential
  • Does increase frequency of firing
51
Q

How does the increase of intracellular calcium allow for the exocytosis of neurotransmitters into the synaptic cleft?

A

Triggers the fusion of the membrane-bound vesicles with the cell membrane at the synapse

52
Q

Neurotransmitter receptors tend to be what? (2)

A
  • Ligand-gated ion channels

- G protein-coupled receptors

53
Q

What are the three mechanisms to remove neurotransmitters from the synaptic cleft?

A

1) Breaking down by enzymatic reactions
2) Brought back into the presynaptic neuron using reuptake carriers
3) Diffuse out of the synaptic cleft

54
Q

What neural structure initiates the action potential?

A

The axon hillock

55
Q

Reflexes only require processing at the level of the ___________

A

spinal cord

56
Q

When reflexes require input from the brain or brainstem, what circuits are used?

A

Supraspinal circuits

57
Q

What is white matter?

A

Axons encased in myelin sheats

58
Q

What is grey matter?

A

Unmyelinated cell bodies and dendrites

59
Q

Does the grey matter lie deeper than the white matter in the brain, or vice-versa?

A

White matter lies deeper than grey matter

60
Q

What are the four divisions of the spinal cord?

A
  • Cervical
  • Thoracic
  • Lumbar
  • Sacral
61
Q

What is the function of the vertabral column?

A

Transmits nerves at the space between adjacent vertebrae

62
Q

Where is the grey and white matter situated in the spinal cord?

A
  • White matter lies on the outside of the cord

- Grey matter is deep within the cord

63
Q

Sensory neurons bring information in from the periphery, and enter where?

A

Enter the dorsal (back) side of the spinal cord

64
Q

Where are the cell bodies of sensory neurons found?

A

In the dorsal root ganglia

65
Q

Where do motor neurons exit the spinal cord?

A

Ventrally, or on the side closest to the front of the body

66
Q

The peripheral component of the automatic nervous system contains how many neurons? What are they?

A
  • Two

- Preganglionic neuron and postganglionic neuron

67
Q

Where is the preganglionic neuron located?

A
  • The soma is in the CNS

- Its axon travels to a ganglion in the PNS

68
Q

How are the preganglionic neuron and postganglionic neuron connected?

A

In the PNS, the axon of the preganglionic neuron synapses on the cell body of the postganglionic neuron, which then affects the target tissue

69
Q

Differentiate the parasympathetic and sympathetic nervous systems.

A
  • Sympathetic: fight-or-flight

- Parasympathetic: rest-or-digest

70
Q

What activates parasympathetic responses? What are its effects?

A
  • Acetylcholine (both preganglionic and postganglionic)
  • Constricts pupils
  • Stimulates flow of saliva
  • Constricts bronchi
  • Slows heartbeat
  • Stimulates peristalsis and secretion
  • Stimulates bile release
71
Q

What activates sympathetic responses? What are its effects?

A
  • Stress
  • Increases heart rate
  • Redistributes blood to muscles of locomotion
  • Increases blood glucose concentration
  • Relaxes the bronchi
  • Decreases digestion and peristalsis
  • Dilates the eyes to maximize light intake
72
Q

What do the sympathetic nervous system neurons release?

A
  • Preganglionic: acetylcholine

- Postganglionic: norepinephrine

73
Q

What does the sympathetic nervous system release into the bloodstream?

A

Epinephrine

74
Q

Which neural circuits control reflexive behaviour?

A

Reflex arcs

75
Q

What is a monosynaptic reflex arc?

A

There is a single synapse between the sensory neuron that receives the stimulus and the motor neuron that responds to it

76
Q

Give an example of a monosynaptic reflex arc.

A

Knee-jerk reflex

77
Q

What is a polysynaptic reflex arc?

A

The sensory neuron may fire onto a motor neuron as well as interneurons that fire onto other motor neurons

78
Q

Give an example of a polysynaptic reflex arc.

A

Stepping on a nail (withdrawal reflex)

MCAT: Biology (12 decks)

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