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MCAT Biology > Ch 4 - The Nervous System > Flashcards

Ch 4 - The Nervous System Flashcards

1
Q

What are neurons?

A

highly specialized cells responsible for the conduction of impulses

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2
Q

How do neurons communicate?

A

using both electrical and chemical forms of communication

  • electrical occurs via ion exchange and the generation of membrane potentials down the length of the axon
  • chemical occurs via neurotransmitter release from the presynaptic cell and the binding of these neurotransmitters to the postsynaptic cell
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3
Q

What are dendrites?

A

appendages that receive signals from other cells

- carry signal toward soma

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4
Q

What are soma?

A

the cell body; the location of the nucleus and organelles like the ER and ribosomes

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5
Q

What is the axon hillock?

A

where the cell body transitions to the axon, and where action potentials are initiated
- integrates excitatory and inhibitory signals from the dendrites and fires and AP if the excitatory signals are strong enough to reach threshold

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6
Q

What is an axon?

A

a long appendage down which an action potential travels

- carry signal away from soma

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7
Q

What is the nerve terminal?

A

(or synaptic bouton) is the end of the axon from which neurotransmitters are released

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8
Q

What is Nodes of Ranvier?

A

exposed areas of myelinated axons that permit saltatory conduction

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9
Q

What is a synapse and the synaptic cleft?

A
  • the synapse consists of the nerve terminal of the presynaptic neuron, the membrane of the postsynaptic cell, and the space between the 2 (synaptic cleft)
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10
Q

What are many axons coated in?

A

myelin, an insulating substance that prevents signal loss

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11
Q

How is myelin created?

A

by oligodendrocytes in the CNS and Schwann cells in the PNS

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12
Q

What does myelin prevent?

A

dissipation of the neural impulse and crossing of neural impulse from adjacent neurons

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13
Q

What are individual axons bundled into?

A

nerves or tracts

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14
Q

What type of information do single nerves carry v tracts?

A
  • single: many types like sensory, motor, or both

- tracts: only one type of information

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15
Q

What is a collection of cell bodies called in the CNS v PNS?

A

CNS: nucleus
PNS: ganglion

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16
Q

What are neuroglia?

A

(or glial cells) other cells within the nervous system in addition to neurons

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17
Q

What do astrocytes do?

A

nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into nervous tissue

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18
Q

What do ependymal cells do?

A

line the ventricles of the brain and produce CSF, which physically supports the brain and serves as a shock absorber

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19
Q

What are microglia and what do they do?

A

phagocytic cells that ingest and break down waste products and pathogens in the CNS

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20
Q

What resting membrane potential do all neurons exhibit?

A

approximately 70 mV
- potassium is high inside the cell and low outside the cell while sodium is high outside the cell and low inside the cell

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21
Q

How is resting potential maintained?

A

using selective permeability of ions as well as the Na+/K+ ATPase

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22
Q

How does the Na+/K+ work?

A

pumps three sodium ions out of the cell for every 2 potassium ions pumped in
- Na wants to go into the cell because the cell is more negative inside and has a lower concentration of Na inside

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23
Q

What type of signals can incoming signals be?

A
  • excitatory: cause depolarization of the neuron

- inhibitory: cause hyperpolarization of the neuron

24
Q

What is the difference between temporal and spatial summation?

A
  • temporal: the integration of multiple signals near each other in space
  • spatial: the addition of multiple signals near each other in space
25
What is an action potential used for?
to propagate signals down the axon
26
What happens to the channels when enough excitatory stimulation occurs?
the cell is depolarized to the threshold voltage and voltage-gated sodium channels open
27
What happens once the voltage-gated sodium channels are opened?
- sodium flows into the neuron due to its strong electrochemical gradient depolarizing the neuron - at the peak of the action potential (~ +35 mV), sodium channels are inactivated and potassium channels open
28
What happens once potassium channels are opened?
- potassium flows out of the neuron due to its strong electrochemical gradient, repolarizing the cell - potassium channels stay open long enough to overshoot the action potential, resulting in a hyperpolarized neuron; then the potassium channels close
29
What restores the sodium and potassium gradients?
- once the potassium channel is closed, the Na+/K+ ATPase brings the neuron back to the resting potential
30
What is the refractory period and the the difference between absolute and relative?
- axon in refractory period while it is hyperpolarized - absolute: cell is unable to fire another action potential - relative: the cell requires a larger than normal stimulus to fire an action potential
31
Why does the impulse propagate down the length of the axon? Why can the action potential only travel in one direction?
- because the influx of sodium in one segment of the axon brings the subsequent segment of the axon to threshold - the fact that the preceding segment of the axon is in its refractory period means that the the action potential can only travel in one direction
32
Where are the neurotransmitters released?
at the nerve terminal into the synapse
33
When to the voltage-gated calcium channels open?
when the action potential arrives at the nerve terminal
34
What does the influx of calcium cause? Where do the neurotransmitters bind?
- fusion of vesicles filled with neurotransmitter with the presynaptic membrane, resulting in exocytosis of neurotransmitter into the synaptic cleft - neurotransmitters bind to the receptors on the postsynaptic cell, which may be ligand-gated ion channels or G protein-coupled receptors
35
Why must neurotransmitters be cleared from the postsynaptic receptors and how are they cleared?
to stop the propagation of the signal - enzymatic degradation - reuptake - diffusion
36
What are the 3 types of neurons in the nervous system?
- motor (efferent) - sensory (afferent) - enter the spinal cord on the dorsal side - internerouns
37
How is the nervous system divided?
- CNS (brain and spinal cord) | - PNS (cranial and spinal nerves)
38
What does white matter and grey matter consist of in the CNS, brain, and the spinal cord?
- CNS: white with myelinated axons, grey with unmyelinated cell bodies and dendrites - brain: white is deeper than grey - spinal cord: grey is deeper than white
39
How is the PNS divided?
somatic (voluntary) | autonomic (automatic)
40
How is the autonomic nervous system divided?
parasympathetic (rest and digest) | sympathetic (fight or flight)
41
How do reflex arcs work?
use the ability of interneurons in the spinal cord to relay information to the source of a stimulus while simultaneously routing it to the brain
42
What is the difference between a monosynaptic and polysynaptic reflex arc?
- mono: the sensory (afferent, presynaptic) neuron fires directly onto the motor (efferent, postsynaptic) neuron - poly: sensory neuron may fire onto a motor neuron as well as interneurons that fire onto other motor neurons
43
Which 2 types of glial cells, if not properly functioning, will make an individual most susceptible to a CNS infection?
- astrocytes nourish neurons and form the blood-brain barrier, which helps protect the brain from foreign pathogens gaining entrance - microglia ingest and break down waste products and pathogens - disruption of wither would increase susceptibility to a CNS infection
44
What type of glial cells are being targeted in an autoimmune disease that cases demyelination of the PNS?
- oligodendrocytes produce myelin in the CNS while Schwann cells produce myelin in the PNS - Schwann cells are being targeted
45
What is saltatory conduction?
signal hops from node to node
46
What is the difference between electrical and chemical transmission in neurons?
- within a neuron, electricity is used to pass signals down the length of the axon - between neurons, chemicals (neurotransmitters) are used to pass signals to the subsequent neuron
47
What neural structure initiates the action potential?
axon hillock
48
What ion is primarily responsible for the fusion of neurotransmitter-containing vesicles with the nerve terminal membrane?
calcium
49
What are the first and second neurons in the autonomic nervous system called?
- 1: preganglionic | - 2: postganglionic
50
What does the myelin sheath do?
- increases the conduction of velocity by insulating segments of the axon so that the membrane is permeable to ions only at the nodes of Ranvier - arranged on the axon discontinuously; the gaps between the segments of myelin are called nodes of Ranvier - action potential jumps from node to node (saltatory conduction)
51
How is the magnitude and speed determined for impulses?
once action potential is triggered, an impulse of a given magnitude and speed is produced
52
When the potential across the axon membrane is more negative than the normal resting potential, what is the state of the neuron?
hyperpolarized, occurs right after an action potential and is caused by excess potassium exiting the neuron
53
Which neurotransmitter is used in the ganglia of both the sympathetic and parasympathetic nervous systems?
Acetylcholine
54
What would happen if a disease blocked the voltage-gated calcium channel?
- no influx of calcium = no release of neurotransmitters | - so the neuron cannot send excitatory signals, neurons cannot communicate
55
What are the consequences of clipping the dorsal root ganglion?
- loss of sensation at that level | - dorsal root contains cell bodies of sensory neurons only

MCAT Biology (12 decks)

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