Chapter 12 Flashcards
(127 cards)
1
Q
What are the three main functions of the nervous system?
A
The nervous system collects information, processes and evaluates it, and initiates a response to the information
2
Q
What is the difference between the central nervous system (CNS) and peripheral nervous system (PNS)?
A
The CNS consists of the brain and spinal cord, while the PNS includes nerves and ganglia
3
Q
What is the difference between the sensory and motor nervous systems
A
The sensory nervous system (afferent) receives sensory information and sends it to the CNS, while the motor nervous system (efferent) transmits motor output from the CNS to effectors.
4
Q
What are the two divisions of the sensory and motor systems?
A
The sensory system has somatic and visceral divisions, while the motor system has somatic and autonomic (with sympathetic and parasympathetic) divisions.
5
Q
What is the difference between cranial and spinal nerves?
A
Cranial nerves extend from the brain, while spinal nerves extend from the spinal cord.
6
Q
What is the functional classification of nerves?
A
Sensory nerves transmit signals to the CNS, motor nerves transmit signals from the CNS, and mixed nerves contain both sensory and motor neurons.
7
Q
what is a ganglion?
A
A ganglion is a cluster of neuron cell bodies in the peripheral nervous system (PNS).
8
Q
cranial nerves extend from
A
brain
9
Q
spinal nerves extend from
A
spinal cord
10
Q
a ganglion is a
A
cluster of neuron cell bodies in the PNS
6
11
Q
What are the main characteristics of neurons?
A
Excitability, conductivity, secretion, extreme longevity, and amitotic.
12
Q
What does “excitability” in a neuron mean?
A
Excitability is the neuron’s ability to respond to a stimulus, causing a change in the cell’s membrane potential.
13
Q
What does “conductivity” in a neuron refer to?
A
Conductivity refers to the neuron’s ability to propagate electrical signals, with voltage-gated channels opening sequentially along the membrane.
14
Q
What is “secretion” in the context of a neuron?
A
Secretion is the release of neurotransmitters in response to electrical activity, which then influence target cells.
15
Q
What does “extreme longevity” mean for neurons?
A
Neurons can live throughout a person’s lifetime
16
Q
What does “amitotic” mean in relation to neurons?
A
after fetal development, most neurons lose the ability to undergo mitosis and do not replicate.
17
Q
What is the cell body (soma) of a neuron?
A
The cell body (soma) contains the nucleus, initiates some graded potentials, receives others from dendrites, and conducts these potentials to the axon.
18
Q
What are dendrites?
A
Dendrites are short, unmyelinated processes that branch off the cell body and receive input to transfer to the cell body.
18
Q
What is the function of the chromatophilic substance (Nissl bodies) in the neuron?
A
The Nissl bodies are made of ribosomes (free and bound) and are involved in protein synthesis within the neuron.
19
Q
What is the function of the axon in a neuron?
A
The axon conducts action potentials and releases neurotransmitters at the synaptic knobs to communicate with other neurons, muscle cells, or glands
20
Q
What is the axon hillock?
A
The axon hillock is the triangular region of the soma where the axon attaches to the cell body
21
Q
What are axon collaterals
A
Axon collaterals are branches that extend from the main axon
22
Q
What are telodendria (axon terminals)?
A
Telodendria are the fine branches at the end of the axon, which terminate in synaptic knobs.
23
Q
What are synaptic knobs (terminal boutons)?
A
Synaptic knobs are the tips of telodendria that house synaptic vesicles containing neurotransmitter.
24
What are multipolar neurons
Multipolar neurons have many dendrites and one axon, and are the most common type of neuron.
25
What are bipolar neurons?
Bipolar neurons have one dendrite and one axon, and are found in limited numbers, such as in the retina of the eye.
26
What are unipolar (pseudounipolar) neurons?
Unipolar neurons have one process that extends from the cell body, which splits into a peripheral process (receptive dendrites) and a central process (leading to synaptic knobs in the CNS).
27
What are anaxonic neurons?
Anaxonic neurons have dendrites but no axons
28
What are sensory neurons (afferent neurons)
Sensory neurons conduct input from somatic and visceral receptors to the CNS, and most are unipolar (a few are bipolar).
29
What are motor neurons (efferent neurons)?
Motor neurons conduct output from the CNS to somatic and visceral effectors, and all are multipolar.
30
What are interneurons (association neurons)?
Interneurons receive, process, and integrate information from many other neurons, communicate between sensory and motor neurons, and are located within the CNS, making up 99% of our neurons. They are generally multipolar.
31
What is a synapse?
A synapse is the place where a neuron connects to another neuron or an effector.
32
What are the two types of synapses?
The two types of synapses are chemical and electrical, with chemical synapses being far more common.
33
What is an electrical synapse
An electrical synapse is where presynaptic and postsynaptic neurons are bound together by gap junctions, allowing for fast signal transmission without synaptic delay
34
What are the components of a chemical synapse?
A chemical synapse consists of a presynaptic neuron's axon terminal, a synaptic cleft, and a postsynaptic neuron's receptor.
35
What happens during synaptic communication?
Neurotransmitters are released from synaptic vesicles in the presynaptic neuron, diffuse across the synaptic cleft, and bind to receptors on the postsynaptic neuron, initiating a postsynaptic potential.
36
What is a synaptic delay?
A synaptic delay is the time it takes for neurotransmitter release, diffusion across the synaptic cleft, and receptor binding to occur.
37
What are glial cells?
Glial cells are nonexcitable support cells found in the CNS and PNS that protect and nourish neurons
38
How do glial cells compare in number to neurons?
Glial cells are approximately the same number as neurons in the nervous system.
39
What percentage of the nervous system's volume do glial cells account for?
Glial cells account for about half of the volume of the nervous system.
40
What are some general characteristics of glial cells?
Glial cells are capable of mitosis, protect and nourish neurons, and provide physical scaffolding for nervous tissue.
41
What role do glial cells play during neural development?
Glial cells guide migrating neurons during development.
42
Why are glial cells critical for synapse function?
Glial cells are critical for normal function at neural synapses.
43
What shape are astrocytes, and where do their processes end?
Astrocytes are star-shaped cells, and their processes end in perivascular feet.
44
What is the most abundant glial cell in the CNS?
Astrocytes are the most abundant glial cell in the CNS.
45
How do astrocytes help form the blood-brain barrier?
Astrocytes wrap their feet around brain capillaries to help form the blood-brain barrier.
46
What do astrocytes regulate in the brain?
Astrocytes regulate tissue fluid composition, such as potassium concentration around neurons.
47
What structural role do astrocytes play in the CNS?
Astrocytes provide structural support for nearby neurons.
48
How do astrocytes assist in neuronal development?
Astrocytes assist in neuronal development and influence synaptic activity.
49
What happens to astrocytes when neurons die?
Astrocytes occupy the space of dying neurons.
50
Where are ependymal cells located, and what is their function?
Ependymal cells line cavities in the brain and spinal cord and are part of the choroid plexus, which produces cerebrospinal fluid.
51
What is the role of microglia in the CNS?
Microglia are phagocytic cells that wander the CNS, replicate in infection, and remove debris.
52
What do oligodendrocytes do in the CNS?
Oligodendrocytes have extensions that wrap around axons of neurons, forming the myelin sheath.
53
What is the function of satellite cells in the PNS?
Satellite cells surround neuronal cell bodies in ganglia, electrically insulate them, and regulate the exchange of nutrients and wastes.
54
What do neurolemmocytes (Schwann cells) do in the PNS?
Neurolemmocytes (Schwann cells) enclose PNS axons with myelin, allowing for faster action potential propagation.
55
What is myelination and what is its purpose?
Myelination is the process of wrapping an axon with myelin, which insulates the axon and increases the speed of action potential propagation.
56
What type of glial cells are responsible for myelination in the PNS?
Neurolemmocytes (Schwann cells) are responsible for myelination in the PNS.
57
What are neurofibril nodes (nodes of Ranvier)?
Neurofibril nodes (nodes of Ranvier) are the gaps between neurolemmocytes that allow for faster signal transmission along the axon.
58
When can PNS axons regenerate after traumatic injury?
PNS axons can regenerate if the neuron cell body is intact and enough neurilemma remains.
59
What factors make PNS axon regeneration more likely to be successful?
Regeneration is more successful if the damage is less extensive and the distance between the injury site and the structure it innervates is shorter.
60
What is the first step in axon regeneration after trauma?
The axon is severed by trauma.
61
What happens to the axon proximal and distal to the injury site during axon regeneration?
Proximal to the cut, the axon seals off and swells; distal to the cut, the axon and sheath degenerate, but the neurilemma survives.
61
What forms the regeneration tube during axon regeneration?
The neurilemma and endoneurium form a regeneration tube.
62
How does the axon regenerate after injury?
The axon regenerates guided by nerve growth factors released by neurolemmocytes.
63
What is the final step in axon regeneration?
The axon reinnervates the original effector or sensory receptor.
64
Why is CNS axon regeneration extremely limited?
Oligodendrocytes secrete growth-inhibiting molecules instead of growth factors.
65
What obstructs regrowth of axons in the CNS?
Large numbers of axons crowd the CNS, and scars from astrocytes and connective tissue obstruct regrowth
66
What is the function of pumps in neurons?
Pumps maintain a concentration gradient by moving substances against their concentration gradient, requiring cellular energy
67
Which pumps are found in the membranes of neurons?
Neurons have sodium-potassium pumps and calcium pumps.
68
What is the function of channels in neurons?
Channels allow ions to m
69
What are leak channels
Leak (passive) channels are always open, allowing continuous diffusion of ions.
70
What are chemically gated channels?
Chemically gated channels are normally closed but open when a neurotransmitter binds.
71
What are voltage-gated channels?
Voltage-gated channels are normally closed but open when the membrane charge changes.
72
What is unique about voltage-gated Na+ channels?
Voltage-gated Na+ channels have activation and inactivation gates
73
What types of channels are found in the receptive segment of a neuron?
The receptive segment contains chemically gated channels, such as chemically gated Cl– channels.
74
What channels are found in the initial segment of a neuron?
The initial segment (axon hillock) has voltage-gated Na+ channels and voltage-gated K+ channels.
75
What channels are found in the conductive segment of a neuron?
The conductive segment (axon and branches) has voltage-gated Na+ channels and voltage-gated K+ channels.
76
What channels are found in the transmissive segment of a neuron?
The transmissive segment (synaptic knobs) has voltage-gated Ca2+ channels and Ca2+ pumps.
77
What happens in the receptive segment (dendrites and cell body) of a neuron?
The receptive segment receives signals through chemically gated channels, generating graded potentials when neurotransmitters bind to receptors.
78
What channels are involved in the receptive segment of a neuron?
Chemically gated channels (e.g., Cl– channels) that open when neurotransmitters bind to receptors.
79
What occurs in the initial segment (axon hillock) of a neuron?
If the graded potential reaches threshold, voltage-gated Na+ channels open, leading to depolarization and initiating an action potential.
80
What channels are involved in the initial segment (axon hillock)?
Voltage-gated Na+ channels and voltage-gated K+ channels.
81
What happens in the conductive segment (axon and branches) of a neuron?
The action potential is propagated along the axon by sequential opening of voltage-gated Na+ and K+ channels, leading to depolarization and repolarization of the membrane.
82
What channels are involved in the conductive segment of a neuron?
Voltage-gated Na+ channels and voltage-gated K+ channels.
83
What occurs in the transmissive segment (synaptic knobs) of a neuron?
The action potential reaches the synaptic knobs, opening voltage-gated Ca2+ channels, causing neurotransmitter release into the synaptic cleft.
84
What channels are involved in the transmissive segment (synaptic knobs)?
Voltage-gated Ca2+ channels and Ca2+ pumps.
85
What triggers the release of neurotransmitters at the transmissive segment?
The influx of Ca2+ through voltage-gated Ca2+ channels at the synaptic knobs
86
What are graded potentials?
Graded potentials are small, short-lived changes in the resting membrane potential (RMP).
87
Where are graded potentials established in a neuron?
Graded potentials are established in the receptive segment of the neuron (dendrites and cell body) by the opening of chemically gated ion channels
88
How long do graded potentials last?
Graded potentials are short-lived, typically lasting only a few milliseconds or less.
89
Do graded potentials vary in size?
es, graded potentials vary in degree of change and direction of the resting membrane potential (RMP).
90
Can graded potentials cause depolarization or hyperpolarization?
Yes, graded potentials can cause either depolarization (less negative) or hyperpolarization (more negative) of the membrane.
91
Are graded potentials always the same size?
No, graded potentials can be large or small depending on the strength of the stimulus
92
What are postsynaptic potentials
Postsynaptic potentials are graded potentials in a postsynaptic neuron, resulting from neurotransmitter binding.
93
What is an excitatory postsynaptic potential (EPSP)?
An EPSP is a postsynaptic potential that results in depolarization of the postsynaptic neuron.
94
What is an inhibitory postsynaptic potential (IPSP)?
An IPSP is a postsynaptic potential that results in hyperpolarization of the postsynaptic neuron.
95
Can a postsynaptic neuron generate multiple postsynaptic potentials?
Yes, a postsynaptic neuron can generate multiple postsynaptic potentials because it can bind many neurotransmitter molecules simultaneously.
96
What causes excitatory postsynaptic potentials (EPSPs)?
EPSPs are depolarizations caused by the entry of Na+ ions into the postsynaptic neuron.
97
What causes inhibitory postsynaptic potentials (IPSPs)?
IPSPs are hyperpolarizations caused by K+ exit or Cl− entry into the postsynaptic neuron.
98
Where does the summation of EPSPs and IPSPs occur, and what happens if the threshold is reached?
The summation occurs at the axon hillock; if the threshold (typically -55 mV) is reached, voltage-gated channels open, and an action potential is generated.
99
threshold membrane
potential s
the minimum voltage change required
100
What happens during depolarization of an action potential?
During depolarization, Na+ enters the neuron through voltage-gated Na+ channels, causing the membrane potential to become more positive.
101
What is repolarization in an action potential?
Repolarization is the return of the membrane potential to a negative value as K+ exits the neuron through voltage-gated K+ channels.
102
How is an action potential propagated down the axon?
An action potential is propagated by sequential opening of voltage-gated channels along the axolemma, generating a nerve signal or nerve impulse.
103
What is the term for the propagation of action potentials along the axon?
The propagation of action potentials along the axon is called a nerve signal or nerve impulse.
104
What ion movement is responsible for depolarization?
Depolarization is caused by the entry of Na+ into the neuron through voltage-gated Na+ channels.
105
What ion movement is responsible for repolarization?
Repolarization is caused by the exit of K+ from the neuron through voltage-gated K+ channels.
106
What happens during depolarization when Na+ enters from an adjacent region?
Voltage-gated Na+ channels open, allowing Na+ to enter the axon, causing the membrane potential to become positive.
107
What causes the membrane to become positively charged during depolarization?
he entry of Na+ into the axon through voltage-gated Na+ channels causes the membrane to become more positive.
108
What role do voltage-gated Na+ channels play in depolarization?
Voltage-gated Na+ channels open to allow Na+ to enter the axon, which leads to a positive shift in membrane potential.
109
What triggers the opening of voltage-gated Na+ channels during depolarization?
The entry of Na+ from an adjacent region triggers the opening of voltage-gated Na+ channels, initiating further depolarization.
110
What happens to Na+ channels during the inactivation state?
Na+ channels close and become inactive, meaning they are temporarily unable to open.
111
How does the action potential continue to propagate after Na+ channels become inactive?
Steps 1 and 2 (Na+ entry and depolarization) repeat in adjacent regions, allowing the action potential to move toward the synaptic knob.
112
What causes the action potential to move toward the synaptic knob?
The sequential opening of voltage-gated Na+ channels and the depolarization of adjacent regions cause the action potential to propagate toward the synaptic knob.
113
What is the role of Na+ channel inactivation in the propagation of the action potential?
Na+ channel inactivation ensures the unidirectional flow of the action potential by preventing backward movement.
114
What happens during the depolarization phase of an action potential?
Depolarization opens Na+ channels, causing Na+ to enter the cell and the membrane potential to become more positive.
115
What occurs when K+ channels open during repolarization?
K+ ions diffuse out of the cell, causing the membrane potential to become more negative (repolarization).
116
What causes hyperpolarization during the action potential?
K+ channels remain open longer than needed, allowing more K+ to exit, making the membrane potential more negative than the resting membrane potential.
117
How is the resting membrane potential (RMP) reestablished after hyperpolarization?
K+ channels close, and the Na+/K+ pump restores the RMP by pumping Na+ out and K+ back into the cell.
118
How does repolarization propagate the action potential?
Steps 3-5 (K+ exit and membrane potential changes) repeat in adjacent regions, propagating the action potential toward the synaptic knob.
119
What is the role of K+ channels in action potential propagation?
K+ channels help repolarize the membrane by allowing K+ to exit, returning the cell to a negative potential and enabling the action potential to move forward
120
What happens when an action potential reaches the synaptic knob?
It opens voltage-gated Ca2+ channels, allowing Ca2+ to diffuse into the synaptic knob.
121
What is the role of Ca2+ in neurotransmitter release?
Ca2+ binds to proteins associated with synaptic vesicles, triggering exocytosis of neurotransmitters.
122
What occurs during exocytosis at the synaptic knob?
Synaptic vesicles fuse with the membrane, releasing neurotransmitters into the synaptic cleft
123
How do neurotransmitters affect the postsynaptic cell?
Neurotransmitters bind to ligand-gated receptors on the postsynaptic cell, initiating a response.
124
Can a neuron release multiple types of neurotransmitters?
Yes, neurons can synthesize more than one neurotransmitter, but only one type is released at a time, depending on the action potential frequency.
125
How does the frequency of action potentials affect neurotransmitter release?
The frequency of action potentials influences how much neurotransmitter is released, as higher frequencies lead to more vesicles being released.
