4.4 Flashcards
1
Q
- Integration of sensory information occurs at all levels of the CNS with the highest level of integration taking place in _____
A
the cerebral cortex -
2
Q
generation and propagation of a series of action potentials in an afferent neuron
A
Neural encoding generation and propagation of a series of action potentials in an afferent neuron
3
Q
conversion of physical energy (chemical, mechanical, thermal, or electromagnetic) into electrochemical energy (local potential) by the receptor
A
Stimulus transduction
4
Q
A sensory receptor organ consists of one or more cells and possibly noncellular structures whose function is _____
A
transduction -
5
Q
the unique type of energy (stimulus) that best activates a specific receptor and therefore a particular type of afferent nerve fiber
A
Adequate stimulus -
6
Q
The ____ of a sensory nerve fiber isn’t absolute
A
specificity
7
Q
If the amplitude of the receptor potential is large enough, the membrane is ____ and an ____ is triggered
A
depolarized to threshold, action potential -
8
Q
- Action potential firing frequency is ___ to the amplitude of the receptor potential
A
proportional
9
Q
- The amplitude of the receptor potential is ____ to the strength of the stimulus
A
proportional -
10
Q
The receptor potential is ____, not all-or-nothing
A
graded -
11
Q
Vibration receptors (Pacinian corpuscles) in subcutaneous tissue adapt in ____
A
hundredths of a second
12
Q
- Chemoreceptors adapt in ____
A
weeks or months
13
Q
- Baroreceptors adapt in ____
A
hours or days
14
Q
Nociceptors adapt in ____
A
let’s just say they don’t
15
Q
- Sensory modality is encoded by a ____ code
A
“labeled line”
16
Q
Since a receptor is maximally sensitive to only one specific stimulus energy, every afferent nerve fiber is a modality-specific ____
A
line of communication (“labeled line”)
17
Q
Each type of receptor and afferent nerve fiber has a different set of ___; whether you feel pain or touch depends on the receptor and its central connections
A
connections in the CNS
18
Q
No matter how a “labeled line” is stimulated, the stimulus will be interpreted by the brain as ____ for which the nerve fiber is specialized.
A
the specific modality -
19
Q
Electrical stimulation of the cochlear nerve in the inner ear will be perceived as a ___, not ___
A
sound, touch or pain
20
Q
Electrical stimulation of the olfactory nerve will be perceived as a ___
A
smell -
21
Q
- This law is responsible for the phenomenon of phantom limb syndrome
A
Law of projection -
22
Q
no matter where a sensory pathway is stimulated along its course to the cerebral cortex, the conscious sensation produced is interpreted as coming from the site of the peripheral receptive field
A
Law of projection -
23
Q
- Higher action potential frequency causes greater ___ at the synapses in a sensory pathway
A
temporal summation
24
Q
in addition to temporal summation, stronger stimuli can also activate a greater number of sensory receptors (spatial summation). Activating more receptors
A
Population code
25
- In slow adapting receptors, stimulus duration is signaled by the interval during which____
- In slow adapting receptors, stimulus duration is signaled by the interval during which____
impulse firing is increased
26
Fast-adapting receptors signal the onset and offset of a stimulus with a ____ or a brief, high-frequency train of action potentials
single action potential -
27
involved with sensing pain
Insula:
28
involved with emotions
Cingulate gyrus
29
involved with fear and its sympathetic response
Amygdala
30
helps form and retrieve memories - Four structural components involved in interpreting pain:
Hippocampus
| helps form and retrieve memories - Four structural components involved in interpreting pain:
31
Because nociceptive signals can be inhibited in the CNS (i.e., antinociception), nociception does not always lead to the ____
perception of pain
32
Nociceptors are ___ in the skin and in most internal structures (periosteum, vessel walls, joint surfaces, dura mater)
widespread -
33
Nociceptors are absent from ___
the brain and spinal cord and lung parenchyma
34
Three major types of nociceptors:
Mechanical nociceptors
Thermal nociceptors
Polymodal nociceptors
35
Respond to intense mechanical pressure applied to the skin, Aδ nerve fibers; medium fast conduction velocity (5-30 meters per second)
Mechanical nociceptors
36
Respond to high-intensity mechanical, thermal (heat or cold), or chemical stimuli
Polymodal nociceptors -
37
Polymodal nociceptors
| what type of fiber
C fibers slow conduction velocity (<1 meter per second)
38
Respond to extreme temps (damaging or potentially damaging levels) of heat and cold (>113° F and <41° F)
Thermal nociceptors -
39
Thermal nociceptors
what type of fiber
two for different sensations
```
Aδ nerve fibers (medium fast conduction velocity [5-30 meters per second]) respond to cool temps
C fibers (slow conduction velocity [0.5-2 meters per second]) respond to heat
```
40
Nociceptors are sensitized by a variety of chemicals released by damaged cells in the vicinity of an injury
lower the threshold -
41
These substances ___ for activation of nociceptors
Examples of chemicals that sensitize nociceptors are:
brady, tom
has
sensitive
palms
bradykinin, histamine, prostaglandins and serotonin (i.e., 5-HT) - Examples of chemicals that sensitize nociceptors are:
42
Neuroactive substances are released by the peripheral end of an activated nociceptive pseudounipolar neuron
backfiring neuron"
43
These peptides contribute to the development of ____ in injured tissue by causing local vasodilation; they also encourage release of ____ which sensitizes the nociceptors
A "backfiring neuron" will release:
Substance P and CGRP
These peptides contribute to the development of edema in injured tissue by causing local vasodilation; they also encourage release of histamine from mast cells which sensitizes the nociceptors
44
```
Fast pain ("first pain")
receptor
transmitted by what fibers?
what type of pain
purpose?
```
Fast pain ("first pain")
Perception begins within 0.1 msec of a stimulus
Transmitted by Aδ fibers that carry signals from thermal or mechanical nociceptors
Carried by medium-to-large diameter, myelinated Aδ fibers that conduct at 5-30 meters per second (intermediate speed)
Associated with "sharp", "stabbing" pain
Purpose: rapidly generates motivation to stop or move away from a damaging stimulus
45
pain from hollow organs
Visceral pain
46
Pain receptors on hollow organs are ____ distributed
diffusely
47
```
Slow pain ("second pain")
receptors?
fiber
pain type
purpose
```
Perception begins within seconds of a stimulus
Transduced primarily by polymodal nociceptors
Carried by small-diameter, unmyelinated C fibers that conduct at <1 meter per second (slow)
Associated with "dull", "aching" persistent pain
Purpose: persistent reminder of tissue injury that provides motivation to care for and protect the injured area
48
Transmission of visceral pain: afferent fibers get into the CNS by traveling within the same nerves (not nerve fibers) that carry ___ to the viscera
autonomic innervation
49
Visceral pain in the pharynx, larynx, trachea, and upper esophagus is transmitted via ___, which also carry parasympathetic nerve fibers
cranial nerves IX and X
50
Visceral pain in the distal colon, rectum, urinary bladder, and testes or cervix is transmitted via ___ which also carry parasympathetic nerve fibers
spinal nerve S2-S4 -
51
Visceral pain in most organs of the thorax and abdomen is transmitted via ___ (e.g., splanchnic nerves) into the spinal cord
sympathetic nerves
52
Characteristics of visceral pain:
a. Extreme unpleasantness, aching, or burning
b. Poorly localized
c. Typically referred to the body surface
53
The CNS has modulatory circuits at many levels (cerebrum, diencephalon, midbrain, pons, medulla and spinal cord) whose function is to alter the ____
perception of pain
54
G protein-coupled opioid receptors are involved in modulating ___
pain perception
55
Opioids (i.e., enkephalin and endorphins) are generally released from ___
inhibitory interneurons
56
Presynaptically, opioid receptor activation causes ___, which depresses neurotransmitter release
closure of voltage gated Ca2+ channels
57
Postsynaptically, opioid receptor activation opens ___, resulting in IPSPs and inhibition of action potential firing
Postsynaptically, opioid receptor activation opens ___, resulting in IPSPs and inhibition of action potential firing
ligand gated K+ channels -
58
The initial site of CNS pain modulation is in ____
the dorsal horn of the spinal cord
59
According to this theory, nociceptive afferents are modified by non-nociceptive (typically tactile) afferents
gate control theory
60
Enkephalin binds to opioid receptors on both the ___ (i.e., C fiber nociceptive afferent) and the ____ (excitatory interneuron) neuron.
presynaptic, postsynaptic
61
Presynaptic effects of Enkephalin:
(i) Closure of voltage-gated Ca2+ channels
(ii) ↓ neurotransmitter release
(iii) Less nociceptive information sent up the spinothalamic tract
62
Involves a ____ and a ____ that synapses on enkephalin- secreting, inhibitory interneuron. The nociceptive afferent and the inhibitory interneuron synapse on the same excitatory interneurons. If the faster-conducting, tactile Aβ fibers are activated concurrently with slower-conducting, nociceptive C fibers, the inhibitory interneurons are activated more often. The net is less transmission of pain information to the brain.
nociceptive afferent, tactile afferent - Mechanism of the gate control theory:
63
Postynaptic effects of Enkephalin:
Postynaptic effects of Enkephalin:
(i) Opening of voltage-gated K+ channels
(ii) Hyperpolarization (i.e., IPSP) of the postsynaptic neuron.
(iii) Decreased probability of activating an action potential in the spinothalamic tract.
64
____ is often referred to as the "fast pain" or "discriminative" or "lateral" pain pathway
The spinothalamic tract - Ascending fast pain pathway
65
The spinothalamic tract brings fast pain primarily to the ____. Most fibers are of the Aδ variety (discriminative nociception) or C fibers for detecting heat
somatosensory cortex -
66
Acute pain is typically both ____. The slow pain aspect of acute pain is carried by these slow pain pathways while fast pain is carried by the spinothalamic tract (a 3 neuron pathway)
fast and slow
67
These pathways terminate on ____ of the CNS (brain stem, portions of the limbic system or non-somatosensory regions of the cortex).
medial aspects - Slow pain pathways typically utilize unmyelinated, polymodal C fibers (slow)
68
The slow pain pathways do not always utilize 3 neurons like the spinothalamic tract but they do tend to run alongside it and are also located in the ____ of the spinal cord
anterolateral columns -
69
Since slow pain pathways do not terminate on the somatosensory cortex, they are not ____ regarding the source of the pain, they are the "diffuse" pathways
well- mapped -
70
There are three slow pain pathways:
Spinomesenphalic
Spinoreticular
Spino-emotional
71
Terminates at the midbrain (periaqueductal gray [PAG])
| PAG activates descending pathways to modulate incoming pain signals
Spinomesenphalic
72
Terminates at the brainstem's reticular formation (center for arousal, attention & sleep-wake cycles)
Thus, slow pain draws attention to the pain and may interrupt sleep
Spinoreticular
73
These pathways receive input from ascending pathways and then send signals back down to the spinal cord in order to inhibit the ascending pain signals.
Descending pain pathways
74
Three primary descending tracts:
Raphespinal tract
Ceruleospinal tract
Unnamed tract originating in the Periaqueductal Gray (PAG
75
Originates in the raphe nucleus of the upper medulla
Receives innervation from the spinoreticular tract and from the Periaqueductal Gray (PAG)
Secretes serotonin
Synapses on an inhibitory interneuron (enkephalin-secreting) that eventually inhibits the ascending pathways
Raphespinal tract
76
Originates in the locus coeruleus ("blue spot") at the junction of the midbrain and the pons
Receives innervation from the spinoreticular tract and from the Periaqueductal Gray (PAG)
Secretes norepinephrine (NE)
Synapses on and suppresses the nociceptive C afferent via presynaptic inhibition
Mechanism of presynaptic inhibition involves α2 receptors, which activate Gi
inhibits voltage-gated Ca2+ channels (i.e., ICa) leads to ↓ norepinepherine release
Ceruleospinal tract
77
Electrical stimulation of ___ produces "electrical analgesia" sufficient to perform surgery on anaesthetized animals
the PAG
78
Neurons here send their axons down to the raphe nucleus and the locus coeruleus and make excitatory connections
Receives innervation from the spinomesenphalic tract and indirectly from the spinoemotional tract
Stimulation of this area causes profound analgesia without the loss of the other modalities of somatosensation (e.g., proprioception, discriminative touch, etc.).
Unnamed tract originating in the Periaqueductal Gray (PAG)
79
Microinjection of ____ into the PAG inhibits GABAergic inhibitory interneurons that tonically suppress the PAG
morphine
80
Microinjection of ___ into the PAG reverses the effects of systemically administered morphine
naloxone
81
Members of the limbic system ____, ____ and ____ are key centers in this level of antinociception;expectations, excitement, distractions and placebos can all play a role in this pathway
Members of the limbic system ____, ____ and ____ are key centers in this level of antinociception;expectations, excitement, distractions and placebos can all play a role in this pathway
the cingulate cortex, the insula and amygdala
82
Hormones and anticonception
endorphins, epinephrine and norepinephrine
83
Anterior pituitary purportedly releases ____
endorphins
84
Adrenal medulla releases ____ that presynaptically inhibit the primary nociceptive afferent (just like the ceruleospinal tract of the descending pain pathways)
epinephrine and norepinephrine
