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Neuroscience - spring 2024 > lec 7 - receptors and reflexes > Flashcards

lec 7 - receptors and reflexes Flashcards

1
Q

Special sensation:

A

vision, smell, taste, hearing, and vestibular sense

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2
Q

General sensation:

A

touch/tactile, pressure, pain/nociception, temperature/thermal, vibration, and proprioception

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3
Q

Touch/tactile:

A

crude (can’t localize) or discriminative (localizable)

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4
Q

Pressure:

A

degree of mechanical distortion of skin

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5
Q

Pain/nociception:

A

nociception is the transduction of noxious/painful stimuli, while pain is the CNS-generated experience of the painful stimulus

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6
Q

Temperature/thermal:

A

hot, warm, cool, cold, external temperature of the environment, and internal body temperature

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7
Q

Vibration:

A

detection of different frequencies (typically measured in Hertz (Hz) with a tuning fork)

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8
Q

Proprioception:

A

body position (primarily, joints and limbs), can be conscious or unconscious

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9
Q

Mechanoreceptors:

A

sense touch, pressure, vibration, and stretch

ex) Merkel’s discs, Ruffini’s endings, and Meissner’s and Pacinian corpuscles

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10
Q

Proprioceptors:

A

specialized mechanoreceptors that are in muscles, tendons, and joints to detect body positioning

sense limb and joint position and muscle stretch and tension

detect mechanical distortion of tissue (e.g., muscle stretch, muscle tension, change in joint angle, etc.)

include muscle spindles and Golgi tendon organs (GTOs)

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11
Q

Thermoreceptors:

A

sense warm and cool stimuli

detect mild-to-moderate temperatures (i.e., warm and cool) that do not cause tissue damage

Different receptors for warm vs. cool temperatures

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12
Q

Cutaneous thermoreceptors are in ___, while other thermoreceptors are in ___

A

skin
viscera and muscle

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13
Q

Extreme heat or cold that causes tissue damage is detected by ___

A

nociceptors

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14
Q

Nociceptors:

A

sense noxious/painful stimuli and tissue damage (may be thermal, pressure, chemical, etc.)

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15
Q

Cutaneous nociceptors are in the ____, while other nociceptors are in _____

A

epidermis of the skin

viscera, muscles, bones, and joints

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16
Q

Different types of noxious stimuli are carried via different primary afferent sensory neurons:

A

Acute, sharp pain is carried via A𝛿 fibers
> Lightly myelinated axons

Chronic pain is carried via C fibers
> Unmyelinated axons

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17
Q

Chemoreceptors:

A

sense changes in blood oxygen and pH as well as taste (taste molecules) and smell (odorants)

> olfaction
gustation

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18
Q

Photoreceptors:

A

sense/detect light levels

rods and cones

in the retina

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19
Q

Olfaction:

A

odorant binds to odorant receptors in nasal mucosa

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20
Q

Gustation:

A

taste molecule binds to taste receptors on tongue

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21
Q

Chemoreceptors in ____ and ____ detect blood pH and solute concentrations

A

carotid body
aortic arch

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22
Q

Types of mechanoreceptors:

A

> Merkel’s discs
Meissner’s corpuscles
Pacinian corpuscles
Ruffini’s endings

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23
Q

Merkel’s discs

A

Function: detect pressure, vibration, touch

Location: epidermis of skin

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24
Q

Meissner’s corpuscles

A

Function: detect pressure, vibration, fine/discriminative touch

Location: dermis of hairless skin (fingertips and soles of feet)

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25
Q

Pacinian corpuscles

A

Function: detect pressure and vibration

Location: dermis and hypodermis of skin, bones, tendons, ligaments, and joints

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26
Q

Ruffini’s endings

A

Function: detect pressure and stretch

Location: dermis and hypodermis of skin and joints

27
Q

Skeletal Muscle Fiber Structure

A

Most is composed of large extrafusal muscle fibers, which are innervated by large diameter ⍺-motor neurons

Small intrafusal muscle fibers are arranged parallel to extrafusal muscle fibers, which are innervated by small diameter 𝛾-motor neurons
> Muscle spindles wrap around intrafusal muscle fibers

28
Q

Muscle Spindles

A

wrap around intrafusal muscle fibers

monitor muscle length and the rate of change in muscle length (i.e., stretch)

activated by stretching of muscle fibers

utilize 1a primary afferent fibers

29
Q

Golgi Tendon Organs (GTOs)

A

> in muscle tendons

> perpendicular to intrafusal and extrafusal muscle fibers

> detect and monitor muscle tension

> Prevent muscle damage from too much tension

> utilize 1b primary afferent fibers

30
Q

Primary Afferent Sensory Neuron Types

A

A-⍺ I (1a)
A-⍺ II (1b)
A-β (2)
A-𝛿 (3)
B
C(4)

31
Q

A-⍺ I (1a) fibers

A

receptors: Muscle spindles

functions: Sense muscle stretch & proprioception

myelination: Myelinated

fiber diameter: Largest

conduction velocity: Fastest

32
Q

A-⍺ II (1b)

A

receptors: Golgi tendon organs (GTOs)

functions: Sense muscle tension & proprioception

myelination: Myelinated

fiber diameter: Large

conduction velocity: Fast

33
Q

A-β (2)

A

receptors: Mechanoreceptors & muscle spindles

functions: Sense touch, stretch, pressure, vibration, & proprioception

myelination: Myelinated

fiber diameter: Medium

conduction velocity: Moderate

34
Q

A-𝛿 (3)

A

receptors: Nociceptors

functions: Sense sharp, acute noxious stimuli (acute pain)

myelination: Lightly myelinated

fiber diameter: Small

conduction velocity: Moderate

35
Q

B

A

receptors: Mechanoreceptors & chemoreceptors

functions: Sense stretch & chemical environment of viscera

myelination: Moderately myelinated

fiber diameter: Small

conduction velocity: Moderate

36
Q

C (4)

A

receptors: Nociceptors

functions: Sense dull, chronic noxious stimuli (chronic pain)

myelination: Unmyelinated

fiber diameter: Smallest

conduction velocity: Slowest

37
Q

A-𝛿 and C Fibers

A

can synapse with 2nd order neurons in marginal zone or substantia gelatinosa

38
Q

Marginal zone neurons:

A

> project to contralateral anterolateral system/ spinothalamic tract

> conveys pain, temperature, and crude touch to cortex

39
Q

Substantia gelantinosa:

A

contains dendrites of neurons whose cell body is in nucleus proprius

Nucleus proprius neurons project to contralateral anterolateral system/ spinothalamic tract

40
Q

A-β and A-⍺ Fibers:

A

can synapse on interneurons or LMNs in ventral horn or enter the dorsal column

41
Q

Synapses with interneurons and LMNs in motor nuclei of ventral horn are involved in ___

A

spinal reflexes

42
Q

Fibers that ascend in ipsilateral dorsal column form:

A

dorsal column medial lemniscus pathway that conveys somatosensory information to cortex

43
Q

Components of a Spinal Reflex

A

> Peripheral receptors detect sensations

> Primary afferent fibers synapse with LMNs or interneurons

> LMN axon exits ventral horn and enters ventral rootlet

> Effector (e.g., muscle) responds to stimulus

44
Q

Primary afferent fibers synapse with LMNs or interneurons =

A

Pseudounipolar sensory neuron cell body in dorsal root ganglion

Integration by interneurons (not required for some reflexes)

45
Q

Stretch/Myotatic/Deep Tendon Reflex

A

Function: monitor muscle length/stretch

Receptor: muscle spindles

Primary afferent fiber type: 1a

Synapses: 1a fiber synapses directly with an ⍺-LMN in ventral horn and with an interneuron

Result/Effector: ⍺-LMN in ventral horn causes agonist muscle to contract and interneuron inhibits the ⍺-LMN innervating the antagonist muscle

46
Q

Common Stretch/Myotatic Reflex Testing

A

Elbow flexion
> Biceps: C5 and C6
> Brachioradialis: C6

Elbow extension
> Triceps: C7

Finger flexion: C8 and T1

Knee extension
> Quadriceps/Patellar/Knee jerk: L4

Ankle plantar flexion
> Achilles/Ankle jerk: S1

47
Q

GTO/Inverse myotatic reflex

A

Function: monitor muscle tension/load

Receptor: Golgi tendon organ (GTO)

Primary afferent fiber type: 1b

Synapses: 1b fiber synapses with an excitatory and an inhibitory interneuron

Result/Effector: inhibitory interneuron inhibits the ⍺-LMN innervating the agonist muscle (agonist relaxes) and excitatory interneuron excites the ⍺-LMN innervating the antagonist muscle (antagonist contracts)

48
Q

Nociceptive Flexor/Withdrawal Reflex

A

Function: detect noxious/painful stimuli

Receptor: cutaneous nociceptors

Primary afferent fiber type: A-𝛿 and C

Synapses: A-𝛿 and C fibers synapse with excitatory interneuron

Result/Effector: excitatory interneuron excites ⍺-LMN innervating agonist muscle (agonist contracts)

A-𝛿 and C fibers also synapse with neurons in marginal zone and substantia gelatinosa (and nucleus proprius) to convey pain information to cortex via anterolateral system/spinothalamic tract

49
Q

Nociceptive crossed extensor reflex

A

Function: detect noxious/painful stimuli

Receptor: cutaneous nociceptors

Primary afferent fiber type: A-𝛿 and C

Synapses: A-𝛿 and C fibers synapse with excitatory interneurons and inhibitory interneurons

Result/Effector: excitatory interneuron excites ⍺-LMN innervating agonist muscle (agonist contracts) and inhibitory interneuron inhibits ⍺-LMN innervating antagonist muscle (antagonist relaxes)

50
Q

Nociceptive crossed extensor reflex

excitatory interneurons =

A

Interneurons also decussate to innervate ⍺-LMNs in contralateral ventral horn to cause appropriate response in opposite limb

A-𝛿 and C fibers also synapse with neurons in marginal zone and substantia gelatinosa (and nucleus proprius) to convey pain information to cortex via anterolateral system/spinothalamic tract

51
Q

Central Pain Pathways and Pain Modulation

A

Gate control theory

Periaqueductal gray area/matter (PAG)

52
Q

Gate control theory

A

Sensory input from A-β fibers reduces pain transmission through dorsal horn of spinal cord

A-β fiber collateral branches synapse on inhibitory interneurons that inhibit pain transmission

Transcutaneous electrical nerve stimulation (TENS) devices reduce chronic pain via this mechanism (activating A-β fibers)

53
Q

Pain modulation involves:

A

interactions between local circuits at the level of the spinal cord dorsal horn and long-range modulatory inputs from the brainstem and cerebral cortex

These signals can upregulate or downregulate pain processing and pain perception

54
Q

This is why shaking your hand after hitting your finger, or touching the skin around a cut reduces pain sensation

A

Gate control theory

> Nociceptive fibers and somatosensory fibers converge on and stimulate the “gate cell”, which is an inhibitory interneuron that inhibits 2nd order neurons in the dorsal horn

> When non-noxious, somatosensory information activates A-beta fibers, the collateral branches of A-beta fibers stimulate an inhibitory interneuron in the dorsal horn to block the pain transmission

55
Q

Periaqueductal gray area/matter (PAG)

A

Contains a large amount of opioid receptors

Receives input from anterolateral system/spinothalamic tract, amygdala, hypothalamus, and cerebral cortex

Activates brainstem regions (e.g., raphe nuclei and locus coeruleus) to inhibit pain transmission

Descending fibers from brainstem can directly modulate pain transmission or activate enkephalinergic interneurons to inhibit pain transmission

56
Q

Descending fibers from brainstem (activated by PAG) can exert presynaptic or postsynaptic inhibition of pain signals

A

Presynaptic inhibition of 1st order neuron conveying noxious stimulus (2 mechanisms)

Postsynaptic inhibition of 2nd order neuron conveying noxious stimulus

57
Q

Presynaptic inhibition of 1st order neuron conveying noxious stimulus (2 mechanisms) =

A

Direct inhibitory synapse on 1st order neuron by descending fibers

Descending fibers synapse with enkephalinergic interneuron that inhibits 1st order neuron

58
Q

Postsynaptic inhibition of 2nd order neuron conveying noxious stimulus =

A

Direct inhibitory synapse on 2nd order neuron by descending fibers

59
Q

Sensory Disturbances

A

Anesthesia
Hemianesthesia
Paresthesia
Dysesthesia
Analgesia

60
Q

Anesthesia:

A

absence of sensation

61
Q

Hemianesthesia:

A

affects one side of the body, common after stroke

62
Q

Paresthesia:

A

sensations (e.g., tingling) perceived without specific stimulation, may be tactile, thermal or painful, may be episodic or constant

63
Q

Dysesthesia:

A

painful sensations (e.g., burning, shooting, pins and needles) elicited by a nonpainful cutaneous stimulus such as a light touch or gentle touch over affected areas of the body

64
Q

Analgesia:

A

absence of pain sensation

Neuroscience - spring 2024 (10 decks)

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