lec 7 - receptors and reflexes

Question 1

Special sensation:

Answer 1

vision, smell, taste, hearing, and vestibular sense

Question 2

General sensation:

Answer 2

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

Question 3

Touch/tactile:

Answer 3

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

Question 4

Pressure:

Answer 4

degree of mechanical distortion of skin

Question 5

Pain/nociception:

Answer 5

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

Question 6

Temperature/thermal:

Answer 6

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

Question 7

Vibration:

Answer 7

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

Question 8

Proprioception:

Answer 8

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

Question 9

Mechanoreceptors:

Answer 9

sense touch, pressure, vibration, and stretch

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

Question 10

Proprioceptors:

Answer 10

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)

Question 11

Thermoreceptors:

Answer 11

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

Question 12

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

Answer 12

skin
viscera and muscle

Question 13

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

Answer 13

nociceptors

Question 14

Nociceptors:

Answer 14

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

Question 15

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

Answer 15

epidermis of the skin

viscera, muscles, bones, and joints

Question 16

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

Answer 16

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

Chronic pain is carried via C fibers
> Unmyelinated axons

Question 17

Chemoreceptors:

Answer 17

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

> olfaction
gustation

Question 18

Photoreceptors:

Answer 18

sense/detect light levels

rods and cones

in the retina

Question 19

Olfaction:

Answer 19

odorant binds to odorant receptors in nasal mucosa

Question 20

Gustation:

Answer 20

taste molecule binds to taste receptors on tongue

Question 21

Chemoreceptors in ____ and ____ detect blood pH and solute concentrations

Answer 21

carotid body
aortic arch

Question 22

Types of mechanoreceptors:

Answer 22

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

Question 23

Merkel’s discs

Answer 23

Function: detect pressure, vibration, touch

Location: epidermis of skin

Question 24

Meissner’s corpuscles

Answer 24

Function: detect pressure, vibration, fine/discriminative touch

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

Question 25

Pacinian corpuscles

Answer 25

Function: detect pressure and vibration Location: dermis and hypodermis of skin, bones, tendons, ligaments, and joints

Question 26

Ruffini's endings

Answer 26

Function: detect pressure and stretch Location: dermis and hypodermis of skin and joints

Question 27

Skeletal Muscle Fiber Structure

Answer 27

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

Question 28

Muscle Spindles

Answer 28

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

Question 29

Golgi Tendon Organs (GTOs)

Answer 29

> 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

Question 30

Primary Afferent Sensory Neuron Types

Answer 30

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

Question 31

A-⍺ I (1a) fibers

Answer 31

receptors: Muscle spindles functions: Sense muscle stretch & proprioception myelination: Myelinated fiber diameter: Largest conduction velocity: Fastest

Question 32

A-⍺ II (1b)

Answer 32

receptors: Golgi tendon organs (GTOs) functions: Sense muscle tension & proprioception myelination: Myelinated fiber diameter: Large conduction velocity: Fast

Question 33

A-β (2)

Answer 33

receptors: Mechanoreceptors & muscle spindles functions: Sense touch, stretch, pressure, vibration, & proprioception myelination: Myelinated fiber diameter: Medium conduction velocity: Moderate

Question 34

A-𝛿 (3)

Answer 34

receptors: Nociceptors functions: Sense sharp, acute noxious stimuli (acute pain) myelination: Lightly myelinated fiber diameter: Small conduction velocity: Moderate

Question 35

B

Answer 35

receptors: Mechanoreceptors & chemoreceptors functions: Sense stretch & chemical environment of viscera myelination: Moderately myelinated fiber diameter: Small conduction velocity: Moderate

Question 36

C (4)

Answer 36

receptors: Nociceptors functions: Sense dull, chronic noxious stimuli (chronic pain) myelination: Unmyelinated fiber diameter: Smallest conduction velocity: Slowest

Question 37

A-𝛿 and C Fibers

Answer 37

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

Question 38

Marginal zone neurons:

Answer 38

> project to contralateral anterolateral system/ spinothalamic tract > conveys pain, temperature, and crude touch to cortex

Question 39

Substantia gelantinosa:

Answer 39

contains dendrites of neurons whose cell body is in nucleus proprius Nucleus proprius neurons project to contralateral anterolateral system/ spinothalamic tract

Question 40

A-β and A-⍺ Fibers:

Answer 40

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

Question 41

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

Answer 41

spinal reflexes

Question 42

Fibers that ascend in ipsilateral dorsal column form:

Answer 42

dorsal column medial lemniscus pathway that conveys somatosensory information to cortex

Question 43

Components of a Spinal Reflex

Answer 43

> 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

Question 44

Primary afferent fibers synapse with LMNs or interneurons =

Answer 44

Pseudounipolar sensory neuron cell body in dorsal root ganglion Integration by interneurons (not required for some reflexes)

Question 45

Stretch/Myotatic/Deep Tendon Reflex

Answer 45

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

Question 46

Common Stretch/Myotatic Reflex Testing

Answer 46

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

Question 47

GTO/Inverse myotatic reflex

Answer 47

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)

Question 48

Nociceptive Flexor/Withdrawal Reflex

Answer 48

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

Question 49

Nociceptive crossed extensor reflex

Answer 49

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)

Question 50

Nociceptive crossed extensor reflex excitatory interneurons =

Answer 50

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

Question 51

Central Pain Pathways and Pain Modulation

Answer 51

Gate control theory Periaqueductal gray area/matter (PAG)

Question 52

Gate control theory

Answer 52

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)

Question 53

Pain modulation involves:

Answer 53

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

Question 54

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

Answer 54

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

Question 55

Periaqueductal gray area/matter (PAG)

Answer 55

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

Question 56

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

Answer 56

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

Question 57

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

Answer 57

Direct inhibitory synapse on 1st order neuron by descending fibers Descending fibers synapse with enkephalinergic interneuron that inhibits 1st order neuron

Question 58

Postsynaptic inhibition of 2nd order neuron conveying noxious stimulus =

Answer 58

Direct inhibitory synapse on 2nd order neuron by descending fibers

Question 59

Sensory Disturbances

Answer 59

Anesthesia Hemianesthesia Paresthesia Dysesthesia Analgesia

Question 60

Anesthesia:

Answer 60

absence of sensation

Question 61

Hemianesthesia:

Answer 61

affects one side of the body, common after stroke

Question 62

Paresthesia: 

Answer 62

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

Question 63

Dysesthesia: 

Answer 63

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

Question 64

Analgesia:

Answer 64

absence of pain sensation