Slpa 853: Neurology - Sensory Systems

Front 1

What are the common organizational features of sensory systems?

Back 1

-sensory receptors -> sensory transduction -> sensory processing (incoming info is transduced into neural codes by sensory receptors and then sent to processing centers by afferent axons)

Front 2

Where is sensory information processed at?

Back 2

primary sensory cortex (just posterior to central sulcus)

Front 3

What is the threshold of a sensory receptor?

Back 3

the threshold of stimulus at which an action potential is generated

Front 4

True or false: All sensory receptors have the same level of sensitivity.

Back 4

False: some are more sensitive than others

Front 5

What is transduction?

Back 5

the process by which a physical stimulus is converted into a neural signal and sent to the CNS

Front 6

True or false: Each sensory unit is most sensitive to only one modality.

Back 6

True (e.g. pressure, temperature,....)

Front 7

The specific modality triggers the sensory receptor at what?

Back 7

the lowest threshold potential

Front 8

Can other modalities trigger a specific sensory receptor? If so, when?

Back 8

Yes, at much higher thresholds (pain)

Front 9

What are the different types of neural encoding?

Back 9

-strength of stimulus (amplitude)
-duration of stimulus
-location of stimulus (activated on sensory cortex - humonculus)
-modality of stimulus

Front 10

What types of strength of stimulus (amplitude) are there for neural encoding?

Back 10

-frequency code (how fast is AP generated - faster)
-population code (how many different APs are generated simultaneously - more neurons activated)

Front 11

How are sensory receptors classified?

Back 11

by the type of energy to which they respond

Front 12

What are the different functional classifications of receptors? AND what do they respond to?

Back 12

-photoreceptors (light - important for visual systems)
-chemoreceptors (recognize shape of molecules - important for taste and smell)
-thermoreceptors (temperature)
-mechanoreceptors (touch, pressure, stretch, motion)
-nocireceptors (pain receptors in skin; naked dendrites)

Front 13

What is another way to classify sensory receptors (2)?

Back 13

-exteroreceptors (somatosensory)
-proprioceptors

Front 14

Describe exteroreceptors as a functional classification of sensory receptors.

Back 14

-somatosensory
-respond to external stimulation
-used to respond to external stimuli that may be harmful
-sensors within skin

Front 15

Describe proprioceptors as a functional classification of sensory receptors.

Back 15

-sensing info inside organs, muscles, tendons, and joints
-used to make adjustments in body position and muscle tone

Front 16

What are the different types of exteroreceptors?

Back 16

-tactile
-temperature
-pain

Front 17

Describe the tactile receptors for exteroreceptors.

Back 17

-mechanorecptors

--activated by mechanical displacement (generate an AP in response to movement)
--responds to touch, pressure, and vibration

Front 18

Describe the temperature receptors for exteroreceptors.

Back 18

thermoreceptors-- activated by changes (not absolute temp) in temperature

Front 19

Describe the pain receptors for exteroreceptors.

Back 19

nocireceptors-- activated by damage to tissue

Front 20

What do proprioceptives receptors provide?

Back 20

provide CNS info for reflexes and coordinated movement

Front 21

Where are proprioceptive receptors located?

Back 21

in muscle, tendons, and joints

Front 22

How are proprioceptive receptors activated?

Back 22

with intitiation or cessation of movements or strain on joint

Front 23

What are the two primary types of proprioceptive receptors?

Back 23

-muscle spindle
-golgi tendon organ

Front 24

What are the two different morphologies of receptors?

Back 24

-nonencapsulated
-encapsulated

Front 25

What are nonencapsilated receptors?

Back 25

-free nerve endings (no tissue wrapped around ending)
-Merkel's Discs

Front 26

What are the different encapsilated receptors?

Back 26

-Pacinian corpuscles
-Meissner's corpuscles
-Ruffini corpuscles

Front 27

True or false: Exterioreceptors are spread throughout the skin's layers.

Back 27

True

Front 28

What are the two types of skin that sensory receptors are in?

Back 28

-hairy
-glabrous

Front 29

What receptors are embedded in the hairy skin?

Back 29

-free nerve endings
-Ruffini corpuscles
-Pacinian corpuslces

Front 30

What receptors are embedded in the glabrous skin?

Back 30

-contains complex mixture of nonencapsulated and encapsulated sensors

--Meissner's corpuscles
--Merkel's discs
--Free nerve endings
--Ruffini
--Pacinian

Front 31

What is glabrous skin?

Back 31

hairless -- fingertips, palms, bottoms of feet

Front 32

What do free nerve endings detect? AND where are they found?

Back 32

-detect painful stimuli; respond to very light touch; slow adapting
-found just below the surface of the skin

Front 33

Where are Merkel's Discs located? AND What are they?

Back 33

-located at the base of epidermis
-primarily pressure receptors (respond to skin indentation --vertical pressure on the skin, but not lateral displacements)
-responds best to pressure
-slow adapting

Front 34

What are Pacinian corpuscles?

Back 34

-mechanoreceptors sensitive to rapid vibration (high-frequency)
-largest sensory end organs in body
-consists of up to seventy onion-like layers wrapped around the dendrite of a single myelinated axon
-responds best to vibration

Front 35

What are Meissner's corpuscles?

Back 35

-rapidly adapting mechanoreceptors
-located at the base of epidermis
-respond to: slow vibration (low-frequency) and brief taps on skin
-important for 2-point discrimination
-found in glabrous skin

Front 36

What are Ruffini corpuscles?

Back 36

-a touch and vibration receptor located in hairy skin
-responds to indentation of skin
-responds best to pressure
-slow adapting

Front 37

Define vibration AND name the receptors that detect it.

Back 37

-alternating changes in stimulation (weak-strong-weak); a pattern of rhythmic pressure
-Pacinian and Ruffini

Front 38

Define pressure AND name the receptors that detect it.

Back 38

-constant stimulation that is gradually changing (weak-strong)
-Merkel's discs, Ruffini, Meissner's, hair follicle, free nerve ending

Front 39

Where are the impulses for vibration carried?

Back 39

in the dorsal columns of spinal cord

Front 40

What is depression of threshold for vibratory stimuli an early sign of?

Back 40

early sign of degeneration of the dorsal column pathway

Front 41

Describe how Pacinian corpuscles work to detect vibration.

Back 41

-membrane depolarizes when corpuscle is bent
-stretch-gated ion channels (receptor potential occurs because dendrite has ion channels that open in response to stretch)
-axon responds immediately when organ is bent and again when it is released- rapidly adapting
-receptor is sensitive to vibration, but not steady pressure

Front 42

What are the two types of classifications for rate of adaption for vibration receptors?

Back 42

-slow adaptors
-rapid adaptors

Front 43

Describe slow adaptors for vibration receptors. AND which receptors are this?

Back 43

-generate impulses for as long as the stimulus is present
-free nerve endings, Merkel's discs, Ruffini's corpuscle

Front 44

Describe rapid adaptors for vibration receptors. AND which receptors are this?

Back 44

-fire only briefly at the onset of the stimulus and then adapt
-Meissner's corpuscle and Pacinian corpuscle

Front 45

What sensory testing is used for vibration? AND describe it.

Back 45

Mechanical Frequency Detection Threshold
-mechanical sinusoidal displacements applied to skin
-behavioral psychophysical procedure:
--ascending/descending
--8 test frequencies (5, 10, 50, 150, 250, 300, 400, & 600 Hz)
--similar procedure as pure tone audiometry

Front 46

What does the perception of pressure require?

Back 46

that the mechanical stimulus be of sufficient magnitude to be detected by subcutaneous receptors

Front 47

Does the body require a mechanism to sense moderate, constant nondamaging stimulus?

Back 47

No, moderate pressure only sensed while changing either location or in magnitude

Front 48

Why does the body adapt to constant stimuli?

Back 48

-to reduce fatigue of physical or depletion of chemical resources
-due to physical construction of the skin and the cutaneous sensory organs
-constant stimulus to skin fails to produce sensation after a while ("Wristwatch Effect")

Front 49

What is stereognosis?

Back 49

-ability to identify objects by touch
-compromised when the dorsal column is damaged
-has large cortical component

Front 50

What is impaired stereognosis an early sign of?

Back 50

early sign of damage to cerebral cortex (primary sensory cortex)

Front 51

Describe hair follicle receptors.

Back 51

-respond to any touch which moves associated hair
-fast adapting

Front 52

Describe the two-point discrimination sensory test given by neurologists.

Back 52

-minimal distance by which 2 stimuli must be separate to be perceived as separate
-touch + cortical component
-receptors (Pacinian, Meissner's, Merkel's discs)
-varies from place to place on body
-smallest where the touch receptors are most abundant
-back ~65 mm or more
-fingers ~3 mm (the diameter of the area of skin supplied by a single sensory unit)

Front 53

True or false: Temperature and pain pathways are the same.

Back 53

True (usually only pain is tested)

Front 54

True or false: The same fibers respond to cold or warm stimuli.

Back 54

False, different fibers respond

Front 55

True or false: Transduction of temperature changes into rate of axonal firing is not entirely understood.

Back 55

True

Front 56

What does pain serve as a functional role of?

Back 56

survival (escape source of tissue destruction)

Front 57

Pain denotes tissue destruction induced by?

Back 57

-thermal stimuli
-mechanical force
-chemical stimulation

Front 58

True or false: Localization of pain is accurate.

Back 58

False

Front 59

In what areas of the body are nocireceptors (pain) located?

Back 59

-skin
-sheath around muscles, internal organs
-cornea of the eye
-pulp of teeth

Front 60

What type of neuron system are ascending pathways (sensory)?

Back 60

three neuron system (dysynaptic)

Front 61

Describe the three neuron system.

Back 61

-first order: has cell body in cranial nerve or spinal ganglia
-second order: has cell body located in brainstem or dorsal gray matter of spinal cord
-third order: has cell body located in thalamus

Front 62

What are the 2 primary pathways for senses?

Back 62

-Dorsal Column-Med Lemniscus
-Anterolateral System

Front 63

What information does the Dorsal Column-Med Lemniscus pathway detect?

Back 63

fine, touch, pressure, and vibration (precisely localized info)

Front 64

What information does the Anterolateral System pathway detect?

Back 64

pain and temperature (imprecisely localized info)

Front 65

Describe the three neuron system pathway for the Dorsal Column-Med Lemniscus.

Back 65

-first order axons ascend thru dorsal columns in white matter (myelinated axons) of spinal cord and project to nuclei in lower medulla
-second order axons project from lower medulla CROSS and ascend thru the medial lemniscus to thalamus
-third order neurons project primary sensory cortex (Brodmann areas 1-3 -- thalamocortical radiation)

Front 66

Describe the three neuron system pathway for the Anterolateral System.

Back 66

-first order neurons synapse in spinal cord on interneurons
-second order neurons decussate (cross over) at the level of spinal cord (ventral white commissure) to anterolateral spinal cord and travel up the spinothalamic tract to project on thalamus
-third order neurons project to primary sensory cortex (Brodmann's areas 1-3 -- thalamocortical radiation)

Front 67

What does damage to the dorsal part of the nerve in the spinal cord cause?

Back 67

ipsilateral numbness

Front 68

What does damage to the anterior part of the nerve in the spinal cord cause?

Back 68

loss of contralateral pain and temperature

Front 69

What does damage in the middle of the nerve in the spinal cord cause?

Back 69

affect both left and right sides