Intro to sensory systems

Question 1

What are the five types of receptors (classified by the stimulus)?

Answer 1

1. Mechano
2. Thermo
3. Photo
4. Chemo
5. Nociceptor

Question 2

What is perception?

Answer 2

The conscious awareness of stimuli

Question 3

What is the process of translating a physical stimulus to a nerve impulse?

Answer 3

Sensory transduction

Question 4

What is receptor potential?

Answer 4

change in the membrane potential produced by a transducer mechanism

Question 5

True or false: the receptor potential is a graded potential

Answer 5

True

Question 6

Most receptor potentials are generated how?

Answer 6

Via depolarization of a receptor

Question 7

How is the rate of receptor potential changed?

Answer 7

Rate at which action potentials are generated increases as receptor potential rises higher above threshold.

Question 8

If the receptor potential is a hyperpolarization, does it generate an action potential?

Answer 8

No

Question 9

What is the labeled line principle?

Answer 9

tells you the sensory modality since there is a chain of connected neurons from the sensory receptor which responds to the stimulus to the brain area that perceives the stimulus

Question 10

How do we know “what” and “where” a stimulus is?

Answer 10

Labeled line principle

Question 11

What is a receptor field?

Answer 11

the region of tissue (e.g. skin) within which a stimulus can evoke a change in the firing rate of the neuron.

Question 12

What is an adequate stimulus?

Answer 12

Under normal circumstances, a specific receptor is affected by only one stimulus modality

Question 13

What is the receptor specificity?

Answer 13

There is only one stimulus that can affect a given receptor

Question 14

True or false: receptor potential change with the size of the stimulus

Answer 14

True

Question 15

True or false: action potential changes with the size of the stimulus

Answer 15

False

Question 16

How do pacinian corpuscles work?

Answer 16

Movement causes Na channels to open. Bigger stimulus = more openings

Question 17

True or false: wherever along the chain of a receptor is stimulated, it will produce the same sensation

Answer 17

True

Question 18

What is the pathway in the spinal cord that transmits proprioception and fine touch? Where do these cross in the spinal cord? Where do these project to?

Answer 18

Dorsal columns (fasciculus cuneatus and gracilis)

These cross in the medulla via the nucleus cuneatus and gracilis to project to the VPL nucleus of the thalamus, then the somatosensory cortex

Question 19

What are the pathways in the spinal cord that transmit pain and crude touch?

Answer 19

Neospinothalamic and paleospinothalamic pathways

Question 20

Where do the neospinothalamic and paleospinothalamic pathways cross over?

Answer 20

At the level (and 1-2 above/below) they enter via the anterior white commissure.

Question 21

What is the area that the axons of the neospinothalamic pathway go up and gown in the spinal cord?

Answer 21

Lissauer’s tract

Question 22

Where are the cell bodies of the primary motor neurons in the dorsal columns and the neo/paleospinothalamic pathways housed?

Answer 22

DRG

Question 23

What is the law of projection?

Answer 23

in a neuron in a sensory pathway is stimulated, the subject perceives the stimulus as being in the location of the sensory receptor for that pathway

Question 24

Where is the primary somatosensory cortex?

Answer 24

Behind the central sulcus

Question 25

Review the homunculus distribution of the sensory cortex if you do not remember

Answer 25

It's not that bad really...

Question 26

What is the blood supply to the medial cortex? Lateral?

Answer 26

``` Medial = anterior cerebral Lateral = middle cerebral ```

Question 27

What are the parts of the body that are represented by the medial part of the somatosensory cortex?

Answer 27

Foot, leg, hip, genitals

Question 28

What are the two ways in which the nervous system codes for stimulus strength?

Answer 28

1. Frequency of nerve impulses | 2. Number of fibers activated

Question 29

What is the concept of lateral inhibition?

Answer 29

When a part of a receptor field is stimulated, the receptors in close proximity are inhibited, thus providing more localized stimulus

Question 30

How does the nervous system code for stimulus duration? (2 different ways)

Answer 30

Maintains continuous signal strength during stimulus Have on-off signal

Question 31

True or false: inhibition is just as useful as excitation in the nervous system

Answer 31

True

Question 32

What causes the adaptation of a sensory receptor?

Answer 32

When a maintained stimulus of constant strength is applied to a receptor, the frequency of the action potentials in the receptor's sensory nerve decreases over time.

Question 33

True or false: all receptor use the same mechanism of adaptation to a stimulus

Answer 33

False

Question 34

What are the non-adapting receptors?

Answer 34

Nociceptors

Question 35

What is a tonic receptor?

Answer 35

A receptor that does adapt, but does so slowly

Question 36

How do tonic receptors adapt?

Answer 36

Initial burst of firing when the stimulus is applied, but then slows down

Question 37

Merkel cell endings are what type of adapting receptors?

Answer 37

Slowly adapting receptors

Question 38

When are slowly adapting receptors useful?

Answer 38

for giving continuous information about stimulus strength and signaling stimulus duration

Question 39

When are slowly adapting receptors NOT useful?

Answer 39

not as useful for signaling stimulus duration at low stimulus intensities

Question 40

Pacinian corpuscles and Meissner's corpuscles are what type of receptors (slow or fast adapting)?

Answer 40

Fast adapting

Question 41

What are phasic or rate receptors?

Answer 41

fast adapting receptors

Question 42

When are fast adapting receptors useful?

Answer 42

useful for signaling beginning and end of stimulus

Question 43

Can fast receptors signal a change in stimulus intensity? If so, how?

Answer 43

Yes--number of action potentials transmitted related to rate at which change is taking place

Question 44

What type of receptors are needed to extract dynamic information e.g. velocity and acceleration

Answer 44

Fast adapting

Question 45

Which type of receptors are useful for sensing when a stimulus begins and ends (fast or slow adapting)?

Answer 45

Fast adapting

Question 46

What type of receptor is useful for sensing stimulus intensity?

Answer 46

Tonic receptors

Question 47

What are the four different types of tactile sensation receptors?

Answer 47

1. Crude 2. Discriminitive 3. Pressure 4. Flutter/vibration

Question 48

What type of receptors are utilized for crude touch? How well are these myelinated?

Answer 48

Free nerve endings (type C unmyelinated fibers)

Question 49

Do the free nerve endings involved in crude touch have a low threshold or high threshold for stimulation? What is the consequence of this?

Answer 49

Low threshold = high sensitivity

Question 50

True or false: discriminative touch is carried by both the dorsal lateral and the aternomedial systems?

Answer 50

False--only the dorsal columns

Question 51

What is the difference between flutter and vibration?

Answer 51

Just frequency--higher = more like vibration

Question 52

What is the tuning fork utilized for testing vibration sense?

Answer 52

128 hz

Question 53

Merkel cell fibers are low or high threshold receptors? Where are they found?

Answer 53

Low (highly sensitive) Found at the base of the epidermis

Question 54

What is an Iggo dome receptor?

Answer 54

Several merkel discs joined together

Question 55

What type of fibers innervate Merkels discs? How well are these myelinated?

Answer 55

A-beta fibers--very myelinated

Question 56

Merkel cells are slow or fast adaptors?

Answer 56

Slow

Question 57

Which receptors have the highest spatial relationship of all the sensory afferents?

Answer 57

Merkels discs

Question 58

What are the receptors that play a role in static discrimination of shapes, edges, and textures?

Answer 58

Merkel cells

Question 59

Ruffini corpuscles sense what?

Answer 59

Joint stretch

Question 60

Meissner's corpuscles are rapidly or slowly adapting fibers?

Answer 60

Rapid

Question 61

Which type of receptors have a very high density in the tips of the fingers?

Answer 61

Meissner's corpuscles

Question 62

Where are Meissner's corpuscles located in the skin?

Answer 62

Just below the epidermis, but closer to the skin than Merkel's discs

Question 63

Information from which receptors are probably the basis for the detection of slippage between the skin and an object held in the hand. Responsible for the sensory feedback information needed for the efficient control of grip.

Answer 63

Meissner's corpuscles

Question 64

Pacinian corpuscles are slowly or rapidly adapting?

Answer 64

Rapid

Question 65

Where in the skin are pacinian corpuscles found?

Answer 65

subcutaneous tissue

Question 66

True or false: pacinian corpuscles adapt more rapidly than Meissner's

Answer 66

True

Question 67

Which receptors can detect vibrations transmitted though objects held in the hand thus contributing to skilled tool use?

Answer 67

Pacinian corpuscles

Question 68

What are the receptors in the base of hairs? What type of fibers are utilized by these receptors?

Answer 68

peritrichial nerve endings--A-delta fibers

Question 69

Which type of receptor is better at detecting change? Which is better for detecting a long stimulus?

Answer 69

Rapid adapting = good for change Slow adapting = good for constant stimulus

Question 70

Itch is sensed by what type of sensors/fibers?

Answer 70

Free nerve endings with C fibers

Question 71

What part of the body has the least ability to detect two separate points? Best?

Answer 71

Best = hands Worst = calves

Question 72

Lack of two point discrimination will indicate damage to what part of the spinal cord?

Answer 72

dorsal columns

Question 73

What are the receptors involved in proprioception?

Answer 73

a. joint receptors b. muscle spindles and Golgi tendon organs c. skin tactile receptors

Question 74

Joint position proprioception is static or dynamic proprioception?

Answer 74

static

Question 75

Joint movement proprioception is static or dynamic proprioception?

Answer 75

Dynamic

Question 76

What is conscious proprioceptions?

Answer 76

Kinesthesia

Question 77

The DC/ML pathway is responsible for what type of sensation?

Answer 77

fine tactile discriminations, vibratory sense (which is just rapid, repeated touch/pressure) and proprioceptive sense.

Question 78

What allows for the precise localization of the DC/ML pathways?

Answer 78

Precise localization is possible because the receptors associated with system can have very small receptive fields

Question 79

Rhomberg test tests what?

Answer 79

Proprioception

Question 80

Where is the somatosensory cortex in the cortex of the brain?

Answer 80

Behind the central sulcus

Question 81

What are the two parts of the homunculus in the medial fissure of the sensory cortex?

Answer 81

Foot and genitals

Question 82

Where does the DC/ML crossover in the spinal cord?

Answer 82

Caudal medulla

Question 83

What is graphesthesia?

Answer 83

Ability to recognize figure drawn into hand or onto skin

Question 84

What is sterognosis?

Answer 84

Ability to recognize 3D objects through touch alone

Question 85

Neurons in the somatosensory II area show what type of responses?

Answer 85

Attention modulated (That is, the responses of the neurons in this area to a stimulus depend on whether the subject is paying attention to the stimulus)

Question 86

What part of the CNS is utilized in graphesthesia?

Answer 86

DC/ML

Question 87

What is a nerve pressure palsy?

Answer 87

Loss of feeling d/t transient ischemia ("foot falls asleep")

Question 88

Why is there a stocking-glove sensory loss?

Answer 88

Leg nerves are longer, and therefore more easily affected by insults

Question 89

Review Brown_sequard syndrome.

Answer 89

DC/ML will show symptoms of the ipsilateral side of the lesion, since it crosses over in the caudal medulla. The neospinothalamic/paleospinothalamic (both parts of the spinothalamic system) decussate at the level (or one to two above) of the lesion. (recall the axons in this path from the DRG go up and down in the tract of Lissauer, then cross over in the anterior white commissure).

Question 90

In Brown-Sequard syndrome, loss or proprioception will by ipsilateral, or contralateral to the side of the lesion. how about pain and temp?

Answer 90

Proprioception ipsilateral Pain and temp contralateral

Question 91

What is the order of the speed of fibers?

Answer 91

``` Aalpha Abeta Agamma Adelta B C C ```

Question 92

What are the fibers involved in motor neurons?

Answer 92

A-alpha

Question 93

What are the fibers involved in GOTs?

Answer 93

A-beta (I-b)

Question 94

What are the fibers that innervate the muscle spindles?

Answer 94

Ia

Question 95

What do A-beta fibers innervate?

Answer 95

Muscle spindle endings

Question 96

What do A-gamma fibers innervate?

Answer 96

Axons of gamma motor neurons

Question 97

What do A delta fibers innervate?

Answer 97

fast pain, some temp

Question 98

What do type C fibers innervate?

Answer 98

Free nerve endings