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EXCI360 > Lecture 3: Somatosensory System > Flashcards

Lecture 3: Somatosensory System Flashcards

1
Q

Somatosensory system:

A

Transmission of somatic (i.e.
body) sensations from body
receptors to CNS.

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2
Q

in the somatosensory system, the information is transmitted to (5) :

A

In order:
1. Spinal cord
2. Brainstem
3. Cerebellum
4. Thalamus
5. Cerebral cortex

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3
Q

three important elements of the somatosensory system:

A
  1. Sensory receptors (reception)
  2. Sensory pathways (transmission)
  3. Sensory centers (processing)
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4
Q

Mechanoreceptive sensations stimulated by:

A

mechanical
displacement (i.e. tissue deformation)

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5
Q

What are the two subtypes of mechanoreceptive sensations?

A

(1) Tactile sensations (skin)
(2) Proprioceptive (position) sensations (muscle and joints)

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6
Q

What are the different tactile sensations (skin) (4):

A
  1. touch
  2. pressure
  3. vibration
  4. tickle and itch
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7
Q

Proprioceptive (position) sensations (muscles & joints) (2):

A
  • Muscle condition sense (e.g. muscle contracted, stretched, relaxed)
  • Joint position sense
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8
Q

Nociceptive sensations (2):

A
  • Detect pain
  • Stimulated by any factor that damages tissue.
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9
Q

Thermoreceptive sensations:

A
  • Detect temperature (heat and cold).
  • Stimulated by change in temperature.
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10
Q

What are the three subdivisions of somatic sensations?

A

(1) mechanoreceptive sensations (tactile + proprioception)
(2) nociceptive sensations
(3) thermoreceptive sensations

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11
Q

Somatosensory receptors are classified based
on:

A

the type of sensation they detect

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12
Q

Mechanoreceptors detect:

A

Tissue deformation

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13
Q

Skin tactile receptors (4) (1/2 mechanoreceptors):

A
  • Free nerve endings
  • Expanded tip receptor (e.g. Merkel’s discs)
  • Encapsulated endings (e.g. Meissner’s
    corpuscle, Pacinian corpuscle, Krause’s
    corpuscle Ruffini’s end-organ…)
  • Hair end-organ (e.g. tactile hair)
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14
Q

Muscle receptors (1/2 mechanoreceptors):

A
  • Muscle spindles
  • Golgi tendon receptor
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15
Q

Nociceptors detect:

A

pain (i.e. tissue damage)

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16
Q

What are the somatosensory receptors of nociceptors:

A

Pain receptors: specialized free nerve
endings

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17
Q

Thermoreceptors detect :

A

change in temperature

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18
Q

What are the somatosensory receptors of thermoreceptors:

A

Specialized free nerve endings:
-Cold receptors
-Warmth receptors

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19
Q

Resting membrane potential:

A

At resting state (in absence of stimulus).

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20
Q

Action potential:

A

Results from transient changes in the resting
membrane potential of a stimulated neuron.

Electrical signal that travels along axons.

Long range transmission of information within the nervous system

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21
Q

Receptor potential:

A

Result from transient changes in the resting
membrane potential in the receptor of sensory
neurons by external stimuli

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22
Q

Synaptic potential:

A

➢ Results from the communication between neurons at synaptic contacts

➢ Recorded at the post-synaptic neuron by the stimulation of the pre-synaptic neuron

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23
Q

Receptor potential:

A

When a stimulus (e.g. touch, pain…) excites the receptor, the electrical
potential of the receptor membrane changes and creates a receptor
potential (like EPSP). Stimulation causes opening of ion channels (Na+,
Ca2+), depolarization of the receptor membrane.

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24
Q

Mechanisms of stimulation of the receptor (4):

A
  • Mechanical deformation, which stretches the membrane (e.g.
    mechanoreceptors)
  • Application of chemicals (e.g acid, alcohol, drugs…)
  • Change in temperature (e.g. thermoreceptors)
  • Tissue damage (e.g. pain receptors)
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25
Q

How does transduction of Sensory Stimuli occcur?

A

The receptor potential rises the membrane potential of the nerve
fiber attached to the receptor.

If the threshold is reached, an
action potentials appear in the nerve fiber.

Action potential travel through the nerve fiber to reach the brain
(i.e. AP transmits encoded sensory information to the brain).

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26
Q

Transduction of Sensory Stimuli: The greater the intensity of the stimulus, the

A

greater the receptor potential amplitude, and the
greater the RATE of action potential generation.

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27
Q

Adaptation of receptors:

A

When a continuous sensory stimulus is
applied, the receptors respond at a high impulse rate at first stimulus
and then progressively slow down their rate of response until many of
them no longer respond

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28
Q

Common examples of adaptation of the receptor:

A

-Adaptation to cold water

-Feeling of clothes on skin

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29
Q

Speed of adaptation varies with:

A

Type of receptors

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30
Q

Slowly adapting receptors:
decrease their rate of response ___

A

slowly

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31
Q

Slowly adapting receptors (3):

A

(1) Pain receptors
(2) Merkel’s discs
(3) Ruffini’s organ

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32
Q

Rapidly adapting receptors:
decrease their rate of response __

A

rapidly

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33
Q

Rapidly adapting receptors (4):

A
  • Thermoreceptors
  • Pacinian corpuscle
  • Hair receptor
  • Meissner’s corpuscle
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34
Q

When a continuous sensory stimulus is applied, the receptors
respond :

A

At a high impulse rate at first stimulus and then
progressively slow down their rate of response until many of them no longer respond.

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35
Q

Rate of adaptation varies with

A

type of
receptor

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36
Q

Pacinian corpuscle adapts

A

very rapidly (< second)

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37
Q

Hair receptor adapts:

A

rapidly (within
a second)

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38
Q

Joint capsule and muscle spindle receptors adapt

A

slowly (> second)

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39
Q

Adaptation of Receptors: Mechanisms of adaptation: 2 ways:

A

(1) Accommodation of the receptor

(2) Accommodation of the nerve fiber

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40
Q

Accommodation of the receptor:

A

The receptor potential
appears at the onset of the stimulus (e.g. compression) but disappears rapidly even though the stimulus continues (i.e. receptor still under compression) (e.g. squeezed ball)

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41
Q

Accommodation of the nerve fiber:

A

Decrease in the firing
rate of APs that is caused by an inactivation of the Na+
channels (i.e. saturation of ions channels).

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42
Q

There are __ different types of tactile receptors:

A

SIX

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43
Q

There are six different types of tactile receptors:

A

(1) Free nerve endings
(2) Meissner’s corpuscles
(3) Merkel’s discs
(4) Hair end-organ
(5) Ruffini’s end-organ
(6) Pacinian corpuscles

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44
Q

Free nerve endings (1/6 types of tactile receptors):

A

-Found everywhere in the skin (mostly at
SUPERFICIAL layers)

  • Connected with a SMALL UNMYELINATED sensory nerve fiber

-Detect CRUDE TOUCH and PRESSURE sensations

-SLOWLY ADAPTING RECEPTORS

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45
Q

Meissner’s corpuscles:

A
  • Elongated ENCAPSULATED nerve endings
  • Connected with a LARGE MYELINATED sensory nerve fiber
  • Located in the SUPERFICIAL LAYERS of the skin (non-hairy part)
  • Detect FINE TOUCH (discriminative, movement of the objects on the surface of the skin) and LOW FREQUENCY VIBRATION

-RAPIDLY ADAPTING RECEPTORS

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46
Q

Merkel’s discs:

A

(1) Located in the SUPERFICIAL layers of the skin (epidermis)

(2) Detect TOUCH and LIGHT PRESSURE

(3) SLOWLY ADAPTING RECEPTORS

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47
Q

Hair end-organ (free nerve endings of hair root):

A
  • In contact with the ROOT of the SKIN HAIR
  • Detects HAIR MOVEMENT
  • RAPIDLY ADAPTING RECEPTORS
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48
Q

Ruffini’s end-organ:

A

-ENCAPSULATED endings located in the DEEPER LAYERS of the skin (dermis)
- Detects HEAVY and PROLONGED TOUCH and DEEP PRESSURE
signals
- SLOWLY ADAPTING RECEPTORS

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49
Q

Pacinian corpuscles:

A

-ENCAPSULATED endings located in the DEEPER LAYERS of the skin (dermis)

  • Detect TISSUE VIBRATION or other RAPID CHANGES IN THE MECHANICAL STATE OF THE TISSUES (deep pressure,
    stretch)
  • RAPIDLY ADAPTING RECEPTORS
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50
Q

Pain sensation occurs when:

A

Tissue is being damaged (e.g. injury, inflammation)

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51
Q

Pain sensations are a __ for the body

A

protective mechanism –> causes individual to remove painful stimulus

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52
Q

What are the two types of pain:

A

(1) Fast pain (pricking pain)
(2) slow pain (aching pain)

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53
Q

Fast pain (pricking pain):

A

Felt within less a second of the stimulus and is sharp in character (e.g. hit a finger or toes by a hard object)

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54
Q

slow pain:

A

begins after a second or more and is throbbing or aching in nature (e.g. headache, tooth, pain)

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55
Q

Pain receptors are:

A

specialized free nerve endings

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56
Q

pain receptors are __ in many locations of the body

A

widespread

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57
Q

Pain receptors are widespread in many locations of the body:

A

(1) Superficial layers of the skin

(2) Internal tissues (e.g. tooth, stomach, …)

(3) Bones, joints and muscle surfaces

(4) Arterial walls (blood)

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58
Q

There are no pain receptors in:

A

The brain

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59
Q

Pain receptors can be stimulated by:

A

(1) Mechanical (tissue damage, strong stretch)
(2) Chemical ( alcohol, bradykinin, potassium ions, lactic acid…)
(3) Thermal (> 45 celscius)
(4) Inflammation

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60
Q

Pain receptors are __ adapting receptors

A

slow

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61
Q

for pain receptors, more stimulus =

A

more response

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62
Q

pain receptors are a protective mechanism to :

A

remove painful stimulus

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63
Q

Thermal sensations can be:

A

graduated

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64
Q

Thermal gradations are discriminated by:

A

3 types of sensory receptors (specialized free nerve endings)

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65
Q

What are the 3 types of sensory receptors (specialized free nerve endings) that discriminate thermal gradations:

A

(1) Cold receptors: sensible to cold temperatures

(2) Warm receptors: sensible to hot temperatures

(3) Pain receptors: sensible to extreme temperatures

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66
Q

Regarding thermal sensations, there are more _ than _ receptors

A

There are more cold receptors than warm receptors

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67
Q

Sensations of Freezing cold and burning hot are:

A

the same sensation because of the stimulation of pain receptors

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68
Q

Thermal receptors are:

A

Rapidly adapting receptors

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69
Q

what is an example of thermal receptors being rapidly adapting receptors?

A

swimming in cold water

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70
Q

The somatosensory receptor is:

A

The peripheral end-
process of the sensory neuron (pseudo-unipolar)
that transmits the sensory information to the CNS

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71
Q

The cell body of the sensory neuron is located in:

A

sensory ganglion (spinal cord).

72
Q

Sensory ganglion (spinal cord)

A

Its specific sensory nerve (labeled line
principle).

73
Q

Transmission of Somatosensory information
from the Receptor to the Brain: Velocity (speed) of transmission depends on:

A

The fiber diameter and the
myelinization of the fiber

74
Q

The larger the nerve fiber diameter:

A

The faster the rate of transmission of
the signal and the highest the quality of information (high discrimination).

75
Q

Velocity of transmission varies from

A

slow (0.5 m/s) to fast (120 m/s)

76
Q

Nerve fiber classification (2):

A

(1) Type A - myelinated fibers of varying size

(2) Type C - unmyelinated fibers: small size - slow transmission speed

77
Q

What are the four subtypes of Type A nerves

A
78
Q

Muscle spindle and Golgi tendon organ
transmit signals through:

A

Type A-a myelinated nerve fibers (e.g. proprioceptive sensation), fast transmission, high discrimination.

79
Q

Meissner’s corpuscles, hair receptors,
Pacinian corpuscles and Ruffini’s organs
transmit signals through:

A

Type A-β & A y -
myelinated nerve fibers (e.g. tactile sensations), fast transmission, high
discrimination

80
Q

Free nerve endings receptors transmit signals through (2):

A

(1) Type A-delta, myelinated nerve fibers (e.g.
fast (pricking) pain, cold sensations)
(2)Type C, unmyelinated fibers (e.g. slow
(aching) pain, cold, warmth, crude touch &
tickle sensations), slow transmission, low
discrimination

81
Q

The more critical the information the _ the rate of transmission

A

The more critical the information the faster
the rate of transmission.

82
Q

Sensory fibers from the body (except the face) transit to the brain through the

A

spinal cord

83
Q

Segmental distribution

A

each part of the body is connected to a specific
portion of the spinal cord

84
Q

Sensory fibers enter the spinal cord through

A

Dorsal root ganglion

85
Q

Where are the cell body of sensory fibers located?

A

In the dorsal root ganglion

86
Q

Two pathways for sensory information:

A

(1) Dorsal Column-Medial Lemniscal System
(2) Antero-Lateral System

87
Q

Sensory fibers in both pathways for sensory information (Dorsal column-medial lemniscal system and anterao-lateral system) :

A

Decussate

88
Q

Decussation:

A

(i.e. cross the midline to the contralateral
side): sensory information in one side of the body will be transmitted to the opposite
side of the brain

89
Q

In both somatosensory pathways (dorsal column-medial lemniscal system and antero-lateral system):

A

Three order neurons make the relay to transmit sensory stimulation from the receptor
to the final point in the cerebral cortex

90
Q

The Dorsal Column -
Medial Lemniscal Pathway transmits:

A

tactile sensations (touch, vibration,
fine pressure) and Proprioceptive sensations
(e.g. muscle stretch, joint position).

91
Q

The Dorsal Column -
Medial Lemniscal Pathway, signal originates from:

A

Tactile receptors (e.g.
meisner’s, Pacinian, Ruffini’s, Merkel’s) or
Proprioceptive receptors (e.g. muscle spindle,
Golgi tendon).

92
Q

The Dorsal Column -
Medial Lemniscal Pathway uses:

A

Large myelinated nerve fibers, such as A-a
A-β fibers for fast signal transmission, and
with high degree of discrimination (e.g. fine
touch)

93
Q

The Dorsal Column -
Medial Lemniscal Pathway : 1st order neuron:

A

1st order neuron has cell body in the DORSAL ROOT GANGLION of the spinal cord. It makes
synapse with 2nd order neuron at the DORSAL COLUMN NUCLEI (Cuneate, Gracial) in the
MEDULLA.

94
Q

The Dorsal Column -
Medial Lemniscal Pathway : 2nd order neuron:

A

-DECUSSSATES at the level of
MEDIAL LEMNISCUS (medulla), and then forms the
MEDIAL LEMNISCUS TRACT (up to the thalamus)
-makes synapse with the 3rd
order neuron at the THALAMUS (ventral posterior
lateral nucleus).

95
Q

The Dorsal Column -
Medial Lemniscal Pathway : 3rd order neuron:

A

Projects into the primary
somatosensory cortex.

96
Q

The Antero-Lateral Pathway
26 (Spinothalamic Tract) transmits:

A

a broad spectrum of sensory
modalities (e.g. pain, thermal sensations,
crude touch & pressure, tickle and itch,
sexual sensations)

97
Q

The Antero-Lateral Pathway
(Spinothalamic Tract) transmits:

A

A broad spectrum of sensory
modalities (e.g. pain, thermal sensations, crude touch & pressure, tickle and itch,
sexual sensations)

98
Q

The Antero-Lateral Pathway
(Spinothalamic Tract) signal originates from:

A

FREE NERVE ENDING RECEPTORS (e.g. pain receptors, thermal
receptors, skin free nerve endings)

99
Q

The Antero-Lateral Pathway
(Spinothalamic Tract) uses:

A

smaller myelinated (A-δ) and
unmyelinated (C) fibers

100
Q

The Antero-Lateral Pathway
(Spinothalamic Tract) uses smaller myelinated (A-δ) and
unmyelinated (C) fibers for:

A

slow transmission, and low degree of discrimination (e.g. vague types of sensory
information, aching pain)

101
Q

The Antero-Lateral Pathway
(Spinothalamic Tract): 1st order neuron:

A

Has cell body in the DORSAL ROOT of the spinal cord.

It makes synapse with 2nd order neuron at the SUBSTANTIA GELATINOSA in the dorsal horn of SPINAL CORD

102
Q

The Antero-Lateral Pathway
(Spinothalamic Tract): 2nd order neuron:

A

-Decussates at the level of the
ANTEROLATERAL QUADRANT in the SPINAL CORD, and then forms the ANTEROLATERAL (SPINOTHALAMIC) tract
(up to the thalamus).
- makes synapse with the 3rd
order neuron at the thalamus (ventral posterior lateral nucleus)

103
Q

The Antero-Lateral Pathway
(Spinothalamic Tract): 3rd order neuron:

A

Projects into the primary
somatosensory cortex.

104
Q

Somatosensory information from the
face & head is conveyed through :

A

the
trigeminal nerve (a cranial nerve).

105
Q

The trigeminal nerve enters into the
CNS trough the

A

brainstem (not spinal
cord).

106
Q

Somatosensory Pathway
of the Face: 1st order neuron:

A

has cell body in the
trigeminal ganglion. It makes synapse
with 2nd order neuron at the Principal
nucleus of trigeminal complex
(brainstem).

107
Q

Somatosensory Pathway
of the Face: 2nd order neuron:

A

-decussates at the level
of Medial lemniscus and form
Trigeminal lemniscus tract (up to the thalamus)
-makes synapse with the
3rd order neuron at the Ventral posterior
medial nucleus of thalamus

108
Q

Somatosensory Pathway
of the Face: 3rd order neuron:

A

projects into the
primary somatosensory cortex.

109
Q

The primary somatosensory cortex is the __ of the somatosensory pathways

A

TERMINAL STATION

110
Q

The primary somatosensory cortex is located in the :

A

Post-central gyrus (the
parietal lobe)

111
Q

Primary Somatosensory Cortex: Highly organized with distinct

A

Spatial orientation (i.e. each area of the cortex is devoted to a given body region, map of the sensor representation)

112
Q

Primary Somatosensory Cortex: Each side of the cortex

A

receives information from the opposite side of
the body

113
Q

Penfield’s Homunculus:

A

Unequal representation
of the body

114
Q

Penfield’s Homunculus:
unequal representation
of the body: which have greatest vs least area of representation?

A

Lips have greatest
area of representation
followed by the face,
thumb, fingers, hand…

Trunk and lower body
have the least area of
representation.

115
Q

More a region of the
body has receptors, the
greatest is

A

its area of
representation in the
somatosensory cortex

116
Q

Somatosensory Cortex is
composed of

A

six cellular layers
(cytoarchitectonic organization).

117
Q

Layer IV in the somatosensory cortex is:

A

The input layer (i.e.
3rd order neurons terminate in layer IV)

118
Q

Within the layers in the somatosensory cortex, the neurons are also arranged in:

A

vertical columns

119
Q

In the primary somatosensory cortex, each vertical column is:

A

Reserved for a specific sensory modality (i.e, pain, touch, pressure, stretch)

120
Q

In the primary sensory cortex, the different columns interact between each other which:

A

allows
the beginning of processing
sensory signals (i.e. giving
meaning to sensory information)

121
Q

The somatosensory association
cortex is located

A

behind the
primary somato-sensory cortex in
the parietal lobe.

122
Q

The somatosensory association cortex receives input from:

A

primary somatosensory cortex,
ventro-basal nuclei of the thalamus,
visual and auditory cortex.

123
Q

The somatosensory association function:

A

is to decode
somatosensory meaning
(information processing) and
integrate it with other sensory
information (e.g. visual, auditory)

124
Q

loss of somatosensory area results in:

A

various symptoms:

  • Inability to recognize complex objects.
  • Loss of high degree of perception on the opposite side of the body
    (e.g. neglect syndrome
125
Q

Sensation modality :

A

Each type of sensation: touch (fine,
crude) pressure (deep, light), stretch, vibration, hair
movement, pain, temperature is called a sensation
modality

126
Q

The labeled line principle:

A

Each sensation modality is
transmitted by specific nerve fibres that terminate at a
specific point in the CNS.

127
Q

The labeled line principle: When the nerve fiber is stimulated (at any level of the
pathway and by any type of stimulus):

A

the sensation is felt
at the original point (e.g. pain receptor in the finger) and
this is determined (processed) by the point in the CNS to
which the fiber leads (i.e. the brain who feels the
sensation, not the peripheral receptor).

128
Q

free nerve ending (Receptor) shape;

A

free nerve endings

129
Q

free nerve ending (receptor) location:

A

Superficial layer of skin

130
Q

Free nerve endings (Receptor) ; sensory modality

A

crude touch
pressure

131
Q

Free nerve endings (receptor): adaptation:

A

Slow

132
Q

free nerve endings; Nerve fiber:

A

C- unmyelinated

133
Q

Free nerve endings: Transmission speed:

A

Slow transmission
Low discrimination

134
Q

Meisner’s corpuscule: Shape:

A

encapsulated nerve ending

135
Q

Meisner’s corpuscule: location:

A

superficial layer of skin

136
Q

Meisner’s corpuscule sensory modality

A

(1) fine touch
(2) low frequency vibration

137
Q

meisner’s corpuscule adaptation:

A

rapid

138
Q

Meissner’s corpuscule: Nerve fiber:

A

A-beta
Myelinated

139
Q

Meissner’s corpuscule: transmission speed

A

Fast transmission
High discrimination

140
Q

Merkel’s discs: shape:

A

expanded tip

141
Q

Merkel’s discs: location:

A

Superficial layer of skin

142
Q

Merkel’s discs: sensory modality;

A

-touch
-light pressure

143
Q

Merkel’s discs: adaptation;

A

slow

144
Q

Merkel’s discs: nerve fiber:

A

A-beta
Myelinated

145
Q

Merkel’s discs: transmission speed:

A

Fast transmission
High discrimination

146
Q

Ruffini’s organ: shape

A

encapsulated nerve endings

147
Q

Ruffini’s organ: location:

A

Deep layer of skin

148
Q

Ruffini’s organ: sensory modality:

A

prolonged touch
Deep pressure

149
Q

Ruffini’s organ: adaptation:

A

slow

150
Q

Ruffini’s organ: nerve fiber:

A

A-gamma
Myelinated

151
Q

Ruffini’s organ: transmission speed:

A

Fast transmission/high discrimination

152
Q

Pacinian corpuscule : Shape:

A

Encapsulated nerve endings

153
Q

Pacinian corpuscule: Location:

A

Deep layer of skin

154
Q

Pacinian corpuscule: sensory modality

A

vibration
stretch

155
Q

Pacinian corpuscule: adaptation:

A

rapid

156
Q

Pacinian corpuscule: Nerve fiber:

A

A-beta
Myelinated

157
Q

Pacinian corpuscule: transmission speed

A

fast transmission
high discrimination

158
Q

Hair end-organ: shape

A

free nerve endings

159
Q

Hair end-organ location:

A

root of skin hair

160
Q

hair end organ: sensory modality:

A

hair movement

161
Q

hair end-organ : adaptation:

A

rapid

162
Q

hair end-organ nerve fiber:

A

A-beta
A-gamma
Myelinated

163
Q

Hair end-organ transmission speed:

A

fast transmission
high discrimination

164
Q

Specialized free nerve endings- pain: shape:

A

free nerve endings

165
Q

specialized free nerve endings - PAIN :location

A

-Superficial layer of skin
-internal tissues

166
Q

specialized free nerve endings - PAIN : sensory modality

A

pain

167
Q

specialized free nerve endings - PAIN : nerve fiber:

A

A-delta myelinated
C - unmyelinated

168
Q

specialized free nerve endings - PAIN : adaptation

A

slow

169
Q

specialized free nerve endings - PAIN : transmission speed

A

slow transmission
low discrimination

170
Q

Specialized free
nerve endings-
Thermal: shape

A

free nerve endings

171
Q

Specialized free
nerve endings-
Thermal: location

A

-Superficial
layer of
skin

172
Q

Specialized free
nerve endings-
Thermal: sensory modality:

A
  • Temperature
173
Q

Specialized free
nerve endings-
Thermal: adaptation:

A

rapid

174
Q

Specialized free
nerve endings-
Thermal: Nerve fiber:

A

A-delta
Myelinated
C-Unmyelinated

175
Q

Specialized free
nerve endings-
Thermal: transmission speed

A

Slow transmission/ Low
discrimination

176
Q

loss of the somatosensory association cortex results in:

A

-inability to recognize complex obects

-loss of high degree of perception on the opposite side of the body (e.g. neglect syndrome)

EXCI360 (7 decks)

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