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Physiology Exam 4, Lecture 5
Somatosensory System, Pain
60
Physiology
Professional
11/02/2011

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Term
List the categories of of skin sensory receptors axpms
Definition
Aβ, Aδ, and C
Term
List the categories of of afferent muscle sensory receptors axons
Definition
Ia: Spindle, Ib: GTO, II, III, and IV
Term
What do Aβ sensory receptor axons detect?
Definition
Touch on the skin
Term
Describe Aδ sensory receptor axons
Definition
Small, myelinated skin sensory receptors
Term
Describe C sensory receptor axons
Definition
Very small, unmyelinated skin sensory receptors
Term
List the categories of of efferent muscle sensory receptor axons
Definition
α motor neurons, γ (smaller)
Term
What are the four classes of senses?
Definition
Superficial, deep, visceral, special
Term
What are the superficial senses?
Definition
Touch, pressure, flutter, vibration, tickle, warmth, cold, pain, itch
Term
What are the deep senses?
Definition
Position, kinesthesia, deep pressure, deep pain
Term
What are the visceral senses?
Definition
Hunger, nausea, distension, visceral pain
Term
What are the special senses?
Definition
Vision, audition, taste, olfaction, balance
Term

Free nerve endings:

a) What axon types do they have?

b) Where is it located?

c) What is its function?

Definition
a) C and Aδ
b) Skin
c) Pain, temperature, crude touch
Term

Meissner's Corpuscles:

a) What axon types do they have?

b) Where is it located?

c) What is its function?

Definition
a) Aβ
b) Skin
c) Touch and pressure (dynamic)
Term

Pacinian corpuscules:

a) What axon types do they have?

b) Where is it located?

c) What is its function?

Definition
a) Aβ
b) Skin
c) Deep pressure, vibration (dynamic)
Term

Merkel's disks:

a) What axon types do they have?

b) Where is it located?

c) What is its function?

Definition
a) Aβ
b) Skin
c) Touch, pressure (static)
Term

Ruffini's corpuscles:

a) What axon types do they have?

b) Where is it located?

c) What is its function?

Definition
a) Aβ
b) Skin
c) Stretching of skin
Term

Muscle spindles:

a) What axon types do they have?

b) Where is it located?

c) What is its function?

Definition
a) Ia, II
b) Muscle
c) Muscle length
Term

Golgi tendon organs:

a) What axon types do they have?

b) Where is it located?

c) What is its function?

Definition
a) Ib
b) Muscle
c) Muscle tension
Term
Define dermatome
Definition
Area of skin innervated by a single dorsal root; each spinal nerve receives input from a certain area of the body
Term
What does a dermatomal map show?
Definition
The areas of skin innervated by a single dorsal root
Term
What information does the dorsal column-medial lemniscal system transmit?
Definition
Touch, pressure, and movement of hairs from the body and back of the head.
Term
Describe the sensory fibers of the dorsal column-medial and where they travel
Definition
They enter spinal cord anywhere along the cord and ascend in the dorsal columns ipsilaterally
Term
What is the name of the fibers in the dorsal column from the lower half of the body?

Where do they synapse?
Definition
Gracile fasciculus; gracile nucleus
Term
What is the name of the fibers in the dorsal column from the upper half of the body?

Where do they synapse?
Definition
Cuneate fasciculus; cuneate nucleus
Term
Describe the path of the the gracile and cuneate nuclei
Definition
They cross to the opposite side and ascend to the thalamus in the medial lemniscus
Term
Where do the gracile and cuneate nuclei fibers in the medial lemniscus synapse?
Definition
In the ventroposterior lateral nucleus of the thalamus
Term
Where do fibers from the ventroposterior lateral nucleus syapse?
Definition
Somatosensory cortex
Term
List the steps in the dorsal column - medial lemniscal system
Definition
1. Primary afferents from body/back of head
2. Enter into spinal cord and ascend in dorsal columns (gracile/cuneate)
3. Terminate on dorsal column nuclei
4. Secondary fibers cross and ascend to medial lemniscus
5. Termination on ventroposterior lateral nucleus
6. Termination on somatosensory cortex
Term
What is the difference between pain and nociception?
Definition
The stimuli is nociception until it reaches the cortex and we decide it is pain
Term
What information does the spinothalamic system transmit?
Definition
Pain and temperature from the body and back of head
Term
Describe the pathway the primary afferents take in the spinothalamic system
Definition
Sensory fibers (primary afferents) enter spinal cord along its whole length, and synapse on spinothalamic tract cells in the dorsal horn.
Term
Describe the pathway of spinothalamic axons
Definition
(They are the secondary fibers)

Immediately cross to the opposite side to ascend in the ventrolateral
quadrant of the spinal cord in the spinothalamic tract, through brainstem, and terminate on ventroposterior lateral nucleus
Term
On what do spinothalamic axons terminate?
Definition
Ventroposterior lateral nucleus in the thalamus
Term
Describe the pathway of the tertiary fibers in the spinothalamic system
Definition
Start in the ventroposterior laeral nucleus of the thalamus and ascend to synapse in the somatosensory cortex
Term
List the steps in the spinothalamic system
Definition
1. Primary afferents for pain/temp ob body and back of head
2. Synapse on spinothalamic tract cells in dorsal horn
3. Immediately cross over and ascend through spinothalamic tract
4. Termination on ventroposterial lateral nucleus in thalamus
5. Synapse to somatosensory cortex
Term
What area of the thalamus does the

A)dorsal column-medial lemniscal system
B)Spinothalamic system
C)Trigeminal system

correspond to?
Definition
A) ventroposterior lateral nucleus
B) ventroposterior lateral nucleus
C) ventroposterior medial nucleus
Term
What cranial nerves are associated with the trigeminal system?
Definition
V, VII, IX, and X
Term
What information does the trigeminal system relay?
Definition
Pain, temperature, and touch for the face
Term
Define crude touch *giggle*
Definition
A touch that is hard to localize, such as a tickle
Term
Describe the pathway of primary afferents of the non-nociceptive trigeminal system
Definition
Synapse on neurons in the trigeminal main sensory nucleus
Term
Is the trigeminal system the same for pain and for touch?
Definition
No, there are separate pathways
Term
Describe the pathway of primary afferents of the nociceptive trigeminal system
Definition
Primary afferents synapse on neurons in the spinal
trigeminal nucleus.
Term
Describe the pathway of secondary neurons of the non-nociceptive trigeminal system
Definition
Axons leaving the main sensory nucleus (secondary axons) cross to the opposite side and ascend to
synapse on cell bodies in the ventroposterior medial nucleus of the thalamus.
Term
Describe the pathway of secondary neurons of the nociceptive trigeminal system
Definition
Axons leaving the spinal trigeminal nucleus (secondary axons) cross to the opposite side and ascend to synapse on cell bodies in the ventroposterior medial nucleus of the thalamus
Term
Describe the pathway of tertiary neurons of the non-nociceptive trigeminal system
Definition
Fibers exiting the ventroposterior medial nucleus (tertiary fibers) ascend to synapse on cell bodies in the face region of the somatosensory cortex.
Term
Describe the pathway of secondary neurons of the nociceptive trigeminal system
Definition
Fibers exiting the ventroposterior medial nucleus (tertiary fibers) ascend to synapse on cell bodies in the face region of the somatosensory cortex.
Term
What is pretty much the only difference between the non-nocieceptive and nocieceptive trigeminal pathways?
Definition
The nucleus that the primary afferents synapse on.

non-nocieceptive: trigeminal main sensory nucleus
nociceptive: spinal trigeminal nucleus.
Term
What do Aδ-fibers transmit?
Definition
Short-latency pricking pain evoked by noxious stimuli
Term
What do C-fibers transmit?
Definition
Second, long-latency pain of burning and less bearable quality
Term
What chemicals can sensitize nociceptors to stimuli?
Definition
a. Bradykinin
b. Serotonin
c. Histamine
d. Prostaglandins
e. Cytokines
Term
Define hyperalgesia
Definition
Enhanced sensation of pain in response to subsequent stimuli when tissues are damaged
Term
Define primary hyperalgesia
Definition
Enhanced sensation of pain at the site of tissue damage
Term
Define secondary hyperalgesia
Definition
Enhanced sensation of pain in the undamaged area surrounding the damaged area
Term
Describe visceral pain
Definition
Poorly localized pain commonly expressed as referred pain
Term
Describe the mechanism of referred pain
Definition
Somatic and visceral information converges onto a common pool of sensory neurons in the spinal cord.

When visceral input stimulates these
same neurons, the brain interprets the input as still coming from somatic structures, and refers the sensation to the somatic structures.
Term
Give an example of referred pain
Definition
A heart attack can be felt as pain in skin, shoulder, chest

Appendicitis can be felt in all of lower abdomen
Term
Define the "Gate Theory"
Definition
Excitation of large diameter fibers, either directly or through other modulatory systems, can ultimately reduce the activity in spinothalamic tract neurons, thereby reducing pain transmission.
Term
How do C-fibers affect the Spinothalamic tract neuron in the gate theory?
Definition
Active C-fibers dis-inhibit the STT
Term
How do Aα/β-fibers affect the Spinothalamic tract neuron in the gate theory?
Definition
It reduces activity in the STT via cognitive control or inhibitory control mechanisms
Term
What is a way that brainstem descending pathways can reduce pain?
Definition
By using enkephalin as a neurotransmitter, releasing endogenous opioids to inhibit the STT
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