Lecture 2: Cutaneous Sensation: Touch and Pain Flashcards
How are cutaneous sensory fibers similar to other sensory fibers?
- some are encapsulated with specialized endings
- some are free nerve ending
How do neurons differ from each other?
by shape of protein
Most receptors of the somatosensory system are what kind of receptors?
mechanoreceptors
Chemoreceptors respond to what?
acidic substances
Nociceptors respond to what?
potential damaging stimuli
What mechanoreceptors are myelinated?
- SA1 (Merkel cell)
- RA (Meisssner corpuscle)
- SA2 (Ruffini corpuscle)
- PC (Pacinian corpuscle)
Which mechanoreceptor is unmyelinated?
RA (free nerve ending)
What is the role of perception of each of the mechanoreceptors?
- SA1: pressure, form, texture
- RA: flutter, motion
- SA2: stretch
- PC: vibration
- RA (nerve ending): pressure; any touch on skin
Mechanoreceptors are mostly what type of fiber?
beta
RA (nerve ending) is the only one that is not beta
Somatosensory is absent in what type of patients? Why?
burn patients because they do not have Merkel and free nerve endings
What do receptors code?
- modality
- spatial location
- stimulus duration
- intensity
The greater the touch = the … channels being open (more or less?)
more
Greater 2 point discrimination means what type of index?
smaller discrimination index
Less 2 point discrimination means what type of index?
higher discrimination index
Where on the body would have a higher discrimination index?
arms, legs, torso, back
Where on the body would have a smaller discrimination index?
face, lips, nose, fingers
Which adapting receptor keeps firing as long as you’re holding something?
slowly adapting
Which adapting receptor only responds to a change in the stimulus?
rapidly adapting
Which mechanoreceptors are rapid adapting?
- Pacinian corpuscles
- Meissner’s corpuscle
Which mechanoreceptors are slow adapting?
- Merkel’s discs
- Ruffini’s ending
What type of fibers come from the dorsal?
sensory fibers
Which tract in the dorsal column/Medial lemniscal system is responsible for the lower body?
gracile tract
Which tract in the dorsal column/Medial lemniscal system is responsible for the upper body?
cuneate tract
Where do the cuneate and gracile tracts cross?
internal arcuate fibers
What is the base of the brainstem and the location of where the tracts synapse?
caudal medulla
Is the upper or lower part of the spinal cord responsible for the lateral portion of the body?
upper
The post. dorsal column is responsible for what in the lemniscal system?
touch, pressure, vibration
The lateral column is responsible for what in the lemniscal system?
pain, temp.
Is the upper or lower part of the spinal cord responsible for the medial portion of the body?
lower
Where is touch info. carried in?
in the medial lemniscus
What is the difference between VPMN and VPLN?
- VPMN= ventral posterior medial nucleus
- VPLN= ventral posterior lateral nucleus
Where is info. integrated?
primary somatosensory cortex
What is the path of segregation of somatosensory info in the cells?
cell body -> dorsal horn -> post. column
Where does the info synapse in the lemniscal system?
in the VPLN
The somatosensory cortex is located in what lobe?
parietal
Is VPLN or VPMN for the body?
VPLN
lateral= lotion/body
Is VPLN or VPMN for the face?
VPMN
medial= makeup/face
What is the pathway for the trigemino-thalmic-cortical (face recognition)?
- cranial nerve carries face info. to trigeminal neuron
- trigeminal neuron info. comes through ganglion
- info. synapses and crosses immediately
- goes to trigeminal lemniscus and VPMN
- ends in somatosensory cortex
What is a dermatome?
slice of skin that one spinal/brainstem cranial nerve root carries info from
How do dermatomes develop?
on an embryological level
What are the characteristics of the somatosensory cortex?
- has plasticity
- has discriminate touch, pain, prociception
What determines how big nuclei are?
density of info.
What si responsible for pain, prociception, and touch in the ventral post. complex?
postcentral gyrus
What is the homunculus?
representation of how much brain processing area there is for each body part
What thermoreceptors are free nerve ending?
both warm and cold
What are the fiber types of the thermoreceptors?
- warm: C
- cold: A delta (acute pain)
Which nociceptors are free nerve ending?
both small,unmyelinated and unmyelinated
What are the fiber types for the nociceptors?
- small, myleinated: A delta (acute pain)
- unmyleinated: C (warm/dull pain)
What is the role of perception of the nociceptors?
- small, myelinated: sharp, localized pain
- unmyelinated: burning
What is an example of an acute pain?
initial sting from a bee
What is an example of a dull/throbbing pain?
long lasting pain after a bee sting
Are all A dekta and C fibers nociceptors?
NO
What is an example of how temp and pain can be carried by the same fibers?
capsaicin
What does capsaicin do?
binds to VR-1 receptor to allow Ca and NA to start signaling
Discriminitive touch stays on the same side as what column?
posterior
What is an example of how discriminitive touch relate to pain signaling?
person with right spinal cord lesion loses discriminitive touch on right side, but loses response to temp on left side
At the spinal cord, where does pain signal come in and where does it cross?
comes in at dorsal horn and crosses at ant. white commissure and goes to opposite side
What is the ant. commissure in the spinal cord?
small bundle of fibers connecting 2 hemispheres in the brain
What is the ant. white commissure in the spinal cord?
where nociceptive info. is processed
What is Lissauer’s tract?
where the pain signal will ascend once int he dorsal horn and cross at multiple levels to help preserve nociceptive info. after an injury
What is the pathway of the pain signal?
comes in at dorsal horn -> crosses at ant. white commissure -> goes to anterolateral tract -> enters brainstem -> ends at primary somatic sensory cortex
The trigeminal system has what type of info.?
info from the face
What is the pathway of info. from the face?
comes in from pons -> drops to medulla -> crosses spinal thalamic tract -> ends at VPMN and primary somatic sensory cortex
Will an injury in the medulla lose sensation on one or both sides?
both
The nociceptic pathway goes through what entire system?
limbic
The periaquiductal grey is responsible for what?
pain control
The superior colliculus is responsible for what?
attention
What is fresponsible to flood the system with histamine and Ach?
reticular formation
What is the most common referred pain?
heart attack
What is allodynia?
perception of normally non-nocicpetive stimuli being painful
Getting a tap on the site of a new shot is an example of what type of sensation a patient can undergo?
allodynia
What is hyperalgesia?
nociceptive stimuli perceived as being more painful than expected
Getting pushed on the arm after getting a shot is an example of what type of sensation a patient can undergo?
hyperalgesia
What is peripheral sensitization?
allodynia/hyperalgesia due ot peripheral mechanisms
What is central sensitization?
allodynia/hyperalgesia due to central mechanisms
What is neurochemistry?
sensitization of NMDA receptors on spinal interneurons
Which type of sensitization delas with perception exaggerated from personal experiences or trauma?
central sensitization
Where do spinotectal fibers synapse?
periaqueductal grey syanpse
Where do PAG neurons project?
to the raphe nucleus and the lateral tegmental nucleus
Raphe nucleus sends what type of projections?
serotonergic
Lateral tegmental nucleus sends what type of projections?
noradrenergic
What 2 things activate enkepheline?
serotonin and norepinephrine
What are the 2 types of pain control in the spinal column?
gated/descending and local
What is gated/descending control of pain?
enkepheline inhibits periaqueductal grey synapse
What is local control of pain?
A beta fibers are activated to decrease the pain going to the brain
Which of the following correctly identifies the mechanoreceptor responsible for sensing deep pressure/vibration and its respective adaptation type?
A. Meissner corpuscle; Rapidly adapting
B. Pacinian corpuscle; Slow adapting
C. Meissner corpuscle; Slow adapting
D. Pacinian corpuscle; Rapidly adapting
D
All of the following regarding the dorsal column/medial lemniscal system are true EXCEPT:
A. Mechanosensory information from the lower body synapses at the gracile nucleus
B. After entering the cerebrum, fibers synapse at the ventral posterior lateral nucleus
C. Mechanosensory information decussates at the anterior white commissure
D. Mechanosensory information from the upper body enters the CNS via a cervical dorsal root ganglia
C
A 37-year-old man is rushed to the ED following a severe motorcycle accident which has altered somatosensory perception in his lower limbs. MRI indicates the patient has a lesion in the right portion of his spinal cord. What symptoms is the patient likely experiencing?
A. Loss of both mechanoreceptive and nociceptive sensation in the right leg
B. Loss of mechanoreceptive sensation on the right leg and nociceptive sensation on the left leg
C. Loss of both mechanoreceptive and nociceptive sensation in the left leg
D. Loss of mechanoreceptive sensation on the left leg and nociceptive sensation on the right leg
B
The anterolateral system sends projections to varying portions of the CNS to elicit physiological responses after pain stimulation. Which of the following structures directs our attention to the source of pain?
A. Superior colliculus
B. Insular cortex
C. Periaqueductal Gray
D. Somatosensory cortex
A
- The perception of normally non-nociceptive stimuli as being painful is often caused by a form of sensitization. Which of the following would lead to peripheral/local sensitization?
A. Loss of primary afferents in the dorsal horn
B. Sensitization of NMDA receptors on spinal interneurons
C. Release of neuropeptides from C fibers
D. Sensitization of NMDA receptors directly on the anterolateral tract
C
