Module D-02 Flashcards
What are the 5 somatosensory modalities?
Touch, vibration,proprioception(muscular),pain and temperature
What type of neurons are the somatosensory receptor neurons?
Pseudounipolar
Where are sensory endings of the somatosensory receptor neurons found?
In skin or in (close to) muscle
Where are cell bodies of the somatosensory receptor neurons found?
Dorsal root and Cranial nerve Ganglia
What are the 2 Cutaneous touch receptors?
1) Merkel’s disks
2) Ruffini’s endings
What type of specific touch is transduced by Merkel’s disks?
discriminative touch
What type of specific touch is transduced by Ruffini’s endings?
skin stretch
What are the 2 Cutaneous receptor specific for Vibration?
1) Meissner’s corpuscles
2) Pacinian corpuscles
What type of vibration do Meissner’s corpuscles have highest sensitivity?
highest sensitivity / lowest threshold for lower frequencies of about 50 Hz
What type of vibration do Pacinian corpuscles have highest sensitivity?
highest sensitivity / lowest threshold for higher frequencies of about 300 Hz
What type of receptors transduce the signal for pain and temperature?
Free nerve endings
What type of free nerve endings for prickling pain and burning pain?
- pricking pain by rapidly adapting mechano-sensitive or thermo-sensitive receptors,
- burning pain by slowly adapting polymodal receptors
What type of free nerve endings for Temperature?
Cold and warm receptors
What type of receptors transduce proprioception (position sense)?
Proprioceptors:
Muscle spindles and Golgi tendon organs
Where are muscle spindles found?
Embedded in extrafusal fibers of working musculature
What type of receptor are the primary receptor of muscle spindle ?
Rapidly adapting receptor with a 1a afferent fiber
Which receptor for deep tendon reflex(myotatic reflex)?
Ia afferent fiber
What type of receptor is the secondary receptor of a muscle spindle?
slowly adapting receptor class II afferent fiber
What type of info does the primary muscle spindle fiber (1a)transduce?
Stretch
What type of info does the secondary muscle spindle fiber (class II) transduce?
Muscle length
Where are golgi tendon organs located?
border between muscle and tendon
What type of receptor is the golgi afferent fiber?
1b
What do the 1b fiber form?
afferent limb of inverse myotatic reflex
Afferent fibers from proprioceptors form which important pathways to the cerebellum ?
dorsal and ventral spinocerebellar tracts (don’t reach consciousness)
Somatosensory receptors use four different fiber types:
1) Large myelinated fibers (muscle 1 and cutaneous A alpha)
2) medium myelinated fibers (muscle II and cutaneous A beta)
3) small myelinated fibers (muscle III and cutaneous A delta)
4) unmyelinated fibers (muscle IV and cutaneous C)
Size and conduction velocity of Large and medium myelinated fibers
diameters : up to 20 μm
conduction velocities : up to 120 m/sec
What type of receptors use Large and medium myelinated fibers?
cutaneous mechanoreceptors and proprioceptors
What type of sensory info do Large and medium myelinated fibers carry?
touch, vibration and proprioception
Size and conduction velocity of small myelinated fibers
diameters: about 1 μm
conduction velocities : 5 m/sec
Size and conduction velocity of unmyelinated fibers
diameter: 0.2 and 1.5 μm
conduction velocities: from about 0.5 to about 2 m/sec.
What type of sensory info do small myelinated and unmyelinated fibers carry?
pain and temperature
Between which vertebrae does the T1 spinal nerve emerge?
btw T1 and T2
At what level does the spinal cord end?
L1/L2
The sensory and motor nerve roots that are below L1/L2 form the___________
cauda equina
Dermatome for back of the head
C2
Dermatome for thumb
C6
Dermatome for Middle finger
C7
Dermatome for Little finger
C8
Dermatome for Nipple line
T4
Dermatome for Umbilicus
T10
Dermatome for Groin
L1
Dermatome for big toe
L5
Dermatome for Little toe
S1
Which pathway carries Touch, vibration and proprioception ?
the dorsal column/ medial lemniscus system
Which pathway carries Pain and Temperature?
anterolateral system (aka spinothalamic tract)
Describe the pathway of fibers going in the Dorsal column/medial lemniscus system.
Fibers of the dorsal root ganglion neurons => enter the dorsal column => ascend within this white matter tract(cuneate and gracile fasciculus) => to the medulla => synapse in the nuclei of the dorsal columns (cuneate and gracile nucleus).
Fibers that ascend in the cuneate fasciculus originate from________
Upper extremities
Fibers that ascend in the Gracile fasciculus originate from________
Lower extremities
Describe the 2 pathways of afferent pain and temp. fibers for Anterolateral system
1) Anterolateral tract:
Enter the spinal cord segments via the dorsal roots of the spinal nerves => central axons of dorsal root ganglion neurons => synapse within the dorsal horn => axons of the second order neurons cross to the contralateral side through the anterior white commissure => ascend in the ALS fiber tract of the spinal cord (white matter)
2) Collateral fibers also go up the dorsolateral tract -Lissauer’s Tract
Where are pain and temp second order fibers from the arm ascend in the anterolateral column?
Medially
Where are pain and temp second order fibers from the leg ascend in the anterolateral column?
laterally
Where does Lissauer’s tract go?
collaterals of the primary afferent fibers may ascend (or descend) one or two segments in the dorsolateral fasciculus
- divergent fibers that synapse on multiple neurons
What virus does Shingles originate from?
Herpes zoster
Describe the symptoms of shingles
painful skin irritations in the dermatomal area innervated by the related ganglion
Where does the herpes zoster virus stay when latent?
in dorsal root ganglion cells or trigeminal ganglion cells
What is Brown Sequard Syndrome?
Hemisection of the spinal cord as a result of a slow growing
mass, or a traumatic lesion interrupting ascending and descending fibers on one side of the cord causing both sensory and motor losses
Key sensory finding in Brown Sequard syndrome
Touch, vibration and proprioception are lost on one side of the body, whereas pain and temperature are lost on the other side of the body
What are the sensory findings AT the level of the lesion in Brown Sequard syndrome?
Ipsilateral side (lesion side): Loss of all 5 somatosensory
modalities
Contralateral side: none are lostWhat are the sensory findings BELOW the level of the lesion in Brown Sequard syndrome?
Ipsilateral side (lesion side): loss of touch, vibration and
proprioception (which started at
the level of the lesion)
continues through all
dermatomes below
Contralateral side: pain and temperature sensations are all
lost except one or two segments that
may be spared due to Lissauer’s tract
Which tract is found in the Lateral column?
Corticospinal Tract
What is Syringomyelia?
pathologic enlargement of the central canal of the spinal cord, that interrupts the fibers of the anterior commisure
What are the sensory losses AT the level of the lesion in Syringomyelia?
Bilateral: Loss of only Pain and temp
What are the sensory losses Below the level of the lesion in Syringomyelia?
Bilateral: No losses
