Flashcards in Peripheral and central somatosensory pathways Deck (23):
What are the 4 main mechanoreceptors?
Merkel complexes, Meissner corpuscle, Ruffini Corpuscles, Paninian Corpuscles
What are the 2 skin types and on which type are mechanoreceptors most significant?
Glabrous and hairy (non-glabrous). Glabrous has skin ridges & is the location of the 4 main mechanoreceptors
What are the features of the Ruffini corpuscles?
DEEP: located in dermis & connected to connective tissue
involved in PROPRIOCEPTION
LARGE receptor Field
What are the features of Pacinian Corpuscles?
DEEP: located in dermis/subcutaneous layer. Onion like appearance.
LARGE receptor fields
respond to VIBRATIONS
What are the features of Meissner corpuscles?
most SUPERFICIAL - located in the epidermis. FAST adapting with SMALL receptor fields. Respond to skin movement
What are the features of Merkel complexes?
SUPERFICIAL- found at the tips of the epidermal ridges and respond to INDENTATION (Give info about grip force). SLOW adapting (turtle). SMALL receptor field.
Which mechanoreceptors have small receptor fields?
M&Ms are small = Merkel complexes and Meisser corpuscles
Which mechanoreceptors have LARGE receptor fields?
Ruffini and pacinian corpuscles = Italians eat pasta and get large
What is a receptor field?
the area of skin that is detected by the receptor that lies underneath it
How are nociceptors different to tactile receptors?
nociceptors respond at a higher range of stimulus -> ie heat that can burn rather than warmth (tactile). Nociceptors tell us that the tissue has been changed, whereas tactile receptors tell us that the external enviro has changed.
Which mechanoreceptor is also found in the peritoneal cavity?
Do the nerve axons for touch, pain, temperature and itch have the same characteristics?
NO. Touch has large myelinated axons.
Pain, temp itch have small diameter axons which can be unmyelinated
How many pairs of spinal nerves are there?
How do you tell from sensory deficits if the damage is in the peripheral nerve or nerve root?
peripheral nerve = deficit in region supplied (multiple dermatomes)
Nerve root = deficit in particular dermatome it supplies (ie C5 dermatome)
Sensory information from the periphery can ascend ipsilaterally or contralaterally - which stimuli follow which path?
contralaterally = Pain (decussates at the level of the spinal cord)
Ipsilaterally = Touch (decussates in medulla)
What are the dorsal columns? how are they arranged?
white matter tracts in the posterior/dorsal region of the spinal cord. Distal regions (lower limb) = medial (Gracile fasciculus), proximal regions (upper limb (cuneate fasciculus), cervical region) added on laterally as the fibres ascend.
How does tactile sensory info get to the cerebral cortex?
picked up by mechanoreceptors which have long large myelinated axons (primary sensory neuron) that ascend in the Dorsal columns (on the ipsilateral side) to the medulla where they meet the next neuron (cuneate or gracile nuclei) and ascend in the medial lemniscus pathway through the brainstem to the ventral posterolateral nucleus in the thalamus where lower limb info ends up lateral, and upper limb info ends up more medial, final neuron projects to the cortex with the lower limb medial and upper limb more lateral
What is the topographical arrangment of upper and lower limb info in the Dorsal Columns, Medial lemniscus and Cortex?
Dorsal column: UL = lateral
Medial Lemnisucs: UL = medial
Cortex: UL = lateral
(LL is opposite)
Where do neurons carrying touch/proprioception and vibration information decussate?
in the internal arcuate band in the medulla
Where is the primary somatosensory cortex (S1) located?
posterior to the central sulcus in the postcentral gyrus
What is the structure of the Primary somatosensory cortex (S1)
Divided into 4 areas which receive info from the thalamus - 3b gets the most info with some segregation of inputs ie Texture is projected to 1, whereas size/shape may go to area 2. Info from distal regions more medially located, info from more proximal regions (face, head) is more laterally located.
Do the somatosensory cortex regions show plasticity?
YES if a digit is amputated the cortical space devoted to that missing digit is taken over by other digits, or if you use one digit more than others the region can expand to a point, also occurs in region devoted to the nipple in breastfeeding mothers. Info suggests the plasticity is not just happening at the cortical level but at each level.