Somatosensory Flashcards
Free Nerve Endings
Pain
Heat
Cold
Meissner’s Corpuscles (encapsulated)
Touch - not present in hairy skin
Aß fibre
Stroking, flutter (RA)
Merkel’s Discs
Touch - also present in moderate numbers in hairy skin
Aß fibre
Pressure, texture (SA)
Krause end bulbs
Touch - at the border of dry skin and mucous membranes
Ruffini endings (encapsulated)
Pressure - within dermis and joint capsule Aß fibre Skin stretch (SA)
Pacinian corpuscles
Vibration and pressure - within dermis and fascia
Aß fibre
Vibration (very RA)
Hair (G), guard (long)
Aß fibre
Stroking, flutter
Hair (D), down (short)
A∂ fibre
Light stroking
Nociceptors (Fibre class and termination in dorsal horn)
A∂ / C fibre
Laminae I,II
LTMs (Fibre class and termination in dorsal horn)
Aß fibre
Laminae III - VI
Proprioceptors (Fibre class and termination in dorsal horn)
Aa fibre
Laminae VII - IX
DCML pathway
Decussation occurs at the level of the brainstem.
Touch and proprioceptive information
Spinothalamic tract
Decussation occurs at point of synapse
Pain and thermosensation
Fasciculus Gracilis
Sensory input to T6 and below (legs and lower trunk)
Fasciculus Cuneatus
Input about T6 (arms and upper trunk)
DCML pathway capabalities
Stereogenesis - ability to recognise an object by feeling it Vibration detection Fine touch Conscious proprioception Weight discrimination
Somatosensory Cortex (SI)
Location: Post central gyrus of parietal cortex - posterior to central sulcus.
Brodmann areas: 1, 2, 3a, and 3b (3b primary somatosensory cortex - SI)
BA 3a (input, modality, effect of lesion)
Input: Proprioceptors (muscle spindles)
Modality: Body position
BA 3b (input, modality, effect of lesion)
Input: BA 3a, Merkel, Meissners
Modality: Touch (texture, shape, stimulus size)
Lesion: Deficits in texture, shape, discrimination
BA 1 (input, modality, effect of lesion)
Input: BA 3b, Cutaneous RA mechanoreceptors
Modality: Texture discrimination
Lesion: Loss of texture discrimination
BA 2 (input, modality, effect of lesion)
Input: BA 3a, 3b, Joint afferents, Golgi tenon organs
Modality: Object perception (size, shape, stereogenesis)
Lesion: Impaired grasping and size and shape discrimination (astereogenesis)
Somatosensory Cortex Layers
Molecular (lamina I) External Granular (lamina II) External Pyramidal (lamina III) Internal Granular (lamina IV) Internal Pyramidal (lamina V) Multiform (lamina VI)
Posterior Parietal Cortex (SII)
Receives information from SI and other cortical areas (visual, auditory) and subcortical areas (thalamus).
Neglect syndrome, damage to the right posterior parietal cortex. Pts believe the left side of the world does not exist etc.
