Somatosensation Flashcards
Review the location of the primary somatosensory cortex (Brodmann’s area
3,1,2, BA 3,1,2)
The primary somatosensory cortex is in the parietal lobe within the post central gyrus, which is directly caudal to the central sulcus.
Define the sensory homunculus and locate the areas of BA 3,1,2 that receive
fine touch and proprioception from the body.
Map along somatosensory cortex of where signals from each part of the body are processed. 3: input from thalamus. FATL. same size for trunk as fingers and face (picture homunculus) 3a—proprioception, 3b—touch sensations. 3b connected to 1 &2, touch sensation processed more in 1 and 2. 1: texture of object, 2: size, shape, proprioception.
Be able to define and identify the anatomy of the medial lemniscal dorsal column
system.
Dorsal column-medial lemniscal pathway. Sensory path of CNS conveys fine touch, vibration, pressure, two point discrimination and proprioception. DCML projects onto primary somatosensory cortex of postcentral gyrus. three nerve system, from sensation into spine then up faciculi into nucleus gracillis
Be able to define and identify the location and pathway of all the neurons in the functional pathway for fine touch and proprioception for the body.
DCML=3 neurons. Sensory axons enter spinal cord and travel in dorsal fasciculi (cuneate-arms, gracile-legs). First synapse in cuneate and gracile in caudal medulla at level of sensory decussation (ipsi). Neurons in cuneate and gracile send axons across midline (contra) as arcuate fibers and form medial lemniscus (in the medulla). Topographically organized and synapse in the VPL. VPL sends its axons in the posterior limb of internal capsule to primary somatosensory cortex (BA 3,1,2). Medial lemniscus is a continuation of the dorsal column that starts within the brainstem. Formed by internal arcuate fibers.
Locate the sensory decussation in the brainstem and use this knowledge to
predict which side of the body will have a sensory deficit based on the location of
a lesion.
The sensory decussation is the cross over of axons from the nucleus gracilis and nucleus cuneatus. The fibres of this decussation are called the internal arcuate fibres and are found at the superior aspect of the closed medulla superior to the motor decussation. When an afferent pathway is damaged somewhere below the site of decussation, the sensory loss will be on the side ipsilateral to the lesion (i.e., the loss is on the same side as the lesion or ipsilesional). When an afferent pathway is damaged somewhere above the site of decussation, the sensory loss will be on the side contralateral to the lesion (i.e., the loss is on the side opposite the lesion or contralesional).
Be able to recognize the sensory deficits caused isolated nerve lesions.
Free nerve endings=pain and temp, Meissner corpuscle=slippage, Merkel cell=points, edges, textures, ruffini corpuscle=stretch, Pacinian corpuscle=high frequency vibrations. C1 has no dermatome.
C2-4=neck C5-T1=arms, T2-L2=chest, abdomen, L3-S1=legs S1-S4=groin
Be able to identify the different segments of the spinal cord and describe how many levels are in each spinal segment.
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
Be able to explain the functional impact of Lissauer’s tract.
Outer rim of spinal cord. Formed by c-fibers going up or down segments of spinal cord.
Be able to explain the relationship of spinal segments to the sensory dermatomes of the body.
Dermatome=area of skin supplied by single spinal nerve. C1 has no dermatome.
C2-4=neck C5-T1=arms, T2-L2=chest, abdomen, L3-S1=legs S1-S4=groin
Be able to predict the sensory and motor deficits of various spinal cord lesion syndromes.
T5 hemisection= brown Sequard syndrome, loss of pain and temperature. Transverse cord lesion: whole section severed, everything below is numb. Central cord syndrome: small lesion in cervical cord extends to topographic region of dorsal column and results in loss of fine touch/proprioception.
Be able to predict sensory and motor deficits caused by lesions in the medial medulla.
Loss of fine touch and proprioception on opposite side of body
Be able to predict sensory and motor deficits caused by a lesion of the ventrolateral thalamus or the somatosensory cortex.
Sensory loss everywhere
Be able to identify the anatomy of the ALS
Spinothalamic tract/anterolateral system is a sensory tract that transmits information from skin to thalamus. Composed of anterior (crude touch and pressure) and lateral (pain and temperature) spinothalamic tracts.
Locate the ventral white commissure in the spinal cord and use this knowledge to predict which side of the body will have pain and temperature deficit based on location of the lesion
Collection of nerve fibers that cross the midline of the spinal cord and transmit information from or to the contralateral side of the brain.
Be able to identify lesion localization based partly on pain and temperature perception of a patient
Spinothalamic tract crosses immediately at ventral white commissure in cervical spinal cord (all pain and temperature contra). DCML crosses in the medulla. If the lesion is in the brainstem of higher, the patient will have loss of pain perception, crude touch, and temperature on the other side of the lesion. With spinal cord hemisections, loss of crude touch and proprioception is ipsi, pain and temperature contra.
