Somatosensory tracts 1: Proprioception and tactile pathways Flashcards
What types of somatosensation travels in the Posterior Column-Medial Lemniscal system (PCMLS)
Two-point discrimination: abillity to discriminate between two stimuli simultaneously
Proprioception: conscious awareness of body position and limb movement in space
flutter vibration
Receptor density gradient
Digits and perioral regions have high densities of tactile receptors
Other regions like the back has low density
Receptive field
area of the skin innervated by a somatic afferent fiber
small receptive fields have high receptor density
large receptive fields have low receptor density
In what position does discrimitive touch, flutter vibration and proprioception enter the spinal cord
the medial division and aspect of the posterior root
Where does first order neurons synapse in the PCML
if it involves reflexes the 1st order neurons synapse on the second order neurons at, above, or below the level of entry.
if it doesent involve reflexes the 1st order neuron travels in the ipsilateral fasciculus gracilis or fasciculus cuneatus, and will synapse on their nuclei (these contain the cell bodies of the 2nd order neuron)
What travels in the fasciculus gracilis
ipsilateral discrimitive touch, vibration, and proprioception from the spinal cord of the sacrum to T6 (contains info from the legs and feet)
What travels in the fasciculus cuneatus
ipsilateral disrimitive touch, vibration, and proprioception
from the spinal cord of the T6 level and up, will contain information from the arms
what is the topographical organization of the Fasciculi Gracile and Cuneatus
Sacral levels are positioned medially and fibers progressively more rostral levels are added laterally
(upper cervical is the farthest lateral region)
(regions that are just below T6 are the farthest laterally in the fasciculus Gracile
What happens if their are lesions to the Fasciculi gracile and Cuneatus
Ipsilateral reduction or loss of Discriminative, proprioception, and vibratory tactile sensations at and below the segmental level of injury
What is sensory ataxia
loss of muscle stretch reflexes and proprioceptive losses from the extremities due to lack of sensory input
Patient may also have a wide based stance and may place the feet to the floor with force
(Tabes dorsalis)
What is the arterial blood supply to the Posterior column
Posterior Spinal A, therefore lesions here would cause issues to projections of ipsilateral Discriminative touch, proprioception and vibration
what is the Pathway of the 2nd order neuron of the PCMLS
once the primary afferent synapses at the cuneatus and gracile nucleus or the bodies of the 2nd order neurons
- THe second order neurons will decussate as the the internal arcuate fibers to the contralateral Medial Leminiscus
- From their the Discrimitive touch, proprioception, and vibration will travel up the contralateral medial leminiscus until it reaches the Ventral Posterolateal nucleus of the thalamus
as the info travels up the the cuneate info will stay more posterior and more medial
What somatototopic arrangement is carried in the Ventral Posterolateral nucleus of the thalamus
foot is the most lateral and the neck is the most medial in the Ventral posterolateral nucleus
what is the pathway of the 3rd order neurons of the PCMLS
the 2nd order neurons will synapse on the Ventral Posterolateral nucleus (contain the third order neuron cell bodies) and then the 3rd order neuron will travel in the posterior limb of the internal capsule to the primary and secondary somatosensory cortices
What is the blood supply of the Vental Posterolateral and the Ventral Posteromedial nuclei of the thalmus
THalamogeniculate arteries which is a branch off the Posterior Cerebral Artery
lesions here would cause contralateral deficits of all tactile sensation over the body and head
What is the blood supply to the primary somatosensory cortex
the medial portion (Foot, LE, hip) by the longitudinal fissure is the Anterior cerebral artery
the lateral and inferior portion (face, hand, UE, chest) is the middle cerebral artery
What is the broadmans area for the Postcentral Gyrus
3a, 3b,1,2
Lateral to medial (3a,3b are in the central sulcus)
Secondary somatosensory cortex
SII
innerface of the upper bank of the lateral sulcus
Inputs from ipsilateal SI cortex and ventral posterior inferior nucleus of the thalamus
Parietal cortical regions also receive tactile inputs therefore lesions here can lead to what
lesions in parietal association area can produce Agnosia
- Contralateral body regions lost from the map
- limb is not recognized as part of the patients own body
- sensation is not radically altered
what are the primary afferents of the face and their associate nuclei
Primarily trigeminal: ophthalmic, maxillary and mandibular nerve
(does pain, temp, nondiscrimitive touch, discrimitive touch)
also have genticulare ganglion: CN VII
superior ganglion: CN IX, CNX
Proprioceptive info arise via the mesencephalic nucleus
What modalities gives rise from the Mesencephalic nucleus
proprioceptive afferents from TMJ, masticatory, and the extraocular muscles
What modalities gives rise from the Principal (chief) nucleus
Discriminative touch and pressure
what modalities gives rise from the nucleus of the spinal tract of the trigeminal (spinal nucleus
pain, temperature, and nondiscriminative touch
what is the pathway of the neurons in the Principal sensory nucleus
the primary afferents relaying discriminative tactile and vibration, synapse on the principle sensory nucleus
information relaying from the oral cavity and located dorsomedial on the nucleus will stay ipsilateral and travel via the Posterior trigeminothalamic tract to the ventral posteromedial nucleus in the pons
information relaying from V1, V2, V3 (located on the ventrolateral division of the nucleus) will crossover at the pons of the brainstem and will travel up the contralateral anterior trigeminothalamic tract
in the Ventral posteromedial nucleus of the thalamus, the 2nd order neurons will synapse and the third order neurons will carry the information to the lateral aspect of the primary sensory cortex via the posterior limb of the internal capsule
what is the blood supply to the trigeminal motor nucleus, principle sensory nucleus, and the mesencephalic tract and nucleus
the superior cerebellar artery:
- Trigeminal motor nucleus
- Principle sensory nucleus
- Mesencephalic nucleus
the Long circumferential branches of the basilar artery and branches of the anterior inferior cerebellar artery:
- principlal sensory nucleus
- trigeminal motor nucleus
- anterolateral systerm (in that area)
Somatotopic arrangement of the Ventral Posteromedial nucleus of the thalamus
Oral cavity is medial
External face is lateral
WHat information synapses on the Mesencephalic nucleus
conveys unconscious proprioceptive and pressure information from the muscles of the jaw teeth and extraocular muscles
then this information will project to the principal and spinal nucleus
some information will go to the trigeminal motor nucleus to form the jaw jerk reflex
Jaw jerk reflex
Stretching the masseter (downard tap on the chin will cause it to contract bilaterally
afferent limb: mesencephaplic trigeminal neuron whese peripheral process innervates the masseter muscle spindle and whose central process synapses on a trigeminal motor neuron (effrnt limb)
reflex is enhanced after UMN damage
