Lesson 6
What is the 3rd order neuron?
-STT
-conveys info from thalamus to cortex
- cell bodies located in the VPL of the thalamus
- projects through internal capsule to primary somatosensory cortex
What happens to a lesion to the thalamus?
-contralateral decrease/ loss of body somatosensation
What is the clinical correlates for tactile defensiveness?
-aversive response to seemingly non-noxious tactile stimuli
- manifests itself in observable behaviors
What is the anatomy for the semicircular canals?
Function?
-3 hollow rings arranged perpendicular to each other
- each canal is filled with endolymph "thick water"
- each canal has a swelling called the ampulla which contains supporting cells and hair cells
(hair cells: embedded in cupola and mechanoceptors)
Function= detects rotary acceleration and deceleration
What is Vestibule- Ocular Reflex (VOR)?
-when head moves in one direction, eyes moves in the opposite direction
- called Doll's eye reflex in newborn infants
- provides stable visual field
- during movement, voluntary shifts in gaze are superimposed on the VOR for stable visual field
What is the trigeminal thalamic tract?
-tactile (pain, discriminative touch. temperature)
- proprioceptive input from the face
What happens with a lesion to the brainstem?
-variable decrease/ loss of body somatosensation
what are the two main types of vestibular Dysfunction?
- underachieve vestibular proprioceptive functions
- over responsive to vestibular sensations (fearful and overwhelmed)
What is the transmission for the semicircular canals?
- when the head is rotated, the force of the endolymph acts against the cupula, displacing the hair cells
-Bending of hair cells leads either to depolarization or hyper polarization
What is vestibular nystagmus?
- typical reflexive eye movements
- induced by angular acceleration
- back and forth eye movements are easily observed during rotation= perrotary nystagmus
- nystagmus continues after rotation ceases= postrotary nystagmus
- the term "vestibular nystagmus" is often used in medicine to refer to these typical reflexes induced by vestibular stimulation
Overview of somatosensation?
-Specialized receptors detect qualities of touch and proprioception
- tactile information travels to the cortex via two major routes:
- DCML: precise, high fidelity tactile and proprioceptive sensations
- STT: discriminative pain, temperature, crude/coarse touch sensations
- Cortex interprets sensations for detailed tactile perception, conscious proprioception, and use of somatosesnroy information to interpret location of body in space and to plan effective actions
What is the clinical correlate to sensory ataxia?
-ataxia: incoordination that is not due to weakness (damage to proprioception)
- sensory ataxia (eyes are close and you fall over)
- pathology: lesion in peripheral sensory nerve, dorsal root or column of spinal cord, or medial lemnisci
- symptoms: impaired conscious proprioception and vibration
- difficulty with balance incoordination
What are the functions of the Vestibular System?
-provides sensory information about head position and body's relationship to gravity
- postural control: detection of head movement, maintenance of equilibrium, facilitation of extensor tone
- control of eye movements: stabilization/direction of gaze
-autonomic functions (nausea/dizzy)
- contributes to emotions: stability, 'fight or flight"
What is the vestibular pathways?
-information from semicircular canals and otolithic organs is transmitted by the vestibulocochlear nerve (CN VIII)
- most information sent to the vestibular nuclei
-4 pairs of nuclei (superior, medial, lateral, inferior)
- Send information: to nearby structures of cerebellum and brainstem, upward to higher brain centers, down the spinal cord
What is vertigo?
Pathology: vestibular system dysfunction (a sudden imbalance of vestibular signals, secondary to a lesion of the vestibular apparatus, vestibular nerve, vestibular nuclei, or vestibulocerebellum)
Symptoms: an illusion of movement (often accompanied by nausea, nystagmus, and ataxic gait)
What is a lesion to Primary somatosensory cortex (S1)?
-contralteral decrease/ loss of body somatosensation
- remember the homunculus
What is the clinical correlate for Spinal Cord injuries?
-complete transaction of SC
- hemisection of Sc
- Pathology: complete transection of SC
- symptoms:
- sensory: loss of all sensation bilaterally below the level of the lesion
motor: bilateral loss below level of lesion
-Pathology: hemisection of SC (damage to right or left half) brown Squared Syndrome
- symptoms:
- sensory: loss of pain/ temperature below and contralateral to the lesion, loss of discriminative touch/ vibration/ conscious proprioception below and ipsilateral to the lesion
- motor: ipsilateral loss below level of lesion
What is the vestibular apparatus?
-inner ear
-its liquidy
-bony labyrinth: 3 semicircular canals and 2 otolithic organs
- membranous labyrinth: endolymph and hair cells (receptors)
What is the lateral vestibulospinal?
What is the medial vestibulospinal?
- lateral vestibulospinal= from lateral vestibular nuclei to spinal cord, descends ipsilaterally to trunk and limbs, supports postural control
- medial vestibulospinal= from medial vestibular nuclei to spinal cord, descends bilaterally to neck and upper trunk, supports control of neck and upper back
What is motion sickness?
Symptoms:
- occurs when there is a conflict between different types of sensory information (vestibular information, visual information)
- people who are susceptible to motion sickness usually have typical vision and vestibular system function
What happens with a lesion to the internal capsule?
-contralateral decrease/ loss of body somatosensation
What is the clinical correlate for referred pain?
-perception of pain in region other than site of injury
- visceral pain is perceived to be somatic pain ( heart attack0
- visceral and cutaneous fibers converge on the same tract (spinothalamic)
What are the 2 sacs in the otolithic organ?
What is the function of the otolithic organ?
Utricle and saccule
Function
- respond to static head position relative to gravity
- respond to linear acceleration and deceleration and static head tilt:
- utricle: horizontal movement and static head tilt
- saccule: vertical movement and static head tilt
-important in the maintenance of postural control
what is the ocular system connections
- medial longitudinal fasciculus?
-projects to: extra ocular muscle nuclei (Cn III,IV,VI), superior colliculus
-function: activates muscles attached to the eyeball (control eye movements, coordinated movements of the eyes and head)
what is sensory integration dysfunction?
-vestibular-bilateral disorders
-postural/ocular disorders
- gravitational insecurity
- vestibular under-responsiveness
-intolerance to movement