Transcript Temporal Aspects of Visual Extinction

Chapter 7 Somatosensory System
 Chris Rorden
University of South Carolina
Norman J. Arnold School of Public Health
Department of Communication Sciences and Disorders
University of South Carolina
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Overview
 >20 types of receptors in skin:
touch, temperature, stretch, etc
 2 pathways to brain
– Dorsal columns
 Precise touch, joint angle, etc.
 Crosses side at medulla
– Antero-lateral Tract
 Coarse information regarding pain
and temperature
 Convergence of information
 Crosses side at entry in spinal
column
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Early Somatosensation
PNS detection of
– Pain
– Temperature
– Touch
– Conscious proprioception
Transfer of information to CNS
3
Cross section of spinal cord
Afferent Fibers
Muscle
Motor Cell
Efferent Fibers
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Hierarchy of Sensory Fibers
 Specialized Receptors
 (Stimuli to Neural Signal)
 Single Nerve Fiber
 Sensory Fiber Bundle
 Spinal Nerve
 Dorsal Root Ganglia
 Dorsal Column Nuclei
 Spinal Motorneurons or Reticular Formation
 Thalamus
 Primary and Association Cortex (Parietal Lobe)
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Organization
Each tract mediates specific modalities of
sensation, somatotopic organization in tracts
and cortex
– Mechanoreceptive
Mechanical displacement of nerve endings
Touch (fine and diffuse), pressure, vibration, kinesthesia
– Thermoreceptive
Cold and Heat
– Nociceptive
Pain
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Specialized Receptors
 Receptors specialize by type of stimulus
 Adaptiveness: Reduction of response to sustained stimuli
 Basic Types of Sensory Receptors
 Encapsulated Endings
– Adapting (tactile)
 Pacinian corpuscle: deep pressure touch and high frequency vibration.
 Meissner’s corpuscle: light touch, such as the fingertips, palms, soles,
lips, tongue, face
 Free Nerve Endings (pain, temp, some tactile)
– Nonadapting
 Expanded Tip Endings (tactile, temp)
– Moderately adapting
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Three neuron Organization
 1st Order
– Dorsal Root Ganglion
 2nd Order
– Enter CNS at spinal cord or brainstem
– Project to opposite side crossing
midline to thalamus
 3rd Order
– Thalamus neurons which project to
cortex
Dorsal root ganglion (‘spinal ganglion’)
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Discriminative Touch
Cerebral Cortex
Bipolar or multipolar
3
Thalmus
2
Dorsal root ganglion
Medulla
Receptors
(skin,
muscle,
joints)
1
Spinal cord
Pseudo-Unipolar nerve
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Anatomical Divisions
 Dorsal Column-Medial Lemniscal (or Epicritic
System)
– Fine discriminative touch, vibration, limb position,
kinesthesia & deep pressure
– Position sense
 Proprioception - Awareness of limb position
 Kinesthesia - Awareness of limb movement
 Anterolateral (or Protopathic System)
– Pain, temperature and diffuse touch
 Lateral spinothalamic tract
 Anterior spinothalamic tract
 Dorsal Column-Medial Lemniscal System
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Dorsal Column-Medial Lemniscal System
 Important for skilled movements
–
–
–
–
Stereognosis - Fine touch discrimination
Graphesthesia - Recognizing numbers written on body
Two and multiple point touch
Deep touch
 Receptors
– Meissner’s and Pacinian Corpuscles
 Encapsulated end receptors
 Highly sensitive and adaptable
– Muscle Spindle Organs
 Kinesthesia
 Proprioception
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Neural Pathways
 Fasciculus Gracilis
(slender, graceful)
 Fasciculus Cuneatus
(wedge-shaped – short)
(think cuneiform writing)
 Path
–
–
–
–
–
Mediate discriminative
Touch from different
Body areas; follow
three-neuron
organization
Spinal Ganglion (1)
Fasciculus Gracilis/Cuneatus tracts (1)
Gracilis or Cuneatus Nucleus (2)
Through Medial Lemniscus to Thalamus (3)
Thalamus to Cortex
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Levels of Reception
Fasciculus Gracilis
– Sacral to Midthoracic Level
– Lower Body
Fasciculus Cuneatus
– Above Midthoracic Level
– Upper Body
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Pathway
Spinal Cord
Brainstem Nuclei
Thalamus (N. Ventral Posterolateralis)
Thalamus through Internal Capsule to Primary
Sensory Parietal Cortex
Primary to Association Cortex
– Mapped spatially (homunculus)
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Dorsal Column-Medial Lemniscal System
In the PNS/Spine
Pacinian corpuscle
Cervical
Fasciculus
cuneatus
Thoracic
Fasciculus
gracilis
Lumbar
Meissner’s corpuscle
Sacral
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Dorsal Column-Medial Lemniscal System
Pons and Medulla
Nucleus gracilis (lower body)
Nucleus cuneatus (upper body)
Medulla
Decussation
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Dorsal Column-Medial Lemniscal System
Midbrain-Cortex
Homonculus
Thalamus
Midbrain
Medial lemniscus
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The homunculus (little man)
The motor strip (red, frontal
cortex) spatially map
corresponding portions of the
contralateral hemisphere.
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Clinical Considerations
 If injury is inferior to decussation, deficit can be
ipsilateral (same side)
 If injury is superior to decussation, deficit will be
contralateral (opposite side)
 Tests
–
–
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–
–
–
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Two Point Discrimination
Stereognosis: ID object with eyes closed
Graphesthesia: number or letter on skin
Vibratory: Tuning fork on bony surface
Romberg: standing with eyes closed
Kinesthesia: movement identified
Association: Identification of object
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Anterolateral system
 Pain, Temperature, & Diffuse Touch
 Three-tier neuron organization system
1. Enter at spinal ganglion (1st)
2. Cross in spinal tract (2nd order)
3. Ventral posterolateral n. of thalamus (3rd)
 Two Tracts
– Lateral Spinothalamic
– Anterospinothalamic
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Lateral Spinothalamic Tract
 Receptors - Free Nerve Endings
 Neural Pathway
– Nocioceptors (pain)
– Dorsolateral spinal cord (up or down several segments)
 spinal cord entrance
– Substantial Gelatinosa and Proprius
 Where 1st order neurons connect with 2nd order neurons
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–
–
–
–
Lateral Spinothalamic Tract
Cross Midline (2nd order)
Spinal Lemniscus (brainstem)
Thalamus (VPL) to Cortex
Collaterals to Subcortical structures
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Pain and Temperature (antero-lateral)
Bipolar or multipolar
Cerebral Cortex
3
Dorsal root ganglion
Receptors
(skin,
muscle,
joints)
Thalmus
2
1
Spinal cord
Pseudo-Unipolar nerve
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Clinical Considerations (lesion locations)
PNS or spinal before midline cross results in
problems ipsilaterally.
Spinal or Brainstem lesion results in problems
contralaterally.
– Chordotomy (surgical lesion) to reduce pain
Dermatomes: Failure to perceive pain
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Dermatome
Dermatome: Refers to the body area
innervated by the neurons in a single dorsal
root ganglion (dorsal part of the spinal nerve)
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Dermatome
Can help distinguish between
psychiatric and neurological
injury.
– Psychiatric conversion disorder:
often glove/stocking anesthesia
– Neurological disorder: follows
dermatomes
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Other Considerations
Referred pain: one site has pain but felt in
another site
Drugs can suppress pain sensitivity or block
pathway
Analgesia: No sensation
Hypalgesia: Decreased pain (higher threshold)
Hyperalgesia: Increased pain (lower threshold)
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Anterospinothalamic Tract
 Discrimination of Diffuse touch
 Receptors: All three types
– Encapsulated endings
– Free nerve endings
– Expanded tip endings
 Neural Pathway
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–
–
–
–
Skin to ganglia (1st)
Dorsolateral spinal cord (up and down seg)
Proprius and Substantia Gelatinosa (2nd)
Go to spinothalamic tract to VPL (thalamus) to postcentral gyrus
Collaterals to subcortical structures
 Clinically, interruption causes no obvious deficit
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Collaterals in the axon
Cortex
VPL in thalamus
Subcortical structures
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Sensation from the head
Face and Head area
– face
– forehead
– anterior half of scalp
– dura mater
– orbital cavities
– nasal and oral cavities
Epicritic (Dorsal) and Protopathic
(Anterolateral) Systems
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Facial sensation
Three Neuron Levels
– 1st order: Semilunar ganglion of Trigeminal Nerve
– 2nd order: Principal sensory nucleus and
trigeminal spinal tract nucleus
– 3rd order: VPL in thalamus to lower third of
postcentral gyrus
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Fine Discriminative Touch
Neural Pathway
– Encapsulated receptors in facial and head skin
– Semilunar ganglion and trigeminal nucleus
– Medial Lemniscus Thalamus to cortex
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Cranial Proprioceptive and Kinesthetic Sensation
Teeth, periodontium palate, TMJ, muscles of
mastication
Involves mesencephalic N. and follows similar
pattern
Mechanism for jaw reflex and bit control
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Cranial Sensation: Clinical Considerations
Lesions can affect only one branch
– Ophthalmic
– Maxillary
– Mandibular
– Or one half of the face
Tests the same for discrimination
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Pain and Temperature from Face
Neural Pathway
– Nocioceptors
– Semilunar ganglion to
nucleus of spinal trigeminal tract (moves caudally)
chief sensory nucleus
– Cross midline to thalamus and some stay
ipsilateral
– Postcentral Gyrus
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Trigeminal Cranial Nerve
Cerebral Cortex
3
Thalmus
2
Brainstem
Spinal Cord
1
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Clinical Considerations
Inflammation of semilunar ganglion causes
severe pain
Tic douloureux - severe pain
Assessment of normal function
– pinching to cause pain
– Quality assessment by patient
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Diffuse Touch from Face
Neural Pathway
– Dorsal and ventral secondary trigeminal tract
– Some to spinal trigeminal tract nucleus
– Some to chief sensory nucleus
To ventral posteromedial nucleus of thalamus
To sensory cortex
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Unconscious Proprioception
 Conscious proprioception by dorsal column-medial
lemniscal system
 Unconscious involved in walking, articulating, writing,
swallowing, and eye movement.
 Two order neural system
 Tracts
– Dorsal Spinocerebellar
– Cuneocerebellar
– Ventral Spinocerebellar
 Receptors
– Muscle spindles and Golgi tendon organs located in
muscles and limb joints
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Ventral Spinocerebellar Tract
Mediates unconscious proprioception
Lower limbs to bilateral cerebellum
Sacral and Lumbar levels through ventrolateral
Spinocerebellar tract to opposite cerebellar
hemisphere
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Dorsal Spinocerebellar Tract
 Mediates unconscious
proprioception
 Lower limbs and middle
regions of body to to
bilateral cerebellum
 Spinal ganglion to nucleus
dorsalis of Clark at third
lumbar segment
 Do not cross and enter
ipsilateral cerebellar
hemisphere
Dorsal spinocerebellar tract –
information about movement (sensory
feedback)
Ventral spinocerebellar - internally
generated information about the
movement.
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Cuneocerebellar Tract
Mediates upper limbs and neck
Uncrossed fibers to ipsilateral external cuneate
nucleus to cerebellum
Clinical Considerations
– Romberg used to determine some function
– Difficult to test clinically
Romberg Test
Ask individual to stand straight with feet together and
hands by the sides. Compare balance with eyes open
versus eyes closed. If less steady with eyes closed
(positive), ataxia is sensory – spinal injury. If there is no
difference (negative) it suggests cerebellar problem.
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MCQ
 Which is the
nucleus?
A. A
B. B
C. C
D. D
A
B
C
D
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MCQ
 Which is the
node of ranvier?
A. A
B. B
C. C
D. D
A
B
C
D
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MCQ
 Which is the
nucleus?
A. A
B. B
C. C
D. D
A
B
C
D
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