Lecture 3 Sensory Tracts & Sensory Cortex

ANATOMICAL & ANATOMICAL & NEUROPHYSIOLOGICAL NEUROPHYSIOLOGICAL

ASPECTS OF SOMATIC SENSEASPECTS OF SOMATIC SENSEASPECTS OF SOMATIC SENSEASPECTS OF SOMATIC SENSEUpdated lecture September,Updated lecture September,20072007

Prof. Dr. Muhammad Abdul AzeemDepartment of Physiology, Ummal Qura University

azenmu@gmail.com

Somatic SenseSomatic Sense

Originates from the receptors classified as:Originates from the receptors classified as:nn Exteroreceptors (body surface)Exteroreceptors (body surface)

Proprioceptors (joints and muscles)Proprioceptors (joints and muscles)

1010//1919//20082008 Prof. Dr.Muhammad Abdul Azeem, Prof. Dr.Muhammad Abdul Azeem, Deptt. Physiology, UQU, Meccah, Deptt. Physiology, UQU, Meccah,

azenmu@gmail.comazenmu@gmail.com

nn Proprioceptors (joints and muscles)Proprioceptors (joints and muscles)nn Visceral receptorsVisceral receptorsnn Deep sensations Deep sensations

Sensory PathwaysSensory Pathways

1.1. Dorsal Leminiscal Dorsal Leminiscal

2.2. AnteriolateralAnteriolateral

CROSS SECTION OF SPINAL CORD, SHOWING CROSS SECTION OF SPINAL CORD, SHOWING LOCATION OF ASCENDING SENSORY PATHWAYS.LOCATION OF ASCENDING SENSORY PATHWAYS.NOTE THAT EACH IS LAMINATED. S=SACRAL, NOTE THAT EACH IS LAMINATED. S=SACRAL, L=LUMBAR, T=THORACIC, C=CERVICALL=LUMBAR, T=THORACIC, C=CERVICAL

The dorsal column and spino-cervical pathways for transmitting critical types of tactile signals.

Projection of Projection of the dorsal the dorsal columncolumn--medial medial lemniscal lemniscal system through system through

system through system through the thalamus to the thalamus to the somatothe somato--sensory cortex.sensory cortex.(Modified from Brodal A: Neurological Anatomy in Relation to (Modified from Brodal A: Neurological Anatomy in Relation to Clinical Medicine. New York: Oxford University Press, Clinical Medicine. New York: Oxford University Press, 19691969, by , by permission of Oxford University Press.) permission of Oxford University Press.)

ANTEROLATERAL PATHWAY

PATHWAY

Cross section of spinal cord, showing gray matter Cross section of spinal cord, showing gray matter and ascending sensory tracts in its white columns. and ascending sensory tracts in its white columns.

SEQUENCE IN SENSORY TRANSMISSIONSEQUENCE IN SENSORY TRANSMISSION1.1. Stimulation of sensory receptor by sensory modality like Stimulation of sensory receptor by sensory modality like

Touch, pressure, pain, cold, vibration etc.Touch, pressure, pain, cold, vibration etc.2.2. Generation of Receptor potentialGeneration of Receptor potential3.3. Generation and propagation of Action potential in sensory Generation and propagation of Action potential in sensory

axonaxon4.4. Sensory nerve carries sensory signal towards spinal cord Sensory nerve carries sensory signal towards spinal cord

through dorsal root ganglion through dorsal root ganglion 5.5. Spinal cord carries sensory signal through in dorsal & Spinal cord carries sensory signal through in dorsal &

anterolateral pathways, crossed & uncrossed tractsanterolateral pathways, crossed & uncrossed tracts

anterolateral pathways, crossed & uncrossed tractsanterolateral pathways, crossed & uncrossed tracts6.6. Processing in brain stem for equilibrium and position Processing in brain stem for equilibrium and position

sensesense7.7. Thalamus receive and relay sensory signals through its Thalamus receive and relay sensory signals through its

nuclei towards sensory cortexnuclei towards sensory cortex8.8. Termination of sensory signal in Primary & Secondary Termination of sensory signal in Primary & Secondary

sensory cortices of cerebral cortexsensory cortices of cerebral cortex9.9. Perception of sense & distribution of signals in cerebral Perception of sense & distribution of signals in cerebral

lobeslobes10.10. Initiation of motor signals from motor cortex in cerebrum.Initiation of motor signals from motor cortex in cerebrum.

How Sensory nerves arise from Receptors and converge on a single large

single large Myelinated Nerve

1.1. Touch sensations requiring a Touch sensations requiring a high degree of localization of high degree of localization of the stimulus & Transmission the stimulus & Transmission of fine gradation of intensity.of fine gradation of intensity.

2.2. Phasic sensations, such as Phasic sensations, such as vibratory sensationsvibratory sensations

3.3. Sensations that signal Sensations that signal

1.1. PainPain2.2. ThermalThermal sensations,sensations, includingincluding

bothboth warmwarm andand coldcoldsensationssensations..

3.3. CrudeCrude touchtouch andand pressurepressuresensationssensations capablecapable ofof onlyonlycrudecrude localizinglocalizing abilityability onon thethe

Dorsal ColumnDorsal Column--Medial Medial Lemniscal SystemLemniscal System

Anterolateral SystemAnterolateral System

3.3. Sensations that signal Sensations that signal movement against the skin movement against the skin

4.4. Position sensationsPosition sensations5.5. Pressure sensations having to Pressure sensations having to

do with fine degrees of do with fine degrees of judgment of pressure judgment of pressure intensity intensity

crudecrude localizinglocalizing abilityability onon thethesurfacesurface ofof thethe bodybody..

4.4. TickleTickle andand itchitch sensationsensation5.5. SexualSexual sensationssensations

10/19/200810/19/2008 Prof. Dr.Muhammad Abdul Azeem, Prof. Dr.Muhammad Abdul Azeem, Deptt. Physiology, UQU, Meccah, Deptt. Physiology, UQU, Meccah,

ASCENDING TRACTSASCENDING TRACTS

nn Sensory or Afferent TractsSensory or Afferent Tracts::nn From periphery to the centre, there are three From periphery to the centre, there are three orders of neurons for sensory transmission orders of neurons for sensory transmission through ascending or sensory tracts. through ascending or sensory tracts.

Sensory CortexSensory Cortex

ThalamusThalamus

22ndnd OrderOrderNeuronNeuron

33rdrd OrderOrderNeuronNeuron

through ascending or sensory tracts. through ascending or sensory tracts. nn These tracts are usually recognized with These tracts are usually recognized with respect to their origin, crossing or no crossing respect to their origin, crossing or no crossing in spinal column or medulla, termination and in spinal column or medulla, termination and their function.their function.

Spinal cord11stst OrderOrderNeuronNeuron

NeuronNeuron

Ascending Tracts Ascending Tracts Cont….Cont….

I.I. Afferent Tracts in the posterior Afferent Tracts in the posterior Column (Funiculus):Column (Funiculus):1.1. Fasciculus gracilis (Tract of Goll)Fasciculus gracilis (Tract of Goll)

1.1. Fasciculus gracilis (Tract of Goll)Fasciculus gracilis (Tract of Goll)2.2. Fasciculus cuneatus (Tract of Fasciculus cuneatus (Tract of

Burdach)Burdach)3.3. Common tract of Schultze (Tractus Common tract of Schultze (Tractus

interfascicularis)interfascicularis)

Ascending Tracts Ascending Tracts Cont…..Cont…..22. Afferent Tracts in the lateral column (Funiculus):. Afferent Tracts in the lateral column (Funiculus):

–– Dorsal spinothalamic tract (Lateral Dorsal spinothalamic tract (Lateral spinothalamic tract).spinothalamic tract).

–– Spinotectal tract.Spinotectal tract.–– Flechsig's tract (Direct or dorsal [posterior] Flechsig's tract (Direct or dorsal [posterior]

spinocerebellar tract).spinocerebellar tract).

spinocerebellar tract).spinocerebellar tract).–– Gower's tract (Indirect or ventral [anterior] Gower's tract (Indirect or ventral [anterior]

spinocerebellar tract)spinocerebellar tract)–– SpinoSpino--olivary tractolivary tract–– Spinoreticular tractSpinoreticular tract–– Spinovestibular tractSpinovestibular tract–– Spinocortical tractSpinocortical tract–– Spinopontine tractSpinopontine tract

Ascending Tracts Cont……Ascending Tracts Cont……33. Afferent Tracts in the Anterior Column . Afferent Tracts in the Anterior Column

(Funiculus)(Funiculus)

–– Ventral (anterior) spinothalamic tractVentral (anterior) spinothalamic tract

Two somatosensory cortical areas somatosensory areas I and II.

REPRESENTATIONOF BODY PARTS INSOMESTHETICCORTEX OFCEREBRUM

NEURONAL LAYERS INCEREBRAL

CEREBRAL CORTEX

DIVERGENCEOF SENSORY SIGNALS IN TRANS-

TRANS-MISSIONTOWARDSSENSORYCORTEX

POWER LAW

Actual StimulusStrength

StrengthInterpreted by Psyche

Interpreted Stimulus Strength= K *(Stimulus-k)y

AssociationOf Neuronal FiringWithKnee

KneeJointMovementImportantFor PositionSense

RepresentationOf SensoryNervesInnervationInRespective

RespectiveAreasOf SkinCalledDermatome

Lecture 3 Sensory Tracts & Sensory Cortex

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