Anterolateral Pathway

Sensory Pathway Ist. Order N. from receptors to the Laminae I IV, V &VI on the same side

Antero-Lateral Path 2nd Order N. From Laminae I,IV,V & VI Cross to opposite side obliquely, Ascend up & relay in Anterior & Lat White columns of the spinal cord 1. Reticular formation of Brain stem. 2. VPL N & Intralaminar Nuclei of the Thalamus 3rd Order N. From Thalamus – Pass through Internal capsule (Post.1/3rd. Of Post Limb) to the Primary Sensory Cortex

Antero-Lateral Path Small myelinated fibers------ few meters/sec to 40 m/sec Sensations that does not need to be transmitted rapidly or with great spatial fidelity. Ability to transmit broad spectrum of sensory modalities

Antero-Lateral Pathway Types of Sensations Carried; Crude touch & Pressure Pain Thermal sensations Heat & Cold Tickle & Itch Sexual Sensations

Spinocerebellar Pathway

Spinocerebellar Pathway Includes : -Ventral spinocerebellar T. (Crossed fibers) -Dorsal spinocerebellar T. (Uncrossed fibers) Dorsal Carries sensation to the cerebellum concerning position of muscles, tendons and joints. Ventral Carries unconscious muscle sense.

Ventral Spinocerebellar Tract

Dorsal Spinocerebeller Tract

Spinotectal Tract Origin:Arises in the anterolateral columns Termination:Inferior and superior colliculi. Function: Passes pain, thermal, tactile information to superior colliculus for spinovisual reflexes. ( brings about the movement of eye and head towards the source of information.)

Spino-olivary Tract Situated in anterolateral part of white column Origin is not specific Termination: Olivary nucleus of medulla oblongata. Function: Proprioception

Spinovestibular Tract Situated in lateral white column of spinal cord Origin: All the segments of spinal cord Termination: Lateral vestibular nucleus Function: Proprioception

Layers of the Cerebral Cortex Molecular Layer Ext. Granular -Incoming sensory signals excites N in layer IV first; then spreads toward the surface of the cortex & deeper layers. Layers I & II receive diffuse, nonspecific input signals from lower brain centers that facilitate specific regions of the cortex. Small Pyramidal Cells Int. Granular Large Pyramidal Cell Fusiform or Polymorphic

Relay of N in Layers of the Cerebral Cortex Molecular Layer Neurons in layer II & III send Axons to related portions of the cerebral cortex on the opposite side of the brain through corpus callosum. Neuron in V & VI send Axon to the deeper parts of the Nervous system. Neuron in V go to Basal Ganglia, Brain Stem & Spinal Cord. N from VI go to Thalamus Ext. Granular Small Pyramidal Cells Int. Granular Large Pyramidal Cell Fusiform or Polymorphic

Vertical Columns of Sensory cortex Functionally Somatosensory Cortex is arranged in Vertical Columns 0.3 - 0.5 mm in Diameter. Each column contains approximately 10,000 Neuronal cell bodies. Each Column detects specific sensory modality. In layer IV the input signals functions entirely separately from one another. At other levels of the column, interaction occurs leading to analysis of the meaning of sensory signals.

Vertical Columns of Sensory cortex e.g. Area 3a deep in the central fissure large share of vertical column respond to muscle, tendon & Joint receptors > directly to motor cortex (Area 4) > activation of sequence of muscle contractions.

Functions of Somatosensory Area-I Function of different areas are studied by: 1. Ablation. 2. Stimulation 3. Studying the Disease process. Widespread bilateral Excision of Sensory-I Causes inability to: 1. Localize the sensation (except Crude sensation) 2. Judge weights of Objects 3. judge critical degree of Pressure 4. Judge shapes, texture or Form of Objects eyes closed . (Astereognosis )

Function of Somatosensory Association Area .Broadmann’s area 5 and 7 Receives information from: 1.Somatosensory Area-II 2.Ventrobasal Nuclei of the Thalamus including other areas of the Thalamus 3.Visual Cortex 4.Auditory Cortex & combines it to give meaningful sensation. Removing of somatosensory Association Area - AMORPHOSYNTHESIS - (Loss of ability to recognize complex objects & Forms felt on opposite half)