Co 17 Chapter 17 Pathways and Integrative Functions

Communication of CNS with body structures through pathways Tracts = groups or bundles of axons that travel together in CNS Nucleus = collection of neuron cell bodies within CNS Somatotropy = correspondence between body area of receptors and functional areas in cerebral cortex Characteristics of Pathways

Somatosensory pathways process stimuli from receptors within skin, muscles, and joints Viscerosensory pathways process stimuli received from the viscera Sensory Pathways 3

two or three neurons primary neuron: dendrites are part of receptor that detects a specific stimulus (pain, texture, vibration, temperature, proprioception) secondary neuron: interneuron; cell body resides in posterior horn of spinal cord or brainstem nucleus –axon projects to thalamus for conscious sensations or cerebellum for unconscious tertiary neuron: interneuron; cell body in thalamus Functional anatomy of sensory pathways 4

Fig Copyright © McGraw-Hill Education. Permission required for reproduction or display. Posterior Anterior Fasciculus cuneatus Fasciculus gracilis Spinocerebellar pathway Anterolateral pathway Posterior spinocerebellar tract Anterior spinocerebellar tract Lateral spinothalamic tract Anterior spinothalamic tract Posterior funiculus-medial lemniscal pathway 3 somatosensory pathways Posterior funiculus-medial lemniscal pathway –projects through spinal cord, brainstem, diencephalon, cerebral cortex –conducts stimuli re: proprioceptive information and discriminative touch, precise pressure, and vibration

Fig – Posterior Funiculus-Medial Lemniscal Pathway Left side of bodyRight side of body Cerebrum Primary somatosensory cortex (postcentral gyrus) Tertiary neuron Thalamus Midbrain Secondary neuron Medial lemniscus Nucleus gracilis Nucleus cuneatus Medial lemniscus Decussation prior to entry into the medial lemniscus Primary neuron Medulla oblongata Receptors for discriminative touch, proprioception, precise pressure, and vibration (from neck, trunk, limbs) Anterior root Posterior root Spinal cord Pathway direction Posterior funiculus Fasciculus cuneatus Fasciculus gracilis Posterior funiculus-medial lemniscal pathway Travels through fasciculus gracilis from lower half of body Travels through fasciulus cuneatus from upper half of body

Fig Copyright © McGraw-Hill Education. Permission required for reproduction or display. Posterior Anterior Fasciculus cuneatus Fasciculus gracilis Spinocerebellar pathway Anterolateral pathway Posterior spinocerebellar tract Anterior spinocerebellar tract Lateral spinothalamic tract Anterior spinothalamic tract Posterior funiculus-medial lemniscal pathway 3 somatosensory pathways Anterolateral pathway –composed of anterior spinothalamic tract and lateral spinothalamic tract –Conduct stimuli related to crude touch and pressure, pain and temperature

Fig Anterolateral Pathway Right side of bodyLeft side of body Cerebrum Primary somatosensory cortex (postcentral gyrus) Tertiary neuron Thalamus Midbrain Secondary neuron Pons Medulla oblongata Receptors for pain, temperature, crude touch, pressure Anterior spinothalamic tract Lateral spinothalamic tract Primary neuron Posterior horn Spinal cord Pathway direction Anterolateral pathway composed of anterior spinothalamic tract and lateral spinothalamic tract Conduct stimuli related to crude touch and pressure, pain and temperature

Fig Copyright © McGraw-Hill Education. Permission required for reproduction or display. Posterior Anterior Fasciculus cuneatus Fasciculus gracilis Spinocerebellar pathway Anterolateral pathway Posterior spinocerebellar tract Anterior spinocerebellar tract Lateral spinothalamic tract Anterior spinothalamic tract Posterior funiculus-medial lemniscal pathway 3 somatosensory pathways Spinocerebellar pathway conducts proprioceptive info

Fig Spinocerebellar Pathway Right side of bodyLeft side of body Cerebellum Pons Secondary neuron Medulla oblongata Spinal cord Pathway direction Posterior spinocerebellar tract Anterior spinocerebellar tract Spinocerebellar pathway Proprioceptive input from joints, muscles, and tendons Primary neuron Spinocerebellar pathway anterior tract conducts impulses from lower half of body posterior tract from upper half of body

Copyright © McGraw-Hill Education. Permission required for reproduction or display. Fig Descending Projection Tracts Posterior Lateral corticospinal tract Rubrospinal tract Anterior corticospinal tract Reticulospinal tract Vestibulospinal tract Tectospinal tract Anterior Motor Pathways composed of cerebral nuclei, parts of cerebellum, descending projection tracts, and motor neurons descending projection tracts originate from cerebral cortex and brainstem

Right side of body Pathway direction Left side of body Cerebrum Primary motor cortex (precentral gyrus) Thalamus Midbrain Cerebral peduncle Corticospinal tracts (combined anterior and lateral tracts) Upper motor neurons Internal capsule Medulla oblongata Fourth ventricle Anterior corticospinal tract Decussation in pyramids of medulla oblongata Lateral corticospinal tract Decussation in spinal cord Spinal cord Lower motor neurons To skeletal muscles Motor Pathways Contain upper and lower motor neurons upper motor neuron housed within cerebral cortex or a nucleus in brainstem –synapse on lower motor neurons or interneurons

Right side of body Pathway direction Left side of body Cerebrum Primary motor cortex (precentral gyrus) Thalamus Midbrain Cerebral peduncle Corticospinal tracts (combined anterior and lateral tracts) Upper motor neurons Internal capsule Medulla oblongata Fourth ventricle Anterior corticospinal tract Decussation in pyramids of medulla oblongata Lateral corticospinal tract Decussation in spinal cord Spinal cord Lower motor neurons To skeletal muscles Motor Pathways Contain upper and lower motor neurons lower motor neuron cell body housed within anterior horn of spinal cord or brainstem –axons project from CNS to skeletal muscle

Right side of body Pathway direction Left side of body Cerebrum Primary motor cortex (precentral gyrus) Thalamus Midbrain Cerebral peduncle Corticospinal tracts (combined anterior and lateral tracts) Upper motor neurons Internal capsule Medulla oblongata Fourth ventricle Anterior corticospinal tract Decussation in pyramids of medulla oblongata Lateral corticospinal tract Decussation in spinal cord Spinal cord Lower motor neurons To skeletal muscles Motor Pathways Upper motor neurons may excite or inhibit lower motor neuron (make more or less likely to contract) Lower motor neurons are always excitatory