Co 17 Chapter 17 Pathways and Integrative Functions

Co 17 Chapter 17 Pathways and Integrative Functions

Characteristics of Pathways • 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

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

Functional anatomy of sensory pathways 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 4

Fig. 17. 1 Posterior Fasciculus gracilis funiculus-medial Fasciculus cuneatus lemniscal pathway Posterior • Posterior funiculusmedial lemniscal pathway Posterior spinocerebellar tract Spinocerebellar Anterior pathway spinocerebellar tract Anterolateral pathway 3 somatosensory pathways Lateral spinothalamic tract Anterior – projects through spinal cord, brainstem, diencephalon, cerebral cortex – conducts stimuli re: proprioceptive information and discriminative touch, precise pressure, and vibration Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display.

Fig. 17. 2 – Posterior Funiculus-Medial Lemniscal Pathway Right side of body Left side of body Cerebrum Primary somatosensory cortex (postcentral gyrus) Tertiary neuron Thalamus Secondary neuron Medial lemniscus Midbrain Medulla oblongata Receptors for discriminative touch, proprioception, precise pressure, and vibration (from neck, trunk, limbs) Anterior root Posterior root Spinal cord Nucleus gracilis Nucleus cuneatus Medial lemniscus Decussation prior to entry into the medial lemniscus Posterior funiculus-medial lemniscal pathway • Travels through fasciculus gracilis from lower half of body • Travels through fasciulus cuneatus from upper half of body Primary neuron Fasciculus gracilis Posterior Fasciculus cuneatus funiculus Pathway direction

Fig. 17. 1 Posterior Fasciculus gracilis funiculus-medial Fasciculus cuneatus lemniscal pathway Spinocerebellar pathway Anterolateral pathway Posterior 3 somatosensory pathways • Anterolateral pathway Posterior spinocerebellar tract Anterior spinocerebellar tract – composed of anterior spinothalamic tract and lateral spinothalamic tract – Conduct stimuli related to crude touch and pressure, pain and temperature Lateral spinothalamic tract Anterior Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display.

Fig. 17. 3 Anterolateral Pathway Right side of body Cerebrum Left side of body Primary somatosensory cortex (postcentral gyrus) Tertiary neuron Thalamus Midbrain Secondary neuron Pons Medulla oblongata Receptors for pain, temperature, crude touch, pressure Primary neuron Posterior horn Spinal cord Anterior spinothalamic tract Lateral spinothalamic tract Anterolateral pathway • composed of anterior spinothalamic tract and lateral spinothalamic tract • Conduct stimuli related to crude touch and pressure, pain and temperature

Fig. 17. 1 Posterior Fasciculus gracilis funiculus-medial Fasciculus cuneatus lemniscal pathway Spinocerebellar pathway Anterolateral pathway Posterior 3 somatosensory pathways • Spinocerebellar pathway • conducts proprioceptive info Posterior spinocerebellar tract Anterior spinocerebellar tract Lateral spinothalamic tract Anterior Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display.

Fig. 17. 4 Spinocerebellar Pathway Right side of body Left side of body Cerebellum Pons Secondary neuron Posterior spinocerebellar tract Anterior spinocerebellar tract Spinocerebellar pathway Medulla oblongata Proprioceptive input from joints, muscles, and tendons Primary neuron Spinal cord Pathway direction Spinocerebellar pathway • anterior tract conducts impulses from lower half of body • posterior tract from upper half of body

Fig. 17. 5 Descending Projection Tracts Posterior Motor Pathways • composed of cerebral nuclei, parts of cerebellum, descending projection tracts, and motor neurons • descending projection tracts originate from cerebral cortex and brainstem Lateral corticospinal tract Rubrospinal tract Anterior corticospinal tract Reticulospinal tract Vestibulospinal tract Tectospinal tract Anterior Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display.

Pathway direction Right side of body Cerebrum Thalamus Left side of body Primary motor cortex (precentral gyrus) Internal capsule Upper motor neurons Midbrain Corticospinal tracts (combined anterior and lateral tracts) Cerebral peduncle Fourth ventricle Medulla oblongata Anterior corticospinal tract To skeletal muscles Lower motor neurons Spinal cord Decussation in pyramids of medulla oblongata Lateral corticospinal tract Decussation in spinal cord 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

Pathway direction Right side of body Cerebrum Thalamus Left side of body Primary motor cortex (precentral gyrus) Internal capsule Upper motor neurons Midbrain Corticospinal tracts (combined anterior and lateral tracts) Cerebral peduncle Fourth ventricle Medulla oblongata Anterior corticospinal tract To skeletal muscles Lower motor neurons Spinal cord Decussation in pyramids of medulla oblongata Lateral corticospinal tract Decussation in spinal cord 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

Pathway direction Right side of body Cerebrum Thalamus Left side of body Primary motor cortex (precentral gyrus) Internal capsule Upper motor neurons Midbrain Corticospinal tracts (combined anterior and lateral tracts) Cerebral peduncle Fourth ventricle Medulla oblongata Anterior corticospinal tract To skeletal muscles Lower motor neurons Spinal cord Decussation in pyramids of medulla oblongata Lateral corticospinal tract Decussation in spinal cord 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