MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 3. ANATOMICAL AND PHYSIOLOGICAL ASPECTS OF THE SELF-REGULATION OF BODY FUNCTIONS

NERVAL PATHWAYS OF THE BRAIN AND SPINAL CORD

1. SENSORY (ASCENDING) PATHWAYS

The Spinal Cord transmits four types of sensitivity: tactile (Touch and pressure sensation), thermal, pain, and proprioceptive (from Muscle and tendon receptors, also known as kinesthetic sense, or the sense of body and limb position and movement). The vast majority of ascending pathways conduct proprioceptive sensitivity.

The pathway for pain and thermal sensitivity is the lateral spinothalamic tract. The Cell body of the first neuron in this pathway is located in the spinal ganglion. The peripheral processes of these Cells form part of the Spinal Nerves and originate from receptors, while their central processes run within the posterior roots to the posterior horns of the spinal cord Gray matter, where the cell body of the second neuron is located. The processes of the second-order Neurons cross to the opposite side via the anterior gray commissure and ascend within the lateral funiculus of the spinal cord to the Medulla Oblongata, pass through the Pons and cerebral peduncles, and terminate in the lateral Nucleus of the thalamus, where the cell body of the third neuron is situated. The processes of the third-order neurons pass through the posterior limb of the internal capsule and terminate in the cortex of the postcentral gyrus.

The anterior spinothalamic tract—the pathway for tactile sensitivity—consists of three neurons located in the same regions as those of the previous pathway, but it runs within the anterior funiculus of the spinal cord.

The pathways for kinesthetic (muscle-joint) sense project to both the Cerebral Cortex AND the Cerebellum.

Two pathways lead to the cerebellum: the anterior and posterior spinocerebellar tracts.

The anterior spinocerebellar tract (Gowers' tract) originates from the Cells of the spinal ganglion, where the first-neuron cell bodies are located (Fig. 3.32 b). The peripheral processes of these cells begin as proprioceptors and run within the spinal nerves, whereas the central processes—part of the posterior ROOT—terminate in The Nucleus of the posterior horn of the spinal cord gray matter, where the second-neuron cell body is located. The processes of the second-order neurons cross to the opposite side through the anterior gray commissure of the spinal cord (first decussation) and, running within the lateral funiculus, reach the superior medullary velum, where the second decussation takes place. This pathway terminates in the cortex of the cerebellar vermis on the same side.

The posterior spinocerebellar tract (Flechsig's tract) (Fig. 3.32 a) also comprises two neurons situated in the same anatomical structures as in the previous pathway; however, the fibers arising from the second-neuron cell bodies do not decussate anywhere and reach the cortex of the cerebellar vermis via the inferior cerebellar peduncles.

Class="center">

Fig. 3.32. Posterior (a) and anterior (b) spinocerebellar, and rubrospinal (c) Neural Pathways:

Two proprioceptive pathways project to the cerebral cortex: the gracile fasciculus (tract of Goll) and cuneate fasciculus (tract of Burdach), which transmit impulses from the proprioceptors of the trunk and limbs (Fig. 3.33). The first neuron of these pathways is located in the spinal ganglion; nerve fibers from it travel within the posterior funiculus of the spinal cord to the corresponding nuclei of the medulla oblongata, where the cell bodies of the second neurons reside. The axons of the second-order neurons form a decussation in the medulla oblongata and ascend to the lateral nucleus of the thalamus, where the third-neuron cell body is located. This pathway terminates in the postcentral gyrus.

Fig. 3.33. Diagram of the cortical-direction proprioceptive sensory pathway (to the cerebral cortex). Arrows indicate the direction of Nerve Impulse propagation