Motor Pathways by origin1. Corticospinal Pathways – neurons in cortex terminate in spinal cord - from the motor system down to the spine.2. Brainstem origins - Named for cell group from which they originate: (tectospinal, rubrospinal, reticulospinal, vestibulospinal) - from brainstem to spine3. Corticobulbar Pathways – neurons in cortex terminate in brainstem - CN motor nuclei -from contex to brainstemMotor Pathways by positionLateral Corticospinal Tract – innervates motoneurons in lateral ventral horn - large, main one. If lesioned you would lose voluntary movement.2 neurons in lateral corticospinal tract (voluntary movement, limbs). This pathway is long. If you’re 7 ft tall, the upper motor neuron is about 5 ft.Poliolesion in ventral root near lower motor neuron can cause paralysis - stab woundRubrospinal Tract – near lateral corticospinal tract - targets upper limb flexor motoneuronsOrigin: red nucleus in midbrainFibers cross in midbrain and projectcaudally in lateral brainstemNSC 4366 1st Edition Lecture 5Outline of Last Lecture I. Spinal CordOutline of Current Lecture II. Spinal Cord continuedCurrent Lecture:Motor Pathways by origin1. Corticospinal Pathways – neurons in cortex terminate in spinal cord - from the motor system down to the spine. 2. Brainstem origins - Named for cell group from which they originate: (tectospinal, rubrospinal, reticulospinal, vestibulospinal) - from brainstem to spine3. Corticobulbar Pathways – neurons in cortex terminatein brainstem - CN motor nuclei -from contex tobrainstemMotor Pathways by position• Lateral Corticospinal Tract – innervates motoneurons inlateral ventral horn - large, main one. If lesioned you wouldlose voluntary movement. • 2 neurons in lateral corticospinal tract (voluntarymovement, limbs). This pathway is long. If you’re 7 ftall, the upper motor neuron is about 5 f. • Polio • lesion in ventral root near lower motor neuron cancause paralysis - stab wound• Rubrospinal Tract – near lateral corticospinal tract - targets upper limb flexor motoneurons • Origin: red nucleus in midbrain • Fibers cross in midbrain and project caudally in lateral brainstemThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-Ventral corticospinal tract - involves movement of your trunk. Very small pathway. less than 5% of the axons are in this pathway.-Ventral corticospinal tract crossesover in the spinal cord (won’t ask about ventral corticospinal tract on test)Tectospinal tract - goes from the tectum (top of the brain stem, tectum means roof, roof of the midbrain) to the spine -activated when there’s a sudden loud noise. for example, hearing a loud bang and reacting involuntarily. Or if you’re thrown off a building, you flail and your head looks up and around-Vestibulospinal Tract - goes from vestibule to spine. When falling off a building you will extend-Reticulospinal tract - in humans this is the least important and least understood (not on test). When your body becomes extended and rigid in response to a stimulusthe pathways are analogous —Cell bodies are in the periphery in the dorsal root ganglion In the sensory pathway 3 neurons are involved, in the motor pathway 2 neuronsare involved. Sensory has 3 because it needs to be faster and reliable. Can lead to chronic pain syndromeCell bodies of second order are in brainstemPrimary somatosensory myelinated axons conveying fine, discriminative touch, pressure, vibratory sensation,and consciousness of joint position project directly into the DC system (fasciculus gracilis for lower body, below T6, and fasciculus cuneatus for upper body, T6 and above), where they are topographically organized They terminate in nuclei gracilis and cuneatus, respectively, from which the medial lemniscus originates This tract crosses (decussates) in the medulla and projects to the ventroposterolateral (VPL) nucleus of the thalamus Axonsof neurons in the VPL nucleus terminate in the primary sensory cortex topographically The entire DC/medial lemniscal system is topographically organized; the lower body is represented medially in the primary somatosensory cortex, and the upper body (and face from trigeminal projections) is represented laterally This representation is sometimes drawn proportionally (the resultant figure is called a homunculus); information from the fingers and hands has far greater representation in the cerebral cortex than information from the back The spinocervical system is a small supplement to the DC system Primary afferent projections terminate in the medial part of the dorsal horn; these neurons project to the lateral cervical nucleus (in C1 and C2 only) This nucleus contributes additional crossed axons with polysynaptic mechanoreceptive informationPrimary somatosensory unmyelinated (C fibers) and small myelinated (A delta fibers) that convey nociceptive information (fast, localizing pain), temperature sensation, and light, moving touch terminate on neurons in lamina I and V These dorsalhorn neurons send crossed axons into the spinothalamictract, projecting to neurons in the VPL nucleus of the thalamus (red) This pool of neurons in the VPL nucleus is different from the pool receiving input from nuclei gracilis and cuneatus from the DC system These thalamic neurons in the VPL nucleus project to the second somatosensory cortex (SII) as well as to the primary sensory cortex Primary sensory C fibers also terminate in the dorsal horn and contribute to alarge, cascading network for bilateral projections into the spinoreticular tract (blue) This system ends mainly in the reticular formation, from whichpolysynaptic projections lead to nonspecific, medial dorsal, and anterior thalamic nuclei Some spinoreticular fibers also terminate in the deeper layers of the superiorcolliculus (spinotectal pathway) and in the periaqueductal gray Cortical regions such as the cingulate, insular, and prefrontal regions then process and interpret nociceptive information related to slow, agonizing, excruciatingpain—Doctor moves patient’s toe up and down and asks what direction. If a patient has lost this function they get it right 50% of the time. If they get it right 0% of the time they’re lying. -one artery in ventral (front) part and two arteries in the dorsal (back)part-if there’s a stroke in the