NSC 4366 1st Edition Lecture 5 Outline of Last Lecture I Spinal Cord Outline of Current Lecture II Spinal Cord continued Current Lecture Motor Pathways by origin 1 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 spine 3 Corticobulbar Pathways neurons in cortex terminate in brainstem CN motor nuclei from contex to brainstem Motor Pathways by position Lateral 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 f tall the upper motor neuron is about 5 f Polio lesion in ventral root near lower motor neuron can cause 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 brainstem These 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 crosses over 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 stimulus the 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 neurons are involved Sensory has 3 because it needs to be faster and reliable Can lead to chronic pain syndrome Cell bodies of second order are in brainstem Primary 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 Axons of 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 information Primary 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 dorsal horn neurons send crossed axons into the spinothalamic tract 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 a large cascading network for bilateral projections into the spinoreticular tract blue This system ends mainly in the reticular formation from which polysynaptic projections lead to nonspecific medial dorsal and anterior thalamic nuclei Some spinoreticular fibers also terminate in the deeper layers of the superior colliculus 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 excruciating pain 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 posterior spinal artery the patient will have sensory loss They will lose touch if there s a stroke in the anterior spinal artery they will be completely paralyzed but their sensation will be okay