NSCI 110 1st Edition Lecture 28 Outline of Last Lecture I The corticospinal tract is divided into ventral and lateral pathways II Extrapyramidal tracts originate in areas excluding the primary motor cortex a Rubrospinal tract controls arm muscles b Tectospinal tract controls head and neck muscles III Reflexes controlled by the spinal cord involve the movement of agonist and antagonist muscles IV The basal ganglia are involved in regulating motor activity through connections to the cortex and thalamus a Volume hypothesis stresses the importance of the globus pallidus and putamen in modulating the activity of this pathway Outline of Current Lecture I The globus pallidus internal is involved in the direct pathway to the cortex and the globus pallidus external is involved in the indirect pathway a Different input to these regions from the putamen results in inhibition or excitation of the thalamus which projects to the motor cortex b The substantia nigra also plays a modulatory role in these pathways II The cerebellum also exhibits homuncular organization a Lateral and medial hemispheres control different body regions b Cerebellar cortex consists of three functionally distinct layers III The cerebellum connects to the brainstem via the cerebellar peduncles a Spinocerebellar tract provides a pathway for information traveling from the cerebellum to the cortex Current Lecture Direct pathway GPi is inhibited pathway is free to produce movement Indirect pathway more complex GPi in activated inhibits the thalamus blocks movement o Glutamate released to the putamen GABA acts on GPe Less GABA released from GPe to subthalamic nucleus More excitatory effect on the GPi More GABA release into the thalamus therefore it is inhibited Globus pallidus and putamen control the release of GABA The substantia niagra has a modulatory role in these pathways o Projects dopaminergic neurons to both pathways o To the putamen D1 receptors depolarization in direct pathway D2 receptors hyperpolarization in indirect pathway 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 Acetylcholine also synapses at the D1 and D2 receptors o Opposite effects of dopamine from the substantia niagra at these receptors The Role of the Cerebellum Anatomy o Flocculus small is involved in eye movements and balance Most inferior portion o Cerebellar cortex and cerebellar deep nuclei o Primary fissure separates anterior from posterior lobes Fissures run mediolaterally Posterolateral fissure separates flocculus from corpus cerebelli main body o Vermis Two hemispheres o Homuncular organization o Lateral movement of limbs hands feet digits o Medial movement of face and midline of body Connects to the brainstem via cerebellar peduncles o Superior main output to the pons midbrain Critical for its main functions o Middle input from the contralateral cerebral cortex o Inferior input carrying sensory information about where the body is in space Tells you what the actual physical movement is that just took place Cerebellar cortex o Three layers Innermost Granule cell layer Small tightly packed neurons Input from mossy fibers project to Purkinje cells Middle Purkinje cell layer Single layer thick Thick dendritic arbors lots of branching Output for cerebellar cortex Inhibitory connections onto cerebellar deep nuclei inhibitory synapses are here Outermost Molecular cell layer o Climbing fibers give excitatory input to Purkinje cells Inferior olive How does it improve movement control o Timing and accuracy error correction compares intended movements with actual movements and adjusts as necessary o Connects to brainstem via peduncles Superior main output of cerebellum Motor cortex cerebrum sends motor instructions to spinal cord Middle input from contralateral cerebral cortex A copy of the same instructions sent to cerebellum Inferior input carrying sensory info of where body is in space Proprioception Sensory receptors on slide o Spinocerebellar tract tells the cerebellum about the origin of the movement feedback from actual action Conveyed to the cortex o Cerebellum has information about both versions of the movement what you intended to do and what you actually did Inferior cerebellar peduncle helps attach cerebellum to the brainstem o Ribbon like structure down the center called the medial lemniscus o Pyramids o Inferior olivary nucleus has a unique squiggle appearance Largest nuclear group in brainstem Tracts that originate here form part of the inferior cerebellar peduncle End as climbing fibers that climb up as Purkinje cells Organization of the Somatosensory System Sensitivity to somatosensory stimuli is a function of the receptor types o Nocioception perception of pain temperature itch Free nerve ending nocioceptors beneath the skin These afferent neurons project to the dorsal root ganglia in spinal cord o Hapsis perception of fine touch and pressure identifying objects we touch Mechanical stimulation of the hair or tissue o Proprioception perception of the body in space Sensitive to the stretch of muscles and tendons joint movement Orientation of limbs body parts moving certain directions Somatosensory receptors o Nocioception Free nerve endings for pain and temperature Information carried by relatively small neurons slow transduction of signals Have little to no myelination A delta fibers little myelination and C fibers no myelination o Hapsis Some are in a small capsule corpuscle of connective tissue Meissner s touch Pacinian flutter looks like onion Ruffini vibration rapid Merkel s steady skin indentation and hair receptors flutter or steady skin indentation slow These axons are large and myelinated overall RAPID Alpha beta neurons o Proprioception Muscle spindles muscle stretch Golgi tendon organs tendon stretch joint receptors joint movement RAPID Largest axons are myelinated A alpha neurons