Lecture 28 Outline of Last Lecture I. The corticospinal tract is divided into ventral and lateral pathwaysII. Extrapyramidal tracts originate in areas excluding the primary motor cortexa. Rubrospinal tract controls arm musclesb. Tectospinal tract controls head and neck musclesIII. Reflexes controlled by the spinal cord involve the movement of agonist and antagonist musclesIV. The basal ganglia are involved in regulating motor activity through connections to the cortex and thalamusa. Volume hypothesis stresses the importance of the globus pallidus and putamen in modulating the activity of this pathwayOutline 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 pathwaya. Different input to these regions from the putamen results in inhibition or excitation of the thalamus, which projects to the motor cortexb. The substantia nigra also plays a modulatory role in these pathwaysII. The cerebellum also exhibits homuncular organizationa. Lateral and medial hemispheres control different body regionsb. Cerebellar cortex consists of three functionally distinct layersIII. The cerebellum connects to the brainstem via the cerebellar pedunclesa. Spinocerebellar tract provides a pathway for information traveling from the cerebellum to the cortexCurrent Lecture- Direct pathway: GPi is inhibited, pathway is free to produce movement- Indirect pathway (more complex): GPi in activated, inhibits the thalamus, blocks movemento 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 pathwayso Projects dopaminergic neurons to both pathwayso To the putamen: D1 receptors  depolarization in direct pathway D2 receptors  hyperpolarization in indirect pathwayThese 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. NSCI 110 1st Edition- Acetylcholine also synapses at the D1 and D2 receptorso Opposite effects of dopamine from the substantia niagra at these receptorsThe Role of the Cerebellum- Anatomyo Flocculus (small) is involved in eye movements and balance Most inferior portiono Cerebellar cortex and cerebellar deep nucleio 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 organizationo Lateral  movement of limbs, hands, feet, digitso Medial  movement of face and midline of body- Connects to the brainstem via cerebellar peduncleso Superior  main output to the pons/midbrain Critical for its main functionso Middle  input from the contralateral cerebral cortexo 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 cortexo 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 layero 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 necessaryo 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 cortexo 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 brainstemo Ribbon-like structure down the center called the medial lemniscuso 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 cellsOrganization of the Somatosensory System- Sensitivity to somatosensory stimuli is a function of the receptor typeso Nocioception  perception of pain, temperature, itch Free nerve ending nocioceptors beneath the skin These afferent neurons project to the dorsal root ganglia in spinal cordo Hapsis  perception of fine touch and pressure (identifying objects we touch) Mechanical stimulation of the hair or tissueo 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 receptorso 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 neuronso Proprioception Muscle spindles (muscle stretch), Golgi tendon organs (tendon stretch), joint receptors (joint movement)  RAPID Largest axons, are myelinated A-alpha