What does the learning I Spinal cord and

What does the learning: I) Spinal cord and brainstem II) Forebrain

Spinal cord and brainstem Spinal cord organization: • four major divisions – Cervical (8) – Thoracic (12) – Lumbar (5) – Sacral (5) • Each spinal segment controls a set of muscles

Spinal cord organization White matters (nerve fibres) lateral dorsal Sensory inflow Dorsal horn medial Ventral horn Grey matters (cell bodies) ventral Motor commands

Spinal cord organization Dorsal root Sensory neuron Interneuron Motor neuron Ventral root

Spinal cord organization Some interneurons project within their own spinal segments, while others relay information to other spinal segments and/or the brain.

Proprioceptive pathways to the brain • Dorsal column-medial lemniscal pathway major pathway by which proprioceptive and touch information ascend to the cerebral cortex • Spinocerebellar tract ascend to the cerebellum

Brainstem organization • like the spinal cord, the brainstem contain motor neurons who axons make up the cranial nerves that innervate the muscles of the tongue, face and eyes etc. • some neurons in the brainstem also project to interneurons and motor neurons in the spinal cord

Medial brain stem pathways Basic postural control Tectum Tectospinal tract Vestibular nucleus Vestibulospinal tract Influence axial & proximal muscles Reticulospinal tract

Medial brain stem pathways Basic postural control Phylogenetically oldest descending motor pathway Individual axons project widely, coordinating different regions of spinal cord In ventromedial cord, contact interneurons, long propriospinal cells, & some MNs Influence axial & proximal muscles

Reticulospinal adjustments • maintaining balance during limb movements • voluntary movements of our arm can have postural consequences, ex. lifting an object • to counter this, leg muscles need to increase their activity just before you pick up the object

Reticulospinal adjustments Cordo & Nashner, 1982 - found activity of the legs precedes the activity of the biceps - depends on the context (sitting vs standing)

Reticulospinal adjustments

Lateral brain stem pathways Goal-directed limb movements, e. g. reaching, manipulation Main path is rubrospinal From red nucleus Crosses midline in brain stem Influence distal muscles

Red nucleus • receives input from the deep cerebellar nuclei, as well as the motor cortex • sends majority of its neurons down the spinal cord (rubrospinal tract) and to the cerebellum through the inferior olive nucleus (source for climbing fibres)

Cerebellum • contains ~70% of all the brain's neurons; contributes to timing, coordination, and the learning of motor skills. • only approx. 10% of the volume • complete removal produces no muscle weakness or loss of perception

Cerebellum: divisions Anterior Lobe vermis Posterior Lobe nodulus flocculus Front View Side View • cerebellar cortex (gray matter), white matter • 2 hemispheres, vermis – ridge in centre • 3 lobes – anterior, posterior, flocculonodular

Lateral zone: participates more directly in reaching and pointing I/O cerebral cortex (via pons) nodulus flocculus Lateral zone Vermis & intermediate zone: mainly controls posture I/O spinal cord Vermis Intermediate zone Cerebellum: divisions

Intrinsic architecture Main inputs: - Mossy fibres (via parallel fibres from Granule cells) - Climbing fibres Granule cell fibre Mossy INPUT Climbing fibres Purkinje cell Mossy fibres Main output: - Purkinje cells Parallel fibre Inferior olive Climbing fibre Deep nuclei OUTPUT

Cerebellum: inputs Climbing fibres (CF) arise from neurons in the inferior olive and terminate of Purkinje cells and the cells in the deep cerebellar nuclei Inputs from CF cause complex spikes – supposed to signal motor errors (teaching signal) or loss of coordination

Cerebellum: inputs Mossy fibres also terminate on the deep cerebellar nuclei as well as granule cells (whose axons make the parallel fibres) Parallel fibres supply a huge & continuous supply of sensory information to the Purkinje cells which cause simple spikes.

Cerebellum: outputs Purkinje cells inhibits neurons in the deep cerebellar nuclei. These deep nuclei send excitatory outputs to a variety of structures, e. g. thalamus, reticulo-spinal system, ION, spinal cord, superior colliculus. Dentate nuclei Interpositus nuclei Fastigial nuclei

Cerebellum

What does the learning: I) Spinal cord and brainstem II) Forebrain

Forebrain comprises the diencephalon & telencephalon Basal ganglia plays an enigmatic, role in motor control and learning, including reaching & pointing Thalamus acts as a key node in recurrent, loops which integrate the cerebral cortex & subcortical motor-control systems. The motor cortex and the posterior parietal cortex make important contributions to reaching and pointing.

Anatomy review: Basal ganglia consists of a group of subcortical nuclei: caudate, putamen, globus pallidus.

Anatomy review: Basal ganglia Clinically includes subthalamic nucleus & substantia nigra These structures are highly interconnected anatomically.

Anatomy review: Basal ganglia Input: striatum { Output: globus pallidus & substantia nigra

Basal ganglia Major inputs to the striatum come from the cerebral cortex & the thalamus Globus pallidus sends GABAergic, inhibitory projections to the brainstem and thalamus. Subthalamic nucleus plays an important role in control of the basal ganglia’s output.

Circuitry of the basal ganglia

Circuitry of basal ganglia The cerebral cortex (and thalamus) projects to the striatum: excitatory. Striatum also receives dopaminergic projections from the SN pars compacta (SNc). The striatum inhibits the globus pallidus (GP) and substantia nigra pars reticulata (SN pr). STN sends excitatory projections to the GPi, GPe & SN pr. GPi or SN pr inhibits (GABAergic) the thalamus. Thalamus projects to the cortex: excitatory.

Circuitry of basal ganglia Direct path: striatum ¢GPi (internal) ¢thalamus ¢cortex Indirect path: striatum ¢GPe (external) ¢STN ¢GPi ¢thalamus ¢cortex

Circuitry of basal ganglia Direct path: -Leads to less inhibition of the thalamus, i. e. striatum inhibits GPi which in turn inhibits normal (inhibitory) action on the thalamus, thus leading to greater excitation from the thalamus to the cortex. -Allows for sustain actions or initiation of action Indirect path: -Excites the GPi thereby increasing its inhibition of the thalamus -Suppresses unwanted movements.

Parkinson disease: Basal ganglia circuitry Abnormal functioning

Circuitry of the basal ganglia

Context switching & Basal ganglia - activity of the legs precede the activity of the biceps depends on the context (sitting vs standing) - but patients who had Parkinson’s disease – couldn’t use their body’s state for predicting the consequences to minimize them

Thalamus • Dorsal thalamus sends its largest outputs to the cerebral cortex and basal ganglia • Ventral thalamus has a diverse pattern of connections, including direct projections to the spinal cord • Thalamus: relay station for all sensory information; maintains two loops (recurrent modules) between 1) the cerebellum and the cerebral cortex & 2) the basal ganglia and the cerebral cortex, on the other hand.

Thalamus loops Cerebellar cortex STN gran GPe Deep Cb Nuclei Thalamus Cortex GPi Pons Thalamus Striatum Cortex

Thalamus SMA VApc GPi VLo M 1 VLc X VPlo Cb

Cortical organization • Cerebrum 1) Allocortex – includes hippocampus & piriform 2) Neocortex – cerebral cortex

Cortical organization • Neocortex has 6 layers of neurons (sheets of cells parallel to the surface of the cortex)

Cortical organization

Cortical organization

Lateral corticospinal tracts Largest descending tract, ~750, 000 fibres from each hemisphere Originates from primary motor, premotor, & somatosensory cortex. Descends through brain in internal capsule; strokes here causes contralateral weakness Crosses at pyramidal decussation In lateral ventral horn, contacts Ins and MNs of distal muscles.

Ventral corticospinal tracts ~ 250, 000 fibres from each hemisphere Originates from premotor and primary motor cortex Remains uncrossed until spinal cord Bilaterally activates MNs of axial muscles

Primary & Non-primary motor cortex M 1 SMA Premotor area (PMA) SMA PMA M 1

PPC