Mark Kozsurek, M.D., Ph.D. mark@kozsurek.hu Motor systems and tracts, pyramidal tract The 2nd lecture today: Structure and connections of the basal ganglia. Motor pathways arising from the brain stem Mark Kozsurek, M.D., Ph.D. mark@kozsurek.hu EM II., 09/10/2017

Motor systems – cortical areas Many different cortical areas: mainly within the frontal lobe

Primary somatomotor cortex precentral gyrus, (Brodmann 4 area) somatotopic arrangement agranular cortex (layer 2 and 4 are thin, giant pyramidal cells - Betz cells in layer 5)

Motor systems – basal ganglia Subcortical groups of neuronal cell bodies developing from the prosencephalic wall (dorsal striatum constituted by the caudate nucleus and putamen, the ventral striatum formed by the nucl. accumbens and the olfactory tubercle, the globus pallidus, the subthalamic nucleus, claustrum, amygdaloid body (red and blue)… It is not correct anatomically, but in clinical practice red nucleus and substantia nigra are also considered as basal ganglia (green)

Motor systems – thalamus Ventral-anterior (VA) and ventrolateral (VL) nuclei of the thalamus are considered as motor nuclei and they are connected to different motor cortical areas.

Motor systems – cerebellum archicerebellum reciprocal connection with the vestibular nuclei (body balance posture) paleocerebellum epicritic and proprioceptive sensory feed-back (spinocerebellar and cuneocerebellar tracts) neocerebellum descending information from the motor cortical areas (corticopontine-pontocerebellar indirect pathways)

Motor systems – brainstem nuclei substantia nigra, red nucleus, reticular formation, superior collicle pontine nuclei, inferior olivary nucl.

Motor systems – spinal cord All kinds of spinal reflexes are automatic responses to a stimulus, when the dicission is made by the spinal neuronal circuits without major influence of higher centres of the nervous system!

Pyramidal and extrapyramidal systems Pyramidal and extrapyramidal systems can only be separated anatomically but not functionally! None of the two systems can work properly alone, they constitute one motor system together!!! Pyramidal system is the chief organizer and executor of voluntary movements. Extrapyramidal system includes all the motor centres and pathways that lie outside the pyramidal system and are beyond voluntary control. Extrapyramidal system: coordinates movements of various groups of muscles both in space and time, regulates job- and sport-specific automatic movements consisting of periodic elements (e.g. walking, running, riding a bike, dancing, driving a car, handwriting or typing, etc.), controls emotional movements, helps to control posture and balance, regulates muscle tone.

Just a sketch: only the principal components can be recognized. PYRAMIDAL SYSTEM

EXTRAPYRAMIDAL SYSTEM Colours, beauty, harmony, regularity, but not more than an abstract art. EXTRAPYRAMIDAL SYSTEM

Taken together: the real world.

(a new and clear structure) The pyramidal system (a new and clear structure)

Sceletal muscles of the head and neck Sceletal muscles of the trunk and limbs

CORTICONUCLEAR TRACT

CORTICOSPINAL TRACT

HEAD IS TOWARD THE MIDLINE! Note the somatotopic arrangement of the corticobulbar and corticospinal tracts! HEAD IS TOWARD THE MIDLINE!

The pyramidal system - Summary Pyramidal system is the chief organizer and executor of voluntary movements. Upper motoneurons are located in the cerebral cortex, while lower motoneurons can be found in the motor nuclei of cranial nerves or in the spinal ventral horn. Descending axons of upper motoneurons that terminate in the motor nuclei of cranial nerves and in the spinal cord constitute the corticonuclear and corticospinal tracts, respectively. The corticonuclear tract reaches the lower motoneurons of both sides (bilateral innervation), while corticospinal fibres target the lower motoneurons of the opposite side only (crossed pathway).

The extrapyramidal system (an ancient and complex network)

Components of the extrapyramidal system cortical areas caudate nucl. putamen thalamus globus pallidus zona incerta, subthalamic nucl. Components of the extrapyramidal system substantia nigra, red nucleus, reticular formation, superior collicle vestibular apparatus cerebellum, pontine nuclei, inferior olivary nucl.

Efferent extrapyramidal pathways rubrospinal tr. tectospinal tr. reticulospinal tr. vestibulospinal tr. olivospinal tr.

The extrapyramidal system - Summary Structures involved in motor functions that lie outside the pyramidal system and are beyond voluntary control of movements. Extrapyramidal system controls automatic, repetitive, emotional movements as well as the posture and balance. Extrapyramidal centres are mainly interconnected by closed loops. From the loops descending efferents arise and target the same lower motoneurons as the pyramidal tracts.

Cortex extrapyramidal pyramidal basal ganglia thalamus brainstem CEREBELLUM lower motoneurons

CSl: lateral corticospinal Csa: anterior corticospinal RuS: rubrospinal ReS: reticulospinal OlS: olivospinal VeS: vestibulospinal TeS: tectospinal CSl RuS ReS ReS CSa VeS TeS OlS alpha motoneurons → to extrafusal muscle fibres gamma motoneurons → to intrafusal fibres of muscle spindles (gamma-loop)

Gamma-loop gamma motoneuron alpha motoneuron

About the gamma-loop Skeletal muscles can be activated directly, by the stimulation of alpha-motoneurons or indirectly, via the gamma loop – proprioceptive reflex arc. Stimulation of gamma-motoneurons results in the contraction of intrafusal fibres of muscle spindles. Shorthening of the muscle spindle (similarly to the stretching of the surrounding muscles) activates the proprioceptive reflex arc. This results in the indirect contraction of extrafusal („working”) muscle fibres.

„Common terminal pathway” - Summary Corticonuclear and corticospinal fibres may terminate directly on alpha-motoneurons (innervating muscles of eyeballs and fingers), but more frequently the connection is indirect and is performed through an interneuron. Extrapyramidal pathways predominantly target gamma- motoneurons (directly or indirectly) and initiate movements via the gamma-loop and the proprioceptive reflex arc.

Cortical areas sensory feedback dorsal column – medial lemnicus spinocerebellar tracts extrapyramidal pyramidal basal ganglia thalamus brainstem CEREBELLUM lower motoneurons

Movement disorders

Peripheral and central facial palsy

Parkinson’s desease Cardinal symptomes: tremor, rigidity, slowness of movement and postural instability. Idiopathic (If the etiology is known we talk about parkinsonism or Parkinson’s syndrome.) Dopamine production of neurons within the substantia nigra is impaired, so there is lack of dopamine in the striatum. Medical treatment: levodopa - precursor of dopamine, passes the blood-brain barrier and transforms into dopamine (and many-many other pills not mentioned now…)

X dopaminergic GABAergic

People with parkinsonism who have enhanced the public's awareness include Michael J. Fox and Muhammad Ali.

Thank you for your attention!