Motor Systems Lecture II - Extrapyramidal Pathways PDF

ANAT1012/1019 Motor system II: Extrapyramidal system Michael Piper The School of Biomedical Sciences [email protected] https://biomedical- sciences.uq.edu.au/research/groups/neural-stem-cells Reading: Krebs 2012, Neuroscience...

ANAT1012/1019 Motor system II: Extrapyramidal system Michael Piper The School of Biomedical Sciences [email protected] https://biomedical- sciences.uq.edu.au/research/groups/neural-stem-cells Reading: Krebs 2012, Neuroscience Pages 142-145; 147, 219 Or Nolte, Chapter 11 ANAT1012/1019: Control of movement Lecture 2: the extrapyramidal system SUPPLEMENTARY MOTOR CORTEX PRIMARY PREFRONTAL SOMATOMOTOR CORTEX CORTEX PREMOTOR CORTEX PYRAMIDAL TRACT EXTRAPYRAMIDAL TRACTS (= descending motor pathways from the brainstem) Collaterals from For unconscious movements pyramidal tract (supraspinal reflexes) 1. Tectospinal tract 2. Rubrospinal tract BRAINSTEM 3. Reticulospinal tract 4. Vestibulospinal tract SPINAL CORD Sensory consequence (Sensory receptor) SKELETAL MUSCLE Lecture 2 key learning objectives Lecture 2 key learning objectives  Descending motor pathways § Descending motor tract that travels through the medullary pyramids is called the pyramidal tract § Descending motor tracts that DON’T pass through the pyramids are called extrapyramidal tracts (+ corticonuclear) 1. Pyramidal system (from cerebral cortex): - corticospinal tract - cortico[bulbar]nuclear tract (from cortex) For conscious (voluntary) movements! 2. Extrapyramidal system (from brainstem): - tectospinal tract (originates from tectum) - rubrospinal tract (originates from red nucleus) - reticulospinal tract (originates from reticular formation) - vestibulospinal tract (originates from vestibular nuclei) For supraspinal reflex (unconscious ) movements!  Hierarchy of motor neurons Upper motor neurons: - Cortical motor neurons within M1 Motor cortex (M1) - Motor neurons within the brainstem (extrapyramidal neurons) e) (fac Brainstem c le s mus etal Skel Spinal cord Lower motor neurons: - Motor neurons in the anterior horn of the spinal cord Skeletal muscles - Motor neurons within the cranial nerve nuclei within the brainstem Lateral view of the brainstem Lateral view of the brainstem Stuctures of the tectum Structure of the tegmentum Structures of the base Important features of the midbrain Important features of the pons Important features of the medulla  Body movement (by skeletal muscles) is a result of the combination of voluntary and involuntary (reflex) actions § skeletal muscles are responsible for voluntary movement and are under conscious (= cortical) control § CEREBRAL MOTOR CORTEX: - is the highest center for control of voluntary movements - controls all skeletal muscles through the pyramidal pathways § skeletal muscles, however, are also directly influenced by “unconscious” CNS centers, i.e. motor neurons of the spinal cord & brainstem: - this leads to involuntary contraction or movement of skeletal muscles (= Reflex movement) - reflexes induced by motor neurons of the: 1. spinal cord are called spinal reflexes 2. brainstem are called supraspinal reflexes (extrapyramidal tracts) Major movement types Proprioceptive reflexes Stereotyped supraspinal reflexes Major movement types  Descending motor pathways § Descending motor tract that travels through the medullary pyramids is called the pyramidal tract § Descending motor tracts that DON’T pass through the pyramids are called extrapyramidal tracts (+ corticonuclear) 1. Pyramidal system (from cerebral cortex): - corticospinal tract - cortico[bulbar]nuclear tract (from cortex) For conscious (voluntary) movements! 2. Extrapyramidal system (from brainstem): - tectospinal tract (originates from tectum) - rubrospinal tract (originates from red nucleus) - reticulospinal tract (originates from reticular formation) - vestibulospinal tract (originates from vestibular nuclei) For supraspinal reflex (unconscious ) movements! The reticulospinal tract (mostly extensor-biased) Postural reflex (reticulospinal) responses adapt to varying goal-directed movements (not stereotyped) Postural reflex (reticulospinal) responses adapt to varying goal-directed movements (not stereotyped) Postural reflex (reticulospinal) responses adapt to varying goal-directed movements (not stereotyped) Postural reflex (reticulospinal) responses adapt to varying goal-directed movements (not stereotyped) The reticulospinal tract Tectospinal tract Vestibulospinal tract Basal ganglia Motor cortex Cerebellum (collateral) (collateral) RETICULOSPINAL TRACT Muscles for upright body posture Gait control The vestibulospinal tracts equilibrium / vestibular: semicircular canals & ducts vestibule contains utricle & saccule knowledge of: 1. position & linear acceleration of head - utricle & saccule each contain a macula 2. rotational movement of head - semicircular ducts each contain a cupula Sensory receptor cells = hair cells! The vestibulospinal tracts There are four vestibular nuclei, but only neurons of the medial and lateral vestibular nuclei of the medulla contribute to the vestibulospinal tracts Lateral vestibulospinal nuclei: generates muscle tone in deep back & limb extensors (antigravity muscles) in response to gravity Maintain stance and balance – vestibulo-spinal reflex  The vestibulospinal tracts There are four vestibular nuclei, but only neurons of the medial and lateral vestibular nuclei of the medulla contribute to the vestibulospinal tracts Medial vestibular nuclei: stabilizes the head during movement, especially rotational movement Vestibulo-cervical reflex Via medial vestibulospinal tract (MVST) Medial vestibular nuclei: Also involved in maintaining fixation of the eyes on an object during head movement Vestibulo-ocular reflex The tectospinal tract The tectospinal tract Visual input from Auditory input from Sensory input from spinal cord retina inferior colliculi (dorsal & anterolateral systems) Superior colliculi (tectum) Tectospinal tract Neck and shoulder muscles § The tectospinal tract controls reflex movements of the head, neck & upper limbs in response to all relevant sensory stimuli (visual, auditory, tectile, temperature, pain etc.). In other words, it changes the visual axis towards the sensory stimulus §The tectospinal tract is, therefore, important for steering the body (change of direction) during gait as we navigate our visual axis in the direction of movement The rubrospinal tract (flexor-biased tract) The rubrospinal tract get input from the pyramidal system The rubrospinal tract MOTOR CORTEX RED NUCLEUS CEREBELLUM Rubrospinal tract INFERIOR OLIVARY NUCLEUS SPINAL CORD The motor cortex and the cerebellum modulate the function of the red nucleus Damage to the pyramidal system Anatomical division of the descending motor pathways § All motor pathways in the spinal cord are located in the lateral or anterior funiculi § All descending motor pathways (tracts) descend along two major pathways - (Dorso)lateral Pathways - (Ventro)medial pathways Anatomical division of the descending motor pathways Anatomical division of the descending motor pathways Anatomical division of the descending motor pathways  Upper motor neuron lesions – above the midbrain Consider the symptoms of a patient with an upper motor neuron lesion above the level of the midbrain  Upper motor neuron lesions – below the midbrain Consider the symptoms of a patient with an upper motor neuron lesion below the level of the midbrain Co-ordination of cortical and brainstem motor activity Co-ordination of cortical and brainstem motor activity – the eye Gaze - is the coordinated, synergistic movement of both eyes - the aim is to focus the image on to the fovea of both eyes v Binocular vision v Gaze requires both cortical and brainstem activity  Co-ordination of cortical and brainstem motor activity – the eye Upper motor neurons from M1- corticonuclear tract OCULOMOTOR CN III TROCHLEAR CN IV ABDUCENS CN VI coordinated movement of 2 eyes 6 extrinsic eye muscles each eye involves 3 pairs of cranial nuclei medial longitudinal fasciculus Co-ordination of cortical and brainstem motor activity – the eye Medial Longitudinal Fasciculus (MLF) Interconnects nuclei of: Oculomotor (III) Trochlear (IV) Abducens (VI) Vestibular (VIII) Co-ordination of cortical and brainstem motor activity – the eye Fig 9.11 Krebs 2018 Co-ordination of cortical and brainstem motor activity – the eye Gaze is the coordinated, synergistic movement of both eyes aim is to focus the image on to the fovea of both eyes there are 2 general categories of eyes movements v conjugate movements v vergence movements Co-ordination of cortical and brainstem motor activity – the eye There are fast & slow conjugate eye movements saccades = fast redirect gaze so a different image falls on the fovea use them when exploring the environment visually initiated by cortical & subcortical centres coordinated by brainstem gaze centres horizontal gaze centre in pons Paramedian Pontine Reticular Formation (PPRF) vertical gaze centre in rostral midbrain rostral Midbrain Reticular Formation (rMRF) Fig.21.12 Nolte 2016 Co-ordination of cortical and brainstem motor activity – the eye the initiation of saccades frontal eye field (FEF) supplementary eye field parietal eye field projects to contralateral PPRF for horizontal saccades +/- ipsilateral superior colliculus (which then projects to contralateral PPRF) or rMRF for vertical saccades Fig.21-13 Nolte 2016 Co-ordination of horizontal conjugate eye movements Left PPRF controls both eyes looking to left Fig 9.12 Krebs 2018 Co-ordination of cortical and brainstem motor activity – the eye There are fast & slow conjugate eye movements smooth pursuit movements = slower used to keep an image on the fovea due to either movement of the object or movement of self use visual and motor cortices, cerebellar & vestibular feedback 2 eyes = 2 fovea ie. both cerebral hemispheres involved. Co-ordination of cortical and brainstem motor activity – the eye Smooth pursuit Used to keep an image on the fovea when the object is moving relative to the background Co-ordination of cortical and brainstem motor activity – the eye Accommodation: changes in object distance require vergence movements 3 requirements for focusing on a near object: 1. Convergence so that the object falls on both foveae 2. Increase curvature of the lens to increase refractive power to focus the image on the fovea 3. Pupillary constriction – reduces blur & increases depth of field  Accommodation: CN II afferents to bilateral LGN (thalamus) Primary visual cortex Visual association cortex Project to pretectal area Oculomotor & Edinger-Westphal nuclei CN III convergence somatic fibres to medial rectus parasympathetic fibres to increase lens curvature ciliary muscle pupillary constriction constrictor pupillae  The basal ganglia Primary Secondary Higher order Prefrontal S P Primary sensory Sensory asssociation cortex M M motor cortex cortex cortex (higher order) C C cortex BASAL GANGLIA LOOP Pyramidal SMC= Supplementary motor cortex tracts PMC= Premotor cortex THALAMUS BRAINSTEM Extrapyramidal tracts Somatosensory Spinal cord input (Somatomotor output) e.g. visual, auditory, tactile