Basal nuclei, cerebellum and movement

Transcription

1 Basal nuclei, cerebellum and movement MSTN121 - Neurophysiology Session 9 Department of Myotherapy

2 Basal Nuclei (Ganglia)

3 Basal Nuclei (Ganglia) Role: Predict the effects of various actions, then make and execute action plans. Include the following nuclei: Caudate: located in the cerebrum Putamen: located in the cerebrum Globus pallidus: located in the cerebrum Subthalamic nucleus: located within the diencephalon Substantia nigra: located within the midbrain Based on anatomic proximity, the cerebral basal nuclei have joint names: Lentiform nucleus: globus pallidus + putamen Striatum: caudate + putamen Ventral striatum: junction of caudate and putamen Nucleus accumbens: part of ventral striatum

4 Basal Nuclei Function Executive Loop DLPFC Conscious awareness of decision making and planning Head of the Caudate Non-conscious decision making projects to thalamus to facilitate the DLPFC

5 Basal Nuclei Function Motor Putamen receives input from motor cortex, via direct pathway putamen disinhibits the thalamus thus facilitating the motor cortex and allowing the initiation of movement

6 Behavioural flexibility and control loop The lateral orbital cortex processes information relating to social disapproval and alters behaviour. The loop is also involved in sifting through relevant and irrelevant information that is being processed.

7 Limbic loop Links emotional, cognitive and motor systems to act on stimuli with reward-guided behaviours. In addition, monitors errors in prediction of future events and when behaviour does not result in pleasure. Thus this is the pleasure seeking loop.

8 Diseases of Basal Nuclei Movement disorders range from hypokinetic to hyperkinetic. Differences in abnormal movements are due to dysfunction in specific parts of basal nuclei, pedunculopontine tegmental nucleus (PPN), and midbrain locomotor region (MLR). Inhibit motor thalamus, PPN, and MLR; excessive inhibition results in hypokinetic disorders, and inadequate inhibition results in hyperkinetic disorders.

9 Parkinson s Disease Red arrows - excitatory. Black arrows - inhibitory. Thick arrows - increased neural activity. Thin arrows - decreased neural activity. Dark pink boxes - normal level of activity. Light pink boxes - decreased activity. A dotted outline surrounding a structure indicates the death of neurons within that structure. In Parkinson s disease, neurons die in the substantia nigra compacta and the pedunculopontine nucleus. The subthalamic nucleus output increases because globus pallidus externus inhibition decreases (not shown). VL: ventrolateral. Decreased dopamine from the substantia nigra compacta is the primary change leading to excessive activity of the globus pallidus internus (GPi).

10 Cerebellum Coordinates movement and postural control by comparing actual motor output with the intended movement and then adjusting the movement as necessary. Is involved in learning timing and rhythm of movements, synchronization of movements, and learning to correct motor errors. Massive amounts of sensory information enter the cerebellum; cerebellar output is vital for normal movement. Severe damage to the cerebellum does not interfere with sensory perception or with muscle strength; coordination of movement and postural control are degraded.

11 Cerebellum Anatomy Purkinje cells output neurons Climbing fibres from inferior olive Mossy fibres from spinal cord/brainstem

12 Lumbar Plexus Cerebellum consists of three lobes: Anterior Posterior Flocculonodular Vertically, the cerebellum can be divided into sections: Midline vermis Paravermal hemisphere Lateral hemisphere

13 Functional Regions of Cerebellum Three broad classes of human movement: Equilibrium: Is regulated by the vestibulocerebellum. Gross movements of the limbs: Is coordinated by the spinocerebellar. Fine, distal, voluntary movements: Are coordinated by the cerebrocerebellum.

14 Vestibulocerebellar System Vestibular nuclei Visual input Flocculonodular lobe Lesions cause: Nystagmus Dysequillibrium Difficulty maintaining sitting and standing balance (truncal ataxia)

15 Spinocerebellar System Fastigial nuclei (vermis) Vestibular nuclei Vestibulospinal, reticulospinal and medial corticospinal tracts Spinal cord (trunk), vestibular nuclei and brainstem nuclei Lesions cause: Gait ataxia wide based, unsteady, staggering, veering gait Dysdiadochokinesia inability to rapidly alternate movements (foot tapping etc) Dysmetria inability to accurately move an intended distance (missing an object when trying to pick it up) Action tremor shaking of limb in voluntary movement Action tremor may arise due to the onset and offset of muscle activity being delayed agonist burst is prolonged and antagonist is delayed causing overshoot of the target.

16 Cerebrocerebellar System - Lateral cerebellum Dentate nuclei Red nucleus, VL of thalamus Cerebral cortex via pontine nuclei Motor and premotor via thalamus Rubrospinal tract Lesions cause: Gait and limb ataxia paravermal Hand ataxia lateral cerebellum difficulty with fine motor skills like playing instruments, typing etc Paravermal and cerebrocerebellar lesions result in dysarthria

17 Cerebellar Disorders Unilateral lesions of the cerebellum affect the same side of the body. Cerebellar signs are ipsilateral because the output paths of the medial descending tracts remain ipsilateral and because cerebellar efferents project to the contralateral cerebral cortex and red nucleus whose descending tracts cross the midline. Ataxia is a movement disorder common to all lesions of the cerebellum. Describes the voluntary, normal-strength, jerky, and inaccurate movements that are not associated with hyperstiffness.

18 Differentiate from Sensory Ataxia Not all ataxia is caused by cerebellar lesions. Interference with transmission of somatosensory information to the cerebellum, either by lesions of the spinocerebellar tracts or by peripheral neuropathy, may also produce ataxia. Sensory deficits or paravermal cerebellar lesions may cause ataxia in the lower limbs. Romberg test, tests of proprioception, vibration sense, and ankle reflexes are tests that differentiate between the two.

19 Motor Control Disorders

20 Normal Motor Control 1 Peripheral: Alpha motor neurons innervate skeletal muscle, muscle spindles provide proprioception which modulates motor output. 2 Spinal: the spinal cord integrates information from other spinal segments, local circuits and from the brain. 3 Descending tracts provide information from the brain corticospinal/reticulospinal etc. 4 Motor control is provided by the cerebellum and basal ganglia adjusting the level of activity in the descending tracts.

21 Types of Movement Three types of movement include: Postural: Is controlled by brainstem mechanisms. Ambulatory: Is controlled by brainstem and spinal regions. Reaching/grasping: Is controlled by the cerebral cortex. All regions of the nervous system contribute to each type of movement.

22 Postural Control Provides orientation and balance. Orientation is the adjustment of the body and head to vertical. Balance is the ability to maintain the center of mass relative to the base of support. Is achieved by central commands to the lower motor neurons; the central output is adjusted to the environmental context by sensory input.

23 Postural Control To orient to the world, three senses are used: Somatosensation: Provides information about weight bearing and the relative positions of body parts. Vision: Provides information about movement and cues for judging upright. Vestibular: Informs a person about head position relative to gravity and about head movement.

24 Ambulation All regions of the nervous system are required for normal human ambulation. Cerebral cortex provides goal orientation and control of ankle movements. Basal ganglia govern generation of force. Cerebellum provides timing, coordination, and error correction. Sensory information is used to adapt motor output appropriately.

25 Reaching and grasping Vision and somatosensation are essential for reaching and grasping. Vision provides information for locating an object in space and assessing its shape and size. Feed-forward is the primary role of visual information; if the movement is inaccurate, vision also guides corrections. Action stream flows from the visual cortex to the posterior parietal cortex.

26 Reaching and grasping Grasping is coordinated with activity of the eyes, head, proximal upper limb, and trunk; orientation and postural preparation are integral to the movement. When the object is contacted, grip force adjusts quickly, indicating feedforward control. After the object is grasped, somatosensory information corrects any error in grip force.

27 Movement Systems Interaction

28 References Lundy-Ekman, L 2013, Neuroscience: fundamentals for rehabilitation, 4th edn, Elsevier, Sydney.

29 Image References Lundy-Ekman, L 2013, Neuroscience: fundamentals for rehabilitation, 4th edn, Elsevier, Sydney.

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