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Download The Cerebral Cortex and Higher Intellectual Functions
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Direct motor pathway Corticospinal pathway Corticospinal pathway Motor Units – Large Versus Small Text Fig. 24-3 Spinal cord Reflexes Major receptors involved in spinal cord reflexes: muscle spindle and golgi tendon organ Text Fig. 17-1 Muscle spindle sense change and rate of change in muscle length Golgi tendon organ sense the force of muscle contraction (tension) Muscle stretch reflex Muscle stretch reflex / Reciprocal inhibition Tendon reflex (autogenic inhibition) Tendon reflex (autogenic inhibition) Flexor (withdrawal ) reflex (nociceptive reflex) Flexor (withdrawal ) reflex (nociceptive reflex) Text Fig. 9-11 Crossed Extension Reflex Text Fig. 9-11 Crossed Extension Reflex Extra-pyramidal System, Basal Ganglia and Cerebellum Organisation of the motor system Visual cortex Cerebellum Somatosensory cortex Prefrontal cortex Supplementary motor cortex Premotor cortex Motor nuclei of the thalamus Basal ganglia Primary motor cortex Brainstem Extrapyramidal Motor pathways Pyramidal tract Motor system includes • Tracts Corticospinal tract (Pyramidal tract ) Extra-pyramidal system • Basal Ganglia (regulator) • Cerebellum (regulator) Corticospinal pathway Motor system includes • Tracts Pyramidal tract (corticospinal tract) Extra-pyramidal system • Basal Ganglia (regulator) • Cerebellum (regulator) Extra-pyramidal System Definition: Tracts other than corticospinal tract are known as Extra-pyramidal tract. Vestibulospinal tract vestibular apparatus & vestibular nuclei Spinal motor neuron Innervating axial & postural muscles (trunk muscles) Function : maintain Posture & balance “head &eye” and balance reflexes Rubrospinal tract Red Nucleus in Midbrain Pass down through Pons & Medulla Ends in ant. Horn of spinal cord Control motor neurons Functions. Control Distal muscle of limbs “especially upper limb” Tectospinal tract Superior & Inferior collicili in midbrain Cervical spinal motor neuron of anterior horn Trunk and head moving muscles Function: Allow turning of the head in response to visual or Auditory stimuli. Reticulospinal Tract The reticular formation in the brainstem. It contains many different nuclear groups. Pontine and medullary nuclei projects to the anterior horn of the spinal cord. Functions: is responsible for regulating muscle tone and maintain posture. Motor system includes • Tracts Pyramidal tract (corticospinal tract) Extra-pyramidal system • Basal Ganglia (regulator) • Cerebellum (regulator) Motor control systems outside the cortex Cerebellum -controls neural ‘programs’ for the executionl of skilled movements Basal ganglia - a group of subcortical forebrain nuclei (caudate nucleus, putamen (= striatum), globus palludus, subthalamic nucleus) - modulate patterns of motor activity Organisation of the motor system Visual cortex Cerebellum Somatosensory cortex Prefrontal cortex Supplementary motor cortex Premotor cortex Motor nuclei of the thalamus Basal ganglia Brainstem Extrapyramidal Motor pathways Primary motor cortex Pyramidal tract Forebrain Input to basal ganglia Midbrain Output to thalamus and cortex Forebrain Midbrain MOVEMENT DISORDERS Parkinson disease Huntingtons disease PARKINSONS DISEASE • Effects dopaminergic neurons • Neurons are lost from substantia nigra • Rarely presents before 50 years • Neurodegenerative disease Neuropathology of Parkinson’s disease • nigro-striatal pathway degeneration • leading to a depletion of striatal dopamine • some degeneration of other dopamine pathways too Dopamine Glutamate XStriatum GABA CLINICAL FEATURES Characterized by: • Tremors • Rigidity • bradykinesia Huntington’s disease • Onset of symptoms usually at 30 to 45 years • Genetically determined (single dominant gene) • Causes degeneration of the output neurones from the striatum, reducing inhibitory modulation of motor function •Progressive disease causing involuntary muscle jerks • Dopamine Glutamate Striatum X GABA HUNTINGTONS DISEASE • Inherited disorder • Autosomal dominant • Males females equally affected • Presents during the 4th decade • Chorea which worsens with time • Cognitive disorders • Dementia Motor control systems outside the cortex Cerebellum -controls neural ‘programs’ for the executionl of skilled movements Basal ganglia - a group of subcortical forebrain nuclei (caudate nucleus, putamen (= striatum), globus palludus, subthalamic nucleus) - modulate patterns of motor activity GROSS STRUCTURE Organisation of the motor system Visual cortex Cerebellum Somatosensory cortex Prefrontal cortex Supplementary motor cortex Premotor cortex Motor nuclei of the thalamus Basal ganglia Brainstem Extrapyramidal Motor pathways Primary motor cortex Pyramidal tract Feed-back and feedback control circuits • Input: Cerebellar connections – Sensory cortex (somato, visual) – Vestibular system – Spinocerebellar tract • Output: – Motor cortex – Thalamus motor nuclei – Extra-pyramidal tracts The main functions of cerebellum: • body equilibrium • regulation of muscle tone • coordination of movements Ataxia • means disturbances of equilibrium of the body and coordination of movements. • Cerebellum lesion produces cerebellar ataxia Cerebellar ataxia • Attactic gait – patient can’t to walk • Disorders of equlibrium – patient can’t to stand • Intention tremor – is dynamic tremor (it is more expressed while moving and disappears while rest) • Nystagmus • Dysmetria (disturbed ability to gauge distances)
