Direct motor 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 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 Crossed Extension Reflex

Text Fig Crossed Extension Reflex

Extra-pyramidal System, Basal Ganglia and Cerebellum

Organisation of the motor system Brainstem Extrapyramidal Motor pathways Cerebellum Basal ganglia Supplementary motor cortex Pyramidal tract Premotor cortex Primary motor cortex Visual cortex Somatosensory cortex Motor nuclei of the thalamus Prefrontal cortex

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.

vestibular apparatus & vestibular nuclei Spinal motor neuron Innervating axial & postural muscles (trunk muscles) Function : maintain Posture & balance “head &eye” and balance reflexes Vestibulospinal 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” Rubrospinal tract

Superior & Inferior collicili in midbrain Trunk and head moving muscles Cervical spinal motor neuron of anterior horn Function: Allow turning of the head in response to visual or Auditory stimuli. Tectospinal tract

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 Basal ganglia - a group of subcortical forebrain nuclei (caudate nucleus, putamen (= striatum), globus palludus, subthalamic nucleus) - modulate patterns of motor activity Cerebellum -controls neural ‘programs’ for the executionl of skilled movements

Organisation of the motor system Brainstem Extrapyramidal Motor pathways Cerebellum Basal ganglia Supplementary motor cortex Pyramidal tract Premotor cortex Primary motor cortex Visual cortex Somatosensory cortex Motor nuclei of the thalamus Prefrontal cortex

Forebrain Midbrain Input to basal ganglia

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

Striatum DopamineGlutamate GABA Neuropathology of Parkinson’s disease nigro-striatal pathway degeneration leading to a depletion of striatal dopamine some degeneration of other dopamine pathways too X

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 Striatum DopamineGlutamate GABA X

HUNTINGTONS DISEASE Inherited disorder Autosomal dominant Males females equally affected Presents during the 4 th decade Chorea which worsens with time Cognitive disorders Dementia

Motor control systems outside the cortex Basal ganglia - a group of subcortical forebrain nuclei (caudate nucleus, putamen (= striatum), globus palludus, subthalamic nucleus) - modulate patterns of motor activity Cerebellum -controls neural ‘programs’ for the executionl of skilled movements

GROSS STRUCTURE

Organisation of the motor system Brainstem Extrapyramidal Motor pathways Cerebellum Basal ganglia Supplementary motor cortex Pyramidal tract Premotor cortex Primary motor cortex Visual cortex Somatosensory cortex Motor nuclei of the thalamus Prefrontal cortex

Feed-back and feedback control circuits

Cerebellar connections Input: –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

A t a x i a 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)