M6-TONE AND POSTURE_250129_113159.PDF

TONE AND POSTURE DR. NORHAZLINA ABDUL WAHAB JABATAN FISIOLOGI FAKULTI PERUBATAN PPUKM CHERAS, KUALA LUMPUR E-MEL: [email protected]  LEARNING OBJECTIVES At the end of the lecture, students should be able to: describe muscle tone...

TONE AND POSTURE DR. NORHAZLINA ABDUL WAHAB JABATAN FISIOLOGI FAKULTI PERUBATAN PPUKM CHERAS, KUALA LUMPUR E-MEL: [email protected]  LEARNING OBJECTIVES At the end of the lecture, students should be able to: describe muscle tone and its relationship to stretch reflex. describe the systems and tracts involve in regulating posture. explain postural reflexes at the spinal cord, brain stem, midbrain, and cortical levels. differentiate between upper and lower motor neuron lesions. explain abnormalities of posture (decerebrate and decorticate).  MUSCLE TONE Defined as the resistance of a muscle to stretch. Keeps the muscle firm, healthy and ready to respond to a stimulus Spinal reflex regulates muscle tone via activation of muscle spindle which elicits reflex contraction γMN keeps the muscle spindle under proper tension while the muscles are relaxed  Myotatic or Stretch Reflex key for maintenance of posture and helps to overcome unexpected impediments during voluntary movement Phasic stretch reflex Tonic stretch reflex Elicited by stretching the Elicited by bending a joint muscle spindles Reflex arc involves both Ia and Reflex arc involves Ia afferent II afferent fibres fibre Helps in maintaining muscle tone and posture  γMN adjust the sensitivity of muscle spindle Descending motor pathways activates αMN and γMN simultaneously Causing a synchronous contraction of extrafusal and intrafusal muscle fibres Thereby maintaining relatively constant muscle tension  LEARNING OBJECTIVES At the end of the lecture, students should be able to: describe muscle tone and its relationship to stretch reflex. describe the systems and tracts involve in regulating posture. explain postural reflexes at the spinal cord, brain stem, midbrain, and cortical levels. differentiate between upper and lower motor neuron lesions. explain abnormalities of posture (decerebrate and decorticate).  POSTURE Posture is the way in which the body is positioned while sitting or standing Functions: Maintenance of the body in an upright, balanced position Provision of stable background for voluntary activity  Postural control Axial (trunk) and proximal limb muscles are concerned with postural adjustments Neural pathways located in brain The ventral corticospinal and stem and spinal corticobulbar tracts cord supply bilateral proximal muscles for Ventromedial posture and other bilateral functions pathways: such as swallowing tectospinal, and wrinkling of the reticulospinal and brows. vestibulospinal tracts  Descending motor pathways Pontine and medullary reticulospinal and vestibulospinal tracts form medial pathways Medial pathways Lateral pathways ends on the terminate in the lateral interneurons in the portions of the gray medial ventral horn matter in SC Control fine movement of Control the axial the distal ends of the muscles for balance limbs and supporting and posture muscles in the proximal ends of limbs  Reticular Formation Neuron cell bodies are scattered in the white matter Regulate muscle tone and posture to support of body against gravity Reticular nuclei Pontine – transmit excitatory signal via pontine reticulospinal tract to excite axial muscles (vertebra & proximal limbs) Receive signal from vestibular nuclei and cerebellum Medullary – transmit inhibitory signal via medullary reticulospinal tract to counterbalance the excitatory signals Receive signal from corticospinal tract, rubrospinal tract & other motor pathways  LEARNING OBJECTIVES At the end of the lecture, students should be able to: describe muscle tone and its relationship to stretch reflex. describe the systems and tracts involve in regulating posture. explain postural reflexes at the spinal cord, brain stem, midbrain, and cortical levels. differentiate between upper and lower motor neuron lesions. explain abnormalities of posture (decerebrate and decorticate).  Postural reflex Automatic body movements related to body positioning alone (basic postural reflexes) and to vestibular input (labyrinthine-spinal reflex) Primitive reflex and postural reflex is the simplest and most frequently used tools to assess the CNS integrity of infants and young children Primitive reflex Brainstem-mediated Commence at birth Highly stereotypical patterns elicited by specific sensory stimuli E.g. Moro, palmar and plantar grasp, sucking, Babinski sign Replaced by postural reflex when CNS matures (Zafeiriou 2004)  TYPES OF POSTURAL REFLEXES Tonic neck reflex Tonic labyrinthine Righting reflex Position of head relative to (vestibular) reflex Altered position of head body Position of head relative to and body Receptors: stretch horizontal plane Receptors: vestibular receptors of neck muscles Stimulus: gravity apparatus, neck stretch Rec: ? receptors, Integration centre: medulla Integration centre: mechanoreceptors oblongata vestibular & reticular Role: to restore posture to Efferent fibre: nuclei in MO normal position corticospinal tract Efferent fibre: vestibulospinal & reticulospinal tracts  LEARNING OBJECTIVES At the end of the lecture, students should be able to: describe muscle tone and its relationship to stretch reflex. describe the systems and tracts involve in regulating posture. explain postural reflexes at the spinal cord, brain stem, midbrain, and cortical levels. differentiate between upper and lower motor neuron lesions. explain abnormalities of posture (decerebrate and decorticate). Motor neurons Upper motor neuron Corticospinal tract neurons that innervate spinal motor neurons Also include brain stem neurons Lower motor neuron Motor neurons that originate in spinal cord and terminate in skeletal muscle  UMNL vs LMNL Features of UMNL Features of LMNL Spasticity Flaccid paralysis Hypertonia Muscular atrophy Hyperactive stretch reflex Fasciculations +ve Babinski sign Hypotonia E.g. stroke, cerebral palsy Hyporeflexia/areflexia E.g. amyotrophic lateral sclerosis (Lou Gehrig ds) Removal of cerebral cortex Upper limbs flexed Lower limbs extended, toes pointing slightly inward Head is extended Complete transection of brain stem between sup & inf colliculi Lower extremities are extended, toes pointing inward Upper extremities extended, fingers flexed, forearms pronate Neck and head extended Thank you