Brainstem for BB - PDF

Presentation by Dr Anna Gould The Brainstem Senior Lecturer Foundations of neuroscience for physiotherapy Intended learning outcomes To identify additional relevant structures of the brainstem and briefly explain their signi...

Presentation by Dr Anna Gould The Brainstem Senior Lecturer Foundations of neuroscience for physiotherapy Intended learning outcomes To identify additional relevant structures of the brainstem and briefly explain their significance To describe the descending tracts originating from the brainstem To explain the motor functions of the brainstem To explain the role of the brainstem in the maintenance of normal muscle tone  AnatomyTV Location Continuous with spinal cord below and diencephalon/cerebrum above What does the brainstem do? Respiratory and cardiac centres (medulla) Centres for automatic responses including swallowing and vomiting The cranial nerves arise from the brainstem Pain modulation​ Sleep/consciousness​ Habituation (ability to direct your attention) Movement: Postural tone (postural stability as a background for distal movement) and movement Cranial Nerves The human cranial nerves and their areas of innervation. Encyclopedia Britannica/UIG/Getty Images Cranial Nerves: Optic (II) Sensory Vision Emerges from midbrain Carries visual information from the retina of the eye to: the thalamus. Then synapse with neurons whose axons extend to the primary visual cortex (occipital lobe). some nerve fibers enter the brain stem. Cranial Nerves: Oculomotor (III), Trochlear (IV) and Control Abducens (VI) muscles that move the eyeballs/ eyelids Motor nerves Oculomotor (III): Raises the upper eyelid Turns eyeball up, down and medially Parasympathetic output – constricts the iris (e.g. bright light) Emerges from midbrain Trochlear (IV) Assists in turning eyeball down and laterally Emerges from midbrain Abducens (VI) Turns the eyeball laterally Emerges from Pons Cranial Nerves: Vestibulocochlear (VII) Sensory nerve Emerges from the pons Two branches: Vestibular (equilibrium) and Cochlear (hearing) Vestibular Branch Carries impulse from the vestibular apparatus From the semicircular canals, saccule and utricle of the inner ear to the vestibular ganglia, where the cell bodies of the neurons are located End in the vestibular nuclei Some sensory axons also enter the cerebellum Tortora: page 640 Additional structures in the brainstem Midbrain: Red nucleus AnatomyTV Red Nucleus Rubrospinal Tract Arises from the red nucleus in midbrain INPUT: Receives input from cortex and cerebellum OUTPUT: Projectes to spinal cord, mostly terminating at cervical level Rubrospinal Tract Functionally parallel system of the lateral corticospinal pathway Facilitate motor neurons that innervate the contralateral muscles of the upper limb: o Fine control of movement o Large muscle groups for gross limb movement Additional structures in the brainstem Reticular Formation​ Small clusters of neurones collectively known as reticular formation​ Core of the brainstem (midbrain, pons and medulla) Ascending and descending pathways​ INPUT: Receives information from cortex (cortical projections), cerebellum and basal ganglia​ Additional structures in the brainstem Reticular Formation​​ Functions of nuclei:​ 1. Cardiovascular and respiratory control​ (medulla) 2. Pain modulation​ 3. Sleep/consciousness​ 4. Habituation (ability to direct your attention) 5. Movement: Postural tone (postural stability as a background for distal movement) and movement Reticulospinal Tracts Pons: Medial reticulospinal tract (facilitates movement and increases tone) Medulla: Lateral reticulospinal tract (inhibits movement and reduces tone) AnatomyTV Medial Reticulospinal Located in the Pons INPUT: Receives information from the cortex, the cerebellum and the basal ganglia OUTPUT: Projects to all levels of the spinal cord Synapses with both alpha and gamma motor neurons Facilitate postural and gross limb movement Increase muscle tone of axial and proximal parts of limbs – background posture and stability Lateral Reticulospinal Located in the Medulla INPUT: Receives information from the cortex, the cerebellum and the basal ganglia OUTPUT: Projects to all levels of the spinal cord Synapses with both alpha and gamma motor neurons Inhibits postural and gross limb movement Reduce muscle tone of axial and proximal parts of limbs What is muscle tone? The force at which muscles resist being lengthened, i.e. its stiffness. Normal muscle tone should be high enough to keep you upright against gravity to low enough to allow selective movement. Both neural and non-neural mechanisms contribute to muscle stiffness – more about this in the third year!  Neural mechanisms controlling tone The degree of activation of the muscles is controlled by the nervous system Close integration of the supra-spinal pathways Descending pathways and spinal circuits modulate spinal cord circuits Descending pathways from the brain directing voluntary movement, but also mediating the Normal response to stretch sensitivity of the muscle spindles to stretch. How the reticulospinal tracts modulate muscle tone Reticulospinal tracts work together to constantly regulate muscle tone by providing excitatory and inhibitory inputs onto gamma motor neurons Gamma motor neurons innervate the ends of the intrafusal muscle fibers Set muscle spindle's sensitivity to stretch  Medial reticulospinal Lateral reticulospinal tract (pontine) tract (medullary) = excitation of the gamma = inhibition of the gamma motor neurones motor neurones = facilitates the stretch = inhibition of the stretch reflex reflex = increases muscle tone = decreases muscle tone Vestibulospinal Tracts Two vestibulospinal tracts; medial and lateral tract Nuclei located in pons and medulla Largely influencing postural tone Additional structures in the brain stem Pyramids are two enlargements on the anterior surface of the anterior surface of the medulla Contain the corticospinal tracts 90% of fibers cross over to the opposite side to form the decussation of the pyramids Anterior view of the brainstem https://www.researchgate.net/publication/ 283448014_Microsurgical_anatomy_and_internal_architectu re_of_the_brainstem_in_3D_images_Surgical_consideration s  Additional structures in the brainstem Posterior view of the brainstem In image B, C is the cuneate tract and G is the gracile tract (PCML pathway) In medulla, 1st order neurons of PCML synapse with nuclei of second order neurons (cuneate and gracile nuclei) 2nd order somatosensory fibers cross to the other side of the medulla via internal arcuate fibers Travel up to thalamus as part of the medial lemniscus Summary of inputs Cortex Basal Ganglia Midbrain Cerebellu Red Nucleus m Reticular Formation Pons Vestibula r Nuclei Medulla Oblongata  Summary of outputs Rubrospinal Tract Midbrain Spinal Cord Red Nucleus Alpha Motor Reticular Formation Neurone Medial Reticulospinal Tract Pons Alpha and Gamma Motor Vestibula Lateral Reticulospinal Tract Neurones r Nuclei Medulla Oblongata Medial Vestibulospinal Tract Lateral Vestibulospinal Tract Intended learning outcomes To identify additional relevant structures of the brainstem and briefly explain their significance To describe the descending tracts originating from the brainstem To explain the motor functions of the brainstem To explain the role of the brainstem in the maintenance of normal muscle tone