Medical Lecture Notes

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Tuesday, 5 December 2017

Brain stem

Brain stem(Mid brain, Pons, Medulla) 

Maintenance of the muscle tone.
Maintenance of equilibrium.
Contains the vital centres for regulation of Respiration, Circulation, & GIT.
Connects the sensory & motor brain areas with the spinal cord.
Contains Reticular activating system.
Muscle tone: Is state of partial maintained contraction, resisting the stretch.
The tone  by increase in gamma motor  neuron discharge & vice versa.
The brain stem contains two regulatory areas to the gamma motor  neuron&  muscle tone:
Facilitatory pontine reticular formation gamma motor  neuron discharge & tone 
Pontine RF has intrinsic activity & is also activated by impulses from:
Inhibitory medullary reticular formation gamma motor  neuron discharge & muscle tone.
Medullary RF has no intrinsic activity & depends on impulses from:
The normal muscle tone is due to balance between these facilitatory & inhibitory effects, 

Receptors are found in the vestibular apparatus in membranous Labyrinth of the inner ear, include.
  Maculae & otolithic organ in the utricle & sacculus for equilibrium during station & linear motion.
The membranous Labyrinth is filled with endolymph.
      The pull of the gravity force  during
station or motion moves the endolymph
 that moves the cilia of the receptor hair
 cells stimulating the receptors. Generating
 recpetor potential then AP in the
vestibular branch of vestibulocochlear
Membraneous Labyrinth of inner ear
Fibers of the vestibular nerve from  equilibrium receptors terminates in the ipsilateral vestibular nucleus.
Most fibers from the semicircular canals
terminate in the superior and medial
divisions of vestibular nucleus and project
to cranial nerves nuclei III, IV, VI controlling
 eye movement.
Most fibers from the utricle and saccule terminate in the lateral division, which then projects to:
Cerebellum via Vestibulocerebellar tract.
Spinal cord via Vestibulospinal tracts.
Reticular formation then to spinal cord via Reticulospinal tracts.
The vestibular nuclei also project to the thalamus and from there to the primary somatosensory cortex.
Equilibrium is maintained by changes in the tone of antigravity (extensor) muscles  mediated by impulses from vestibulo-spinal & reticulo-spinal tracts.

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