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Lecture 2

HTHSCI 1H06 Lecture Notes - Lecture 2: Multiple Sclerosis, Simon Baron-Cohen, Gracilis Muscle

Health Sciences
Course Code
Peter Helli

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-the ability to maintain the center of gravity of a body within the base of support
with minimal postural sway
1) Static
a. Standing up with line of gravity centered
b. Cerebellum tries to minimize sway
c. Drinking alcohol causes sway to get larger
i. Cerebellum is impaired
2) Dynamic Adaption
a. Body is moving and center of gravity is shifting
b. During sports etc.
c. Multiple sensory input into muscles to correct balance
i. How to change contractions of muscles in order to maintain
3) Static Adaption
a. Balance has been pushed off while standing up
b. Multiple sensory input to correct center of gravity (change contraction of
*Multiple sensory inputs integrated together to give you correcting action of muscles
Cranial Nerves involved in Balance
Input to CNS
Optic (II): Vision
Vestibulo Cochlear (VIII): Hearing and balance
Output from CNS (maintains orientation)
Oculomotor (III): muscles moving eyes
-scan periphery to make sure we are taking in as much info as possible
Trochlear (IV): muscles moving eyes
Abducents (VI): muscles moving eyes
Accessory (XI): muscles moving head
-keeps head straight
-innervates sternocleidomastoid and trapezius
The Eye
-Ganglion cells in fovea: high visual acuity and colour vision
opathway: retina to lateral geniculate nucleus
-Ganglion cells in para fovea: motion and direction detection
otuned to be able to pick up motion
osuperior colliculus
Primary and Secondary Visual Pathways
-the fovea of retina is primary visual pathway for high acuity colour vision
ogoes to lateral geniculate nucleus of thalamus and then occipital of brain to
give high definition conscious vision
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-second visual pathway comes from outside of fovea
omotion and intensity of light
ogo to area of brainstem called superior calculi
oregulates pupil size, day/night cycle, convergence of eyes,
accommodation, regulating balance by providing input to cerebellum
Spinal Nerves involved in Balance
-information comes in from proprioceptors coming from deep muscle receptors of
“balance muscles”
-go into the spinal pathway  cerebellum in order for coordination of muscle group
-muscles in axial skeleton and 3 muscles in thigh minimize sway
-brain is able to stimulate these muscles of balance
The Ear
-Vestibular apparatus (inner ear)
ocranial nerve 8 is actually 2 nerves
auditory nerve
vestibular nerve (comes from complex of canals – dilated areas)
macula of utricle
macula of saccule (big sac)
Crista of semicircular canals: sensory cells coming from the
macula that make up the axons that contribute to vestibular
part of CN 8
oStatic equilibrium: detects where our head position is
oDynamic equilibrium: head movement
oCochlea, macula and semicircular canals are filled with CSF
Membranes are floating in CSF (cochlear duct floating in
perilymph = CSF
ofluid drainage problems = dizziness & ringing, glaucoma of ear (vertigo
and tinnitus) & Meneres disease (affecting vestibular apparatus)
high pressure in fluid system affecting sensory cells
Location of Sensory Cells in the Vestibular Apparatus
-in both macula and semicircular canals are sensory receptors:
osense static equilibrium in macules
odetection dynamic equilibrium in ampulla of semicircular canals
1) Static Equilibrium – Head position
a. Gravity sensor
b. Sensory cells that detect static equilibrium are embedded in rocks
c. Mass of calcium carbonate crystals (otholiths) embedded in geletnes mass
and sticking on the surface of hair cells
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