This document discusses the vestibular system and its role in balance and equilibrium. It describes the bony and membranous labyrinths that contain the semicircular canals and otolith organs. The semicircular canals detect rotational acceleration and help maintain equilibrium during rotation. Stimulation causes nystagmus, changes in autonomic tone and muscle tone, and vertigo. Nystagmus involves a slow eye movement in one direction and a fast movement in the other direction. The vestibular system is important for spatial orientation and motor control.

1. Gawad
Neuroscience Physiology
Lecture 18
Saturday, December 22, 2018 1

4. bony labyrinth
membranous labyrinth
bony labyrinth
membranous labyrinth

8. Utricle

9. Utricle

10. Utricle

11. Saccule

15. Non motile kinociliummotile stereocilia
gelatinous
matter
vestibular nerve

20. ● Functions of semicicular canals
• 1. Detection of (rotation).
• 2. Equilibrium during rotation

21. ● Stimulants of SCC
• 1. Angular acceleration (rotation)
• 2. Caloric stimulation:
– irrigation of external ear with hot water (44°C) or cold water
• 3. Galvanic stimulation:
– to the mastoid process
• 4. Motion sickness:
– In airplanes, ships
• 5. Labyrinthine disease:
– labyrinthitis, vestibular neuritis and meniere’s disease.

22. ● Mode of action of SCC during
HORIZONTAL rotation

23. Utricle
Ampullae

24. Utricle
Ampullae
Utricle
Ampullae
Lt Rt

25. Utricle
Ampullae
Utricle
Ampullae
Lt Rt
sense of rotation to
right side

26. Utricle
Ampullae
Utricle
Ampullae
Lt Rt30 seconds after onset of rotation
loss of sense of rotation

27. Utricle
Ampullae
Utricle
Ampullae
Lt RtOn stop of rotation
vertigo

28. ● Central connections of the
vestibular apparatus
SCCVest
G
Vest
N
RF
Dentate
Thalamus
3
4
6
3
4
6
Spinal cord
Superior
temporal
gyrus

29. Effects of SCC stimulation
• 1. Autonomic changes:
• nausea and vomiting, bradychardia,
hypotention and pallor.
• as a result of stimulation of reticular
formation ?????

30. Effects of SCC stimulation
• 2. Muscle tone changes:
• a. increased muscle tone at ………………
• b. decreased muscle tone at ………………
• a & b are by controlling of ???????

31. 3. Vertigo:
• sensation of rotation in absence of actual
rotation.

32. 3. Vertigo:
• Mechanism:
after stoppage of rotation.

33. 3. Vertigo:
Pathway - Dentato- Thalamo-Cortical
SCC
Vest
GVest
N
Dentate
Thalamus
MO
Superior
temporal
gyrus

34. 3. Vertigo:
• - Causes:
• 1. after stoppage of rotation.
• 2. Labyrinthine disease e.g. Meniere’s disease
• 3. Motion sickness.
• 4. Overdose of streptomycin.
• 5. Errors of refraction.
• 6. Chronic alcoholism.
• 7. Caloric or galvanic stimulation of SCC.

35. 4. Nystagmus
• Repetitive rhythmic oscillation of eye balls

36. • - Causes
• 1. Physiological causes of nystagmus:
• - Angular acceleration (rotation)
• - Looking from the window of a rapidly moving
car (optokinetic nystagmus).
• 2. Pathological nystagmus:
4. Nystagmus

37. • - Causes
• 2. Pathological nystagmus:
• - Cerebellar syndrome.
• - Inner ear disorders.
• - Defective vision (searching nystagmus).
• - Lesion in floor 4th cerebral ventricle that
causes irritation of vestibular nucleus.
4. Nystagmus

38. • - normally develops:
– a- at the start of rotation for about 30 seconds
(rotatory nystagmus),
– b- at the end of rotation, for a period of 30
seconds (post rotatory nystagmus).
Rotation & Nystagmus

39. Rotatory Nystagmus
• - Components of rotatory nystagmus:
• a- Slow component:
– slow
– towards the opposite direction
of rotation
• b- Rapid component:
– rapid jumping of both eyes
– in the same direction of rotation.

40. Rotatatory Nystagmus
Pathway
SCC
Vest
G
Vest
N
RF
3
4
6
3
4
6
Primary direction (slow)
Secondary direction (fast)