Why am I dizzy?

Question 1

What are the components needed to achieve good coordination and balance?

Answer 1

• Know where the head is.
• Know where the limbs are.
• Be able to detect position of body parts.
• Be able to detect motion - in all planes, acceleration and deceleration.
• Integrate with vision.
• Central control systems - voluntary and involuntary.
• Integrate motor control and output.

Question 2

What is the commonest cause of vertigo?

Answer 2

BPPV (benign paroxysmal positional vertigo)

Question 3

What is BPPV?

Answer 3

• Benign paroxysmal positional vertigo - due to an inner ear problem.
• Vertigo is an abnormal sensation of movement.

Question 4

What are the different parts of the body which can be affected by dizziness?

Answer 4

Question 5

The vestibule has 2 otolith containing organs.

What are they?

What is their function?

Answer 5

• Saccule macula (continuous with cochlea).
• Utricle macula (continuous with semi-circular canals).
• Monitor position of head relative to force of gravity.
• Saccule - monitors vertical movements (s for sky!).
• Utricle - monitors horizontal movement.

Question 6

What is static tilt and linear translation?

Answer 6

• Hair cells, project hairs into an otolithic (ear stone) containing gelatinous structure.
• Cilia + kinocilium - provide directional information.
• Movement of otolithic membrane (from tilting or translational movement) bends the cilia / kinocilium in a very direction specific way.
• A 0.5 micron of the kinocilium opens / closes the hair cell cation channels.

Question 7

How is static tilt and linear translation translated to head position?

Answer 7

Question 8

How is rotational acceleration detected?

Answer 8

• Rotational acceleration is detected by the semicircular canals.
  
  • Monitors rotational acceleration and deceleration.
  • Three planes of orientation.
  • Within each canal is semi-circular duct.
  • Within duct, ampulla.
  • In the ampulla there are supporting cells, hair cells, cilia and kinocilium.

Question 9

What are the directions of rotation?

Answer 9

• Roll
• Pitch
• Yaw

Question 10

How is dynamic equilibrium detected?

Answer 10

• Measures the changes in rotation.
• Signal transduction (as before).
• Resting rate of transmitter release.
• Bending in one direction (towards the kinocilium) results in depolarisation and increased action potential rate.
• One side of the head depolarises; the other hyperpolarises.

Question 11

Describe the test used to detect a particle in the semicicrular canals.

Answer 11

• Upbeat nystagmus to the side of the lesion upon lying the patient down with head over the end of the bed.

Question 12

Describe the epley manoeuvre.

Answer 12

https://www.youtube.com/watch?v=kEM9p4EX1jk

Question 13

What is Ménière’s disease?

Answer 13

• The vestibular apparatus is bathed in endolymph.
• Normally drains to venous sinus.
• Build-up can cause Ménière’s disease (vertigo, nausea, tinnitus and hearing loss).

Question 14

Describe the caloric test.

Answer 14

• A test for the condition of the brainstem.
• Putting warm water in the external meatus of a patient sets up calorically induced movements in the labyrinth system.
• Nystagmus pattern for a movement towards the irrigated ear with warm water is slow away from direction of rotation and a fast return in the same direction of rotation.
• Cold water does the opposite (COWS - cold opposite, warm same - refers to fast component).
• In comatose patients there is no fast saccade, only the slow component.
• Brain stem death, no vestibulo-ocular reflexes. I.e. if there is no nystagmus upon the injection of hot or cold water, the patient is brainstem dead.

Question 15

Summarise the systems for movement.

Answer 15

Question 16

Describe how the components of the cerebellum function in coordination of motor output.

Answer 16

Question 17

What is the function of the cerebellum?

Answer 17

• Modulates motor output based on integration of :
  
  1. Activity in the pre-motor and motor areas as well as spinal motor circuits (information about potential motor output).
  2. Sensory feedback from vestibular system, visual system, and ascending proprioceptive information (about real motor output).
• Modulation by the cerebellum is effected at the motor cortex and brainstem.
• A patient with cerebellar damage has to think about each movement they make.

Question 18

Identify the structures.

Answer 18

Question 19

Identify the features of the flattened cerebellum.

Answer 19

Question 20

Identify each feature of the cortical cerebellar structure.

Answer 20

Question 21

What are the principal afferents of the cerebellum?

Answer 21

Question 22

What are the afferents of the vestibular system in the cerebellum?

Answer 22

• Inputs from vestibular nuclei (balance) project to the vestibulocerebellum (flocculonodular lobe) and vermis.
• The flocculonodular is involved with maintaining balance and posture.

Question 23

Describe the proprioceptive feedback to the cerebellum.

Answer 23

• Inputs from ascending sensory spinal pathways derived principally from proprioceptors to the spinocerebellum (= andterior lobe + vermis + intermediate vermis).
• The spinocerebellum modulates axial or antigravity muscles and eye movement.
• The spinocerebellum contains a somatotopical map of the body.

Question 24

Describe the cortical input to the cerebellum.

Answer 24

• Inputs from the motor and pre-motor cortex as well as somatosensory cortex via multiple pontine nuclei project to the cerebrocerebellum.
• The cerebrocerebellum is involved with motor planning, and feeds information back towards the cerebra.
• Functions to sequence and coordinate distal muscles especially during locomotion or juggling etc.

Question 25

Describe the cerebellar output.

Answer 25

* **All via deep nuclei.** * From lateral to medial: * Dentate nucleus * Emboliform nucleus * Globose nucleus * Fastigial nucleus

Question 26

What are the features of cerebellar syndrome?

Answer 26

* Nystagmus * Dysarthria (scanning speech) * Wide-based gait * Inability to walk heel to toe * Finger-nose ataxia (dysmetria, past-pointing) * Intention tremor * Dysdiadochokinesis (fast attenuating hand movements) * Romberg's test * Truncal ataxia (vermis lesions)

Question 27

What are the causes of cerebellar syndrome?

Answer 27

* Inherited * Acquired: * Vascular * Toxic * Inflammatory * Endocrine * Neoplastic * Paraneoplastic * Infective * Post-infective * Idiopathic