[W4] The Ears: Position + Balance Flashcards
What is static equilibrium?
Detecting head position when stationary (e.g. sitting still in a lecture).
What is linear acceleration?
Detecting changes in head position in a straight line (e.g. lift, car, plane).
What is rotational movement?
Detecting spinning or circular head movements (e.g. turning head, twirling).
What are the three key structures involved in balance?
Utricle, saccule, and semicircular ducts.
Which structures detect static equilibrium and linear acceleration?
Utricle and saccule (and their maculae).
Which structures detect rotational movement?
Semicircular ducts.
What is the otolithic membrane?
A gel layer with otoliths that sits atop stereocilia and kinocilium in the macula.
What happens when the head is vertical?
A baseline nerve signal is sent—standard frequency.
What happens when stereocilia bend toward the kinocilium?
Excitation occurs – increased neurotransmitter release → higher nerve firing rate.
What happens when stereocilia bend away from the kinocilium?
Inhibition occurs – reduced neurotransmitter release → lower nerve firing rate.
What fluid is involved in detecting rotational movement?
Endolymph.
What causes the sense of spinning during and after rotation?
Inertia of endolymph causes displacement of the cupula, which continues moving even after rotation stops.
Why does the spinning sensation persist after stopping rotation?
Because endolymph keeps moving, stimulating hair cells until it settles.
Which nerve carries balance signals to the brain?
Vestibular branch of the vestibulocochlear nerve (CN VIII).
Where do signals from the vestibular complex go first?
To the medulla oblongata and cerebellum.
What does the medulla oblongata control in balance?
Eye muscle coordination and skeletal muscle response.
What does the cerebellum do in balance?
Coordinates skeletal muscle activity for posture and balance.
What is the final relay point for conscious awareness of balance?
The cerebral cortex via the thalamus.
