Block 4 - The sensory systems Flashcards by Dannie McQueen

How is sound conducted?

Oscillation between compression and rarefaction

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Wavelength equation

Wavelength = velocity / frequency

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What is the standard in terms of decibels?

Mean human threshold of hearing
10^12 Wm

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What is the range of human hearing?

20-20000Hz

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At which point can the amplitude of sound cause damage to hearing?

140 Db

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What is age-related reduction hearing?

Presbycusis - typically affecting higher frequencies

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How many octaves of hearing are there?

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What do tuning curves indicate?

Responsiveness of individual neurons to specific frequencies
The lower the threshold, the better

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What are the 3 bones of the middle ear?

Malleus
Incus
Stapes

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What becomes blocked when we get a cold which prevents the free movement of the tympanic membrane?

Eustachian tube

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What do the bones of the ear push against, and what happens?

Oval window
Movement of fluid in the cochlea

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What is the role of the middle ear?

Convert high amplitude/low force motion at the tympanic membrane to low amplitude/high force motion at the oval window

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What is the stapedius reflex?

Contraction of muscles to pull stapes from oval window to decrease vibrational energy to cochlea to prevent damage

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What 2 muscles are used in the stapedius reflex?

Tensor tympani
Stapedius

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Name the 3 scalae of the cochlea

Vestibuli
Media
Tympani

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What partof the ear converts sound to a neural signal?

Organ of Corti

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What activates the hair cells of the Organ of Corti?

Vestibuli and tympani scalae cause vibration of basilar membrane
Causing motion of tectorial membrane
Movement towards kinocilium increases release of neurotransmitter
Increasing rate of firing

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How does the ear discriminate between frequenices?

Length of basilar membrane

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What are the roles of the inner and outer hair cells?

Inner - sensations
Outer - amplification

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What is the frequency for hearing speech?

400-3000Hz

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What formation detects the differences in ears in which different sounds come from?

Superior olive

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Where is sound delivered to in the brain?

Wernicke’s area

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How is direction of sound judged? (3)

Inter-aural timing delay - delay to neurons
Volume differences
Spectral colouring - pinna

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What is defined as a false start in athletics?

Movement within 100ms

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What can decrease reaction time?

Increasing sound intensity

What muscle changes the shape of the lens?

Ciliary muscle

What is the focussing power of health human lens?

12D

Purpose of the lens?

To manipulate focusing power to accommodate image onto the retina

What happens to the lens when you move an object closer?

Ciliary muscles contract Zonular fibres slacken Rounded lens to focus on object

What is myopia and how is it corrected?

Short-sighted - image focussed forward of retina Concave shape glasses

What is hypermetropia and how is it corrected?

Long-sighted - image focussed behind image Convex shape glasses

What is presbyopia?

Age-related reduction in lens focusing power

By how many times does the pupil reduce the amount of light?

16 fold Pupil can vary from 2-8mm

What muscles control the size of the pupil, and what are there functions?

Sphincter - constrict Dilator - dilate

What is the optic disk?

Apart of the eye that allows no light Blindspot

Why are photoreceptors located at the back of the retina? (2)

Close to the blood supply Reduces scatter

Describe the process of phototransduction.

Light bleaches rhodopsin - separating into retinal and opsin Opsin activates PDE via G protein PDE converts cGMP to GMP Sodium channels close - hyperpolarise Releases glutamate Changing membrane potential of bipolar cell and ganglion

Name 4 Mechanisms of adaptation to luminance

Pupil size Switch over of photoreceptors Dark adaptation Field adaptation

What is the lateral inhibition?

Stimulation of peripheral - excites ganglion Stimulation of central - inhibits

Why is there a three channel system for cone cells?

To discriminate colours at different light levels and intensities

What is colour opponency?

Tricks the eye and thinks no light is entering and will produce a different colour output

Where does the optic nerve split?

Optic chiasm

What is proprioception?

The sense of a relative position of neighbouring parts of the body

What are the mechanoreceptors of proprioception and what do they detect?

Muscle spindles - position and velocity Golgi tendon - force

What did Fitzpatrick conclude from a test of balance?

First identify movement when testing proprioception

What is galvanic vestibular stimulation?

Stimulus gives sense of head rotation in one direction to produce movement in the opposite

What did a study suggest proprioception was related to?

Better strength, not age

What is visual vection?

Movement of the train is so slow that the vestibular system has not been activated

What do the otolith organs detect?

Linear acceleration and tilt

Name the otolith organs?

Utricle Saccule

What do the semi-circular canals detect?

Angular velocity/rotation

How many semi-circular canals are there, and what are there names?

3 Anterior Posterior Horizontal

In which direction does movement increase firing of afferent of the main hair cell - what is the name of this hair cell?

Stereocilium - towards the stereocilium

How is angular velocity and acceleration determined in the vestibular system?

Differences in the two systems = angular velocity or acceleration

What is the function of the hair cells?

Detect balance and posture

In which direction do the otolith organs sit when the head is upright?

Utricle - horizontal Saccule - vertical

Where are the hair cells located in the semi-circular canals?

In the capula, in the ampulla

Why doesn't the canals detect orientation?

Capula is the same density as surrounding endolymph

What happens to the vestibular system after alcohol consumption?

Capula becomes lighter Rises when lying down Horizontal canal detects spinning sensation Producing left beating nystagmus in the left ear

What happens to the vestibular system after consumption of heavy water?

Capula becomes heavier Sinking when lying down Producing right beating nystagmus in the left ear

What allows the VOR to have a very short latency?

Only comprised of 3 neurons Vestibular nucleus to ocular nucleus to eye muscles

What muscles are recruited in the VOR?

Left and right medial rectus Left and right lateral rectus

Describe caloric vestibular stimulation of the VOR

Ear irrigated with warm or cool water Water causes convection current Warm water increases firing = turn towards irrigated ear Cool water decreases firing = opposite ear

Describe the galvanic vestibular stimulation

Stimulation of electrode increases firing leading to movement towards the electrode

What did the study of vestibular system at height indicate?

Smaller movements made to suppress sway