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Biomedicine II > 18. Sense Organs > Flashcards

18. Sense Organs Flashcards

1
Q

Hearing

A

The ear is the organ of hearing.

•The nerve supply is the eighth cranial nerve — vestibulocochlear nerve.

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2
Q

Ear Anatomy

A
  1. Outer ear.
  2. Middle ear.
  3. Inner ear.

The middle ear is connected to the nasopharynx by the eustachian tube

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3
Q

Outer Ear

A

1.Auricle / pinna
2.External auditory canal.
3.Tympanic membrane (ear drum):
•A thin semi-transparent partition between the external auditory canal and middle ear.
•Lined with simple cuboidal epithelium, elastic and collagen fibres.
•Transmits sound from the outer ear (outside) to the auditory ossicles. Converts sound waves into mechanical vibration.

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4
Q

Auricle / pinna

A

•Flap of elastic cartilage covered by skin that traps and directs sound waves into the External auditory canal

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5
Q

Tympanic membrane (ear drum)

A
  • A thin semi-transparent partition between the external auditory canal and middle ear.
  • Lined with simple cuboidal epithelium, elastic and collagen fibres.
  • Transmits sound from the outer ear (outside) to the auditory ossicles. Converts sound waves into mechanical vibration.
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6
Q

Middle Ear

A

A small air-filled cavity in the temporal bone.
• Contains the auditory ossicles:
• The three smallest bones in the body.
• Malleus (hammer), incus (anvil), stapes (stirrup).
• Transmits sound in the form of vibration from the tympanic membrane to the cochlea.
• Stapes attaches to base of stapes ‘oval window’, which connects to the cochlea.
• A small muscle called ‘stapedius’ dampens large vibrations and is innervated by the facial nerve (protects the oval window) -> hence auditory symptoms in Bell’s palsy.

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7
Q

Middle Ear Bones

A

Malleus (hammer)
Incus (anvil)
Stapes (stirrup).

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8
Q

Inner Ear

A

The inner ear is also called the labyrinth because of its complicated series of canals.
•Consists of an outer bony labyrinth that encloses an inner membranous labyrinth.
•The bony labyrinth consists of a series of cavities in the temporal bone, divided into:
•Three semicircular canals and vestibule (receptors for balance).
•Cochlea (receptors for hearing).
•The vestibule is the oval central portion.
The labyrinth contains perilymph and endolymph (fluid).
•The inner ear provides information on balance and hearing.

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9
Q

Cochlea

A
  • Anterior to the vestibule — a spiralled, hollow chamber that makes almost three turns around a central bony core.
  • Contains epithelial cells lined with hair cells (sensory cells topped with 40–80 cilia each, called ‘stereocilia’).
  • Stereocilia are the receptors for hearing that extend into the endolymph.
  • Fluid movement (vibration) causes stereocilia movement and initiates an electrical impulse.
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10
Q

Vestibulocochlear Nerve

A

The vestibulocochlear nerve (cranial nerve VIII) provides sensory information for hearing and balance.
•The nerve contains two parts: Vestibular fibres and cochlear fibres.
•The vestibular fibres consist of nerve branches that synapse with receptors for balance.
•The cochlear nerve provides ‘hearing’.
•The vestibulocochlear nerve ganglia are located within the brainstem (pons / medulla oblongata).
•The nerve can be damaged with a basilar skull fracture.

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11
Q

Sound Sensation

A

Sound wave (pressure waves) - > Mechanical vibration -> Fluid waves -> Nerve Impulse

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12
Q

Sound Physiology

A
  1. The auricle (pinna) concentrates the waves, directing them along the external auditory canal causing the tympanic membrane to vibrate.
  2. Vibrations are transmitted through the middle ear by movement of the three auditory ossicles.
  3. The footplate of the stapes (stirrup) rocks at the oval window setting up fluid waves in the cochlear perilymph.
  4. Pressure waves are transmitted into the cochlea, which causes the round window to bulge into the middle ear.
  5. This pressure wave is transmitted into the endolymph.
  6. This results in vibration of the basilar membrane and hair cells.
  7. The bending of hair cell stereocilia creates a receptor potential — generating an action potential.
  8. The nerve impulses which have been generated, pass to the brain via the vestibulocochlear nerve.
  9. The vestibulocochlear nerve transmits the impulses to the hearing area in the cerebrum where sound is perceived.
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13
Q

Properties of Sound

A

Pitch

Volume

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14
Q

Pitch

A
  • Frequency of sound waves, measured in Hz (Hertz).

* The higher the frequency of vibration, the higher the pitch.

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15
Q

Volume

A

• Amplitude of sound waves, measured in decibels (dB).

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16
Q

Decibel scale

A
  • Smallest audible sound (near total silence) is 0 dB.
  • A sound 10 times more powerful is 10 dB.
  • A sound 100 times more powerful is 20 dB.
  • A sound 1,000 times more powerful is 30 dB.
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17
Q

White Noise

A

A constant noise that contains all the different frequencies of sound (a mixture of different sound waves).
• A background noise that the brain ignores.
• Used to mask other sounds — privacy enhancers, sleep aids, tinnitus masking.
• White noise CDs, when used with headphones, can aid concentration by blocking out irritating or distracting noises in a person’s environment.

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18
Q

Eustachian Tube (‘Auditory Tube’)

A

The eustachian tube connects the nasopharynx to the middle ear.
• The tube is closed but can open for air to equalise pressure between the middle ear and atmosphere -> ‘ears popping on aircraft’.
•Yawning and swallowing contracts the neck muscles, opening the tube.
• It is essential that air can escape the middle ear, or damage would occur with pressure changes.
• The eustachian tube also functions to drain mucus and is a common route for infection to spread between the pharynx and middle ear (more horizontal in children).

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19
Q

Balance

A

The semi-circular canals and vestibule provide information about head position.
• The walls of the vestibule and semicircular canals contain specialised hair cells with stereocilia.
• A dense layer of calcium carbonate crystals extends over and rests on the hairs called the ‘otolithic membrane’.
• Any change in head position causes movement in the perilymph and endolymph  bending hair cells and stimulating the sensory nerve endings.
• This action potential (via CN VIII) is transmitted to the cerebellum.

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20
Q

Balance and Cerebellum

A

The cerebellum makes postural adjustments in order to maintain balance. This occurs through its input of:
• Vestibular feedback (from inner ear).
• Visual feedback (from eyes).
• Proprioceptors in the skeletal muscles, joints and surrounding ligaments.
• The three sources of information are coordinated and efferent impulses pass to the cerebrum and skeletal muscles.

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21
Q

The Eye

A

The eye is the organ of the sense of sight, situated in the orbital cavity and supplied by the optic nerve (CN II).

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22
Q

Eyeball Layers

A

Outer Layer
Middle Layer
Inner Layer

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23
Q

Outer Layer

A

Sclera (white of the eye) and cornea anteriorly.

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24
Q

Middle Layer

A

Uvea (consists of iris, ciliary body and choroid — highly vascular).

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25
Q

Inner Layer

A

Retina

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26
Q

Iris

A

The coloured portion of the eye is called the ‘iris’ and controls the amount of light reaching the retina by adjusting pupil size.

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27
Q

Lens

A

The ‘lens’ is located behind the pupil and further focuses light (along with the cornea).

28
Q

Eye Accessory Structures

A 
The eye has several accessory organs for protection:
•Eyebrows: 
•Eyelids / eyelashes: 
•Conjunctiva: 
•Lacrimal apparatus: 
•Blinking
29
Q

Eyebrows

A

Prevent sweat / materials entering eye.

30
Q

Eyelids/eyelashes

A

Spread secretions over eye, protect the eye.

31
Q

Conjunctiva

A

Thin transparent mucous membrane of columnar epithelial cells lining the internal eyelids and anterior eyeball, protects the cornea. Eyelid margins secrete oily material to delay tear evaporation.

32
Q

Lacrimal apparatus

A

Produces tears.
Tears have an essential role in eye function. They protect the eye from infection and lubricate movements of the eye.
•Tears are secreted under the control of the trigeminal nerve (CN V).
•Tears contain IgA and lysozymes. Tears, of course, also have an emotional function.
•Tears are produced by the lacrimal gland and are swept across the eye by blinking. They enter the lacrimal punctum and then enter the nose via the nasolacrimal duct.

33
Q

Blinking

A

•Blinking spreads tears and closing the eyelid protects from injury.

34
Q

Light

A

The eyes are responsible for detection of visible light (part of electromagnetic spectrum).
• Wavelengths are 400–700nm and exhibit colours depending on wavelength.
• Objects appear the colour of wavelength that is reflected.
• White light is a combination of all the colours of the visible spectrum.
• To achieve clear vision light must be focused on to the retina. This involves:
- Refraction of the light rays.
- Accommodation of the eyes.
- Changing the size of the pupils.

35
Q

Refraction

A

Refraction describes the ‘bending’ of light rays. It occurs when light moves from one substance to another which has a different density.
• The cornea and, to a lesser extent, the lens refract light rays helping to focus the image on the retina.
• Images focused on the retina are inverted and left-right reversed too. The brain learns to coordinate this.
• When objects are closer than 6m the light rays need to be refracted more if they are to be focused on the retina.
• This is achieved by ‘accommodation’.

36
Q

Accommodation

A

As lens curvature becomes greater, its focusing power increases.
•The lens of the eye is convex on its anterior and posterior surfaces. The lens will refract incoming light towards each other.
•The lens can change its refractive power to project a sharp image on to the retina:
1. When an object is close, the ciliary muscle contracts. This reduces suspensory ligament tension and the lens becomes more convex -> greater refraction.
2.When an object is distant, the ciliary muscle relaxes, increasing the tension on the suspensory ligaments and flattening the lens -> less refraction.
•Looking at near objects tires the eyes (use of the ciliary muscle).

37
Q

Pupil Size

A
  • Contraction of the circular muscle fibres of the iris constricts the pupils.
  • Contraction of the radiating (radial) muscle fibres of the iris dilates the pupils.
  • Sympathetic stimulation contracts the radial muscle fibres to dilate the pupils.
  • Parasympathetic stimulation contracts the circular muscle fibres to constrict the pupils.
38
Q

Eyeball Convergence

A

Convergence describes the medial movement of two eyeballs so that both are directed towards the object.
•Extra-ocular muscles move the eyes in a coordinated way under autonomic control.
•The closer an object, the greater the eye rotation.
•If convergence is not complete, two images are sent to the brain leading to double vision (‘diplopia’).

39
Q

Eyeball Convergence

A

Convergence describes the medial movement of two eyeballs so that both are directed towards the object.
•Extra-ocular muscles move the eyes in a coordinated way under autonomic control.
•The closer an object, the greater the eye rotation.
•If convergence is not complete, two images are sent to the brain leading to double vision (‘diplopia’).

40
Q

Binocular Vision

A
  • In humans, both eyes focus on one object which allows for the perception of depth and 3D nature.
  • The two images from the two eyes are fused in the cerebrum so that only one image is perceived.
  • As the image highlights, the optic nerve crosses over in the brain. This location is known as the optic chiasma.
  • The optic chiasma is located next to the pituitary gland, which is why pituitary tumours can cause ‘tunnel vision’.
41
Q

The Retina

A

The retina is the inner layer of eye, lining the posterior three-quarters of the eyeball.
• The retina is the beginning of visual pathway.
• Can be viewed through an ophthalmoscope.
• Only place where blood vessels and a nerve can be viewed.
• Optic disc -> The location where the optic nerve exits the eyeball — ‘blind spot’. Bundled together with the central retinal artery and vein.

42
Q

The Retina: Structure

A
  • The retina contains a pigmented layer of melanin-containing epithelial cells and a layer of ‘photoreceptors’ — specialised visual cells.
  • Rod cells
  • Cone cells
  • The optic disc is also called the ‘blind spot’ because it contains no rod or cones.
43
Q

Rod Cells:

A

120 million. Allow us to see in dim light but don’t provide colour. Instead rod cells provide black, white and greyscale.

44
Q

Cone Cells

A

6 million. Produce colour vision. There are three types of cone cell: Blue, red and green. Colour vision results from combinations.

45
Q

Macula Lutea

A

The macula lutea is a yellowish spot at the exact centre of the retina.
• ‘Fovea centralis’ -> a small depression in the centre of the macula lutea that contains only cone cells.
• The fovea centralis is the area of highest visual acuity (this is why we move our eyes and head to look at things).
• Rod cells are more plentiful at the periphery of the retina.

46
Q

Photopigments

A

Rod and cone cells form invaginations of their cell membrane to create stacks of ‘discs’.
• Photo-pigments are transmembrane proteins within the discs of both rod and cone cells.
• When light hits the photo-pigment, it changes shape initiating an action potential.
• These pigments are derived from vitamin A.
• Once activated, a photo-pigment must then be regenerated / restored.
• The pigmented layer of the retina stores a large quantity of vitamin A which contributes to the regeneration of rod cells.

47
Q

Vitamin A

A

Vitamin A derivatives are called retinoids. Retinoids include retinol, retinal and retinoic acid.
• In the retina, vitamin A in the form of retinal binds to a protein called ‘opsin’ to produce photopigments.
• Preformed vitamin A is found in foods of animal origin (i.e. liver, egg yolk).
• Carotenoids are precursors of vitamin A. They are metabolised to retinol in the intestines. Carotenoids are also powerful antioxidants:
- Carotenes are found in fruit and vegetables such as carrots, sweet potato, leafy greens, squash and mango.
- These carotenoids are not considered toxic (absorption is regulated), unlike preformed vitamin A.

48
Q

Photopigments: Light to dark

A

Light and dark adaptation:
• When you emerge from dark to light, the eyes adjust quite quickly -> ‘light adaptation’.
• The visual system adapts in seconds by decreasing its sensitivity.
• Going from light to dark sensitivity increases slowly over some minutes. Adaptation occurs quicker if abruptly moving into light.
• Rods and cones must regenerate photo-pigments (cones regenerate within the first eight minutes, rod cells take much longer).

49
Q

Smell

A

Olfaction is the sense of smell.
•The nose contains 10–100 million receptors for olfaction contained within a tiny area (5cm2) called the olfactory epithelium.

50
Q

Olfactory Epithelium

A

Olfactory receptors
Supporting cells
Basal cells

51
Q

Olfactory receptors

A

Neurons attached to olfactory hairs. Respond to chemical stimulus of odorants by producing an action potential.

52
Q

Supporting Cells

A

Provide physical support, nourishment and help detoxify odorant chemicals

53
Q

Basal Cells

A

Stem cells that continually divide to produce new olfactory receptors (live one month).

54
Q

Smell: Process

A
  • Taste and smell are ‘chemical senses’ because they arise from interaction with molecules.
  • Olfactory glands, in the connective tissue supporting the olfactory epithelium, produce mucus that is carried to the surface by ducts.
  • The secretion moistens the olfactory epithelium and helps to dissolve odorants.
  • Inflammation of the nasal mucosa inhibits olfaction (i.e. rhinitis).
55
Q

Smell Sensation (CNS)

A

Sense of smell involves the olfactory nerve (CN I).
• Nerve axons extend through about 20 olfactory foramina in the cribriform plate of the ethmoid bone to the temporal lobe.
• Olfactory bulb -> olfactory tract -> olfactory area in the temporal lobe.
• Some of the axons of the olfactory tract project into the limbic system (hence relation between smell and emotion).
• Sense of smell may also affect appetite and mood.
• The sense of smell in human beings is less acute than in many animals.

56
Q

Smell Sensation

A

Like all the special senses, olfaction has a low threshold and only a few molecules need to be present for us to detect a smell.
• Adaptation: Decreased sensitivity to odours occurs rapidly. Olfactory receptors adapt by 50% in first second. Odours seem 80% less powerful after a few minutes of exposure.
• Prevents smelling bad odours; e.g. working near a foul odour gets to the point where olfactory adaptation is 100%.
• The actual aim of adaptation is to protect from danger — if the scent is not a danger, olfaction re-calibrates to be able to detect other smells which might indicate harm.

57
Q

Taste

A

Taste is also known as ‘gustation’.
• Stimulation of chemoreceptors by dissolved chemicals in salvia.
• The tongue is formed of eight muscles, which are innervated by the hypoglossal nerve (CN XII).

58
Q

Taste Buds

A

• 10,000 in adult. Most on the tongue, but some are on the soft palate, pharynx and epiglottis. Taste buds contain:

1) Gustatory receptor cells: Detect taste, living for about 10 days.
2) Basal cells: Stem cells that produce new receptor cells.
3) Supporting cells.

59
Q

Papillae

A

Taste buds are found in elevations on the tongue called ‘papillae’.

60
Q

Papillae: Types

A

Circumvate
Fungiform
Foliate

61
Q

Circumvate Papillae

A

The largest papillae, V-shaped at the back of the tongue.

62
Q

Fungiform Papillae

A

Mushroom- shaped and are present all over the tongue. They contain about five taste buds each.

63
Q

Foliate Papillae

A

Located in small trenches at lateral margins of tongue; most degenerate in childhood.

64
Q

Filiform Papillae

A

The whole surface of the tongue has filiform papillae — tactile receptors that help the tongue move food.

65
Q

Taste Physiology

A

Once tastants are dissolved in saliva, they encounter the cell membrane of gustatory hairs, which generates an action potential (receptor potential arises differently for different tastants).
• For example: Salty food, sodium enters channels.
• Taste is simpler than smell, we can only detect five tastes: Sour, sweet, bitter, salty, ‘umami’.
• The complex flavours we enjoy every day arise from different strengths and combinations of stimulation.
• Sense of taste triggers salivation and gastric juice secretion (in preparation).
• There is no tongue ‘map’ — responsiveness to the five basic modalities is present in all areas of the tongue.

66
Q

Taste Physiology (CNS)

A
  • The facial nerve innervates taste in the anterior two-thirds of the tongue.
  • The glossopharyngeal nerve innervates both taste and general sensation of the posterior one-third of the tongue.
  • The trigeminal nerve supplies general sensation to the anterior two-thirds of the tongue.
  • The vagus nerve innervates the throat and epiglottis.
  • Information goes to the gustatory nucleus in medulla oblongata and some fibres to the limbic system.

Biomedicine II (16 decks)

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