Sense Organs Flashcards
List the 4 senses
Hearing, Sight, Smell, Taste
Which cranial nerve supplies the ear?
The 8th cranial nerve - Vestibulocochlear nerve
Anatomically the ear can be divided into 3 parts. Name them.
Outer, middle, inner
Which cranial nerve supplies the ear / hearing?
Nerve 8 - Vestibulocochlear nerve
Which structure connects the middle ear to the nasopharynx?
The eustachian tube (or ‘pharyngotympanic tube’)
Name the 3 bones found in the middle ear.
- Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup)
What is the auricle, or pinna?
The outermost structure of the ear.
What is the role of the auricle/pinna?
It traps and directs sound waves into the external auditory canal
What is the tympanic membrane?
A thin, semi-transparent membrane between the external auditory canal and the middle ear. Also known as the ear drum.
What is the role of the tympanic membrane?
It converts sound waves into mechanical vibrations.
It transmits sound waves from outside the ear, to the auditory ossicles.
What are the auditory ossicles?
The 3 tiny bones found in the middle ear (the 3 smallest bones in the body)
Where in the ear structure would you find the tympanic membrane (ear drum)?
In the outer ear
List the 3 components of the outer ear.
- Auricle/pinna
- External auditory canal
- Tympanic membrane (ear drum)
Define the ‘middle ear’
A small air-filled cavity in the temporal bone which contains the auditory ossicles.
What is the role of the auditory ossicles?
They transmit sound (in the form of vibration) from the tympanic membrane to the cochlea.
How/where does stapes connect to the cochlea?
At the oval window
In terms of the structure of the ear, what is the oval window?
The point at which stapes (the 3rd auditory ossicle) meets the cochlea.
What is the name of the small muscle in the middle ear which dampens large vibrations (protecting the oval window) and is innervated by the facial nerve?
Stapedius
Which cranial nerve innervates the stapedius muscle?
The facial nerve
Why might a patient with Bell’s Palsy experience hearing/auditory symptoms?
Because Bell’s Palsy affects the facial nerve, which is the nerve that innervates the stapedius muscle (which dampens large sound vibrations, thus producing clear hearing)
What is the inner ear also known as (because of its complicated series of canals) ?
The labyrinth
The inner ear consists of an outer bony labyrinth that encloses an inner ________ labyrinth.
Membranous
The bony labyrinth (inner ear) consists of 3 parts. Name them.
- Three semicircular canals
- Vestibule
- Cochlea
Which parts of the inner ear have receptors for balance?
The semicircular canals and vestibule
Which part of the inner ear has receptors for hearing?
The cochlea (snail shell!)
The labyrinth contains 2 types of fluid. Name them.
The perilymph and endolymph
Where would you find the perilymph and endolymph?
In the inner ear / labyrinth
Which part of the ear provides information on balance and hearing?
The inner ear
Which ear structure sits anterior to the vestibule and is a spiralled, hollow chamber that makes almost 3 turns around a central bony core?
The cochlea
What are stereocilia?
Sensory cells in the inner ear, which are topped with 40 - 80 cilia each.
What is the name given to the receptor cells for hearing, which extend into the endolymph?
Stereocilia
What initiates a nerve impulse / action potential from the inner ear?
The movement of stereocilia in endolymph fluid, caused by vibration
What can kill stereocilia?
Strong movement of endolymph fluid (very loud noise)
Name cranial nerve 8
Vestibulocochlear nerve
What is the role of cranial nerve 8, the Vestibulocochlear nerve?
It provides sensory information for hearing and balance.
Is the Vestibulocochlear nerve sensory, motor or both?
Sensory
The vestibulocochlear nerve contains 2 parts: _________ fibres and _______ fibres
Vestibular fibres and cochlear fibres
Where are the ganglia of the vestibulocochlear nerve located (where does it feed into / originate from)?
The brainstem (between the pons and medulla oblongata)
List the 4 stages of sound sensation.
Sound waves > Mechanical vibration > Fluid waves > Nerve Impulse
What are sound waves?
Vibrations in the air
What causes fluid waves in the cochlear perilymph?
The footplate of stapes rocking at the oval window.
The vestibulocochlear nerve transmits nerve impulses to the hearing area in the _______ (area of the brain) where sound is perceived.
Cerebrum
Define ‘pitch’
The frequency of sound waves
the higher the frequency of vibration, the higher the pitch
Define ‘volume’
The amplitude of sound waves
What is pitch measured in?
Hertz (Hz)
What is volume measured in?
Decibels (Db)
Prolonged noise above ____ Db can result in permanent hearing loss. An example of this would be a lawnmower.
90 decibels
Define ‘white noise’
A constant noise that contains all the different frequencies of sound / a mixture of different sound waves.
What is the name given to a background noise that the brain ignores?
White noise
What is white noise used for?
To mask other sounds
The eustachian tube connects the nasopharynx to the _____ ear.
Middle ear
Why is the eustachian tube a common route for middle ear infection?
In which population is this more common and why?
Because it also functions to drain mucus.
More common in children because their eustachian tube is more horizontal (and so less effective at draining mucus away from the ears).
Which structure can open in order for air to equalise pressure between the middle ear and the atmosphere?
The eustachian tube.
Which 2 structures in the ear specifically provide information about head position?
The semi-circular canals and vestibule.
The walls of the vestibule and semi-circular canals contain specialised hair cells with ________
Stereocilia
What is the otolithic membrane?
A fibrous, gelatinous structure located in the vestibular system of the inner ear, in which the hairs of stereocilia are floating.
Where would you find the otolithic membrane?
In the vestibular system of the inner ear
Is the otolithic membrane involved in hearing or balance?
Balance
A dense layer of ________ _________ crystals extends over and rests on the otolithic membrane.
Calcium carbonate crystals
What type of crystals would you find in the inner ear?
Calcium carbonate crystals.
Any change in _____ position causes movement in the perilymph and endolymph, bending hair cells and stimulating sensory nerve endings.
Head position
Which part of the brain interprets and makes postural changes in order to maintain balance?
The cerebellum
Which 3 sources of information does the cerebellum need in order to maintain physical balance of the body?
- Vestibular feedback (from the inner ear)
- Visual feedback (from the eyes)
- Proprioception (from the muscles, joints and ligaments)
Which cranial nerve supplies the eye?
The optic nerve (cranial nerve 2)
Name the 3 layers of the eyeball.
- Sclera & cornea (outer layer)
- Uvea (middle layer)
- Retina (Inner layer)
What is the sclera?
The white of the eye
The middle layer of the eye is called the Uvea and consists of 3 parts. Name them.
- Iris
- Ciliary body
- Choroid
What is the function of the iris?
It controls the amount of light reaching the retina, by adjusting pupil size
Where in the eye is the lens located?
Behind the pupil
What is the role of the lens?
To further focus light (along with the cornea)
List 3 accessory organs that function to protect the eye.
- Eyebrows - prevent sweat entering the eye
- Eyelids - spread secretions over the eye
- Conjunctiva - Thin membrane, protects the cornea
What is the conjunctiva?
A thin, transparent membrane lining the internal eyelids and anterior eyeball, which protects the cornea.
What is the role of the lacrimal apparatus?
Production of tears
Why is blinking important?
It spreads tears across the eye and closing the eyelids protects the eye from injury.
Why are tears essential?
They protect the eye from infection (they contain IgA) and lubricate the eye’s movement.
Which cranial nerve controls the secretion of tears?
Trigeminal nerve (CN5)
How do tears contribute to immunity?
They contain IgA and lysozymes. They also have an emotional function.
What does the lacrimal gland do?
Produces tears
How do tears move across the eye?
Tears are produced by the lacrimal gland and swept across the eye by blinking. They enter the lacrimal punctum and then drain down the nose via the nasolacrimal duct.
What is the lacrimal punctum?
The small fleshy part in the inner corner of the eyes. Tears enter the lacrimal punctum then are drained down the nose via the nasolacrimal duct.
To achieve clear vision, light must be focused on the retina. This involves:
- __________ of the light rays
- __________ of the eyes
- Changing the ______ of the pupils
- Refraction of the light rays
- Accommodation of the eyes
- Changing the size of the pupils
Light is part of the ________ spectrum.
Electromagnetic
What is refraction?
The bending of light rays
When does refraction occur?
When light moves from one substance to another with a different density.
The _______ and ______ refract light rays, helping to focus the image on the retina.
Cornea and lens
What is ‘accommodation’ of the eyes?
When the lens curvature becomes greater, to increase its focusing power.
When the curvature on the lens becomes greater, its focusing power ________.
Increases
Which muscle contracts to make the lens more convex (increasing refraction and therefore focusing power)?
The ciliary muscle
Which muscle is associated with accommodation of the eye?
The ciliary muscle
Why does looking at objects close up tire the eyes?
Because close objects require more focusing power from the lens, which in turn requires the ciliary muscle to contract. Lots of ciliary muscle contraction = tired eyes.
In relation to the iris:
Sympathetic stimulation contracts the ______ muscle fibres to ______ the pupils.
Radial muscles, dilate the pupils
Pupil size is dictated by the contraction of muscles in the ______
Iris
There are 2 types of muscle in the iris, which function to adjust pupil size. Name them.
- Circular muscle (innermost) - constricts pupils
2. Radial muscles (outer) - dilates pupils
Define eyeball convergence
The movement of the 2 eyeballs so that both are directed towards the same object.
If eyeball convergence is not complete, two different images are sent to the brain leading to ______ vision (also known as _____)
Double vision (diplopia)
In humans, both eyes focus on one object, which allows for the perception of ______ and ____ nature.
This is called ________ vision.
Depth and 3D nature.
Binocular vision.
What is the optic chiasma?
The point at which the optic nerve crosses over in the brain.
The two images from the two eyes are fused in the ______ area of the brain, so that only one image is perceived.
Cerebrum
What is the optic chiasma located next to in the brain?
The pituitary gland.
Why can pituitary tumours often cause double vision?
Because the pituitary gland sits right next to the optic chiasma (the point at which the optic nerve crosses over in the brain and 2 images from 2 eyes becomes one single perceived image).
What is the retina?
The inner layer of the eye.
What lines the posterior three-quarters of the eyeball?
The retina
The retina can be viewed using which medical instrument?
An opthalmoscope
Which part of the eye is the only place in the body where blood vessels and a nerve can be seen?
The retina
What is the optic disc?
The location where the optic nerve exits the eyeball.
Which structure exits the eyeball at the optic disc?
The optic nerve
Where is the ‘blind spot’?
At the point of the optic disc.
Describe the anatomy of the retina
It contains a pigmented layer of melanin-containing epithelial cells, and a layer of photoreceptors.
What are photoreceptors and where are they found?
Specialised visual cells. Found in the retina.
Do our eyes contain more rod cells or cone cells?
Rod cells - around 120 million
Cone cells - around 6 million
Which cells allow us to see in dim light?
Rod cells
Which cells provide vision in black, white and greyscale?
Rod cells
Which cells allow us to see in colour?
Cone cells
Name the 3 types/colours of cone cell.
Blue, red and green
Why is the optic disc also called the blind spot?
Because it doesn’t contain any rod or cone cells.
What is the macula lutea?
A yellowish spot at the exact centre of the retina.
What is the name given to the yellowish spot at the exact centre of the retina?
The macula lutea
What is the fovea centralis?
A small depression in the centre of the macula lutea that contains only cone cells.
Where in the eye would you find an area that only contains cone cells?
The fovea centralis, at the centre of the macula lutea.
What is special about the fovea centralis?
It is the area of the highest visual acuity.
Which part of the eye is the area of highest visual acuity?
The fovea centralis
Why do we move our eyes and head when trying to focus on something?
Because we need the light to hit the fovea centralis on the retina, which is the point of highest visual acuity.
Are rod or cone cells more plentiful at the periphery of the retina?
Rod cells
What are photo-pigments?
Transmembrane proteins found within the discs of rod and cone cells.
Where would you find photo-pigments?
Within the cell membrane of rod and cone cells (photo-pigments are transmembrane proteins)
When light hits a photo-pigment it changes shape, initiating an ____ ______
Action potential
Which substance are photo-pigments (transmembrane proteins) derived from?
Vitamin A
Why is vitamin A so important for vision?
Because photo-pigments within the cell membranes of red and cone cells are derived from vitamin A.
Which layer of the eye stores a large quantity of vitamin A?
The retina
Why is there a large quantity of vitamin A stored in the retina?
Because vitamin A is needed to regenerate the photo-pigments within rod cells.
Vitamin A derivatives are called _______
Retinoids
What are retinoids?
Vitamin A derivatives
In the retina, vitamin A in the form of ________ binds to a protein called opsin, to produce photopigments.
Retinal
What is the name of the protein that binds to retinal (vitamin A) in the retina, to produce photo-pigments?
Opsin
Photo-pigments are produced in rod and cone cells when _____ binds to _____.
Retinal binds to opsin
_________ are precursors of Vitamin A.
Carotenoids
Where in the body are carotenoids metabolised to retinol?
In the intestines
Nutritionally, where would you find pre-formed vitamin A?
In animal foods such as liver and egg yolk.
Name 3 food sources of carotenoids / carotenes.
- Carrots
- Sweet potato
- Squash
- Mango
- Leafy greens
Why does ingested pre-formed vitamin A come with a risk of toxicity?
Because too much vitamin A is toxic and eating it in pre-formed form means that your body can’t decide how much to convert into the active form itself (absorption is unregulated).
Which cells are able to regenerate their photo-pigments quicker - rod cells or cone cells?
Cone cells regenerate quicker.
What is olfaction?
The sense of smell.
What is the olfactory epithelium?
The area within the nose that contains the receptors for olfaction (smell).
Name the 2 ‘chemical senses’.
Taste and smell
Why are taste and smell known as the ‘chemical senses’?
Because they arise from interaction with molecules.
The olfactory epithelium within the nose contains 3 things. Name them.
- Olfactory receptors
- Supporting cells
- Basal cells
Olfactory receptors are produced from ______ cells, which are stem cells that continually divide.
Basal cells
Describe olfactory receptors.
Neurons attached to olfactory hairs, found in the olfactory epithelium within the nose. They respond to the chemical stimulus of odourants by producing an action potential.
Which structure produces nasal mucus?
Olfactory glands (within the connective tissue supporting the olfactory epithelium) produce mucus.
Name a pathology that inhibits olfaction and describe why.
Rhinitis. Because it causes inflammation of the nasal mucosa, which inhibits olfaction.
Which cranial nerve is involved in sense of smell?
Olfactory nerve (CN1)
Why is there a link between smells and emotions?
Because some of the axons of the olfactory tract project into the limbic system.
In smell sensation, nerve axons extend through about 20 olfactory _______ in the __________ plate of the ethmoid bone to the ________ lobe.
Olfactory foramina
Cribriform plate
Temporal lobe
What is gustation?
Taste
How many muscles is the tongue formed of?
8
The 8 muscles of the tongue are innervated by which cranial nerve?
Hypoglossal nerve (CN7)
Where are taste buds found?
Mostly on the tongue, but also on the soft palate, pharynx and epiglottis.
What is the role of gustatory receptor cells?
Taste detection
Describe the physiology of taste.
The stimulation of chemoreceptors by dissolved chemicals in saliva.
Taste buds contain 3 types of cells. Name them.
- Gustatory receptor cells
- Basal cells (stem cells)
- Supporting cells
How long do gustatory receptor cells live?
About 10 days
What are papillae?
Elevations on the tongue that contain taste buds and help the tongue move food.
List the 2 functions of papillae.
- Taste
2. Movement of food
List the 3 types of papillae involved in taste.
- Circumvallate papillae
- Fungiform papillae
- Foliate papillae
Name the type of papillae that help the tongue move food.
Filiform papillae
Why is taste impaired when the mouth is dry?
Because saliva is needed to dissolve the taste molecules and help them reach the cell membranes of gustatory receptor cells.
We can only detect 5 tastes. What are they?
- Sweet
- Salty
- Sour
- Bitter
- Umami
Describe the physiology of taste
Tastants dissolved in saliva > encounter the cell membrane of gustatory hairs > generates an action potential.
Which cranial nerve innervates taste in the anterior two-thirds of the tongue?
Facial nerve
Which cranial nerve innervates taste and general sensation in the posterior third of the tongue?
Glossopharyngeal nerve
Which 2 cranial nerves innervate taste in the tongue?
Facial nerve and glossopharyngeal nerve
Which 2 cranial nerves innervate general sensation in the tongue?
Trigeminal nerve and glossopharyngeal nerve
Which cranial nerve innervates the throat and epiglottis?
Vagus nerve
Why are particular tastes sometimes associated with particular emotions?
Because some of the nerve fibres associated with gustation go into the limbic system.
Where (in the brain) is taste processed?
The gustatory nucleus in the medulla oblongata
