Sense organs Flashcards
Explain the role of the ‘stapedius’
A small muscle stop & reduce/ cushion large vibrations and is innervated by the facial nerve -> hence auditory symptoms in Bell’s palsy. (excessive sound due to the loss of cushion by stapedius)
Describe specifically the structure of the inner ear.
called the labyrinth because of its complicated series of canals. Consists of an outer bony labyrinth that encloses an inner membranous labyrinth:
3 semicircular canals & vestibule (receptors for balance).
Describe how ‘stereocilia’ trigger an electrical impulse
Fluid movement (vibration) causes stereocilia movement and initiates an electrical impulse.
Name which cranial nerve provides sensory information for hearing and balance
The vestibulocochlear nerve (cranial nerve VIII) provides sensory information for hearing and balance.
Describe in specific detail how external sound waves are perceived as ‘sound’ in the cerebrum of the brain
Sound wave (pressure waves) - > Mechanical vibration -> Fluid waves -> Nerve Impulse-> cerebrum
List TWO functions of the Eustachian tube
- Ventilate the middle ear,
- Equalize pressure in middle ear (to avoid damage with pressure changes).
- Drain mucus
Explain why children are more prone to middle ear infections
Eustachian tubes and is a common route for infection to spread between the pharynx and middle ear (more horizontal, flat & short in children).
Describe the structure of the ‘otolithic’ membrane’
A dense layer of calcium carbonate crystals extends over and rests on the hairs
Name the THREE layers of the eyeball
Outer Layer: Sclera
Middle Layer: Uvea
Inner Layer: Retina
Describe the main role of the ‘iris’
Iris controls the amount of light reaching the retina by adjusting pupil size.
Describe how the following protect the eye : Eyebrows
Prevent sweat / materials entering eye.
Describe how the following protect the eye: Eyelids/eyelashes
Eyelids: Spread secretions over eye, Eyelashes: trap small particles to protect the eye.
Describe how the following protect the eye: Conjunctiva
Thin transparent mucous membrane of columnar epithelial cells lining the internal eyelids and anterior eyeball, protects the cornea. and secrete oily material to lubricate eyeball
Describe how the following protect the eye: Lacrimal apparatus
They protect the eye from infection and by tear lubricate movements of the eye.
Describe how the following protect the eye: Blinking
•Blinking spreads tears and closing the eyelid protects from injury.
List THREE ways in which clear vision is achieved by the eyes
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.**
Name ONE eye component that refracts most light rays
Cornea
Describe in detail the difference between:
a. Greater refraction
b. Less refraction
(HINT: Think ciliary muscles, lens and suspensory ligaments)
a. When an object is close, the ciliary muscle contracts. This reduces suspensory ligament tension and the lens becomes more convex -> greater refraction.
b. 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).
Describe how the pupil size is affected by:
a. Sympathetic nervous system
b. Parasympathetic nervous system
a. Sympathetic stimulation contracts the radial muscle fibres to dilate the pupils.
b. Parasympathetic stimulation contracts the circular muscle fibres to constrict the pupils.
- Name one investigative tool that can be used to view the retina
- Name the location where the optic nerve exits the eyeball
- Ophthalmoscope
- Optic disc or blind spot
List TWO layers of the retina
- Pigmented layer
- Photoreceptors layers
Describe THREE differences between ‘rod cells’ and ‘cone cells’
- Rode cells have a rode appearance and cone cells cone appearance
- Rode: provide black, white greyscale/ Cone: Blue, red & green scale
- Rode: 120 million cells / Cone: 6 million
Describe TWO features of the ‘fovea centralis’
‘Fovea centralis’ :
- contains only cone cells.
- Area of highest visual acuity (this is why we move our eyes and head to look at things).
- State where Vitamin A is stored in the eye
- Name the protein bound to Vitamin A in the eye
- the pigmented layer of the retina stores vit. A.
- Opsin
Describe how the eyes adjust in the following situations:
a. Moving from dark to light sensitivity
b. Moving from light to dark sensitivity
a. Dark to light, the eyes adjust quite quickly -> ‘light adaptation’. decreasing its sensitivity.
b. Light to dark : increases slowly over some minutes. Photopigments take time to regenerate.
Name the cranial nerve responsible for sense of smell
Olfactory nerve (CN I)
Name the cranial nerve which innervates the tongue.
Hypoglossal nerve (CN XII).
Explain what is meant by ‘papillae’
Papillae : Taste buds in elevations on the tongue: gripping food & taste
Describe the difference between the following:
a. Circumvallate papillae
b. Fungiform papillae
c. Foliate papillae
a. Circumvallate: the largest at the back of the tongue
b. Fungiform: mushroom shaped all over the tongue
c. Foliate: at the margins of the tongue but most degenerate in childhood (breastfeeding, milk)
- Name TWO cranial nerves involved in taste physiology.
- Name ONE cranial nerves involved in touch/ sensation
- The facial nerve / 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.
List TWO main functions of the inner ear.
Receptors for balance semicircular & vestibule canals and hearing (cochlea)
List THREE ways in which the cerebellum can make postural adjustments to maintain balance
- Vestibular system (inner ear) -Head position
- Visual feedback (from eyes) ⇒ Need B12
- Proprioceptors in skeletal muscles, joints & ligaments
What 2 bones in the inner ear send neve impulses for balance?
Vestibule and semicircular canals
Explain how tears play an important immune role
Tears contain IgA and lysozymes
Name the cranial nerve that controls tear secretion
Tears are secreted under the control of the trigeminal nerve (CN V).
List two food sources of:
- Pre-formed vitamin A
- Carotenoids
- liver, eggs
- Fruits/ Veggies
Explain why carotenoids are not considered to be toxic
because absorption is regulated
What is meant by optic disc?
where optic nerve exit the eyeball
