Human Ear, Eye and Skin

Question 1

Sensory receptor

Answer 1

Specialized structure which can detect a specific stimulus and convert the stimulus energy into a changing membrane potential to be transmitted to the CNS as action potentials for sensory perception and interpretation.

Question 2

Characteristics of sensory receptors

Answer 2

Detect the stimulus is at or above the threshold level
Convert the energy of the stimulus into a changing membrane potential to be later transmitted as an action potential
Always connected with the nervous system
During the conversion of stimulus energy to action potentials sensory signals can be strengthened known as amplification
If the stimulation is continuous, responsiveness of the receptors decreases known as sensory adaptation

Question 3

Types of sensory receptors

Answer 3

Chemoreceptors
Thermo receptors
Photoreceptors 
Mechanoreceptors
Pain receptors

Question 4

5 sensations of taste

Answer 4

Sweet, sour, salty, bitter and Umami

Question 5

Taste recepters

Answer 5

Specialized epithelial cells organized into taste buds found in the papillae which are small projections found in the tongue. Taste bud contains taste cells, supporting cells and sensory nerve endings. Substances to be tasted should be dissolved in the fluid surrounding the sensory cells and diffuse to receptor cells through the taste pore.

Question 6

Olfactory receptors

Answer 6

In olfaction receptor cells are neurones. Located within the epithelium of the upper part of the nasal cavity. Respetive ends of the cells extend into the mucous layer of the nasal cavity. Then the nerve impulse is sent along their axons into the olfactory bulb in the brain.

Question 7

Thermo receptors found in the skin

Answer 7

Krause end bulbs (detect cold)
Ruffini corpuscles (detect warmth)
Free nerve endings

Thermo receptors found in the hypothalamus are specialized neurones.

Question 8

Main types of photoreceptor cells and their functions

Answer 8

Rods - They are more sensitive to light but do not distinguish colours. They enable us to see at night but only in black and white. Rhodopsin

Cones - They provide colour vision but they contribute very little to night vision as they are not much sensitive. 3 types of cons red, blue and green. Photopsin

Question 9

Mechanoreceptors

Answer 9

Respond to stimuli arising from mechanical energy deformations such as pressure, touch, stretch, motion and sound.

Touch receptors - Meissner’s corpuscles (sensitive to light pressure), Merkel discs (sensitive to light touch) and free nerve endings.

Pressure receptors- Pacinian corpuscles sensitive to deep pressure

Vibration receptors- Most of the touch receptors (Meissner corpuscles, pacinian corpuscles)
Specific hair cells in the organ of corti in inner ear detects sound waves
Hair cells of the vestibule of the inner ear detect gravity where as hair cells of the semicircular canals detect motion.

Question 10

Conjuctiva

Answer 10

Fine transparent membrane that lines the iris and front of the eye ball.

Question 11

Sclera and cornea

Answer 11

Sclera - white, opaque and is the outermost layer of the posterior and lateral aspects of the eye. Maintains the shape of the eye ball and gives attachments to extrinsic muscles of the eye. There are 3 pairs of extrinsic muscles.

Cornea - Passage through which light enters retina. It is devoid of blood vessels. Cornea is convex anteriorly and involved in refraction of light rays to focus on the retina.

Question 12

Aqueous humour and vitreous body

Answer 12

Infront of the lens, a watery substance is present which is called the aqueous fluid (blockage of ducts draining this fluid produce glaucoma causing vision loss). Aqueous fluid supplies nutrients and removes wastes from the cornea, lens and lense capsule which have no blood supply.

Behind the lens a clourless and transparent jelly like vitreous humour is present. It maintains enough intra ocular pressure to support the retina against choroid and prevents the eye ball from collapsing.

Question 13

Retina

Answer 13

Consists of 3 layers. Outer pigmented layer, middle photoreceptive layer and inner layer consisting of neurones. At the center of the posterior part of the retina contains macula lutea (yellow spot). In the center of yellow spot contains a little depression known as fovea centralis which contains only cones. The small area of retina where the optic nerve leaves the eye is the blind spot (optic disk). It lacks photoreceptors.

Question 14

Neurones present in the retina

Answer 14

Several types invluding bipolar cells and ganglion cells

Question 15

Which nervous system supply to cilliary body controls

Answer 15

Parasympathetic

Question 16

Mechanism of converting light energy to be transmitted to the brain

Answer 16

Image produced at the retina is upside down
Bipolar cells receive information from photoreceptor cells and each ganglion cell gathers inputs from several bipolar cells.
Ganglion cells form the optic nerve fibers which transmits sensations from the eye as action potentials to the brain
The optic nerve transmits this nerve impulse into occipital lobe. Then the visual objects are perceived in the correct way.

Question 17

Monocular vision

Answer 17

Seeing the visual feild using only 1 eye is called monocular vision. However when 1 eye is used 3-dimensional vision is impaired

Question 18

Binocular vision

Answer 18

Seeing the visual feild using 2 eyes with greater overlapping feilds of view is called binocular vision

Question 19

Human ear

Answer 19

Contains 3 areas known as outer ear, middle ear and the inner ear.
Outer ear consists of the pinna and the external acoustic meatus (auditory canal). Tymphanic membrane is situated between the outer ear and the middle ear. Middle ear (tympanic cavity) is an air filled cavity. Tympanic membrane is connected to ear ossicles which contains malleus, incus and stapes. In the medial wall of the middle ear 2 openings are present known as oval and round window. A long tube known as the eustachian tube connects the middle ear to the pharynx. Inner ear is composed of 3 semi-circular canals, vestibule and cochlea. Cochlea has 3 parts, upper part of vestibule canal, lower part of tympanic canal and middle cochlear duct. The floor of the cochlear duct is composed of the basilar membrane which bears the organ of corti. It is composed of supporting cells and specialized cochlear hair cells containing mechanoreceptors. Many hairs are attached to the tectorial membrane that combines to form the auditory nerve.

Question 20

Auditory area of the brain

Answer 20

Temporal lobe of the cerebrum

Question 21

Epidermis consists of

Answer 21

Stratified keratinized squamous epithelium

Question 22

What factors affects the skin colour

Answer 22

Melanin secreted by melanocytes
Oxygen saturation in the circulating blood in the dermis, excessive levels of bile pigments and carotenes in the fat layer

Question 23

Main cells found in the dermis

Answer 23

Fibroblasts
Macrophages
Mast cells

Question 24

What is coverted to vitamin D

Answer 24

Lipid based substance Dehydrocholestrol

Question 25

Functions of human skin

Answer 25

Protection
Regulation of body temperature 
Cutaneous sensation
Synthesis of vitamin D
Excretion