Module 3.2- Special Senses Flashcards
What are the “special senses”?
Olfaction (smell), Gustation (taste), vision, hearing (and balance) and specialised receptor cells (located in sensory areas and protected by surrounding tissues).
How does the olfaction sense vary between species?
Widely, proportionate to the number of odour receptors contained within the nose (or area used)
How does the sense of olfaction work?
Odorants pass into the nose, dissolve in mucus within the nose and bind with chemoreceptors which generate neural signals which are sent to the brain for interpretation.
How does sniffing enhance the perception of smell?
Increased amounts of odoriferous substances pass over nasal mucosa and thus there are more which can potentially bind to receptors.
How/where are olfatory organs typically found in vertebrates?
Paired, located either side of the nasal septum in the nasal fossae
In vertebrates, what does the olfactory epithelium consist of?
Supporting cells (bowmans glands)
Olfactory receptor cells
Basal cells
What do Bowman’s glands do?
Secrete mucus to moisten surface of nasal passages and dissolve odoriferous substances
What do olfactory receptor cells do?
Capable of detecting different components of odours, odour activates characteristic combination of cells and the information is pooled in olfactory bulb.
Describe the structure of olfactory receptor cells
Each olfactory receptor cell has a tuft of 5 olfactory cilia which bear receptor proteins for various odour molecules.
Roughly how many kinds of different odour receptors are there?
Roughly 1000
Describe the olfactory bulbs
Complex structures consisting of a variety of structures able to detect a myriad of odours. Each bulb is lined with neural-junction layer of glomeruli.
How do olfactory bulbs work?
Each glomeruli receives information from only one type of olfactory receptor. Olfactory nerve synapses with mitral cells within each glomerulus. These send information about odours to the limbic system and cerebral cortex via the hypothalamus
What behavioural reactions are associated with olfactory stimuli?
Feeding (e.g. salivation), mating (oestrus behaviour), direction orientation (locate prey/predators)
Where are Pheremone receptors?
Subset of olfactory neurons outside the olfactory epithelium
What are pheremones?
Hormones created by animals, important for behaviours (such as communication) in many species
What are pheremones important for?
Reproductive behaviours, communication of directions (e.g. ants, bees) or scent marking of territory (e.g. lions)
Are there any known human pheremones?
None yet discovered
Describe the sense of gustation
Associated with dissolved substances contacting specialised receptor cells on the tongue and throat region (in mammals). These receptor cells are called taste cells
How are taste cells arranged?
They are found arranged in groups called taste buds which consist of the receptor taste cells and other supporting cells.
Where are taste buds located in mammals?
Primarily on the tongue, found along the walls of structures called papillae (small elevations on the surface of the tongue). Some also found in throat, hard palate, pharynx and epiglottis.
How are taste buds situated in the tongue?
Embedded in the tongue epithelium and open at the taste pores
How are taste buds distributed on the tongue?
Unevenly.
What are the three kinds of papillae found on the tongue?
Vallate papillae (large, at the back of the tongue) Fungiform papillae (Medium sized, spotted unevenly along middle to tip of tongue) Filiform papillae (small, evenly distributed over middle to tip of tongue)
What are the 5 types of taste buds (flavours) humans have?
Sweet, sour, salty, bitter and umani
Where are the sweet taste buds found in humans?
Near the tip of the tongue
Where are the sour taste buds found in humans?
Along the margins of the tongue
Where are the salty taste buds found in humans?
On the tip and upper front portion of the tongue
Where are the bitter taste buds found in humans?
Near the back of the tongue
What flavour does the umani taste buds respond to in humans?
Meaty, savoury flavours given off by certain amino acids
How does the brain perceive flavours?
As an overall weighted average of taste messages received from the 5 types of taste buds.
Where are microvilli found on the tongue?
At the end of the elongated taste cells
What is the function of the microvilli on the tongue?
They bear receptor proteins for certain chemicals. Molecules bind to these receptor proteins which then generate sensory nerve impulses which are sent to brain corticular areas which interpret them as tastes
Does every human have the same number of taste papillae and taste buds?
No, some have more than others
How are humans distinguished as ‘super-tasters’?
By an increased density of fungiform papillae and extreme sensitivity to the chemical n-propylthiouracil.
What is a ‘super taster’?
A person with 165 taste papillae per square cm
More women than men
Tend not to like green vegetables and fatty foods
Roughly what percentage of the human population are considered ‘super tasters’?
Roughly 25%
What is a ‘normal taster’?
A person with 127 taste papillae per square centimetre
Roughly what percentage of the human population are ‘normal tasters’?
Roughly 50%
What is a ‘non-taster’?
A person with 117 taste papillae per square centimetre
What percentage of the human population are considered ‘non-tasters’?
Roughly 25%
What is the Sclera?
Connective tissue outer, protective layer of the eye, connected to cornea
What is the Cornea?
Outermost transparent layer of the eye, allows transmission of light into eye
What is the anterior chamber (cavity)?
Fluid (aqueous humor) filled chamber beneath the cornea in the eye
What is the aqueous humor?
Fluid found in the anterior chamber of the eye
What is the iris?
2 layers of smooth muscle that act as a diaphragm in the eye which control the amount of light entering the eye
What is the pupil?
Hole in the iris in the eye trough which light passes on it’s way to the retina
What is the posterior cavity (chamber)?
Filled with vitrious humor, underlies the iris but overlies the lens of the eye
What is the lens?
Biconvex elastic structure in the eye which is responsible for focusing images on the retina
What is the ciliary body?
Tissue connecting choroid and iris in the eye. It contains ciliary muscles which have attached zonular fibres.
What is the function of ciliary muscles and zonular fibres of the eye?
The contraction and relaxation of the muscles (connected to the lens by the fibres) manipulates the shape of the lens, allowing the eye to focus.
What are zonular fibres?
They connect the ciliary muscles to the lens in the eye
What is the vitreous chamber?
Lies between the lens and retina of the eye, filled with vitreous humor
What is the choriod?
Highly pigmented tissue in the eye containing a dense network of blood vessels
What is the retina?
Innermost layer of the eye which contains photoreceptors, fovea and the optic disk
What is the optic disk?
Area where multipolar ganglion cells merge into the optic nerve in the eye
What is a fovea?
Central part of the retina in the eye where light from the centre of vision is transmitted to.
What is the macula?
Area immediately surrounding the fovea in the eye. It consists of cone light receptors and the number of rod light receptors increases as the distance from the fovea increases.
What do cone photoreceptors do?
Detect colour.
What do rod photoreceptors do?
Detect light and dark, allowing animals to see in black and white
Which kind of photoreceptor (rod or cone) requires more light but has greater acuity?
Cones
What do photoreceptors do?
They detect light from the environment and convert it to nerve impulses, sent to the brain via the optic nerve (bipolar and ganglion cells)
What does a bipolar cell, found in the middle layer of the retina, do?
Intermediary cell that transmits electrical signals from rod and cone photoreceptors to ganglion cells
What layer of the retina contains bipolar cells?
Middle
What do Ganglion cells in the retina do?
They are the cell bodies of the optic nerve, with a nervous connection to the central nervous system. They synapse with bipolar cells to transmit the electrical signal of the rod and cone photoreceptors to the central nervous system
How does the structure of the bird eye vary from the human eye?
They have 2-3 fovea instead of just one
How does the structure of the dog eye vary from the human eye?
They have a visual streak instead of a fovea
Where, in the retina, are no cone photoreceptors found? What effect does this have on vision?
In the fovea
Poor vision of objects in dark when looking directly at them
Which layers of the eye must light pass through before reaching the photoreceptors?
Inner and middle layer
Where does light strike the retina directly?
The fovea
What is a Tapetum Lucidum?
A reflective layer of material in the eye of noctournal animals that enables them to see in dimly lit situations by reflecting light that has already been transmitted through the retina, back again to further stimulate the rod photoreceptors.
Which cells carry out phototransduction?
The rod and cone photoreceptors
What is phototransduction?
The process by which light stimulus is converted to electrical energy that can be transmitted by neurons to the central nervous system
What absorbs light in the eye?
Light is absorbed by Rhodopsin (photopigment) contained in membranous disks of rod and cone photoreceptors.
How many kinds of photopigments are there in rod photoreceptors?
One, Rhodopsin
How many kinds of photopigments are there in cone photoreceptors and how do they vary?
Three; blue, red and green. They vary in which wavelengths of the visible portion of the light spectrum that they absorb.