Lecture 23: Sensory 2

Question 1

Name the 5 basic tastes that are detected by the human tongue and using a sketch show the areas of the tongue that are most sensitive to each if these basic tastes

Answer 1

Sour (sides)
Salty (front sides)
Sweet (tip)
Bitter (back) 
Umami (tip)

Question 2

Describe the general structure of human taste buds and explain how type 1, 2 and 3 cell contribute to the detection of the 5 basic tastes.

Answer 2

Taste buds contain 3 types of receptor cells:
Type 1: (support or glial like) cells detect Na+ ions via ion channels
Type 2: (receptor) cells detect either sweet, umami or bitter tastes
-signal afferent nerves and type 3 cells via ATP
Type 3: (presynaptic) cells detect sour tastes
-only cells to synapse with afferent nerves, signalling via serotonin

Question 3

Sensory signal transduction can occur either via the specialised dendritic zone of the afferent neuron or via a receptor cell that is separate to the afferent neuron. Relate to taste or olfactory signals

Answer 3

• neural pathway for taste: taste receptors send signals along afferent nervous pathway that terminates in the ingustory cortex area of the brain
• area of somatosensory cortex corresponding to mouth
• taste signals decided by brain enabling particular taste to be perceived

Question 4

Chemoreception: smell (olfaction)

Answer 4

In olfaction chemicals must dissolve in mucus in nasal passage before they can bind to specific chemoreceptors on afferent neurons

• signals travel to olfactory cortex where various odours are recognised
• so the receptor neurons travel to the olfactory bulb through series of small holes in skull (cribriform plate) to synapse in olfactory bulb.

Question 5

Vomeronasal organ in animals

Answer 5

It’s an accessory olfactory organ which is involved in detection of pheromones

Question 6

Photoreception: the eyes and vision

Name the main areas of the eye

Answer 6

Outermost layer:
-sclera: tough connective tissue coat covering most of eye, makes up white of eye
-cornea: transparent structure in front of eye, allows light to enter
Middle layer:
-choroid: vascular end pigmented layer under sclera, provides blood to retina
-ciliary body: contains ciliary muscles, which attach to lens by zonula fibres. changes shape of lens to focus light
-lens: focuses light on retina
-iris: located in front of lens, regulates amount of light entering eye by adjusting diameter of pupil
Innermost layer
-retina: neural tissue which detects light
-2 types of photoreceptors (rods and cones)
-fovea: we’re light from centre if visual field strikes retina, area of greatest visual acuity
-optic disc: where optic nerve and blood vessels supplying eye pass through retina, no photoreceptors cells, also called blind spot

Question 7

What are the 2 internal chambers of the eye?

Answer 7

The lens and ciliary body separate eye into 2 chambers:

1. Anterior (front) chamber contains clear, watery fluid (aqueous humour) which supplies nutrients to the cornea and lens
2. Posterior (rear) chamber contains firm, jelly-like material (vitreous humour) -maintains spherical structure of the eye

Question 8

Refraction of light waves by the eye

Answer 8

Both the cornea and lens have convex surfaces, causing light waves entering eye to converge onto retina

• a given point in visual field comes to focus on a single point in retina
• passage of light waves through convex lens causes retinal image to be inverted and reversed…brain fixes it

Question 9

How do mammals and birds focus on objects that are close and distance

Answer 9

Do so by changing the shape of their lens

Question 10

What are the characteristics (differences) of rods and cones (photoreceptors) 
Type of vision 
Sensitivity to light 
Abundance 
Visual acuity

Answer 10

Type of vision: 
Rods- provide ability to see black and white in low light conditions 
Cones-provide ability to see colour, but only in bright light 
Sensitivity to light:
Rods- high
Cones- low 
Abundance: 
Rods- 100 million per retina
Cones- 3 million per retina
Visual acuity:
Rods-low
Cones-high

Question 11

Explain phototransduction

Answer 11

Light- fark that

Slide 29

Question 12

What is the neural pathways for vision?

Answer 12

From ganglion cells, signals travel in optic nerve

• optic nerve exits eye at optic disc
• 2 optic nerves combine in optic chiasm
• in animals, nerve fibres cross over to enter opposite side of brain
• information from right and left sides of visual field processed in left and right sides of brain, respectively

Question 13

How is the amount of light entering the eye regulated?

Answer 13

Contraction or relaxation of inner circular muscle of iris smooth muscle regulates how much light enters eye.

• in bright light, parasympathetic stimulation contracts inner circular muscle causing papillary constriction, decreasing amount of light entering eye
• in low light, lack of parasympathetic stimulation relaxes inner circular muscle, causing pupillary dilation, increasing amount of light entering the eye.