Chapter 9: Senses

Question 1

Define stimulus and sensation.

Answer 1

Stimulus is something that promotes growth or reaction within a human body.
Sensations result only from those stimuli that reach the cerebral cortex. It can be special or general.

Question 2

List and describe the receptors associated with the general senses.

Answer 2

Mechanoreceptors: responds to mechanical stimuli
Chemoreceptors : responds to chemicals
Photoreceptors : responds to light
Thermoreceptors : responds to temperature
Nocireceptors :responds to stimuli relating in pain

Question 3

How does pain occurs and how it can be modified.

Answer 3

Pain occurs by unpleasant sensation (shape or diffuse).

It can be modified as gated, referred or phantom.

Question 4

Explain about the types of pain sensations.

Answer 4

There are superficial pain sensations (highly localised) or deep visceral sensations (not highly localised). The Superficial pain Sensations are a simultaneous stimulation of pain receptors in tactile receptors which helps to localize the source of pain stimuli. The Deep or viseral pain Sensations are the cause of the absence of tactile receptors in deeper structures and thus diffuse the pain.

Question 5

Define and explain referred pain.

Answer 5

Referred: painful Sensations perceived to originate in another region of the body
Sensed in skin, other superficial structures
Due to internal organs that are damaged or inflamed. The sensory neurons from superficial areas from this visceral area Converge on to the same ascending neurons in the spinal cord and because the brain cannot differentiate both of them as a cause referred pain.

Question 6

Describe the process by which airborne molecules produce the sensation of smell.

Answer 6

The airborne molecules from the air are dissolved in the mucus when inhaled and they bind to receptors. The odorants must dissolve in mucus before binding to the receptors. This causes the depolarisation of the olfactory neurons. There is a low threshold for detection of odors, thus very few odorants bound to an olfactory neuron can initiate an action potential.

Question 7

How is the sense of taste related to the sense of smell?

Answer 7

They are related due to the influence of the olfactory neuron. For example, when you pinch your nose, your food might taste different due to the scent not reaching the olfactory receptors.

Question 8

What are the five primary tastes?

Answer 8

Sour, salty, bitty, sweet, umami.

Question 9

How do they produce many different kinds of taste sensations?

Answer 9

Through the taste pathway.
The taste Impulses from anterior 2/3 of tongue past in cranial nerve, impulses from posterior 1/3 of tongue and other posterior parts of mouth are transmitted by glossopharyngeal nerve, and you taste signals from base of the time in other posterior parts are carried by vagus nerve. These three cranial nerves synapse in a gustatory portion of brainstem nuclei. The axons of neurons in brainstem nuclei synapse in Thalamus to The Taste area in the parietal lobe of cerebral cortex.

Question 10

Describe the following structures and state their functions: eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye muscles.

Answer 10

They are accessory structures that protect, lubricate and move the eye.
Eyebrow: protect eyes by preventing perspiration, shade eye from sun
Eyelids: protect eye by closing, opening rapidly (blink reflex) and it keeps eyes lubricated by spreading tears
Conjunctiva: thin, transparent mucous membrane covering the inner surface of eyelids and anterior surface of eye
Lacrimal apparatus: produce tears
Extrinsic eye muscles: 6 muscles which move the eyeball

Question 11

Name the three layers (tunics) of the eye.

Answer 11

Retina (nervous tunic), fibrous tunic, vascular tunic

Question 12

Describe the retina.

Answer 12

The retina is a thin layer of tissue that lines the back of the eye on the inside. It is located near the optic nerve. The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.

Question 13

Describe the fibrous tunic.

Answer 13

Fibrous tunic: it’s the outer layer which consists of sclera and cornea
Sclera is the firm, whiter outer connective tissue layer which maintains the shape of the eye, protects internal structures, and provides a site of attachment for muscles.
Cornea is a transparent, anterior layer which permits light to enter the eye and bend and refract light.

Question 14

Describe the vascular tunic.

Answer 14

Vascular tunic: it’s the middle layer which contains most blood vessels of the eye. It consists of the iris, ciliary body and choroid. The iris is attached to the anterior margin of the ciliary body, anterior to the lens and the smooth muscle that surrounds the pupil. The ciliary body is continuous with anterior margin of choroid, contains smooth muscle called ciliary muscle which attaches to the perimeter of the lens by suspensory ligaments. The lens is a flexible, biconvex transparent disc. The choroid is a posterior portion with a thin structure of a vascular network and contains melanin pigments so it’s black in color.

Question 15

Describe the vitreous chambers of the eye, the substances that fill each, and the function of the substances.

Answer 15

Vitreous chamber:
Filled with vitreous humor
Helps maintain pressure, bends light, no circulation

Question 16

Describe the anterior and posterior chambers of the eye, the substances that fill each, and the function of the substances.

Answer 16

Anterior and posterior chamber:
Filled with aqueous humor
Is located between cornea, lens and separated by iris
Helps maintain pressure, bends light, returned to circulation through venous ring (surrounds cornea)

Question 17

Describe the lens of the eye and how it is held in place.

Answer 17

The lens is embedded in the anterior segment of the eye and held in place by a ring of fibrous tissue, it is curved and transparent. Its purpose is to reflect light rays onto the retina at the back of the eye with the help of the cornea.

Question 18

Describe the arrangement of cones and rods in the fovea centralis and in the periphery of the eye.

Answer 18

Cones are concentrated in the fovea centralis. Rods are absent there but dense elsewhere. Measured density curves for the rods and cones on the retina show an enormous density of cones in the fovea centralis. To them is attributed both color vision and the highest visual acuity.

Question 19

What is the blind spot of the eye, and what causes it?

Answer 19

The blind spot is the optic disc and it is called that because there are no receptors to light and therefore no response to light.

Question 20

What causes the pupil to constrict and dilate?

Answer 20

The pupil allows light to pass through. Its diameter is regulated by iris.
When the parasympathetic stimulation from the oculomotor nerve causes circular smooth muscles of iris to contract and this causes pupillary contraction.

When the sympathetic stimulation of radial smooth muscles contracts, this causes pupillary dilation of the pupils.

LIGHT INTENSITY INCREASES = PUPIL CONSTRICTS
LIGHT INTENSITY DECREASES = PUPIL DILATES

Question 21

What causes light to refract? What is a focal point?

Answer 21

Refraction is an effect that occurs when a light wave, incident at an angle away from the normal, passes a boundary from one medium into another in which there is a change in velocity of the light. Light is refracted when it crosses the interface from air into glass in which it moves more slowly.

Question 22

What is a focal point?

Answer 22

A focal point is a point of crossing of light when it enters a convex lens surface. This occurs anterior to the retina and the tiny image is compared with the actual object.

Question 23

Define accommodation. What does accommodation accomplish?

Answer 23

It is the ability of the eye to retain clear vision when the objects are brought closer than 20 feet. It accomplishes the reduction of tension suspensory ligaments of lean and allows lean to assume a more spherical form which has a more complex structure and causes greater refraction of light.

Question 24

Describe the external region of the ear,

• naming the structures found in the region
• functions

Answer 24

External: auricle and tympanic membrane
Functions: auricle is the fleshy part of the external ear which opens into external acoustic meatus, tympanic membrane is the thin membrane that separates external to middle ear and sound waves cause it to vibrate

Question 25

Describe the middle region of the ear,

• naming the structures found in the region
• functions

Answer 25

Middle:
oval window, round window: connects middle ear with inner ear
Auditory tube
Auditory ossicles: transmit vibrations for tympanic membrane to oval window
Malleus attaches to medial surface of tympanic membrane
Incus connects malleus to stapes
Stirrup base is seated in oval window, surrounded by flexible ligaments

Question 26

Describe the inner region of the ear,

• naming the structures found in the region
• functions

Answer 26

Inner:
Body labyrinth: inner ear consists of interconnecting tunnels and chambers
Membranous labyrinth: filled with clear fluid - endolymph
Semicircular canals, vestibules : for balance
Cochlea: for hearing and contains a bony core
Spiral lamina: base of Y
Cochlear duct: space between vestibular (branch of Y) and basilar membrane (other brain of Y)

Question 27

Describe the relationship between the tympanic membrane, the ear ossicles, and the oval window of the inner ear.

Answer 27

The tympanic membrane separates the external ear from the middle ear. Sound waves striking the tympanic membrane vibrate the membrane and attached auditory ossicles. The auditory ossicles transmit vibrations from the tympanic membrane across the middle ear to the oval window of the inner ear.

Question 28

Describe the structure of the cochlea.

Answer 28

The inner ear structure called the cochlea is a snail-shell like structure divided into three fluid-filled parts. Two are canals for the transmission of pressure and in the third is the sensitive organ of Corti, which detects pressure impulses and responds with electrical impulses which travel along the auditory nerve to the brain.

Question 29

Describe the maculae and their function.

Answer 29

Maculae is the path of epithelium in the chambers, it is surrounded by endolymph. It is located in the two chambers of the vestibule; utricle and saccule. It’s function is to maintain balance, since endolymph tends to remain stationary when the head moves.

Question 30

What is the function of the semicircular canals? Describe the crista ampullaris and its mode of operation.

Answer 30

Function: enables the person to detect movements in any direction
The crista ampullaris is the sensory organ of rotation. They are found in the ampullae of each of the semicircular canals of the inner ear, meaning that there are 3 pairs in total. The function of the crista ampullaris is to sense angular acceleration and deceleration.