Somatic Senses and Special Senses

Question 1

Define sensation and perception, and discuss the components of sensation.

Answer 1

Sensation:

• conscious or subconscious awareness of changes in the external or internal environment

Perception:

• conscious awareness and interpretation of sensations
  
  • primarily a function of the cerebral cortex

For a Sensation to occur, 4 steps must happen which include.

1. Sensory Activation
   
   1. stimulus must be strong enough to activate sensory neurons can be from
      
      • light
      • heat
      • pressure
      • mechanical energy
      • chemical energy
2. Electrical Signal
   
   • sensory receptor must convert stimulus to electrical signal
3. Neural pathway conduction
   
   • nerve impulse must conduct along neural pathway from receptor to brain
4. Brain Receives and integrates
   
   • region of brain must recieve and integrate the impulse to a sensation

Question 2

What are the Senses the body sends to the CNS system.

Answer 2

Speical Senses, structures associated with

• smell
• taste
• balance
• hearing
• vision

General Senses consist of somatic and viseral senses

• somatic senses
  
  • tactile sensations
    
    • touch
    • pressure
    • vibrations
  • termal sensations
    
    • warm
    • cold
  • pain sensation
  • proprioceptive sensations
    
    • muscle
    • joint position
• Visceral Senses
  
  • provide info for internal conditions of organs

Question 3

Describe the types of sensory receptors.

Answer 3

Free Nerve Endings

• simplest type of receptor
• dendrites lack special structures
• receptors for
  
  • pain
  • temperature
  • tickle
  • itch
  • some touch sensations

Encapsulated Nerve Endings

• have encapsulated endings
• dendrites covered in connective tissue structure
• receptors for other somatic and visceral sensations
  
  • touch
  • pressure
  • vibration

Separate Cells

• specialized separate cells that synapse with sensory neurons
  
  • eg: hair cells on the inner ear

Question 4

Describe the location and function of the receptors for tactile, thermal, and pain sensation.

Answer 4

Tactile Receptors: (mechanoreceptors)

• Corpsulses of Touch (Meissner corpuscles)
  
  • found in the papillary layer of the dermis
  • responsible for touch and low-frequency vibrations
• Hair Root Plexus
  
  • Found surrounding a hair follicle
  • detects motion on the skin surface
• Type 1 cutaneous mechanoreceptors
  
  • found in stratum Basale layer of skin
  • continuous touch/ pressure
• Type 2 cutaneous mechanoreceptors
  
  • Found in the dermis, subcutaneous, and other body tissues
  • senses tissue stretching and pressure
• Lamellated Corpuscles
  
  • Found in the dermal and subcutaneous layer of skin
  • sense high-frequency vibrations
• Free Nerve
  
  • found in the epidermal and dermal layers
  • senses pain, itch, tickle, warmth, cold

Thermal Sensations (thermoreceptors)

• Cold Free Nerve endings
  
  • located in the epidermal layer of skin
  • detect cold in temperatures of 10-35 degrees
• Warm Free Nerve Endings
  
  • located in the dermal layer of skin
  • detect warmth in temperatures of 30-45 degrees

Pain Sensations (nociceptors)

• located in every tissue except the brain
• Free nerve endings
• responds to
  
  • excessive stimulation of sensory receptors
  • excessive stretching,
  • prolonged muscle contraction
  • inadequate blood to organs
  • certain chemical substances

Question 5

Name the five special senses.

Answer 5

• Balance
• Vision
• Smell
• Taste
• Hearing

Question 6

State the Location and function of proprioceptive sensation.

Answer 6

Location:

• Receptors for proprioception are located in the
  
  • Skeletal Muscles
  • tendons,
  • around joints,
  • in the internal ear

Function

• conveys nerve impulses related to
  
  • muscle tone,
    
    • movement of body parts
    • body position.
• the proprioceptive or kinesthetic sense
  
  • provides awareness of the activities of
    
    • muscles,
    • tendons
    • joints
    • balance/equilibrium.

Question 7

Define the term olfaction; name the type of sensory receptors involved in olfaction; name the location of these receptors; and identify the responsive portion of these receptors.

Answer 7

Olfaction:

• 10-100 million receptors in the nose that are responsible for the sense of smell.

Located:

• in the upper portion of the nasal cavity

Consists of 3 types of cells.

• Olfactory receptor cells
  
  • olfactory cilia are responsive portion of this receptor
• supporting cells
  
  • found btw olfactory receptor cells
  • provide support, nourishment, and conductivity to olfactory receptor cells
• basal cells
  
  • stem cells
  • located btw the bases of supporting cells.
  • produce new olfactory cells

Question 8

With respect to a stimulated olfactory chemoreceptor, track the nerve impulse to its site of interpretation in the brain.

Answer 8

Olfactory receptors convey nerve impulses to

1. olfactory nerves,
2. olfactory bulbs,
3. olfactory tracts,
   
   • the temporal lobe of the cerebral cortex,
   • the limbic system.

Question 9

Define gustation; name the type of sensory receptors involved in gustation; name the location of these receptors, and identify the responsive portion of these receptors.

Answer 9

Gustation

• the term used for the sensation of taste.

Function:

• To be detected, molecules must be dissolved.
• Taste stimuli classes are
  
  • sour,
  • sweet,
  • bitter,
  • salty
  • umami.
  • Other “tastes” are a combination of the five taste sensations plus olfaction.

The receptors for gustation, the gustatory receptor cells, are located in the taste buds.

• The taste buds consist of
  
  • gustatory receptor cells
  • Support Cells
  • Basal Cells.
• Receptor potentials developed in gustatory hairs cause the release of neurotransmitters,
  
  • give rise to nerve impulses.

Question 10

With respect to a stimulated gustatory chemoreceptor, track the nerve impulse to its site of interpretation in the brain

Answer 10

Gustatory receptor cells convey nerve impulses to

• cranial nerves VII, IX, and X;
• the medulla;
• the thalamus;
• the parietal lobe of the cerebral cortex.

Question 11

List and describe the accessory organs of the eye in terms of their names, location, and functions.

Answer 11

Accessory Organs of the eye Include;

• Eyelids
  
  • shade eyes
  • protect from excessive light and objects
  • spreads lubricant
  • composed of the conjunctiva
    
    • thin mucous membrane that lines the inner aspect of the eyelids
    • reflected onto the anterior surface of the eyeball.
• Eyelashes and Eyebrows
  
  • help protect the eyeballs from
    
    • foreign objects
    • perspiration
    • direct rays of the sun.
• extrinsic muscles
  
  • allow movement of the eyeballs
• lacrimal apparatus
  
  • consists of structures that produce and drain tears.

Question 12

Name the three tunics of the eye; give a general function for each, and name the specific components of each tunic.

Answer 12

The eyeball is constructed of three layers:

• fibrous tunic,
• vascular tunic,
• retina.

Fibrous tunic

• is the outer coat of the eyeball.
• It can be divided into the following two regions:

1. Posterior sclera
   
   • At the junction of the sclera and cornea is an opening known as the scleral venous sinus or canal of Schlemm.
   • makes up the white of the eye
   • composed of dense fibrous tissue that covers the entire eyeball
   • gives shape to the eyeball
   • protects the inner portion of the eye
   • The posterior surface is pierced by the optic nerve
2. Anterior cornea

• nonvascular, transparent, fibrous coat through which the iris can be seen.
• The cornea refracts light.

Vascular tunic

• is the middle layer of the eyeball,
• composed of the following three parts

1. Choroid
   
   • absorbs light rays so that they are not reflected and scattered within the eyeball
   • provides nutrients to the posterior surface of the retina
2. Ciliary body
   
   • composed of 2 structures
   1. Ciliary muscle
      
      • smooth muscle that alters the shape of the lens for near or far vision.
   2. Ciliary processes
      
      • consist of protrusions or folds on the internal surface of the ciliary body
      • epithelial lining cells secrete aqueous humor
3. Iris
   
   • coloured portion seen through the cornea
   • there are 2 parts
     
     • circular iris smooth muscle fibres (cells)
     • radial iris smooth muscle fibres (cells)
       
       • arrange to form a doughnut-shaped structure.
   • The pupil is the black hole in the centre of the iris,
     
     • the area through which light enters the eyeball.
     • regulates the amount of light entering the posterior cavity of the eyeball (see Fig. 12.7).

Retina (nervous tunic)

• the inner coat of the eye lines the posterior three-quarters of the eyeball
• beginning of the visual pathway.
• The optic disc is the site where the optic nerve enters the eyeball.
• consists of 2 layers
  
  1. Pigmented layer (nonvisual portion
     
     • aids the choroid to absorb stray light rays
  2. Neural layer (visual portion). The pigmented layer.
     
     • contains three zones of neurons;
     • named in the order in which they conduct nerve impulses
       
       • the photoreceptor layer
       • bipolar cell layer
       • ganglion cell layer

Question 13

Identify the location of the lens, and state its function.

Answer 13

Location:

The eyeball contains the nonvascular lens, which is located behind the pupil and iris.

Function:

The Lens fine-tunes light rays in order to create clarity of vision.

Question 14

Compare and contrast the two types of photoreceptors of the retina of the eye.

Answer 14

The photoreceptor layers are called rods or cones because of the different shapes of their outer segments.

Rods:

• specialized for black-and-white vision in dim light;
• enable discrimination between different shades of dark and light,
• permit us to see shapes and movement.

Cones:

• Cones are specialized for colour vision and sharpness of vision (high visual acuity) in bright light;
• most densely concentrated in the central fovea,
  
  • a fovea is a small depression in the centre of the macula lutea.
  • The macula lutea is in the exact centre of the posterior portion of the retina;
    
    • it corresponds to the visual axis of the eye.
  • The fovea is the area of sharpest vision due to its high concentration of cones.
  • Rods are absent from the fovea and macula and increase in density toward the periphery of the retina.

Question 15

Explain why we possess a blind spot

Answer 15

• The optic disc does not contain rods or cones
• when light strikes this area of the eye, an image is not formed.

Question 16

Explain how the eye is divided into cavities and chambers, and name the fluid that fills each.

Answer 16

The interior of the eyeball is a large space divided into two parts:

• the anterior cavity
  
  • lies in behind cornea and in front of lens
  • filled with aqueous humor
    
    • a watery fluid
    • the cilary process behind the iris constantly secretes this fluid
• the vitreous chamber
  
  • posterior to the lens.
  • is the larger cavity of the eyeball that lies between the lens and the retina
  • contains a gel called the vitreous body
    
    • formed during embryonic life and is not replaced thereafter.

The aqueous humor flows forward from the posterior chamber through the pupil into the anterior chamber, and drains into the scleral venous sinus (canal of Schlemm) and then into the blood.

The aqueous humor is mainly responsible for producing the pressure in the eye called the intraocular pressure. The intraocular pressure, along with the vitreous body, maintains the shape of the eyeball and keeps the retina smoothly applied to the choroid to produce clear images.

Glaucoma, excessive intraocular pressure, causes a degeneration of the retina and blindness.

Question 17

Discuss the physical principles involved in image formation, and list four abnormalities of refraction.

Answer 17

Image formation

• on the retina
• involves the refraction of light rays by the cornea and lens,
• the accommodation of the lens,
• the constriction of the pupil.

Refraction is the bending of light rays at the interface of two different media to focus on the retina.

• The anterior and posterior surfaces of the cornea
• the lens refracts incoming light rays

Accommodation is an increase in the curvature of the lens,

• initiated by ciliary muscle contraction that enables the lens to focus on near objects.

The constriction of the pupil narrows the diameter of the hole through which light enters the eye.

• This process occurs simultaneously with the accommodation of the lens,
• functions to prevent light rays from entering the eye through the periphery of the lens.

4 abnormalities of refraction:

• Presbyopia is an inability to read print at close range.
  
  • Myopia is nearsightedness.
  • Hypermetropia is farsightedness.
• Astigmatism is a refraction abnormality due to an irregular curvature of either the cornea or lens.
• Convergence occurs when both eyes focus on a single object.

Question 18

Discuss the physiology of vision: trace a photon of light from where it penetrates the cornea of the eye to where it is interpreted in the brain.

Answer 18

The first step in vision is the absorption of light by the photopigments (visual pigments) in the rods and cones (photoreceptors).

Photopigments are coloured proteins that undergo structural changes when they absorb light.

The single type of photopigment in rods is called rhodopsin. Three different types of cones exist, and each type contains a different kind of photopigment.

All the photopigments involved in vision contain a glycoprotein called opsin, and a derivative of vitamin A called retinal.

Retinal is the light-absorbing component of all visual photopigments.

Opsins exist as four different types―one for each cone photopigment and one for rhodopsin.

When receptor potentials develop in rods and cones, they release neurotransmitters that induce graded potentials in bipolar cells.

Bipolar cells transmit both inhibitory and excitatory signals to ganglion cells, which depolarize and initiate nerve impulses.

Impulses from ganglion cells are conveyed through the retina to the optic nerve, the optic chiasma, the optic tract, the thalamus, and the occipital lobes of the cortex.

Question 19

Name the three parts of the ear; list the specific components within each; and name a general function for these structures.

Answer 19

The ear includes the following three anatomical subdivisions:

The external (outer) ear collects sound waves and passes them inwards. It consists of the:

• Auricle (pinna)
• External auditory canal (meatus)
• Tympanic membrane (eardrum)

Ceruminous glands in the external auditory canal secrete cerumen (earwax) to help prevent dust and foreign objects from entering the ear.

The middle ear (tympanic cavity) is a small, air-filled cavity in the temporal bone that is lined by epithelium. It contains the:

• Auditory (Eustachian) tube
• Auditory ossicles (middle ear bones, the malleus, incus, and stapes)
• Oval window (border between middle ear and inner ear)

The internal (inner) ear, also called the labyrinth because of its complicated series of canals, includes:

Round window that leads into the labyrinth, which has two main divisions:

• An outer bony labyrinth that encloses
• An inner membranous labyrinth

The bony labyrinth is a series of cavities in the temporal bone. It can be divided into three areas based on shape:

• Semicircular canals (containing receptors for equilibrium)
• Vestibule (containing receptors for equilibrium)
• Cochlea (containing receptors for hearing)

The bony labyrinth, lined with periosteum, contains a fluid called perilymph. This fluid, chemically similar to cerebrospinal fluid, surrounds the membranous labyrinth.

The membranous labyrinth is a series of sacs and tubes lying inside, and having the same general form as, the bony labyrinth. The membranous labyrinth is lined with epithelium and contains a fluid called endolymph, which is chemically similar to intracellular fluid.

The vestibule is the oval central portion of the bony labyrinth. The membranous labyrinth in the vestibule consists of two sacs called the utricle and saccule.

Projecting upward and posteriorly from the vestibule are the three bony semicircular canals. Each is arranged at approximately right angles to the other two. The anterior and posterior semicircular canals are oriented vertically, whereas the lateral semicircular canal is oriented horizontally. One end of each canal enlarges into a swelling called the ampulla.

Anterior to the vestibule is the cochlea, which consists of a bony spiral canal that makes almost three turns around a central bony core called the modiolus.

Cross sections made through the cochlea show that it is divided into three channels by partitions that together have the shape of the letter Y.

The channel above the bony partition is the scala vestibuli, which ends at the oval window. The channel below is the scala tympani, which ends at the round window. The scala vestibuli and scala tympani both contain perilymph, and are completely separated except at an opening at the apex of the cochlea called the helicotrema.

The third channel (between the wings of the Y) is the cochlear duct (scala media). The vestibular membrane separates the cochlear duct from the scala vestibuli, and the basilar membrane separates the cochlear duct from the scala tympani. The spiral organ (organ of Corti), the organ of hearing, rests on the basilar membrane.

The tectorial membrane, a delicate and flexible gelatinous membrane, projects over and is in contact with the hair cells of the spiral organ.

Question 20

Define frequency and pitch as they apply to hearing

Answer 20

The frequency of a sound vibration is its pitch. Higher-pitched sounds have shorter wavelengths, and lower-pitched sounds like a bass guitar have longer wavelengths. The greater the intensity (size) of the vibration is, the louder the sound (as measured in decibels [dB]).

Question 21

Discuss the physiology of hearing: trace the pathway of sound from where sound waves reach the auricle to where they are interpreted in the brain.

Answer 21

The following steps describe the pathway of sound from the auricle to the brain:

1. The auricle directs sound waves into the external auditory canal.
2. Sound waves strike the tympanic membrane, causing it to vibrate.
3. The vibration conducts from the tympanic membrane through the ossicles, through the malleus to the incus, and then to the stapes.
4. The stapes vibrate, pushing the membrane of the oval window in and out.
5. The movement of the oval window sets up fluid pressure waves in the perilymph of the cochlea (scala vestibuli).
6. Pressure waves in the scala vestibuli are transmitted to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear.
7. As the pressure waves deform the walls of the scala vestibuli and scala tympani, they push the vestibular membrane back and forth and increase and decrease the pressure of the endolymph inside the cochlear duct.
8. The pressure fluctuations of the endolymph move the basilar membrane slightly, which moves the hair cells of the spiral organ against the tectorial membrane; the bending of the hairs produces receptor potentials that generate nerve impulses in the cochlear nerve fibres.

Differences in pitch are related to differences in the width and stiffness of the basilar membrane, and to the sound waves of various frequencies that cause specific regions of the basilar membrane to vibrate more intensely than others.

Hair cells convert a mechanical force (stimulus) into an electrical signal (receptor potential); hair cells also release neurotransmitters, which initiate nerve impulses.

Nerve impulses from the cochlear branch of the vestibulocochlear nerve pass to the cochlear nuclei in the medulla. Then, most impulses cross to the opposite side of the brain and travel to the midbrain, the thalamus, and finally to the auditory area of the temporal lobe of the cerebral cortex.

Question 22

Discuss the physiology of balance

Answer 22

Two kinds of equilibrium exist:

Static equilibrium refers to the maintenance of the position of the body (mainly the head) relative to the force of gravity.

Dynamic equilibrium is the maintenance of body position (mainly the head) in response to sudden movements, such as rotation, acceleration, and deceleration.

The maculae of the utricle and saccule are the sense organs of static equilibrium; however, they also contribute to some aspects of dynamic equilibrium by detecting linear acceleration and deceleration.

The maculae consist of hair cells―which function as sensory receptors―and supporting cells.

The three semicircular ducts, along with the saccule and utricle, maintain dynamic equilibrium.

The cristae in the semicircular ducts are the primary sense organs of dynamic equilibrium.

Question 23

What are taste buds? How do they work?

Answer 23

Taste buds

• found in the papillae on the tongue
• Papillae appear as elevations on the tongue,
  
  • classified as
    
    • circumvallate,
    • fungiform,
    • filiform.

Function:

• Receptor potentials developed in gustatory hairs cause the release of neurotransmitters,
  
  • give rise to nerve impulses.
• Individual gustatory receptors in certain regions of the tongue are more sensitive than others to the primary taste sensations.
• Taste thresholds vary for each of the primary tastes, with the threshold for bitter being the lowest, followed by sour, and finally salty and sweet.
  
  • Adaptation to taste occurs quickly with a loss of sensitivity occurring in 1 to 5 minutes of continuous stimulation.