Chapter 6: The Peripheral Nervous System: Afferent Division; Special Senses

Question 1

Stimulus

Answer 1

• change detectable by the body
• afferent neurons have sensory receptors at their peripheral endings
• responds to stimuli in both the external world and the internal environment
• stimuli bring about receptor potentials in the receptor
• sensory transduction

Question 2

Types of receptors

Answer 2

• photoreceptors
• mechanoreceptors
• thermoreceptors
• osmoreceptors
• chemoreceptors
• nociceptors

Question 3

Receptor Potential

Answer 3

• stimulus alters the receptor’s permeability
• receptor potentials may initiate action potentials in the afferent neuron
• large receptor potential triggers opening of voltage-gated Na+ channels

Question 4

Types of receptors according to their speed of adaption

Answer 4

• tonic and phasic receptors

Question 5

Tactile Receptors

Answer 5

• mechanoreceptors
• hair receptors, Merkel’s disc, Pacinian corpuscle, Ruffini endings, and Meissner’s corpuscle
• mechanism of adaption in Pacinian corpuscle
• receptor ending consisting of concentric layers of connective tissue wrapped around the peripheral terminal of an afferent neuron

Question 6

Somatosensory Pathways

Answer 6

• visceral afferents carry subconscious input
• sensory afferents carry conscious input
• each somatosensory pathway is labelled according to modality and location
  Labelled Lines: first-order, second-order, and third-order sensory neurons
  Phantom Pain: may arise from extensive remodeling of the brain region that originally handled sensation

Question 7

Acuity and Perception

Answer 7

Acuity: influenced by receptive field size and lateral inhibition
Receptive Field- region of the skin surface surrounding the somesthetic sensory neuron
Lateral inhibition- each activated signal pathway inhibits the pathways next to it
Perception: conscious awareness of surroundings
- derived from interpretation of sensory input

Question 8

Pain

Answer 8

• primarily a protective mechanism triggered on stimulation of danger-sensing nociceptors
• brings to conscious awareness tissue damage that is occurring or about to occur
• storage of painful experiences in memory helps us avoid potentially harmful events in the future

Question 9

Pain and Nociceptors

Answer 9

• stimulation of nociceptors elicits the perception of pain, and motivational and emotional responses
• categories of pain receptors: mechanical, thermal, and polymodal
• fast and slow afferent pain fibers: delta fibers and C fibers
• higher-level processing of pain input: substance P and glutamate

Question 10

The brain has a build-in analgesic system

Answer 10

• suppress transmission in the pain pathways as they enter the spinal cord
• endorphins released during exercise
• stress-induced analgesia
• acupuncture analgesia

Question 11

Eye: Vision

Answer 11

• eyes capture patterns of illumination in the environment as an optical picture on a layer of light-sensitive cells, the retina
• coded image on the retina is transmitted through the steps of visual processing until it is finally consciously perceived

Question 12

Eye: Protective Mechanisms and Layers

Answer 12

• protective mechanisms help prevent eye injuries
• eyelids and eyelashes
• tears and lacrimal gland
• the eye is a fluid-filled sphere enclosed by three specialized tissue layers
• sclera/cornea
• choroid/ciliary body/iris
• retina

Question 13

Eye: processing Light

Answer 13

• the amount of light entering the eyes is controlled by the iris
• thin, pigmented, smooth muscle
• form a visible ringlike structure within the aqueous humor
• the eye refracts entering light to focus the image on the retina
• process of refraction
• the eye’s refractive structures

Question 14

Eye: Accomodation

Answer 14

• increases the strength of the lens for near vision
• strength of the lens depends on its shape
• regulated by the ciliary muscle
• light must pass through several retinal layers before reaching the photoreceptors

Question 15

Eye: Phototransduction

Answer 15

• by retinal cells converts light stimuli into neural signals
• photoreceptors consists of an outer/inner segment and synaptic terminal
• rod and cone cells

Question 16

Eye: Rods and Cone

Answer 16

• rods provide indistinct gray vision at night
• cones provide sharp color vision during the day
• rods have high sensitivity; cones have lower sensitivity
• cone vision has high acuity; rod vision has low acuity
• cones provide color vision; rods provide vision in shades of gray

Question 17

Eye: Color and Adaption

Answer 17

• color vision depends on the ratios of stimulation of the three cone types
• each cone type is most effectively activated by a particular wavelength of light in the range of color indicated by its name
• trichromatic theory and opponent-process theory
• the sensitivity of the eyes can vary markedly through dark and light adaption

Question 18

Eye: Visual Information Processing

Answer 18

• visual information is modified and separated before reaching the visual cortex
  Visual Field: field of view that can be seen without moving the head
• the thalamus and visual cortex elaborate the visual message
• depth perception
  -hierarchy of visual cortical processing

Question 19

Eye: Other Sensory Processing

Answer 19

• visual input goes to other areas of the brain not involved in vision perception
• non-sight activities depend on input from the rods and cones
• some sensory input may be detected by multiple sensory-processing areas in the brain
• brain regions devoted almost exclusively to a certain sense actually receive a variety of sensory signals

Question 20

Ear: Hearing and Equilibrium

Answer 20

• ear consists of 3 parts
• external, the middle, and inner ear
• sound waves consist of alternate regions of compression and rarefaction of air molecules
  Hearing: neural perception of sound energy
  Sound Waves: traveling vibrations of hair
  Sound Characteristics: pitch (tone), intensity (loudness), and timbre (quality)

Question 21

Ear: External Ear

Answer 21

• plays a role in sound localization
• consists of the pinna (ear), external auditory meatus (ear canal), and tympanic membrane (eardrum)
• tympanic membrane vibrated in unison with sound waves in the external ear
• stretched across the entrance to the middle
• vibrates when struck by sound waves

Question 22

Ear: Middle Ear

Answer 22

• middle ear bones convert tympanic membrane vibrations into fluid movements in the inner ear
• facilitated by a moveable chain of three small bones, or ossicles
  Malleus
  Incus
  Stapes

Question 23

Ear: Cochlea and Organ of Corti

Answer 23

• contains the organ of corti, the sense organ for hearing
  Cochlea: pea-sized, snail-shaped, hearing portion of the inner ear
• hair cells in the organ of the corti transduce fluid movements into neural signals
• role of the inner/outer hair cells

Question 24

Ear: Discrimination

Answer 24

• pitch discrimination depends on the region of the basilar membrane that vibrates
• ability to distinguish among various frequencies of incoming sound waves
• loudness discrimination
• depends on the amplitude of vibration
• the auditory cortex is mapped according to tone
• tonotopically organized

Question 25

Ear: Loss of Hearing and Equilibrium

Answer 25

• deafness is caused by defect in either conduction or neural processing of sound waves
• loss of hearing
• the vestibular apparatus is important for equilibrium by detecting head position and motion
• role of the semicircular canals and the otolith organs

Question 26

Chemical Senses: Taste and Smell

Answer 26

Chemoreceptors: receptors for taste and smell
- generate neural signals on binding with particular chemicals in their environment
Sensations of taste and smell associated with food intake
- influence flow of digestive juices and affect appetite
- induces pleasurable or objectionable sensations: seek or avoid

Question 27

Chemical Senses: Taste

Answer 27

• taste receptor cells are located primarily within tongue taste buds
• bud consists of about 50 long, spindle-shaped taste receptor cells
• packaged with supporting cells in an arrangement like slices of an orange
• taste discrimination is coded by patterns of activity in various taste bud receptors
• salty, sour, sweet, bitter, and umami tastes

Question 28

Chemical Senses: Other Areas of Taste

Answer 28

• the gut and airways taste
• cells in the stomach and intestine have same GPCRs and gustducin-activated pathways for tasting
• the olfactory receptors in the nose are specialized endings of renewable afferent neurons
• olfactory receptor cells, supporting cells, and basal cells

Question 29

Chemical Senses: Smell

Answer 29

• various parts of an odor are detected by different olfactory receptors and sorted into smell files
• separate components of an odor are sorted into different glomeruli
• one component per file
• odor discrimination is coded by patterns of activity in the olfactory bulb glomeruli
• each odorant activates multiple receptors and glomeruli in response to odor components

Question 30

Chemical Senses: Adaptation

Answer 30

• olfactory system adapts quickly and odorants are rapidly cleared
• sensitive, highly discriminating and quickly adaptive
• the vomeronasal organ detects pheromones
• nonvolatile chemical signals passed subconsciously between individuals of the same species

Question 31

On a very hot day in July, you buy a nice, cold canned diet drink containing an artificial sweetener. Upon drinking the beverage you experience a bitter taste instead of the normal sweet taste. How would you explain this?

Answer 31

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Question 32

A patient complains of severe dizziness when riding the elevator to her job on the 15th floor. Explain how she could solve this problem without walking up the stairs.

Answer 32

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