1. Chapter 6 Other Sensory Systems
Module 6.1:
Audition
Module 6.2:
The Mechanical Senses
Module 6.3
The Chemical Senses

2. Audition: The Sense of Hearing
Physical stimulus: sound waves
Sound waves are periodic compressions of air, water or other media.
Sound waves are “transduced” into action potentials sent to the brain.

3. Audition
Amplitude refers to the height and subsequent intensity of the sound wave.
Loudness refers to the perception of the sound wave.
Amplitude is one factor.

4. Audition
Frequency refers to the number of compressions per second and is measured in hertz.
Related to the pitch (high to low) of a sound.

5. Anatomy of the Ear The ear is divided into 3 parts: Outer ear
Middle ear
Inner ear

6. Neuroanatomy Handout #5: The Auditory System
The outer ear includes:
pinna (pl: pinnae) (A):
focus sound waves into middle ear
help locate the source of a sound
external auditory canal (B):
pathway to middle ear

7. Neuroanatomy Handout #5: The Auditory System
The middle ear includes:
Tympanic membrane (C) (eardrum)
vibrates when struck by sound waves
3 middle ear bones transmit information to the inner ear:
malleus (D)
incus (E)
stapes (F)

8. Neuroanatomy Handout #5: The Auditory System The Inner Ear
The inner ear includes:
Oval window (G): a second membrane, like the eardrum
Semicircular canals (H): part of the vestibular system, involved in balance and equilibrium

9. Neuroanatomy Handout #5: The Auditory System
Cochlea (I): a snail shaped structure containing
three fluid-filled tunnels
auditory receptors (hair cells)
Hair cells: auditory receptors
(A,B) frogs
(C) cat
(D) lizard

10. Neuroanatomy Handout #5: The Auditory System
Organ of Corti (K)
Hair cells and two surrounding membranes in the cochlea

11. The Organ of Corti Hair cells (K1): auditory receptor cells
Supporting cells (K2): attached to flexible basilar membrane (L)
Tectorial membrane (J) is more rigid and runs along other end of hair cells

12. Audition Auditory nerve (M)
exits the inner ear and carries information about sound to the auditory cortex

13. Theories of Pitch Perception
Frequency theory - the basilar membrane vibrates in synchrony with the sound and causes auditory nerve axons to produce action potentials at the same frequency (explains low frequency range).
Place theory - each area along the basilar membrane is tuned to a specific frequency of sound wave (explains higher range).

14. Theories of Pitch Perception
Volley principle states that the auditory nerve can have volleys of impulses (up to 5000 per second) even though no individual axon approaches that frequency by itself.
There is power in numbers…

15. Audition
Which part of the brain helps process information about hearing?
Primary auditory cortex located in the superior temporal cortex
Each hemisphere receives most of its information from the opposite ear.

16. Audition The primary auditory cortex provides a tonotopic map
cells are responsive to preferred tones
Damage can lead to deficits processing auditory info:
loss of ability to identify a song or voice
It does not result in a loss of hearing

17. Hearing Loss
About 99% of hearing impaired people have at least some response to loud noises.
Two categories of hearing impairment include:
Conductive or middle ear deafness
Nerve deafness

18. Hearing Loss Conductive or middle ear deafness:
Bones of middle ear fail to transmit sound waves properly to cochlea
Caused by disease, infections, or tumerous bone growth near the middle ear.
Can be corrected by surgery or hearing aids that amplify the stimulus.

19. Hearing Loss Nerve or inner-ear deafness:
Results from damage to cochlea, hair cells or auditory nerve
Can be confined to one part of the cochlea
people can lose certain frequencies
Can be inherited or caused by prenatal problems or early childhood disorders

20. Audition Tinnitus: frequent or constant ringing in the ears
Experienced by many people with nerve deafness
Sometimes occurs after damage to cochlea

21. Sounds that cause hearing loss
Heavy city traffic = 90 decibels
Car horn = 110 decibels
Headphones = 120 decibels (common volume)
Jackhammer = 130 decibels
Rock band at close range = 140 decibels
Rocket launching = 180 decibels

22. The Mechanical Senses
Mechanical senses respond to pressure, bending, or other distortions of a receptor.
Mechanical senses include:
Audition (discussed in Module 6.1)
Vestibular sensation (balance/equilibrium)
Touch
Pain
Other body sensations (sense of kinesthesis, or movement, discussed in movement chapter)

23. The Mechanical Senses
The vestibular sense refers to the system that detects the position and the movement of the head.
Directs compensatory movements of the eye and helps to maintain balance.

24. The Mechanical Senses
Vestibular organ: in inner ear, adjacent to cochlea, consists of:
two otolith organs
calcium carbonate particles (otoliths) activate hair cells when head tilts
three semicircular canals
oriented in three different planes
filled with jellylike substance that activates hair cells when the head moves

25. The Mechanical Senses
Which part of the brain helps process information about our vestibular sense?
Angular gyrus
integrates balance and movement info with other sensations
Located at border between parietal and temporal cortex

26. The Mechanical Senses
Somatosensory system refers to sensation of the body and its movements:
Involves mechanoreceptors:
discriminative touch
deep pressure
pain
Itch
tickle
position and movement of joints
Involves thermoreceptors:
warm
cold

27. The Mechanical Senses Touch receptors can be:
simple bare neurons (pain, warm, cold)
elaborated neuron ending (pressure)
bare ending surrounded by non-neural cells that modify its function (pressure)

28. The Mechanical Senses
Pacinian corpuscle: type of touch receptor that detects sudden displacement or high-frequency vibrations on skin
Mechanical pressure bends membrane
increases flow of sodium ions and triggers an action potential

29. The Mechanical Senses
Pain depends on many axon types, neurotransmitters, and brain areas.
Mild pain triggers the release of glutamate.
Strong pain triggers the release of glutamate and several neuropeptides (including substance P and CGRP (calcitonin gene-related peptide).
Substance P results in the increased intensity of pain.

30. The Mechanical Senses
Emotional pain can activate the same neural pathways as physical pain

31. The Mechanical Senses
Itch occurs with damage and healing in the nervous system
Can signal individual to remove foreign object from skin
Histamines (chemical messengers) are released by individual and cause itchy feeling

32. The Mechanical Senses
Which part of the brain helps process information about touch?
Somatosensory cortex of parietal lobe
Info from touch receptors in head enters CNS through cranial nerves
Info from receptors below head enters spinal cord and travels through spinal nerves to brain

33. The Mechanical Senses 31 spinal nerves
each has a sensory component and a motor component
connects to a limited area of the body
Dermatome: the skin area connected to a single sensory spinal nerve

34. The Chemical Senses: Taste
Taste refers to the stimulation of taste buds by chemicals.
Our perception of flavor is the combination of both taste and smell.
Taste and smell axons converge in the endopiriform cortex.

35. The Chemical Senses: Taste
Taste receptors
modified skin cells
excitable membranes release neurotransmitters and excite neighboring neurons
replaced every 10 to 14 days

36. The Chemical Senses: Taste
Papilla(e): structure(s) on surface of tongue that contain up to 10 taste buds
Each taste bud contains approx. 50 receptors
Most taste buds are located along the outside of the tongue in humans.

37. The Chemical Senses: Taste
Western societies have traditionally described sweet, sour, salty and bitter tastes as the “primary” tastes and four types of receptors.
Evidence suggests a fifth type of glutamate receptor that detects savory taste (umami).

38. The Chemical Senses: Taste
Various areas of the brain are responsible for processing different taste information.
Somatosensory cortex responds to the touch aspect of taste
The insula is the primary taste cortex.

39. The Chemical Senses: Smell
Olfaction: detection and recognition of chemicals that contact membranes inside the nose
Olfactory cells: receptor cells for smell
Olfactory epithelium:
membrane in rear of nasal passage
Contains olfactory cells

40. The Chemical Senses: Smell
Neural processing:
Axons from olfactory receptors carry information to the olfactory bulb in the brain.
The olfactory bulb sends axons to many areas of the cerebral cortex.
Coding in the brain is determined by which part of the olfactory bulb is excited.

41. The Chemical Senses: The VNO
Pheromones: chemicals released by
an animal that affects the behavior of
others of the same species
Vomeronasal organ (VNO): set of receptors located near the olfactory receptors that are sensitive to pheromones
The VNO and pheromones are important for most mammals, but less so for humans
It is tiny in human adults and has no receptors.
Humans unconsciously respond to some pheromones through receptors in the olfactory mucosa.
Example: synchronization of menstrual cycles

42. Integration of the Senses
Synesthesia is the experience of one sense in response to stimulation of a different sense.
Suggests some axons from one area have branches to other cortical regions.
Video clip, “Seeing Life in Colors: Crosswired Senses” (3m):
Optional documentary, “The Boy with the Incredible Brain” (48m):