Chapter 6 Other Sensory Systems

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Chapter 6 Other Sensory Systems

• Module 6.1

• Audition

Module 6.2
The Mechanical Senses

• Module 6.3

• The Chemical Senses

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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.

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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.

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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.

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Anatomy of the Ear

• The ear is divided into 3 parts
• Outer ear
• Middle ear
• Inner ear

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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

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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)

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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

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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

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Neuroanatomy Handout 5 The Auditory System

• Organ of Corti (K)
• Hair cells and two surrounding membranes in the
  cochlea

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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

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Audition

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

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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).

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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

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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.

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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

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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

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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.

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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

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Audition

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

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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

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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)

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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.

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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

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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

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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

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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)

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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

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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.

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The Mechanical Senses

• Emotional pain can activate the same neural
  pathways as physical pain

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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

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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

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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

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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.

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The Chemical Senses Taste

• Taste receptors
• modified skin cells
• excitable membranes release neurotransmitters and
  excite neighboring neurons
• replaced every 10 to 14 days

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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.

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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).

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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.

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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

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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.

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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

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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) http//www.youtube.com/watch?vKApi
  eSGlyBkfeaturerelated

• Optional documentary, The Boy with the
  Incredible Brain (48m)

https//www.youtube.com/watch?v_N7eV7wXm-w