Download The Mechanical Senses

Chapter 6
Other Sensory Systems
Module 6.1:
Audition
Module 6.2:
The Mechanical Senses
Module 6.3
The Chemical Senses
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.
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.
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.
Anatomy of the Ear
• The ear is
divided into 3
parts:
– Outer ear
– Middle ear
– Inner ear
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
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)
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
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
Neuroanatomy Handout #5:
The Auditory System
• Organ of Corti (K)
– Hair cells and two
surrounding
membranes in the
cochlea
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
Audition
• Auditory nerve (M)
– exits the inner ear
and carries
information about
sound to the
auditory cortex
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).
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…
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.
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
Hearing Loss
•
About 99% of hearing impaired people have at
least some response to loud noises.
• Two categories of hearing impairment include:
1. Conductive or middle ear deafness
2. Nerve deafness
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.
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
Audition
• Tinnitus: frequent or constant ringing in the ears
– Experienced by many people with nerve
deafness
– Sometimes occurs after damage to cochlea
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
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)
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.
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
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
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
The Mechanical Senses
Touch receptors can
be:
• simple bare neurons
(pain, warm, cold)
• elaborated neuron
ending (pressure)
• bare ending
surrounded by nonneural cells that
modify its function
(pressure)
The Mechanical Senses
• Pacinian corpuscle:
type of touch receptor
that detects sudden
displacement or highfrequency vibrations
on skin
• Mechanical pressure
bends membrane
– increases flow of
sodium ions and
triggers an action
potential
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 generelated peptide).
– Substance P results in the increased
intensity of pain.
The Mechanical Senses
• Emotional pain can activate
the same neural pathways
as physical pain
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
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
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
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.
The Chemical Senses: Taste
• Taste receptors
– modified skin cells
– excitable
membranes release
neurotransmitters
and excite
neighboring neurons
– replaced every 10 to
14 days
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.
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).
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.
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
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.
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
Integration of the Senses
• Synesthesia is the
• Optional
documentary,
experience of one sense in
“The Boy with
response to stimulation of a
the Incredible
different sense.
Brain” (48m):
– Suggests some axons
https://www.youtu
be.com/watch?v=
from one area have
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branches to other
cortical regions.
– Video clip, “Seeing Life
in Colors: Crosswired
Senses” (3m):
http://www.youtube.com/watch?v=KA
pieSGlyBk&feature=related