Download The Mechanical Senses

Chapter 7
The Other Sensory
Systems
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
Fig. 7-3, p. 192
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.
• Place theory - each
area along the basilar
membrane is tuned to
a specific frequency of
sound wave.
Theories of Pitch Perception
• The current pitch theory combines modified
versions of both the place theory and
frequency theory:
– Low frequency sounds best explained by
the frequency theory.
– High frequency sounds best explained by
place theory.
Theories of Pitch Perception
• Volley principle states that the auditory nerve
can have volleys of impulses (up to 4000 per
second) even though no individual axon
approaches that frequency by itself.
– provides justification for the place theory
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:
– Vestibular sensation (balance)
– Touch
– Pain
– Other body sensations
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 and includes:
– discriminative touch
– deep pressure
– cold
– warmth
– pain
– itch
– tickle
– position and movement of joints
The Mechanical Senses
• Touch receptors can
be:
– simple bare
neurons
– elaborated neuron
ending
– bare ending
surrounded by nonneural cells that
modify its function
Fig. 7-11, p. 201
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
• 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 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 substance P.
– Substance P results in the increased
intensity of pain.
– Morphine and opiates block pain by
blocking these neurotransmitters.
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.
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
• Which part of the brain helps process
information about smell?
– 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: Smell
The Chemical Senses: The VNO
• Vomeronasal organ (VNO): set of
receptors located near the olfactory
receptors that are sensitive to pheromones
• Pheromones: chemicals released by an animal to
affect the behavior of others of the same species
– 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
experience of one
sense in response
to stimulation of a
different sense.
– Suggests some
axons from one
area have
branches to other
cortical regions.