Download External ear

Лекция 18
ОРГАНЫ
ОЩУЩЕНИЯ
(продолжение)
Механорецепторы
СЛУХ
Ухо
• External ear
– Auricle or pinna:
elastic cartilage
– External auditory
meatus
• Lined with hairs
and ceruminous
glands
– Tympanic
membrane
• Vibrated by
sound waves
• Middle ear
– Auditory or
eustachian tube
• Opens into
pharynx,
equalizes
pressure
• Ossicles:
malleus, incus,
stapes:
transmit
vibrations
• Oval window
Ухо
человека
Ухо человека
• External ear: Hearing; terminates at eardrum
• Middle ear: Hearing; contains auditory ossicles
• Inner ear: Hearing and balance; interconnecting
fluid-filled tunnels and chambers
(a)
External ear
Middle ear
outer ear
bones of
middle ear
Inner ear
vestibular system
(detects head
movement and gravity)
The human
ear
auditory nerve
to brain
auditory
canal
(b)
tympanic
membrane
bony
cochlear
wall
oval
to
cochlea
window
pharynx
auditory
(beneath round
tectorial
tube
window
stirrup)
membrane
(Eustachian tube)
(c) tectoral
membrane
basilar
membrane
axons of
auditory nerve
basilar membrane
auditory
nerve
hair
cells
hair
cell
Вестибулярные и слуховые органы
человека
Scheme (inner ear,crossection):semisircular canal.
Hair cells, ampulla,cupula, vestibular nerve,
endolymph
Hair cells are the sensory receptors of both the
auditory system and the vestibular system in all
vertebrates. In mammals, the auditory hair cells
are located within the organ of Corti on a thin
basilar membrane in the cochlea of the inner
ear. They derive their name from the tufts of
stereocilia that protrude from the apical surface
of the cell, a structure known as the hair bundle,
into the scala media, a fluid-filled tube within the
cochlea. Mammalian cochlear hair cells come in
two anatomically and functionally distinct types:
the outer and inner hair cells. Damage to these
hair cells results in decreased hearing sensitivity,
i.e. sensorineural hearing loss.
Механосенсорные волосковые клетки
• Пучки волосков как детекторы звука
и усилители сигнала
• Внутренние волосковые клетки уха
проводят сигнал от звукового
колебания до нейронов мозга
• Внешние волосковые клетки уха аккустические усилители
Пучки волосков как звуковые детекторы и
умножители сигнала
• Outer hair cells do not send neural signals to the brain, but that
they mechanically amplify low-level sound that enters the
cochlea. The amplification may be powered by movement of
their hair bundles, or by an electrically driven motility of their
cell bodies. The inner hair cells transform the sound vibrations
in the fluids of the cochlea into electrical signals that are then
relayed via the auditory nerve to the auditory brainstem and to
the auditory cortex.
• Mammals apparently have conserved an evolutionarily earlier
type of hair-cell motility. This so-called hair-bundle motility
amplifies sound in all non-mammalian land vertebrates. It is
effected by the closing mechanism of the mechanical sensory
ion channels at the tips of the hair bundles. Thus, the same
hair-bundle mechanism that detects sound vibrations also
actively “vibrates back” and thereby mechanically amplifies
weak incoming sound.
Внутренние волосковые клетки – преобразование
звукового сигнала в нервный импульс
• The deflection of the hair-cell stereocilia opens mechanically gated ion
channels that allow any small, positively charged ions (primarily potassium
and calcium) to enter the cell. Unlike many other electrically active cells,
the hair cell itself does not fire an action potencial. Instead, the influx of
positive ions from the endolymph in Scala media depolarizes the cell,
resulting in a receptor potencial. This receptor potential opens voltage
gated calcium channels; calcium ions then enter the cell and trigger the
release of neurotransmitters at the basal end of the cell. The
neurotransmitters diffuse across the narrow space between the hair cell and
a nerve terminal, where they then bind to receptors and thus trigger action
potentials in the nerve. In this way, the mechanical sound signal is
converted into an electrical nerve signal. The repolarization in the hair cell
is done in a special manner. The perilymph in Scala tympani has a very low
concentration of positive ions. The electrochemical gradient makes the
positive ions flow through channels to the perilymph.
• Hair cells chronically leak Ca+2. This leakage causes a tonic release of
neurotransmitter to the synapses. It is thought that this tonic release is what
allows the hair cells to respond so quickly in response to mechanical
stimuli. The quickness of the hair cell response may also be due to that fact
that it can increase the amount of neurotransmitter release in response to a
change as little as 100 μV in membrane potential.
Внешние волосковые клетки – умножители звукового сигнала
• In mammalian outer hair cells, the receptor potential triggers active
vibrations of the cell body. This so-called somatic electromotility
consists of oscillations of the cell’s length, which occur at the
frequency of the incoming sound and in a stable phase relation.
Outer hair cells have evolved only in mammals. They have not
improved hearing sensitivity, which reaches similarly exquisite
values also in other classes of vertebrates. But they have extended
the hearing range from about 11 kHz (maximum in some birds) to
about 200 kHz (maximum in some marine mammals). They have
also improved frequency selectivity (frequency discrimination),
which is of particular benefit for humans, because it enabled
sophisticated speech and music.
• The molecular biology of hair cells has seen considerable progress
in recent years, with the identification of the motor protein (prestin)
that underlies somatic electromotility in the outer hair cells.
Prestin's function is dependent on chloride channel signalling and
that it is compromised by the common marine pesticide tributylin
(TBT). Because this class of pollutant bioconcentrates up the food
chain, the effect is pronounced in top marine predators such as
Orcas and toothed whales.
Структура улитки
(млекопитающие)
Колебания перегородки улитки
Настройка волосковой клетки
Нейральные контакты
• Neurons of the auditory or vestibulocochlear nerve (the VIIIth cranial
nerve) innervate cochlear and vestibular hair cells. The
neurotransmitter released by hair cells to stimulate the dendrites of
afferent neurons is thought to be glutamate. At the presynaptic
juncture, there is a distinct presynaptic dense body or ribbon. This
dense body is surrounded by synaptic vesicles and is thought to aid
in the fast release of neurotransmitter.
• Nerve fiber innervation is much denser for inner hair cells than for
outer hair cells. A single inner hair cell is innervated by numerous
nerve fibers, whereas a single nerve fiber innervates many outer
hair cells. Inner hair cell nerve fibers are also very heavily
myelinated, which is in contrast to the unmyelinated outer hair cell
nerve fibers.
• Efferent projections from the brain to the cochlea also play a role in
the perception of sound. Efferent synapses occur on outer hair cells
and on afferent (towards the brain) dendrites under inner hair cells.
The presynaptic terminal bouton is filled with vesicles containing
acetylcholine and a neuropeptide called Calcitonin gene-related
peptide (CGRP). The effects of these compounds varies, in some
hair cells the acetylcholine hyperpolarized the cell, which reduces
the sensitivity of the cochlea locally.
Зародыш млекопитающего
Развитие вестибулярного аппарата человека
Главные пути передачи звукового
сигнала
Соматосенсорный кортекс
(a)
hair cells
scar
(b)
Громкие
звуки могут
повреждать
волосковые
клетки
X hours before hearing can be damaged
loudness range
jet takeoff
(at 200 ft)
1/4
rock concert
subway, stereo headphones
(high volume)
motorcycle, lawn mower
2
8
urban street
normal talking
quiet
background
0
20
40
60
decibels
80
100
120
ВКУС
• Вкусовые рецепторы
организованы в виде
кластеров на языке
Вкус
• Detected by taste
buds
• Taste types
– Sour
– Salty
– Bitter
– Sweet
– Umami
(a) The human tongue
papillae
(b) Taste bud
epithelium
of tongue
taste
receptor
cells
microvilli
taste pore
supporting
cells
nerve fibers
to brain
Клетки вкусовых рецепторов находятся во
вкусовых сосочках
Развитие вкусовых сосочков
Нейрон
поддерживает
ионные
градиенты
Na+
Cl–
Na+
Cl–
Na+
K+
Org–
K+
K+
Org–
Org–
K+
K+
Org–
Cl–
Na+
Cl–
K+
(cytoplasm)
Na+
Na+
Org–
Cl–
Cl–
(extracellular fluid)
K+
axon
Механизмы передачи вкусовых
сигналов
Структура вкусовых сосочков. Taste buds (left) are composed of 50–150
taste-receptor cells (TRCs) depending on the species, distributed across
different papillae. b, Recent molecular and functional data shown there is no
tongue 'map' modalities are present in all areas of the tongue.
Различные модели восприятия
вкуса у мышей (Northcutt, 2004)
• a, In the labelled-line model, receptor cells are tuned to
respond to single taste modalities — sweet, bitter, sour, salty
or umami — and are innervated by individually tuned nerve
fibres. In this case, each taste quality is specified by the
activity of non-overlapping cells and fibres.
• b,c, Two contrasting models of what is known as the 'acrossfibre pattern'. This states that either individual TRCs are
tuned to multiple taste qualities (indicated by various tones of
grey and multicoloured stippled nuclei), and consequently the
same afferent fibre carries information for more than one taste
modality (b), or that TRCs are still tuned to single taste
qualities but the same afferent fibre carries information for
more than one taste modality (c). In these two models, the
specification of any one taste quality is embedded in a
complex pattern of activity across various lines. Recent
molecular and functional studies in mice have demonstrated
that different TRCs define the different taste modalities, and
that activation of a single type of TRC is sufficient to encode
taste quality, strongly supporting the labelled-line model.
Although many details of the development of the
innervation of taste buds are still unknown, it is now clear
that taste buds are induced from either ecto- or
endodermal epithelia, rather than arising from either
placodes or neural crest. At present, there are
two developmental models of taste bud induction: The
neural induction model claims that peripheral nerve
fibers induce taste buds, whereas the early specification
model claims that oropharyngeal epithelium is specified
by or during gastrulation and that taste buds arise from
cell-cell interactions within the specified epithelium.
There is now substantial evidence that the early
specification model best describes the induction of taste
buds.
Кора переднего мозга содержит
центры обработки первичных
сигналов вкуса, слуха и зрения