Transcript Neurobiology of the Senses

Types of Sensory Neurons
• PHYSICAL:
• Photoreceptors (for
vision)
• Mechanoreceptors
(for touch & hearing)
• CHEMICAL:
• Also known as
“Chemoreceptors”:
• Odor receptors
(for smell)
• Gustatory receptors
(for taste)
Taste buds contain sensory
neurons w/ taste receptors
Hearing
• Exploring the structure of the human ear
1
2 The middle ear and inner ear
Overview of ear structure
Incus
Middle
ear
Inner ear
Outer ear
Skull
bones
Semicircular
canals
Stapes
Malleus
Auditory nerve,
to brain
Pinna
Tympanic
membrane
Auditory
canal
Hair cells
Cochlea
Eustachian
tube
Tectorial
membrane
Tympanic
membrane
Oval
window
Eustachian
tube
Round
window
Cochlear duct
Bone
Vestibular canal
Auditory nerve
Basilar
membrane
Figure 49.8
Axons of
sensory neurons
4 The organ of Corti
To auditory
nerve
Tympanic canal
3 The cochlea
Organ of Corti
Hair cells containing mechanoreceptors
are inside the cochlea
Cochlea
Stapes
Axons of
sensory
neurons
Oval
window
Vestibular
canal
Perilymph
Apex
Base
Round
window
Tympanic
canal
Basilar
membrane
Cochlea
(uncoiled)
Basilar
membrane
Apex
(wide and flexible)
500 Hz
1 kHz (low pitch)
2 kHz
4 kHz
8 kHz
16 kHz
(high pitch)
Base
(narrow and stiff)
Frequency
producing maximum
vibration
The Vertebrate Eye
• The structure of the vertebrate eye
Sclera
Choroid
Retina
Ciliary body
Fovea (center
of visual field)
Suspensory
ligament
Cornea
Iris
Optic
nerve
Pupil
Aqueous
humor
Lens
Vitreous humor
Central artery and
vein of the retina
Figure 49.18
Optic disk
(blind spot)
• Humans and other mammals
– Focus light by changing the shape of the
lens
Front view of lens
and ciliary muscle
Lens (rounder)
Ciliary muscles contract, pulling
border of choroid toward lens
Choroid
Suspensory ligaments relax
Retina
Ciliary
muscle
Lens becomes thicker and rounder,
focusing on near objects
Suspensory
ligaments
(a) Near vision (accommodation)
Ciliary muscles relax, and border of
choroid moves away from lens
Suspensory ligaments
pull against lens
Lens becomes flatter, focusing on
distant objects
Figure 49.19a–b
(b) Distance vision
Lens (flatter)
Lateral view of the vertebrate
eye
2 Types of Photoreceptors:
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RODS:
More numerous (125 x 106)
More sensitive to light
Responsible for night vision
Absent from the fovea
Lower resolution
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CONES:
Less numerous
Sensitive to (wavelength)
Responsible for color vision
Come in 3 types: red, green,
blue (photopsins)
• Higher resolution
Photoreceptors in the retina
Looking inside a
photoreceptor
Retinal pigment changes
shape when light strikes it
Signal Transduction in Rods
Light
EXTRACELLULAR
FLUID
INSIDE OF DISK
Active rhodopsin
PDE
• Absorption of light by retinal
Membrane
potential (mV)
– Triggers a signal transduction pathway
CYTOSOL
Plasma
membrane
0
Dark Light
Inactive rhodopsin
Transducin
cGMP
Disk membrane
– 40
GMP
Na+
1 Light
isomerizes
retinal, which
activates
rhodopsin.
Figure 49.21
2 Active
rhodopsin
in turn
activates a G
protein called
transducin.
3 Transducin
activates the
enzyme phosphodiesterae(
PDE).
4 Activated PDE
detaches cyclic
guanosine
monophosphate
(cGMP) from
Na+ channels in
the plasma
membrane by
hydrolyzing
cGMP to GMP.
– 70
– Hyperpolarization
Time
Na+
5 The Na+ channels
close when cGMP
detaches. The
membrane’s
permeability to
Na+ decreases,
and the rod
hyperpolarizes.
• Three other types of neurons contribute
to information processing in the retina
– Ganglion cells, horizontal cells, and
amacrine cells
Retina
Optic nerve
To
brain
Retina
Photoreceptors
Neurons
Cone Rod
Amacrine
cell
Figure 49.23
Optic
nerve
fibers
Ganglion
cell
Horizontal
cell
Bipolar
cell
Pigmented
epithelium
A bird’s eye view…
An overview of visual
processing
Message travels from RETINA
to VISUAL CORTEX (oc.lobe)
The brain tries to make sense
of missing visual information
Which yellow line is longer?
The brain applies perspective to understand different sizes