Transcript AP Chap 50 Sensory Perception

Sensory and Motor
Mechanisms
AP Chapter 50
Notice
• You do not need to know the specific
neuroanatomy of the sensory organs,
rather the mechanisms of how they work,
ie: type of receptors, generally how signal
is carried (by vibrations, photopigments,
etc), signaling mechanisms or opening of
ions channels. Even though more
information is included in the power
point, just read for information purposes.
The brain’s processing of sensory input and
motor output is cyclical rather than linear
• The way it ISN’T: sensing  brain analysis 
action.
• The way it is: sensing, analysis, and action are
ongoing and overlapping processes.
• Sensations begin as different forms of energy that
are detected by sensory receptors.
– This energy is converted to action potentials
that travel to appropriate regions of the brain.
• The limbic region plays a major role in
determining the importance of a particular sensory
input.
Sensory receptors transduce stimulus energy
and transmit signals to the nervous system
4 Functions common to all sensory
pathways
1.
2.
3.
4.
Sensory Reception
Sensory transduction
Transmission
Perception
Sensory receptors are categorized by the type of
energy they transduce.
Categories of sensory receptors
1. Mechanoreceptors – pressure, touch,
motion, sound, hair cells
2. Chemoreceptors
general – solute conc
specific – molecules; gustatory (taste),
olfactory (smell)
3. Electromagnetic
4. Thermoreceptors
5. Photoreceptors
6. Pain receptors – in humans, nociceptors in
epidermis, located in skin and other areas,
aspirin/ibuprofen blocks prostaglandins
Mechanoreceptors for hearing and equilibrium
• Utilize moving fluid and settling particles
• Mammals – pressure waves picked up by
ears and converted into nerve impulses
• Fish – lateral line systems
• Invertebrates – statocysts with ciliated
receptor cells with sand granules
• Insects – body hairs that vibrate, some have
ears
Our Hearing and Balance
• Energy of fluid into energy of action
potentials
• Uses sensitive hair cells
• True organ of hearing – the organ of
Corti located in the cochlea
• Balance – semicircular canals
Hearing animation
Hearing
http://msjensen.cehd.umn.e
du/1135/Links/Animations/F
lash/0019swf_effect_of_soun.swf
The three small bones transmit vibrations
To the inner ear which contains fluid-filled canals.
Air pressure vibrates fluid in canals which
vibrate the basilar membrane, bending the
hairs of its receptor cells against the
tectorial membrane which opens ion
channels and allows K+ to enter the cells
and cause a depolarization and releases
neurotransmitters to continue to the
auditory nerve to the brain.
Fig. 50-9
“Hairs” of
hair cell
–50 Receptor potential
Signal
Action potentials
0
–70
0 1 2 3 4 5 6 7
Time (sec)
(a) No bending of hairs
Less
neurotransmitter
–70
Signal
–70
Membrane
potential (mV)
–50
Membrane
potential (mV)
Signal
Sensory
neuron
More
neurotransmitter
0
–70
0 1 2 3 4 5 6 7
Time (sec)
(b) Bending of hairs in one direction
–50
Membrane
potential (mV)
Neurotransmitter at
synapse
–70
0
–70
0 1 2 3 4 5 6 7
Time (sec)
(c) Bending of hairs in other direction
Frequency (pitch) determined by
areas of basilar membrane that
vibrate at different frequencies;
areas are thick and thin
Volume is controlled by amplitude of wave –
stronger bends hair cells more and more
action potentials
The inner ear also contains the
organs of equilibrium
• Balance in the semicircular canals is also
a response to hair cells; different head
angles stimulate different.
• Hair cells; lateral line systems in fish and
some amphibians work like this too.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Many invertebrates have gravity sensors
and are sound-sensitive
• Statocysts are mechanoreceptors that function
in an invertebrates sense of equilibrium.
– Statocyst function
is similar to that of
human semicircular canals
– Use ciliated (hairlike cells)
Fig. 49.21
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
A diversity of
photoreceptors
has evolved
among
invertebrates.
Planaria – eyecup for
light and direction
Insects/crustaceanscompound eyes
(ommatidia)
Jellyfish, spider,
mollusks – single
lens eye
Taste and Smell
• Odor/taste molecules bind to ciliated
receptor cells and trigger a signaltransduction pathway that involves a Gprotein and, often, adenylyl cyclase and
cyclic AMP’s.
• cAMP to open Na+ channels,
depolarizing the membrane and
sending action potentials to the brain.
Fig. 49.24
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 50-13
Sugar molecule
G protein
Sweet
receptor
Tongue
Taste pore
Taste
bud
Sugar
molecule
Phospholipase C
SENSORY
RECEPTOR
CELL
PIP2
Sensory
receptor
cells
IP3
(second
messenger)
Sensory
neuron
Nucleus
ER
IP3-gated
calcium
channel
Ca2+
(second
messenger)
Sodium
channel
Na+
Vertebrate eyes
• Rods and cones are photoreceptors
located in the retina of the eye.
• Rods are more light sensitive and are
concentrated toward the edge of the
retina.
• Cones are more color sensitive and are
concentrated in the center of the visual
field called the
Vertebrates have single-lens eyes
• Is structurally analogous to the invertebrate
single-lens eye.
How does this work?
• Rods and cones synapse with bipolar
cells in the retina, which synapse with
ganglion cells, whose axons form the
optic nerve.
• R/C
BP
Ganglion Cells
Light hits the retina
and then comes back
through the cells to the
optic nerve.
Photoreceptors
Rods and cones have visual pigments
embedded in a stack of folded membranes or
disks in each cell.
Retinal is the light-absorbing
pigment and is bonded to a membrane
protein – opsin. Combo – rhodopsin.
When retinal absorbs light, it changes shape and
separates from opsin. In the dark, the retinal is
converted back to its original shape.
Opsin activates a G protein and opens/closes Na
channels to continue/discontinue the nerve
impulse.
Fig. 49.13
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Notice in the
light, the Na+
channels are
closed.
remember…
The ultimate perception of the stimulus
depends on the area of the brain that is
stimulated!
In summary:
Touch – mechanoreceptors, dendrites of
neurons pick up ions
Smell, taste – chemoreceptors, gen (solute
conc), specific (individual molecules), G
protein activates a second messenger
that controls a Na or K ion channel
Sight (light) – electroreceptors, trans
retinal activates a G protein cascade that
opens/closes Na channels
Hearing, balance –
mechanoreceptors, moving fluid,
settling particles, bending of hair
cells open ion channels
Locomotion and muscle action
The muscle cell’s structure is conducive to
its purpose which is to contract upon
receiving a stimulus.
How the muscle cell is organized
for energy
This is ONE
muscle cell,
called a
muscle fiber.
Animations
The muscle fiber (cell) is made up of many myofibrils
which in turn are made up of sarcomeres, the units of
contraction.
• The sarcoplasmic
reticulum (SR) is a
special type of
smooth ER found in
smooth and striated
muscle.
• The SR contains
large stores of
calcium ions, which
it releases when the
cell is depolarized.
Action potential
Is spread in the
T tubules
Fig. 50-25b
The contracting unit is the sarcomere.
TEM
M line
0.5 µm
Thick
filaments
(myosin)
Thin
filaments
(actin)
Z line
Z line
Sarcomere
This is what gives skeletal muscles and heart
muscles their striated appearance.
The sliding filament model
When the
sarcomere
contracts,
the filaments
slide over each
other.
Animation: Sarcomere
Contraction
How does this happen?
a closer look: Myosin
Myosin is made of
polypeptides
twisted to form a
fiber helix with a
globular end,
which has ATPase
activity & an affinity
to bind to actin.
a closer look: Actin
Actin is a globular
protein;
each globular
actin unit
contains a
myosin binding
site.
Remember – Actin – Ac”thin”
Mechanism of action
1. The Neuromuscular Junction – neuron to
muscle
• Signal travels from motor neuron by
acetycholine (excitatory) to the skeletal
muscle cell and depolarizes it.
• An action potential is spread in the T tubules
and changes the permeability of the
sarcoplasmic reticulum which releases Ca+.
2. Actin involvement
Myosin-binding sites
are blocked by a strand
of tropomyosin whose
position is controlled by
Troponin complex molecules.
Ca+ ions bind to the complex
and move the tropomyosin and
expose the binding sites for
myosin.
3. Myosin Involvement
-
-
The globular heads of the myosin are
energized by ATP and bind to actin forming
a cross-bridge
When relaxing to its low-energy state, the
myosin head bends and pulls the attached
actin toward the center of the sarcomere
4. Completion
When its’s over, Ca+ returns to the
sarcoplasmic reticulum and
tropomyosin recovers binding sites on
actin.
Acetylcholine is degraded at the
synapse.
Mechanism of Filament Sliding
at the Neuromuscular Junction
Animation: Action Potentials and
Muscle Contraction
Interactions between myosin and actin
generate force during uscle contractions
• The sliding-filament model of muscle contraction.
Fig. 49.33
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Protein models of muscle action
Contraction
• Of single muscle fiber – all or none
• Twitch: slow – less SR, Ca in longer,
fibers must have many mitochondria, a
good blood supply (myoglobin better
which picks up O2 better and stores it)
• Fast – rapid and powerful contraction
• Tetanus – smooth, sustained
contraction; action potentials arrive
rapidly
Muscle Fatigue
• Depletion of ATP, loss of ion gradient,
accumulation of lactic acid
Skeletons support and protect the animal body and are
essential to movement
• Hydrostatic skeleton: consists of fluid held
under pressure in a closed body compartment.
– Form and movement is controlled by
changing the shape of this compartment.
– Advantageous in aquatic environments and
can support crawling and burrowing.
– Does not allow for running or
walking.
• Exoskeletons – supportive, protective but
do not grow (molted)
• Endoskeletons – supportive, grow with the
organism, less protective