ANIMAL SENSORY SYSTEMSAND MOVEMENT (lec 22)
How do moths and vertebrates hear?
• Sensing changes in the environment and moving in response to this information is
fundamental to how animals work.
• The ability to sense a change in the environment depends on four processes:
1. Transduction, the conversion of an external stimulus to an internal signal in the
form of an action potential.
2. Amplification of the signal.
3. Transmission of the signal to the central nervous system (CNS).
4. Integration pr processing with other incoming signals
Moths fly through the night sensory neurons will relay info about conditions in/out an animal to
the to the CNS. After integrating the info from many sensory neurons the CNS sends signal to
Integrate sensory input-info from sensory neurons- and respond with motor output via electrical
signals, to specific muscle groups (effectors)
• Each type of sensory information is detected by a sensory neuron or by a specialized
receptor cell that makes a synapse with a sensory neuron.
• Transduction requires a sensory receptor cell to convert light, sound, tension, or some
other stimulus into an electrical signal.
• Sensory receptors are located throughout the body and are categorized by the type of
• Although sensory receptors can detect a remarkable variety of stimuli, they all transduce
sensory input—including light, sounds, touch, and odors—to a change in membrane
• This change in potential allows different types of stimuli to be transduced to a common
type of signal—one that can be interpreted by the brain.
• If a sensory stimulus induces a large change in a sensory receptor’s membrane potential,
there is a change in the firing rate of action potentials sent to the brain. • The amount of depolarization ( ion flow causes the interior to become more positive) or
hyperpolarization ( ion channels cause the cell interior to become more negative than the
resting potential ) of the sensory receptor is proportional to the intensity of the stimulus.
• Sensory stimulus (large enough) change in a sensors receptors membrane
potential change in the firing ofAPs sent to the brain
• For example, the amount of depolarization that occurs in a sound-receptor cell is
proportional to the loudness of the sound.
• Animals have a variety of mechanisms for sensing changes in pressure.
• The best-studied type of pressure-sensing is called hearing.
• Hearing is the ability to sense sound, which consists of waves of pressure in air or water.
• The number of pressure waves that occur in one second is called the frequency of the
• We perceive differences in sound frequency as different pitches.
• Virtually all animal pressure-sensing systems are based on the same mechanism, a
mechanoreceptor cell that responds to
In verterbrates ion channels which respond to pressure are found in hair cells.
Pressure receptor cells
Have many sterocilia( microvilli reinforced by actin filaments) and one kinocilium (true cilium
with 9+2 arrangement of microtubules)
Sterocilia found in increasing height. If Sterocilia bent in direction of Kinocilium (above right
figure), bending opens ion channels
If sterocilia other way then K+ channel will close, cell hyperpolarize, results in decrease in
neurotransmitter released neuron less likely to trigger action potential
The Mammalian Ear The human ear is made up of the outer ear, middle ear, and inner ear, each separated from the
others by a membrane.
The Outer Ear
Reception of sound
Outer ear collects pressure waves, propels from head and funneled in tube known as ear canal,
end of ear canal wave strikes Tympanic membrane (ear drum) seperates outer and innear ear. The
membrane will vibrate bc o air compression. Vibration passed onto ossicles.
The Middle Ear
Transfers sound wave
The vibrations from the eardrum set the ossicles into motion. The ossicles are three tiny bones
vibrate against each other one of the bones stapes (stirrup) in the last ossicles which further
amplify the sound.
The stapes vibrates against membrane known as oval window , the oval window that seperates
the middle ear from the inner ear.
The Inner Ear
The sound waves enter the inner ear and then into the cochlea, a snail shaped organ. The cochlea
is filled with a fluid that moves in response to the vibrations from the oval window.As the fluid
moves, nerve endings are set into motion. These nerve endings transform the vibrations into
electrical impulses that t