Sensory and Motor Mechanisms

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Chapter 49
IB-202-16-06

• Sensory and Motor Mechanisms
• (pp 1045-1062)

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Sensory input, motor output and behavior!

• The detection and processing of sensory
  information and the generation of motor output is
  the physiological basis for all animal behavior.
  Behavior is not a linear sequence of sensing,
  brain analysis and action, but rather a
  continuing process. As animals move they are
  probing the environment through that movement,
  sensing changes and using the information to
  generate the next action. It is a continuous
  cycle.

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An example of sensing and acting

• Bats use sonar to detect their prey
• Moths, a common prey for bats can detect the
  bats sonar with sensory hairs in the abdomen and
  attempt to escape by diving in a spiral pattern
  towards the ground.
• Both of these organisms have complex sensory
  systems that facilitate their survival.

Figure 49.1
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• The sensory and effector structures that make up
  these systems have been transformed by evolution
  into diverse mechanisms that sense various
  stimuli and generate the appropriate physical
  movement

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• The first step is converting the stimulus into
  another form. Sensory receptors transduce
  stimulus energy to electrical signals. The
  electrical signals are transformed into action
  potentials and travel to the the brain via
  sensory neurons
• And the brain interprets them as a perception of
  the stimuli and generates an appropriate
  response. (Cross talksome people see colors when
  they hear music!What is going on?) Action
  potentials going from ear to visual center????

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• Sensations begin with the detection of stimuli by
  sensory receptors
• There are many kinds of receptors heat, cold,
  pain, pressure, light, hearing, osmotic, oxygen
  etc. Some are located in the surface tissues of
  the body and others within the brain, circulatory
  system and visceral organs.
• Locations
• Exteroreceptors
• Detect stimuli coming from the outside of the
  body such as pressure waves, light and heat/cold.
• Interoreceptors
• Detect internal stimuli chemoreceptors,
  osmoreceptors, pressure etc.

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Functions Performed by Sensory Receptors

• All stimuli represent forms of energy
• Sensation involves converting this energy into a
  change in the membrane potential of sensory
  receptors

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• Sensory receptors perform four functions in this
  process
• Sensory transduction, amplification,
  transmission, and integration
• The stretch receptor and hair receptor represent
  these processes.

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• Two types of sensory receptors exhibit these
  functions
• A stretch receptor in a crayfish

Action potential has much more energy than a
decrease in receptor potential! An example of an
amplification!
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• A hair cell found in vertebrates

Hyperpolarization of hair cell. Less likely to
generate an action potential!
Depolarization of hair cell!
of action potentials in the sensory neuron.
Bending in the other direction has the opposite
effects. Thus, hair cells respond to the
direction of motion as well as to its strength
and speed.s
Use of a neurotransmitter step and amplification
step!
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Sensory Transduction

• Sensory transduction is the conversion of
  stimulus energy into a change in the membrane
  potential of a sensory receptor
• This change in the membrane potential is known as
  a receptor potential (resting potential changes
  from -70 to -60)

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• Many sensory receptors are extremely sensitive
• With the ability to detect the smallest physical
  unit of stimulus possible

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Transmission

• After energy in a stimulus has been transduced
  into a receptor potential
• Some sensory cells generate action potentials,
  which are transmitted to the CNS

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• Sensory cells without axons
• Release neurotransmitters at synapses with
  sensory neurons

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Integration

• The integration of sensory information
• Begins as soon as the information is received
• Occurs at all levels of the nervous system

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• The integration of sensory information begins as
  soon as the information is received. It occurs at
  all levels of the nervous system
• Some receptor potentials are amplified through
  summation
• Some receptor potentials are decreased
  (attenuated) with repeated stimulation. This is
  called sensory adaptation.
• Both of these responses can be viewed as
  integration at the receptor level.

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Types of Sensory Receptors

• Based on the energy they transduce, sensory
  receptors fall into five categories
• Mechanoreceptors
• Chemoreceptors
• Photoreceptors
• Thermoreceptors
• Pain receptors
• Electromagnetic receptors includes (photo,
  electrical and magnetism)

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Mechanoreceptors

• Mechanoreceptors sense physical deformation
• Caused by stimuli such as pressure, stretch,
  motion, and sound

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• The mammalian sense of touch relies on
  mechanoreceptors that are the dendrites of
  sensory neurons. These are naked nerves and
  depolarization of the endings leads to an action
  potential.

Figure 49.3
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Pain Receptors

• In humans, pain receptors, also called
  nociceptors
• Are a class of naked dendrites in the epidermis
• Respond to excess heat, pressure, or specific
  classes of chemicals released from damaged or
  inflamed tissues

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Chemoreceptors

• Chemoreceptors include
• General receptors that transmit information about
  the total solute concentration of a solution
• Specific receptors that respond to individual
  kinds of molecules. Best example is that of a
  male moths antennae sensing pheromone
  (bombykol) put out by female moth a mile
  upwind. Male responds when only 40 receptors
  bind compound / sec out of 20,000 receptors.

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• The most sensitive and specific chemoreceptors
  known is present in the antennae of the male
  silkworm moth

Figure 49.4
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Electromagnetic Receptors

• Electromagnetic receptors detect various forms of
  electromagnetic energy
• Such as visible light, electricity, and magnetism

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• Many mammals appear to use the Earths magnetic
  field lines to orient themselves as they migrate.
  There is also good evidence that birds use
  magnetic field lines during long migrations.

Figure 49.5b
(b) Some migrating animals, such as these beluga
whales, apparentlysense Earths magnetic field
and use the information, along with other cues,
for orientation.
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Thermoreceptors

• Thermoreceptors, which respond to heat or cold
• Help regulate body temperature by signaling both
  surface and body core temperature.
• Infrared reception in pit vipers (rattlesnakes).

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Pit Vipers (rattlesnakes) have infrared receptors.

• Some snakes have very sensitive infrared
  receptors
• That detect body heat of prey against a colder
  background

Snake can detect .002C temp change within the
pit. Can sense a rat 40 cm away if its body temp
10C above the environmental. Receptor just
branched ending of the sensory axon.
Pits below eyes.
Can also sense direction because of depth of pit!
Figure 49.5a
(a) This rattlesnake and other pit vipers have a
pair of infrared receptors,one between each eye
and nostril. The organs are sensitive enoughto
detect the infrared radiation emitted by a warm
mouse a meter away. The snake moves its head
from side to side until the radiation is detected
equally by the two receptors, indicating that
the mouse is straight ahead.
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• Concept 49.2 The mechanoreceptors involved with
  hearing and equilibrium detect settling particles
  or moving fluid
• Hearing and the perception of body equilibrium
• Are related in most animals

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Sensing Gravity and Sound in Invertebrates

• Most invertebrates have sensory organs called
  statocysts
• That contain mechanoreceptors and function in
  their sense of equilibrium

Statolith is a secretion of protein and calcium
carbonate! In fish they increase in size as the
fish grows and can be used to age fish by
counting the annual rings!
Figure 49.6
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• Many arthropods sense sounds with body hairs that
  vibrate or with localized ears consisting of a
  tympanic membrane and receptor cells. Cockroach
  escape response!

Figure 49.7
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Sensory Perception in Aquatic Vertebrates

• The lateral line system of fishes and tadpoles
  contains mechanoreceptors
• With hair cells that respond to water movement

Water flows through the channel and deforms the
cupula. Also pressure waves in the water deform
it!
Neuromast includes the gelatinous cupula, sensory
hairs and hair cells!
Figure 49.12
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Hearing and Equilibrium in Vertebrates.

• In most terrestrial vertebrates
• The sensory organs for hearing and equilibrium
  are closely associated in the ear

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Deformation of hair cells basis for hearing in
mammals.
3 chambers!
Figure 49.8
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Hearing

• Vibrating objects create percussion waves in the
  air
• That cause the tympanic membrane (ear drum) to
  vibrate
• The three bones of the middle ear
• Transmit the vibrations to the oval window on the
  cochlea to the fluid of the inner ear.

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• These vibrations create pressure waves in the
  fluid in the cochlea
• That travel through the vestibular canal and into
  the tympanic canal. They ultimately strike the
  round window where they are dissipated.

Figure 49.9
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• The pressure waves in the vestibular canal
• Cause the basilar membrane to vibrate up and down
  causing its hair cells to bend
• The bending of the hair cells depolarizes their
  membranes
• Sending action potentials that travel via the
  auditory nerve to the brain

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• The cochlea can distinguish pitch
• Because the basilar membrane is not uniform along
  its length (thinner at one end), it vibrates more
  vigorously at a certain frequency! Louder
  greater amplitude deforms hair more.

Receptor potential causes influx of Ca which
in turn causes release of transmitter and action
potential!
Figure 49.10
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Equilibrium

• Several of the organs of the inner ear
• Detect body position and balance

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Equilibrium

• The utricle, saccule, and semicircular canals in
  the inner ear function in balance and equilibrium

Figure 49.11
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Hearing and Equilibrium in Other Vertebrates

• Like other vertebrates, fishes and amphibians
• Also have inner ears located near the brain

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• Concept 49.3 The senses of taste and smell are
  closely related in most animals
• The perceptions of gustation (taste) and
  olfaction (smell)
• Are both dependent on chemoreceptors that detect
  specific chemicals in the environment

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• The taste receptors of insects are located within
  sensory hairs called sensilla
• Which are located on the feet and in mouthparts

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EXPERIMENT Insects taste using gustatory
sensilla (hairs) on their feet and mouthparts.
Each sensillum contains four chemoreceptors with
dendrites that extend to a pore at the tip of the
sensillum. To study the sensitivity of each
chemoreceptor, researchers immobilized a blowfly
(Phormia regina) by attaching it to a rod with
wax. They then inserted the tip of a
microelectrode into one sensillum to record
action potentials in the chemoreceptors, while
they used a pipette to touch the pore with
various test substances.
To brain
Chemo-receptors
Sensillum
Microelectrode
To voltagerecorder
RESULTS Each chemoreceptor is especially
sensitive to a particular class of substance, but
this specificity is relative each cell can
respond to some extent to a broad range of
different chemical stimuli.
Pore at tip
Pipette containingtest substance
Chemoreceptors
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Number of action potentials in first second of
response
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CONCLUSION Any natural food probably stimulates
multiple chemoreceptors. By integrating
sensations, the insects brain can apparently
distinguish a very large number of tastes.
10
0
0.5 MSucrose
Honey
0.5 MNaCl
Meat
Figure 49.13
Stimulus
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• The receptor cells for taste in humans are
  modified epithelial cells organized into taste
  buds
• Five taste perceptions involve several signal
  transduction mechanisms
• Sweet, sour, salty, bitter, and umami (elicited
  by glutamate)
• Transduction in taste receptors
• Occurs by several mechanisms
• Na and H (sour) diffuse through channels on the
  taste receptor depolarizing it. Glutmate binds to
  Na channel opening it. Quinine (bitter) binds to
  K channels and closes them (depolarizing). All
  generate action potential. Sweetness next slide!

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• Sensing sweetness

Cell depolarizes because K builds up in the cell
from the Na/K ATPase pump.
Figure 49.14
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Smell in Humans

• Olfactory receptor cells
• Are neurons that line the upper portion of the
  nasal cavity

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Olfaction

• When odorant molecules bind to specific receptors
• A signal transduction pathway is triggered,
  sending action potentials to the brain

1000 ordorant receptors in humans. Represents 3
of human genes! Probably dont use them all
anymore.
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• Concept 49.4 Similar mechanisms underlie vision
  throughout the animal kingdom
• Many types of light detectors
• Have evolved in the animal kingdom and may be
  homologous

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Vision in Invertebrates

• Most invertebrates
• Have some sort of light-detecting organ.
  Flatworms, some jelly fish, scallops (molluscs),
  crustaceans and insects.

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• One of the simplest is the eye cup of planarians
• Which provides information about light intensity
  and direction but does not form images

Eyes positioned so that light coming from one
side does not illuminate eye on opposite side.
Figure 49.16
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• Two major types of image-forming eyes have
  evolved in invertebrates
• The compound eye and the single-lens eye

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Compound Eyes

• Compound eyes are found in insects and
  crustaceans and consist of up to several thousand
  light detectors called ommatidia

Figure 49.17ab
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• Single-lens eyes
• Are found in some jellies, polychaetes, spiders,
  and many molluscs
• Work on a camera-like principle

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The Vertebrate Visual System

• The eyes of vertebrates are camera-like
• But they evolved independently and differ from
  the single-lens eyes of invertebrates

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Structure of the Eye

• The main parts of the vertebrate eye are
• The sclera, which includes the cornea
• The choroid, a pigmented layer
• The conjunctiva, that covers the outer surface of
  the sclera

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• The iris, which regulates the pupil
• The retina, which contains photoreceptors
• The lens, which focuses light on the retina

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• The structure of the vertebrate eye

Figure 49.18
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• Humans and other mammals
• Focus light by changing the shape of the lens

Figure 49.19ab
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• The human retina contains two types of
  photoreceptors
• Rods are sensitive to light but do not
  distinguish colors
• Cones distinguish colors but are not as sensitive

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Sensory Transduction in the Eye

• Each rod or cone in the vertebrate retina
• Contains visual pigments that consist of a
  light-absorbing molecule called retinal bonded to
  a protein called opsin

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• Rods contain the pigment rhodopsin
• Which changes shape when it absorbs light

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Processing Visual Information

• The processing of visual information begins in
  the retina itself. This is accomplished by the
  interconnections with three types of cells before
  an action potential is transmitted to the brain
  via the optic nerve. Some of these connections
  are inhibitory while others are stimulatory.

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• Absorption of light by retinal
• Triggers a signal transduction pathway

Figure 49.21
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• In the dark, both rods and cones
• Release the neurotransmitter glutamate into the
  synapses with neurons called bipolar cells, which
  are either hyperpolarized or depolarized

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• In the light, rods and cones hyperpolarize
• Shutting off their release of glutamate
• The bipolar cells
• Are then either depolarized or hyperpolarized

Figure 49.22
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• Three other types of neurons contribute to
  information processing in the retina
• Ganglion cells, horizontal cells, and amacrine
  cells

Figure 49.23
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• Signals from rods and cones
• Travel from bipolar cells to ganglion cells
• The axons of ganglion cells are part of the optic
  nerve
• That transmit information to the brain

Figure 49.24
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• Most ganglion cell axons lead to the lateral
  geniculate nuclei of the thalamus
• Which relays information to the primary visual
  cortex
• Several integrating centers in the cerebral
  cortex
• Are active in creating visual perceptions