Animal Sensory Systems and Movement

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Animal Sensory Systems and Movement

• Chapter 46

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Animal Sensory Systemsand Movement

• Movement is fundamental to how animals work
• Sensory information must be accurate for animals
  to move effectively
• Sensory cells convert sound, light, and other
  stimuli to a change in membrane potential
• Send action potentials to the brain, where the
  signals are processed and integrated.

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How Do Sensory Organs Convey Information to the
Brain?
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Sensing a Stimulus

• The process of sensing a stimulus has four
  components
• Transductiontheconversion of an external
  stimulus to an internal signal in the form of an
  action potential
• Amplification of the signal
• Transmission of the signal to the central nervous
  system (CNS)
• Integration or processing with other signals

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Sensory Transduction

• 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
• It is a graded potential whose magnitude changes
• Many sensory receptors are extremely sensitive
• With the ability to detect the smallest physical
  unit of stimulus possible

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Amplification and Transmission

• The strengthening of stimulus energy by cells in
  sensory pathways
• After energy in a stimulus has been transduced
  into a receptor potential
• Some sensory cells generate action potentials,
  which are transmitted to the CNS
• Like motor neurons
• Sensory cells without axons
• Release neurotransmitters at synapses with
  sensory neurons
• Such as the hair cells in the ear

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Transmission

• The magnitude of affects the frequency of action
  potentials that travel to the CNS
• Many sensory neurons spontaneously generate
  action potentials at a low rate
• A stimulus does not switch the production of
  action potentials on or off, it modulates action
  potential frequency

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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
• Some receptor potentials
• Are integrated through summation
• Another type of integration is sensory adaptation
• A decrease in responsiveness during continued
  stimulation
• Reduces continuous sensation of common stimuli

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Types of Sensory Receptors

• Based on the energy they transduce, sensory
  receptors fall into five categories
• Mechanoreceptors
• Chemoreceptors-
• Electromagnetic receptors
• Thermoreceptors
• Pain receptors
• Mechanoreceptors sense physical deformation
• Caused by stimuli such as pressure, stretch,
  motion, and sound

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Mechanoreceptors

• The mammalian sense of touch
• Relies on mechanoreceptors that are the dendrites
  of sensory neurons

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Chemoreceptors

• Include
• General receptors that transmit information about
  the total solute concentration
• And specific receptors that respond to individual
  kinds of molecules
• Two of the most sensitive and specific
  chemoreceptors known
• Are present in the antennae of the male silkworm
  moth

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Electromagnetic Receptors

• Electromagnetic receptors detect various forms of
  electromagnetic energy
• Such as visible light, electricity, and magnetism
• Some snakes have very sensitive infrared
  receptors
• That detect body heat of prey against a colder
  background

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Electromagnetic Receptors

• Many mammals appear to use the Earths magnetic
  field lines
• To orient themselves as they migrate

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Thermoreceptors

• Respond to heat or cold
• Help regulate body temperature by signaling both
  surface and body core temperatures

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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
• Prostaglandins increase sensitivity of pain
  receptors to pain
• Analgesics such as aspirin and ibuprophen reduce
  prostaglandin synthesis and reduce sensitivity

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Hearing and Equilibrium
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Hearing and Equilibrium

• 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
• Produce receptor potentials when some part of the
  membrane is bent
• Most invertebrates have sensory organs called
  statocysts
• That contain mechanoreceptors and function in
  their sense of equilibrium

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Hearing and Equilibrium
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Hearing and Equilibrium

• Many arthropods sense sounds with body hairs that
  vibrate
• Or with localized ears consisting of a tympanic
  membrane and receptor cells

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Hearing and Equilibrium In Terrestrial Vertebrates
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Hearing

• Vibrating objects create percussion waves in the
  air
• That cause the tympanic membrane to vibrate
• The three bones of the middle ear
• Transmit the vibrations to the oval window on the
  cochlea
• These vibrations create pressure waves in the
  fluid in the cochlea
• That travel through the vestibular canal and
  ultimately strike the round window

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Hearing
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Hearing

• 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
• At the end near the round window, the hair bends
  the other way and reduces neurotransmitter
  release and frequency of sensations
• Volume and pitch are determined by rapidness of
  the vibration and length of vibration

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Hearing

• The cochlea can distinguish pitch
• Because the basilar membrane is not uniform along
  its length
• Each region of the basilar membrane vibrates most
  vigorously
• At a particular frequency and leads to excitation
  of a specific auditory area of the cerebral cortex

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Equilibrium

• Several of the organs of the inner ear
• Detect body position and balance
• The utricle, saccule, and semicircular canals in
  the inner ear
• Function in balance and equilibrium
• Different body angles cause different hair cells
  and their sensory neurons to be stimulated
• Decreases or increases the release of
  neurotransmitter
• Spinning causes disruption in the equilibrium of
  the semicircular canals and you become dizzy

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Equilibrium
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Vision
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Vision

• Many types of light detectors
• Have evolved in the animal kingdom
• Most invertebrates
• Have some sort of light-detecting organ
• One of the simplest is the eye cup of planarians
• Provides information about light intensity and
  direction but does not form images

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Eyes

• Two major types of image-forming eyes have
  evolved in invertebrates
• The compound eye and the single-lens eye
• Compound eyes are found in insects, crustaceans
  and some polychaetes
• Consists of several thousand light detectors
  called ommatidia
• Presents a mosaic image
• Good at detecting movement
• Some can see in the ultraviolet range, like bees

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Eyes

• Single-lens eyes
• Are found in some jellies, polychaetes, spiders,
  and many molluscs
• Work on a camera-like principle
• Eye has only one hole through which light enters
  the eye
• Iris changes the diameter of the pupil
• A single lens focuses light on a layer of
  photoreceptors
• The eyes of vertebrates are camera-like
• But they evolved independently and differ from
  the single-lens eyes of invertebrates

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

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Focusing the Eye

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

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Photoreceptors

• The human retina contains two types of
  photoreceptors
• Rods are sensitive to light but do not
  distinguish colors
• Enable us to see at night
• Cones distinguish colors but are not as sensitive
• Color vision is found in all vertebrate classes
  but not in all species ( most mammals do not)

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Photoreceptors

• The human retina contains about 125 million rods
  and about 6 million cones
• Account for about 70 of all the receptors in the
  body
• 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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Photoreceptors

• Rods contain the pigment rhodopsin
• Which changes shape when it absorbs light
• Cones have three classes of visual pigments
  called photopsins red, green and blue
• Depending on which class of pigment is more
  stimulated is what color you will see

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How Do Rods and ConesDetect Light?

• Rods and cones have segments packed with
  membrane-rich disks

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Photoreceptors

• The membranes contain large quantities of a
  transmembrane protein called opsin associated
  with one retinal pigment molecule
• Retinal changes shape when it absorbs a photon of
  light, leading to a change in opsins
  conformation
• This change, in turn, leads to a series of events
  that culminates in a change in the cells
  membrane potential

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Visual Processing

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

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Visual Processing

• Signals from rods and cones
• Travel from bipolar cells to ganglion cells
• The axons of ganglion cells are part of the optic
  nerve
• Horizontal and amacrine cells help integrate
  signals before it is sent to the brain

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Taste and Smell
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Taste in Humans

• The receptor cells for taste in humans
• Are modified epithelial cells organized into
  taste buds
• Scattered in several areas of the tongue and
  mouth
• Five taste perceptions involve several signal
  transduction mechanisms
• Sweet, sour, salty, bitter, and umami (elicited
  by glutamate)
• Respond to a broad range of chemicals but is
  responsive to a particular type of substance
  (chemoreceptors)

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Smell

• Olfactory receptor cells
• Are neurons that line the upper portion of the
  nasal cavity
• When odorants reach the nose, they diffuse into a
  mucus layer in the roof of the nose and activate
  olfactory receptor neurons via membrane-bound
  receptor proteins
• When odorant molecules bind to specific receptors
• A signal transduction pathway is triggered,
  sending action potentials to the brain

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Movement
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Skeletons

• Information about the environment is useless
  unless an animal can respond to it, usually by
  moving
• All movement relies on muscles working together
  against some type of skeleton
• Animal skeletons function in support, protection,
  and movement
• The three main types of skeletons are
• Hydrostatic skeletons, exoskeletons, and
  endoskeletons

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Hydrostatic Skeletons

• A hydrostatic skeleton
• Consists of fluid held under pressure in a closed
  body compartment
• This is the main type of skeleton
• In most cnidarians, flatworms, nematodes, and
  annelids
• Animals control their form and movement by using
  muscles to change the shape of fluid-filled
  compartments
• Annelids use their hydrostatic skeleton for
  peristalsis

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Hydrostatic Skeletons
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Exoskeletons

• An exoskeleton is a hard encasement
• Deposited on the surface of an animal
• Exoskeletons
• Are found in most molluscs and arthropods
• Muscles are attached to the shell

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Endoskeleton

• An endoskeleton consists of hard supporting
  elements
• Such as bones, buried within the soft tissue of
  an animal
• Endoskeletons
• Are found in sponges, echinoderms, and chordates
• The mammalian skeleton is built from more than
  200 bones
• Some fused together and others connected at
  joints by ligaments that allow freedom of movement

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The Human Skeleton

• Vertebrate skeleton can be divided into two main
  parts
• The axial skeleton consists of the skull,
  vertebral column and rib cage
• The appendicular skeleton made up of limb bones
  and the pectoral and pelvic girdle that anchor
  the appendages to the axial skeleton
• Joints at the appendages provide flexibility for
  body movements

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The Human Skeleton
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Endoskeletons

• Endoskeletons are composed of the connective
  tissues cartilage and bone

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Cartilage and Bone

• Cartilage is made up of cells scattered in a
  gelatinous matrix of polysaccharides and protein
  fibers
• Bone is composed of cells in a hard extracellular
  matrix of calcium phosphate with small amounts of
  calcium carbonate and protein fibers
• Bones meet and interact at articulations, or
  joints. Bones articulate in ways that allow limbs
  to swivel, hinge, or pivot

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Skeletal Muscles and Movement

• Muscles move skeletal parts by contracting
• The action of a muscle
• Is always to contract, they can extend only
  passively
• Skeletal muscles are attached to the skeleton in
  antagonistic pairs
• With each member of the pair working against each
  other

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Skeletal Muscles and Movement
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How Do Muscles Contract?

• Vertebrates have three types of muscle tissue

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Types of Muscle Tissue

• Skeletal muscle consists of unbranched,
  multinucleate cells.
• Cardiac muscle contains branched cells whose ends
  are connected via specialized regions called
  intercalated discs.
• Smooth muscle is unbranched, lacks myofibrils,
  and is often organized into thin sheets.
• Vertebrate skeletal muscle
• Is characterized by a hierarchy of smaller and
  smaller units

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Vertebrate Skeletal Muscle

• A skeletal muscle consists of a bundle of long
  fibers
• Running parallel to the length of the muscle
• A muscle fiber
• Is itself a bundle of smaller myofibrils arranged
  longitudinally
• The myofibrils are composed to two kinds of
  myofilaments
• Thin filaments, consisting of two strands of
  actin and one strand of regulatory protein
• Thick filaments, staggered arrays of myosin
  molecules

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Sliding Filament Model of Muscle Contraction

• According to the sliding-filament model of muscle
  contraction
• The filaments slide past each other
  longitudinally, producing more overlap between
  the thin and thick filaments
• As a result of this sliding
• The I band and the H zone shrink

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Sliding Filament Model of Muscle Contraction
0.5 ?m
(a) Relaxed muscle fiber. In a relaxed muscle
fiber, the I bandsand H zone are relatively wide.
Z
H
A
Sarcomere
(b) Contracting muscle fiber. During contraction,
the thick and thin filaments slide past each
other, reducing the width of theI bands and H
zone and shortening the sarcomere.
(c) Fully contracted muscle fiber. In a fully
contracted muscle fiber, the sarcomere is shorter
still. The thin filaments overlap,eliminating
the H zone. The I bands disappear as the ends of
the thick filaments contact the Z lines.
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Sliding Filament Model of Muscle Contraction

• The sliding of filaments is based on
• The interaction between the actin and myosin
  molecules of the thick and thin filaments
• The head of a myosin molecule binds to an actin
  filament
• Forming a cross-bridge and pulling the thin
  filament toward the center of the sarcomere

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Sliding Filament Model of Muscle Contraction
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Muscle Contraction

• A skeletal muscle fiber contracts
• Only when stimulated by a motor neuron
• The stimulus leading to the contraction of a
  skeletal muscle fiber
• Is an action potential in a motor neuron that
  makes a synapse with the muscle fiber
• The synaptic terminal of the motor neuron
• Releases the neurotransmitter acetylcholine,
  depolarizing the muscle and causing it to produce
  an action potential

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Muscle Contraction

• Action potentials travel to the interior of the
  muscle fiber
• Along infoldings of the plasma membrane called
  transverse (T) tubules
• The action potential along the T tubules
• Causes the sarcoplasmic reticulum to release Ca2
• The Ca2 binds to the troponin-tropomyosin
  complex on the thin filaments
• Exposing the myosin-binding sites and allowing
  the cross-bridge cycle to proceed

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