1. Chapter 50
Sensory and Motor Mechanisms

2. Sensory Pathway
• Sensory Receptions: Detection of a stimulus by
sensory cells or sensory receptors.
• The sensory receptors transfer the physical and
chemical stimulus to a membrane potential, this
process is known as transduction.
• Transduction triggers transmission, which is the
conversion of membrane potential to action
potentials which is then sent to the CNS.
• Perception is the final step and it is when the
action potential is interpreted by the brain and
perceived either as sound, color, smell or taste.

3. Fig. 50-2
Sensory Pathway
potential (mV)
Weak
Membrane
potential (mV)
Action potentials
Membrane
receptor
–50 potential
0
–70
Slight bend: –70
weak 0 1 2 34 5 6 7 Brain perceives
stimulus Dendrites Stretch Time (sec) slight bend.
receptor
1 2 4
Axon
3 Brain
Muscle Brain perceives
Action potentials
potential (mV)
large bend.
Membrane
Large bend:
potential (mV)
strong Strong receptor 0
Membrane
stimulus potential
–50 –70
1 Reception
–70 0 1 2 34 5 6 7
Time (sec)
2 Transduction 3 Transmission 4 Perception
Types of Receptors:
Chemoreceptors, Electromagnetic Receptors, Thermoreceptors, Pain Receptors

4. Hearing Through Mechanoreceptors
• Humans have a tympanic membrane which is
a hair covered membrane in the ear that
receives sounds and transmits them to the
brain.
• Where sound vibrations enter the ear they
travel through the cochlear duct and the
vibrations are converted to pressure waves.
This information is taken to the brain and two
things are analyzed from the pressure waves,
volume and pitch.

5. Fig. 50-8
Middle
Outer ear ear Inner ear
Skull Stapes
Semicircular
bone
Incus canals
Malleus
Auditory nerve Cochlear Bone Auditory
to brain duct nerve
Vestibular
canal
Tympanic
Cochlea canal
Oval
window Eustachian
Pinna Auditory tube
canal Tympanic Round Organ of Corti
membrane window
Tectorial
Hair cells membrane
Hair cell bundle from
a bullfrog; the longest
cilia shown are
about 8 µm (SEM). Basilar Axons of To auditory
membrane sensory neurons nerve

6. Taste and Smell
• Taste is detected by taste buds on a mammals
tongue.
• Taste buds have receptors that can read only
one taste, when a receptor accepts its
respective molecule it attaches it to a protein
that then sends it through a pathway to a
sensory neuron that interprets the taste of the
molecule.

7. Fig. 50-15
Taste and Smell
Brain
Action potentials
Olfactory
bulb
Odorants
Nasal cavity Bone
Epithelial
cell
Odorant
receptors Chemo-
receptor
Plasma Cilia
membrane
Odorants Mucus

8. Electromagnetic Reception(Seeing)
• Different Types of Eyes
– Compound eyes are found in insects and crustaceans
and consist of up to several thousand light detectors
called ommatidia
– Single-lens eyes are found in some jellies, polychaetes,
spiders, and many molluscs
– Vertebrate Eye; the eye ball, detects color and light, but
the brain assembles the information and perceives the
image

9. Fig. 50-17
2 mm
(a) Fly eyes
Cornea
Crystalline Lens
cone
Rhabdom
Photoreceptor
Axons
Ommatidium
(b) Ommatidia

10. Use of Photoreceptors
• In vertebrates the eye detects color and light, but the
brain assembles the information and perceives the
image.
• Absorption of light by retinal triggers a signal
transduction pathway that hyperpolarizes(increases
in polarity) the photoreceptors , causing them to
release less neurotransmitters. Synapses transmit
information from photoreceptors to the brain.
• Rods are light-sensitive but don’t distinguish
colors(peripheral vision).
• Cones distinguish colors but are not as sensitive to
light.

11. Fig. 50-18
Sclera Choroid
Retina
Ciliary body
Suspensory Fovea (center
ligament of visual field)
Cornea
Iris Optic
nerve
Pupil
Aqueous
humor
Lens
Central artery and
vein of the retina
Vitreous humor
Optic disk
(blind spot)

12. Microfilaments and Macrofilaments
Underlie our Muscles
• Myosin heads (thick muscle filaments) bind to
myofibrils (thin muscle filaments) forming
cross-bridges.
• When the myosin heads are energized by ATP
a cycle starts that causes the myosin heads to
bend and slide over the myofibrils, this
process contracts the muscle.
• Cardiac muscle, only within the heart, are
electrically connected striated muscle cells.

13. Fig. 50-26
Sarcomere
0.5 µm
Z M Z
Relaxed
muscle
Contracting
muscle
Fully contracted
muscle
Contracted
Sarcomere

14. Skeletal Systems
• Skeletal muscles provide movement by contraction of
the muscle pulling against the skeleton.
• Types
– Hydrostatic Skeleton: Found in most flatworms, nematodes
and annelids, consists of fluid under pressure in a closed
body compartment.
– Exoskeletons: Found in most molluscs and arthropods, are
hard coverings deposited on the surface of an animal.
– Endoskeletons: Found in sponges, echinoderms, and
chordates, are rigid supporting elements embedded with
an animal’s body.

15. Energy Costs
• Animals that specialize in swimming spend
less energy per meter traveled than any other
type of locomotion for an animal their size.

16. Fig. 50-37
RESULTS
Flying Running
102
Energy cost (cal/kg•m)
10
1
Swimming
10–1
10–3 1 103 106
Body mass (g)