Chapter 50Sensory and Motor Mechanisms

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.

Fig. 50-2

Slight bend:weakstimulus Stretch

receptor

Mem

bran

epo

tenti

al (m

V)

Axon

Dendrites

Strong receptorpotential

Weakreceptorpotential

Muscle

–50

–70M

embr

ane

pote

ntial

(mV)

–50

–70

Action potentials

Action potentials

Mem

bran

epo

tenti

al (m

V)

Large bend:strongstimulus

Reception

Transduction

0

–70

0

–70

1 2 3 4 5 6 7

Mem

bran

epo

tenti

al (m

V)

Time (sec)

1 2 3 4 5 6 7Time (sec)

Transmission Perception

Brain

Brain perceiveslarge bend.

Brain perceivesslight bend.

1 23

4

1

2 3 4

0

0

Sensory Pathway

Types of Receptors:Chemoreceptors, Electromagnetic Receptors, Thermoreceptors, Pain Receptors

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.

Fig. 50-8

Hair cell bundle froma bullfrog; the longestcilia shown areabout 8 µm (SEM).

Auditorycanal

EustachiantubePinna

Tympanicmembrane

Ovalwindow

Roundwindow

Stapes

Cochlea

Tectorialmembrane

Incus

Malleus

Semicircularcanals

Auditory nerveto brain

Skullbone

Outer earMiddle

ear Inner ear

Cochlearduct

Vestibularcanal

Bone

Tympaniccanal

Auditorynerve

Organ of Corti

To auditorynerve

Axons ofsensory neurons

Basilarmembrane

Hair cells

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.

Fig. 50-15

Olfactorybulb

Odorants

Bone

Epithelialcell

Plasmamembrane

Odorantreceptors

Odorants

Nasal cavity

Brain

Chemo-receptor

Cilia

Mucus

Action potentials

Taste and Smell

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

Fig. 50-17

Rhabdom

(a) Fly eyes

Crystallinecone

Lens

(b) OmmatidiaOmmatidium

PhotoreceptorAxons

Cornea

2 m

m

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.

Fig. 50-18

Opticnerve

Fovea (centerof visual field)

Lens

Vitreous humorOptic disk(blind spot)

Central artery andvein of the retina

Iris

RetinaChoroidSclera

Ciliary body

Suspensoryligament

Cornea

Pupil

Aqueoushumor

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.

Fig. 50-26

Z

Relaxedmuscle

M Z

Fully contractedmuscle

Contractingmuscle

Sarcomere0.5 µm

ContractedSarcomere

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.

Energy Costs

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

Fig. 50-37

Body mass (g)

Running

Swimming

Flying

Ener

gy c

ost (

cal/

kg•m

) 102

103

10

1

10–1

10–3 1061

RESULTS

Assessment Questions1) Which part of the eye specializes in peripheral vision?• A) cones• B) sclera• C) choroid• D) rods2) Which form of locomotion is best per meter traveled, for animals?• A) running• B) driving• C) swimming• D) flying3) Which of the following sensory receptors is correctly paired with its category?• A) Rod- electromagnetic receptor• B) Hair cell- chemoreceptor• C) Myofibrils- electromagnetic receptor• D) Thermoreceptors – Pain Receptors