Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DU action potential video...

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• http://www.youtube.com/watch?v=SCasruJT-DU action potential video (review)


Chapter 49 Types of Sensory Receptors

• Based on the energy they transduce, sensory receptors fall into five categories

– Mechanoreceptors

– Chemoreceptors

– Electromagnetic receptors

– Thermoreceptors

– Pain receptors


• The mammalian sense of touch

– Relies on mechanoreceptors that are the dendrites of sensory neurons

Figure 49.3

Heat

Light touch Pain

Cold

Hair

Nerve Connective tissue Hair movement Strong pressure

Dermis

Epidermis


• Exploring the structure of the human ear

Figure 49.8

Pinna

Auditory canal

Eustachian tube

Tympanicmembrane

Stapes

Incus

Malleus

Skullbones

Semicircularcanals

Auditory nerve,to brain

Cochlea

Tympanicmembrane

Ovalwindow

Eustachian tube

Roundwindow

Vestibular canal

Tympanic canal

Auditory nerve

BoneCochlear duct

Hair cells Tectorialmembrane

Basilarmembrane

To auditorynerve

Axons of sensory neurons

1 Overview of ear structure 2 The middle ear and inner ear

4 The organ of Corti 3 The cochleaOrgan of Corti

Outer earMiddle

ear Inner ear


• Vibrations of the ear bones and oval window create pressure waves in the fluid in the cochlea

– That travel through the vestibular canal and ultimately strike the round window

Figure 49.9

Cochlea

Stapes

Oval window

Apex

Axons ofsensoryneurons

Roundwindow Basilar

membrane

Tympaniccanal

Base

Vestibularcanal Perilymph


• The cochlea can distinguish pitch Because the basilar membrane is not uniform along its length

• Test your hearing: http://video.google.com/videosearch?q=hearing+test&hl=en&sitesearch=

Cochlea(uncoiled)

Basilarmembrane

Apex(wide and flexible)

Base(narrow and stiff)

500 Hz(low pitch)1 kHz

2 kHz

4 kHz

8 kHz

16 kHz(high pitch)

Frequency producing maximum vibration

Figure 49.10


Taste pore Sugar molecule

Sensoryreceptorcells

Sensoryneuron

Taste bud

Tongue

G protein Adenylyl cyclase

—Ca2+

ATP

cAMP

Proteinkinase A

Sugar

Sugarreceptor

SENSORYRECEPTORCELL Synaptic

vesicle

K+

Neurotransmitter

Sensory neuron

Taste

• Transduction in taste receptors

– Occurs by several mechanisms

Figure 49.14

4 The decrease in the membrane’s permeability to K+ depolarizes the membrane.

5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell.

6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter.

3 Activated protein kinase A closes K+ channels in the membrane.

2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A.

1 A sugar molecule binds to a receptor protein on the sensory receptor cell.


Smell

• When odorant molecules bind to specific receptors

– A signal transduction pathway is triggered, sending action potentials to the brain

Brain

Nasal cavity

Odorant

Odorantreceptors

Plasmamembrane

Odorant

Cilia

Chemoreceptor

Epithelial cell

Bone

Olfactory bulb

Action potentials

MucusFigure 49.15


Structure of the Eye

• The main parts of the vertebrate eye are

– The sclera, which includes the cornea

– The choroid, a pigmented layer

– The iris, which regulates the pupil

– The retina, which contains photoreceptors

– The lens, which focuses light on the retina

Ciliary body

Iris

Suspensoryligament

Cornea

Pupil

Aqueoushumor

Lens

Vitreous humor

Optic disk(blind spot)

Central artery andvein of the retina

Opticnerve

Fovea (centerof visual field)

Retina

ChoroidSclera


• The structure of the vertebrate eye

Figure 49.18

Ciliary body

Iris

Suspensoryligament

Cornea

Pupil

Aqueoushumor

Lens

Vitreous humor

Optic disk(blind spot)

Central artery andvein of the retina

Opticnerve

Fovea (centerof visual field)

Retina

ChoroidSclera


• 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


• spot the sixes visual test http://video.google.com/videosearch?q=visual+test+sixes&hl=en&sitesearch=

–

Figure 49.24

Leftvisualfield

Rightvisualfield

Lefteye

Righteye

Optic nerve

Optic chiasm

Lateralgeniculatenucleus

Primaryvisual cortex


Vertebrate Skeletal Muscle

• Vertebrate skeletal muscle

– Is characterized by a hierarchy of smaller and smaller units

Figure 49.28

Muscle

Bundle ofmuscle fibers

Single muscle fiber(cell)

Plasma membrane

Myofibril

Lightband Dark band

Z line

Sarcomere

TEM 0.5 mI band A band I band

M line

Thickfilaments(myosin)

Thinfilaments(actin)

H zoneSarcomere

Z lineZ line

Nuclei


• Sliding filament theory

– The I band and the H zone shrink

Figure 49.29a–c

(a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bandsand H zone are relatively wide.

(b) Contracting muscle fiber. During contraction, the thick andthin 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 musclefiber, the sarcomere is shorter still. The thin filaments overlap,eliminating the H zone. The I bands disappear as the ends ofthe thick filaments contact the Z lines.

0.5 m

Z HA

Sarcomere


• Myosin-actin interactions underlying muscle fiber contraction

Figure 49.30

Thick filament

Thin filaments

Thin filament

ATPATP

ADPADP

ADP

P i P i

P i

Cross-bridge

Myosin head (low-energy configuration)

Myosin head (high-energy configuration)

+

Myosin head (low-energy configuration)

Thin filament moves toward center of sarcomere.

Thick filament

ActinCross-bridge binding site

1 Starting here, the myosin head is bound to ATP and is in its low-energy confinguration.

2 The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration.

P

1 The myosin head binds toactin, forming a cross-bridge.

3

4 Releasing ADP and ( i), myosinrelaxes to its low-energy configuration, sliding the thin filament.

P

5 Binding of a new mole-cule of ATP releases the myosin head from actin,and a new cycle begins.


• When a muscle is at rest

– The myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin

Figure 49.31a

ActinTropomyosin Ca2+-binding sites

Troponin complex

(a) Myosin-binding sites blocked


• http://www.youtube.com/watch?v=DK7Z-Z7kKEY

• http://www.youtube.com/watch?v=WRxsOMenNQM

http://www.youtube.com/watch?v=ZscXOvDgCmQ

Figure 49.31b

Ca2+

Myosin-binding site

(b) Myosin-binding sites exposed


• 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

– Acetylcholine depolarizes

– Ca++ released from sarcoplasmic reticulum

– Ca++ binds to troponin/tropomyosin complexexposing myosin binding sites

Figure 49.32

Motorneuron axon

Mitochondrion

Synapticterminal

T tubule

Sarcoplasmicreticulum

Myofibril

Plasma membraneof muscle fiber

Sarcomere

Ca2+ releasedfrom sarcoplasmicreticulum


ACh

Synapticterminalof motorneuron

Synaptic cleft T TUBULEPLASMA MEMBRANE

SR

ADP

CYTOSOL

Ca2

Ca2

P2

Cytosolic Ca2+ is removed by active transport into SR after action potential ends.

6

• Review of contraction in a skeletal muscle fiber

Figure 49.33

Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber.

1

Action potential is propa-gated along plasmamembrane and downT tubules.

2

Action potentialtriggers Ca2+

release from sarco-plasmic reticulum(SR).

3

Myosin cross-bridges alternately attachto actin and detach, pulling actinfilaments toward center of sarcomere;ATP powers sliding of filaments.

5

Calcium ions bind to troponin;troponin changes shape,removing blocking actionof tropomyosin; myosin-bindingsites exposed.

4

Tropomyosin blockage of myosin-binding sites is restored; contractionends, and muscle fiber relaxes.

7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DU action potential video...

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