Chapter 49—Sensory & Motor

Mechanisms

If a tree falls in the forest and no one is there to hear it, does it

make a sound?

I. Sensory Reception

• Sensory Transduction

– energy from stimulus → receptor membrane potential

• Amplification– strengthening stimulus energy

• Transmission– conduction of impulse to CNS

• Integration– processing of information

Types of Sensory Receptors

• Based on the type of energy they detect:– Mechanoreceptors

• pressure, touch, stretch, motion, sound

– Pain Receptors• pain, discomfort

– Thermoreceptors• heat, cold

– Chemoreceptors• taste, smell

– Electromagnetic Receptors• light, electricity, magnetism

Stimuli start action potentials

(opens ion channels)

Taste (Gustation)

Type of receptor?

Common themes seen

before?

Smell (Olfaction)

Why is sense of taste

reduced when you are

sick?

Sensory Receptors in Skin

Mechanoreception

(hair cell inside ear)

II. Photoreceptors & Vision

Where are the photo

receptor cells located?

Eyes contain 70% of

total sensory receptors

in body!

Which part focuses the

image?

How?

Focusing in the Eye

Focus is achieved by changing

shape of lens

Photoreceptors: Rod Cells vs.

Cone Cells

If you are a nocturnal mammal, which

do you have more of?

What actually senses the light?

Where are

we?

Rhodopsin = visual pigment

Signal Transduction in a Rod cell

Common themes seen before?

How does all of this get to the

brain?

…as action potentials along the optic

nerve

Left is right, and right is left…

III. Hearing & Equilibrium

Hearing

What type of receptor is involved?

Where are receptors located?

Sound waves create vibrations

that are conducted into the ear →

Vibrations make waves in cochlear

fluid →

hairs brush membrane →

release neurotransmitters →

triggers action potential →

brain hears sound

Equilibrium

More fluid, hair cells, and action potentials…

IV. Movement & LocomotionAnimal movement comes from contraction of muscles

against a skeleton

Organization of Skeletal Muscle

Human Endoskeleton

> 200 bones

3 types of

skeletons:

� hydrostatic

skeleton

� exoskeleton

� endoskeleton

3 functions of a

skeleton:

� support

� protection

� movement

Muscle MovementMuscles do work by contracting

� skeletal muscles come in

antagonistic pairs� flexor vs. extensor

� contracting = shortening

� moves skeletal parts

tendons

� connect bone to muscleligaments

� connect bone to bone

Structure of Skeletal Muscle

Striated due to repeating light and dark

bands in myofibril

A band (dark) = thick filaments = myosinI band (light) = thin filaments = actin

Sarcomere—functional unit of muscle

contraction

Figure 49.31, pg. 1081

Sliding Filament Model of Muscle Contraction

Thick & thin filaments slide past each other

(sarcomere shortens)

Caused by interaction between actin and

myosin (form cross-bridges)

Figure 49.32, pg. 1081

Actin & Myosin generate force for

muscle contraction

Actin & Myosin generate force for

muscle contraction

Actin & Myosin generate force for

muscle contraction

Actin & Myosin generate force for

muscle contraction

Figure 49.33, pg. 1082

Where does energy for contraction

come from? What happens when

you run out?

What is the trigger for muscle

contraction?

Skeletal muscle contracts only when

stimulated by motor neuron

Nerve signal (action potential)

stimulates muscle cell’sSarcoplasmic reticulum (SR) to

release stored Ca2+ into cytoplasm

Ca2+ triggers muscle action

At rest, troponin molecules hold

tropomyosin molecules so that

they cover the myosin-binding

sites on actin (no contraction)

Binding of Ca2+ exposes myosin

binding sites (contraction can

occur)

Figure 49.34, pg. 1083

Review of Skeletal Muscle Contraction

Figure 49.36, pg. 1084

um…study

this.Slow

muscle

fibers vs.

fast muscle

fibers?

How do you contract a whole muscle?

Repeated action potentials, or…

Using…motor units

Motor unit—a single motor neuron and all

the muscle fibers it controls

Many fibers can contract as a group

Botox—blocks release of

acetylcholine