Chapter 50Sensory and Motor Mechanisms

Complex sensory systems that facilitate survival.

Bats use sonar to detect prey.

Moths can detect the bat’s sonar.

Include diverse mechanisms that sense stimuli and generate appropriate movement.

2. Describe the four general functions of receptor cells…

Introduction of Sensory Reception

All stimuli represent forms of energy.

Sensation involves converting energy into a change in the membrane potential of sensory receptors.

All stimuli represent forms of energy.

Function of sensory pathways: sensory reception, transduction, transmission, an integration.

Sensation and perceptions begin with sensory reception.

Detection of stimuli by receptors – both inside and outside of the body.

3. Distinguish between sensory transduction and…

Introduction of Sensory Reception

Sensory transduction: conversion of stimulus energy into change of membrane potential.

Change is called receptor potential – many are very sensitive.

Transmission: sensory cell facilitate the movement of action potentials.

Larger receptor potential = more rapid action potentials.

Integration: receptor potentials integrated through summation.

4. Since all action potentials are the same, explain how the brain distinguishes…

Introduction of Sensory Reception

Perception: the brain’s construction of stimuli

Brain distinguishes stimuli from different receptors by the area where the action potentials arrive.

6. Explain the importance of sensory adaptation.

Introduction of Sensory Reception

Type of Sensory Receptors

7. List the five categories of sensory receptors…

Introduction of Sensory Reception

Mechanoreceptors: sense physical deformation.

TOUCH!

Chemoreceptors: information about the total solute concentration of a solution.

Respond to individual kinds of molecules.

Electromagnetic receptors: detect electromagnetic energy such as light, electricity and magnetism.

Thermoreceptors: respond to heat or cold.

Regulate body temp. by signaling both surface and core temp.

Nociceptors: naked dendrites in the epidermis.

Pain receptors.

8. Explain the role of mechanoreceptors in hearing and balance.

Hearing and Equilibrium

Hearing and perception of body equilibrium are related in most animals.

Mechanoreceptors

9. Describe the structure and function of invertebrate statocysts..

Hearing and Equilibrium

Most invertebrates maintain equilibrium using statocysts.

Detect movement of granules called statoliths.

10. Explain how insects may detect sound.

Hearing and Equilibrium

Many arthropods sense sounds with body hairs that vibrate.

“Ears” consisting of tympanic membrane and receptor cells.

11. Refer to a diagram of the human ear and give the function of each structure.

Hearing and Equilibrium

Vibrations create percussion waves that vibrate tympanic membrane.

Bones of the middle ear transmit the vibrations.

Vibrations create waves of fluid that move through vestibular canal.

Waves cause the basilar membrane to vibrate, bending hair cells.

12. Explain how the mammalian ear functions as a hearing organ.

Hearing and Equilibrium

Bending of hair cells depolarizes the membranes.

Sends action potential to the brain via the auditory nerve.

13. Describe how the ear conveys information about volume and pitch of sound to the brain.

Hearing and Equilibrium

Ear conveys information about volume and pitch.

15. Describe the hearing and equilibrium system of nonmammalian vertebrates.

Hearing and Equilibrium

Fishes have only a pair of inner ears near the brain.

Also have lateral line system that detect and respond to water movement.

16. Distinguish between tastants and odorants.

Chemoreception: Taste and Smell

Taste and smell rely on similar set of sensory receptors.

Terrestrial animals:Gustation: Taste, detection of chemicals called tastants.Olfaction: Smell, detection of odorant molecules.

Taste and smell rely on similar set of sensory receptors.

Taste buds detect five taste perceptions: sweet, sour, salty, butter, and umami – different regions of the tongue.

19. Describe what happens after an odorant binds to an ordorant receptor…

Chemoreception: Taste and Smell

Olfactory receptors are neurons that line the upper portion of the nasal cavity.

Photoreception and Vision

22. Refer to a diagram of the vertebrate eye…

Photoreception and Vision

The basic structure of the vertebrate eye.

Muscle Function

Muscle activity is a response to input from the nervous system.

The action of a muscle is always to contract.

• Skeletal muscle characterized by a hierarchy of smaller and smaller units.

• Consists of a bundle of long fibers – each a single cell – running the length of the muscle.

• Each muscle fiber is a bundle of smaller myofibrils.

Two kinds of myofilaments.

Thin: two strands of actin, one strand of regulatory protein.

Thick: staggered arrays of myosin molecules.

Skeletal muscle also called striated muscle – arrangement of myofilaments create light and dark bands.

Functional unit of a muscle is called a sarcomere – bordered by Z lines.

Sliding-filament model: filaments slide past each other, producing overlap.

Based on interaction between actin of thin filaments and myosin of the thick filaments.

Fig. 50-27-1

Thinfilaments

ATP Myosin head (low-energy configuration

Thick filament

Thin filament

Thickfilament

Fig. 50-27-2

Thinfilaments

ATP Myosin head (low-energy configuration

Thick filament

Thin filament

Thickfilament

Actin

Myosin head (high-energy configuration

Myosin binding sites

ADP

P i

Fig. 50-27-3

Thinfilaments

ATP Myosin head (low-energy configuration

Thick filament

Thin filament

Thickfilament

Actin

Myosin head (high-energy configuration

Myosin binding sites

ADP

P i

Cross-bridgeADP

P i

Fig. 50-27-4

Thinfilaments

ATP Myosin head (low-energy configuration

Thick filament

Thin filament

Thickfilament

Actin

Myosin head (high-energy configuration

Myosin binding sites

ADP

P i

Cross-bridgeADP

P i

Myosin head (low-energy configuration

Thin filament movestoward center of sarcomere.

ATP

ADP P i+

Skeletal muscle fiber contract only when stimulated by a motor neuron.

Muscle at rest, myosin-binding sites on thin filament blocked by protein tropomyosin.

• For a muscle fiber to contract, myosin-binding sites must be uncovered

• This occurs when calcium ions (Ca2+) bind to a set of regulatory proteins, the troponin complex

• Muscle fiber contracts when the concentration of Ca2+ is high; muscle fiber contraction stops when the concentration of Ca2+ is low

• The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine

• Acetylcholine depolarizes the muscle, causing it to produce an action potential

Action potentials travel to the interior of the muscle fiber along transverse (T) tubules

The action potential along T tubules causes the sarcoplasmic reticulum (SR) to release Ca2+

The Ca2+ binds to the troponin complex on the thin filaments

This binding exposes myosin-binding sites and allows the cross-bridge cycle to proceed

Types of Skeletal Muscle Fibers• Skeletal muscle fibers can be classified

– As oxidative or glycolytic fibers, by the source of ATP

– As fast-twitch or slow-twitch fibers, by the speed of muscle contraction

Oxidative and Glycolytic Fibers• Oxidative fibers rely on aerobic respiration to

generate ATP• These fibers have many mitochondria, a rich

blood supply, and much myoglobin• Myoglobin is a protein that binds oxygen more

tightly than hemoglobin does

• Glycolytic fibers use glycolysis as their primary source of ATP

• Glycolytic fibers have less myoglobin than oxidative fibers, and tire more easily

• In poultry and fish, light meat is composed of glycolytic fibers, while dark meat is composed of oxidative fibers

Fast-Twitch and Slow-Twitch Fibers• Slow-twitch fibers contract more slowly, but

sustain longer contractions• All slow twitch fibers are oxidative• Fast-twitch fibers contract more rapidly, but

sustain shorter contractions• Fast-twitch fibers can be either glycolytic or

oxidative

• Most skeletal muscles contain both slow-twitch and fast-twitch muscles in varying ratios