The Chemical Context of Life

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Fast-Twitch and Slow-Twitch Fibers

Slide 71

Other Types of Muscle

In addition to skeletal muscle, vertebrates have cardiac muscle and smooth muscle.

Cardiac muscle, found only in the heart, consists of striated cells electrically connected by intercalated disks.

Cardiac muscle can generate action potentials without neural input.

Slide 72

In smooth muscle, found mainly in walls of hollow organs, contractions are relatively slow and may be initiated by the muscles themselves.

Contractions may also be caused by stimulation from neurons in the autonomic nervous system.

Slide 73

Skeletal systems transform muscle contraction into locomotion

Skeletal muscles are attached in antagonistic pairs, with each member of the pair working against the other

The skeleton provides a rigid structure to which muscles attach.

Skeletons function in support, protection, and movement.

Slide 74

The interaction of antagonistic muscles and skeletons in movement

Grasshopper

Human

Biceps contracts

Triceps contracts

Forearm extends

Biceps relaxes

Triceps relaxes

Forearm flexes

Tibia flexes

Tibia extends

Flexor muscle relaxes

Flexor muscle contracts

Extensor muscle contracts

Extensor muscle relaxes

Slide 75

Types of Skeletal Systems

The three main types of skeletons are:

Hydrostatic skeletons (lack hard parts)

Exoskeletons (external hard parts)

Endoskeletons (internal hard parts)

Slide 76

Hydrostatic Skeletons

A hydrostatic skeleton consists of fluid held under pressure in a closed body compartment

This is the main type of skeleton in most cnidarians, flatworms, nematodes, and annelids.

Annelids use their hydrostatic skeleton for peristalsis, a type of movement on land produced by rhythic waves of muscle contractions.

Slide 77

Crawling by peristalsis

Circular muscle contracted

Circular muscle relaxed

Longitudinal muscle relaxed (extended)

Longitudinal muscle contracted

Bristles

Head end

Head end

Head end

Slide 78

Exoskeletons

An exoskeleton is a hard encasement deposited on the surface of an animal.

Exoskeletons are found in most molluscs and arthropods.