Chapter 30 How Animals Move

I. Movement and Locomotion

1. Movement is a distinguishing characteristic of animals. Most animals are fully mobile by swimming, walking and running, hopping, crawling, and flying.

2. Locomotion is an active movement from place to place for invertebrates.

3. Locomotion requires energy to overcome friction and gravity.

4. Crawling:

(1)  Animals that have no limbs or very short limbs drag their bodies along the ground in a crawling movement, such as snakes.

(2)  These animals mainly spend energy to overcome friction rather than gravity.

(3)  Earthworms craw by peristalsis, a type of locomotion produced by rhythmic waves of muscle contractions passing from head to tail.

(4)  To move by peristalsis, an animal needs:

1)   a way to anchor its body to the ground, such as bristles

2)  a set of circular muscle that elongates the body

3)  a set of longitudinal muscle that shortens the body

5. Skeletons function in support, movement, and protection.

6. There are 3 main types of skeletons:

(1)  Hydrostatic skeletons: consist of fluid held under pressure in a closed body compartment, such as many aquatic animals and terrestrial animals (earthworm)

(2)  Exoskeletons: a hard external skeleton that protects an animal and provides points of attachment for muscles.

(3)  Endoskeletons: consist of hard supporting elements situated among the soft tissues of vertebrates

II. The Vertebrate Skeleton

1. Axial skeleton contains components of the skeletal system that support the central trunk of the body, including the skull, vertebral column (backbone), and rib cage in a vertebrate.

2. The vertebrae, the definitive characteristic of vertebrates, consist of a series of individual bones joined by cartilage discs.

3. An adult human has 24 (33) vertebrae, while a python has 400.

4. The vertebral column can be divided into cervical (neck; 7), thoracic (chest; 12), lumbar (5), sacral (5-fused), and coccygeal (caudal; tail; 4-fused) vertebrae.

5. Appendicular skeleton contains components of the skeletal system that support the non-axial portions, such as the fins of a fish or the arms and legs of a land vertebrate.

(1)  Appendicular skeleton is made up of the bones of the appendages and the bones that anchor the appendages to the axial skeleton.

(2)  Appendicular skeleton includes the pectoral (shoulder) girdle and the pelvic girdle providing a base of support for the bones of the forelimbs and hind limbs.

6. Bone matrix consists of flexible fibers of the protein collagen with crystals of calcium and phosphate. The collagen keeps the bone flexible and nonbrittle, while the hard mineral matrix resists compression.

7. Bone marrow is a specialized tissue that produces blood cells or store fat in the central cavity of a bone or vertebra.

8. Osteoporosis is a skeletal disorder characterized by low bone mass (thinning and porous) and easily broken bones.

9. Ligament is a type of fibrous connective tissue that joins bones together at joints.

(1)  Ball-and-socket joints are found at the pectoral and pelvic girdles.

(2)  Hinge joints are found at elbows and knees.

(3)  Pivot joints are found at elbows.

III. Muscle Contraction and Movement

1. The skeleton and muscles interact in movement.

2. A tendon is a fibrous connective tissue connecting a muscle to a bone.

3. A muscle consists of many bundles of muscle fibers (muscle cells; myofibers).

4. Myofibril is a contractile strand in a muscle cell, made up of many sarcomeres.

5. Sarcomere is the fundamental unit of muscle contraction, composed of thin filaments of the contractile protein actin and thick filaments of the contractile protein myosin; the region between two dark lines (Z lines or Z discs) in a myofibril.

6. According to the sliding-filament model of muscle contraction, a sarcomere contracts (shortens) when actins slide along myosins.

(1)  During contracting, the Z lines have moved closer together.

(2)  Contraction shortens the sarcomere without changing the lengths of actin and myosin.

(3)  A whole muscle can shorten about 35% of its resting length when all sarcomeres contract.

(4)  Myosin acts as the engine of movement. Each myosin molecule has a globular head and a long tail regions.

(5)  Each myosin head has two binding sites: one is the binding site to actin to form a cross-bridge and another is ATP binding site.

(6)  Each myosin head repeats back and forth in a limited arc as it changes shape from a low-energy configuration to a high-energy configuration and back again.

7. The action potential from a motor neuron propagates along a muscle fiber and extends deep into the interior of the muscle fiber by transverse (T) tubules.

(1)  The T tubules are in close contact with the endoplasmic reticulum (ER; sarcoplasmic reticulum SR).

(2)  The action potential causes channels in the ER to open, releasing calcium ions (Ca²⁺) into the cytosol.

(3)  When a muscle fiber is in a resting state, the regulatory proteins tropomyosin and troponin block the myosin-binding sites on the actin.

(4)  When Ca²⁺ binds to troponin, the tropomyosin moves away from the myosin-binding sites, allowing contraction to occur.

(5)  When motor neurons stop sending action potentials to the muscle fibers, the ER pumps Ca²⁺ back out of the cytosol, binding sites on the actin are again blocked, the sarcomeres stop contracting, and the muscle relaxes.