Download Chapter 30: How Animals Move 30.1 Locomotion requires energy to

Chapter 30: How Animals Move
30.1 Locomotion requires energy to overcome friction and gravity
 Most animals spend much of their time and energy moving in search of food, mates, or escaping from danger.
Active travel from one place to another is called locomotion, and it requires animals to expend energy to
overcome friction and gravity which would keep it stationary.
 Swimming – Gravity is not much of a problem for swimmers, as water supports most of the body weight.
Friction, however, is difficult to overcome. Swimming is as diverse as the animal that swims. Insects swim
using their legs to push against water, squids and jellies can be jet propelled by taking in and squirting water,
fish move their body and tail from side to side, whales undulate the body.
 Locomotion on land: hopping, walking, running, and crawling – Gravity is more of an issue for land movement
than friction because air offers little resistance. To move on land, a powerful muscle and skeletal system must
be present.
o Hopping – Large muscles of the legs generate a lot of power. Tendons in the legs momentarily store
energy, which is available for the next hop.
o Crawling – Since much of the body is in contact with the ground, friction is a problem. Many crawling
animals (like snakes) move in an undulating fashion where the body is moved from side to side.
o Flying – To become airborne, the wings must develop enough lift to overcome gravity. All wings are
airfoils, or shapes that alter air currents to create lift. The shape makes air passing over the wing travel
farther than the air passing under the wing. The resulting air molecules are space farther apart above
the wing than below it creating greater pressure underneath. This pressure provides the lift for flight.
 All types of movement are similar at the cellular level and result from two contractile systems, the microtubules
and microfilaments.
30.2 Skeletons function in support, movement, and protection
 Animals could not move without a skeleton, nor could they support their own weight. Skeletons also provide
protection for an animal’s soft parts. Three types of skeletons exist and all three have multiple functions.
 Hydrostatic skeleton – consists of fluid held under pressure in a closed body compartment. It helps protect body
parts, cushions from shocks, gives the body shape, and provides support for muscle action. Animals such as
earthworms and cnidarians (hydra, jellies) have this type. Most animals with this type are soft and flexible; they
may have an expandable body that allows them to extend and squeeze into openings. This type cannot support a
terrestrial form of locomotion where the body is held off the ground.
 Exoskeletons – A rigid external skeleton. Found in a variety of aquatic and terrestrial animals such as insects,
crustaceans, and other arthropods. Muscles attach to parts of the exoskeleton to move the jointed body parts.
The skeleton is thinner at the joints to allow movement and flexibility.
o It gives protection, support, and flexibility. It is excreted by living cells, but does not grow with the
animal. Therefore, it must be shed for the animal to grow; this shedding is termed molting.
 Endoskeletons – hard or leathery support elements inside the soft tissues of the animal. Vertebrates have a
skeleton consisting of cartilage, bone or a combination.
30.3 Vertebrate skeletons are variations on an ancient theme
 The human skeleton supports an upright body that sits on its hindquarters or walks/runs on two legs. All
skeletons have similarities.
 The axial skeleton supports the axis, or trunk. It consists of the skull enclosing the brain, the vertebral column
(backbone) that encloses the spinal cord, and a rib cage around the lungs and heart.
 The appendicular skeleton made up of the bones of the appendages and the bones that anchor them to the axial
skeleton. In land vertebrates, the shoulder girdle and pelvic girdle provide bases of support for the forelimbs and
hind limbs.
 Housing a large brain, the skull is large and flat-faced. The rounder part is the largest brain case, relative to
body size. The skull sits atop the backbone with the spinal cord exiting directly underneath. The backbone is Sshaped to help balance the body on a vertical plane. The pelvic girdle is shorter and rounder, and the hands and
feet are adapted for strong gripping and precise manipulation. The feet have a ground touching heel, a straightfacing big toe for propulsion, and shock absorbing arches.
 The human skeleton is not perfect. The backbone is unevenly weighted, carrying most of the weight in the
lower back.
30.4 Bones are complex living organs
 Bones consist of several types of moist living tissues. Fibrous connective tissue covers the outside surface and
helps form new bone in the event of a fracture. Cartilage forms a cushion surface for joints and protects the ends
of bones as they move against each other. The bone itself contains cells that secrete material, matrix made of the
protein collagen, calcium and phosphate. The collagen keeps the bone flexible and non-brittle while the matrix
resists compression.
 The shaft of long bones is compact bone that has a dense structure. The central cavity contains yellow marrow,
which is usually stored fat. The ends of the bone have an outer layer of compact bone and an inner layer of
spongy bone. The cavities contain red marrow that produces blood cells.
 Blood vessels go through the channels of bone bringing in nutrients and regulatory hormones. Nerves help
regulate the traffic of materials between bone and the blood.
30.5 Healthy bones resist stress and heal from injuries
 Bones are rigid but not inflexible and will bend in response to external forces. The skeletal system does have its
limits, if too much force is applied, the bone can break. The average American will break two bones in a
lifetime, most commonly the forearm, unless they are over 75 and it will be the hip.
 Usually a fracture comes from a sudden impact, and can be prevented with use of protective gear. Stress
fractures can occur from long-term repeated forces.
 Human bones are continuously broken down and rebuilt. This natural process helps healing fractures. Treatment
comes in two stages:
o Putting the bone back in its normal place
o Immobilizing it until the body repairs the break. A splint or cast is usually used to promote healing and
prevent movement
 In more severe breaks, the bone may be put in traction, where external pressure is used to align the bone. In
some cases, plates, rods, and/or screws repair bones surgically.
 Once it heals, the bone is stronger and thicker than it was before. In some cases, the bone is beyond repair and
must be replaced. Hip joints have been replaced artificially for many years, but the used of bone grafts has
become a usable technique.
 The risk of fracture increases if bones are weak. Osteoporosis symptoms include low bone mass and
deterioration of bone tissue. Throughout our lives, bone is constantly repaired and replaced by new tissue. If
bone is replaced too slowly, then osteoporosis results.
 While always a concern for older women, it is being seen in more men, and surprisingly, in young people.
Because people are getting less exercise, they are not getting the weight-bearing exercise they need to keep
them strong.
30.6 Joints permit different types of movement
 Much of the skeleton’s versatility comes from joints. Ligaments are bands of fibrous tissue that hold together
the bones of movable joints.
 Ball and socket joints allow for the rotation of limbs in several planes. These are found in the shoulders as well
as the hips.
 Hinge joints only allow movement in a single plane. They are especially vulnerable to injury from quick turns
that can pull the joint sideways. These types are found in the elbows and knees.
 Pivot joints allow enables rotation and make precise manipulations. They also allow for rotation from side to
side as in the vertebrae that allow for the head to “shake no.”
30.7 The skeleton and muscles interact in movement
Muscles interact with bones that act as levers, to produce movements. Muscles connect to bone by tendons. The
action of muscle is to contract, shorten. Animals have antagonistic pairs of muscles that apply forces to move parts
of the skeleton.
30.8 Each muscle cell has its own contractile apparatus
 Skeletal muscle is attached to the skeleton and produces movement and is made up of groups of smaller and
smaller cells. A muscle consists of bundles of parallel muscle fibers; each fiber is a single cell with many
nuclei.
 Each muscle fiber is a bundle of smaller myofibrils, each consisting of repeating subunits called sarcomeres.
Skeletal muscles are striped because the sarcomeres produce alternating bands of light and dark fibers.
Functionally, the sarcomere is the contractile apparatus of the myofibril. Each one is composed of a thin
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filament made of two strands of a protein called actin and two strands of a regulatory protein wrapped around it.
Thick filaments contain multiple strands of the protein myosin.
The dark band centered in the centromere is where the thick fibers are, and they are interspersed with thin one
that project towards the center of the sarcomere.
The arrangement of thin and thick filaments is related to the mechanics of muscle contraction.
30.9 A muscle contracts when thin filaments slide across thick filaments
Sliding Filament Model
1. A sarcomere contracts when its thin filaments slide across its thick filaments. When the muscle is fully
contracted, the thin filaments overlap in the center of the sarcomere. Contraction shortens the sarcomeres,
but does not change the lengths of the thick and thin filaments. Here’s how it happens:
2. ATP binds to the myosin head, causing it to detach from its binding site on actin
3. The myosin head reduces ATP to ADP, releasing energy that changes its shape and extending it to a high
energy position
4. The energized myosin head binds to an exposed binding site on actin
5. The power stroke is the event that actually leads to sliding. ADP is released from the myosin head and it
bends back to the low-energy position, pulling the filament to the center of the sarcomere.
6. After one power stroke, the whole process repeats. As long as sufficient ATP is present, the muscle will
continue to contract.
30.10 Motor neurons stimulate muscle contraction
 Sarcomeres must be stimulated by a motor neuron. A typical motor neuron can stimulate many muscle fibers
because each neuron has many branches. Motor units consist of a neuron and all of the muscle fibers it controls.
The motor neuron has its dendrites and cell bodies. Its axons form synapses, the neuromuscular junctions.
 When a motor neuron sends out an action potential, it releases acetylcholine in the synapse. Acetylcholine
diffuses across the junction to the muscle fiber and making the motor unit contract simultaneously.
 This organization of neurons and muscle cells into motor units is the key to the action of whole muscles. The
ability to vary the force our muscles develop depends on the nature of the motor unit. Forceful contractions
result when several motor units are activated. How does it happen?
1. Acetylcholine diffuses across the junction and changes the permeability of the muscle fiber’s plasma
membrane
2. This change triggers action potentials that move across the muscle cell membrane
3. The action potentials make the ER release calcium into the cytoplasm
4. Calcium moves the regulatory protein so that myosin heads can bind to actin and initiate filament sliding
5. When motor neurons stop sending action potentials, the calcium flow is sent back to the ER and the
muscles stop contracting
30.11 Aerobic respiration supplies most of the energy for exercise
 There is a point at which muscles will no longer contract. Usually we do not push our muscles to that point,
total fatigue. ATP is required for muscle contraction. If ATP supply does not keep up with demand, muscle
contractions cease. This can happen in many ways: circulation is not supplying oxygen, muscle fibers could not
generate ATP…
 Athletes can compete physically because they use training programs to increase stamina and muscle strength.
Aerobic exercise increases efficiency and the fatigue resistance of muscles. It can also increase the number of
muscle mitochondria, improves blood flow to muscles, and strengthens the heart and circulatory system. In
addition, it strengthens bones and the gas exchange of the lungs is more efficient.
 Most of ATP for aerobic exercise comes from the aerobic reactions of cellular respiration, which breaks down
glucose into usable energy.
 Muscles are supplied by blood vessels that bring in oxygen and take out carbon dioxide. Breathing and heart
rate during exercise facilitate the exchange of gases.
 Glucose for breakdown is available from the bloodstream, and the muscles supply glycogen, which is broken
down to provide more glucose.
 Anaerobic exercise builds larger muscle and generates greater power. This is usually to add strength by
increasing the size of muscle fibers and enabling them to generate force.
 If there is not enough oxygen available, then lactic acid fermentation can be run, but will only supply a fraction
of the necessary energy.
30.12 Characteristics of muscle fiber affect athletic performance
 The overriding theme of all organ systems is homeostasis. The other key is that structure underlies function.
 Each cell through organ system has a job to perform.
 Fibers making up muscles are not all alike. Fast twitch fibers are rapid and fire powerful, but they fatigue
quickly. Slow twitch fibers can sustain repeated contractions and are slow to fatigue, but their contractions are
less forceful. Each muscle has a combination of fast, slow, and intermediate fibers. The differences among the
fibers can be traced to the myosin that constructs the fibers. Each fiber contains different forms of myosin that
break down ATP at different speeds.
 The fastest fibers cycle through cross bridges rapidly and produce forceful contractions in brief, powerful
motions. In slow fibers, the cross bridges are made more slowly and result in a sustained, but less forceful
contraction.
 Exercise can change the content of the muscle fibers to an extent. The muscle responses correspond to the
stresses place on them.
o Weight lifting stimulates the production of more myofibrils
o In aerobic exercise, more myoglobin is produced, increasing the number of mitochondria. This leads to
changes that increase endurance and are less prone to fatigue.