Muscles Locomotion

Locomotion

Organization of muscles into musculoskeletal

systems allows the of translation cellular

contraction into animal locomotion.

Musculoskeletal system interacts with the

nervous system to control position and

movement of appendages.

Locomotion

Invertebrates

Most worm-like inverts crawl using

overlapping layers of muscle fibers.

Hydrostatic skeleton:

◦ Simple muscles work in combination with

fluid-filled internal chamber.

Nematodes

Earthworms

Locomotor striated muscles organized

into circular longitudinal layers.

Segmented = more control

◦ Peristaltic waves of contraction

Earthworms

Squid

One of fastest

aquatic invertebrates

Circular muscle that

surrounds the mantle

is composed of 3

layers

Squid

Jet propulsion:

◦ Water enters mantle

◦ Mantle contracts – ejected thru siphon

◦ Creates flume of water, pushing the squid forward

Vertebrates

Fish

Tetrapods:

◦ Amphibians

◦ Reptiles

◦ Birds

◦ Mammals

Fish

2 main types of muscle fibers:

White muscle:

◦ glycolytic fiber type, responsible for high

intensity, burst swimming

Red Muscle:

◦ oxidative fiber type, supports slow steady

state cruising activity.

Fish

White Muscle =

◦ 85% of muscle

◦ 60% of body mass

Red Muscle =

◦ Along Lateral Line

◦ Base of Fins

Fish

Myotome:

◦ Blocks of parallel white muscle fibers

connected by thin layers of connective tissue.

Fish

Each myotome connected to posterior

region by tendons.

Skin acts as sheath that connects different

myotomes:

◦ Integrates force of many contractile units

Contraction of a myotome generates a force

that is transmitted to the next myotome.

Muscle Contraction

Oxidative (red) & glycolytic (white)

muscles differ in contractile properties

and produce different types of movement.

Muscle Contraction

Fish:

◦ Red muscle = slow swimming

◦ White muscle = higher velocities

Pattern of sequential activation of muscle contraction = recruitment

Determined by motor neurons, under control of the CNS

Fish

Tetrapods

Build individual muscles using

combinations of fiber types.

Muscle fiber types are used in different

combinations to perform many distinct

styles of movement.

Tetrapods

Limb Movements

Flexion: when a limb bends at a joint

Extension: limb straightens

Induced in response to the contraction of

antagonistic muscles.

Limb Movement

Antagonistic muscles:

◦ muscles which work in opposition

Locomotor Module:

◦ all of the muscles responsible for a type of

movement.

Fiber Types

3 Main Types:

◦ Different species have different types with

different mechanical properties matched to

their biochemistry and morphology.

1. Slow Oxidative (SO)

2. Fast Oxidative Glycolytic (FOG)

3. Fast Glycolytic (FG)

Fiber Types

Muscle Description Metabolic

Features

Slow Oxidative

(SO)

Red Muscles

Slow Twitch

Endurance Muscles

Marathoners

Fast Oxidative

Glycolytic

(FOG)

White – Pink

Mixed

Oxidative based

metab.

Fatigue Resistant

Fast Glycolytic

(FG)

White

Fast Twitch

Fatigue Sensitive

Quick Response

Muscle Description Metabolic

Features

Slow Oxidative

(SO)

Red Muscles

Slow Twitch

Endurance Muscles

Marathoners

Fast Oxidative

Glycolytic

(FOG)

White – Pink

Mixed

Oxidative based

metabolism

Fatigue Resistant

Fast Glycolytic

(FG)

White

Fast Twitch

Fatigue Sensitive

Quick Response

Fiber Types

Fiber composition varies with:

1. Training

2. Muscle Type

3. Animal species / athlete

Fiber Types

Animal %SO %FOG %FG

Sea Otter 56 2 42

Dolphin 43 10 47

Sea Lion 44 18 39

Narwhal 87 ? 13

Energy Metabolism & Muscle Types

Muscle activity demands a great deal of

energy, mainly in the form of ATP.

Locomotor activity is supported by some

combination of anaerobic glycolysis and

mitochondrial aerobic metabolism.

Energy Metabolism & Muscle Types

These two pathways differ in 5 main respects that determine how they support muscle activity:

1. Metabolic Efficiency

2. Rate of ATP Production

3. Dependence on Oxygen

4. Fuel Diversity

5. Range of Mobilization

Metabolic Efficiency

Anaerobic

2 ATP / Glucose

Used during fast /

explosive movements

Aerobic

36 ATP / Glucose

Used during

endurance events

Used during rest and

recovery periods

Rate of ATP Production

Anaerobic

Less Efficient

Much Faster

Runs out of fuel fast

Fatigues

Aerobic

Efficient

Slower

Sustainable

Dependence on Oxygen

Anaerobic

Only option when no

oxygen is present

Aerobic

Needs oxygen

During high intensity activity, oxygen cannot be

delivered to muscles fast enough to meet ATP

demands by oxidative phosphorylation and tissues

become functionally hypoxic.

Fuel Diversity

Anaerobic

Glycolysis relies

exclusively on

carbohydrates

Aerobic

Able to utilize:

◦ carbohydrates

◦ lipids (fatty acids)

◦ proteins (amino acids)

Rate of Mobilization

Muscles possess low levels of fuels that can be oxidized immediately (glucose, fatty acids, glycerol, free amino acids).

These fuels are consumed rapidly, so animals must be able to mobilize stored fuels to sustain muscle activity.

Glycogen stores mobilized much faster than lipid stores

Mitochondrial Content

Mitochondria are the site of oxidative

phosphorylation.

Mitochondrial content is an important

determinant of aerobic capacity.

Mitochondrial Content

Mitochondrial content varies widely

among muscle types and species.

◦ High [Mitochondria] = slow twitch oxidative

◦ Lower [Mitochondria] = fast twitch glycolytic

Fiber Types

Slow Oxidative (SO):

◦ Dense with capillaries

◦ Rich in mitochondria and myoglobin

Fast Oxidative Glycolytic (FOG):

◦ Less dense in mitrochondria and myoglobin

Fast Glycolytic (FG):

◦ Least dense in mitochondria and myoglobin

Muscle Recovery

High intensity activity is fueled by

intramuscular stores of glycogen.

As fast twitch muscles undergo glycolysis,

lactate is produced.

Muscles become exhausted from a

combination of energetic shortfalls, ion

disturbances, and PH imbalance.

Muscle Recovery

Muscles must:

◦ Replenish energy stores

(glycogen, ATP, PCR)

◦ Reestablish ion gradients

(Ca2+ stores and pH)

◦ Remove lactate.

Lactate Removal

1. Used in muscle to rebuild glycogen stores.

1. Blood-born lactate can be oxidized by

other aerobic tissues (eg. Heart)

2. Export lactate to be processed elsewhere.

Cori Cycle

Lactate Removal

Muscle Recovery

Oxygen consumption increase with increasing activity.

Oxygen stores must be replenished.

Muscles must:

◦ Resynthesize ATP, PCR, and glycogen

◦ Reestablish ion gradients

◦ Repair damaged muscles

Restoring Oxygen Levels

Energy for these processes is provided by

mitochondrial oxidative phosphorylation.

Recovering animals often show elevated

rates of oxygen consumption long after

exercise has ceased = oxygen debt.

Muscle Recovery

Recovery requires both energy & oxygen.

Muscles & Locomotion

Metabolic processes must be precisely

coordinated to ensure that ATP

synthesis matches ATP demand.

Hummingbirds

Hummingbirds

Morning/ first flight - oxidizes fatty acids.

◦ After first nectar it switches to carbohydrate utilization and lipid storage.

Actively feeding - dietary carbohydrates

◦ Stores extra surcose as glycogen and lipid.

Rest - relies on stores.

◦ Also becomes hypometabolic – lowers body temp to reduce MR.

Hummingbirds

Salmon

Salmon

Early Stage of Migration:

◦ large fat stores

Mid Migration:

◦ begin breaking down proteins:

muscles and intestinal tract

Late in migration:

◦ glycogen and glucose support

Salmon