Week 5: Muscle Physiology and Locomotion

Define locomotion

Moving from one place to another

Active process that is initiated and controlled by the animal

Is being faster better

Yes in many cases, natural selection favours higher locomotory performance

e.g. faster males collared lizards have more offspring than slower individuals

What is a muscles fuel supply sometimes more important than

Muscles contractile apparatus

What does the rate of muscle energy work equal

Rate of ATP supply

What are the types of muscle energy systems

Immediate, glycolytic and oxidative

What is immediate muscle energy

Uses ATP already present

What is glycolytic muscle energy

Synthesises ATP by breaking down carbs, anaerobic with no oxygen, produces ATP quicker but not as efficient

What is oxidative muscle energy

Synthesises energy through the breakdown of food molecules

Describe glycolysis briefly

• Breaks down glucose in blood and glucose-6 phosphate from glycogen

• Doesnt need oxygen

• Produces ATP quick

• Glucose to pyruvate produces 2 ATP (through enzyme catalysed steps)

• End product is pyruvate - starting product for tricarboxylic acid cycle

What are the three different types of muscle energy

Immediate, glycolytic, oxidative

Briefly describe the TCA cycle

Pyruvate from glycolysis converted to acetyl co-a

Catalysed through series of enzyme catalysed steos

Converted to two atp molecules eventually

Name three ways cells control the rate of ATP producyion through the TCA cycle

1. Regulate concentrations of reactants

2. Regulate enzyme levels

3. Catalytic activity of enzymes

What does an electron transport chain create

An electrochemical gradient to drive ATP syntheses

Is in the mitochondria

Where does the majority of ATP production in aerobic metabolism take place

Electron Transport Chain

What is the electron transport chain catalysed by

Key enzymes- including cytochrome c oxidase

What are the key differences between oxidative and glycolytic energy sources

1. Efficiency: oxidative ATP production 18x more efficient vs only 2ATP per glucose

2. Rate of ATP mobilisation/production: glycolysis much faster than oxidative, but can’t be sustained

3. Oxygen: glycolysis does not rely on sufficient oxygen availability while oxidative does

4. Fuel diversity: glycolysis can only use carbohydrates, while oxidative ATP production from any food/stored resource

Where does muscle fuel come from

• Carbs in muscle

• Muscle lipid storage

• Glucose in blood from food breakdown

• Lipid in blood from breakdown of lipoproteins

What does the Krogh model of oxygen show and focus on

Delivering oxgen to vertebrate muscles

Structure and function of capillary networks to support oxygen delivery to the muscle

What does the Krogh model assume

1. Each capillary is the only oxygen supply for a surrounding tissue

2. Partial pressure of oxygen of the blood vessel wall is equal to that of the blood

3. There is no decline in oxygen partial pressure along the cappilary

4. Oxygen diffuses radially from the capillary

5. Oxygen consumption is uniform in muscle tissue

Name the different types of animal movement

Crawling, jet propulsion, swimming

How does crawling movement work in animals

• Supported by a hydrostatic skeleton

• Circular and longitudinal layers of striated muscle allows peristaltic waves of contraction

How does jet propulsion movement work in animals

• Radial muscles extend from inside of mantle to outside, contract to reduce mantle wall thickness/circumference

• Mantle- three layer- thick inner mitochondria in the outer layer

• Water enters mantle when muscle relaxes and is rapidly ejected upon contraction

How does swimming movement work in animals

• Fish use slow oxidative and glycolytic muscle fibers- in layers called myotomes

• Fish have two myotomes

Describe muscle fibres and name two types

Dictated by primary locomotory purpose

Two primary types:slow oxidative (red) and glycolytic (white)

Why are slow oxidative muscle fibres named that way

Slow- speed to contract and develop tension

Oxidative- fiber is poised primarily to make ATP aerobically

What are slow oxidative fibres like

• High no of aerobic enzymes for krebs cycle

High ability to take up o2:

• High conc of mitochondria

• Rich in myoglobin

• Red in colour due to oxygen

• Low peak mechanical power but fatigue resistant

Why are fast glycolytic muscle fibers named this

Fast- speed to contract and develop tension

Glycolytic- optimised for anaerobic metabolism

What are fast glycolytic fibres like

• High levels of anaerobic enzymes to catalyse glycolysis

• Sparse mitochondria and myoglobin

• Fibres whitish in color due to low oxygen

• High peak mechanical power output but fatigue quickly

How are muscle fibers differently distributed in muscle fibers

Mammalian skeletal muscles are typically more heterogenous than in fish

Fish tend to be primarily either red or white

Mammals tend to have greater pink (mix of types)

How can you study muscle

• Fit muscles with electrodes of an electromyograph

• Compare power output to locomotor frequency

• Red muscle recruited at lower speeds

Are all red muscles creates equal

no

• animal dependent

• mitochondrial content dependent

Why does body shape vary in fish

Different locomotion

• Fast swimmers

• Burst speed/maneuverability

• Demersal

• Narrow spaces

What body shape do fast swimmers have and give species examples

Long, streamlines, fins serve as rudders

e.g. tuna, shark, mackrel

What body shape fish needing burst speed and manoeuvrability have and give species examples

Laterally compressed, capable of rapid burst speed

e.g. angelfish, snapper, damselfish

What body shape fish favouring a demersal lifestyle have and give species examples

Dorsoventrally flattened

e.g. flounder, rays, halibut

What body shape do fish living in narrow spaces have and give species examples

Elongated, flexible bodies

e.g. eels, pipefish, trumpetfish

Define muscle fatigue

Exercise induced reduction in muscles ability to generate peak forces and maintain power output

What are the 4 main causes of muscle fatigues

1. Lactic Acid

2. Glycogen depletion

3. Hyperthermia

4. Dysfunction at cellular and molecular leve,How

How does lactic acid cause muscle fatigue

Occurs in humans and other vertebrates when intense exercise involves sustained net lactate production

• By product of anaerobic metabolism

• Serve as an indicator fatigue will occur

How does glycogen depletion cause muscle fatigue

Occurs when glycogen is depleted in the body’s tissues primarily in skeletal muscle

• Glycogen stores in muscle used first during exercie and supplemented by stores in the liver as needed

• Fuels aerobic metabolism

How does hyperthermia cause muscle fatigue

Due to unusually high body temp, caused when edogenous heat production surpasses the capacity for heat release to surroundings

What is hyperthermia leading to muscle fatigue primarily related to

1. Changes in the CNS leading to central fatigue and dysfunction of neurotransmitters

2. Impairments of cardiovascular function reducing oxygen delivery

What is dysfunction at cellular and molecular level

Contraction of muscle entail coordination of proteins, ATP, ion balance and other cellular molecules so dysfunction can occur due to any of these constituents

• Excitation and contraction of muscle occurs through ion fluxes across cellular and intracellular membranes

What behaviour defines steady state locomotion

Cruising/routine behaviour: fuelled aerobically primarily using red muscle fibres

• Sustained for long periods of time

Examples of steady state locomotion

Fish swimming around reef

Humans going for a light jog

Foraging antelopes

What behaviour defines unsteady state locomotion

Sudden intense exertion:fuelled anaerobically primarily utilizing white muscle fibers

• Causes lactate accumulation

• Can lead to fatigue

• Only use carbohydrates as fuel

Examples of unsteady state locomotion

• Cod trying to avoid a trawling net

• Salmon leaping waterfalls

• Zebra escaping an attacking lion

• Crayfish tail flipping

What methods can be used to measure locomotion

Treadmill for aquatic species- swim tunnel

Can measure traits such as: Oxygen needs at different swim speeds, tail beat frequency at different swim speeds, gait transition speed, critical swimming speed

Describe the behaviour of burst swimming in fish

• High energy burst swimming either from rest or during periods of steady state swimming

• Important for predator-prey interactions

• Can be categorised as c starts or s starts based on body shape at the end of first contraction

Describe the escape response of fish

Stimulus t=0

Stage one- contract into c shape

Stage 2= other side bends to create a second axial bend to execute propulsion

Stage 3= fish either use new movements or use energy from stage 1 or 2

Define latency in terms of unsteady state locomotion

How long it takes them to react

Define turning rate in terms of unsteady state locomotion

How long it takes for an animal to achieve max shape and what angle does body achieve

Define distance in terms of unsteady state locomotion

How far it moved in stage 1 and 2

What is excess post exercise oxygen consumption (epoc)

the increased oxygen your body uses after exercise to return to its resting state, burning extra calories to restore hormones, replenish energy stores, repair tissues, and manage body temperature

What is light submaximal exercise

Requires that requires less than MMR

• No lactate accumulation

• EPOC only related to replenishing oxygen and phosphagen stores

• Recovery occurs rapidly

What is heavy submaximal exercise

Requires MMR or close to it

• Lactate accumulation

• EPOC relates to lactated to lactate metabolism replenishign oxygen and phosphagen stores

• Longer recovery than light submaximal exercise

What is supra maximal exercise

Exercise that exceeds MMR and AS requiring anaerobic glycolysis to meet ATP demand

• Large lactate accumulation to point of potential debilitating fatigue

• Leads to need for rest and recovery, and period when further super maximal exertion impaired

How do species emphasise aerobic versus anaerboic pathways

Based on species life history stages

e.g. frogs have an increased LDH than toads

How does phenotypic plasticity relate to locomotory performance

Can occur within a species to optimize aerobic vs anaerobic pathways given the indivduals envuroneent

e.g. body does not change based on exercise you do

Give an experimental example where locomotory plasticity is shown in fish

• Fish swam at 60% of their critical swimming speed over 4 weeks in swim tunnel

• Increased overall critical swimming speed

• In open field test trained fish swam further for longer with higher avg and max velocity

How does neuromuscular control relate to plasticity

Acetylcholine and its receptors are involved in general motor function

Influences locomotor speed dictated by motorneuron type

Mode of action is dependent on receptor type

Reconfiguration of receptor types may act as mechanism for neuromuscular plasticity

Name some other cotransmitters that can also contibute to plastcity in spinal circuits during exefcise/injury

Glutamate in nerotransmitters