Bioveterinary Sciences &
Biological Sciences Notes
Royal Veterinary College, D300
Contents
ANIMAL LOCOMOTION
Evolution and Adaptation ......................................................................................................... 1
Introduction to the Moving Animal ................................................................................................ 1
Evolution and the Adapted Animal ................................................................................................. 3
Diversity of Animal Movement - Terrestrial ................................................................................... 6
Introduction to the Nervous System .............................................................................................. 9
Introduction to Anatomy .............................................................................................................. 22
Diversity of Animal Movement - Flight ......................................................................................... 28
Diversity of Animal Movement – Aquatic and Terrestrial Locomotion in Frogs .......................... 34
Integrative Perspectives on Animal Movement ....................................................................... 39
Integration of Locomotion and Ventilation .................................................................................. 39
Metabolic Energy Cost of Terrestrial Locomotion ........................................................................ 46
Muscle Function in Terrestrial Locomotion .................................................................................. 52
Neural Control of Locomotion ...................................................................................................... 59
Form, Function, and Development of Musculoskeletal Tissues................................................. 66
Bone - Development ..................................................................................................................... 66
Bone – Form and Function............................................................................................................ 75
Bone – Remodelling ...................................................................................................................... 83
Action Potentials ........................................................................................................................... 90
Muscle - Development .................................................................................................................. 96
Muscle – Form and Function ...................................................................................................... 101
Muscle – Innervation and Excitation .......................................................................................... 111
Joints – Form and Function......................................................................................................... 119
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Introduction to the Moving Animal
Overview of module organisation and teaching and learning approach.
How to get the best out of 'The Moving Animal' (TMA) module.
Feedback opportunities and assessment format.
Some 'big picture' themes of Animal Locomotion.
Many key adaptive features of animal structure and function are associated with locomotion.
Locomotion and mobility are, therefore, critical for health and welfare throughout the lifespan.
The purpose of this module is to:
1. Introduce principles of animal movement across organisational levels
2. Provide a framework for understanding integrated structure and function
3. Develop skills essential to becoming an informed scientific/medical professional
The ‘top-down’ approach: whole animal interacting with its environment, integrated body systems,
tissues, and cells.
Simple physical principles can explain many features of whole animal movement, but these alone do
not explain the diversity of animal form and function. To understand diversity and integrated animal
behaviour, we need biological principles from:
Evolution Biomechanics Development
Anatomy Physiology Molecular biology
The integrative perspective entails:
Interactions between body and environment
Interactions among body systems
Musculoskeletal, neural, respiratory, cardiovascular
Integrated function across organisational levels
Whole animal, body systems, organs, tissues, cells, and molecules
Some of the ‘big picture’ questions are:
How do morphology and behaviour co-evolve?
What functional demands and trade-offs do animals face when moving through their
environment?
How do animals integrate musculoskeletal and sensory systems to achieve agile locomotion?
How can we enable robots and prosthetics to move with the agility, economy, and stability of
animals?
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Gaits
Gait is the pattern of movement
of the limbs of animals, including
humans, during locomotion over
a solid substrate.
Most animals use a variety of
gaits, selecting gait based on
speed, terrain, the need to
manoeuvre, and energetic
efficiency.
Gaits are generally classed as
"symmetrical" and
"asymmetrical" based on limb
movement. It is important to
note that these terms have
nothing to do with left-right
asymmetry. In a symmetrical
gait, the left and right limbs of a pair alternate, while in an asymmetrical gait, the limbs move together.
Asymmetrical gaits are sometimes termed "leaping gaits", due to the presence of a suspended phase.
The key variables for gait are the duty factor and the forelimb-hindlimb phase relationship. Duty
factor is simply the percent of the total cycle which a given foot is on the ground. Duty factors over
50% are considered a "walk", while those less than 50% are considered a run. Forelimb-hindlimb phase
is the temporal relationship between the limb pairs. If the same-side forelimbs and hindlimbs initiate
stance phase at the same time, the phase is 0 (or 100%). If the same-side forelimb contacts the ground
half of the cycle later than the hindlimb, the phase is 50%.
Bipedal gaits: walk, run, hop, skip Quadrupedal gaits: walk, run, trot, gallop
A lot of animals deploy similar movement strategies, despite different morphology. There is a
continuum of gaits, but some possible gaits are avoided because they are not efficient.
Primary forces involved in locomotion
Terrestrial: gravity and inertia (air resistance drag is low)
Aerial: gravity, inertia, drag (high speeds = higher air resistance)
Aquatic: inertial and drag forces (buoyancy supports body weight)
The similarity of gait across species: physical demands govern movement patterns as well as the
environmental medium:
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Evolution and the Adapted Animal
Explain what adaptation is.
Apply evolutionary methods to test for adaptations.
Outline non-adaptive explanations for animal design.
Provide examples of important evolutionary novelties and constraints in
vertebrate locomotor design.
Phylogeny: The pattern of Evolution
How do we reconstruct it?
Anatomical, genetic, behavioural, fossil,
and other data
Computer algorithms: find a pattern
(phylogeny) that represents the best
estimate of evolutionary patterns
(minimising assumptions involved etc.)
What is it?
The diversification of lineages through evolution and how they are related to each other
Any scale – from populations to species
Temporal (millions of years) or just relative (no timeline) sequence
Phylogeny is not about gross similarity, it’s
about the relationships between species.
Phylogeny emphasises shared novel (new)
traits, not primitive traits.
The simplest, formative phylogenetic tree
consists of three groups as it allows us to say
which two groups are most closely related to
each other.
Nodes represent a common ancestor of the two
species lineages (clades). We can use the nodes
to pinpoint certain characteristics specific to that group. It doesn’t matter if we rotate the branches
as the relationship stays the same.
What uses are phylogenies?
Track pattern of evolution of traits: youngest, oldest, rate of evolution, the timing of changes
Test for convergent evolution (independent evolution of similar traits)
Examine correlation of “trait” evolution at any scale, e.g. species and continents, hosts and
parasites, adaptation and diversification
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Adaptation
A trait that enhances fitness and hat arose historically as a result of natural selection for its current
biological role. Adaptation requires:
1. A feature, e.g. a gene, behaviour, or an anatomical structure
2. Resulting in more offspring reproducing
3. Favoured by natural selection
4. Appeared in conjunction with its current function in its environment, i.e. was not previously used
for another function
Key innovations lead to adaptive radiations
Key innovation = a novel trait that originates in a particular lineage, providing evolutionary
“advantages” such as increased speciation, leading to adaptive radiation.
Adaptive radiation = explosion of speciation in a lineage, that can be causally linked to its key
innovation. Involves ecological and phenotypic diversification.
These two agents MUST coincide (by definition). We can use phylogeny to test whether they explain
a part of biodiversity.
Examples: Darwin’s finches, Hawaiian honeycreepers, cichlid fish, beetles
Alternative explanations for adaptations
Phylogenetic constraint or “baggage”, e.g. an appendix in humans
Design constraints prevent the optimal, e.g. an eagle will never evolve a jet engine
Sexual selection, e.g. peacock tails, elk antlers etc. can sometimes go against natural selection
Neutral features (“spandrels”), e.g. junk DNA, blind animals which don’t use their eyes
Covariation with other traits, e.g. big teeth covary with a big jaw
Exaptation, features acquire functions for which they were not originally adapted or selected
Random genetic drift, e.g. Genetic Bottleneck / The Founder Effect
Evolution of the vertebral column and its adaptive role in locomotion
Living vertebrates primitively use mediolateral (side to side) motion of their vertebral columns to
move. Correlated with a sprawling posture in tetrapods. Mammals and crocodiles are the few
vertebrates to use the dorsoventral undulation.
The function of the vertebral motion
Earliest vertebrates: body segments organised into
myomere with a block of muscle separated by
myosepta. Contracted in waves to propel the body
forward.
Evolution of aquatic locomotion
Pectoral, then pelvis fins evolved to supplement
role of axial column in generating thrust and lift.
Both fins gained bony supports that expanded
distally in fish closely related to tetrapods.
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Limbs
Fish have fins, but lobe-finned fish have muscular fins. Fossil forms had segmented rays/bones in their
“fins”. In fossils, there is a very blurry boundary between a fin and a limb. There is also a very similar
genetic control over fin and limb formation. The first recognisable limbs appeared in gilled, aquatic
forms. Limbs are an exaptation, not an adaptation as they were present previously (in form of fins).
Archosaurian reptiles
Locomotor system emphasised the hindlimbs; more
erect posture, hinge-like joints, and parasagittal gait.
Birds inherited bipedalism from ancient dinosaurs.
Specialisation related to a wider activity range in
archosaurs:
- Erect posture
- 4-chambered heart
- Parasagittal gait
- Hinge-like joints
- Enlarged pelvis and limb muscles
- Later (first dinosaur): bipedalism
- Endothermy
Mammalian design
Enlarged pectoral (and pelvic) girdle. More erect
posture and parasagittal gait. Vertebral motion:
dorsoventrally flexible (lumbar region).
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Diversity of Animal Movement: Terrestrial
Appreciate the diversity of terrestrial animal locomotion
Discuss how morphology relates to locomotor function
Discuss adaptive features for the economy, endurance and high speed
The diversity of terrestrial animal movement
Many key adaptive features of animal structure and function are associated with locomotion. Animal
movement can be classed according to the following categories:
Different substrates:
- Cursorial (run) - Fossorial (dig)
- Scansorial (climb) - Arboreal (in trees)
Number of legs:
- Bipedal - Octapedal
- Quadrupedal - Pentapedal
- Hexapedal - None
Leg posture:
- Sprawled - Straight/upright
Movement patterns and gaits:
Bipedal: walk, run, hop, skip
Quadrupedal: walk, trot, gallop, pace, pronk, bound, half-bound
Hexapedal: walk, alternating tripod (trot), pace, pronk
Snakes: rectilinear, concertina, side-winding
Gaits normally change with increasing speed.
Evolution of form and function
Competition for resources such as food and mates leads to selection pressures.
Survival requires economic, versatile locomotion. Natural selection leads to optimisation for different
environments (forest, plains) and lifestyles (migratory, predatory).
Form and function are, however, a subject to constraints and trade-offs associated with inherited
morphology and multiple functions. The optimisation is a continual process and optimal does not
mean perfect, optimal means better adapted for a certain function.
The diversity of form and function reflects both adaptations for different environments are
phylogenetic history constraints.
, 7
Features of early tetrapod locomotion
Sprawling limb posture
Lateral bending of the trunk during locomotion
Relatively massive distal limbs
Same muscles used for ventilation and trunk stabilisation
Limited endurance and aerobic scope
Short bursts of locomotion
Morphological specialisations for endurance and speed
Upright, parasagittal limb posture
Elongated legs, reduction in distal mass
Passively stable trunk
Large body size
“Springy” tendons for elastic energy cycling
Quadrupedal mammals: ungulates
Specialists in endurance and speed
Deer, camel, horse, zebra, elephant etc.
Swift grazing animals
Migratory
Reduction and fusion of distal limb bones
Fusion and elongation of distal bones. Elongation of
the limb helps to increase the speed that the limb can
reach:
Increased stride length
Increased distance travelled per stride
Longer legs are therefore more beneficial for high-
speed locomotion.
The specialisation for economy and speed:
Continuum of limb posture plantigrade
digitigrade unguligrade
Elongation of the distal limb for speed
Lightening of the distal limb to minimise the
cost of leg swing
Reduction in the number of bones
Muscle replaced by energy-efficient tendons
that act as pulleys and springs
Motion restricted to a sagittal plane
, 8
Bipedal animals: theropod dinosaurs and birds
Theropod Ostrich Cheetah Vigcugna
Are humans ‘good’ runners?
For Against
Relatively long legs Big, heavy legs. High energy cost of swinging
Upright posture Plantigrade posture (unusual amongst cursors)
Relatively well developed calcaneal tendon Energetically costly locomotion
Well adapted for endurance running Relatively low top speed
, 9
Introduction to the Nervous System
List the different parts of the nervous system.
Classify the NS according to morphology, the direction of flow of impulses and
physiology.
Describe the general function of the NS.
Explain the functional unit of the NS.
List the other different cell types in the CNS.
The nervous system controls a huge number of
organs and processes, voluntary and
involuntary. Abnormalities of the nervous
system lead to disorders and diseases. The
nervous system was an important factor in our
evolution and it holds the essence of our
personalities and is the key to humanity. It
enables skills, thought, self-control, appreciation
of art and so on.
The nervous system is concerned with the
perception of processes that take place inside
(enteroception) or outside (exteroception) and
with internal and external communication.
Given the diversity of these interrelated tasks,
the body is endowed with a complex nervous
system, which can be divided based on:
a) The direction of the flow of information
Afferent system: nerves that transmit impulses towards the brain and spinal cord.
Efferent system: the nerve that transmits impulses away from the brain and spinal cord.
Often, the same nerve is a part of both systems.
