Mammalian Locomotion Flashcards
What are the factors for locomotion?
- bipedal/quadrupedal
- environment & terrain
- size
- body plan
- speed
- gravity
What is the general function of cylindrical/long bones?
adapted to act as levers
Describe short bones
- typically seen in carpus and tarsus
- no dimension that greatly excees any other
- helps with complex movements such as rotation and may reduce concussion
Describe flat bones
- many in skull or pelvis
- offer protection to soft parts
- provide attachment sites for large muscle masses
Describe irregular bones
- examples include vertebrae
- similar structure to short bones but less uniform
- lie on mid-line and are unpaired
- often specialized function
What are the 3 primary regions of skeleton?
- axial skeleton: vertebral column, ribs, sternum & skull
- appendicular skeleton: bones of limbs
- Splanchnic/visceral skeleton: bones developed in substance of soft organs
What is an example of teh splanchnic skeleton?
penis bone in cats
What are the functions of the axial - appendicular skeletons?
- postural control
- proprioceptive reflex arcs
- pelvic orientation
Describe how the axial-appendicular skeleton provides postural control
- shift in centre of gravity where top heavy biped needs greater postural control
- quadruped has 4 vertical appendages to suspend body in a balanced way
How does the axial-appendicular skeleton form proprioceptive reflex arcs?
- myotatic reflex
- activation of stretch receptors in muscle spindle stimulates contract of muscle
- inhibits contraction of antagonist flexor muslce of limb
- similar reflex arcs to stimulate extensors and inhibit flexor muscles of the limb in response to gravity forcing flexion of limb joints
How does the axial-appendicular skeleton assist pelvic orientation?
- functions of associated muscles
- gluteus medius extends hip
- hamstring rotates pelvis away from femur - extends hip joint and pushes pelvis forward during locomotion
What are the advantages and disadvantages of quadrupedal structure?
- advantage: naturally resolves balance issue
- disadvantage: issue of attaching limbs to a horizontally orientated body and how they should move in order to make body work
Describe quadrupal evolution of vertical limbs underneath the animal
- shifted from horizontal to vertical attachment
- causes limbs to rotate instead of protract and retract backwards and forwards
- significant reduction of bony aspect of sternum with coracoid and interclavicle bones lost - only clavicle left
Describe the evolution of the clavicle bone
- present in mammals with prehensile forelimbs
- absent in sea mammals and those adapted for running
- absence improves running effiecny as scapula not restrained
Describe pectoral and pelvic girdles
- no longer bony attachment of forelimb to main part of body due to lost clavicle
- attachment of forelimb is muscular by thoracis sling or pectoral girdle
Describe the scapular spine
- divides supraspinous and infraspinous fossae
- bony protrusion that runs down length of scapula
Describe the glenoid fossa
- point of insertion of humerus via humeral head
- at bottom of scapular
What are the primary functional components of the scapula?
- blade width from teres process to cranial border - moment arms of flexors and extensors in shoulders
- orientation of scapular axis - extent of scapular contribution to limb flexion and extension
- size and shape of acromion and coracoid processes - size and moment arms of shoulder muscles
How does the blade width from teres process to cranial border in the scapula affect moment arms of shoulder muscles?
the wider the blade, the increase in moment arm and the shift from speed to power lever
What does the type of lever relate to the point of fulcrum in relation to?
forces coming from effort and from resistance or weight
Describe the lever and moment arm in relation to the human head
- contraction of neck muscles act on joint of head atlas to base of head
- acts againstt downward force of weight of head
- fulcrum in middle position and reasonable mechanical advantage
Describe levers and moment arms in relation to raising the human heel from the ground
- action of calf muscle is at other end of fulfrum with resistance at mid point
- system of high mechanical advantage where force applied is less than force of resistance
- power lever and slow acting
Describe levers and moment arms in relation to the human bicep
- point of action of muscle very close to fulcrum with resistance (weight of hand) at other end of the lever
- mechanical disadvantage - force applied greater than resistant force
- fast acting
Describe power vs speed levers
- if load close to fulcrum and effor far from fulcrum - small effort over large distance can move large load over small distance (power lever, mechanical advantage
- if load far from fulcum and applied near fulcrum - force exerted must be greater than load (mechanical disadvantage, speed lever)
Which 2 types of mammals have developed scapular adaptations?
- cursorial / running mammals
- fossorial / digging & natatorial / swimming mammals
Describe the scapular adaptations of cursorial mammals
- longer, narrower scapulae positioned vertically compared to ambulatory mammals
- increased rotational ability of scapula which has an overall effect of increasing stride length
- narrow scapula - reduces moment arms of muscles running from scapula to humerus - speed lever
- small acromium process reflects small lateral muscle of shoulder joint - very little rotation or abduction of limb
Describe the scapular adaptations in fossorial and natatorial mammals
- triangular scapulae and larger teres process
- increased leverage from teres major muscle - more powerful adduction of forelimb
- absence of large acromium that gives power leverage to deltoid muscles
Describe the deltoid muscles
- teres major and deltoid muscles flex shoulder joint and run from scapula to humerus
- deltoid responsible for abducting the shoulder
- muscle moment determined by deltoid tuberosity (point of insertion)
Describe deltoid tuberosity adaptations in antelopes and otters
- Antelopes: deltoid tuberosity 1/4 distance down shaft, moment arm for deltoid and teres major is rapid but weak extension/flexion of arm
- Otters: deltoid tuberosity further down shaft, greater power
What is key to solving the quadruped issue of transferring propulsive forces from hindlimb through to main part of the body?
- joint between pelvis and spine (pelvic girdle)
- free-ranging movement
- efficient transfer of propulsive force
What does the rigidity of spine determine?
forms of gallop: transverse or rotatory
Describe a rotatory gallop
- placement of second hindfoot followed by ipsilateral forefoot
- sequence of footfalls appears to rotate around body
- faster than transverse
- more rigid body
Describe transverse gallop
- two hindfeet placed in sequence
- placement of second hindfoot followed by contralateral forefoot and then by remaining forefoot
What are the most important biomechanical determinants of gallop type?
- body mass
- relative length of limb segments
- aspect ratio - body height/body length
Describe appendicular attachment in relation to stride sequence
- largely for maintaining balance
- range of variations of stride sequence or gait - speed and species dependent
- central pattern generator - rhythmic patterened outputs with sensory feedback
- key function is to provide correct timing and sequence of action potentials along motor neurons
Describe appendicular attachment in relation to stride sequence in quadrupeds
- one or more limbs have to be lifted off the ground for locomotion to occur
- can cause instability - important that centre of gravity maintained within triangle of support or aligns with line of support if 2 limbs are simultaneously off the ground
What happens when an incorrect timing and sequence of action potentials occur along motor neurons?
- will correct sequence of muslce in relation to gait being performed
- incorrect sequence firing in humans affects functionality and efficiency of gait
Describe the forefoot
- carpal bones downwards
- includes metacarpals and phalanges
- sometimes referred to as the manus
Describe the hindlimb
- from tarsal bones downwards
- includes metatarsals and phalanges
- sometimes referred to as the pes
What are the different types of digit evolution?
- plantigrade
- digitigrade
- unguligrade
Describe plantigrade digit evolution
- entire foot on ground
- greater forward propulsion from muscles that attach to back of the foot than digitigrade and unguligrade mammals
- humans, bears
Describe digitigrade digit evolution
- digits on ground, ankle/wrist raised
- propulsion comes from retraction of whole limb
- extra limb segment - longer distal limbs - longer strides to increase speed
- forward thrust more dependent on proximal limb
- dogs, cats
Describe unguligrade digit evolution
- digit tips on ground, cursorial
- extension of limb length exaggerated further
- more limb segments - longer metacarpals
- quicker, more efficient movement
- horses, antelopes
Describe scansorial adaptations
- climbing mammals
- mobile limbs
- capable of pronation or supination
- clavicle stabilizes shoulder
- triangular scapula
Describe fossorial mammal adaptations
- specialized digging mammals
- strength of forelimbs rather than speed
- long teres (scapula) and olecranon (ulna) processes
- leads to longer moment arms
- shortened and inflexible manus elements
- mole humerus has large tubercles to support short, bulky muscles
Describe natatorial mammal specializations
- similar forelimb specializations to fossorial mammals but hindlimbs also specialized
- elongated manus, esp digits
- shortened femur and long crus (knee to ankle)
- long tibias
- paddle-like pes may be webbed
Describe graviportal mammal specializations
- mammals with extremely large body masses
- limb bones have large diameters to support mass
- vertical orientation of ilium of the pelvis
