Adaptions for Erect Posture and Locomotion (18) Flashcards
What has had to change (general) for humans to be able to stand on two legs + walk bipedal with striding gait
skeletons and muscles
Define Adaption
any characteristic that helps an organism survive and reproduce in its natural environment
What are the 8 adaptions that enabled an erect posture
o Position of foramen magnum, curvature of spinal column, jaw, the pelvis, the carrying angle, the knee, the foot, center of gravity
What is the foramen magnum
- Where brain joins spinal chord= hole in skull
What are the locations of the foramen magnum in humans and apes
Humans- Located centrally underneath skull
Apes- Towards back of skull
What is the change in foramen magnum and why did it change
(During evolution) FM gradually moved forward until skull is able to balance on top of vertebral column
What is the differences in neck muscles of apes and humans
Humans- Weight of skull is borne by vertebral column so large neck muscles not required
Apes-Needs large neck muscles to hold head in position
What are the two shapes of spinal column of humans and apes
Humans- double curvature, S
Apes- C
How is the lumbar region vertebras structured that contributes to the S shape in human spinal columns
wedged shaped from front to back= forming forward- jutting curve
What does the lumbar curve do (3)
o Improves body balance in upright position
o enables head to balance on top of neck
What does the cervical curve in neck do
brings vertebral column directly under center of gravity of skull
What is the difference in jaws for apes and humans
- Apes= Protruding Jaw
- Human= flatter facial profile
What is the trend in jaw size
During evolution from ape like ancestor= size and protrusion of human jaw grad. Reduced
What has the reduce in size of jaw allowed
o Change Important in allowing skull to balance on top of spine, because weight in front of foramen magnum is approx.. equal to weight behind
o // balance achieved with minimum muscular effort
Describe humans pelvis in relation to apes
- pelvis in humans= broader + shorter from top to bottom than in apes
Bowl shaped
What does the bowl shaped pelvis allow
- upports abdominal organs while standing erect + females to support developing fetus during pregnancy
o Female pelvis= slightly broader than male to allow passage of infant at birth
What do broad hip bones allow space for
- space for attachment of large buttocks muscles= which move the legs and keep upper body erect
Define carrying angle
the arrangement of the thigh bones to form an angle to the vertical
What structure allows weight to be transferred from pelvis to legs
- Shape + orientation of pelvis hip joint directly under trunk and head
Where does the head of the femur fit
acetabulum
What has the broadness of the hips caused the femurs to do
= hip sockets wide apart, but femurs tend to converge towards knees
what does the carrying angle arrangement allow (3)
♣ Ensures weight distribution remains close to central axis of body when walking
♣ Allows for greater stability when walking as enables the body to be rotated about the lower leg and foot, and each footstep to follow more-or-less straight line
♣ Enables humans to have a striding gait instead of swaying side to side (as gorillas) when walking on two legs
Where does weight transmission tend to fall in apes and humans
Humans- fall outside femur
apes- reverse
Explain structure of the knee joint
- = two-part hinge joint= one hinge on either side of ligaments in the middle of each joint
What does the fact that weight is transmitted down outside of each leg do to the knee
outer hinge= its larger + stronger than inner one
what produces the natural resistance of the knee
o Although weight of body transmitted down outside of each leg, center of gravity tends to fall through a line just in front of knees
♣ = force that tries to bend knee backward but is resisted by ligaments making up knee joint
This natural resistance produces knee joint that requires no energy to support standing body position
Why is tibia larger
weight transmitted through tibia
What has been lost from feet abilities when becoming highly specialised locomotory organ and where is this most seen
- lost grasping ability, prehensility
o Most notable with big toe= in humans is large and aligned with other toes
Explain the two arches of the foot
o Enabled humans perfect bipedal locomotion a. Longitudinal arch ♣ Running from front to back b. Transverse arch ♣ Running from side to side Unique to humans
What is the striding gait
- walking in such a way that hip and knee are fully extended
what is the proportions of legs to arm length in humans and apes
- Unlike apes, humans= legs that are longer than arms
What has long legs allowed in humans
o Increase length of stride when walking
o Serve to lower center of gravity of body, the point at which all weight of body appears to be concentrated
Compare leg to body ratio length
- In contrast to humans (where almost half of total height= in leg length) ape only about one third of total height taken up in leg length
What has the fact that legs the up half of height allowed (CoG)
o Results in center of gravity being further up body
o Apes Centre of gravity at chest/ humans= level of pelvis
♣ Humans lower COGravity= contributes to stability when moving bipedally or standing erect
What arch do gorillas have
only longitudinal
What is muscle tone
partial contraction of skeletal muscles
Where is sustained muscle tone evident (+human examples)
- evident in muscles that support body in upright position
o In humans:
♣ Those that bring movement of spine, hip, knee, ankle
♣ Abdominal muscles
What maintains tone in msucles
nervous system and variety of sense organs
explain apes attempted upright locomotion looks like
o apes have bent knees and bodies bent forward at hips
Explain movement of striding gait
- In striding gait, when foot hits ground, weight= transmitted from heel along outside of foot as far as ball, crosses ball (via transverse arch) and finally borne by big toe
- At final moment of striding, whole weight of body propelled by big toe
what appendage was the foot and what is it now
- Human foot evolved into weight bearing appendage rather than a grasping one
When walking, how does the trunk rotate and what compensates for the natural rotation
- rotates about pelvis
- Forward swinging of arms compensates for natural rotation;
o right arm naturally swings forward as left is extended and vise versa
- Forward swinging of arms compensates for natural rotation;
what does the swinging of the arms cause
♣ keep shoulders at right angles to the direction of travel
♣ reduces amount of energy expended
what would happen if arms didn’t move as they do
energy wasted in reversing rotation of body after each stride
why do chimps sway when the walk
- lack wide pelvis + carry angle
o // when walking on two legs they must sway side to side so body weight is over each leg in turn
What does the arrangement of carrying angle cause in stability of walking
o also allows for stability during walking, as body can be rotated about the lower leg and foot, // allowing each step to follow a more or less straight line
o Weight distribution to remain close to central axis of body while walking
