Adaptations to Bipedalism Flashcards
Classifications of Apes and Humans
- Hominoidea (Hominoids - lesser apes, great apes and humans)
- Hominids - great apes and humans
- Hominines - chimps, gorillas and humans
- Hominins - modern humans and extinct ancestors
Adaptations to Bipedalism
- There are 6 areas of the human body that have been adapted to allow humans to stand upright and allow bipedal locomotion
- Skull
- Vertebral column
- Pelvic girdle
- Knee joint
- Legs
- Feet
Adaptations to the skull - Foramen Magnum
- Foramen Magnum
- Centrally located directly underneath the cranium
- Allows head to remain balanced over body on top of the vertebral column
Additions to the skull - Jaw
- Humans facial profile is much flatter
- The jaw is smaller and less prognathic compared to apes and enables the skull to balance over vertebral column
Adaptations to Vertebral Column
- Humans have a double curvature S-shape contributing to an upright stance
- 2nd curve (cervical curve)
- brings the body (neck) directly underneath the foramen magnum allowing the head to balance directly over the body
- 3rd curve (lumbar)
- created due to wedge shaped vertebrae, it allows the hips to sit directly underneath the shoulders of humans
- The robust lumbar vertebrae allows them to support the weight of the body above them
Adaptations to the Pelvic Girdle
Support of viscera (abdominal organs)
- Pelvic girdle is broader, shorter and tilts backwards to facilitate the modified roles of the gluteal and hamstring muscles
- This allows the pelvis to bear the weight of the upper body and contributes to the carrying angle
- The bowl shape supports abdominal organs when standing erect
Carrying Angle
- The head of the femur is larger and has become strengthened and angled so that when we stand with our legs together our knees touch
- This inward angling of the femur is called the carrying angle (valgus angle) and centres our body weight directly over our feet
- Pelvis is broad and hip sockets wide apart, femurs converge towards the knees
- This arrangement forms an angle to the vertical that ensures weight distribution remains close to the central axis. It allows for greater stability during walking as the body can rotate about the lower leg and foot. At each step, the pelvis tilts downwards slightly on each side to centre the body weight over the supporting foot
Adaptations to the knee joint
- Weight is transmitted down the outside of the femur to the knee
- Strong knee joints help support your body’s weight on one leg at a time while walking long distances
Outer hinge
- Robust outer condyle allows weight to be transmitted along the outside of the knee
- Valgus angle (carrying angle) present
Adaptations to the legs
- Length
- Longer legs lower the centre of gravity in humans to the pelvic region resulting in greater stability when walking
- This occurs as having longer legs results in a heavier mass in the lower half of the body, whereas with apes because they have short legs and a very muscular torso and arms, they’re heavier in the top half of their bodies, resulting in a COG in their chest region
- A longer femur also acts to lengthen our stride making bipedal locomotion very efficient
Adaptations to the feet
Foot Arches
- Two arches, a longitudinal and transverse arch. The longitudinal arch allows the transmission of weight from the heel (calcaneus) to the base of the big toe. The transverse arch acts as a shock absorber and help to distribute weight when standing
Calcaneus (Heel bone)
- Elongated and more robust to bear the impact of the body’s weight while walking to aid propulsion
Non opposable big toe
- A robust big toe that is aligned next to the other toes
- All other toes have become shorter to withstand the stresses of walking while also providing some grip
- The big toe acts to propel the body forward therefore to withstand the weight of the body it has become very robust and inline with the other toes
Locomotion
- Bones and muscles need to be considered when looking at how humans walk. Humans are the only animals with a perfect striding gait
- Humans walk upright in such a way that the hip and knee are fully straightened. When walking, the foot hits the ground so that the weight is transmitted from the heel along the houtside of the foot (along the transverse arch) and given to the big toe. At the final moment of striding the weight is on the big toe
- When walking, the trunk rotates about the pelvis. It can be seen how this natural rotation is compensated by the forward swinging of the arms. Right arm = left leg
- It helps to keep the shoulders at right angles to the direction of travel, and reduces the amount of enery expended. If it didn’t, energy would be wasted in reversing the rotation of the body after each stride
2 phases in the walking cycle:
- Supporting Leg Phase
- Swing Phase
Walking and foot in stance phase 60% of the time. In swing phase 40% of the time.
Supporting Leg Phase
- The leg starts to support the body weight from the time the heel touches the ground. Body weight is supported progressively forward on the foot as the body passes over. While the body is supported on this leg, the other leg is swung forward and placed on the ground = swinging leg phase
- Muscles involved:
- gluteals contract to maintain stability at hip joint
- Quads gradually relax allowing the leg to bend at the knee
- Hamstrings are gradually contracting to bend the knee
- Calf is stabilising the foot as it takes weight and propels the body forward by the big toe
Swing Phase
- Leg is swung forward until heel touches ground
- Requires co-ordination
- Hip bent and knee straightened
- Quads involved with straightening the knee and throwing the lower leg forward
- Anterior Tibialis prepares the foot for contact, it contracts, bending the foot at the ankle
Support Against Gravity
- Muscle Tone: is the maintenance of partial contraction of the skeletal muscle. At any give time, some muscles fibres are contracted while others are relaxed. Such partial contraction tightens a muscle but not enough fibres are contracting at any particular time to bring about movement.
- Role of eyes: the eyes provide basic information about the position of the body in space but other inputs are also important
- Balance organ in ears: in the inner ear, provide essential information about the position of the head (fluid)
- Stretch Receptors: Found in joints and associated ligaments and tendons, they provide the brain with a continual source of information about the position of the parts of the body. They inform the brain when the degree of stretch in the muscles, tendons and joints are altered
- Postural Reflexes: the automatic adjustments of the body. These occur below the level of consciousness as the cerebellum receives sensory input from the ears and eyes and makes the small changes necessary to the strength of contraction of the required muscles. These reponses is to counteract the change in the body’s position.
