Neuroanatomy S3 E3: The Lower Limb #neuroanatomy #ubcmedicine

this looks pretty normal people walking [Music] but if we stop to examine what we're witnessing this is amazing and a little bit weird most terrestrial mammals walk on four legs which makes sense it's more stable it's faster and more efficient and yet we humans have evolved to walk on two legs and through a set of anatomical adaptations we've made it work a balance between stability and mobility between efficiency and performance these competing forces have shaped the anatomy of our entire musculoskeletal system all of these adaptations together with our brains and the use of our hands have set us on the path to not only survive on this planet but thrive in all climates and environments so why did this transition to bipedal gait happen it turns out we needed our hands to feed ourselves rather than use them for locomotion but that's another story today let's have a look at the anatomy of walking and standing let's see how the conflict between mobility and stability between performance and efficiency has been resolved when we stand remarkably little energy is required to maintain an upright position even on two relatively spindly legs and when we walk our bodies moves smoothly through space with little up and down or side to side motion [Music] so how do we efficiently distribute our body's weight to our lower limbs well first we need to stabilize her center of gravity regardless of where how or if we're even moving in humans the body's centre of gravity is in the pelvis immediately anterior to the second sacral vertebra right here it's centered over our feet and much of the anatomy of the lower limb helps to maintain it their curvatures in the vertebral column Center the weight of our upper body and transmitted it through the pelvis to our thigh the femur however is angled to bring the knees closer to the midline under the center of gravity and over the feet if we bend our hips and knees our muscles are working to carry the weight of the body we can't do this for long now when we stand upright like this we can do this for hours well maybe not today to make standing easy our joints lock into place which transfers to work away from muscles and on to our ligaments and bones standing is energy efficient and mainly passive let's see what happens when the joints unlock and we begin to walk when we walk the body's center of gravity barely changes this is indicated by the line drawn by the marker in fact our center of gravity only moves about five centimeters up and down here stability wins so how do joints and muscles collaborate to minimize fluctuations and maximize efficiency it starts with the pelvis as the swing leg moves forward the center of gravity moves upward over the standing leg to counter this upward movement the pelvis simply tilts downward towards the swing leg abductor muscles in the standing leg limit this downward movement and stabilize the drop let's have a look at these abductors in dissection this is a dissection of the gluteal region behind the hip joint to see the major abductors we need to reflect gluteus maximus here is gluteus medius and when I reflect that you can see gluteus minimus both of these abductors of the hip joint run from the lateral aspect of the pelvis to the greater trochanter the femur and controlled downward movement of the pelvis we stabilize the pelvis with these muscles it's a way to maintain mobility when we walk as we step the swing leg moves forward and that side of the pelvis rotates forward with it while the pelvis associated with the stance leg stays behind this rotation on the swing leg side effectively lengthens our stride and helps to prevent excessive drop in the center of gravity we achieve this rotation through the forward momentum of the swing leg along with back and abdominal muscles a somewhat surprising feature of walking is that the knee of the stance limb is not fully extended and does not lock as the body moves over it it stays slightly flexed this keeps our movement fluid and also keeps the center of gravity low and the body more stable now let's have a look at the large flexors and extensors of the knee here in the anterior compartment is the quadriceps the tendon of this muscle reaches over the joint and extends the knee here in the posterior compartment are the hamstrings together they flex the knee during each step the knee of the swing leg is brought close to the midline so that the foot is planted in front of the other foot this limits lateral deflection in the center of gravity during walking large adductor muscles in the thigh are actually responsible for moving the knee closer to the midline let's take a closer look at these muscles this is the medial compartment of the thigh it contains the abductors which bring the knee closer to the midline everything we've talked about till now has served to stabilize our center of gravity and keep it near the midline but if we left it at that our feet would also point inwards and we're not walking to the midline we want to move forward so how do we keep our gait pointed forwards we need to introduce some lateral rotation to balance things out hi lateral rotation in the hip joint keeps the swing foot pointed directly forward counteracting the inward rotation of the pelvis let's see how this works this is the gluteal region on one side of the body I'm going to reflect the large gluteus maximus so that we can see the small rotators deep to the muscle here they are these keep our stance balanced and the entire limb oriented so that the foot faces forward now that the center of gravity is stable and the foot is oriented forward we're ready to put our foot down first contact is with the heel gravity's on our side and honestly we just fall on to our foot a controlled fall that we'll have to stabilize as the foot hits the ground both the knee and the ankle joints need to be stabilized cruciate and other ligaments together with the mighty quadriceps muscle prevent the knee from lunging forward too much the ankle is more of a true hinge joint and is restricted in its mobility by a set of strong ligaments it's still the smallest and least stable of the three major joints in the lower limb it doesn't lock when we stand like the knee and hip joint do and it's decreased mobility when walking makes it vulnerable to injury after the heel hits the ground weight is transferred onto the sole of the foot this lower limb is now our stance leg next the heel lifts off the ground followed by the toes this movement requires powerful muscles in the posterior compartment of the leg together this is the forward propulsion of what once again becomes the swing leg here is the posterior compartment of the leg the biggest muscles are the gastrocnemius here and soleus here their function is to lift the heel off the ground and begin to propel the body forward underneath these more superficial muscles are others their tendons pass into the foot where they attach these muscles help with the control roll off of the foot and transition the stance leg to being the swing leg lifting it off the ground this incredible cycle allows us to walk with ease and fluidity wherever the road may take us [Music] [Music]

Channel: UBC Medicine - Educational Media

Views: 56,037

Keywords: gait, lower limb, walking, neuroanatomy, knee, ankle, stability, mobility, ubc, 4k

Id: LJn7ZApt1NA

Length: 10min 43sec (643 seconds)

Published: Thu Jun 07 2018