A Little Bit More
The mechanism that enables a bird to perch while sleeping is a little more involved than the poster suggests. Not only is the tendon stretching over the ankle important, but the same tendon in the area of the toes has special properties that help to keep a bird firmly atop its perch. The undersurface of each toe tendon has a bumpy or ridged surface. The portion of the tendon sheath (tube-like covering of the tendon) that is adjacent to the ridged undersurface of the tendon is also ridged, on its inner surface. When the bird rests its weight on the perch, the ridges of the toe tendons and ridges of the tendon sheaths mesh. Once these two structures “lock”, the bird’s grip is sufficient to permit the relaxation of its body muscles in sleep. Pretty neat!
Although most of us see birds almost daily, the basic anatomy of a bird’s leg is often misunderstood. Birds do not walk on or perch with their feet, but with their toes! What many puzzle over as a “backward bending knee” is actually the bird’s ankle. The area from ankle to knee is the lower leg (often called drumstick), just as it is in mammals. However, a bird’s leg is not as easy to see, tucked up alongside the body and covered with feathers; hence the confusion.
Activities
Tendons In Action
Objectives: Better understanding of function of tendons
Materials: Bare forearm
When we think of tendons, we generally think of some basic component of our anatomy that is out of sight, deep within our body. However, this is not necessarily true – we can easily see some of our tendons in action without any special preparations – we just have to look in the right place.
1. Initially, we need a subject to demonstrate so students know what to look for. Select someone whose arms have rather distinct muscles and “bony” hands (men have less fat just under their skin than women and make better subjects for this demo). They should bare their forearm, have their hand in clear view, palm down, and then wiggle their fingers as if they’re typing. As the fingers move, it should be easy for everyone to see the tendons on the back of the hand (chord-like structures) move in concert with the fingers. These tendons can’t move on their own but are responding to the muscle movements in the forearm which MAY be visible on some subjects.
2. Pair up your students and have each bare one forearm. Student A can demonstrate the “typing” activity as student B watches but with one variation. Have student B place a hand around the upper part of student A’s demo forearm (just below the elbow). As student A moves his/her fingers, student B will not only be able to see the tendons move on the back of the hand, but will be able to feel the muscular movement of the forearm that makes this possible. Now have student A and B reverse their roles.
3. Be sure to emphasize to the students that tendons connect muscles to bone. This demonstration shows how shortening (contracting) of the forearm muscles pulls on the attached finger tendons and moves the fingers.
4. Now have each demo student raise his fingers several times as if they’re telling someone to stop, so the other student can feel the muscles on the “hairy or top” of the forearm contract. Now have the demo student lower, or curl, her fingers back against her own palm so the muscles on the underside of the forearm can be felt. They should quickly see the connection between muscle, tendon, and finger movement. When muscles on the top part of the forearm contract, the fingers are pulled upward, when muscles on the lower part of the forearm contract, the fingers are pulled downward.
People regularly confuse ligaments with tendons so you may what to reiterate that:
tendons connect muscle to bone
ligaments connect bone to bone.
Key Concepts
Structures and Functions
Questions
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Posted by brianna kasman on June 13, 2003 at 08:14 AM
Q: Hi! We have a cockatoo who is very friendly & cuddly. When she will lay down on you like a nest & snuggle with you with her neck stretched out. Her toes will be on your chest & flat. What makes her able to do that? Her legs are bent & by reading-her toes would be curled. When she is on the post-her toes are curled. Now I'm confused how she can have her feet flat & bend down. Thank you
A: If I understand your question correctly, you're curious how your cockatoo can have her toes both flat and curled, depending on where she is perched. If you think about your own fingers, you too can either have your fingers flat, as when your hand if flat, palm-down on a table, for example, or curled, as when you are holding a ball. Keep in mind that your bird's toes are as flexible as your own fingers. Hope this helps.