Information

How are arms different than legs?


Ok, this is a bit of a tangent question, but it came up yesterday and I didn't know the answer: How are arms and legs defined physiologically? For example, we say humans have two arms and two legs, while cats have four legs, and some monkeys (appear) to have four arms (although I guess they could be legs too). It's really unclear to me how we make these distinctions.

So:

What is the physiological definition of both "arm" and "leg"? How are they different?


I think that's more of a matter of linguistics rather than any scientific/physiological reason. For instance, in Portuguese, you wouldn't call legs to a cat or a dog's limbs. You would say they have 4 "patas" (roughly translated as "paws"). And calling them legs, in Portuguese at least, would be weird.

When veterinary doctors refer to animal limbs, they usually use anterior and posterior limbs. In fact, anatomically speaking, anterior limbs in cats and dogs (and probably in other animals too) have more in common with human arms (upper limbs) that with their own posterior limbs.


Also, as rg255 commented, maybe the reason behind the colloquial nomenclature is quite simple…

To (miss)quote Nancy Sinatra:

These "legs" are made for walking

And that's just what they'll do


The Difference between Medial and Lateral, Proximal and Distal, and Superior and Inferior (Biomechanics)

There are a host of terms used by healthcare professionals and biomedical engineers to describe anatomical positions.

There are a host of terms used by healthcare professionals and biomedical engineers to describe anatomical positions and relative locations of muscles, organs, bones, and other structures in the human body. Some can be confusing. Here are explanations of three pairs of anatomical opposites. (Note: They all apply to a standing human body.)

Medial and lateral: Medial refers to being toward the midline of the body or the median plane, which splits the body, head-to-toe, into two halves, the left and right. Lateral is the side of the body or part of the body that is away from the middle. So arms are lateral to the torso while the torso is medial to the arms. And the medial side of the knee is the inside part or side nearest to the other knee, while the lateral side of the knee faces away from the center of the body and is farthest from the other knee.

Ipsilateral refers to things on the same side of the body, the right or the left as defined by the median plane. So a person’s left arm and leg are ipsilateral. And if a person had a rash only on the right side of his torso and head, the rash would be ipsilateral. The spleen and descending colon, both on the left side of a body, are also ipsilateral. Contralateral refers to things on opposite sides of the median plane. That makes a person’s arms contralateral as well as his legs, ears, and lungs.

Proximal and distal: These two terms are almost always used in reference to relative locations of parts or places on the limbs. Proximal then refers to something closer to the torso while distal refers to parts and places away from the torso. So a finger is distal to the wrist, which is distal to the elbow, which is distal to the shoulder. Or, similarly, the femur is proximal to the knee, which is proximal to the ankle, which is proximal to the toes.

Superior and inferior: These terms reference the body’s vertical axis, and a body part higher than another or above it is said to be superior to it conversely, the other body part is inferior to the first. So the head is superior to the neck, the neck is superior to the torso, and the torso is superior to the legs.

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This Is What Your Sex-Position Bucket List Should Look Like

Some things in life are better on repeat: Friends, perfectly sunny beach days, your trusty manicure. Your sexcapades, though? Definitely not one of them. Even the hottest spark in the bedroom needs new sex positions to stoke the flames from time to time&mdashotherwise things get boring, fast.

&ldquoAnytime you introduce something fresh and novel into the bedroom, you set yourself up for a more stimulating experience and bigger finish,&rdquo says Vanessa Marin, a licensed sex therapist in L.A. In short, your brain craves newness, and especially for women, your brain is very involved in your excitement and satisfaction.

It can also work wonders for your relationship. "One significant challenge to intimacy is the loss of novelty in the bedroom," says Shawntres Parks, licensed marriage and family therapist in San Diego. Exploration between the sheets amps up emotional intimacy and encourages risk-taking and growth. New sex positions will encourage you and your partner to be more vulnerable with one another in the bedroom and otherwise. And in the end, you&rsquoll find your relationship injected with an extra dose of trust.

In some cases, switching up positions might even be a must. &ldquoIf you're thinking &lsquoouch&rsquo when the offer of sex is put on the table, you could definitely benefit from exploring diverse positions that are more comfortable for folks with diverse abilities, as well as those with chronic pain, or pain from penetration,&rdquo Parks adds. But even once you&rsquove found that pain-free position, that doesn&rsquot mean it&rsquos your only option. While it&rsquos easy to become a creature of habit as soon as you&rsquove nailed that go-to, comfortable, climax-every-time position, Parks urges you to keep mixing it up. There are SO many possibilities out there that your imagination might not have even thought up yet.

Ah, but where to begin? How about with any of these 46 orgasm-inducing positions that'll blow you and your partner's d*mn minds.


MATERIALS AND METHODS

Participants

Twelve collegiate sprinters and 12 height-matched non-athletes not engaged in competitive sports participated in the study(Table 1). Seven of the sprinters were specialists in the 100 m (or long jumpers who trained with sprinters) who had self-reported personal best times ranging from 10.7 to 12.3 s, and the other five had 200 m times between 23.3 and 24.0 s. Participants gave informed consent and all procedures were approved by the Institutional Review Board of The Pennsylvania State University.

Anthropometric characteristics and ages of the sprinter and non-sprinter subjects

. Sprinters . Non-sprinters . P-value .
Stature (cm) 181.4±8.0 180.9±7.6 0.874
Body mass (kg) 77.0±6.5 76.8±9.5 0.954
Age (years) 19.3±1.2 25.4±2.8 <0.001
Fibular head to lateral malleolus (cm) 41.1±2.6 44.1±3.5 0.026
Heel to toe (cm) 27.4±1.1 26.9±2.0 0.473
Heel to 1st metatarsal head (cm) 19.2±0.9 19.5±1.6 0.485
Heel to lateral malleolus (cm) 5.5±0.7 5.6±0.3 0.594
Lateral malleolus to 1st metatarsal head * (cm) 13.7±0.7 13.9±1.4 0.589
Lateral malleolus to toe * (cm) 21.9±0.9 21.3±1.8 0.305
First metatarsal head to toe * (cm) 8.2±1.0 7.3±0.9 0.032
. Sprinters . Non-sprinters . P-value .
Stature (cm) 181.4±8.0 180.9±7.6 0.874
Body mass (kg) 77.0±6.5 76.8±9.5 0.954
Age (years) 19.3±1.2 25.4±2.8 <0.001
Fibular head to lateral malleolus (cm) 41.1±2.6 44.1±3.5 0.026
Heel to toe (cm) 27.4±1.1 26.9±2.0 0.473
Heel to 1st metatarsal head (cm) 19.2±0.9 19.5±1.6 0.485
Heel to lateral malleolus (cm) 5.5±0.7 5.6±0.3 0.594
Lateral malleolus to 1st metatarsal head * (cm) 13.7±0.7 13.9±1.4 0.589
Lateral malleolus to toe * (cm) 21.9±0.9 21.3±1.8 0.305
First metatarsal head to toe * (cm) 8.2±1.0 7.3±0.9 0.032

Values are means ± 1 s.d. P-values are for two-tailed t-tests for mean differences between groups

These quantities were not measured directly, but were derived by subtraction from measured quantities

Ultrasonography

Ultrasonography was used to collect images of the lateral gastrocnemius and Achilles' tendon from which musculoskeletal structural properties were estimated. To determine muscle fascicle lengths and pennation angles, B-mode ultrasonography (Aloka 1100 transducer: SSD-625, 7.5 MHz and 39 mm scan width Wallingford, CT, USA) was used to capture images from the central region of the right lateral gastrocnemius muscle(Fig. 1) while each participant stood quietly in anatomical position with the probe aligned along the muscle belly. The lateral gastrocnemius muscle was chosen primarily because it is superficial but also because it has the longest fascicle lengths of any of the triceps surae, thus giving it greater potential to generate force during explosive movements requiring higher shortening velocity(Kumagai et al., 2000). Ultrasound aqueous gel was applied to the skin to enhance propagation of the ultrasonic waves. Ultrasound images were enhanced and digitized using routines custom-written in MATLAB (Mathworks, Inc Natick, MA, USA). The pennation angle was measured as the angle between the fascicular path and the deep aponeurosis (Abe et al., 2001 Abe et al., 2000 Kumagai et al., 2000). Fascicle length lf was estimated using the muscle thickness t, the distance between the superficial and deep aponeuroses, and the pennation angle θ according to lf=t/sinθ(Abe et al., 2001 Abe et al., 2000 Kumagai et al., 2000). Measurements were repeated on a second day for three non-sprinter subjects to assess reliability average differences in fascicle length and pennation angle were 1.2 mm and 0.5 deg., respectively.

Ultrasound imaging was also used to determine tendon excursion during ankle plantarflexion in order to compute the plantarflexion moment arm of the Achilles' tendon. Each participant sat with the right knee fully extended and the thigh held in place with respect to the base of the test apparatus(Fig. 2). The right foot was secured with Velcro® straps to a foot platform that was hinged so that it rotated in the sagittal plane. The hinge axis was directed mediolaterally and was approximately aligned with the malleoli, and a potentiometer (Midori Precisions, CP-2FK, Tokyo, Japan repeatability ±0.005%, linearity±1%) attached to the foot platform was used to record the ankle joint rotation. Potentiometer voltages were linear with platform rotation(calibration coefficient= 68.9 deg./1 V R 2 =0.9991) and were recorded using a data acquisition system consisting of a National Instruments analogue to digital (A/D) converter (Dataq Instruments, DI, 148U,OH, USA) and a personal computer. The A/D converter had a measurement range of±10 V and resolution of ±19.5 mV and a maximum sample rate of 240 Hz. The data acquisition software (Windaq/Lite, Dataq Instruments, OH,USA) averaged the signal such that the output had a resolution of ±2 mV.

Ultrasound image of the lateral gastrocnemius. The arrow indicates the musculotendinous junction, the landmark used for tracking excursion of the Achilles' tendon during applied ankle rotation.

Ultrasound image of the lateral gastrocnemius. The arrow indicates the musculotendinous junction, the landmark used for tracking excursion of the Achilles' tendon during applied ankle rotation.

During a trial, one experimenter manually rotated the foot from approximately 10 deg. dorsiflexion to 20 deg. plantarflexion in 3 s while a second experimenter held the ultrasound probe against the skin longitudinally on the posterior distal third of the leg at the appropriate musculotendinous junction, where the gastrocnemius muscle inserts into the Achilles' tendon. Ultrasound images captured at 30 Hz during each trial were digitized and saved to a personal computer with a frame grabber card (Scion Corporation, LG-3,Frederick, MD, USA) with the imaging software, Scion Imaging (Scion Corporation). Participants were instructed to plantarflex maximally during these trials to minimize artefacts resulting from variation in tendon tension during the movement (Maganaris et al.,1998a). Tendon excursion was measured as the displacement of the musculotendinous junction computed from the ultrasound images using an automated algorithm for tracking image features between frames(Lee et al., 2008). Five foot rotation trials were performed for each participant.

Schematic diagram of the apparatus used to apply foot rotations. The subject's right foot was strapped to a platform (P) that was rotated manually from dorsiflexion to plantarflexion about a mediolateral axis (A) with respect to the base of the apparatus (B) by one experimenter while sagittal plane rotation was recorded using a potentiometer and a second experimenter held an ultrasound probe (U) against the shank. The ultrasound probe was fitted into a custom-made foam pad that reduced slipping of the probe along the skin. The thigh was held in place relative to the base by a padded aluminium arch(T).

Schematic diagram of the apparatus used to apply foot rotations. The subject's right foot was strapped to a platform (P) that was rotated manually from dorsiflexion to plantarflexion about a mediolateral axis (A) with respect to the base of the apparatus (B) by one experimenter while sagittal plane rotation was recorded using a potentiometer and a second experimenter held an ultrasound probe (U) against the shank. The ultrasound probe was fitted into a custom-made foam pad that reduced slipping of the probe along the skin. The thigh was held in place relative to the base by a padded aluminium arch(T).

The plantarflexion moment arm of the Achilles' tendon was calculated as the first derivative of tendon excursion versus joint angle(An et al., 1984). Achilles'tendon excursions were generally linear with respect to ankle angle, and the slopes of lines fitted to these data were taken to represent the moment arm for each trial. Each participant's moment arm was found by averaging the five foot rotation trials. Measurements were repeated on a second day for three non-sprinter subjects to assess reliability the average difference in moment arm was 3.2 mm.

Anthropometry

Distances between various bony landmarks on the right lower legs of all subjects were made using a millimetre-graded tape measure. Subjects stood in anatomical position while the experimenter measured, (1) the distances between the head of the fibula and the lateral malleolus, (2) the anteroposterior (AP)distance from the most posterior point on the heel to the most anterior point on the toes, (3) the AP distance from the heel to the first metatarsal head,and (4) the AP distance from the heel to the lateral malleolus. Additional measurements of distances between landmarks on the foot were derived post-hoc by subtracting these measurements from one another.

Statistics

Two-tailed t-tests were used to test for differences(α=0.05) between sprinters and non-sprinters in lateral gastrocnemius thickness, lateral gastrocnemius pennation angle, lateral gastrocnemius fascicle length, Achilles' tendon moment arm, the ratio of fascicle length to moment arm, and the various anthropometric measures.

Computer model

To study how sprint performance is affected by muscle and joint structure in the context of the movement dynamics, a planar, forward-dynamic computer simulation of a sprinter's push-off was developed(Fig. 3). The mass mof the sprinter (75 kg) was concentrated at a point 1 m above the ankle connecting the `body' segment to the `foot' segment. The foot was a massless link with 14 cm between the ankle and metatarsophalangeal (MTP) joint, where another revolute connected the foot to a third massless `toe' link, 7.5 cm long. The distal end of the toe link was connected to ground by a third revolute joint, and the proximal end of the toe was supported by a damped spring (k=2.0×10 5 N m –1 b=250 Ns m –1 k is stiffness and bis the damping coefficient) that resisted penetration of this point into the floor. Torsional springs with stiffness of 100 Nm rad –1 resisted ankle plantar flexion beyond 60 deg. and toe extension beyond 60 deg. Two Hill-type muscle-tendon actuators(Hill, 1938) represented the collective triceps surae and toe flexor muscle groups. The maximum isometric force for the plantarflexor and toe flexor actuators were set at 6660 N and 948 N, respectively. These values were obtained by summing the values for each group as represented in the lower extremity model of Delp et al.(Delp et al., 1990) and then multiplying by 1.5 to reproduce the hypertrophy that would be expected in a sprinter. The plantarflexor actuator originated 40 cm proximal to the ankle on the body segment and inserted posterior to the ankle on the foot segment (see below), whereas the toe flexor originated 20 cm proximal to the ankle, wrapped around cylindrical surfaces with radii of 15 mm and 6 mm at the ankle and MTP joints, and inserted 10 mm distal to the MTP joint on the toe segment. Pennation angles for both muscle-tendon actuators were set at 0 deg. across simulations. Optimal fibre length lo was 4 cm for each muscle-tendon actuator and tendon slack length was chosen such that optimal fibre lengths were attained in 30 deg. plantarflexion, a choice guided by the sarcomere lengths recently reported for the triceps surae and toe flexors by Ward et al. (Ward et al.,2009). Actuator tendons were compliant, with normalized force–length curves defined according to Zajac(Zajac, 1989). Muscle force was computed using a Hill-type model developed by Schutte(Schutte, 1992). The force–length and shortening force–velocity relations used were those specified by Hatze (Hatze,1977) and Hill (Hill,1938). The maximum shortening velocity vmaxfor each muscle actuator was set at 10 los –1 (Zajac,1989). The equations of motion for the system were developed and integrated using SIMM with Dynamics Pipeline (Musculographics, Inc. Santa Rosa, CA, USA) and SD/FAST (Parametric Technology Corp. Needham, MA,USA).

Planar three-segment, three-degree-of-freedom computational model used to simulate a sprinter's push-off. The simulation began with the point mass, m,translating forward with velocity v0=2 m s –1 and ended when contact was broken at the toe (T). The proximal end of the toe segment was supported at the metatarsophalangeal joint(M) by a damped spring with stiffness k and the damping coefficient b. Excitation controls for plantarflexor (PF) and toe flexor (TF)actuators were determined using parameter optimization. The plantarflexion moment arm of the PF actuator was approximated by the distance dbetween the ankle A and the actuator's insertion on the foot segment.

Planar three-segment, three-degree-of-freedom computational model used to simulate a sprinter's push-off. The simulation began with the point mass, m,translating forward with velocity v0=2 m s –1 and ended when contact was broken at the toe (T). The proximal end of the toe segment was supported at the metatarsophalangeal joint(M) by a damped spring with stiffness k and the damping coefficient b. Excitation controls for plantarflexor (PF) and toe flexor (TF)actuators were determined using parameter optimization. The plantarflexion moment arm of the PF actuator was approximated by the distance dbetween the ankle A and the actuator's insertion on the foot segment.

One set of simulations of sprint push-off were conducted with d,the posterior distance from the ankle to insertion of the tendon, varying between 25 mm and 50 mm in 5 mm increments while toe length was held at 75 mm. The distance d differed from the perpendicular distance from the ankle to the plantarflexor muscle in neutral position by less than 1% and so was taken to be a reasonable approximation of the plantarflexor moment arm in that position (although d differed from moment arm at high plantarflexion angles). A second set of simulations was conducted with d fixed at 35 mm while the length of the toe link was varied from 65 mm to 90 mm in 5 mm increments. Each simulation began with the ankle in 10 deg. dorsiflexion, the toes extended by 35 deg., and the point mass travelling to the right at v0=2 m s –1 . For each simulation, the horizontal impulse was computed as the change in the horizontal momentum occurring over the course of the simulation. Horizontal impulse was selected as the output of interest because it represents the increase in forward velocity and the forward impulse delivered during individual steps in the acceleration phase of the sprint has been shown to correlate with overall sprint performance(Hunter et al., 2005).


Limb Differences

"Limb" is another name for the arms or legs. Limb differences are when an arm or leg is not shaped in the usual way. For example, a child's legs may be curved or one might be shorter than the other. Or, a bone in the arm may be short or missing.

A limb difference that a child is born with is called congenital. A limb difference that happens after birth is called acquired.

What Are the Signs & Symptoms of a Limb Difference?

Signs of a limb difference depend on which limb is affected and how severe the difference is. Some limb differences are so mild that you can't notice them. Others are quite noticeable and affect the way a child moves or walks.

There are many types of limb differences. For example, fibular hemimelia is when a baby is born with short and sometimes missing bones in the leg and foot. Limb length discrepancy is when one arm or leg is longer than the other. Sometimes, the knees bow out (bowlegs) or bend inward (knock knees).

A limb difference also can happen after an injury.

How Is a Limb Difference Diagnosed?

To diagnose a limb difference, orthopedic specialists (doctors and other providers who treat bone and muscle problems) talk to the family and the child, and do an exam. Tests such as X-rays or CT scans usually are done and can help the specialists decide on the best treatment.

How Is a Limb Difference Treated?

To give the best treatment, health care providers consider how severe the limb difference is, whether it makes regular activities (such as walking or writing) hard, how old the child is, and whether the difference is likely to get worse and cause other problems. Sometimes no treatment is needed.

When treatment is needed, it may include:

What Else Should I Know?

Your orthopedic team will help you find the best treatment for your child. Take time to understand exactly what will happen at each stage of the treatment plan. This way, you and your child know what to expect and can follow the plan.

Remember that your care team is there to answer any questions and help you get the best result for your child.


Anatomy of Bones of the Arm

In spite of its extreme flexibility, the arm consists of just three long bones. The following article will cover some information related these bones and their function.

In spite of its extreme flexibility, the arm consists of just three long bones. The following article will cover some information related these bones and their function…

The arms and hands are one of the most frequently used body parts. The use of our limbs comes so naturally to us that we never realize the science behind their functioning. The study of the anatomy of the human arm will give you an idea as to how complex these seemingly simple functions can be. Without the arms one would not be able to do even a simple task like eating food or holding a spoon.

Arm Bones and Muscles

The upper arm bones and muscles consist of the humerus, biceps, and triceps. The biceps are made up of two different heads and are located in the front of the arms. They help in bending the arm towards the shoulders. The triceps are present on the rear part of the upper arm and is made up of three muscles. The function of the triceps is to help the arm extend forward. The forearm bones and muscles consist of two bones and a group of several muscles, which are responsible for bending your wrist.

Anatomy

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The arm consists of three bones that make up the upper arm and the lower arm. The upper arm is made up of the humerus, and the lower arm consists of the radius and the ulna.

Humerus

The upper arm bone that extends from the shoulder to the elbow is called the humerus. This is a long bone that helps in supporting and moving the upper arm. The humerus is divided into 3 parts, the round head, the narrow neck, and the tubercles. There are many muscles and ligaments attached to the humerus.

The muscles of the humerus include the following:

  • Deltoid
  • Supraspinatus
  • Pectoralis major
  • Teres major
  • Latissimus dorsi
  • Infraspinatus
  • Biceps brachii
  • Brachialis
  • Coracobrachialis
  • Brachioradialis
  • Triceps brachii
  • Anconeus

Radius

The lower arm or forearm bone is the radius. It extends from the elbow to the wrist. The radius is long and curved in shape and runs parallel to the ulna. The function of the radius is to help in movement and supporting the arm. Muscles attached to the radius include:

  • Supinator
  • The flexor digitorum superficialis
  • The flexor pollicis longus
  • Musculus extensor ossis metacarpi pollicis
  • Extensor primi internodii pollicis
  • The pronator teres muscle
  • Supinator longus tendons

The last, but not the least, bone of the arm is the ulna. This bone is present between the elbow and the wrist running parallel to radius. The ulna is longer and slightly curved just like the other arm bones. The function of the ulna is also the same, to assist in support and movement of the arm.

The muscles and ligaments attached to the ulna are as follows:

  • Triceps brachii
  • Anconeus
  • Brachialis
  • Pronator teres
  • Flexor carpi ulnaris
  • Flexor digitorum superficialis
  • Flexor digitorum profundus
  • Pronator quadratus
  • Extensor carpi ulnaris
  • Supinator
  • Abductor pollicis longus
  • Extensor pollicis longus
  • Extensor pollicis brevis
  • Extensor indicis

Pain in the arm can occur due to various reasons. Some of the common arm bone pain reasons include fracture of the bones, muscle pulls, torn ligaments and tendons, osteoarthritis, Paget’s disease, peripheral neuropathy, bone cancer, etc.


Pinpointing ZRS

Visel and his colleagues began looking at the genomes of "early" snakes that were closer to the base of the snake family tree &mdash such as the boa and python &mdash that have vestigial legs, or tiny bones buried within their muscles. The scientists also studied "advanced" snakes, including the viper and cobra, which do not have any limb structures.

During their investigation, the researchers focused on a gene called sonic hedgehog, which is key in embryonic development, including limb formation. Sonic hedgehog's regulators, located in the ZRS sequence of DNA, had mutated, they found.

However, the researchers needed proof that the ZRS mutations were responsible for limb loss. To find out, they used a DNA-editing technique called CRISPR (short for "clustered regularly interspaced short palindromic repeats") to cut out the ZRS stretch in mice embryos and replace it with the ZRS section from other animals, including snakes.

When the mice had ZRS DNA from other animals, including humans and fish, they developed limbs just like any regular mouse would. But when the researchers inserted the python and cobra ZRS into the mice, the mice's limbs barely developed, the researchers found.

Next, the researchers took an in-depth look at the snakes' ZRS, and found that a deletion of 17 base pairs (that is, paired DNA "letters") within the snakes' DNA appeared to be the cause of the limb loss, they said. When they painstakingly "fixed" the mutations in the snake ZRS and inserted it into mice embryos, the mice grew normal legs, they found. [Photos: Weird 4-Legged Snake Was Transitional Creature]

However, creatures usually have redundant DNA that protects against mutations such as these, so it's likely that multiple evolutionary events led to limb loss in snakes, Visel said.

"There's likely some redundancy built in the mouse ZRS," he said. "A few of the other mutations in the snake ZRS probably also played a role in its loss of function during evolution."


Arms and legs

The arm of a mammalian skeleton is made up of three bones: the humerus, ulna and radius. The humerus fits into the pectoral girdle with a ball and socket joint. The ulna and radius connect to the bones of the wrist and humerus to make the elbow. The arrangement of the radius and ulna in humans allows the rotation of the hand from the elbow, a skill absent in four legged mammals.

The hand is made up from the carpel bones in the wrist, five metacarpals which make the palm phalanges in fingers and thumbs. Humans and other high order primates have a saddle joint between the metacarpal and carpel of the thumb which gives their thumbs a very large range of movements and creates the opposable thumb.

The leg also consists of three long bones very similar to that of the arm but in humans we also have a fourth bone, the kneecap or patella. The patella helps to lock the knee to save energy and prevent over-extension of the knee-joint.

The femur is the longest bone in the human body and is similar in length to the humerus in many four legged mammals. It connects to a socket in the pelvic girdle, similar to the humerus in the shoulder joint. The lower end of the femur connects to the tibia and fibula bones which extend from the knee to the foot.

The tibia is the major bone of the lower leg and provides the majority of strength the fibula runs down the outside of the tibia and extends lower than the tibia to connect to the side of the foot. In horses the fibula is partially fused with the tibia.

The foot is very similar in structure to the hand. It has a number of tarsal bones that form the ankle, equivalent to the carpel bones of the wrist. The tarsals connect to five metatarsals which extend along the length of the foot to the toes. The bones of the toes, phalanges, are the same as the finger bones but are much shorter in humans and other primates.


Difference Between Tentacles and Arms

It would always be interesting to compare and contrast the tentacles and arms as they both sound alike, and at the same time, the differences could also be understood. The information presented here about tentacles and arms are sensible to the reader, as there is specific comparison between the characteristics of the two subjects.

Tentacles are flexible and elongated external processes or organs, found mainly in invertebrate animals. Tentacles are also known as bothridia, and sometimes it is referred to describe the leaves of insectivorous plants. Tentacles are important for animals in feeding, sensing, grasping, and locomotion. Those are well equipped for the particular function or functions. Suckers present on the tentacles of squids and octopus species, so that the grasping of a prey would be easy. The suckers on the tentacles of cephalopods are more powerful in comparison with those in the rest of the molluscs. The small antennae in the snails and slugs are another type of tentacles, which are useful in sensory function or in sensing the environment. The tentacles of Jellyfish are functioning in a fascinating modus operandi, which mainly includes the paralysing of prey animals via venomous shocks from their nematocysts. The magnitude of this method could be very high, as they can sometimes paralyse a shark or large tuna fish. Large colonies of jellyfish make those venomous stingy areas in the sea by having nematocysts on their tentacles. In addition, the specialized tentacles of jellyfish can also perform the capturing and digestion of their food or prey. Despite the presence of tentacles in invertebrates and sometimes in plants, the potencies are always considerable.

Arms are highly diversified organs, but mainly the forelimbs of animals. Usually, arms are found in both vertebrates and invertebrates. However, the main difference between those is that, the invertebrate arms are more flexible than the vertebrate arms. The arms of primates are particularly interesting, as there are opposable fingers, in vertebrates. Therefore, they can climb on trees using these prehensile appendages. The invertebrate arms mainly include the ones in squids, octopus, and cuttlefish. They all have two arms in each animal. The invertebrate arms have suckers to help grasping food items. The transverse muscles of their arms enable to manipulate finely via bending movements. In addition, the invertebrate arms are useful for them to attach to surfaces while resting. On the other hand, human and other primate arms are equipped with finely moveable fingers. Therefore, the effectiveness of the primate arms is very high. In other words, arms are value added external appendages of animals.

What is the difference between Tentacles and Arms?

• Tentacles are usually found among invertebrates and sometimes in certain plants, whereas arms are present in both vertebrate and invertebrate animals.

• Tentacles are elongated structures, and the length is always higher in comparison to the arms.

• Arms of the invertebrates have suckers along the whole length, but the suckers are found at the tip of tentacles usually.

• In case of vertebrate arms, the fingers are very important features, while the suckers and nematocysts are the stand out features of tentacles.

• The tentacles of snails and slugs have chemosensory glands, but not in any type of arms do those feelings.

• Arms can perform finer and nicer workouts compared to tentacles.

• The tentacles mainly used to catch the pray, and the arms active secondarily and assist to gasp the prey in invertebrates.


Do men really have more upper body strength than women?

If 10-year-old Naomi Kutin wasn't the strongest girl in the world in 2012, then she'd be among the brawniest. That year, at a weightlifting meet in Corpus Christi, Texas, the 99-pound (44.9-kilogram) Kutin deadlifted a staggering 209.4 pounds (94.9 kilograms) and squatted slightly less [source: Zeveloff]. To put that Herculean feat into perspective, the New Jersey elementary schooler successfully squatted around 215 percent of her body weight -- the same body weight percentage a 180-pound (81.6-kilogram) adult man could likely squat [source: Cross Fit].

Her young age aside, Kutin's accomplishment was twice as significant considering her female physiology. Gender differences in athletic performance have narrowed over the past century as more sports have opened up to women and more attention and funding have been directed toward female athletic training through initiatives such as the Title IX law in the United States. But certain fundamental sex differences exist between men's and women's physical prowess. Men's greater upper body strength is a prime example. So while Naomi Kutin may be able to handily out-lift all her male classmates, she's an impressively strong exception to the rule.

Women's lower body strength tends to be more closely matched to men's, while their upper body strength is often just half that of men's upper body strength. In a 1993 study exploring gender differences in muscle makeup, female participants exhibited 52 percent of men's upper body strength, which the researchers partially attributed to their smaller muscles and a higher concentration of fatty tissues in the top half of the female body [source: Miller et al]. Another study published in 1999 similarly found women had 40 percent less upper body skeletal muscle [source: Janssen]. Even controlling for athletic aptitude doesn't tip the upper body strength scales in favor of the female an experiment comparing the hand grip strength of non-athletic male participants versus elite women athletes still revealed a muscle power disparity in favor of the menfolk [source: Leyk et al].

Acknowledging this gender difference doesn't imply that weight-lifting women can't combat this bit of biological determinism and beef up their biceps instead, men simply have a head start in that department thanks to their elevated levels of testosterone. The sex hormone has anabolic effects, meaning it promotes muscle development. Secreted by the pituitary gland, testosterone binds to skeletal fiber cells and stimulates the growth of proteins, the building blocks of meaty muscles [source: Roundy]. At the same time, however, testosterone also may shave off men's strength for the long haul.

Do women have more endurance than men?

For a glaring manifestation of biological sex differences in strength, look no farther than the pull-up. The process of hoisting oneself eye-level with an overhead bar is no big deal to plenty of men. Not so, however, for women. In fact, Marines require male recruits to complete at least three chin-ups in order to pass their physical entrance exam, while female hopefuls aren't asked to execute a single one [source: Parker-Pope]. That isn't letting military women off the hook easily the female body simply isn't optimally built -- what with weight distribution and less testosterone-fueled muscle mass -- for the exercise.

The short bursts of energy required for weight lifting might not be the forte of the female body, but as more women have begun participating in endurance sports, such as running marathons, conflicting research has prompted a debate over whether they're better tailored for the long haul than men. The fastest male runners are swifter than the fastest female runners due to innate factors including muscle mass, higher oxygen intake and lower resting heart rates. That said, some studies have indicated that in ultradistance running -- beyond 30 miles (48 kilometers) -- the fattier female body can keep moving more efficiently than the muscular male frame since the fat represents more lasting, slower-burning energy stores [source: Maharam]. Estrogen may also offer an advantage of protecting against muscle fatigue, although its effects can vary by athlete and running conditions [source: Crowther]. Those biological benefits may help explain women's sudden surge in Iditarod races, the grueling Alaskan dog sledding competition, bringing home championships four years straight from 1985 through 1988 [source: Library of Congress].

Meanwhile, what isn't up for argument is that on average, women win at the ultimate endurance competition: life. Even as public health improvements have increased lifespans around the world, women still tend to live longer than men by five or six years [source: Kirkwood]. Evolutionary biology points to women's responsibility as child bearers for why the female body ultimately may be more resilient, having evolved heartier healing capacities on a cellular level [source: Dillner]. Another explanation for that consistent gender gap circles back to testosterone, the hormonal culprit behind gender unequal upper body strength. In addition to being anabolic (muscle-building), testosterone also is characterized as androgenic (or masculinizing), which can take the form of men indulging in riskier behaviors that could eventually curb their life expectancies. Not that it has to signal an early death sentence for men by keeping those muscular bodies in shape, courtesy of testosterone, they can possibly ward off its more deleterious effects.

Recent studies have suggested that people don't need to size up a man's shoulders and biceps to accurately judge how much he can powerlift. A 2008 study out of the University of California, Santa Barbara, for instance, discovered that participants could infer a man's upper body strength from his facial features [source: University of California -- Santa Barbara]. A couple years later, the same Santa Barbara researcher concluded that men and women could likewise assess male upper body strength solely from hearing their voices [source: Callaway]. What remains unknown is why those sight and sound correlations exist.

Author's Note: Do men really have more upper body strength than women?

I'll admit that I'm not going to be breaking through any glass ceiling in the weight lifting department anytime soon -- or ever, to be honest. I have a textbook case of female physiology with a decent amount of lower body strength (at least that's what I tell myself) and little-to-no upper body strength to speak of. Despite regularly exercising, I've never successfully completed a single pull-up my entire life. Now, thanks to my research for this article investigating the gender differences in muscle mass and distribution, I can mentally surrender to the hormonal fact that push-ups, pull-ups and even monkey bar crossings will never be in my physical wheelhouse because I simply don't have the testosterone for it. Good thing I prefer jogging anyway.


Eat more to grow more arms…if you’re a sea anemone

An international group of researchers, led by scientists from EMBL Heidelberg, have discovered that the number of tentacle arms a sea anemone grows depends on the amount of food it eats. The results are presented in Nature Communications.

These four images show the development process of the characteristic tentacle arms of a sea anemone. Credit: Anniek Stokkermans/EMBL

Your genetic code determines that you will grow two arms and two legs. The same fate is true for all mammals. Similarly, the number of fins a fish has and the number of legs and wings an insect has are embedded in their genetic code. Sea anemones, however, defy this rule and have a variable number of tentacle arms.

Until now it’s been unclear what regulates the number of tentacles a sea anemone can grow. Scientists from the Ikmi group at EMBL Heidelberg, in collaboration with researchers in the Gibson lab at the Stowers Institute for Medical Research in Kansas City, have shown that the number of tentacles is defined by the amount of food consumed. “Controlling the number of tentacle arms by food intake makes the sea anemone behave more like a plant developing new branches than an animal growing a new limb,” explains group leader Aissam Ikmi. Defining what environmental factors trigger morphological changes is a particularly important question given the longevity of sea anemones, with some species living for more than 65 years. “As predominantly sessile animals, sea anemones must have evolved strategies to deal with environmental changes to sustain such a long lifespan,” adds Ikmi.

The scientists have shown that the growth of new tentacles happens not only when the sea anemone is a juvenile, but also throughout adulthood. “We can conclude that the number of tentacle arms must be determined by the interplay between genetic and environmental factors,” says Ikmi, who started this project when he was still a postdoc in the lab of Matt Gibson. While the sea anemone uses different strategies to build tentacles in the different stages of its life, the final arms are morphologically indistinguishable from each other. “If humans could do the same, it would mean that the more we ate, the more arms and legs we could grow,” says Ikmi. “Imagine how handy it would be if we could activate this when we needed to replace damaged limbs.”

When Ikmi’s group studied the locations at which the new arms form, they found that muscle cells pre-mark the sites of new tentacles. These muscle cells change their gene expression signature in response to food. The same molecular signalling employed to build tentacles in sea anemones also exists in many other species – including humans. So far, however, its role has been studied mainly in embryonic development. “We propose a new biological context in which to understand how nutrient uptake impacts the function of this developmental signalling: a situation that is relevant for defining the role of metabolism in guiding the formation of organs during adulthood” explains Ikmi. “Sea anemones show us that it is possible that nutrients are not converted into excess fat storage – as it is the case in all mammals – but instead transformed into a new body structure.”

While this finding is novel on its own, it also shows that sea anemones, which are traditionally used for evolutionary developmental studies, are well suited to study morphogenesis in the context of organism–environment interactions.

To build the branching map of new tentacles, researchers analysed more than 1000 sea anemones one by one. “Scoring such a massive number of tentacles is, in some ways, a story in itself,” says Mason McMullen, laughing. McMullen, a clinical pharmacist at the University of Kansas Health System, spent months imaging sea anemones’ heads to score their tentacle number and location.

Knowing that the number of tentacles in sea anemones is determined by their food intake, the group plans to define the key nutrients critical to this process. Ikmi and his group also want to further investigate the unconventional role of muscles in defining the sites where new tentacles form. “We’re currently investigating this novel property of muscle cells and are eager to find out the mystery behind them,” he concludes.


Watch the video: Σκυταλοδρομία στο GNTM 2 - Ποια κατάφερε να τερματίσει 1η; (January 2022).