what about goosebumps ?

porcupineThere’s one thing that porcupines will always do better than humans: having goosebumps. Ok, ok, we cannot¬†raise our quills when threatened, simply because we do not have quills. But when we have goosebumps, our body hairs behave exactly in the same way as porcupine quills do. Cutis anserina, a definitely less catchy way to call it, consists in the formation of bumps on the skin. The curious thing is that this phenomenon is involuntary ūüôā let’s try to understand how this happens.

goosebumpsA feeling of cold, a sudden strong emotion of¬†fear,¬†pleasure,¬†euphoria¬†and, yes, also¬†sexual arousal… Our body reacts to all these events in the simplest way possible: trying to protect itself. And we cannot control it, since it’s a reflex (click here to read about another reflex typical of human body). In a previous post we learnt an interesting thing about human body thermoregulation: homeostasic processes (that we saw also here) always try to keep our Body Temperature¬†(BT) of 37¬įC despite environment conditions. When outside it’s too cold, our energy losses get more important and our BT lowers too fast. We know that, for example, if we do some physical exercise (even a short run) we’ll warm up again quite fast. This is because the activation of muscles develops that energy needed to warm up the body and restore proper BT conditions. But when a sudden feeling of cold occurs, our skin receptors immediately send this information to the brain via the sympathetic nervous system. Our¬†brain cannot wait for us to take a decision and, as previously said,¬†automatically activates a protective action: shivering.
By doing this, our muscles produce really fast contractions that we cannot control (don’t forget we’re always dealing with a reflex!).

arrector pili muscles

The twitching movements of muscles produce heat, which helps to raise BT. The contraction of the arrector pili muscles, that are the tiny muscles at the base of each hair, pulls the hair erect. In that moment our body acts like that of a porcupine, even if the latter experiences this reflex when threatened (by appearing larger, the animal intimidates enemies).

In exactly the same way, if our¬†jaw muscles begin to shiver, we start chattering our teeth. The mechanism is always the same: BT lowering is detected and an automatic response is activated to raise it up again. In an extremely¬†stressful¬†situation, it is possible to have goosebumps also after experiencing the so-called fight or flight response, when (from this webpage) “the¬†sympathetic nervous system¬†floods the blood with¬†adrenaline¬†(epinephrine), a hormone that speeds up¬†heart rate,¬†metabolism, and body temperature in the presence of extreme stress”. But this is another story that we’ll see later. For tonight, don’t forget to feed your porcupine with a wonderful home-made soup (possibly warm)!

other sources: uno, due e tre


just wipe that Cataract out of your eye

macchina fotoWe live in the Instagram era, when even a simple cup of coffee suddenly becomes one of the most artistic things to be photographed. After sharing your shot with all your friends on the web (so that you’ll have shown that you DO have a social life, yop!), you put back your Reflex (the best camera ever for shooting cups of coffee, we all know that) and notice that its lens is a bit misted up. Inside. So you’ll never be able to get rid of it and all your shots will look blurry. You’ll be able to post only photos of blurry coffee served in blurry cups on blurry tables. You’ll be a blurry person, forever.

Now, transpose this “blurriness” to one of your eyes. Imagine you have one eye which “works” perfectly, like HD vision, and the other one with some misted up lens inside, so that everything you see looks blurry. This is clearly a much worse problem than not being able to shoot cool photos. This problem is called Cataract and nowadays is¬†the most common cause of vision loss in people aged over 40.

human eyeHuman eye is composed of different layers. Without giving too many details, a very important component of the eye is a transparent tissue known as crystalline lens. This lens is able to change its thickness so that the eye is able to focus on objects at various distances. The changes of thickness are controlled by a suspensory ligament, called Zonule of Zinn, that connects the crystalline to the ciliary body of the eye. Their combined movements are really important for correctly focusing light onto the back of the eye (the retina) so that images appear clear and without distortion.

The crystalline lens is¬†made mainly of water and proteins and it is¬†nourished by the aqueous fluid that is present between the cornea and the crystalline lens.¬†Metabolic changes of the crystalline lens fibers over time lead to the development of¬†opacifications, mainly due to the proteins that clump together. As a consequence, the lens gets “clouded” and this clouding is actually known as Cataract. This process normally worsens the way light enters the eye and, as a result, our sight is blurry.

Cataract vs Normal

Nowadays, modern cataract surgery is one of the safest and most effective surgical procedures.¬†Over 90% of operations are successful in restoring useful vision, with a low complication rate. The operation itself is typically performed¬†using only local anesthesia and in one-day hospitals.¬†Very often, the postoperative recovery is really quick and¬†can greatly reduce the patient’s dependence on¬†eye glasses.

cataract surgeryThe most common surgical procedure for removing cataract is the so called phacoemulsification.

By using a microscope, the surgeon focuses on the lateral side of the eye and makes a small incision on the cornea.

Then, a tiny ultrasound probe is inserted into the eye in order to break the lens. The high vibration frequency (40 kHz) of the probe tip causes the emulsification of the lens material, which gets broken in very small fragments.

By accessing the eye always through the same incision, the crystalline pieces are removed through an aspiration probe.

Next, the same tool is employed again, this time to insert an artificial intraocular lens that actually replaces the crystalline. The artificial lens is usually made of plastic, silicone or acrylic compounds and is supposed to remain in place for the rest of the patient’s life. No stitch is generally necessary, just¬†a protective shield is usually placed over the eye to keep it safe in the early recovery stages.

Recently, lasers have been approved for use in cataract surgery: they improve the accuracy of the surgery, since they reduce the need for surgical blades and other hand-held tools. Moreover, they result to be more efficient than ultrasonic probes for crystalline fragmentation. Laser-assisted cataract surgery is fairly new and significantly increases cataract surgery cost. However, medical consultation is always the best way to evaluate all the possible surgical risks.

sources: one, two and three

Patellar Reflex

definition _

Patellar Reflex, also called knee-jerk, is a stretch reflex associated with quadriceps femoris muscle stretching.

how it works _

The stretch is created by a blow upon the patellar tendon (positioned just below the Patella). This blow, usually performed with a specific tendon hammer, activates the muscle spindle in the quadriceps femoris muscle.

Muscle spindle is a particular type of sensory receptor, normally embedded in muscle fibers, able to¬†detect changes in the length of the muscle itself. Once “activated” by the external blow, this receptor sends a signal to the spinal cord. Instead of involving higher nervous centres (it would take too long), at the level of the spinal cord an alpha-motor neuron is immediately activated.

The alpha-motor neuron conducts an efferent impulse directly back to the quadriceps femoris muscle, leading to its contraction. At the same time, an inhibitory interneuron¬†relaxes the hamstring muscle,¬†which is the quadricep’s antagonistic muscle.

The result of such coordinated contraction-relaxation, causes the “kick movement” of the leg. In normal health conditions, the leg extends once and then comes back to rest.¬†It only takes about 50 milliseconds between the tap and the start of the leg kick.

why it is useful _

Patellar Reflex is a proprioceptive reflex which helps keeping posture and balance. The fact that everything “happens” at the level of the spinal cord, without involving higher nervous centres, allows for instance to keep balance without effort (actually, one does not have to focus on keeping an upright position). Energies are saved for more complex activities.¬†Moreover,¬†Patellar Reflex helps avoiding strong muscle contractions which could tear the tendon.

clinical interest _

As said, there is no interneuron in the pathway leading to contraction of the quadriceps muscle. Patellar Reflex can be used, for example, to check the conditions of the connections between the spinal cord and the muscles.

The absence or decrease of the Patellar Reflex is known as¬†Westphal’s sign. On the other hand, multiple oscillation of the leg following the blow may be a symptom of¬†cerebellar diseases.

source: contents taken from Wikipedia’s page