The Special Senses

What we see, hear, taste, smell, and our balance are all part of our special senses.  They are called special senses because their sensory receptors are located within large sensory organs in our heads (the nose, eyes, ears, and tongue). 

Fun fact:  Touch is not considered a special sense but a generalized one.

Chemical receptors that respond to changes in chemical concentrations are call olfactory receptors.  In the nose, chemicals must be dissolved in the mucus in order to activate smell receptors.  The receptors are located in the olfactory organ which is found in the upper part of the nasal cavity.  Once the smell receptors are activated, they send the information to the olfactory nerves who send it to olfactory bulbs and tracts to different areas in the cerebrum.  From there, it is determined as to what particular smell it is.  

Fun facts: -Because there are fewer smell receptors in humans and because the chemicals have to diffuse all the way up the nasal cavity, our sense of smell is poor compared to an animal. 

                -The same chemical can only stimulate smell receptors for a short period of time and then they no longer respond to that odor (it can no longer be smelled).  This is called sensory adaption.

  

Our tongues consist of tiny little bumps (papillae) that are our taste receptors.  Taste cells and supporting cells make up each taste bud.  Taste cells are types of chemoreceptors like the olfactory cells of smell.  Chemicals that are in the foods and drinks we in ingest have to be dissolved in saliva in order to activate the taste cells.  There are 4 types of taste cells:

• Sweet- found on the tip of the tongue.
• Sour- found on the sides of the tongue
• Salty- found on the tip and sides of the tongue
• Bitter- found at the back of the tongue

Fun fact:  Spicy is not an actual taste sensation.  Spicy foods activate pain receptors that interpret the food as hot or spicy.

Our eyes are complex organs.  They process light in order to produce the images we see throughout the day.  There are 3 layers of the eye:

• The outer layer is the white of the eye called sclera.  Light cannot pass through this layer and covers everything except the front of the eye which is transparent and acts as a window to let light in called the cornea.  
• The middle layer is the choroid.  Most of the eyes blood vessels are located here.  It contains the iris or colored part of the eye and the ciliary body.  The iris is made of muscular tissue that contracts and relaxes to make the center (pupil) grow smaller or larger.  The purpose of this is to regulate the amount of light the eye takes in.  The ciliary body controls the shape of the lens, allowing us to view close or distant objects.  
• The inner layer consists of the retina.  The nerve cells of the retina sense light.  The optic disc is where the optic nerve enters the retina and there are no sensory nerves.  This area is also known as the blind spot.  There are 2 types of nerve cells which are rods and cones.  Rods are sensitive to light and function in dim light.  Cones work best in bright light and are sensitive to color and provide us with sharper images.

Accessory organs of the eye include the orbits, eyebrows, eyelids and eyelashes, conjunctivas, the lacrimal apparatus, and the extrinsic eye muscles. The eye orbits (eye sockets) are the protective shell around the eye.  Eyebrows, eyelashes and eyelids are all protective organs to help keep particles out of the eye as well as eyelids are to help prevent the mucous on the eye from drying out.  Conjunctivas are the mucous membranes that line the eyelids and cover the surface of the eye to keep the eyeball moist. The lacrimal apparatus contain lacrimal ducts that produce tears.  Tears contain enzymes that help to destroy bacteria and viruses that the eyeball may come in contact with.  Extrinsic eye muscles are what move the eyeball so that we can look different ways.  In order for us to see, light is reflected from an object and enters the eye through the cornea.  From the cornea, it goes through the pupil, lens, and fluids and onto the retina by bending it (refraction).  At this point the image is upside-down.  The retina takes the light and converts it into nerve impulses which are sent along the optic nerve to the brain where it is sent to the visual area in the occipital lobes of the cerebrum and interpreted.  Half of what we see in the right eye is interpreted in the left side of the brain and the left eye in the right side where it is brought together and turned right-side up to develop the image of object.

Fun fact:  Newborns do not produce tears.  We don't start producing tears until about 4 weeks old.

Our ears are what provides our sense of hearing.  Like the eye, the ear is divided into 3 parts

• The external ear which is composed of the auricle and external auditory canal.
• The middle ear which begins with the tympanic membrane and ends at the oval window.  It also contains the eustachian tube that helps maintain equal pressure on both sides of the eardrum.
• The inner ear consists of complex systems of communicating chambers and tubes known as labyrinth.

The auricle is where sound waves are collected.  They are carried through the auditory canal to the tympanic membrane.  The canal also contains hairs and glands the produce cerumen, (earwax) that traps dirt, dust, and other microbes.  Once the sound waves reach the tympanic membrane it causes vibrations.  When it vibrates, it causes the ossicles (3 tiny bones known as the malleus, incus, and stapes) to vibrate and hit a membrane called the oval window.   The labyrinth is divided into 3 portions:  semicircular canals, a vestibule, and a cochlea.  There are 3 semicircular canals.  These canals detect the body's balance.  The cochlea contains the hearing receptors including the organ of Corti, which is the largest organ of hearing.  The area between the semicircular canals and the cochlea is the vestibule and it also helps in equilibrium.  When the head moves, fluids in the canals and vestibule move to activate both the equilibrium and the hearing receptors.  The equilibrium receptors send the information along the vestibular nerves to the cerebrum to be interpreted.  Sound waves consists of different frequencies that move through the air and when it is collected they are channeled to the tympanic membrane.  The vibrations are amplified and cause the hairs of the cochlea to move triggering nerve impulses.  The auditory nerve transmits the impulses to the brain where they are recognized as sounds.  

Without our senses, we wouldn't have the privilege to experience all unique features the world has to offer.  Our brains are working constantly to allow our senses to be interpreted.  Even though they are unconscious acts to us, we don't realize how important they are until we no longer have the ability to enjoy them. 

  

  

The Skeletal System

Fun fact: There are 206 bones in your body!

The skeletal system is made up of two major divisions: the axial skeleton and the appendicular skeleton.  The axial skeleton contains 80 bones.  Included in this division is the skull, vertebral column, rib cage, and hyoid bone.  It protects the brain, spinal cord, and the organs in the thorax and supports the head, neck, and truck.  The appendicular division includes the body's other 126 bones which are the bones of the arms, legs, pectoral girdle, and pelvic girdle.  

All of our bones are made up of both compact and cancellous bone and are classified according to their shape.  There are 5 different types of bone: long, short, flat, irregular, and sesamoid.  Long bones are located in the arms and legs.  Short bones are those of the wrists and ankles.  Flat bones are found in the skull and ribs.  Irregular bones include the vertebrae and pelvic girdle and sesamoid bones are like the kneecap, small and rounded.  

 

In order to have healthy bones, many things influence it.  A healthy diet and good nutrition is key for proper bone growth during the early stages in our lives.  It plays a big factor in maintaining healthy bones in adulthood.  The obvious calcium and vitamin D are needed to keep our bones strong and dairy products, broccoli, kale, spinach, salmon, sardines, egg yolks, whole grains, and fruit are great bone building nutrients.  You should also have bone-healthy exercises and a bone-healthy lifestyle.  Exercises would include anything weight-bearing and strength training.  Jogging, walking, and playing sports will also increase bone density.  In order to have a bone healthy lifestyle you would want to avoid smoking and consuming alcohol. Smoking depletes body of calcium and smokers are twice as likely to develop osteoporosis.  

The skull is divided into two types of bones.  The top, sides, and back of the skull make up the cranial  bones and the facial bones form the face.  The cranial bones include the frontal bone, parietal bones, occipital bone, temporal bones, sphenoid bone, ethmoid bones, and the eat ossicles as well as external auditory meatus also known as the ear canal.  The facial bones include the mandible, maxillae, zygomatic bones, palatine bones, and the vomer.  

Fun fact:  The male skull is heavier and larger than a females. 

Seven cervical vertebrae, twelve throacic vertebrae, five lumbar vertebrae, a sacrum, and a coccyx make up the spinal column.  The cervical vertebrae are the smallest and lightest and are located at the neck. Following them are the thoracic and then lumbar. The sacrum is at the bottom of the lumber vertebrae is where the scrum and coccyx are located. They are both triangular- shaped bones.  The sacrum consists of five vertebrae fussed together and the coccyx, more commonly known as the tailbone, consists of three to five vertebrae fused together.  

Twelve pairs of ribs and the sternum make up the rib cage.  The first seven pairs of ribs are called true ribs because they attach directly to the sternum or breastplate.  Rib pairs eight, nine, and ten are considered false ribs because they are attached to rib pair seven instead of to the sternum.  The last two pairs of ribs are called floating ribs because they do not attach to the sternum or to any other structure.  

The last parts of our skeletal system include our shoulders, arms, legs, hands, hips, and feet.  Listed blow are the parts and the bones they include:

• Shoulders:  clavicles and scapulae
• Arms:  the humerus, radius, and ulna
• Hands:  carpals, metacarpals, and phalanges
• Hips:  ilium, ischium, and pubis bones
• Legs:  femur, patella, tibia, and fibia
• Feet:  tarsals, metatarsals, and phalanges

The skeletal system gives the body its structure, support, and protection.  Without it, we would be a glob of goo!

The Reproductive System

One of the most fascinating things about the human body is its reproductive system.  Its remarkable how a man and a woman can come together and create a tiny human being.  Without the different parts from each sex, it wouldn't be possible.  

The male is responsible for production of the sperm cells used to fertilize a females ovum, or egg.  The testes are the primary organs of the male reproductive system because they make the sperm and a hormone called testosterone which is responsible for the development of male secondary sex characteristics.  Each sperm cell has 3 parts. The head, which holds the nucleus and contains an enzyme that allows them to penetrate the ovum called acrosome. The midpiece, which gives the sperm the energy needed to move. Lastly, the tail propels it forward.

  

The internal accessory organs that go along with the testes in the male reproductive system are the epididymis, vas deferens, seminal vesicles, prostate gland, and bulbourethral glands.  All of these organs are connected and work together to get the sperm cells where they need to be in order to leave the male body.  It begins with the maturing of the sperm cells in the epididymis and then a tube (the vas deferens) carries them to the urethra.  The seminal vesicles secrete seminal fluid that sperm cells use to make energy and also stimulates muscular contractions in the female reproduction system in order to help propel sperm forward.  This mixture of sperm and fluid create semen.  The prostate gland also produces a milky fluid that helps to protect the sperm when they enter the female.  Both these products are released just before ejaculation.  

Males also have 2 external reproductive organs: the scrotum and the penis.  The scrotum is the pouch that holds the testes away from the body in order to keep the temperature about a degree lower so that the sperm can remain alive.  The penis is made up of erectile tissue that surrounds the urethra which runs through the penis.  Its functions are to deliver the semen and for urination.

Fun fact:  The total semen volume is between 1.5 and 5.0 mL per ejaculation with a sperm count between 40 to 250 million/mL.  Normal sperm count is 80+ million.

In the female reproductive system the ovaries are the primary female sex organ because they produce the female sex cells known as ova and the hormones estrogen and progesterone.  Most females have two ovaries.
Fun fact:  Unlike the fact that males continuously make sperm cells, females are born with the maximum number of oocytes (immature ovum) that she will ever produce.  

The internal accessory reproductive organs of a female consists of the fallopian tubes, uterus, and vagina.  The fallopian tubes grab and transport an ovum from the ovary.  The uterus is a muscular organ that receives a developing embryo and maintains it during development.  It consists of 3 layers: the endometrium, myometrium, and the perimetrium.  The vagina is the muscular organ that extends from the uterus to the outside of the body which allows the body to receive and erect penis during sexual intercourse so that sperm cells can fertilize an ovum.  

The cycle that the female reproductive system goes through is called a menstrual cycle.  It consists of a monthly "period" or bleeding due to shedding of the uterine lining.  This happens when a ovum has not been fertilized.  The first menstrual period is known as menarche.  When menstrual cycles cease, this is known as menopause.  

After sexual intercourse, sperm cells make their way to the ovum.  Even though many will reach the ovum, only one will actually unite with it.  Once united, enzymes are released to prevent other sperm from penetrating it.  The nucleus of each the sperm cell and ovum come together to make one that contains 46 chromosomes.  The product of this is called a zygote.  After about a day after a zygote is formed it begins mitosis.  During this process the zygote is implanted into the uterus wall and becomes an embryo.  

The embryonic period extends from the second week to the eighth week.  During this period, the placenta, amnion, umbilical cord, and yolk sac are formed along with most of the internal organs and external structures of the embryo.  The placenta allows nutrients and oxygen pass to the embryonic blood and waste products from the fetal blood to pass into the maternal blood. Amnion is the fluid that protects the embryo.  The umbilical cord exchanges oxygenated and deoxygenated blood to and from the placenta and embryo and the yolk sac makes new blood cells for the embryo as well as determine the sex cells of the baby. 

The fetal period picks up from the eighth week and ends at birth.  During this time, the offspring is called a fetus and growth is rapid.  All parts and organs of the fetus are formed and begin functioning.  The fetus gains weight and positions itself upside down for delivery.  

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The birth process ends pregnancy.  The cervix thins and softens. Contractions are regular and the amniotic sac ruptures either own its own or by a surgical puncture.  Once the cervix is dilated to about 10 cm, contractions and abdominal compressions (the pushing stage) force the fetus out of the vagina.  After birth, the placenta separates from the uterine wall and is expelled from the body.  If the fetus is not in the head down position a c-section may be required to remove the fetus from the body.  

The reproductive system in both male and female are completely different.  They are simple yet complicated.  When you put the two together you create life and a family!  

The Cardiovascular System

   
     Over the course of class this week, we covered four different systems.  Of those, I found great interest in the cardiovascular system.  This system consists of the heart and blood vessels and is responsible for delivering oxygen and nutrients to all the organ systems in our bodies.  It also circulates waste products to the appropriate organ systems so that they can be removed.
     Contrary to popular belief of how the heart looks, it is actually a cone-shaped organ about the size of a fist.  The hearts wall is composed of three different layers: the epicardium which is the outermost layer, the myocardium which is the middle layer, and the endocardium which is the innermost layer.  It also has four chambers and four valves.  The upper chambers are called the right and left atria and the lower chambers are the right and left ventricles.  The four valves it contains are the tricuspid valve, bicuspid valve, pulmonary semilunar valve, and the aortic semilunar valve.  All these make up the basic parts which work together to make one "lubb-dubb" also know as one heartbeat, or cardiac cycle.




     The heart also has its own natural pacemaker called a sinoatrial node (SA node) which creates rhythmic contractions.  It sends the impulse to the atrioventricular node (AV node) causing the atria to contract and send the impulse to the bundle of His followed by the purkinje fibers.  This cycle is known as the cardiac conduction system.  Physicians use tests called electrocardiograms (EKG) to determine if this system is functioning properly.                                                    


     There are two routes the blood takes.  The first one is from the heart to the lungs and back to the heart.  This is called pulmonary circulation and its purpose is to oxygenate the blood.  The second route is from the heart through the body and back to the heart.  Its purpose is to deliver oxygen and nutrients to the body cells and to pick up carbon dioxide and waste products.  This circuit is known as the systemic circuit.

Fun fact:  It only takes blood about 20 seconds to make and entire trip around your body!



   
     The blood circulation takes place in blood vessels and include arteries, arteriols, veins, venules, and capillaries.  These parts help to determine our blood pressure.  When the ventricles contract the pressure is at its highest in the arteries, this is called your systolic pressure, and at its lowest when the ventricles relax called diastolic pressure.  If blood pressure becomes to low, vasoconstriction happens.  This is when the blood vessel walls tighten to help raise it back up.  If blood pressure becomes to high the blood vessels widen, called vasodilation, allowing the pressure to decrease.

Fun fact:  An adult's body only contains about 4 to 6 liters of blood.



     The cardiovascular system is truly a remarkable one.  Without it, the rest of our body systems and organs wouldn't be able to function and we would cease to live so please be good to your heart and take care of your body so it can take care of you!