Penis -The penis is the male organ for sexual intercourse. It has three parts: the root, which attaches to the wall of the abdomen; the body, or shaft; and the glans, which is the cone-shaped end of the penis.
Scrotum -The scrotum is the loose pouch-like sac of skin that hangs behind the penis. It contains the testicles (also called testes), as well as many nerves and blood vessels. The scrotum has a protective function and acts as a climate control system for the testes.
Testicles (testes)- The testes are oval organs about the size of large olives that lie in the scrotum, secured at either end by a structure called the spermatic cord. Most men have two testes. The testes are responsible for making testosterone, the primary male sex hormone, and for generating sperm.
Epididymis -The epididymis is a long, coiled tube that rests on the backside of each testicle. It functions in the transport and storage of the sperm cells that are produced in the testes.
Vas deferens - The vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to the urethra in preparation for ejaculation.
Ejaculatory ducts - These are formed by the fusion of the vas deferens and the seminal vesicles. The ejaculatory ducts empty into the urethra.
Urethra -The urethra is the tube that carries urine from the bladder to outside of the body. In males, it has the additional function of expelling (ejaculating) semen when the man reaches orgasm. When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.
Seminal vesicles -The seminal vesicles are sac-like pouches that attach to the vas deferens near the base of the bladder. The seminal vesicles produce a sugar-rich fluid (fructose) that provides sperm with a source of energy and helps with the sperms' motility (ability to move). The fluid of the seminal vesicles makes up most of the volume of a man's ejaculatory fluid, or ejaculate.
Prostate gland - The prostate gland is a walnut-sized structure that is located below the urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the ejaculate. Prostate fluids also help to nourish the sperm. The urethra, which carries the ejaculate to be expelled during orgasm, runs through the center of the prostate gland.
Bulbourethral glands -The bulbourethral glands, or Cowper's glands, are pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present due to residual drops of urine in the urethra
Labia majora: The labia majora enclose and protect the other external reproductive organs. Literally translated as "large lips," the labia majora are relatively large and fleshy, and are comparable to the scrotum in males. The labia majora contain sweat and oil-secreting glands. After puberty, the labia majora are covered with hair.
Labia minora: Literally translated as "small lips," the labia minora can be very small or up to 2 inches wide. They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body).
Bartholin's glands: These glands are located next to the vaginal opening and produce a fluid (mucus) secretion.
Clitoris: The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect. Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.
Uterus (womb): The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit.
Ovaries: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.
Fallopian tubes: These are narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants to the uterine wall.
The fast block to poly-spermy is achieved by changing the electric potential of the egg plasma membrane. This membrane provides a selective barrier between the egg cytoplasm and the outside environment, and the ionic concentration of the egg differs greatly from that of its surroundings. This concentration difference is especially significant for sodium and potassium ions. Seawater has a particularly high sodium ion concentration, whereas the egg cytoplasm contains relatively little sodium. The reverse is the case with potassium ions. This condition is maintained by the plasma membrane, which steadfastly inhibits the entry of sodium ions into the oocyte and prevents potassium ions from leaking out into the environment. Within 1-3 seconds after the binding of the first sperm, the membrane potential shifts to a positive level. This change is caused by a small influx of sodium ions into the egg. Although sperm can fuse with membranes having a resting potential of -70 mV, they cannot fuse with membranes having a positive resting potential, so no more sperm can fuse to the egg.
The eggs of sea urchins (and many other animals) have a second mechanism to ensure that multiple sperm do not enter the egg cytoplasm. The fast block to polyspermy is transient, since the membrane potential of the sea urchin egg remains positive for only about a minute. This brief potential shift is not sufficient to prevent polyspermy, which can still occur if the sperm bound to the vitelline envelope are not somehow removed. This removal is accomplished by the cortical granule reaction, a slower, mechanical block to polyspermy that becomes active about a minute after the first successful sperm-egg attachment.
In the process of gastrulation, a primitive streak first appears on the dorsal surface of the epiblast. As cells move past the primitive streak, they elongate and pass through to form ventral layers beneath the initial epiblast. At the end of the streak there is a small, well defined node - called Hensen's node. Migrating epiblastic cells that pass through this node form a mesenchymal structure called the notochord. By the end of gastrulation, a notochord and three distinct germ layers (endoderm, mesoderm, and ectoderm) have formed. Each germ layer gives rise to specific tissues and organs in the developing embryo. The ectoderm gives rise to epidermis, and to the neural crest and other tissues that will later form the nervous system. The mesoderm is found between the ectoderm and the endoderm and gives rise to somites, which form muscle; the cartilage of the ribs and vertebrae; the dermis, the notochord, blood and blood vessels, bone, and connective tissue. The endoderm gives rise to the epithelium of the digestive system and respiratory system, and organs associated with the digestive system, such as the liver and pancreas Cleavages in mammalian eggs are among the slowest in the animal kingdom—about 12-24 hours apart. In addition to the slowness of cell division, there are several other features of mammalian cleavage that distinguish it from other cleavage types. The second of these differences is the unique orientation of mammalian blastomeres with relation to one another. The first cleavage is a normal meridional division; however, in the second cleavage, one of the two blastomeres divides meridionally and the other divides equatorially. This type of cleavage is called rotational cleavage The third major difference between mammalian cleavage and that of most other embryos is the marked asynchrony of early cell division. Mammalian blastomeres do not all divide at the same time. Thus, mammalian embryos do not increase exponentially from 2- to 4- to 8-cell stages, but frequently contain odd numbers of cells. Fourth, unlike almost all other animal genomes, the mammalian genome is activated during early cleavage, and produces the proteins necessary for cleavage to occur. The fifth, and perhaps the most crucial, difference between mammalian cleavage and all other types involves the phenomenon of compaction. As seen in, mouse blastomeres through the 8-cell stage form a loose arrangement with plenty of space between them. Following the third cleavage, however, the blastomeres undergo a spectacular change in their behavior. They suddenly huddle together, maximizing their contact with one another and forming a compact ball of cells. This tightly packed arrangement is stabilized by tight junctions that form between the outside cells of the ball, sealing off the inside of the sphere. The cells within the sphere form gap junctions, thereby enabling small molecules and ions to pass between them. The cells of the compacted 8-cell embryo divide to produce a 16-cell morula. The morula consists of a small group of internal cells surrounded by a larger group of external cells. Most of the descendants of the external cells become the trophoblast (trophectoderm) cells. This group of cells produces no embryonic structures. Rather, it forms the tissue of the chorion, the embryonic portion of the placenta. The chorion enables the fetus to get oxygen and nourishment from the mother. It also secretes hormones that cause the mother's uterus to retain the fetus, and produces regulators of the immune response so that the mother will not reject the embryo as she would an organ graft. The embryo proper is derived from the descendants of the inner cells of the 16-cell stage, supplemented by cells dividing from the trophoblast during the transition to the 32-cell stage. These cells generate the inner cell mass (ICM), which will give rise to the embryo and its associated yolk sac, allantois, and amnion. By the 64-cell stage, the inner cell mass (approximately 13 cells) and the trophoblast cells have become separate cell layers, neither contributing cells to the other group. Thus, the distinction between trophoblast and inner cell mass blastomeres represents the first differentiation event in mammalian development. This differentiation is required for the early mammalian embryo to adhere to the uterus. The development of the embryo proper can wait until after that attachment occurs. The inner cell mass actively supports the trophoblast, secreting proteins (such as FGF4) that cause the trophoblast cells to divide. a. Sensory Input: sensory neurons transmit information from external stimuli (light, sound, touch, heat, smell, and taste) and internal conditions (blood pressure, blood CO2 level, and muscle tension, for example). This info is sent to the CNS for processing.
b. Integration: In the CNS, interneuron analyze and interpret the sensory input taking into account the immediate context and what happened in the past. The CNS the decides how to respond.
c. Motor Output: leaves the CNS via motor neurons to effector cells which can be either muscle cells or endocrine glands, which then do something (move or release hormones, for example)
a. Cell body-(Soma) is the factory of the neuron. It produce all the proteins for the dendrites, axons and synaptic terminals and contains specialized organelles such as the mitochondria, Golgi apparatus, endoplasmic reticulum, secretory granules, ribosomes and polysomes to provide energy and make the parts, as well as a production line to assemble the parts into completed products.
b. Dendrites- These structures branch out in treelike fashion and serve as the main apparatus for receiving signals from other nerve cells. They function as an "antennae" of the neuron and are covered by thousands of synapses. The dendritic membrane under the synapse (the post-synaptic membrane) has many specialized protein molecules called receptors that detect the neurotransmitters in the synaptic cleft. A nerve cell can have many dendrites which branch many times, their surface is irregular and covered in dendritic spines which are where the synaptic input connections are made.
c. Axon.- the main conducting unit of the neuron, capable of conveying electrical signals along distances that range from as short as 0.1 mm to as long as 2 m. Many axon split into several branches, thereby conveying information to different targets
d. Neuronal membrane serves as a barrier to enclose the cytoplasm inside the neuron, and to exclude certain substances that float in the fluid that bathes the neuron.
e. Synapses are the junctions formed with other nerve cells where the presynaptic terminal of one cell comes into 'contact' with the postsynaptic membrane of another. It is at these junctions that neurons are excited, inhibited, or modulated. There are two types of synapse, electrical and chemical
In Alzheimer's disease, there is an overall shrinkage of brain tissue. The grooves or furrows in the brain, called sulci (plural of sulcus), are noticeably widened and there is shrinkage of the gyri (plural of gyrus), the well-developed folds of the brain's outer layer. In addition, the ventricles, or chambers within the brain that contain cerebrospinal fluid, are noticeably enlarged. In the early stages of Alzheimer's disease, short-term memory begins to fade (see box labeled 'memory') when the cells in the hippocampus, which is part of the limbic system, degenerate. The ability to perform routine tasks also declines. As Alzheimer's disease spreads through the cerebral cortex (the outer layer of the brain), judgment declines, emotional outbursts may occur and language is impaired. As the disease progresses, more nerve cells die, leading to changes in behavior, such as wandering and agitation. In the final stages of the disease, people may lose the ability to recognize faces and communicate; they normally cannot control bodily functions and require constant care. The exact cause of Parkinson's disease is unknown, but several factors appear to play a role, including:
Your genes. Environmental Triggers
In addition, numerous changes are found in the brains of people with Parkinson's disease. The role of these factors in the development of the disease, if any, isn't clear, however. These changes include:
A lack of dopamine. Many symptoms of Parkinson's disease result from the lack of a chemical messenger, called dopamine, in the brain. This occurs when the specific brain cells that produce dopamine die or become impaired. Why and exactly how this happens isn't known.Low norepinephrine levels. People with Parkinson's disease also have damage to the nerve endings that make another important chemical messenger called norepinephrine. Norepinephrine plays a role in regulating the autonomic nervous system, which controls automatic functions, such as blood pressure regulation.The presence of Lewy bodies. Unusual protein clumps called Lewy bodies are found in the brains of many people with Parkinson's disease. How they got there and what type of damage, if any, Lewy bodies might cause is still unknown.
Sensation is the result of your body's senses sensing something: heat, cold, pain, moisture, dryness, whatever. Your mind converts many sensations into "feelings" (a sensation with a name!) which can then, if you wish, express to others through an emotion. Perception is how you view your world, what you see and fail to see in it, what you see that isn't there, etc.