• sperms and oocyte,the male and female gametes,are highly specialized sex cells.
  • the formation of male gametes is called spermatogenesis and formation of female gametes is called oogenesis.
  • gametes are formed during meiosis in which number of chromosomes are reduced by half.
  • primordial germ cells originate in the wall of the yolk sac of the embryo and migrate into the gonad region.
  • it is a special type of cell division that involve two meiotic cell divisions(first meiotic division and second meiotic division),which occurs only during the production of gametes.
  • it result in the formation of four gametes containing 23 chromosomes and 1N amount of DNA.
  • it provides constancy of the chromosome number from generation to generation by reducing the chromosome number from diploid to haploid,thereby producing haploid gametes.
  • Allows random assortment of maternal and paternal chromosomes between the gamtes.
  • In meiosis crossing over of chromosome segments shuffles the genes and produces a recombination of   genetic material.
Disturbances of meiosis during gametogenesis.e.g nondisjunction,result in the formation of abnormal gametes.These gamtes can cause abnormal development such as occur in infants with Down syndrome.

  • Primordial germ cells(46,2N) arrive in the ovary at week four of embryonic development and differentiate into oogonia(46,2N).
  • Oogonia enter first meiotic division and undergo DNA replication to form primary oocytes(46,4N).
  • All primary oocytes are formed by the fifth month of fetal life and  remain dormant in prophase (diplotene) of meiosis 1 until puberty.
  • during women ovarian cycle.a primary oocyte complete the meiosis1 to form the secondary oocyte(23,2N) and first polar body which will degenerate.
  • secondary oocyte enters second meiotic division and ovulation occur when chromosomes align at metaphase.The secondary oocyte remains arrested in metaphase of second meiotic division until fertilization occur.
  • At fertilization,secondary oocyte completes second meiotic division to form a muture oocyte(23,1N) and second polar body.
  • Primordial germ cells(46,2N) arrive in the indifferent gonad at week four of embryonic development and remain dormant until puberty.
  • At puberty, Primordial germ cells differentiate into type A spermatogonia.which serve as stem cell throughout adult life.
  • some type A spermatogonia differentiate into type B spermatogonia.
  • Type B spermatogonia enter first meiotic division to form primary spermatocytes.
  • Primary spermatocytes form two secondary spermatocytes.
  • Secondary spermatocytes form two spermatids.
  • Spermatids undergo spermatogenesis,which result in mature sperms.
Retroperitoneal organs are:

S - Suprarenal glands (aka the adrenal glands)
A - Aorta/IVC
D - Duodenum (second and third segments [some also include the fourth segment] )
P -Pancreas (tail is intraperitoneal)
U - Ureters
C - Colon (only the ascending and descending colons, as transverse and sigmoid retain mesocolon)
K - Kidneys
E - Esophagus
R - Rectum

Synaptic Transmission:

Types of Synapses:
a)One to one synapse-such type of synapses are found in neuromuscular junction where an action potential in presynaptic element produces an action potential in postsynaptic element.

b)Many to one Synapse-such types of synapses are found on spinal motor neurons where many cell synapses on postsynaptic cell are required to depolarize.The synaptic input may be excitatory or inhibitory.

Excitatory postsynaptic potentials(EPSPs)
  • EPSP is produced by depolarization of the postsynaptic cell membrane immediately under the presynaptic ending.
  • it is excitatory because membrane potential moves towards  its threshold.
  • produced as a result of increase in conductance to Na+ and Ka+.
  • Na+ influx causes depolarization.
  • The EPSPs at synapses between neurons are similar to the  EPSPs at neuromuscular junctions.
  • Excitatory neurotransmitters include ACh,Norepinephrine, Epinephrine,Dopamine,Glutamate,and Serotonin.
Inhibitory postsynaptic potentials(IPSPs):
  • It hyperpolarizes the postsynaptic cell,moving away from threshold.
  • Hyperpolarization is caused by opening of Cl- channels.
  • Inhibitory  neurotransmitters are glycine and GABA.
Summation at synapses:
  • Spatial Summation occurs when two excitatory inputs arrive at postsynaptic neurons simultaneously and produce greater depolarization
  • Temporal  Summation occurs when  two excitatory inputs arrive at postsynaptic neurons in a rapid succession.because resulting postsynaptic depolarization overlap in time,they add in stepwise fashion.
Neuromuscular Transmission

Neuromuscular junction is the is the synapse between axons of motorneurons and muscle.
Events occuring during Neuromuscular Transmission.
  • when a action potential is produced in a axon it travels down towards the motor axon terminal.It depolarizes the presynaptic terminal that open Ca2+ channels and  Ca2+  ions moves into the presynaptic terminal down it's electrochemical gradient.
  • Ca2+  uptake causes release of ACh into the synaptic cleft by exocytosis.
  • ACh diffuse to the postsynaptic membrane,ACh bind to it's receptors which opens ligand gated  Na+ and Ka+ channels and Na+ influx occurs.
  • Influx of Na+ causes local depolarization.The magnitude of depolarization produced is referred to as End Plate Potential(EPP).EPP is not a action potential,but a local depolarization.
  • when the end plates depolarizes,local currents causes depolarization and action potential in the adjacent muscle tissue.
  • ACh is degraded by acetylcholinestrase(AChE ) into acetyl CoA and choline on the muscle end plate.

Agents interfering Neuromuscular junction:
  • Botulinus toxin-it blocks the release of ACh from presynaptic terminal.
  • Curare-it binds with the ACh receptors on motor end plate.
  • Neostigmine-it prevents the ACh degradation by inhibiting the AChE.
  • Hemicholinium-blocks reuptake of choline into presynaptic terminal.