MCAT Biology Embryogenesis and Nervous system

• 2 diff eggs released
• 2 diff sperm
• implants on uterine wall and develops own placenta

• incomplete division of when a single zygote splits into 2
• share same structure except amnion for monozygotic

• nuclear to cytoplasmic
• surface area to value ratio for gas exchange and nutrient exchange

• trophoblast
• inner cell mass

second portion of the fallopian, tube It is an intermediate dilated portion, which curves over the ovary,common site of human fertilization

a tube like structure formed from sperm which extends to puncture cell mem

puncture of cell mem and release calcium ions

depolaized and impenetrable mem that occurs after the sperm has penetrated the membrane and has entered

cells that can develop into complete organisms

cells with fates that are already determined

solid mass of cells after several divisions

hollow ball of cells with fluid filled cavity known as blastocoel

• surround blastocoel and give rise to chorion and placenta
• specialized to create an interface between the maternal blood supply and developing embryo
• form chorionic villi

protrudes in blastocoel and gives rise to organism itself

extraembryonic mem that develops into the placenta

microscopic fingerlike projections that penetrate endometrium and support maternal fetal gas exchange

• two arteries and 1 vein encased
• carries fresh oxygen blood with nutrients from placenta embryo

supports embryo until placenta is functional and is the site of early blood cell development

invlove in early fluid exchange between embryo and yolk sac

• surrounds the allantois
• serves as shock absorber during pregnancy
• forms placenta
• chorion adds another level of protection

• ectoderm
• mesoderm
• endoderm

• epidermis
• epithelium
• lens of eye and nervous system

• musculoskeletal, circulatory,excretory system
• gonads
• muscular and connective tissue layers
• digestive and respiratory systems
• adrenal cortex

• epithelial linings of digestion and respiratory tract
• pancrease,thyroid,bladder, and liver

ability of one group of cells to influence the fate of other nearby cells, which is mediated by inducers (chemical substances)

development of the nervous system

• rod of mesoderm
• forms along the axis of the organism like a spine

• notochord forms along axis
• notochord induces overlying ecto to slide inward to form neural folds
• neural folds grow toward each other to form neural tube
• neural crest cells migrate to form PNS as well as other specific cell types
• ectoderm cells migrate over neural tube and crest to cover NS

substances that interfere with development causing defects or even death of embryo

• genetics
• exposure and rate of placental transmission of teratogens
• alcohol, drugs, viruses, bacteria
• environmental chemicals

increase blood glucose and causes baby to be too large w/hypoglycemia

prevent closure of neural tube which leads to spinal bifida

• after being determined, the cell can become any cell type and will commit to a specific lineage
• can be determined during cleavage (asymmetrical spliting between 2 daughter cells, specific mrna molecules result in determining)
• secretion of specific molecules from nearby cell

• cause nearby cells to follow a particular development pathway
• closer to morphogen to the cell, the more it will differentiate into comparison to those that are further(unique combo of morpho exposure and causes diff of specific cell types)

changing in structure, function, and biochem of the cell to match cell type the cell is determined to be

the ability of a stem cell to differentiate into a specific cell

greatest potency, ultimately differentiate into any cell type in fetus or placenta

• any cell differentiation
• any cell differentiation except those in placental structures
• multiple cell types within a particular group

cell comm can occur between autocrine, paracrine, jucxtacrine, or endocrne system

same cell that secreted the signal first

cells in the local area

they act directly by stimulating receptors adjacent to the cell

secrete hormone that travel through the blood to distant tissue

peptides that promote differentiation and mitosis in certain tissue and can code for particular tissues

cell undergone changes in morphology and divides into many pieces that can be digested by other cells

cell death in which cell dies due to injury

• ability of an organism to regrow certain parts of the body
• (stem cells travel to place where it needs to be regenerated)

lost or damaged tissues replaced with identicle tissues

newly formed tissue is not identical in structure or function to the tissue that has been injured or last

• exhibits greater affinity for O2
• assists in transfer of O2 into fetal circulatory system

carry deoxygenated blood and waste products away from the fetus toward the placenta

carry oxygenated blood toward fetus from placenta as well as nutrients

body constructs 3 shunts to divert blood away from organs

• 1)foramen ovale - one way reroute blood from lungs. Blood entering RA from inferior VC to flow to LA instead of RV
• 2)ductus arteriosus - blood goes from pulmonary artery to aorta
• 3)ductus venosus - shunts blood returning from placenta via UV directly to inferior VC

• major organ development
• heart beats
• bones harden
• embryo becomes fetus

• fetus grows
• moves
• face looks more human
• toes/fingers elongate

• rapid growth & brain development
• antibody transport mother to fetus for protection from outside world
• growing slows and fetus is less active

• cervix thins
• amniotic sac ruptures
• uterine contraction=birth of fetus
• after birth

location of ER and ribo and is locted in the cell body of the axon where the nucleus is

receive incoming messages from cells and transmitted through cell body before reaching axon hillock

integrate incoming messages from other cells and sums the excitatory or inhibitory signals received by dendrites

• transmission of eletrical impulses down the axon
• axon hillock receives signals from dendrites (excit inhibit) to and if signal strong enough will cause action potential

insulated to prevent loss of signal or signal crossing

maintains electrical signal with one neuron and increases speed of conduction in axon

• oligodendrocytes (CNS)
• schwann cells (PNS)

• between myelin sheaths on axon
• critical for rapid signal conduction

• end of neuron
• enlarged and flattened to maximiize neutransmission to next neuron and ensure proper release of NT to other neurons

nerve terminal, synaptic cleft,post synaptic cleft

multiple neurons bundled together (sensory, motor, or mixed neurons can make them up) into ganglia

CNS neurons bundled together to form tracts that carry one type of info

cell bodies of neurons in the same tract (bundle of neurons that carry one type of info)

nourish neurons and form blood brain barrier

line ventricles of brain and produce cerebrospinal fluid

phagocytic cell

an electrical potential difference between the inside of the neuron and the extracellular space

• Na gets higher, K gets lower outside of cell
• Vice versa for inside of the cell
• cell is more negative, outside is more positive due to for every K molecule, 3 Na molecule come out leaving a more negative charge for the inside

• a - resting potential is generated by a - charged protein w/in the cell that increase + permeability
• the Na/K ATPase helps restore the gradient after action potential has occurred as well as gradients that have been dissipated by action potential

raising mem potential from resting and makes neurons more likely to fire an action potential which allows the ions to cross, but can only cross once excitatory input reaches a threshold (can be multiple signals to reach threshold or one large one)

lowers mem potential from resting potential thus makes neurons less likely to fire an action potential

additive effects of multiple signals from neurons which can be either or excitatory and inhibitory signals

• temporal-multiple signals integrated during a short period of time
• spatial-the effects are based on the number and location of incoming signals

• closed-occurs before reaching threshold
• open-once threshold is reached
• inactive-when it comes down from threshold

• absolute-no stim causes action to occur
• relaive-greater than normal stim to cause action potential

signals to be conveyed to another neuron, action potential must travel down axon and initiate NT release

• Na+ rushes into segment of axon, depolar in surrounding regions occur
• depolar bring segments of axon to threshold and opens NA+ in the segments
• continues until AP is in a wave like fashion until it reaches nerve terminal, one segment of axon has been fired, the segment beome refractory and can only go in one direction

• Length-longer axon, higher resistance, slower conduction
• cross section-increase CS faster propagation due to lower resistance

signal down the axon hops from node to node

• presynaptic neuron-before synaptic cleft
• postsynaptic neuron-after synaptic cleft

neuron signals to a gland or a muscle, the post synaptic cell

once NT is released into synapse after exiting mem bound vessicles to be exocytosized , the NT molecules diffuse across the cleft and bind to receptors on the post syn cell

• NT broken down by enzymatic rections
• reuptake carriers bring NT back into the presynaptic neuron (serotonin,dopamine,and norepinephrine are carriers)
• NT may diffuse out of synaptic cleft (NO nitric oxide)

• ligand gated ion (hyper or depolar)
• G protein coupled receptors (change in levels of cAMP)

afferent, transmit sensory info from receptors to spinal cord and brain

efferent, transmit motor info from brain and spinal cord to muscles

most numerou,locayed in brain and spinal cord and are linked to reflexes

• cervical
• thoracic
• lumbar
• sacral

• protects spinal cord
• transmits nerves at the space between adjacent vertebrae

• preganglionic and postganglionic
• soma of pregang (release acetycholine) is in the CNS and its axon travels down gang to PNS, there it synapses to postgang (norepinephrine) which affercts the target tissue

• monosynaptic - single synapse between sensory neuron that receives stimulus and motor neuron responds
• polysynaptic - one interneuron between the sensory and motor neurons

patellar tendon is stretched, info travels up sensory neuron to SP where it interfaces with motor neuron that contracts the quadricep muscles which results in extension of leg and tension lessens on patellar

person places foot on ground to remain balanced. the motor neuron controls the quadriceps in the opp leg and must be stim, extending the leg. Interneurons in SP provide the connections from sensory info to motor neurons in supporting leg