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fraternal twins description
- 2 diff eggs released
- 2 diff sperm
- implants on uterine wall and develops own placenta
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conjoined twins description
- incomplete division of when a single zygote splits into 2
- share same structure except amnion for monozygotic
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by dividing into smaller cells, the cells increase 2 ratios:
- nuclear to cytoplasmic
- surface area to value ratio for gas exchange and nutrient exchange
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2 cells groups of blastoysts (mammal blastula)
- trophoblast
- inner cell mass
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Ampulla
second portion of the fallopian, tube It is an intermediate dilated portion, which curves over the ovary,common site of human fertilization
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acrosomal apparatus
a tube like structure formed from sperm which extends to puncture cell mem
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cortical reaction
puncture of cell mem and release calcium ions
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fertilization mem
depolaized and impenetrable mem that occurs after the sperm has penetrated the membrane and has entered
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indeterminate cleavage
cells that can develop into complete organisms
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determinant cleavage
cells with fates that are already determined
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morula
solid mass of cells after several divisions
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blastula
hollow ball of cells with fluid filled cavity known as blastocoel
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the trophoblast cells function
- 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
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inner cell mass function
protrudes in blastocoel and gives rise to organism itself
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chorion function
extraembryonic mem that develops into the placenta
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chorionic villi
microscopic fingerlike projections that penetrate endometrium and support maternal fetal gas exchange
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umbilical cord function
- two arteries and 1 vein encased
- carries fresh oxygen blood with nutrients from placenta embryo
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yolk sac
supports embryo until placenta is functional and is the site of early blood cell development
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allantois
invlove in early fluid exchange between embryo and yolk sac
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umbilical cord is formed from remnants of the yolk sac and the allantois
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amnion
- surrounds the allantois
- serves as shock absorber during pregnancy
- forms placenta
- chorion adds another level of protection
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deuterosomes (humans) blastopores develops into anus
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protosomes blastopore develops into mouth
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3 primary germ layers (outer into inner)
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ectoderm gives rise to 3 things
- epidermis
- epithelium
- lens of eye and nervous system
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mesoderm gives rise to these 5
- musculoskeletal, circulatory,excretory system
- gonads
- muscular and connective tissue layers
- digestive and respiratory systems
- adrenal cortex
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endoderm gives rise to these 2 things
- epithelial linings of digestion and respiratory tract
- pancrease,thyroid,bladder, and liver
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induction
ability of one group of cells to influence the fate of other nearby cells, which is mediated by inducers (chemical substances)
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neurulation
development of the nervous system
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notochord
- rod of mesoderm
- forms along the axis of the organism like a spine
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4 steps of neurulation
- 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
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neural tube gives rise to CNS
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teratogens
substances that interfere with development causing defects or even death of embryo
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cause of teratogens
- genetics
- exposure and rate of placental transmission of teratogens
- alcohol, drugs, viruses, bacteria
- environmental chemicals
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diabetes in babies is due to
increase blood glucose and causes baby to be too large w/hypoglycemia
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maternal folic acid deficiency causes
prevent closure of neural tube which leads to spinal bifida
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2 ways for determination of what a cell will be
- 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
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morphogens (determination)
- 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)
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cells first are determined and then differentiate into the cell they were determined to be
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differentiation
changing in structure, function, and biochem of the cell to match cell type the cell is determined to be
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potency
the ability of a stem cell to differentiate into a specific cell
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totipotent
greatest potency, ultimately differentiate into any cell type in fetus or placenta
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as cells begin to differentiate, they lose their potency
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totipotent>pluripotent>multipotent
- any cell differentiation
- any cell differentiation except those in placental structures
- multiple cell types within a particular group
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after egg is fertilized, the embryo develops into a gastrula contains 3 germ layers which woulde differentiate into diff tissue types in the human body
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the ability to induce a stem cell to be a specific type is not easy, depends on complex structures of organs and diff cell types which require diff signals
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cell diff depends on location of cell and surrounding cells
cell comm can occur between autocrine, paracrine, jucxtacrine, or endocrne system
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autocrine signals act on what cells
same cell that secreted the signal first
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paracrine signals act on what cells
cells in the local area
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juxtacrine signals act on what cells
they act directly by stimulating receptors adjacent to the cell
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endocrine signals act on what cells
secrete hormone that travel through the blood to distant tissue
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growthfactors (inducers for cell differentiation)
peptides that promote differentiation and mitosis in certain tissue and can code for particular tissues
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cells can disconnect from their location and travel to reach the correct location once they are determined
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apoptic blebs
cell undergone changes in morphology and divides into many pieces that can be digested by other cells
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nercosis
cell death in which cell dies due to injury
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regenerative capacity
- ability of an organism to regrow certain parts of the body
- (stem cells travel to place where it needs to be regenerated)
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complete regeneration
lost or damaged tissues replaced with identicle tissues
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incomplete regeneration
newly formed tissue is not identical in structure or function to the tissue that has been injured or last
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a large amount of C & G knot off the ends of the telomeres
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HbF fetal hemoglobin function
- exhibits greater affinity for O2
- assists in transfer of O2 into fetal circulatory system
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placenta produces progesterone, estrogen, and HCG which helps maintain pregnancy
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umbilical arteries function
carry deoxygenated blood and waste products away from the fetus toward the placenta
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umbilical vein function
carry oxygenated blood toward fetus from placenta as well as nutrients
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gas exchange occur in placenta along with waste exchange, lungs of fetus doesnt function until birth
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detox and metab are controlled by mothers liver because their lungs and liver are underdeveloped and sensitive to increased BP
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How the baby's body deals with the sensitiveness to BP?
body constructs 3 shunts to divert blood away from organs
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function of 3 shunts
- 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
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4 occurrences of 1st trimester
- major organ development
- heart beats
- bones harden
- embryo becomes fetus
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4 occurrences of 2nd trimester
- fetus grows
- moves
- face looks more human
- toes/fingers elongate
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3 occurrences of 3rd trimester
- rapid growth & brain development
- antibody transport mother to fetus for protection from outside world
- growing slows and fetus is less active
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4 occurrences of birth
- cervix thins
- amniotic sac ruptures
- uterine contraction=birth of fetus
- after birth
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soma function and location
location of ER and ribo and is locted in the cell body of the axon where the nucleus is
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dendrites function
receive incoming messages from cells and transmitted through cell body before reaching axon hillock
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axon hillock function
integrate incoming messages from other cells and sums the excitatory or inhibitory signals received by dendrites
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action potentials
- 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
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myelin ( mammal nerve fibers)
insulated to prevent loss of signal or signal crossing
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myelin sheath function
maintains electrical signal with one neuron and increases speed of conduction in axon
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myelin is produced by these two in what 2 locations
- oligodendrocytes (CNS)
- schwann cells (PNS)
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function of nodes of ranvier and location
- between myelin sheaths on axon
- critical for rapid signal conduction
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nerve terminals function and location
- end of neuron
- enlarged and flattened to maximiize neutransmission to next neuron and ensure proper release of NT to other neurons
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neurons dont physically touch b/c small space w/in terminal portion of axon (synaptic cleft) release NT which bind to dendrites of post synaptic neurons
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synapse is made up of these 3
nerve terminal, synaptic cleft,post synaptic cleft
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nerve
multiple neurons bundled together (sensory, motor, or mixed neurons can make them up) into ganglia
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tracts
CNS neurons bundled together to form tracts that carry one type of info
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nuclei
cell bodies of neurons in the same tract (bundle of neurons that carry one type of info)
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axons carry neural signals away from soma, dend carry signals toward soma
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astroytes function
nourish neurons and form blood brain barrier
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ependymal cells
line ventricles of brain and produce cerebrospinal fluid
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microgalia
phagocytic cell
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resting mem potential
an electrical potential difference between the inside of the neuron and the extracellular space
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Na/K ATPase maintains negative environment
- 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
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the neuronal plasma mem is impermeable to charged species and is polar so crossing cannot be done. What happens to allow it to cross?
- 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
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once a neuron receives a excitatory or inhibitory input, it causes an action potential from a resting potential or causes it to go from action to resting
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excitatory input from neurons cause depolarization which does what
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)
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inhibitory input from neurons causes hyperpolarization which does what
lowers mem potential from resting potential thus makes neurons less likely to fire an action potential
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summation
additive effects of multiple signals from neurons which can be either or excitatory and inhibitory signals
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2 types of summation and their definitions
- temporal-multiple signals integrated during a short period of time
- spatial-the effects are based on the number and location of incoming signals
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in an electrochemical gradient, the interior of the cell is more negative than the outside, so there will be an influx of + charged ions into the cell
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3 states sodium channels exist in during action potential
- closed-occurs before reaching threshold
- open-once threshold is reached
- inactive-when it comes down from threshold
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positive potential inside of the cell causes the voltage gated sodium channels to become inactive and the potassium channels to open releasing K+ (3 for 1). there will be a restoration of negative mem once k+ is out (repolarization)
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too much K+ cause hyperpolarization of the neuron refractory which furthers action potentials
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2 types of refractory periods and their functions
- absolute-no stim causes action to occur
- relaive-greater than normal stim to cause action potential
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impulse propagation
signals to be conveyed to another neuron, action potential must travel down axon and initiate NT release
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how impulse propagation works?
- 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
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speed of action potential depends on these 2
- Length-longer axon, higher resistance, slower conduction
- cross section-increase CS faster propagation due to lower resistance
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saltatory conduction
signal down the axon hops from node to node
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all AP within same type of neuron have same potential diff during depolarization. increased intensity does not result in increase potential diff of the AP but increased frequency of firing
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- presynaptic neuron-before synaptic cleft
- postsynaptic neuron-after synaptic cleft
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effector
neuron signals to a gland or a muscle, the post synaptic cell
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how does the message from one neuron travel down to others
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
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NT must be regulated by being removed from the synaptic cleft by these 3 mechanisms
- 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)
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3 type of NT receptors
- ligand gated ion (hyper or depolar)
- G protein coupled receptors (change in levels of cAMP)
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sensory neurons
afferent, transmit sensory info from receptors to spinal cord and brain
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motor neurons
efferent, transmit motor info from brain and spinal cord to muscles
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interneurons
most numerou,locayed in brain and spinal cord and are linked to reflexes
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4 divisions of Spinal cord
- cervical
- thoracic
- lumbar
- sacral
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vertebral function
- protects spinal cord
- transmits nerves at the space between adjacent vertebrae
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white matter inside SP
greay matter outside SP
inside SP are axons of motor and sensory neurons
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autonomic NS, two neurons work in series to transmit messages from SP, what are the two neurons and their functions
- 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
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2 types of reflex arc and functions
- monosynaptic - single synapse between sensory neuron that receives stimulus and motor neuron responds
- polysynaptic - one interneuron between the sensory and motor neurons
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knee jerk reflex explained (monosyn)
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
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withdrawal reflex explained (polysyn)
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
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