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MCAT Biology Lecture 4


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nuclear envelope
double phospholipid bilayer
area in nucleus where rRNA transcribed, subunits of ribosomes constructed
membrane surrounds and takes in matter inside vesicles. Types include phagocytosis, pinocytosis, receptor mediated endocytosis
rough endoplasmic reticulum
covered with ribosomes, translated proteins injected into ER lumen... proceed to Golgi.
Golgi apparatus
Recieves proteins from ER in vesicles, organizes and concentrates proteins, based on their signal sequence.
Originate in Golgi, vesicles filled with enzymes that break down macromolecules. "Recycle"
secretory vesicles
protein filled vesicles from Golgi that are ejected from cell... ejected via exocytosis, so help build membrane.
smooth endoplasmic reticulum
hydrolizes glucose 6-phospate to glucose, produces triglycerides->fat droplets, &steroids. Oxidizes & detoxes foreign substances, incl toxins pollutants etc.
cells containing mainly fat droplets, used for energy storage and temperature regulation.
vesicles associated with smooth ER. Self-replicating. Produce and breakdown hydrogen peroxide, regulate oxygen, lipid synthesis etc. Not necessary for most cells.
Larger than microfilaments. Made from tubulin polymer.
Smaller than microtubules. Made from polymerized actin. Produce contracting force in muscle, also make cytoplastmic streaming in amoebas.
Eukaryotic flagella and cilia composition
"axoneme", 9 pairs of microtubules around two lone pairs of MTs, 9+2. Dynein bridges connect pairs. Cilia whip, flagella wiggle.
prokaryotic flagella
thin strand of protein flagellin. Motion is rotatation.
mitotic spindle is made from...?
tight junctions
water tight seal around cell, fluid barrier. Restrict membrane protein motion. Helps keep material inside organs by forming epithelial layer.
cell spot weld, joining two cells at a single point. Do not prevent fluid flow, found in tissue under physical stress.
gap junctions
tunnels connecting cells, let small molecules move between cells.
endosymbiont theory
theory that mitochondrea were bacteria that became incorporated into eukaryotes.
Parts of mitochondria
Outer membrane, intermembrane space, crista, inner membrane, mitochondrial matrix.
extracellular matrix
secreted by cell, surrounds cell. Examples are bone, blood, etc.
four different tissue types
epithelial, muscle, connective, nervous. (Ex. skin, muscle, blood, neurons)
Neuronal communication
Nervous System, rapid direct and specific.
Hormonal communication
Endocrine system, slower spread throughout body, affects many cells and tissues in diff ways.
Paracine System
Local mediators released into interstitial acting on nearby cells.
neuron anatomy and process
dendrites receive signal. axon hillock is disrupted, generates action potential. action potential travels down axon to synapse. synapse passes to another cell.
resting potential
potential established by Na+/K+ pump, expels 3Na+ and lets 2K+ in. Makes interior of membrane negative.
action potential
disturbance in membrane potential, away from resting potential.
voltage gated sodium channels, and voltage gated potassium channels.
change in voltage opens channel, allows sodium or potassium through. Sodium channels faster than potassium.
Steps in action potential.
1. Membrane at rest, Na+, K+ channels closed.
2. Sodium channels open, depolarize cell.
3. Potassium channels open as Sodium channels start to inactivate.
4. Sodium channels inactivated, potassium opened repolarize.
5. Potassium closes, membrane equilibrates.
Complete depolarization. Threshold stimulus exceeded, but always same size potential.
electrical synapse
Neuron interface, composed of gap junctions to transfer signal. Very fast but rare.
chemical synapse messenger. Must be removed from synaptic cleft or will re-trigger neuron. Acetylcholine is an example of neurotransmitter.
second messenger system
exterior signal activates molecule inside a cell, which causes some change to occur... ex. activating gene transcription.
chemical synapse
Interface between neurons. Unidirectional, releases chemicals into synaptic cleft, receptors on other neuron receieve and create new signal. Slowest point of nervous signal transfer.
nodes of Ranvier
gaps between myelin
electrically insulating sheats produced by Schwann cells. Exists in white matter, not in grey matter. Only in vertebrates.
Neuron Types
Sensory - recieves signals from receptor cell exposed to environment
Interneurons - neuron to neuron transfer
Motor - carry signals to muscle or gland (effecor).

Sensory neurons dorsally located on spine, motor neurons ventral.
central nervous system (CNS)
brain and spinal cord, integrates signals between sensory and motor neurons.
peripheral nervous system (PNS)
connects CNS to peripheral parts of body. Divided into somatic and autonomic nervous systems (ANS).
somatic nervous system
response to external env. innervates skeletal muscle, voluntary. Uses acetylcholine.
autonomic nervous system
recieves signals from organs. conducts signals to smooth muscle, cardiac muscle and glands. Divided into sympathetic and parasympathetic. (Fight or flight, rest and digest).
specific neurotransmitters
acetylcholine - somatic and parasympathetic NS
epinephrine, norepinephrine (adrenaline, noradrenaline) - sympathetic NS
lower brain parts and function
medulla, hypothalamus, thalamus, cerebellum. Subconscious activities, salivation, emotions, reactions to pain/pleasure, balance.
higher brain
cerebrum or cerebral cortex, - memories and thought processes
sensory receptors
transduce physical stimulus to neural signals.
lights hits first, is bent.
spherical, except that ciliary muscle stretches it thin. This changes focal length.
images projected onto... consists of rods and cones, rods for light intensity, cones for frequency.
color part around pupil, pupil dialated by sympathetic NS, contrafcted by parasympathetic.
parts of middle ear
tympanic membrane
3 bones - malleus, incus, stapes
transfers wave to inner ear.
parts of inner ear
cochlea, sound wave moves through.
haircells in organ of corti transduce into neural signals.

Semicircular canals also present.. for balance.

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