uworld bio rev Flashcards
what comprises the inner wall of all blood vessels
a single layer of endothelial cells
single layer of endothelial cells forms a
barrier that regulate entry/exist of materials into/out of bloodstream
what do endothelial cells secrete?
chemical signals that prevent clotting
injury to a blood vessels triggers
1) formation of platelet plug
2) clot is strengthened
formation of platelet plug means…
endothelial damage exposes connective tissue outside blood vessels
platelets bind connective tissue (i.e. collagen fibers) to form PLATELET PLUG out of vessel
where are platelets derived from
bone marrow
bound platelets and endothelial cells near site of damage continue…
to release signals that enhance platelet aggregation
where are clotting factors synthesized
mainly in the liver
clotting factors are specialized…
proteins that activate in response to platelet aggregation + signaling factors outside vessel
activated clotting factors induce processes that lead to…
formation of the enzyme thrombin
thrombin induces
protein strands (i.e. fibrin) to form an adhesive mesh-like structure over the platelet plug (reinforcing clot)
synapses are
gaps b/w presynaptic and postsynaptic neuron
can be electrical or chemical in nature
synapses are important in allowing
communication bw an axon terminal of a presynaptic neuron
AND dendrites of a postsynaptic neuron from an action potential
neurons communicate with
one another via action potentials
an action potential travels down the…
signaling cell (presynaptic neuron) until it reaches the axon terminals
axon terminals are responsible for
signal transmission across synapse to the postsynaptic neuron
synaptic transmission via ligand-gated ion channels
1) action potentials reach axon terminal
2) Ca2+ channels open
3) Ca2+ ions enter cell
4) Ca2+ triggers neurotransmitter release via exocytosis
5) neurotransmitter binds ligand-gated ion channels to allow ions thru
6) inhibitory or excitatory cell response
glutamate (glu)
primary excitatory neurotransmitter of CNS
involved in learning and memory
GABA
primary inhibitory neurotransmitter of brain
glycine (gly)
primary inhibitory neurotransmitter of the spinal cord
dopamine (DA)
can be excitatory or inhibitory
involved in cognition, attention, movement, reward
serotonin (5-HT)
mainly inhibitory
involved in sleep, appetite, mood
norepinephrine (NE)
can be excitatory or inhibitory
involved in sympathetic signaling in the ANS
acetylcholine (ACh)
involved in parasympathetic signaling in the ANS
released by motor neurons at neuromuscular junctions of the somatic NS –> excites skeletal muscle
synaptic transmission of excitatory neurotransmitters
1) AP reaches axon terminal
2) AP causes Ca2+ channels to open –> Ca2+ in presynaptic neuron’s axon terminal
3) Ca2+ triggers neurotransmitter release via exocytosis
4) excitatory NT binds ligand-gated ion channels to allow Na+ ions into postsynaptic neuron
5) Na+ ions depolarize membrane potential + promote AP initiation
synaptic transmission of inhibitory NTs
1) AP reaches axon terminal
2) AP causes Ca2+ channels to open
3) release Ca2+ into presynaptic neuron’s axon terminal
4) inhibitory NT binds ligand-gated ion channel to allow Cl- ions into post synaptic neuron
5) Cl- ions cause membrane potential to hyperpolarize + inhibit AP initiation
what happens to chemical synapses?
AP in presynaptic neuron releases NTs
NTs bind receptors on membrane of postsynaptic neuron
classification for NTs
excitatory - AP MORE likely to occur in the postsynaptic neuron
inhibitory - AP LESS likely to occur in postsynaptic neuron
APs are electrical signals that travel from
a neuron’s cell body down its axon and to its axon terminals
during APs, membrane potential of the neuron…
changes due to opening/closing of voltage-gated Na+ and K+ ion channels
at rest, a neuron maintins a potential difference known as…
resting membrane potential (RMP) of ~ -70 mV
meaning that intracellular space is 70 mV more neg than extracellular space
RMP is maintained by the
Na+/K+ pump and K+ leak channels
Na+/K+ pump and K+ leak channels are always..
open and allow passive diffusion of K+ across membrane
stimulus may cause voltage-gated Na+ channels to open and then….
Na+ rushes into cell –> depolarize membrane
membrane potential is (+)
if depolarization is enough to reach a certain…
threshold, an AP is initiated in the neuron
if the threshold is reached…
voltage-gated Na+ channels remain open
futher rapid depolarization of membrane occurs
Na+ entry causes AP to reach its
peak (overshoot) –> membrane potential is at most positive
voltage gated Na+ channels close and voltage gated K+ channels open to go back to RMP
K+ rushes out of neuron after K+ channels open and result in
REPOLARIZATION
voltage gated K+ channels close more slowly so…
membrane potential becomes more neg briefly than the RMP (i.e. HYPERPOLARIZATION)
when voltage gated K+ channels close…
RMP is restored
during an AP, the opening/closing of voltage gated channels determines
state of membrane polarization and propogation of AP
if voltage gated K+ channels are downregulated…
repolarization would occur more slowly
results in neuron hyperexcitability
neurons are responsible for
sending electrical signals to other cells
neuroglia provide support functions to
neurons and the nervous system
types of neuroglia in CNS
ependymal cells
oligendrocytes
microglia
astrocytes
what type of cell lines compartments and produced cerebrospinal fluid
ependymal cells
what do oligondendrocytes do
form myelin sheath around axons to reduce ion leakage
decrease capacitance
increase AP propagation speed along axon
microglia serve as
immune cells which phagocytize pathogens/damaged cells/waste materials
astrocytes
contact blood vessels
regulate blood flow to coordinate synaptic activity/chem changes
important in maintaining extracellular fluid/ion/pH/NT homeostasis
provide nutrient for neuron function
types of neuroglia in PNS
schwann cells
satellite cells
schwann cells form
myelin sheaths around axons to increase conduction speed
satellite cells provide
structural support and support nutrients to neurons
oligendrocytes myelinate
CNS axons
pathway of fluid/liquid transport in lympathic system
interstitial fluid
lymph capillaries
lymph vessels
lymph duct
vein
reflexes are involuntary responses to
stimuli
may or may not require input from brain
a reflex arc is the specific neuronal pathways that
helps the direct muscular or glandular effect associated w a specific reflex
reflex arcs begin with the
stimulation of a sensory neuron
electrical impulse then travels down spine/brain along sensory nerve
electric impulse from reflex arc can be transmitted either:
directly
indirectly
direct impulse transmission
directly transmitted to effector neuron (monosynaptic reflex arc)
indirect impulse transmission
indirect transmission through interneuron
interfaces w/ effector neuron (i.e. polysynpatic reflex arc)
electrical impulses initiated in effector neurons leave the CNS and…
travel along effector neuron to stimulate muscle fiber/gland/ganglionic neuron
this is done either directly or after synapsing w/ a postganglionic effector neuron
when the effector neuron synapses with a muscle fiber, it is referred to as
a motor neuron
autonomic reflex arcs are always
polysynaptic
e.g. gustatory-salivary reflex
reflexes can be modulated by…
input from the brain
in the case of polysynaptic reflexes, this modulation takes the form of…
descending signals from higher areas in the CNS that act on preganglionic neurons in the reflex arc
soma of both interneuron + preganglionic neuron within CNS could be….
acted upon by descending input from higher brain centers to alter gustatory-salivary reflex
what are reflexes mediated by?
reflex arcs
neuronal pathways (incl a sensory neuron)
an effector neuron
possibly an interneuron
membrane-bound receptors respond to ligands that are either:
endogenous (originating from organism)
exogenous (foreign to organism)
agonists are ligands that
activate the receptor and promote its downstream effects
antagonists are ligands that
deactivate or inhibit the receptor
prevent its downstream effects
cholinergic signaling involves
acetylcholine (ACh)
cholinergic neurons secrete
ACh which binds to cholinergic receptors
parasympathetic pathways utilize ACh for signaling between
pre and postganglionic neurons
as well signalling bw the postganglionic neuron and target tissue (e.g. salivary glands)
the gustatory-salivary reflex arc is mediated primarily by
parasympathetic pathways
exerts effects (i.e. stimulation of salivation) through cholinergic signaling
name what the parasympathetic division of the NS promotes
E conservation and storage
lower heart rate
decreased air flow
stimulating digestion (e.g. salivation, release of digestive enzymes, peristalsis)
inc glucose uptake
glycogenesis
name what the sympathetic division of the NS promotes
oxygen delivery to skeletal muscles is maxed
increased heart rate
dilated airways
constricted blood vessels
glycogen in liver –> glucose to provide energy for skeletal muscles
pupils dilate to max light intake
step 1 of neural process of receiving/acting on sensory info in a reflex arc
sensory receptors detects stimulus
sensory receptors are highly specialized nerve endings that
respond/recognize to highly specific types of stimuli (e.g. chemical, light, pressure, vibration)
2nd step of neural process
activated sensory neuron sends an afferent sensory signals (electrical impulse) –> CNS
elec impulse is transmitted to an interneuron or effector neuron
remember: Afferent Approaches CNS
3rd step in neural process
interneurons in cns in brain/spinal cord act as integration center
sensory/CNS input are processed and consolidated
interneurons can relay sensory info to brain + integrate signals from brain into reflex response
interneurons transmit signal directly to effector neuron
interneurons are not present in every reflex arc
input from brain is not always needed for reflex completion
4th step in neural process
effector neuron generates/sends an efferent signal that travels TOWARD the target organ (muscle or gland)
REMEMBER: Efferent info Exits CNS
5th step in neural process
effector (target) organ generates desired response to stimulus
within the gustatory-salivary reflex, the sensory neuron makes up the
afferent component of the reflex arc
sensory neuron transmits impulses toward the CNS
pre and postganglionic fibers make up the
efferent component of the reflex arc
fibers transmit impulses away from the spinal cord
preganglionic neuron corresponds to
the efferent component of the gustatory-salivary reflex
pregang neuron sends impulses AWAY from CNS
sensory neuron corresponds to the
afferent component of the gustatory salivary reflex
sensory neuron sends impulses TOWARD the CNS
interneuron propogates signals within the
CNS
impulses are not generated
impulses do not travel directly or away from the CNS
interneurons is neither afferent/efferent
input from higher areas in the CNS can modulate
activity of reflexes by either strengthening or weakening magnitude of the response
the nodes of Ranvier increase the rate of
depolarization toward the axon terminal
nodes of Ranvier are sites of
ion flux across myelinated axons
nodes of ranvier are sites of interrupted myelination that
contain voltage-gated channels
when and where are an AP generated?
generated in a neuron when
the soma depolarizes enough that membrane potential reaches a threshold for voltage-gated channels opening
after AP is generated, voltage-gated channels open in a…
coordinated fashion, allowing a series of ionic movements across plasma membrane to occur
ionic movements across plasma membrane allow…
rapid maximal depolarization of a small area of the membrane due to Na+ transport into cell
after maximal depolarization of membrane occurs…
rapid repolarization as Na+ channels close and K+ channels open
allowing K+ to leave the cell
APs ‘move’ along an axon toward the
axon terminal as successive regions are depolarized
manner in which APs move is
influenced by myelin
what forms myelin
formed by plasma membrane from glial cells
portions of glial cell plasma membrane are wrapped….
many times around an axon
insulating axon and preventing ion flow across axon membrane
wave of ion transport is continuous along…
myelinated axons
but ‘jumps’ in a discontinuous fashion along myelinated axon bc of the insulation provided by myelin
what influences rate at which a neural impulse is conveyed?
axon size
myelination
larger diameter axon that are myelinated transmit
neural impulses FASTER than smaller/unmyelinated axons
myelination can prevent
the loss of current along an axon
by exposing a short segment of an unmyelinated axon, the node of Ranvier promote…
entry of extracellular Na+ into axons
while limiting number of open ion channels
GREATLY increases rate at which neural impulses conduct along myelinated axons
drug that blocks release of adrenocorticotropic hormone from anterior pituitary would
decrease secretion of cortisol from adrenal cortex
viroids are
subviral infectious particles that consist of short circular single strand of RNA
viriods have regions where
RNA binds with itself
creating some double-stranded areas of circular genome
RNA-composing viroids does not
generally code for protein unlike VIRUSES that have protein coats (capsids)
when infecting cells, viroids can bind….
host cellular RNA sequences
results in gene silencing preventing synthesis of necessary proteins
ribosomes are composed of
specific proteins and rRNA
ribosomes translate…
mRNA sequences into proteins in all cells
substituting first (5’) nucleotides often
alters the AA
substituting the second nucleotide always
alters the AA
substituting the 3rd (3’) nucleotides doesn’t
often alter the AA
64 codons =
genetic code
64 codones code for how many AAs
20 AAs
what does it mean that the genetic code is degenerate?
multiple codons can code for the same AA
protein-coding genes consist of
multiple codons
sequences of three nucleotides that code for a specific AA
during translation, each mRNA codon base-pairs with…
a corresponding tRNA that is charged w/ a specific AA
DNA mutations in the protein-coding regions of a gene may alter…
the sequences of transcribed mRNAs
creating changes in AA structure of encoded proteins
what do silent mutations alter
DNA/RNA sequences
silent mutations DON’T alter
protein structure