LS 2 midterm 2 Flashcards
cell response to a signal molecule (3 steps)
- signal binds to a receptor in the cell (often in outside surface of plasma membrane)
- signal binding conveys a message to the cell
- the cell changes its activity in response to the signal
signal transduction pathways
a sequence of molecular events and chemical reactions that lead to a cell’s response to a signal
(all involve a signal, a receptor, and a response)
autocrine
signals that diffuse to and affect the cells that make them
example of autocrine signal
tumor cells reproducing uncontrollably because they both make, and respond to, signals that stimulate cell division
juxtacrine
signals affect only cells adjacent to the cell producing the signal
when is juxtacrine signaling common
during development
paracrine
signals diffuse to and affect nearby cells
local mediators
e.g. histamines, EGFS
example of paracrine signaling
a neurotransmitter made by one nerve cell that diffuses to a nearby cell and stimulates it
hormones
signals that travel through the circulatory systems of animals or the vascular systems of plants
crosstalk
interactions between different signal transduction pathways
what is an inhibitor (or antagonist)
molecule that can also bind to a receptor protein instead of the normal ligand
example of an inhibitor
caffeine - the nucleoside adenosine acts as a ligand that binds to a receptor on nerve cells, initialing a signal transduction pathway that reduces brain acitivity, but caffeine has a similar structure to adenosine and binds to the adenosine receptor, but doesn’t initial the signal transduction pathway, allowing continued nerve cell activity and arousal
2 types of receptors
cell surface/membrane receptors and intracellular receptors
example of need for a membrane receptor
insulin - protein hormone that cannot diffuse through membrane, so needs a transmembrane receptor with an extracellular binding domain
example of need for intracellular receptors
estrogen - small, lipid soluble steroid hormone that can diffuse across cell membrane so it binds to a receptor inside the cell
where are most plant light receptors located?
intracellular
3 main categories of plasma membrane receptors (eukaryotic)
ion channels, protein kinase receptors, and G protein linked receptors
ion channels
proteins that allow ions to enter/exit cell by responding to a specific signal such as sensory stimuli or chemical ligands
example of ion channel
acetyl choline receptor - gated ion channel - 2 molecules of Acetyl choline bind to receptor protein, it opens for 1000th of a second and allows Na+ to to move into the cell via simple diffusion and this change in concentration inside the cell initiates events that result in muscle contraction
protein kinase receptors
when activated they catalyze the phosphorylation of themselves/or other proteins, thus changing shape and therefore function
example of protein kinase receptor
insulin - a protein hormone - its receptor has 2 copies each of 2 different polypeptide subunits (alpha and beta) and when insulin binds to the receptor, the receptor becomes activivated and phosphorylates itself and insulin response substrates which initiates other cellular responses including insertion of glucose transporters into the plasma membrane
G protein linked receptors
seven transmembrane domain receptors; roles include photreceptors (light detection), olfactory detection (smell); and regulation of mood and behavior
example of g-protein receptors in action
oxytocin and vasopressin hormone binding which affect mating behavior in voles
common number of polypeptide subunits in G proteins
3
what 3 types of molecules can G proteins bind to
the receptor; GDP and GTP; an effector protein
intracellular receptors
located inside the cell and respond to physical signals such as light or chemical signals that can diffuse across the membrane
g-protein steps
- hormone binding to the receptor activates the G protein. GTP replaces GDP.
- part of the activated G protein activates an effector protein that causes changes in cell function
- The GTP on the G protein is hydrolyzed to GDP
intracellular receptor cortisol steps
- receptor chaperone complex cannot enter the nucleus
- cortisol enters the cytoplasm and binds to the receptor
- causing the receptor to change shape and release the chaperone
- which allows the receptor and the cortisol ligand to enter the nucleus
what is the result of a signal cascade of events
- proteins interact with other proteins which interact with other proteins until desired effect is achieved
- the initial signal can be amplified and distributed to cause several different responses in the target cell
what are protein kinase receptors important in
binding signals called growth factors that stimulate cell division in both plants and animals
what happens with abnormal ras
it’s a g-protein and abnormal form is always active because it’s permanently bound to GTP and thus caused continuous cell division
how normal ras works
- receptor activation leads to activation of the G protein, RAS
- brief stimulation of cell division
- after a brief time in the active form, RAS returns to inactive form
how abnormal ras works
receptor leads to activation of RAS, which stays active
2. constant stimulation of cell division
example of a protein kinase cascade
- growth factor binds to its receptor
- phosphorylates itself
- activated receptor initiates a series of events that allow ras to bind GTP and become activated
- activated ras binds and activates Raf
- activated Raf is a protein kinase that phosphorylates many molecules of MEK
- activated MEK is a protein kinase that phosphorylates many molecules of MAP kinase
- MAP kinase, when activated by phosphorylation, can enter the nucleus and lead to cellular responses
why are protein kinase cascades useful signal transducers (4 reasons)
- at each step, the signal is amplified because each newly activated protein kinase is an enzyme that can catalyze the phosphorylation of many target proteins
- the info from a signal that originally arrived at the plasma membrane is communicated to the nucleus where the expression of multiple genes is often modified
- the multitude of steps provides some specificity to the process
- different target proteins at each step in the cascade can provide variation in the response
experiment to discover a second messenger causes the activation of glycogen phosphorylase
- liver tissue is homogenized and separated into plasma membrane and cytoplasm fractions
- the hormone epinephrine is added to the molecules and allows to incubate
- the membranes are removed by centrifugation, leaving only the solution in which they were incubated
- drops of membrane-free solution are added to the cytoplasm
result: glycogen phosphorylase in the cytoplasm is activated
conclusion: a soluble second messenger, produced by hormone activated membranes, is present in the solution and activates enzymes in the cytoplasm
example of calcium ions working as messengers
7.14
fertilization in a starfish egg causes a rush of Ca 2+ from the environment into the cytoplasm (represented as red dye) from start to finish egg goes from mostly blue to almost all red
calcium signaling triggers cell division in fertilized eggs, initiating development
IP3/DAG second messenger system steps
7.13
- the receptor binds the hormone
- the activated g-protein subunit dissociates and activates phospholipase C
- the activated enzyme produces the second messengers DAG and IP3 from PIP2
- IP3 opens Ca2+ channels, leading to an increase in cytostolic Ca2+
- DAG and Ca2+ activate protein kinase c (PKC)
- PKC phosphorylates enzymes and other proteins
Nitric oxide in signal transduction (signal: acetylcholine; effect: smooth muscle relaxation)
(7.15)
- acetylcholine binds to receptors on endothelial cells of blood vessels; activation of the receptor causes production of IP3
- IP3 opens Ca2+ channels on the ER membrane, releasing Ca2+ into the cytostol
- Ca2+ stimulates NO synthase (enzyme that makes NO gas from arginine)
- NO diffuses to the smooth muscle cells, where it stimulates cGMP synthesis
- cGMP promotes muscle relaxation
signals can lead to production of active transducers; what are the 3 kinds
and the enzymes that remove or inactivate them
(7.16)
a. protein kinases – removed by – protein phosphatase
b. g proteins – removed by – GTPase
c. cAMP – removed by – phosphodiesterase
pathways for a scent
7.17
- binding of an odorant to its receptor activates a g-protein
- the g-protein activates the synthesis of cAMP
- cAMP causes ion channels to open
- changes in ion concentrations (Na+ and Ca2+) inside the cell initiate a signal to a specific area of the brain, which perceives the signal as a scent
example of liver cells responding to epinephrine cascade
7.18
- phosphorylation induced by epinephrine binding INACTIVATES glycogen synthase, preventing glucose from being stored as glycogen
- protein kinase cascade amplifies signal (every molecue of epinephrine, 20 cAMPs are made, each of which activates 1 PKA)
- phosphorylation ACTIVATES glycogen phosphorylase, releasing stored glucose molecules from glycogen
- release of glucose fuels ‘fight or flight’ response
how do animal cells coordinate activities
7.19 A
gap junctions (~1.5 nm channel) connecting the ~2 nm gap between cells
how do plant cells coordinate activities
7.19 B
plasmodesmata; desmotubule comes from smooth ER and fills up most of the space inside
what can pass through gap junctions
ions and small signal molecules
what can pass through plasmodesmata
small metabolites and ions
what makes up the wall of gap junctions
integral membrane proteins from the adjacent plasma membranes and connexons which form thin channels between 2 adjacent cells
what makes up the wall of plasmodesmata
lined by the fused plasma membranes and filled with a desmotubule
evolution from single celled to multicellular organisms
- aggregation of cells into a cluster
- intercellular communication within the cluster
- specialization of some cells within the cluster
- organization of specialized cells into groups
possible cellular responses to a signal
- opening of ion channels
- alteration of enzyme activities
- changes in gene expression
what happens during protein kinase binding
covalently add phosphate groups to target proteins
what happens during cAMP binding
binds target proteins noncovalently
what does cAMP and PK binding both do
change the target protein’s conformation to expose or hide its active site
how can we infer the evolution of cell communication and tissue formation
(7.20)
from exisiting organisms like certain green algae (e.g. volvocine line of aqauatic green algae) can see range from single celled to complex multicellular organisms
how does photosynthesis work?
10.1
- sugars (organic products of photosynthesis) are transported throughout the plant body
- CO2 enters and O2 and H2O exit te leaves through pores called stomata
experiment proving H2O is the source of oxygen in photosynthesis rather than CO2
- give some plants isotope labeled water and unlabeled CO2 and give others isotope labeled CO2 and unlabeled water
- test O2 products to see if they had the isotope markers
- results: oxygen released was labeled for the labeled H2O and unlabeled for unlabeled H2O
conclusion: H2O is the source of O atoms in O2 produced by photosynthesis
revised equation for photosynthesis
6CO2 + 12H2O –> C6H12O6 + 6O2 + 6H2O
what gets oxidized and reduced in photosynthesis
oxygen atoms (in reduced state in H2O) get oxidized to O2 carbon atoms (in oxidized state in CO2) get reduced to carbohydrate and water
what do ‘light’ reactions do
convert light energy into chemical energy in the form of ATP and and the reduced electron carrier NADPH + H+
what do ‘dark’ reactions (calvin-benson cycle) do
CO2 and ATP plus NADPH + H+ produced in the light reactions are used in the Calvin-Benson cycle to produce sugars
what carries the electron between the oxidation and reduction reactions
NADP+
2 main pathways for photosynthesis process
light reactions and light-independent reactions (dark reactions/calvin-benson cycle)
why do even the dark reactions stop in the dark
ATP synthesis and NADP+ reduction require light
what is a granum
stack of thylakoids
what is the fluid in a chloroplast
stroma
what is chlorophyll where is it located in the chloroplast
photosynthetic pigment; in the thylakoids
how does photosynthesis work? (basic flow)
10.3
- light strikes chlorophyll embedded in the thylakoid membrane
- makes ATP through chemiosmosis and reduces NADP+
why do the ‘dark’ reactions stop in the dark
calvin benson cycle needs ATP and NADP from the light reactions
3 properties of light
- Light is a form of electromagnetic radiation
- Exists as photons which exhibit wave-like properties
- Energy content of a photon is inversely proportional to the wavelength of the light
equations for light
c (speed of light) = vlambda (frequencywavelength)
E (energy of a photon) = h(plancks constant)*v
E = c/lambda
what 3 things can happen when a photon meets a molecule?
- the photon may bounce off the molecule and be scattered or reflected
- the photon may pass through the molecule - transmitted
- photon may be absorbed by the molecule, adding energy
what happens when a molecule acquires the energy of a a proton
it is raised from a ground state (lower energy) to an excited state (higher energy)
wavelengths with most energy
shorter wavelengths (gamma)
waves from shortest wavelength to longest
gamma – radio
what is the difference in free energy between the molecule’s excited state and its ground state
approximately that of the free energy of the absorbed photon
what does the increase in energy from an absorbed photon do and how does it affect stability
boosts one of the electrons in the molecule into a shell farther from its nucleus - held less firmly, making the molecule unstable and chemically reactive
how does fluorescence work?
t
what is a pigment
molecules that absorb wavelengths in the visible spectrum
what color light does chlorophyll absorb
blue and red (so we see green)
what is an absorption spectrum
plot of light absorbed by a purified pigment against wavelength
what is an action spectrum
plot of the rate of photosynthesis carried out by an organism against the wavelengths of light to which it is exposed
4 steps to determining an action spectrum
- place organism in a closed container
- expose it to light of a certain wavelength for a period of time
- measure the rate of photosynthesis by the amount of O2 released
- repeat with light of other wavelengths
which photons can an atom absorb
only those corresponding to the atom’s available electron energy levels
what is the major pigment used to drive the light reactions of oxygenic photosynthesis
chlorophyll a
chlorophyll a structure
ring structure with magnesium at center and a fatty acid (hydrocarbon) chain to anchor it in the thylakoid membrane
how do the other pigments fit in with chlorophyll a
there is a large complex called a photosystem spanning the thylakoid membrane and accessory pigments are arranged in light harvesting complexes (atenna systems)
what are some accessory pigments in chloroplasts
chlorphylls b, c, carotenoids, and phycobilins
what happens to light energy in the accessory pigments
it is released by one pigment molecule and absorbed by another
how is light energy passed from molecule to molecule in the satellite system
not as electrons but in the form of chemical energy called resonance
what happens to energy at the reaction center of the photosystem (chlorophyll)
absorbs energy and becomes excited when it returns to ground state, it doesn’t pass the energy on - it converts the absorbed light energy into chemical energy
what happens to chlorophyll (Chl*) (the reaction center) chemically to convert light energy to chemical energy
- (Chl*) loses its excited electron in a redox reaction and becomes Chl+
- as a result of the transfer of an electron, the chlorophyll gets oxidized, while the acceptor molecule is reduced
- At a proton-pumping channel, proton translocation occurs resulting in ATP synthesis by chemiosmosis
what are accessory pigments
pigments that absorb photons in the region between blue and red carotenoids
difference between chlorophyll a and b
b is the the same as a, but it has a methyl instead of an aldehyde
what is resonance energy transfer
a vibrational energy transfer from one chlorophyll to another through the antenna system which increases the efficiency of the process
photosystem 1
reaction center contains a chlorophyll a (P700) - 700 nm wavelength absorption and passes excited electrons to NADP+, reducing it to NADPH
photosystem 2
reaction center contains a chlorophyll a (P680) - 680 nm wavelength absorption
requires more energetic photons than I
oxidizes water molecules and passes energized electrons through a series of carriers to produce ATP
what percent water is a human
60%
what fraction of total body water is ECF
1/3
distribution of ECF in the body
20% plasma and 80% interstitial fluid
tissue
cluster of multiple cells
organs
assemblages of tissues
4 kinds of tissues
epithelial, muscle, connective, and nervous
types of tissues in organs
always has more than one of the 4 tissue types
what type of tissues in the outer layer of skin
epithelial cells
what do cells need to survive
nutrients, glucose, and ENERGY
what is the role of the digestive system
ensure food is properly broken down so we can extract nutrients
what do proteins get broken into
amino acids
what do carbohydrates get broken into
monosaccharides
what do lipids get broken into
fatty acids
what does the digestive system need to carry out its function
enzymes
purpose of blood vessels
delivery oxygen and nutrients (they are the highway)
how can blood flow and other functions go against gravity
heart/cardiovascular system
how many organ systems
11
what does the brain do
regulates everything to make sure it’s working properly
2 regulatory systems
endocrine and nervous system
what do systems do
ensure homeostasis
what is homeostasis
constant internal environment
what 4 things contribute to homeostasis
sodium levels, glucose levels, pH, temperature
3 components of homeostatic system
receptors, control center, effectors
what do receptors do to maintain homeostasis
Provide information about specific conditions (measures) (organ/cell/protein)
what does the control system do to maintain homeostasis
Evaluates the information from receptors - compares to Set point (tells what a particular value should be)
what does an effector do to contribute to homeostasis
Respond to restore the deviation from the set values of the internal environment
what temperature should our body be
98 degrees F
endotherm
regulate body temperature by generating metabolic heat and/or preventing heat loss
(All mammals and birds)
ectotherm
Depend on external heat sources to maintain body temperature
positive feedback
more change, then more changes
- e.g. breastfeeding - have baby, make milk, baby drinks milk, make more milk
negative feedback
change, then stops (most systems in body)
how do neurons communicate with each other and other cells
through electrical and chemical signals
what is the most abundant tissue in the body
muscle
3 types of muscle tissue
skeletal, cardiac, smooth
skeletal muscle
responsible for locomotion and other body movements
cardiac muscle
makes up the heart and is responsible for the beating of the heart and the pumping of blood
smooth muscle
makes up the walls of many hollow internal organs such as the gut, bladder, and blood vessels
how are the cells of connective tissue organized
dispersed in an extracellular matrix that the cells themselves secrete
dominant protein in the extracellular matrix
collagen
arrangement of skeletal muscle cells
looks striped because of the regular arrangement of actin and myosin
arrangement of cardiac muscle
individual cells are branched and form a strong structural meshwork
arrangement of smooth muscle
actin and myosin filaments of smooth muscle are not regularly arranged so it doesn’t look striped
neurons
ecode and conduct information as electrical signals
composition of organs
epithelium and one or more other kinds of tissue
why do endotherms generate heat
metabolic processes and working muscles are less efficient and more ‘leaky’ to ions so ions leak out and they have to expend energy to maintain the ion gradients, thus generating heat
how do ectotherms regulate body temperature if they can’t do it with internal metabolic heat production
use behavior - e.g. basking in the sun, seeking shade
what happens when you place a mouse and lizard in a room and decrease the temperature
mouse’s metabolic rate increases (more heat) while the lizard’s temperature decreases as the air temp decreases
4 avenues of heat exchange
radiation, convection, conduction, and evaporation
radiation
heat moves from warmer objects to cooler via exchange of IR radiation (like a fire)
convection
heat transfers to a surrounding medium such as air or water as that medium flows over the surface (e.g. windchill)
conduction
heat transfers directly between 2 objects when they have contact (ice pack)
evaporation
heat transfers away from a surface when water evaporates on that surface (sweating)
Where are elastin fibers abundant?
Tissues that are regularly stretched - walls of lungs and large arteries
Where are elastin fibers abundant?
Tissues that are regularly stretched - walls of lungs and large arteries
3 types of connective tissue
Cartilage and bone; blood; adipose cells
What do cartilage and bone do
Connective tissues that provide firm structural support
What does blood consist of
Connective tissue consisting of cells dispersed in an extensive, liquid extracellular matrix, the blood plasma
What do adipose cells do
Form loose connective tissue that stores lipids - adipose tissue (fat) is a major source of stored energy, cushions organs, and layers under the skin can provide a barrier to heat loss
What do neurons do
Encode and conduct information as electrical signals; release chemical signals that are recieved by target cells
Possible target cells for neurons
Other neurons, muscle cells, or cells that secrets hormones and other molecules& substances, such as saliva
What do glial cells do
Provide a variety of support functions for neurons; do not generate electrical signals, but they can communicate info through the release of chemical signals
Example of glial cell function
Creates a barrier between blood vessels and neural tissue that protects the nervous system from potentially harmful chemicals circulating in the blood
When do proteins tend to denature
Above 45C
Function of the nervous system
Informational system - encode, process, and store a wide variety of info from the external and internal environments and use the info to control and regulate physiological processes and behavioral actions of the organism
What 2 types of cells enable the nervous system
Glial cells and nerve cells
What does it mean for a neuron to be excitable
Can generate and transmit electrical signals
What are action potentials
Electric signals generated by neurons
4 general regions of neurons
- Dendrites
- Cell body
- Axon
- Axon terminals
What do dendrites do
Receive information from other neurons
What is the neuron cell body
Contains the nucleus and most cell organelles
What happens to the info collected by dendrites
Integrated in the axon hillcock, which generates action potentials
What does the axon do
Conducts action potentials away from the cell body
What do axon terminals do
Synapse with a target cell
What is the presynaptic cell
Originating cell body
What is the postsynaptic cell
The receiving target cell
What is the axon terminal
On the postsynaptic cell, where the axon divides into a spray of fine nerve endings and at the tip of each ending is a swelling called the axon terminal
How fast can actions potentials travel
Up to 100 m/s
what do axons do
carry information in the form of action potentials away from the presynaptic cell to the postsynaptic cell (away from soma)
what forms of energy can synapses be
chemical or electrical
electrical synapses
allow the action potential to pass directly between two neurons
what form are synapses in most vertebrets
chemical
how do chemical synapses work
a space about 25 nm wide separates the pre and post synaptic membranes and an action potential arriving at the axon terminal causes it to release chemical messenger molecules (neurotransmitters) which diffuse and bind to receptors on the plasma membrane of the postsynaptic cell
what is axon hillock
initial branching of axon
what protein structures are in axons
microtubules for transport
oligodendrocytes
glia that wrap around the axons of neurons, covering them with concentric layers of insulating plasma membrane
schwann cells
glia outside the brain and spinal cord that wrap axons with concentric layers of insulating plasma membrane
myelin
covering produced by oligodendrocytes and scwann cells that give many parts of the nervous system a glistening white appearance; insulating layers of plasma membrane
example of demyelineating disease and effects
multiple sclerosis - autoimmune disease which produces antibodies to proteins in myelin in the brain and spinal cord resulting in damage to the nervous system; commonly results in motor impairment
guillain-barre - result of severe infection which attacks myelin outside the brain and spinal cord
what are nodes of ranevier
gaps in myelin sheath along axon
astrocytes
contribute the blood-brain barrier; permeable to fat soluble substances
tripartite synapse
idea that synapses include pre and postsynaptic neurons and connections from astrocytes
feature common to all neurons
all process information in the form of action potentials; all excitable; always have lots of branches (no matter classification) because sending and receiving so much info)
afferent neurons
send information to the central nervous system; aka sensory neurons; info comes from specialized sensory cells that convert various stimuli into action potentials
interneurons
connect nuerons within the CNS; integrate and store information and communicate between afferent and efferent neurons
efferent neurons
send info from the CNS; carry commands to phsyiological and behavioral effectors like muscles and glands
3 classifications of neurons based on function
sensory, inetrneurons, and motor neurons
3 classification of neurons based on structure
multipolar, bipolar, unipolar
multipolar neurons
one cell body with many branches; one axon and many dendrites; most common type of neuron; motor neurons and interneurons; found in the brain and spinal cord
bipolar neurons
have 2 extensions; found in ears, nose, and eyes; sensory neurons
unipolar neurons
one branch extension from the cell body; sensory neurons (e.g. sense of touch)
do neurons work in seclusion
no, always as a network
synapse
junction between neurons
axil somatic
axon terminals synapsing on cell soma (cell body)
axil dendritic
axon terminals synapsing with dendrites of other neurons
what is the ‘wire’ which moves ions through our body to generate current
cell plasma membranes
what causes electricity in our body
movement of ions across membranes
what is diffusion
movement of ions from high conecentration to low concentration without the expendtiture of energy
why can’t ions move through the lipid membrane and how do they overcome this
they are charged so move through ion channels
2 requirements for diffusion to occur and which is always there
- driving force (i.e. concentration gradient) – always there
- permeability to move – not always there
range of mV for an action potential
-70 – +30
what is the threshold in mV for a potential to take off
-55
where does an action potential graph come from
change in voltage over change in time
about how long does an action potential take
4 msec
what occurs instead of an action potential in the the cell body and dendrites
a slight fluctuation in electrical activity or a graded potential
what occurs at an axon and axon hillock
major fluctuations which is an action potential and neurotransmitter release where it goes from electrical signal to chemical
what causes the potential difference in neurons
difference in net charge across the plasma membrane
charges inside cell vs outside
inside is more negative
resting membrane potential
-70 mV
why don’t we want equilibrium in neurons
we will lose the driving force
how big is the concentration gradient usually
at least 30 fold
ions on either side of neural plasma membrane
Na+ more outside and K+ more inside
what order is the amount of charges on
10^12
how to increase the rate of diffusion
increase the concentration difference
how do Na+ and K+ get from outside to inside and vice versa?
sodium leak channels and potassium leak channels – leaks constantly (small amounts of Na in and small amounts of K out)
in spite of slow rate of diffusion, how else to prevent equilibrium from occuring
Na/K pump
what is a Na/K pump
active transport (requires ATP) - for 1 ATP pumps 2K in and 3Na out to maintain the concentration gradient
which ion channel is more permeable
K ion channel
why do scientists use squid to study neurons
squid neurons are very large in size so easier to study
what is depolarization
membrane becoming less negative than resting potential (Na entering a neuron);
what is repolarization
membrane returning to original state from depolarization or hyperpolarization
what is hyperpolarization
becoming more negative than resting potential (K leaves a neuron)
is any polarization constant?
no, dynamic state of going back and forth
threshold of an action potential
-50 - -55mV
what gets an action potential to the threshold
ionic permeability - Na and K leak channels
what does an action potential do to polarization?
depolarizes, repolarizes, and hyperpolarizes
what do the Na and K leak channels trigger
the opening of voltage gated Na channels and voltage gated K channels
why is the VGSC unique?
doesn’t have binary state - can be open, closed, or inactivated (during refractory period)
when is the VGSC closed
at resting potential (-70mV)
when is the VGSC open
-55mV to +30 mV (threshold to peak)
when is the VGSC inactivated
+30 mV to -70mV (peak to resting)
what is the VGSC
voltage gated sodium channel
integral protein embedded in membrane
protein channel that is specific to sodium and opens when it reaches a voltage threshold
how does the inactivation state of the VGSC work?
it is closed and incapable of opening
what is the voltage gated potassium channel?
VGPC
typical on/off binary
when is the VGPC open
+30 to -80mV; from peak to after hyperpolarization
when is the VGPC closed
resting (-70 mV) to +30 mV; delayed opening triggered at threshold, but doesn’t open until peak
are the VGPC/SC or the K/Na leak channels more permeable?
VGPC/SC are waaayyyyyy more permeable – leak channels are insignificant in comparison
steps of the action potential
- at rest: At rest both VGSC and VGKC are closed
- When threshold is reached, the VGSC are triggered to open but VGKC are still closed
- Sodium ions flow through the VGSC causing the membrane to be depolarized
- Once the membrane reaches +30 mV the VGSC inactivate blocking the flow of sodium ions
- VGKC open causing potassium ions to flow out and repolarize the membrane
- More potassium ions flow out so Further repolarization of the membrane
- Membrane hyperpolarizes, refractory period occurs
and VGKC start to close - Both voltage gated channels are closed and membrane comes back to resting potential
what do the leak channels do
drive voltage to threshold point
what happens at threshold
goes from slow depolarization to fast depolarization
why is the refractory period of VGSC important?
prevents sodium (causes depolarization) from coming in at the same time K is leaving (causes repolarization) because then nothing would happen
what does the puffer fish release and what does it do
toxin (TTX - tetrodotoxin) which blocks VG channels so neurons can’t communicate anymore
uses for TTX
blocks VGCs and inhibits pain receptors (novocaine and other local anesthetics)
where does an action potential start
at the axon hillock
how does the action potential get propogated along to the end of the presynaptic neuron?
saltatory conductance – because of the nodes of ranvier on the myelin where the VGSC can cluster and the positive charges repel each other to the next node and continue the depolarization along the axon
why is saltatory conductance unidirectional if repulsion occurs in all directions
because VGSC are inactivated - have to close before they can open again so it can only go one way
what happens in the gap between the pre and post synaptic neuron
- depolarization of the action potential stimulates the voltage gated calcium channels to open
- that causes the mobilization of the vesicles containing neurotransmitters
- neurotransmitters are released by exocytosis
- Neurotransmitters bind to receptors on postsynaptic neuron
- Depolarization occurs causing series of events that leads to action potential in the postsynaptic neuron
- Neurotransmitter is broken down
what causes depolarization during the synapse
neurotransmitters are ligands so the ligand gated ion channels let ions go through causing
depolarization
main function of interneurons
processing
main function of efferent neurons
motor
where are sensory neurons located
part on CNS and part on PNS
which neurons exist entirely on CNS
interneurons
cell surface receptor characteristics
water soluble
peptides/proteins
catecholamines
intracellular receptor characteristics
lipid soluble
steroid hormones
what is the endocrine system composed of and what types of activities does it regulate
composed of all endocrine glands located throughout the body
regulates activities that require duration, not speed
types of hormones (3)
peptide, amine, steroid
peptide hormones
most common type (e.g. insulin)
secreted by hypothalamus, anterior, posterior pituitary gland, pancreas, parathyroid
amine hormones
derived from tyrosine
includes the thyroid, adrenal medulla (adrenal medullary secretes catecholamines)
steroid hormones
cholesterol precursors, secreted by adrenal cortex, ovaries, testes
mechanisms of action for hydrophilic peptides/catecholamines
poorly soluble in lipids so need cell surface receptors
produce a secondary messenger (cAMP) to amplify the signal
can alter cell permeability by opening/closing certain channels
mechanisms of action for lipophillic hormones
can readily cross lipid bilayer so bind to intracellular receptors
activate transcription of certain genes –> transcription factor –> proteins
has longer lasting effects
example of a lipophillic hormone and action
epinephrine – produced by adrenal medulla (catacholamine), is released during times of stress, and causes contraction of smooth muscle, relaxtion of respiratory airway smooth muscle, breaks down glycogen to glucose in the liver, redircets blood flow to essential body parts
types of cell surface receptors
ligand gated channels, G-protein linked receptors, enzyme linked receptors
ligand gated channel example
nicotinic Ach receptor found in the neuromuscular junction
linked to an ion channel (usually sodium) and ion channel opens when the ligand binds
causes depolarization which propogates the signal and leads to excitation of muscle
enzyme linked receptor example
enzyme binds to insulin receptor which dimerizes and autophosphorylates into the insulin receptor substrate which causes a cellular response
when/where does the glycogenolytic cascade occur and what stimulates it
when breaking down glycogen to get glucose (occurs in the liver) and is stimulated by epinephrine
how does the glycogenolytic cascade work
epinephrine binds to a GPCR on the ER and the alpha GTP releases and goes to adenylcycic aglaces which converts ATP to cAMP (inactivates glycogen synthesis) and inactive pka to active PKA which activates phosphorylate kinase which turns glycogen into glucose-1-pyrones which gets converted to glucose and is released from the cell
how is an action potential “all or none”
positive feed-back mechanism: if membrane is depolarized slightly, some voltage gated Na channels open which depolarizes it more, opening more channels, and so on –> generates action potential
how is an action potential self-regenerating
spreads by local current flow to the adjacent regions and so on down the length of the axon; jumping along ndoes of ranvier due to positive repulsion
NONCYCLIC ELECTRON TRANSPORT
Uses photosystems I and II to produce NADPH + H+ together with ATP
Electrons from H2O replenish chlorophyll molecules which gave up electrons
O2 is a by-product of the breakdown of H2O
why is cyclic electron transport necessary
if the noncyclic was the only light reaction, there may not be sufficient ATP for carbon fixation
What does the parasympathetic nervous system do
“Rest and digest” – housekeeping
What does the parasympathetic nervous system do
“Rest and digest” – housekeeping
what produces the csf
group of cells and blood vessels collectively known as the choroid plexus
How many types of glial cell
6
how does the csf circulate
from the lateral ventricles through the interventricular foramen to the third ventricle
It then goes to the fourth ventricle via the cerebral aqueduct
From the fourth ventricle it goes to the spinal cord via the central canal
Most abundant glial cells
Astrocytes
Function of the Cerebrospinal Fluid
- Bathes the brain
- Acts as a shock absorber
- Transports nutrients, chemical messengers, and waste products
What do astrocytes do
Link neurons to adjacent blood vessels and help maintain chemical consistency of cell
how many lobes make up the brain
5
What do microglial cells do
Clean and remove unwanted debris/material from around neurons; similar to immune cells
name 4 lobes
frontal, temporal, parietal, occipital
What do ependymal cells do
Produce cerebrospinal fluid
function of frontal lobe
somatic movement (skeletal muscle movement)
What does csf do
Bathes and surrounds brain for protection
function of parietal lobe
sense of touch, sensation
Avg size of brain
1350 - 1400 g
function of temporal lobe
hearing; vision - visual association area for facial
recognition, olfaction
Function of csf
Acts as shock absorber from hard skull
function of occipital lobe
seeing, vision
What are ventricles
C-shaped vesicles which have ependymal cells and produce& circulate csf
what does it mean for the brain to be contralateral
right side of brain controls left side of body and left side of brain controls right side of body
How many ventricles
4
4 areas of the frontal lobe
premotor cortex, primary motor cortex, brocas area, prefrontal association cortex
Names of ventricles
Right lateral ventricle, left lateral ventricle, third ventricle, fourth ventricle
primary motor cortex
area responsible for initiating skeletal muscle motor movement (executing movement)
What does the interventricular foramen do
Connect right and left ventricles
premotor cortex
area of brain where you plan movement (planning movement); makes sure nothing crashes into each other and goes where it’s supposed to
What is the cerebral aqueduct
Connects 3rd and 4th ventricle
Prefrontal association cortex
complex tasks and cognitive functions - higher order thinking; e.g favorite 20 shows in alphabetical order or mathmatical equations
What is the central canal
Comes after the 4th ventricle and sends csf to the spinal cord and around the brain
Brocas area
responsible for speech initiation and execution of voice
nickname of primary motor cortex
motor homonculus
2 areas of parietal lobe
Somatosensory cortex, Wernickes
Somatosensory cortex
spacial discrimination
— precise, can tell where movement or sensation came from; e.g. knowing where right hand is; Conscious awareness of general somatic senses
Wernickes
Overlaps in temporal lobe; responsible for speech comprehension
nickname of Somatosensory Cortex
sensory humonculus
area of occipetal lobe
visual cortex
4 major components of the brain
cerebellum, thalamus, hypothalamus, brain stem
thalamus
- relay center
- called this because all senses go here (except sense of smell - has a different pathway)
- Crude awareness of sensation
- Motor control
e. g. hearing goes to thalamus and then to temporal lobe
hypothalamus
(hypo means below)
- just under thalamus
- regulatory center - recognizes when homeostasis has been affected and sends signals to correct
- works as a receptor and a control center
- temperature control, urine, fullness sensors
- endocrine role: controls hormones
- internal clock sleep/wake center
- formation of memory
cerebellum
“small brain”
- coordinate movement (in addition to frontal lobe and thalamus)
- Maintenance of balance
- Coordination and planning of skilled voluntary muscle activity
cerebellum is ipsilateral
what is ipsilateral
same side e.g. right side of cerebellum controls right side of body
3 parts of brain contributing to movement
cerebellum, frontal lobe, and thalamus
brain stem
“gateway to brain”
– Origin of majority of peripheral cranial
nerves
– Control centers for digestive, respiratory, and cardiovascular centers
– Equilibrium and posture
– Integration of inputs from spinal cord
e.g. sets heart rate; when to breathe
3 types of damage to the brain
• Trauma • Stroke • Seizure
trauma
blow to the head (falling from high place, car accident, etc)
stroke
blood vessels that supply the brain rupture or get blocked (cerebral vascular accident)
seizure
brain starts to fire uncontrollably - poorly understood as to root cause
trauma to frontal lobe
= paralysis, but could still feel because parietal lobe is not affected
damage to brain stem
universal damage
how is the brain bilateral
one on each side, except for speech (brocas and wernickes are only on left hemisphere), speak from our left side, right is for emotional aspect of speech - not for initiation
2 types of aphasia
- Wernickes aphasia
* Broccas aphasia
• Wernickes aphasia
damage to wernicke they can speak but they can’t make sense of what they’re saying - words come out normally but don’t make sense
• Broccas aphasia
broccas is where they can understand but they can’t speak
Right Parietal Lobe Damage
• Contralateral neglect syndrome
• Contralateral neglect syndrome
unconventional condition, we don’t understand
damage to right parietal lobe - would think they would lose sensation on left side, but actually they just lose interest in the left side (would only shave right side of face, eat only right half of plate, neglect left)
Split-Brain Patient
sometimes have to split corpus callosum to prevent disease to spread from one side to another (e.g. seizures)
seem normal, but left side doesn’t know what right side is doing
what is the corpus callosum
connects left and right side
reason to severe corpus callosum
seizures tend to spread so if nothing else works, they have to sever the corpus callosum to prevent the seizures from spreading from left to right or vice versa
what happens when you ask a split brain patient to touch objects with hands and why
can feel it with left hand but can’t say it
have them touch with right hand and can figure it out
touch with left hand, info goes to right hemisphere — but corpus collosum is blocked, so it can’t make it to the speech side (left) of the brain
with right hand it goes straight to the speech side (left hemisphere)
