Exam 2 Flashcards
What are animal signal forms?
Sounds, scents, and visual cues
what is within animal signal forms?
chemical and electrical
what are the most types of signals (aka systems)?
the nervous and endocrine system
What does the complexity of animal physiology and behavior require?
diversity of signaling mechanisms
What causes cell signaling?
environmental trigger- need a cue for the production
Cell signaling Steps (3):
- produciton of a signal in one cell
- transport of that signal (chemical messenger) to a target cell
- the messenger binds to a receptor to transduce signal into the target cell to cause a response
What are the different types of direct signaling?
gap junctions and connexins
what are the different types of indirect signaling?
autocrine, paracrine, endocrine, neural, exocrine
Direct Signaling’s local communicaiton is
contact-dependent
the chemical messengers pass through what in direct signaling
gap junctions or specialized membrane junctions or even directly
what type of messengers are in direct signaling
ions, small molecules, and water
is direct signaling an active diffusion?
no passive: opened and closed to regulate the communication of substances between cells
steps for indirect cell signaling (3):
- release of a chemical messenger from signaling cell into the environment
- transport of chemical messenger through environment to target cell
- communication of signal to target cell by receptor binding
Indirect signaling’s local communication is
contact independent and endocrine signaling
Autocrine Signaling
messenger affects the signaling cell
itself
Paracrine Signaling
messenger affects nearby cells
How does distance affect the diffusion of the messengers in indirect signaling?
limits the rate of diffusion
diffusion is insufficient to carry signals to distant target cells
is there a high chance of the messenger getting to a farther location regarding diffusion
the longer the distance= the lower chance the messenger gets to its target cell
what are the messengers for endocrine signaling
hormones
Glands
secretory cells of the exocrine and endocrine tissues are often grouped together into structures
What system carries the hormones from the signaling cell to the target cell?
circulatory system
What is the messenger for Neural signaling?
neurohormones
does a electrical signal travel long or short distances?
long
neurotransmitter
reaches terminus trigger release of a chemical messenger
Once reaching the target cells the neurohormone binds to what structure
receptor
Can all neurons secrete neurotransmitters directly into the circulatory system
no, some!
do neurohormones act like hormones
yes!
the most important distinction among the different indirect signaling systems is
distance messenger travels
speed of communication
speed of communication for autocrine and paracrine
milliseconds to seconds
speed of communication for nervous
milliseconds
speed of communication for endocrine
seconds to minutes
do endocrine signaling last longer
longer-lived
exocrine signaling
pheromone
What affects the way signaling is accomplished?
structure of the messenger
Hydrophobic Messengers
can diffuse freely across cell membrane
what holds hydrophobic messengers in a solution
protein carriers
hydrophilic messengers
cannot diffuse acorss the cell membrane
what process do they (hydrophilic messengers) do to exit cell
exocytosis
do hydrophilic messengers have carriers to travel to target cell?
no, they have to dissolve to transport to target cell
Ligands
a molecule that binds to another molecule called a receptor to send signals within or between cells.
What are the main classes of chemicals known to participate in cell signaling in animals?
Peptide messengers (hydrophilic)
Steriod Messengers (hydrophobic)
Biogenic Amine Messengers
Lipid Messengers (hydrophobic)
Purine Messengers
Gass messengers (ex: CO)
Peptide Messengers
Amino Acid residues
- hydrophilic or hydrophobic
- act as neurotransmitters
Peptides < 50 amino acids chains
Hydrophilic
Proteins > 50 amino acids chain
Hydrophilic
Where and how are peptide messengers synthesized?
ribosomes on the rough ER;
synthesized as large inactive polypeptides
Preprohormones
large inactive polypeptides
What do peptide messengers possess that target the polypeptide for secretion?
signal sequence
Prohormone (inactive)
prior to being packaged into secretory vesicles, signal sequence is cleaved from the preprohormone
Biogenic Amine Messengers: aka….
Small Water Soluble Hormones
Why do biogenic amine messengers require specific receptors?
- cannot cross plasma membrane
- too large
- carry a charge at physiological pH
Where are biogenic amine messengers to be stimulated?
vascular system
biogenic amine messengers are carried _____ to needed site
freely
examples of biogenic amine messengers:
- Epinephrine (Adrenaline)
- Norepinephrine (Noradrenaline)
- Serotonin
- Histamine
What receptors typically recognize hormones?
intracellular receptors (not cell surface receptors)
Where are hormones synthesized and secreted from?
Synthesized from cholesterols (hydrophobic); endocrine cells to act on distinct target sites in the human body
Examples of Steroid Hormones
estrogen, progesterone, testosterone
examples of thyriod hormones
thyroxin, retinoids (vitamin A), cortisol and vitamin D
What happens if there is no receptor for a signal?
cell will never be able to detect it
What is cell signaling?
- Extracellular signaling molecule (1st Messenger)
recognized by the receptor. - Leads to the production of small transient signaling
inside the cell (2nd Messenger) - Leads to alter the activity of the next component of
the transduction pathway. - Formation of chains of molecules (cascades), where
each molecule passes the message to the next. - Until the final signal causes the desired cell event.
What are the four criteria that must be met by a functioning receptor?
1) Has to have specificity
2) Binding affinity must be high
enough to detect ligands in
concentration found in
vicinity of cell
3) Must be able to transmit
message into the cell.
4) Needs to be turned off once
the message is received and
acted on
Agonist:
A ligand that binds to a receptor and it activates
the receptor.
Roles of receptors: Signal Detection
- The location of receptors can
vary. - Receptor dysfunction
can/will lead to disease. - Capacity of a cell to recognize
a signal will not be constant;
receptors change over time.
Antagonist:
A ligand that binds to a receptor and it does not
activate the receptor
If the ligand can bind to multiple receptors, the target’s cell receptor _____ response
Specificity
One ligand can have one or multiple receptors
multiple
Example of a ligand that can bind to multiple receptors
epinephrine (adrenaline) - sympathetic nervous system
breakdown of epinephrine receptors
α-Receptors on
intestinal blood
vessels will cause
vasoconstriction
* β2
-Receptors on some
skeletal muscle
vessels will cause
vasodilation
can receptors become saturated? Why?
yes
- the receptor activity reaches a maximum rate due to the limited number of receptors on cell membrane
- Allowing for flexibility to vary responses based on extracellular conditions and internal needs
Down-regulation (desensitization)
decrease receptor number to desensitize cell response
Sustained Agonist Activity -> Endocytosis -> Recycling or Degradation -> Synthesis of New Protein -> Incorporation into Membrane
Up-regulation:
increase receptor number to sensitive cell response
Receptor Downregulation -> Increase total number of receptors -> decrease down-regulation -> withdrawal of antagonist -> elevated number of receptors can produce exaggerated response
High-Affinity Ligand Binding
results from greater
intermolecular force between the ligand and its receptor
High-affinity binding involves a __ ___ ___ for the ligand at its receptor binding site
longer residence time
What type of energy can be used to cause a conformational change in a receptor regarding high-affinity ligand binding?
physiologically important binding energy
Low-affinity ligand binding
results from lesser
intermolecular force between the ligand and its receptor.
Low-affinity binding involves a __ ___ __ for the
ligand at its receptor binding site
lesser residence time
What is the general sequence that ligand binding will initiate?
1) Binding causes a conformational change in the
outer domain of receptor.
2) Change is transmitted through membrane to
induce conformational change in the intracellular
domain of receptor.
3) Change will either activate or inhibit receptors
intrinsic activity to interact with intracellular
proteins
What are the five main classes of receptors?
1) G protein-coupled receptors
(GPCRs)
2)Ion channel linked receptors
3)Intrinsic enzymatic receptors
4) Tyrosine kinase-linked receptors
5)Intracellular receptors
Where are G protein-coupled receptors found?
only in eukaryotes, yeast, and animals (maybe in plants….)
Large diversity of receptors and intracellular effectors
involved in many diseases
GPCRs
Receptors are coupled to ____ G proteins and function as ___ exchange factors to transduce signal
trimeric; guanine
GPCRs target ___ of all modern medicinal drugs
40%
G PROTEIN-COUPLED RECEPTOR-LIGAND BINDING
Activation Cycle include:….
- GEF- Guanine nucleotide exchange Factor
- RGS- Regulator of G Protein
Signaling - GAPs- GTPase accelerating
Proteins.
Membrane-bound receptors
Ligand-gated channels
Transient event
The ion channels open for a short time,
after which the ligand dissociates from the receptor and
the receptor is available once again for a new ligand to
bind.
Ligand-gated channels are involved in the detection of _____ and __ ___ used in synaptic signaling on electrically excitable cells
neurotransmitters; peptide hormones
What does the conformational change affect in ligand-gated channels?
Alters the ion permeability and charge across the plasma
membrane.
What undergoes a conformational change when a ligand binds forming a “water tunnel” allowing passage of specific molecules, such as sodium (Na+) or potassium (K+)?
Ligand-gated channels
Ligand-gated ion channel : Clinical Relevance
Likely to be the major site at which anesthetic
agents and ethanol have their effects, GABA.
* Drugs such as barbiturates used to treat insomnia,
depression and anxiety have been linked to
receptors.
* Diseases include schizophrenia, Parkinson’s
disease, Alzheimer’s disease, epilepsy and autism
have been linked, in part, to receptor defects.
Snake venom ( - α
neurotoxins)- antagonists
- Bind tightly and
noncovalently to nAChRs of
skeletal muscles - Block the action of ACh at
the postsynaptic membrane,
inhibiting ion flow - Leading to paralysis and
death
nAChRs normal vs agonist binding
Normally: nAChRs may exist in different interconvertible
conformational states.
Agonist binding: Stabilizes the receptor in the open
* allowing positively charged ions to move across it
* It will remain open until the agonist diffuses away.
* Usually takes about 1 millisecond
Nicotinic Acetylcholine
Receptor (nAChRs)
* Function:
– When acetylcholine is
bound, alter the receptor’s
configuration and cause an
internal pore to open.
– Pore allows Na+
ions to flow
into the cell.
– Inward flow Na+
ions
depolarizes the
postsynaptic membrane
sufficiently to initiate an
action potential.
Commonalities of Intraceullar Receptors
- small and hydrophobic
- allows for free passage into the cell
- insoluble in aqueous fluids
Intracellular receptors
- Steroid hormones
– Thyroid hormones
– Retinoids
– Fatty acids
– Prostaglandins
– Leukotrienes
Cytosolic and Nuclear Receptor are all
transcription factors
Depending upon the intracellular steroid hormone Cytosolic and Nuclear Receptor bind, having two modes of action
– Located in the cytosol and move to the cell nucleus upon
activation
– Located in the nucleus waiting for the steroid hormone
to enter and activate them
– Covered up by heat shock proteins (HSP) which binds
the receptor until the hormone is present
Cytosolic-
Hormone binding causes receptor
conformational change, freeing the receptor from
HSP and the receptor-hormone complex enter the
nucleus to act affect changes in transcription
Nuclear-
Hormone binding causes receptor
conformational change, freeing the receptor from
HSP and the receptor-hormone complex can act
upon transcription factor
Regulation of Cell Signaling
- sensor (regulated variable)
- integrating center
- effector
- negative and positive feedback
Feedback Regulation: local vs long distance
local level: paracrine and autocrine
long distance: nervous and endocrine
Step 1 in a Response Loop for Feedback Regulation
Stimulus: Change in a variable that sets the pathway in motion
Step 2 in a Response Loop for Feedback Regulation
- Sensor or Receptor: Monitors environment for changes in variable; must reach
Threshold: Minimum stimulus needed to start reflex response
Step 3 in a Response Loop for Feedback Regulation
- Afferent Pathway: Sends input signal to Integrating Center
Step 4 in a Response Loop for Feedback Regulation
- Integrating Center: Compares variable with set point to determine if it is out of range. If so, initiates output signal
Step 5 in a Response Loop for Feedback Regulation
- Efferent Pathway: Electrical or chemical signal that travels to target
Step 6 in a Response Loop for Feedback Regulation
- Target or Effector: Cell or tissue that carries out the appropriate Response to bring variable back to homeostasis
direct feedback loop
- Endocrine system only: No
CNS/PNS integrating center - Endocrine cell itself senses
a change in the extracellular
environment and releases a
chemical messenger that
acts on target cells
elsewhere in the body. - The endocrine cell acts as
the integrating center that
interprets the change in the
stimulus variable
First-Order Feeback Loop
Direct feedback loop but nervous
system becomes involved
* A sensory organ perceives a
stimulus and sends a signal via the
nervous system to an integrating
center (brain) that interprets the
signal.
* Neurons then transmit the signal
(neurotransmitter or neurohormone) to a specific target organ,
causing a response.
* Only a single step links the
integrating center and the response
Second-Order Feedback Loop
Second order feedback loops:
* There are 2 steps that link integrating
center and the response.
* Sense organ perceives a stimulus and
sends a signal to the integrating center
* Integrating center will then sends a
signal by a neuron telling the neuron to
secrete either a neurohormone or a
neurotransmitter
* Act on an endocrine glands will secrete
a hormone into the blood
* Travel to the target cell to cause a
response
Third-Order Loop
3 steps link integrating center and response
* Every step in a response loop may act as a
control point over the pathway
* Provide the most sophisticated and tightly
regulated feedback
* Sense organ perceives a stimulus and sends a
signal to the integrating center
* Sends a signal by a neuron telling the neuron
to secrete either a neurohormone or a
neurotransmitter
* Act on an endocrine glands to secrete a
hormone into the blood
* Travel to the target cell of second endocrine
gland, which will then induce a response.
Endocrine can refer to
a class of glands (exocrine & endocrine)
type of hormonal action (chemical signaling)
exocrine glands
secrete products externally (ex: sweat, salivary, sebaceous, mucous glands)
endocrine glands
secrete products internally (ex: pituitary, thyroid, pancreas, adrenal glands)
Chemical signaling can be
autocrine, paracrine, or endocrine
ectocrine & intracrine signaling
hormones are responsible for
long-term, on-going functions of body
Hormone functions of the body are
growth and development
metabolism
regulation of the internal environment
reproduction
what makes a chemical a hormone?
- Secreted by a discrete and identifiable cell or group of cells derived from epithelial cell lineage
- Secreted into the blood
- Transported to a distant target and bind to target receptor
- Exert their effect at very low concentrations (sometimes femtomolar)
the root word of hormones
to excite
3 Basic ways hormones act on target cells
By controlling rates of enzymatic reactions
By controlling the transport of ions or molecules across cell membranes
By controlling gene expression and synthesis of proteins
Four main classes of hormones
- Peptide/Protein Hormones
- Steroid Hormones (cholesterol derived hormones)
- Amino Acid Derived
- Miscellaneous (immune hormones)
Hormone release follows the basic pattern of a reflex
- stimulus
- sensor by receptor
- signal input
- signal integration
- signal output
- response
The endocrine cell is a sensor
simplest reflex control pathway
cell directly senses stimulus and responds by secreting hormone
cell acts as both a sensor and an integrating center
the output signal is the hormone released
negative feedback turns off reflex
Peptide Hormone Mechanism
acts through cAMP second messenger system of signaling cascade
example of peptide hormone
insulin (pancreas)
Cholesterol Dervied Hormones are ___ and can ___ diffuse through cell membranes
lipophilic; passively
Cholesterol Derived Hormones aka
Steroid Hormones
Cholesterol Derived Hormones are ___ soluble in plasma; bind to ___ protein (either ___ or ___)
not; carrier; globulin; albumin
Bound steroid is protected from degradation; meaning
extends hormone half-life, but blocks cell entry (must be unbound to act)
Low-Density Lipoprotein-
a wide array of sizes and densities; stays in circulation longer and more easily enter arterial walls
which one is bad cholesterol ?
low density lipoprotein
Why is lipoprotein considered bad cholesterol?
can create plaques, stay in the stream pretty long
High-Density Lipoprotein
smaller than LDLs; transport cholesterol from peripheral tissues to the liver. The liver can convert to bile acids and secreted in the bile
Why is high-density lipoprotein considered “good cholesterol”?
it removes excess cholesterol
Cholesterol is translocated into the mitochondria via consecutive actions of __ __ ___ ___ and the __ __ __ ___
steroid acute regulatory protein (StAR); 18 kDa translocator protein (TSPO)
cholesterol metabolized to pregnenolone by ____ and further metabolized in the __ ___
P450scc; smooth ER
Classic (Transcription) Steroid Hormone Receptors
- direct interaction with intracellular nuclear receptors
- takes longer to produce biological effect (minutes to days)
Steroid Hormone Receptors two general categories:
classical; non-traditional
Non-traditional Steroid Hormone Receptors
- Non-nuclear actions that alter nuclear receptor activation or cell signal transduction
- Rapid production of biological effect (seconds to minutes)
Examples of ligand: receptor complexes:
*Progesterone:Progestin Receptor
*Estradiol:Estrogen Receptor
*Testosterone:Androgen Receptor
*Cortisol:Glucocorticoid Receptor
In the resting state, some ___ ____ ___ are tethered in the cytosol, some are always nuclear, and some shuttle back and forth
nuclear steroid receptors
Biogenic Amines: Two Families from Tyrosine
Catecholamines and Thyroid Hormones
Catecholamines
Epinephrine (Adrenaline)
Norepinephrine (Noradrenaline)
Dopamine
Neurohormones: 3 major groups
- Catecholamines – tyrosine-derived neurohormones (Dopamine, Epinephrine, Norepinephrine)
- Hypothalamic neurohormones secreted from the posterior pituitary
- Hypothalamic neurohormones that control hormone release from the anterior pituitary
Thyroid Hormones (T3,T4)
Behave like steroids and have intracellular receptors
Anterior Pituitary Gland
- true endocrine gland
- hormones are adenohyophyseal secretions
- second-order feedback loop system
Median eminence
functional connection between the hypothalamus and the pituitary gland
6 Anterior Pituitary Neurohormones (tropic hormone controls secretion of other hormones)
- Prolactin (PRL)- Milk production
- Thyrotropin (TSH)- Thyroid stimulating hormone
- Adrenocorticotropin (ACTH)- Adrenal cortex hormone synthesis and secretion
- Growth hormone (GH)- Somatotrophin- affects cellular metabolism
- Follicle-stimulating hormone (FSH)-Gonadotrophin; females and males
- Luteinizing hormone (LH)- Gonadotrophin hormone; females and males
Posterior Pituitary Gland
- false endocrine gland, extension of neural tissue in the brain
- hormones made in the hypothalamus and neurphypophyseal secretions
- Third-order feedback loop system
Posterior Pituitary Neurohormones
Vasopressin (Antidiuretic Hormone-ADH) and Oxytocin
Vasopressin acts on the ___ ___ in the kidney nephrons to ____ ____ in the body
collecting ducts; retain water
why is vasopressin released?
released in response to low blood volume
Vasopressin ___ blood vessels
constrict
What does the decreased release or decreased sensitivity of vasopressin lead to?
diabetes insipidus, hypernatremia (increased blood sodium concentration), polyuria (excess urine production), and polydipsia(thirst)
High levels of vasopressin might lead to
hyponatremia (low sodium levels) and hypervolemia (high fluid volume)
what does oxytocin play an important role in?
neuroanatomy of social trust, intimacy/sexual reproduction
what does oxytocin do during childbirth?
by it being released in large amounts, it causes the distension of the cervix and uterus
does oxytocin use positive or negative feedback mechanisms
positve feedback mechansims
after childbirth, what does oxytocin do?
facilitates maternal bonding, and lactation and milk ejection
oxytocin greek
“quick birth” to to refer to agents from Claviceps purpurea (“rye ergot fungus”)- Ergometrine
Oxyoticin is the first ____ ____ to be sequenced and synthesized (du Vigneaud et al. in 1953)
polyphenol peptide
what is the slowest negative feedback loop?
long feedback loop; taking days
Negative feedback loop types
short, fast, long
the release of what promotes the anterior pituitary release of ACTH
CRH
what activates hypothalamic secretion of CRH
stress
what activates adrenal cortisol production
release of ACTH
Cortisol acts back on the hypothalamus to ___ ___ release and its own production
terminate CRH
What is also stimulated by stress other than hypothalamic secretion of CRH?
gonadal steriod production
Similar to ____ steroids, gonadal steroids act back on the brain at the level of the pituitary to ___ ___/____ release, which stops their own production
adrenal; terminate LH/FSH
Clinical Estrogen/Progestogen Drug Targets:
Ant. Pit.: Inhibition of negative feedback for oral contraception
Ovary: Inhibition of ovarian function for oral contraception
Aromatase: Inhibition of estradiol formation for cancer
Receptor: Antagonism of ER in ER+ cancers; Agonism for HRT
sex hormone-binding globin (SHBG)
vacuums testosterone that is circulating
Clinical Androgen Drug Targets
Hypothalamus: Inhibition of GnRH feedback for prostate cancer; agonism for HRT
Testis: Inhibition of testicular function for Cushing’s or refractory prostate cancer
5α-reductase: Inhibition of DHT formation for benign prostatic hyperplasia
Receptor: Antagonism for prostate cancer; agonism for HRT
Cell types of CNS
neurons and neuroglia
support cells of the neuroglia
oligodendrocytes, microglia, astrocytes
parts of neuronal signaling
Neuronal Zones
* Dendritic Signaling
* Synapse
Neurons
functional unit of the nervous system
communicates and transports signals
neuroglia
highly vasculature, tons of energy used; maintains privileged environment; blood-brain barrier
oligodendrocytes
forms myelin sheaths around neurons
(important for regulating action potential)
Microglia
immune cells of the brain; least abundant; inactive/active phenotypes; macrophage-like (engulfing the bad things)
Myelin
lipoprotein that surrounds thicker axons
astrocytes
most abundant; major support cell of the brain; essential for brain homeostasis
Oligodendrocytes function
an insulating layer that prevents leakage of electrical current; increases speed of impulse conduction along axon; energy efficient; enhances electrical impulse jumping (leaping down the axon )
What are the three phenotypes of microglia?
Resting
M1 (pro-inflammatory)
M 2 (anti-inflammatory)
Function of Microglia
- cellular debris clearance
- phagocytic of living/dying/dead cells
- release diffusible factors (pro/anti- inflammatory cytokines)
Astrocytes are major support cell of brain ___ ___ ____
especially for neurons
Astrocytes maintains
pH, brain homeostasis, and elicits signals
Astrocytes are the ____ between the neurons and environment (signals within the blood)
communicator
Astrocytes prove ____ _____ and sweep up extra ______
necessary materials (parents); neurotransmitters
Astrocytes modulate _____ ______ and _____ uptake/conversion
synapse formation; glutamate
Unipolar neuron
the cell body is on one end (no dendrites) -> myelin-> axon terminal
What are the commonalities between the multiple types of neurons?
cell body
axon
dendrite
Multiple types of neurons
unipolar
bipolar
pseudounipolar
multipolar
bipolar neuron
cell body is between sensory receptor (bottom) and axon terminal (end)
pseudounipolar neuron
no myelin and is more common
sensory receptors at end
cell body is hanging off?
Multipolar neuron
dendrite (multiple sources) on cell body -> myelinated axon -> axon terminal
The cell body of a neuron
enlarged part of cell
that contains the nucleus and
organelles
Axon Transport Types
slow and fast
the axon of a neuron
long cytoplasmic extension;
specialized for signal transduction
the dendrites of a neuron
cytoplasmic extensions from the cell body; receive incoming signals
Slow axonal transport
cell components are transferred from the cell body to axon
terminal
* *used for materials not consumed rapidly by the cell; e.g., enzymes and cytoskeleton proteins)
Fast axonal transport
transported vesicles “walk” with the aid of attached foot-like
motor proteins with the use of stationary molecules (microtubules) as tracks
* mitochondria, lipids, synaptic vesicles, proteins, and other organelles
* Neuroinvasive Viruses (i.e., Rabies and West Nile Viruse) uses retrograde fast axonal transport to
infect the CNS
Types of fast axonal transport
anterograde and retrograde
Anterograde
“forward” cell body to axon terminal
Retrograde
“backward” axon terminal to cell body
Signal reception zone
dendrites and the cell body: receiving incoming signals
Singal integration zone
axon hillock: where the cell body meets the axon; if there is a large enough
stimulus, the stimuli is converted to an electrical signal (change in
membrane potential) that is sent down the axon
Signal Conduction Zone
axon: nerve fiber that conducts electrical signals
signal transmission zone
collaterals (axon terminals): swelling at axon terminus where comes in close contact with the
target cell; does not touch
* electrical signal is converted to a chemical signal
(neurotransmitter)
what is the importance of surface area for synapses within the dendrites?
wide range of communication between a microenvironment
Boutons (Pre) and Spines (Post)
convert chemical signal to electrical signal
ion channels opening or closing
alter membrane potential
In the signal reception zone:
* Terminal _____ and ______
* Synaptic _____-_____ ____ between cells where chemical
communication/transmission occurs
* Changes in ______ ______ elicit chemical release from the presynaptic cell
boutons and synapse
cleft-small gap
membrane potential
function of the axon
transmit outgoing electrical signals from the integrating center to the target cells at the end of the axon
axon hillock is where the summation of signals are from the
boutons
physiology of the axon
axon extends from the axon hillock
length (2uM -1m)
What does the electrical signals from the integrating center cause?
neurotransmitters
Resting Membrane potential
the separation of intracellular potassium ions from anions across the cell membrane of the cell; concentration gradient of potassium ions must be set up
What pump is used in the resting membrane potential?
Sodium-Potassium Pump (Na+/K+-ATPase)
is Na+ mostly found in the intraceullar or extracellular
extracellular
is K+ found mostly in the intracellular or extracellular
intracellular
A resting (unstimulated) cell and membrane has
the potential to conduct
electrical signal or action
potential
Sodium Potassium Pump
- 3 sodium ions pumped out of the cell
- 2 potassium ions pumped into the cell
- Creates a deficit of positive ions on the inside
of the cell - So inside is more negative than the outside
The resting membrane potential is not an ____ potential, meaning it requires ATP
equilibirum
3 important factors to establish a membrane potential
- The distribution of ions across the
plasma membrane (at rest) - The permeability of the membrane
to these ions (highly permeable to
a certain ion) - Charge on the ions that are moving
Goldman Equation -
describe the effects these factors have on the
membrane potential; predicts the equilibrium potential for certain ions
If the membrane is ______ _______ to an ion, the ion _______ ______ ______to the membrane potential
not permeable; does not contribute
If the membrane is _____ _____ to an ion, that ion ______ ___ _____ ________ to the membrane potential
highly permeable; makes a large contribution
Excitable cells selectively alter the permeability of their membranes to ions
- By opening and closing gated ion channels in the membrane.
- Changing ion permeability alters the membrane potential and generates
electrical signals
Potassium has the highest permeability since
they have leak charges that allow for the movement of potassium across the membrane to achieve equilibrium potential
Goldman Equation: Sodium and Potassium
sodium: +60 mV
potassium: -90 mV
Most membrane potentials are around this range
Vm= -70 mV
If you increase the extracellular sodium,
it would make the membrane potential less negative and more positive.
Inside of the cell membrane is more ____ charged than outside
negatively
Defined as a relativly stable, groud value of ____ ____ in animal and plant cells regarding resting membrane potential
transmembrane voltage
Stimulus of resting membrane potential
positive ions influx
Steps of Action Potentials:
threshold, depolarization, depolarization, hyper-polarization
What voltage does threshold potential need to reach to be excitatory potentials?
-55 mV
What are some possible inhibitors?
too sub-threshold potentials
too supra-threshold potentials
Threshold Potential
are graded potentials need to be reached for action potential to “fire”
so what happens at -55 mV?
voltage-gated Na+ channels on the membrane open allowing an influx of Na+ cations
Depolarization
membrane potential becomes less negative either through more positive charged ions entering cell or more negative charged ions leave the cell
Depolarzaiotn what type of channels ?
sodium/potassium leaky channels; very leaky to potassium not so leaky to sodium (potassium leaks out of the cell)
what does the sodium/potassium leaky channels do?
stop the cell from reaching threshold potential
Repolarization
cell returns to the normal resting membrane potential though negative charged ions entering or postive charged ions leave the cell
what reestablishes the resting membrane potential (repolarization)
Na+/K+ ATPase pump
Hyperpolarizartion
cell becomes more negative either through negative charged ions entering the cell or positive charged cells leaving (this reestablished resting membrane potential)
which of the discussed mechanisms restores resting potential?
leaky channels
Integration of Graded Signals: Two types
spatial and temporal summation
spatial summation
Interaction
of graded potentials from
different receptors will “meet” at
the axon hillock
* add together to fire an AP
* different sites
Temporal Summation
Interaction of graded potentials
that occur at slightly different
times at the axon hillock
* add together to fire an AP
* different times
Regulating excitability types
Excitatory Post-Synaptic Potentials and
Inhibitory Post-Synaptic Potentials
EPSPs (Excitatory Post-Synaptic Potentials)
change in membrane
potential following influx of
positively charged ions (e.g. Na+).
IPSPs (Inhibitory Post-Synaptic Potentials)
-change in membrane
potential following influx of
negatively charged ions (e.g. Cl-)
More narrow the dendrite, the _____ the propagation
faster
Farther away, ___ the signal to AIS
weaker
