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What are effectors?

They are responsible for body responses (ex. muscles and glands)


What is the definition of total body water

The volume of water contained in all compartments of the body -- composed of water and dissolved material
- subdivisions are call body fluids and are located in compartments


What is the definition of physiology

the science of body functions (the study of the normal functioning of a living organism and its component parts, including all its chemical and physical processes) -- literally means "Study of nature"


What is Intracellular fluid

All fluid contained within cells -- including plasma and tissue fluid (interstitial fluid)


What is Extracellular fluid

Fluid outside the cells but within the body (considered the "internal environment") -- including plasma and tissue fluid (interstitial fluid)


What is Interstitial fluid

Aka tissue fluid, the fluid surrounding other cells


What are negative and positive feedback systems and how do they relate to homeostasis

Negative: a self correcting response when a regulated variable decreases, the system responds to make it increase (regulator) and vice versa (opposes og stimulus)
Positive: the response of the system goes in the same direction as the change that set it in motion (magnified so response occurs much faster) (ex. cattle running = increased panic -- on and on)


What are the 2 major principles in physiology

1) simplification through classification
2) realizing that body functions are integrated (everything works together and relies on one another)


4 names of cells

1) purkinje
2) pyramidal
3) basket
4) stellate


what are the 6 levels of organization to form an organism

1) chemical
2) cell
3) tissue
4) organ
5) organ system
6) organism
Each forms the next step


What do neurons do?

transmit electrical signals -- receive info from receptors, transmit info from muscles to glands and can process info
- use branches to transmit or receive


What are epithelial cells?

Also know as the epithelium, they line external body surfaces such as skin, hollow body tubes and organs. They act as a barrier and as a transport membrane. They also form glands (endocrine and exocrine) that secrete hormones.


Exocrine glands

They secrete hormones through ducts into hollow tubes (exo = outside) ex. sweat and salivary glands
*note: inside of the gland is called the lumen


Endocrine glands

They secrete hormones without ducts into the blood system (endo = inside) ex. pituitary glands and adrenal glands


What is connective tissue?

An extracellular matrix made of fibrous proteins called elastin (elasticity) and collagen (strength) -- all while supporting other structures such as organs in the body
- bones: support to all body structures
- tendons: anchors muscles to bones
- ligaments: connects bones together
- blood: delivers oxygen to the body
- lymph: returns leaked materials into the blood
- fat cells


What do organs do and what are they composed of

They are composed of at least 2 different types of tissues that work together in systems that perform coordinated large scale functions, like nourishing the body (digestive sys) or protecting the body from attack (immune sys)


What is the external environment and what is the order of exchange

the external side of the epithelial body barrier
ex. surrounds external to the skin, air in your lungs, food in the stomach, urine in the bladder

order of exchange: external - blood - tissue fluid - cell


What are the body fluid compartments?

extracellular fluid and intracellular fluid -- body is divided into compartements that are separated by epithelial cells whose membranes are semi permeable (transport occurs between cells)


What is a regulated variable

The variable that is maintained by the body in homeostasis (blood glucose, plasma levels, temp, etc.) -- it is regulated but can still go up and down


What is the set point

The expected value of the regulated variable (pH, glucose, temp) -- what is the norm basically


What are receptors?

Sensors which detect internal or external stimuli
ex. thermoreceptors, chemoreceptors, baroreceptors (blood vessels)


What are integrating centers?

With many found in the brain, they orchestrate an appropriate response for the effector to respond to stimuli (located in the hypothalamus)


What do signals do?

allow components to communicate - inputs (receptor to integrating center) and outputs (integrating center to receptor)
- are chemical (hormones) or via neurons


What is the difference between passive and active transport?

Passive: occurs spontaneously in a downhill movement (down the force/outward)
Active: occurs non-spontaneously in an uphill movement, requiring cell E (ATP/ADP) (against the force/inward)


What are some factors that affect the rate of active transport?

the speed of individual carrier proteins


What affects the permeability of membranes by simple diffusion?

Cholesterol, lipid solubility of diffusing substance, size and shape of the diffusing particle, membrane SA, lipid bilayer composition


What is the difference between carriers and ion channels?

Carrier: a transmembrane protein that binds to specific molecules and transports them by changing their shape/confirmation
Ion channel: a transmembrane protein that functions as a passageway/pore that is substance specific (only certain ions - leak and gated channels)


What is the difference between primary and secondary active transport?

Primary: requires E from ATP hydrolysis to directly transport molecules
Secondary: leeches off primary, uses the E of a concentration or electrochemical gradient from previous active transport by primary


What are the 4 general functions of the cell membrane

1. physical isolation (acts as a barrier between intra and extra fluid)
2. Regulation of exchange with the environment (controls entry and exits)
3. Communication between the cell and the environment (contain proteins that react to environment)
4. Structural support (maintain cell shape)


The magnitude of electrical driving force depends on what? (x2)

1. strength of the membrane potential
2. the amount of charge on a particle (its valency)


What is equilibrium potential (Ex)?

when chemical = electrical driving forces (when electrochemical = 0)


How do molecules move across membranes (physically and energetically)

Phys: by diffusion and by crossing with a membrane protein (transport protein)
E: passive (no E) and active (E) transport


What are the 3 types of passive transport?

1. Simple diffusion: move in and out of the lipid bilayer, no E required
2. Facilitated diffusion: needs protein carrier with a binding site, no E
3. Diffusion through channels: needs protein carrier and E


What is diffusion?

The movement of molecules based on their thermal motion (the E each molecule has) from high to low concentration


What is active transport?

The movement of ions or molecules across a cell membrane using a pump (membrane protein) into a region of higher concentration, assisted by enzymes and requiring energy.


What are the 4 types of cells and tissues in the animal body

Cells: neurons, muscle cells, epithelial cells, connective tissue cells
Tissues: nerve tissue, muscle tissue, epithelial tissue (epithelium), connective tissue



The fluid surrounding blood cells (liquid part of blood)


What is the Internal environment composed of

Extracellular fluid (plasma and tissue fluid/interstitial fluid)


Homeostasis -- what is the importance?

The ability to maintain a relatively constant internal environment - a dynamic constant
Regulating: temperature (narrow limits), volume (of extracellular fluid), composition (of elements in the body)
- 9/10 organs contribute to homeostasis (not reproductive system - works to maintain species homeostasis)
- disruption is the basis for disease and death


What do muscle cells do and what are the 3 types

Contract both voluntarily or involuntarily creating mechanical force
1. skeletal (voluntary)
2. cardiac (involuntary)
3. smooth (involuntary)


Where is material exchanged between the internal and external environments?

- lungs
- gastrointestinal tract (through absorption and secretion)
- kidneys (through filtration, reabsorption and secretion)


What is an error signal

The difference between the value of the set point and regulated variable (between expected value of regulated and regulated)


What are the 4 components that regulate and enable homeostasis

1. receptors (sensor cells all over the body)
2. integrating centers (aka hypothalamus, signals an effector to respond to stimuli)
3. effectors
4. signals (electrical, etc.)


What are the roles of chemical, electrical and electrochemical driving forces in passive transport?

Chemical: pushes particles "down" the gradient (from high to low concentration) across the membrane
Electrical: occurs when there's an unequal distribution of charges across the membrane (ion: charged / anion: neg / cation: pos) giving the membrane a membrane potential (Vm - difference in electrical potential)
Electrochemical: a combo of chemical and electrical (the total force acting on particles)
- cells are negative inside and positive outside (charged)
- most cell's voltage is -70 mV = Vm


What are some factors that affect the rate at which a substance can be passively transported across a membrane?

The concentration gradient and the membrane (how permeable is it?)


4 factors affecting the rate of simple diffusion

magnitude of driving force, membrane surface area, membrane permeability, membrane charge


What is facilitated diffusion?

Passive transport through a carrier (transmembrane protein) that has binding sites for particular particles and binds one side at a time (limit at a plateau whereas simple diffusion is a straight line - no limitations since theres no carriers)


What are some factors that affect the rate of transport for facilitated diffusion?

Carrier speed, number of carriers and the magnitude of the concentration gradient


What are auqaporins?

Channels that only water can pass through - most water passes through these


What is a pump in a membrane?

- a type of membrane protein
- functions as transport protein and enzyme
- can use E from ATP to change its shape
- contains specific binding sites


What do symport and antiport mean

Symport: same direction
Antiport: different directions


What are the 5 major functional classes of chemical messengers? (who releases and how do they get to the target cell)

1. hormone -- long range chemical messenger
2. neurotransmitter -- communicates among adjacent cells
3. neuropeptide -- protein sequence which acts as a hormone/neurotransmitter
4. pheromone -- a chemical factor that triggers a social response in members of same species


How many cells are in a cow

370 trillion


What are the 2 general mechanisms of intercellular communicaiton?

1. Directly through gap junctions
2. indirectly through chemical messengers
- ligand gets made at the source then travels to the target


How does a gap junction work?

Direct communication through connexions between the cytosol of 2 cells


How do chemical messengers work?

Produced by a source cell, they travel indirectly through interstitial fluid to the receptor of a target cell


What is a ligand

A chemical messenger released into interstitial fluid or blood


What are 3 ways to classify a chemical messenger

1. by function
2. chemical class
3. solublility properties


What are the 3 messengers

1. paracrines - chemical for nearby cell (subclass being autocrines, chemical for itself)
2. neurotransmitters - a messenger produced by neurons
3. hormones - produced by endocrine cells, secreted into the blood by interstitial fluid diffusion (subclass being neurohormone, produced by neurons and secreted into the blood through diffusion)


Lipophobic ligand vs Lipophilic ligand

Lipophobic: likes water, not fat - doesn't cross cell membrane easily, requiring a pump or channel
- target response is enzyme activation and membrane permeability changes to certain ions
Lipophilic: likes fat, not water - goes through lipid bilayer membrane easily
- target response is gene activation


What 4 Amino acids function as messengers?

1. glutamate
2. aspartate
3. glycine
4. Gamma-aminobutyricacid (GAMA)
- all are lipophobic and target receptors on the cell membrane


Characteristics of Amines and where do they come from

- lipophobic (except thyroid hormones)
- target receptors are on the cell membrane
- made or derived from an amino acid and contain an amine group NH2
ex. thyroiid hormones, histamine, serotonin


characteristics of peptide/protein messengers, what are they made out of and where are the target receptors?

**-Most abundant type of ligand**
-Target receptors on the cell membrane
-Made of chains of amino acids
--Peptide ligand (less than 50 amino acids)
--Protein ligand (more than 50 amino acids)


What are steroid ligands, where are they derived from and what are their functions?

- Lipophilic
- All are derived from cholesterol
- All steroid messengers (ligands) function as hormones


What are Eicosanoid ligands and where are they derived from

- Lipophilic
- Intracellular target receptors
- Most are derived from arachidonic acid, a cell membrane phospholipid


Lipophilic ligands characteristics and what are they released by

- synthesized on demand
- immediate release from source
- release rate depends on synthesis (cannot be stored / contained since they permeate membranes)
- released by exocytosis


What are amino acids made out of, where are they synthesized, where are they stored and how are they released

- made from glucose, glutamate or 3-phosphoglycerate
- synthesized within neurons
- stored in vesicles then released by exocytosis


Where are amines produced, where are they released and what are some examples

- produced in cytosol, stored in vesicles and released by exocytosis
ex. tyrosine, dopamine, epinephrine, norepinephrine


Where are peptides and proteins stored and how are they released

stored in secretory vesicles, released by exocytosis


Where do steroids come from

They are derived from a cholesterol molecule (cannot be stored)


Where do eicosanoids come from and what are their 2 major synthetic pathways

Derived from arachadonic acid
1. cyclooxygenae pathway
2. lipoxygenase pathway


What is the difference between diffusion through interstitial fluid and blood-bourne transport

inter: source and target are close, quickly degraded
blood: source and target are at a distance
- lipophobic dissolve in plasma
- lipophilic bind to carrier protein


What is messenger half life?

time for a chemical to decrease its concentration by half
- indicator for how long a hormone is active in the body
- dissolved in plasma = short half life
- bound to plasma protein = long half life


What is signal transduction

The transfer of molecular signals from the exterior to the interior of a cell


Where do lipophilic/lipophobic ligands bind to a receptor

philic: within the cell
phobic: on the cell membrane


What does down regulation mean

-reduces number of receptors
-cell less sensitive to hormone and tolerance develops
-happens with long-term exposure to high hormone concentrations


What does up regulation mean

number of receptors is increased; sensitivity is increased


What are the 2 types of signal transduction?

1. intracellular-mediated response
2. membrane-bound receptor-mediated response


Intracellular-Mediated response characteristics and how do their cells respond?

Characteristic of hydrophobic/lipophilic ligands
Receptors are in the cytosol or nucleus
Cell response is via gene activation or inactivation


Membrane-Bound receptor-mediated response characteristics and where are its receptors?
3 examples

Used by hydrophilic/lipophobic ligands
Receptors on the cell surface of the plasma membrane
response due to the movement of ions or phosphorylation of enzymes
Channel-linked receptors
Enzyme-linked receptors
G protein-linked receptors


What happens during fast ligand-gated channels

-Receptor and channel-- same protein
-Action is direct
-Binding of ligand causes the channel to open or close
-change in transport of ions through the channel causes the target response
-ion movement down the concentration gradient


How do enzyme linked receptors participate in cell signaling

participate in cell signaling through extracellular ligand binding activates the enzyme - direct


G-protein linked receptors

slow ligand gated channels where the receptor and the channel are linked by a g protein
- when the ligand binds, it activates the g protein which in turn activates the channel


What are G proteins?

Regulatory proteins (molecular switches)


What are the first and second messengers of g proteins

1. ECF - extracellular fluid
2. intracellular messenger (gets activated by the first messenger which activated amplifier which activates second messenger -- signal amplification)


What is the most common type of second messenger system

Cyclic AMP (cAMP)


What are the primary endocrine gland and which hormone is it associated with?

hypothalamus, pituitary, pineal, thymus, thyroid, parathyroids, pancreas, adrenal glands, ovaries, testes, placenta
- main function is to produce hormones


What are the secondary endocrine gland and which hormone is it associated with?

heart, liver, stomach, kidney, small intestine, skin, adipose tissue
- produces hormones but it isn't their first priority


What is the role of the infundibulum

It connects the hypothalamus to the pituitary gland


antidiuretic hormone (ADH)

Hormone produced by the neurosecretory cells in the hypothalamus that stimulates water reabsorption from kidney tubule cells into the blood and vasoconstriction of arterioles.



A hormone released by the posterior pituitary that stimulates uterine contractions during childbirth and milk ejection during suckling


tropic hormones

hormones that stimulate other glands to release their hormones


Prolactin Releasing Hormone (PRH)

stimulates release of prolactin (stimulates mammary gland development and milk secretion)


Prolactin inhibiting hormone (PIH)

aka dopamine, Inhibits secretion of prolactin (PRL)


Thyrotropin-releasing hormone (TRH)

a hypothalamic hormone that regulates the release of thyroid-stimulating hormone from the anterior pituitary


Corticotropin-releasing hormone (CRH)

Promotes secretion of adrenocorticotropic hormone (ACTH)
- then releases hormones that deal with metabolism when the body is stressed


Growth hormone-releasing hormone (GHRH)

Promotes secretion of growth hormone (GH) and stimulates the secretion of insulin-like growth factors (IGF's) by the liver


Growth hormone inhibiting hormone (GHIH)

(somatostatin) inhibits release of GH and decreases release of IGF by the liver


Gonadotropin-releasing hormone (GnRH)

Promotes secretion of gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH)


short loop negative feedback

a pituitary hormone feeds back to decrease hormone secretion by the hypothalamus
- prevents buildup


Pineal gland

secretes melatonin
- involved in circadian rhythms and production


What 2 thyroid hormones does the thyroid gland produce

T4: tetraiodothyronine
T3: triiodothyronine
- both act to regulate body metabolism



Regulates and lowers blood calcium levels


parathyroid hormone (PTH)

regulates and increases calcium levels in the blood
- acts on the bones, kidneys and intestines


What is the thymus and where is it located?

The thymus is the site of T cell maturation and regulates t cell (part of the immune function) function -- located in the top part of the chest


adrenal glands (suprarenal glands)

located on the superior surface of each kidney; the adrenal cortex secretes steroid hormones, and the adrenal medulla secretes epinephrine and norepinephrine


What are the 3 layers of the adrenal glands

outer: zona glomerulosa
middle: zona fasciculata
inner: zona reticularis


What do Mineralocorticoids (aldosterone) do?

regulates sodium reabsorption and potassium secretion
- a mineral cortecoid


What do Glucocorticoids (cortisol) do?

Regulates metabolism and bodys response to stress
- comes from the zonae fasciculata and reticularis


What do Sex hormones (androgens) do?

regulates reproductive functions


What are chromaffin cells and when do they respond?

the cells in the adrenal medulla that secrete epinephrine and norepinephrine
- responds during emergencies with a release of adrenaline into the blood circulation


What are the Exocrine functions of the pancreas

acinar and duct cells secrete enzymes and fluid into the gastrointestinal tract
- rich in bicarbonate
- neutralizes fluid from the stomach into the duodenum


What are the Endocrine functions of the pancreas

Islets of Langerhans: beta cells produce insulin, alpha cells release glucagon
- in preganant women, helps determine pregnancy (chorionic gonadotropin in humans through estrogens and progesterone)


What do Delta cells secrete

secrete somatostatin (inhibits insulin and glucagon secretion)


What do F cells secrete

secrete pancreatic polypeptide (inhibits gallbladder contraction and pancreatic exocrine secretion)


Testes function

produce sperm, androstenedione and testosterone


Ovaries function

Produce oocytes, estradiol, progesterone, estrogen


What are the 3 factors that affect the concentration of a hormone in the blood?

1. rate of hormone secretion
2. amount of hormone bound to the plasma membrane
3. the rate of hormone metabolism (degradation)


Where is the suprachiasmatic nucleus (SCN) located and what is its function

A small brain structure that uses input from the retina to synchronize its own rhythm with the daily cycle of light and dark; the body's way of monitoring the change from day to night.
- has to do with melatonin secretion


circadian rhythm

the biological clock; regular bodily rhythms that occur on a 24-hour cycle
- responds to changes in the environment


What are 3 sites of hormone metabolism (degradation)

1. target cell
2. blood (broken down by enzymes)
3. liver (degraded by enzymes)


What are the 2 parts of the nervous system?

1. Central Nervous System
- consists of the brain and spinal cord
- receives and processes info from the sensory organs and viscera
- makes decisions and determines the internal and externals environment state
- site of learning, memory and emotions
2. Peripheral Nervous System
- consists of neurons that provide communication between the CNS and organs
- afferent and efferent


afferent vs efferent (PNS)

Afferent: transmits sensory and visceral info from the organs to the CNS (back)
- includes: somatic and special senses and visceral info
- mostly pseudo-unipolar neurons in a ganglion
Efferent: transmits information from the CNS to organs in the periphery (effector organs -- muscles and glands) (there)
- somatic and autonomic


somatic vs autonomic nervous system

Somatic: voluntary (SNS)
- motor neurons that regulate skeletal muscles
Autonomic: involuntary (ANS)
- neurons that regulate the function of internal organs
- parasympathetic and sympathetic nervous systems


What is the Enteric nervous system and what does it communicate with

network of neurons in the walls of the digestive tract
- communicates with the autonomic / parasympathetic nervous systems


Sympathetic vs Parasympathetic nervous system

The sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response.
The parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.
- opperate in tandem to maintain homeostasis


What is a neuron?

Building blocks of the nervous system, communicate by transmitting electrical impulses and signals called action potentials
- excitable
- primary class of cell found in the nervous system


What is the soma made up of and what does it do? (soma = cell body)

contains: nucleus, mitochondria, endoplasmic reticulum, golgi apparatus and ribosomes
role: protein synthesis and cellular metabolism


What are dendrites?

receives signals from other neurons at synapses
(signal goes from dendrites to the axon terminal)


What is the axon's role and what is it composed of?

role: to transmit electrical impulses called action potentials
beginning of the axon: axon hillock
- where it originates and where action potentials are initiated
End of the axon: axon terminal
- releases neurotransmitter


Leak channels

channels that are always open and allow ions to move along their gradient
- for sodium and potassium


ligand-gated channels

open in the presence of a specific binding substance, usually a hormone or neurotransmitter
- located in the dendrites and cell body


voltage gated channels

open and close in response to changes in membrane potential
- for sodium, potassium and calcium
- located throughout neuron but mostly in the axon hillock for sodium and potassium and in the axon terminal for calcium


Pseudo-unipolar neurons

have a single process extending from the cell body -- mostly sensory neurons


Bipolar neurons

A neuron that has only two projections (one axon/one dendrite) from the cell body
- only found in the retina of the eye and the olfactory (smell) epithelium


multipolar neurons

neuron with one axon and many dendrites; most common type of neuron



neurons located only in the CNS and account for 99% of the neurons in the body
- perform all the functions if the CNS (process info, create and send commands, complex functions)


What is the nuclei?

cluster of neuron cell bodies in CNS


tract vs nerve

tract: bundle of axons in CNS
nerve: bundle of axons in PNS



axons travel together in bundles from one brain hemisphere to the other


Nerve vs gangli

nerve: bundle of axons in PNS
ganglia: bundle of neurons in the PNS


What are the 5 types of glial cells?

1. Schwann Cells.
2. Oligodendrocytes.
3. Astrocytes.
4. Microglia.
5. Ependymal cells.

- secondary class of cell found in the nervous system
- provides structural integrity to the nervous system and chemical and anatomical support to neurons to carry on their functions


What are oligodendrocytes?

A type of glial cell that forms insulating myelin sheaths around the axons of neurons in the central nervous system. (allows it to transmit action potentials easier and faster)


What are schwann cells?

A type of glial cell that forms insulating myelin sheaths around the axons of neurons in the peripheral nervous system.


What is the resting membrane potential?

-70mV (for neurons)
described as the potential inside the cell relative to that outside of the cell
- established by Na/K pump


What 2 factors determine resting membrane potential?

1. concentration gradients for sodium and potassium
2. membrane permeability to those ions


What does equilibrium mean?

when there is no net force for an ion to move across a membrane
chemical force = negative electrical force = 0


What is equilibrium for potassium and which way does it go in the cell?

61 mV x log (4mV/140mV)
= -94 mV
diffuses out of the cell
***membrane is much more permeable to potassium than it is to sodium and more potassium leaves the cell than sodium enters
located inside the cell with organic anions


What is equilibrium for sodium and which way does it go in the cell?

61 mV x log (145/15)
= +60 mV
diffuses into the cell
located outside of the cell with chloride (Cl)


What are the properties of graded potentials

- proportionate in amplitude to the size of the input stimulus
- depolarizing or hyperpolarizing
- temporal or spatial
- don't require voltage gated channels


How do graded potentials in neurons trigger an action potential

Graded potentials bring the membrane to the threshold and act as a regenerative mechanism -- membrane depolarization to threshold


What is the ionic basis of an action potential

the action potential is triggered by a graded potential that causes the membrane to depolarize until it reaches the threshold for activation of voltage-gated sodium channels


What are the gating mechanisms for voltage gated channels (4 steps)

activation, deactivation, inactivation and reactivation for Na and K channels


Propagation of action potentials

goes from the soma to the axon terminal, depolarizing as it goes along


What is the purpose of a graded potential?

they determine if an action potential will occur or not


Excitatory vs Inhibitory graded potentials

Excitatory: depolarizing (bump goes up/positive)
- action potential
Inhibitory: hyperpolarizing (bump goes down/negative)
- no action potential


Action Potentials

large changes of membrane potential (voltage), communicate over long distances and don't decrease in size
- travel along axons from the cell body to the axon terminal (afferent: from receptor to terminal)
- excitable membranes can generate them
- looks like a big bump on the diagram


What does threshold mean?

the level of depolarization necessary to elicit an action potential


What does temporal summation mean (graded potential)?

Repeated same stimulus close together in time (second one happens before the first is even over)
- triggered from one


What does spatial summation mean (graded potential)?

When different stimulli overlap in time
- triggered from many close together


Sub vs suprathreshold

Subthreshold: doesn't generate an action potential (not quite enough)
- decreases in strength
Suprathreshold: generates an action potential


Action Potentials

large changes of membrane potential (voltage), communicate over long distances and don't decrease in size
- travel along axons from the cell body to the axon terminal (afferent: from receptor to terminal)
- excitable membranes can generate them
- unidirectional
- looks like a big bump on the diagram


What is depolarization caused by?

by an increased Na+ permeability


What happens with Na and K channels at the action potential (top of the hill)

Na channels close while K channels open


What are the permeabilities for K and Na at resting

K is 25x stronger than Na


What 2 gates are associated with Na

1. Activation gate (always closed, positive feedback (cell is depolarized, activation gates remain open), opens at threshold and depolarization and is voltage dependent) -- located at the axon hillock and axon
2. Inactivation gate (voltage and time dependant, close during repolarization, open during depolarization)


How do voltage gated potassium channels operate

they have one channel that is voltage and time dependent that runs on negative feedback


What is the threshold

the minimum depolarization necessary to induce the regenerative mechanism for the opening of Na channels
- supra and regular threshold will cause an action potential


What is the refractory period?

the period of decreased excitability following an action potential


Absolute vs relative refractory periods

Absolute: all of depolarization and most of repolarization phases, second action potential cannot be generated and sodium gates are inactivated

Relative: last part of the repolarization and hyperpolarization phases (longer than absolute)
- a second AP can be generated with a stronger stimulus
- due to the increased permeability to K+ that continues beyond the repolarization phases


What is the all or none principle when it comes to refractory periods?

- action potentials cannot sum
- due to the absolute refractory period prevents an overlap of AP

*** states that the strength of a response is not dependent on the strength of the stimulus


How is information about stimulus intensity stored?

Encoded by changes in the frequency of AP or the # of AP generated


How are action potentials "transported" aka propagated

moves down from the axon hillock to the axon terminal
- flows to adjacent areas of the plasma membrane by electronic conduction (the passive spread of voltage changes along a neuron)


How does transportation of AP through myelinated vs unmyelinated axons vary?

Myelinated: requires activation of voltage-gated sodium channels only in the nodal areas
Unmyelinated: requires activation of voltage-gated sodium channels along the entire length of the axon


How does transportation of AP through myelinated vs unmyelinated axons vary?

Myelinated: requires activation of voltage-gated sodium channels only in the nodal areas (nodes of ranvier)
Unmyelinated: requires activation of voltage-gated sodium channels along the entire length of the axon


What are 3 factors that'll affect propagation (aka AP transportation)

1. the refractory period
2. axon diameter
3. myelination


Absolute vs relative refractory periods

Absolute: all of depolarization and most of repolarization phases, second action potential cannot be generated and sodium gates are inactivated
- caused by the inactivation of sodium channel that were originally opened to depolarize the membrane

Relative: interval of time during which a second action potential can be initiated (requiring a greater stimulus than before)
- last part of the repolarization and hyperpolarization phases (longer than absolute)
- a second AP can be generated with a stronger stimulus
- due to the increased permeability to K+ that continues beyond the repolarization phases
- caused by the inactivation gate of the Na+ channel


How does communication occur across chemical synapses?

At a chemical synapse, an action potential triggers the presynaptic neuron to release neurotransmitters.
- communicate via action potentials and neurotransmitters


How are neurotransmitters released in synapses?

nerve impulse arrives at the presynaptic terminals causing movement towards the presynaptic membrane or synaptic vesicles, which fuse with the membrane and release a neurotransmitter.


Fast vs. Slow responses (at synapses)

Fast: electrical
Slow: chemical


What is neural integration? what does the axon hillock do in this process

a way of opening up the communication pathways in the brain that may have become blocked or shut down because of stress
- axon hillock is the manager, sums the total inhibitory and excitatory signals


What is a synapse?

A structure that allows a neuron or nerve cell to pass an electrical or chemical signal to another neuron or effector organ (muscle/gland)
- connects presynaptic and postsynaptic cells together


What are the 2 parts of a synapse?

1. axon terminal of the presynaptic cell
2. membrane of the postsynaptic cell


What type of cells are postsynaptic

neurons or nonneuronal cells


What are electrical synapses?

two neurons that are linked together by gap junctions
- mechanical and electrically conductive link
- bidirectional


Where are electrical synapses located?

- retina. ofthe eye
- certain areas of the cortex
- areas of the brainstem that regulate breathing
- hypothalamic neurons


Where are electrical synapses located?

- retina of the eye
- certain areas of the cortex
- areas of the brainstem that regulate breathing
- hypothalamic neurons


What is a synapse?

A structure that allows a neuron or nerve cell to pass an electrical or chemical signal to another neuron or effector organ (muscle/gland)
- connects presynaptic and postsynaptic cells together
- most are chemical


What are electrical synapses?

two neurons that are linked together by gap junctions
- pass an electrical signal / current from the cytoplasm of one cell to another through gap junction pores
- mechanical and electrically conductive link
- bidirectional


What is the synaptic cleft?

the area between a presynaptic and postsynaptic cell (small space with fluid)


What are the 4 types of neuron to neuron synapses?

1. axodendritic
2. axosomatic
3. axoaxonic
4. dendro-dendritic


Why do synaptic delays occur?

caused by changes in calcium and the release of the neutrotransmitter
- takes time to open, enter and trigger release of the neurotransmitter from vesicles


What are channel linked receptors? aka ligand gated ion channels

aka ionotropic receptors
- have the receptor and transducing functions as part of the same protein molecule
- fast and direct responses


What are g-protein linked receptors?

largest family of cell surface receptors
- aka metabotrophic receptors
- slow acting responses
- mediate responses to signal molecules


What does a fast response in a postsynaptic neuron mean?

occurs when a neurotransmitter binds to a channel link receptor
- always related to the opening of ion channels


What is a postsynaptic potential?

aka a graded potential - a fast response resulting in a change in membrane potential (electricity) in response to receptor-neurotransmitter binding


What does a slow response in a postsynaptic neuron mean?

G-protein receptor response
- can trigger the opening/closing of ion channels
- can also trigger the activation/inhibition of a second messenger system


What are the 3 G-proteins?

alpha, beta and gamma


What are ionotropic receptors?

membrane-bound receptor proteins that respond to ligand binding by opening an ion channel and allowing ions to flow into the cell, either increasing or decreasing the likelihood that an action potential will fire


What are the 2 types of postsynaptic potentials and how do they affect synapses?

Excitatory: depolarizing -- more likely to produce an action potential
Inhibitory: hyperpolarizing -- less likely to produce an action potential (membrane stabilization)


What does depolarizing a postsynaptic cell do?

brings the membrane potential closer to the threshold (-55mV)


What are the concentrations during a fast EPSP?

sodium electrochemical forces are stronger than potassium, meaning more sodium moves in than potassium moves out (negative inside - depolarization)


What is divergence?

It allows a neuron to communicate with multiple others in a network
* think diverges out


What is convergence?

it allows a neuron to receive communication from multiple other neurons
* think converges in


What 2 things determine if an AP is generated or not?

the axon hillock and threshold


What is neural integration?

the summing of input from various synapses at the axon hillock of the postsynaptic neuron to determine if it'll generate AP's


What is summation and what are the 2 types?

adding effects of action potentials
- to create an AP
1. temporal (one synapse releases NT over a period of time -- AA creates it)
2. spatial (several presynaptic neurons release NT at the same time -- AB creates it)


What are neurotransmitters

chemical messengers of neurons


What are 4 of the most common neurotransmitters?

1. Acetylcholine (choline derivative)
2. Biogenic Amines (dopamine, epinephrine, norepinephrine, serotonin, histamine)
3. Amino acid neurotransmitters (glutamate, aspartate, glycine, GABA)
4. Neuropeptides (TRH, Vasopressin, oxytocin, endorphins, etc.)


What is the most abundant neurotransmitter and where is it found

located in the PNS and CNS however it is most abundant in the PNS
- found in efferent neurons of both somatic and autonomic branches


Where is acetylcholine synthesized and what enzyme is used?

in the cytosol of the axon terminal -- uses choline acetyl transferase (CAT)
acetyl CoA + choline = acetylcholine + CoA


Where is acetylcholine degraded and what enzyme is used?

occurs in the synaptic cleft -- uses acetylcholinesterase (AChE)
acetylcholine = acetate + choline


What is a cholinergic synapse?

a synapse using acetylcholine


What are the 2 types of cholinergic receptors?

1. nicotinic cholinergic receptors (ionotropic -- 2 binding sites -- nicotine binds to it)
2. Muscarinic cholinergic receptors (metabotropic -- muscarine binds to it)


Where are nicotinic receptors located? (x3)

1. skeletal muscles
2. ANS
3. CNS


Where are muscarinic receptors located? (x3)

1. smooth and cardiac muscles
2. endo and exocrine glands
3. CNS


What are biogenic amines?

Products of amino acids (NH2)


what are the 3 catecholamines, where do they come from and why?

they are a group of substances released into the blood in response to physical or emotional stress
- derived from tyrosine
1. dopamine
2. norepinephrine
3. epinephrine

1 - CNS
2/3 - smooth/caridac muscle cells and CNS


Where is serotonin derived from and where is its receptor?

derived from tryptophan, CNS


Where is histamine derived from and where is its receptor?

from histidine, CNS


What 2 enzymes degrade biogenic amines?

1. monoamine oxidase (MAO)
- found in synaptic cleft, mitochondria of the axon terminal and glial cells
2. catechol-o-methyltransferase (COMT)
- found in synaptic cleft


What are the 3 steps of synthesis of biogenic amines

1. begins in the cytosol of the axon terminal
2. packaged into synaptic vessels
3. released


Beta 2 has an affinity for what?



Alpha 1/2 and Beta 1 have affinity for what?



Beta 3 has an affinity for what?

equal amounts for epinephrine and norepinephrine


Where is serotonin located and what are its primary functions?

located in the brainstem, functions in sleep regulation and as a mood stabalizer


Where is histamine located and what are its primary functions?

located in the hypothalamus, gets released when the immune system is defending against a potential allergen
(paracrine actions)


What amino acid neurotransmitters are excitatory and which are inhibitory?

excitatory: aspartate and glutamate
inhibitory: glycine and GABA


What are neuropeptides?

short chains of amino acids, also known as hormones
- modulate responses caused by other neutrotransmitters
- synthesized in the cell body and transported by vesicles to the axon terminal
ex. opium (inhibitory), TRH, endorphins, oxytocin, vasopressin, substance p


What is the difference between neuropeptides and neurotransmitters?

peptides: large, slow acting, prolonged action
transmitters: small, fast acting, short term response


What hormone does alpha cells secrete?

glucagon -- controls blood sugar levels


What hormone does beta cells secrete?

Insulin -- allows the body to use glucose for energy