Chapter 7 - The Nervous System Flashcards
What is the main cell and structural and functional unit of the nervous system?
neuron
What are the TWO main divisions the nervous system is divided into?
Describe what is contained within these divisions
Which of these divisions contains further subdivisions?
- Central Nervous System (CNS): brain and spinal cord
- Peripheral Nervous System (PNS): cranial nerves and spinal nerves
We know the two main divisions of the nervous system are the CNS and the PNS.
The PNS can be divided into further subdivisions. Name them and describe their functions.
- Somatic Nervous System (SNS): voluntary control of body function via skeletal muscle
- Autonomic Nervous System (ANS): involunatry control of body function + regulate glands (cardiac muscle + smooth muscle) -> has 2 divisions sympathetic NS vs parasympathetic NS
The autonomic nervous system (ANS) can be divided into two divisions known as the __________ __________ ________ vs. ___________ _________ ___________
sympathetic nervous system (SANS)
parasympathetic nervous system (PANS)
Neurons are also known as ________ cells
nerve
What cells make up the nervous system tissue?
neurons
neuroglia
What is the overall function of neurons?
conduct electrochemical impulses
usually cannot divide
What is the function of neuroglia?
supporting/helper cells that assist in the function of neurons
cannot conduct impulses, but can divide
We know that neuroglia assists in the function of neurons. How do they do this? Be specific
- make myelin (fatty substance/phospholipids that wraps around axon)
- release nutrients for neurons
- involved in immune response
Neuroglia are _________ common than neurons; ___:____ - _____:____
more
5:1 - 10:1
Which cells are examples of neuroglia? Name their function
If possible, name which division of the NS they are involved in
SOMA (COPS)
- Schwann cells: myelination of axon in PNS
- Oligodendrocytes: myelination of axon in CNS
- Microglia: engulf things and clear debris in NS
- Astrocytes: provide barrier between nervous tissue + blood
What does the term “electrochemical” impulse mean/refer to?
- “electro” charge because of ion movement across the cell membrane
- “chemical” refers to the neurotransmitters release
- flow of charges across the membrane leads to the release of a neurotransmitter
What is myelin?
Which neuroglial cell makes myelin?
fatty substance that wraps around an axon
Schwann cells
Oligodendrocytes
Generally describe the way in which the nervous system works.
- Receive a stimulus (information)
- Transmits information to the integration center (CNS)
- CNS processes/integrates information
- CNS transmits information to effectors (muscles and glands)
Neurons use ____________ signals to ________/_______ information
electrochemical
transmit/process
In which ways do neurons use electrochemical signals to transmit/process information?
- electrical signals (impulse): action potentials (AP); involved charges (ions)
- chemical messengers: neurotransmitters (NT)
AP must be conducted to release NT
Name the different parts to a neuron and describe their function
- Dendrites: branched cellular extentions; information recieving end of neuron
- Soma (Cell body): contain nucleus
- Axon Hillock: generate impulse (AP)
- Axon: Sends information out
- Axon terminal: release chemical messengers (NT); NT can be excitatory or inhibitory
An action potential travels along the _______
axon
Neurons can be classified based on their ________ or _________ _____ _________
function
mode of transmission
Classify the neurons based on their function
Describe their function
sensory neurons (afferent neurons): transmit information INTO the CNS from the environment
interneuron: found in integrating center/CNS
motor neurons (efferent neurons): transmit information OUT of CNS to effectors
Sensory neurons are also known as ________ neurons
afferent
Motor neurons are also known as _______ neurons
efferent
Classify the neurons based on their mode of transmission
Describe their function
excitatory neurons: stimulates target cell -> release excitatory NT
inhibitory neurons: inhibit target cell -> release inhibitory NT
Define a neurotransmitter (NT), and where are they released from?
- chemical messengers
- released from axon terminals (from excitatory/inhibitory neurons)
Define an action potential (AP). Where would you find an AP in the neuron?
- an electrochemical signal/impulse
- originates from the axon hillock.
Describe the movement of an action potential (AP)
- electrochemical signal/impulse originals from axon hillock
- travels along the axon
- to axon terminal
- release neurotransmitters (NT)
The axon hillock is located between the ________ and the _______
soma
axon
Define membrane potential (MP)
- difference in charge between the inside and outside of the cell (neurons axon)
- creates an electrical voltage across the cell membrane
Describe the relationship between membrane potential (MP) and the Na+/K+ pump
MP is maintained by the Na+/K+ pump (makes the inside of the cell negative)
What creates a charge potential/voltage across a cell membrane?
Na+/K+ pump because more positive ions (3Na+) are moving out, while only 2K+ ions are moving in; uneven charge
MP for a neuron “at rest” is called the ________ _________ ________
resting membrane potential (RMP)
Although the RMP values may ______ among different neurons, the _______ are ALWAYS _________
differ
values
negative
What is the voltage of the RMP for a typical neuron
-70 mV (interior of neuron
If a neuron measures at -70mV, what does this mean?
neuron is “at rest” and is not receiving a information/stimulus
Why is RMP value always negative?
bc of the uneven distribution of ions due to Na+/K+ pump
The existence of MP allows for the generation and propagation of an _______ _______ along the _______
action potential (AP)
axon
Facilitators, such as channels, help substance move from an area of _________ to ________ concentration (____________ _________)
high
low
facilitated diffusion
Describe what happens to the inside/internal charge of the axon membrane when Na+ channels open and K+ channels open
- when Na+ channels open, the inside of the cell becomes more positive due to an influx of cations
- when K+ channels open, the inside of the cell becomes more negative due to an efflux of cations
What happens to the MP when a neuron receives a stimulus?
rapid change in MP across the axon from negative to positive -> then back to negative
Electrical changes travel along the axon and these electrical charges can be measured by a __________ in _____
voltmeter
mV
Charge differences are displayed by an _________ ________ _______
action potential (AP) graph
Define depolarization
Provide an example
becomes more positive inside -> move away RMP (cations entering/anions exiting)
ex: Na+ influx/entering
Define repolarization
Provide an example
becomes more negative inside -> move toward RMP (cations exiting/anions entering)
ex: K+ efflux/exiting
Define hyperpolarization
becomes VERY negative inside; further away from RMP
Neurons are stimulated by a _________ (ex: ___________)
ligand
neurotransmitter
What is a ligand?
a chemical substance that attaches to another molecule (ex: neurotransmitters)
What is the function of ligand?
ligands bind to LG ion channels and OPENS for cations (at dendrite)
Cations involved: Na+, Ca2+, K+
A channel is open when _______ to a ________
bound
ligand
Describe what is happening on an AP graph where initial depolarization occurs.
Na+ influx at axon hillock due to LG Na+ channels opening (NOT real depolarization)
What opens at the end of RMP?
LG Na+ channel (initial depolarization)
What does Na+ want to enter the cell instead of exit?
- want to enter via facilitated diffusion due to high [Na+] outside cell due to Na+/K+ pump
- Na+ attracted to negative charge inside cell
- wants to follow electrochemical gradient
Ligand-gated (LG) ion channels can exist in ______ states: ________ and ________
2
open (no ligand bound)
closed (ligand bound)
What is threshold?
the minimum mV needed for an action potential to occur
What is the value of the threshold of an action potential?
-55 mV
What causes a neuron to reach threshold?
influx of Na+ inside due to opening of LG Na+ channel
What happens when a neuron reaches threshold?
voltage-gated (VG) Na+ channels open at axon hillock -> more Na+ enters
When does rapid depolarization occur?
occurs when VG Na+ channels open and let in more Na+
more VG Na+ channels will open due to positive feedback
How does positive feedback contribute to rapid depolarization?
more VG Na+ channels will open
True or False: A neuron must (at the very minimum) reach a threshold value in order to have an AP
True, the threshold is the minimum needed for AP to occur
What is the voltage value at the peak of a neuronal AP? What happens at peak (what opens and closes at peak)
peak: +30-40 mV
VG Na+ channel close -> depolarization STOPS
VG K+ open (K+ efflux, cell becomes more negative inside; repolarization occurs)
When the VG Na+ channel close and the VG K+ open, what happens?
repolarization occurs as the cell becomes more negative inside due to loss of cations (move toward RMP)
What is the difference between LG-ion channels and VG-ion channels
- LG-ion channels respond/open when a ligand is bound to it
- VG-ion channels respond to a certain voltage and will open when a certain mV/voltage is reached
What happens when repolarization overshoots?
hyperpolarization
Why does repolarization overhshoot?
VG K+ channels are slow to close -> K+ keeps leaving -> makes inside too negative (past RMP); will eventually close
What part of the AP graph indicated when the VG K+ channel fully closes
the bottom-most trough of hyperpolarization
How does the AP return to RMP after hyperpolarization?
Na+/K+ pump brings MP back to RMP
Be familiar with the 9 steps of how to generate an AP
Neuron stimulated (receives info @ dendrite) by ligand -> LG Na+ channel opens at dendrite
Na+ influx at axon hillock -> neuron becomes more positive inside -> initial depolarization
MP eventually reaches the threshold of AP at -55mV
At threshold, VG Na+ channel open at axon hillock
More Na+ enter + more VG Na+ channel open by positive feedback -> rapid depolarization
MP reaches +30-40mV (peak of AP) -> VG Na+ channels close, VG K+ channels open
K diffuses out -> repolarization (more NEG inside)
Repolarization overshoots due to slow closing of VG K+ channels = hyperpolarization
Na+/K+ pump brings back to RMP
Compare the location of a LG ion channel vs VG ion channel
LG ion channel: dendrite, soma
VG ion channel: axons; axon hillock
AP are generated through the involvement of the opening of __________ and _________
LG ion channels
VG ion channels
Draw an AP graph and label the following: RMP, opening of LG- Na+ channels, (initial) depolarization, threshold, opening of VG- Na+ channels, (rapid) depolarization, peak, closing of VG- Na+ channels, opening of VG- K+ channels, the slow closing of VG- K+ channels, VG-K+ channels all closed, hyperpolarization.
Check answer on slide #19 on ch 7
True or False: If you double the stimulus size/strength, the amplitude (peak) of the AP will also double
Explain your answer
False, AP are all-or-nothing; once hit 40mV VG Na+ channel will close and VG K+ will open, causing depolarization. Increasing stimulus size/strength will increase frequency
APs are described as an “all-or-none” process. What does this statement mean?
The AP is always a full response; AP will happen only once threshold has been reached
will 100% happen or not happen at all
AP have the same _______/________ regardless of stimulus strength; neuronal AP will always reach a peak of ______ - ________mV
amplitude/magnitude
+30 - 40mV
What happens to an AP if the stimulus strength is weak?
if stimulus strength is not enough to reach threshold -> no AP
What happens to an AP if the stimulus strength is increased?
AP frequency will increase
What is a refractory period?
period of time when a 2nd stimulus cannot generate another AP, regardless of stimulus strength
1st AP must finish before a 2nd AP begins
What controls the frequency of AP?
refractory periods (stimulus strength too)
What are the two types of refractory periods?
absolute refractory period (ARP)
relative refractory period (RRP)
Compare Absolute Refractory Period vs Relative Refractory Period
ARP: cannot have a 2nd AP due to VG Na+ channels are inactivated from peak to end of repolarization at -70mV
RRP: low probability because the inside neuron is very negative (way below threshold and less likely to reach threshold) -> due to hyperpolarization (slow closing of VG K+ channels)
During which of the refractory periods would you definitely not be able to generate an AP?
ARP
Identify the area of ARP and RRP on an AP graph
check answer on slide #23 ch. 7
What is myelin composed of, what is its function, and where does it come from?
- layer of phospholipids (fat)
- increases the speed of AP propagation via saltatory conduction
- oligodendrocytes (CNS) + Schwann cells (PNS)
Myelin does not _____ the entire ______ length
wrap
axon
What are nodes of ranvier? Function?
myelin gaps (gaps w no myelin) -> help improve electrical transmission
True or False: AP can occur where myelin is present
false
Why can’t AP occur where myelin is present?
myelin blocks all the VG Na+ channel -> no AP
What area(s) of the axon do AP occur? (note: NOT asking for where they are generated)
Nodes of Ranvier
Describe saltatory conduction
AP travels and leaps from node to node until it reaches the axon terminal -> allows for faster conduction of AP
Name the diseases that damage the myelin sheath/covering
Name which division of the NS that they damage myelin in
- multiple sclerosis: axon of CNS
- gullain-barre syndrome: axon of PNS
What is multiple sclerosis and what are the symptoms?
- autoimmune disease; immune system destroys myelin of neurons in CNS
- vision, bladder, bowel problems; fatigue, numbness, walking difficulty
Why do people with Multiple Sclerosis have the inability to walk/contract their muscles in the later stages of the disease?
Poor AP propagation due to loss of myelin = slower/no communication with skeletal muscle cells
Define synapse
space/site of communication between neuron and target cell
Give some examples of target cells that neurons communicate with
neurons, muscle cells, glands
What are the three types of synapses?
Define them (hint: based on specific target cell)
- Neuronal synapse: synapse between neuron and neuron
- Neural Muscular Junction (NMJ): synapse between neuron and muscle cell
- Neuroglandular junction: synapse between neuron and glandular cell
Aside from the Na+/K+ pump present at the axonal membrane (axon hillock), what other 2 important transporters (Ex - channels) are present along the axonal membrane?
VG Na+ and K+ channel
T/F: A neuron typically communicates with only one neuron.
False, each neuron can make about 7000 connections to many other neurons
In neuron-to-neuron communication, communication is between what parts of the pre and post-synaptic neuron?
pre-synaptic: axon terminal boutons
post-synaptic: dendrite spine
there are multiple points of contact that can change overtime
What is the site of communication between neurons and other neurons/target cells?
synapse/synaptic cleft
What are the components of a neuronal synapse?
Describe each (location/function)
pre-synaptic membrane: membrane of axon terminal
NT vesicles: membrane-bound pouches that contain NT in axon terminal
post-synaptic membrane: membrane at surface of target cell
NT receptors: on surface of post-synaptic membrane; protein receptors that recognize and bind to specific NT
Synaptic cleft: gaps between pre and post-synaptic neuron; space where NT are released into
Where are NT vesicles typically found? What do you call the space where the NTs are released into when two neurons are communicating with each other?
NT vesicles are found: axon terminal (of presynaptic cells)
NT released when two neurons are communicating: synapse/synaptic cleft
List the sequence of events/steps involved in the release of NT
Neuron is stimulated -> AP generated -> AP reaches axon terminal
VG Ca2+ channels on presynaptic membrane (axon terminal) open -> Ca2+ enters (naturally high outside and wants to enter)
Ca2+ causes NT vesicles to fuse with presynaptic membrane
NT released into synaptic cleft
NT bind to NT receptors present on the post-synaptic membrane
NT receptors become activated: post-synaptic neuron will either be “excited” or “inhibited” (depending on NT or NT receptor involved)
What do NTs do after they have been released?
NT binds to NT receptors on the post-synaptic membrane
Compare excitatory and an inhibitory neuron
Give an example
excitatory neuron: release excitatory NT and excite post synaptic cell/target (Glutamate)
inhibitory neuron: release inhibitory NT and inhibit post synaptic cell (ex: GABA)
What types of neurons have EPSP and which ones have IPSP? Which ones are more/less likely to have an AP?
Excitatory neuron: have EPSP -> “initial/slow” depolarization -> 2nd cell very likely to have AP if reaches threshold
Inhibitory neuron: have IPSP -> very unlikely to have AP
What is the main excitatory NT in the CNS?
What is the main inhibitory NT in the CNS?
excitatory: Glutamate (ligand/chemical/NT)
inhibitory: GABA (ligand/chemical/NT)
Explain how glutamate leads to an EPSP
Once glutamate is released from axon terminal and is in the synaptic cleft, it acts as a ligand to bind to glutamate receptors (glutamate ion channels)
note: IS the LG Na+ channel/Glutamate/Na+ channel
Once bound, opens ion channels either directly or indirectly and allows of influx of Na+ (sometimes Ca2+) into the post synaptic cell (dendrite)
This causes the initial depolarization at end of RMP, AKA EPSP
Is an EPSP a “real” AP?
EPSP is not a real AP, because true AP starts once threshold has been met -> rapid depolarization
Does the pre-synaptic or post-synaptic cell create an EPSP/IPSP?
post-synaptic cell
What must a LG ion channel act as first, before it can perform its second function?
- receptor
- channel
must bind to ligand first (receptor), before it can open and act as a channel
What ions are usually involved in the generation EPSP? In what part of the neuron are EPSP generated?
Na+ (sometimes Ca2+)
Dendrite of post-synaptic neurons
What are some properties/characterisics of EPSP?
- move MP closer to threshold -> likely to have AP
- additive and can summate; several neurons can have excitatory inputs on one post-synaptic membrane/target cell
Explain how GABA leads to an IPSP
Once GABA is released from axon terminals into the synaptic cleft, it acts as a ligand and binds to GABA receptors (GABA ion channels)
note: is the GABA Cl- channel
Once bound, channel opens (directly/indirectly) and allows for influx of Cl- at the post synaptic membrane/dendrite.
This causes hyperpolarization, which occurs at end of RMP, AKA IPSP
What channels do GABA open? Which is the main one?
Both make MP more negative
LG Cl- channel: Cl- influx (main one)
LG K+ channel: K+ efflux
What channels does Glutamate open? Which is the main one?
Both make MP more postive
LG Na+ channel : Na+ influx (main one)
LG Ca2+ channel : Ca2+ influx
What are some properties/characterisitcs of IPSP?
- move MP farther from threshold -> unlikley to reach threshold and generate AP
- are additive and summative; several neurons can have inhibitory inputs on one post-synaptic membrane (target cell)
Why do IPSPs make it very unlikely that a neuron will have an AP?
IPSP leads to an influx of Cl- (or efflux of K+), making the MP more negative, moving it farther from the threshold (-55mV). Without reaching threshold, an AP will never occur.
What ions are usually involved in generating IPSP? In what part of the neuron are IPSPs generated?
Cl- (influx) or K+ (efflux)
Generated at dendrite of post-synaptic cell/neuron
True or False: A neurons dendrite can have receptors for both glutamate and GABA (on the same neuron)
True, a neuron has receptors for several NT, but a neuron can only release one type of NT
What do you call a neuron that produces/releases GABA?
What do you call a neuron that produces/releases Glutamate?
Gabaergic neuron: GABA
Glutamatergic neuron: Glutamate
Neurons can often receive both excitatory and inhibitory input…
at the same time
What are the two main types of neurotransmitter receptors?
ionotropic NT receptors
metabotropic NT receptors
How do iontropic NT receptors function? What are they also known as? Location?
- receptor for NT
- channel for ion
dendrite postsynaptic membrane
ex: LG ion channel
How do metabotropic NT receptors function? What are they also known as? Location?
- only as a receptor for NT -> a channel is involved but is separate from the receptor
dendrite of postsynaptic membrane
ex: G-protein-coupled receptors
True or False: A neuron’s axon terminal can release both glutamate and GABA at the same time
False, only releases one type
True or False: Glutamate, GABA and ACh can bind to ionotropic receptors
True, but they can also bind to both ionotropic and metabotropic receptors
Which ligands/NT are able to bind ionotropic and metabotropic receptors?
- Glutamate
- GABA
- ACh (acetylcholine)
What is the specific name of the receptor that ACh binds to?
nicotinic ACh receptor (ionotropic NT receptor)
What is unique about the opening of nicotinic ACh receptor, compared to other NT receptors such as Glutamate receptor/GABA receptors
nicotinic ACh requires 2 ligands (ACh) to be bound to the receptor in order for it to open
Where is the nicotinic ACh receptor located?
dendrite of post-synaptic membrane
What ions does the Nicotinic ACh receptor allow passage of? Does this lead to an EPSP or IPSP?
Na+ (sometimes K+, Ca2+, Cl-)
EPSP because influx of positive ions from Na+
What does it mean when we say that metabotropic NT receptors “indirectly” open ion channels?
Indirectly opens channels further along the post-synaptic membrane by activating signal transduction pathways (sequence of intracellular events)
True or False: G proteins (found inside the neuron) are couples/linked to ionotropic NT receptors?
False, G proteins are coupled/linked with metabotropic NT receptors
What NT, when binds to its receptor, activates G protein
Norepinephrine (NE)
Explain how G-protein Coupled Receptors (Noradrenergic Norepinephrine Receptors) work
Norepinephrine binds to metabotropic receptor that has G protein (3 subunits)
G protein is activated
G proteins ɑ subunit dissociates and travels through the cell membrane to activated adenylate cyclase (enzyme) that is embedded in cell membrane
Adenylate Cyclase catalyzes hydrolysis of ATP into cAMP
cAMP activates protein kinase (PK)
Protein kinase (PK) phosphorylates ion channel
(embedded in cell membrane) -> ion channel opens -> diffusion of ions
What is an example of a metabotropic NT receptor?
AKA?
What NT does it act as a receptor for?
Noradrenergic (Norepinephrine) receptor
(AKA G-protein coupled receptor)
receptor - for Norepinephrine
With regards to a sequence of intracellular events taking place inside the neuron dendrite’s post synaptic membrane, what is the function of cAMP (what enzyme does it activate)?
cAMP activates protein kinase (PK)
True or False: ACh always acts as an excitatory NT, and GABA always acts as an inhibitory NT
False, both ACh and GABA can act as either excitatory or inhibitory NT depending on the type of receptor they bind to and the location of the receptor in the body
Many NT have ______ receptors
multiple
T/F: Glutamate and GABA can ONLY bind to ionotropic receptors.
Explain your reasoning
False, Glutamate can bind to ionotropic and metabotropic glutamate receptors. GABA can bind to ionotropic and metabotropic GABA receptors
Name the different types of ionotropic glutamate receptors
KAN
(3) ionotropic glutamate receptors: Kainate, AMPA, NMDA
Name the different types of metabotropic glutamate receptors
mGluR1 through MGluR2
Name the different types of ionotropic and metabotropic GABA receptors
ionotropic = GABAA
metabotropic = GABAB
Some NT can be excitatory or inhibitory, depending on the _____ of receptor they bind to and ______ of the receptor in the body
type
location
What type of receptors will make ACh excitatory? Inhibitory? Are they ionotropic or metabotropic? Include location
excitatory - when bound to nicotinic receptor (ionotropic) on skeletal muscle
inhibitory - when bound to muscarinic receptor (metabotropic) on smooth muscle; will relax
In what specific location will GABA act as an inhibitory and excitatory NT?
inhibitory - mature/adult brain (Cl- influx; K+ efflux)
excitatory - immature/developing brain (children; efflux of Cl-)
Explain why GABA acts as an excitatory NT in an immature/developing brain?
Cl- gradient is reversed in the immature brain
high Cl- inside -> Cl- leaves cell -> more POS inside -> depolarization (excitatory)
What is nitric oxide (NO)?
NT and gas
What is unique about nitric oxide (NO) compared to the other NT we learned about?
NO is able to DIFFUSE across presynaptic membrane without a vesicle and diffuse into the target cell
What does nitric oxide (NO) do when it diffuses into the post-synaptic cell and describe the series of events that happen
Diffuses into a target cell and binds to Guanylyl Cyclase (INSIDE THE TARGET CELL!!)
Guanyly Cyclase acts as a receptor and enzyme (dual function)
Activates production of cGMP (GTP -> cGMP)
cGMP activates Protein Kinase G (PK G) = relaxes smooth muscle = vasodilation
What is the function of protein kinase G (PK G)
relaxes smooth muscles, causing vasodilation
Explain why PDE 5 inhibitors lead to continued vasodilation
PDE 5 inhibitors increase the concentration of cGMP -> more PKG -> more vasodilation
What is the function of Guanylyl Cyclase
- receptor for nitric oxide (NO)
- enzyme (turns GTP to cGMP)
What else, besides PKG, can cGMP be converted into?
What enzyme does it need to facilitate this conversion?
GMP
uses enzyme called PDE-5 to break down cGMP into GMP
What NT does the nicotinic ACh receptor bind to?
acetylcholine (ACh)
Signal transduction pathways involve…
G-protein coupled receptors
Give an example of a G-protein coupled receptor
Noradrenergic (Norephinephrine) Receptor
