Unit 2: Neurophysiology Flashcards
The nervous system is one of two key __________ _________
control structures (the other being the endocrine system)
List some functions of the nervous system related to information
receives info, integrates info, and transduces info
What is the pathway of signalling in order
stimulus, sensor, afferent pathway, integration centre, efferent pathway, target, response
What are the two main parts of the nervous system
CNS (central nervous) and PNS (peripheral nervous)
What is the CNS made up of
brain & spinal cord
What is the PNS made up of
sensory (afferent) and motor (efferent) neurons (parts of nervous system outside of the brain/spinal cord)
What are the two cell types of the nervous system
neurons and glial cells
What are neurons
information messengers that generate and transmit signals over long distances
What are neurons made up of
soma, dendrites, axon, and axon terminals
What is the soma of a neuron
“cell body” of the neuron, that contains the nucleus and all biosynthetic materials
Why is the soma of a neuron so important
center for all chemical processes that keeps the neuron functioning and alive
Clusters of cell bodies in the CNS are called
nuclei
Clusters of cell bodies in PNS are called
ganglia
What are dendrites
the projections of the soma that receive information (dendron = “tree”; look like the ‘branches’ of the soma)
What direction do dendrites relay info
TOWARD the soma (opposite to axons)
What is an axon
cytoplasmic extension that relays information
What are bundles of axons in the CNS called
tracts
What are bundles of axons in the PNS called
nerves
In which direction do axons relay info
AWAY from the soma (opposite to dendrites)
What is an axon terminal
self-explanatory; the ends of an axon that connect the neuron to other cells
What is the state of an axon terminal and what process does it contribute to
presynaptic: contributes to the synapse
What is a synapse
the region where an axon terminal connects to its postsynaptic target cell
What is the state of the target cell in relation to synapse
postsynaptic
What is the connection between the presynaptic axon terminal and the postsynaptic target cell
synaptic cleft
What are the 5 structural classifications of neurons
- pseudounipolar
- bipolar
- anaxonic
- multipolar-CNS
- multipolar-efferent
What are pseudounipolar neurons
somatic sensory neurons
- axon and dendrites fuse during development into a single long process
What are bipolar neurons
smell/vision sensory neurons
- single axon & dendrite
What are anaxonic neurons
interneuron with no apparent axon (anaxonic - meaning not axonic)
What are multipolar-CNS neurons
interneuron of the CNS
- highly branched neurons with numerous dendrites
- no long extension for the axon
What are multipolar-efferent neurons
contains 5-7 dendrites and a single long axon (similar to multipolar-CNS but has one extension vs none)
What are the 3 functional classifications of neurons
- Afferent neurons
- Interneurons
- Efferent neurons
What does the term interneuron mean
in the CNS
What are afferent neurons
receive info from the receptor cells and transmit sensory info TOWARD the CNS
- cell bodies located outside the CNS
- has long cytoplasmic extensions that transmit info to the cells
What are interneurons
located inside of the CNS (96% of all neurons), which transmit info within the CNS and integrate information received by afferent neurons and transmit signals to efferent neurons
(basically the connection of signalling info from afferent to efferent)
- main role is to figure out what to do with information and transmit the signal forward
What are efferent neurons
receive info FROM interneurons and carry AWAY from CNS
- cell bodies located within CNS
- cytoplasmic extensions transmit information to the effectors/targets
What are glial cells
associated with neurons as helpers, but do not carry signals over long distances like neurons do, they communicate only with each other and with nearby neurons
What are the two ways glial cells contribute to neuron function
- aid in nerve impulse conduction
- maintain the microenvironment around neurons
What are the 2 PNS glial cell types
Schwann cells & satellite cells
What do Schwann cells form
myelin (layers of membrane)
What is myelin
layers of membrane that act as an electrical insulator (formed by Schwann cells in the PNS)
What are satellite cells
non-myelinating Schwann cells
What do satellite cells do instead of create myelin
support nerve cell bodies (soma)
What do Schwann cells secrete
neurotrophic factors
What is the node of ranvier
section of unmyelinated axon membrane between two Schwann cells
What is the myelin sheath
Schwann cells wrapped around a single PNS axon
What are the 4 types of CNS glial cells
- oligodendria (oligodendrocytes)
- astroglia (astrocytes)
- microglia
- ependymal cells
(review figures 2.4 & 2.5**)
What are oligodendrocytes
CNS version of Schwann cells
- wrap around axons & forms myelin to insulate CNS axons
What are astrocytes
small star-shaped cells that contact blood vessels and neurons to maintain the microenvironment to help maintain homeostasis in extracellular fluid
What are microglia
small specialized immune cells (like macrophages) that function to remove damaged cells and foreign invaders
What are ependymal cells
epithelial cells that produce cerebral spinal fluid (CSF)
- creates selectively permeable barriers between compartments of the brain
Review and write out the concept map for the nervous system unit
(found on LEARN page under concept maps)
**Review and write out the concept map for the nervous system unit
(found on LEARN page under concept maps**)
nervous system = CNS and PNS
CNS = brain & sinal cord
PNS = afferent (sensory) & efferent (motor)
Efferent (motor) = somatic & autonomic
Autonomic = sympathetic & parasympathetic
What is the ONLY target of somatic motor neurons
skeletal muscle
What are the main targets of autonomic motor neurons
cardiac muscle & smooth muscle
(main focus for this course, but there are others eg. adipose tissues)
How do neurons transmit electrical impulses
via energy, stored as an electrochemical gradient
The human body is electrically ____________
neutral
Separating positive and negative charges requires ________
energy
How does the body specifically separate charges
the cell membrane acts as an electrical insulator
A difference in charge between the ICF and the ECF creates an ____________ ________________
electrical gradient
What structure allows for movement of charge through the membrane
ion channels
The difference of +ve (cations) vs -ve (anions) charge between inside and outside of cell is called…
membrane potential
What does it mean when saying all living cells have a membrane potential?
they are polarized electrically (to varying extents)
Which cells are able to use changes of membrane potential to complete a function
excitable cells
(eg. neurons are excitable b/c changes in membrane potential allow them to relay information)
What unit is membrane potential quantified in
millivolts (mV)
What two factors determine membrane electrical properties
- an unequal distribution between the inside (ICF) and outside of the cell (ECF)
- eg. Na+, Ca2+, & Cl- are higher in ECF while K+ is higher in ICF [anions (large, negatively charged proteins) usually higher in ICF] - selective movement of these ions across the membrane
- eg. because of size, anions cannot move across membrane
IN CLASS REVIEW: Clusters of cell bodies in the PNS are known as…
a. ganglia
b. nuclei
c. tracts
d. nerves
e. ganglia and nerves
a. ganglia
(ganglia=soma in PNS, whereas nuclei=soma in CNS)
(tracts=bundles of axons in CNS, nerves=bundles of axons in PNS)
What are the 4 types of selective ion channel
K+ channel
Na+ channel
Cl- channel
Ca2+ channel
What is higher concentration in ICF
K+
What is higher concentration in ECF
Na+, Ca2+, & Cl-
What are anions
large, negatively charged intracellular molecules in ICF
What are cations
large, positively charged extracellular molecules in ECF
Why do anions not move across the membrane
because of their size
What are leak channels
passive transport channels (don’t require energy input and are not gated)
Does K+ or Na+ have a greater concentration of passive channels in the membrane
K+: there are more passive K+ channels so K+ can move much more freely across the membrane compared to Na+
What is equilibrium potential
membrane potential that exactly opposes the concentration gradient of an ion (this is where the electrical and chemical forces acting on the ion are equal and opposite)
What is the Nernst equation
E(ion) = (61/z) log ([ion]out/[ion]in)
(looks at what the membrane potential would be for the membrane to be permeable to only one ion)
What does the value E(ion) represent
equilibrium potential
What does the value z represent
electrical charge of the ion
What are the equilibrium potentials for K+ and Na+ in a typical neuron
K+ : -90mV
Na+ : +60mV
What is the basic concept of the Nernst equation
looks at what membrane potential would be if the membrane was only permeable to one ion
What is the deviation between the Nernst equation and living cells
the Nernst equation focuses on only one ion but living cells have multiple ion types crossing the membrane
What concentrations do you need to know in order to complete the Nernst equation
concentration of ion IN & concentration of ion OUT
What is resting potential
the charge difference between ICF and ECF at rest
What is typical resting potential for a neuron
-70mV
When is the neuron no longer at resting membrane potential
when it sends a signal
What determines a cells resting membrane potential
the concentrations of ions (K+ greater in ICF, and Na+, Cl-, and Ca2+ greater in ECF) and their relative permeabilities to the membrane
What is meant by “excitable” in relation to a cell
the cell will change its membrane potential to complete a job
The ion contribution to the resting membrane potential is proportional to _______________
permeability
- this means the more permeable to the membrane, the more important it is for resting membrane potential
What type of molecule cannot contribute to the resting membrane potential
molecules that cannot move across the cell membrane (ie. Ca2+ because it moves via gated channels)
What is the purpose of the GHK equation
predicts membrane potential using multiple ions (more relative to living cells)
What does the value Vm represent
resting membrane potential
What does P represent
permeability of the membrane to a specific ion
What is the permeability of Ca2+ (remember Ca2+ travels via gated channels NOT leak channels)
0; it does not cross the membrane via leak channels (therefore is excluded from membrane potential equations)
What does the K+-Na+ pump offset
the passive flow of Na+ and K+ at rest
What is depolarization
decrease in membrane potential difference, membrane becomes LESS negative
What is hyper polarization
increase in membrane potential, membrane becomes MORE negative
What are the 3 types of gated channels
- mechanically gated: found in sensory neurons (open in response to physical force)
- chemically gated: respond to ligands like neurotransmitters
- voltage-gated: respond to changes in voltage (important in conduction of electrical signals along axons)
The gated channels in neurons are for which 4 ions
K+, Na+, Ca2+, and Cl-
What are the two types of signal generated by neurons
short-distance signals & long-distance signals
IN CLASS ACTIVITY: match the ion to its associated change in the membrane…
1)Na+
2)Cl-
3)K+
4)Ca2+
…predicting whether it will hyper-polarization or depolarization the cell
1) depolarizing (adding positive charges will take it from -70 to less negative)
2) hyper-polarize (adding negative charges will take from -70 to more negative)
3) hyper-polarizing (taking away positive charges will make it more negative)
4) depolarizing (adding positive charges will take it from -70 to less negative)
What are graded potentials
can be depolarizing or hyper-polarizing, and occur in the dendrites of the neuron
- triggered by opening or closing of ion channels
- started by ions entering the cell from the ECF
Why are graded potentials called “graded”
the amplitude of the potential is relative to the strength of the triggering event
Why do graded potentials lose strength as they travel
- current leak: some charges leak back with the depolarization wave
- cytoplasmic resistance: cytoplasm resists the movement of the current
Since graded potentials lose strength as they move, what distance are they travelled
short distances
What causes an ion to enter the cell
initiates by ions binding to membrane receptors and opening ion channels
What events occur after neurotransmitters bind
Ion channel opens, ions move in/out, and depolarization/hyper-polarization spreads through the cell
What determines signal strength
the number of ions entering/exiting the cell
As graded potential travels, ________ is decreased
strength
What is another (simpler) term for graded potential
signal
What is the different type of signalling used for long distances?
action potential
What are characteristics of action potential
- action potentials don’t deviate, they are identical (no variation in strength, on or off only)
- action potentials don’t diminish in strength as they travel, the signal remains strong the entire distance
How is action potential initiated
at the trigger zone (otherwise known as the integrating centre)
Where is the trigger zone in a neuron
it varies depending on the type of neuron
Where is the trigger zone in sensory neurons
adjacent to the receptor
In relation to action potential, if only one action potential occurs, what is the effect on the cell
barely any effect, concentration gradient remains essentially unchanged
- therefore LOTS of action potentials are needed to change the gradient
When is the Na+ channel activated during the action potential time frame
at threshold (absolute refractory period)
When is the Na+ turned off and when is K+ channel opened during action potential time frame
Na+ closes after threshold, and K+ channels open (absolute refractory period)
When do K+ channels close during action potential time frame
relative refractory period
Recite the phases of action potential! This is important for the midterm*
do this on a whiteboard and check answers in course notes
What are the two key refractory periods
absolute and relative refractory periods
When does the absolute refractory period begin
as soon as Na+ channel is opened
When does relative refractory period begin
at hyper-polarization (when action potential is lower than -55mV)
if this is unclear look at the graph in course notes and study the curve!
What types of channels are the Na+ and K+ channels in action potential
voltage-gates channels
What are nodes of ranvier concentrated with?
Na+ channels
What is the term used to describe when signals jump from node to node on a myelinated axon
saltatory conduction
How is myelin insulation significant
hyperpolarization within the axons is strong enough by the time it hits the next myelinated area
Describe the events that occur at the synapse! this is an important concept for the midterm*
check course notes and study this area if unclear
What is the space in between the axon terminal and the post-synaptic cell
synaptic cleft
When action potential arrives at the axon terminal and the docking protein is activated, what happens?
the docking protein moves off of the axon terminal and becomes a synaptic vesicle, calcium entry from the voltage-gated channels instigates exocytosis of the neurotransmitters, which end up binding to receptors on the postsynaptic cell to relay a signal
Summarize somatic, sympathetic, and parasympathetic neurons and their functions. This is important for the midterm*
Read figure 11.9 in course notes and study it
What is the target tissue for the autonomic pathway
cardiac and smooth muscle (involuntary muscle types)
What is the target tissue for the somatic pathway
skeletal muscle
For autonomic pathways, how many neurons are involved?
2
Know the receptors released by the pre and post ganglionic neurons and what receptors they each bind to!
For parasympathetic preganglionic neurons, what neurotransmitter is released
acetylcholine (binds to nicotinic receptor)
For parasympathetic postganglionic neurons, what neurotransmitter is released
acetylecholine (binds to muscarinic receptor)
For sympathetic preganglionic neurons, what neurotransmitter is released
acetylcholine (binds to nicotinic receptor)
For sympathetic postganglionic neurons, what neurotransmitter is released
norepinephrine (binds to A, B1, and B2 adrenergic receptors)
What is another term for sympathetic (think response)
fight or flight
For adrenal sympathetic preganglionic neurons, what happens
acetylcholine is released from the axon terminals to the chromaffin cells on the adrenal medulla (on the adrenal gland), then epinephrine is released by the chromaffin cells on the adrenal medulla into the bloodstream
For adrenergic receptors, do cells contain multiple types of receptors or just one?
cells only project 1 type of receptor (different cell types have different receptor types)
What do B1 and B2 (beta) receptors initiate
cAMP production
What do A (alpha) receptors initiate
increase Ca2+ levels in the cytoplasm
Nicotinic receptors act via ___ __________
ion channels
Muscarinic receptors act via __ __________
G proteins
What type of neuron is a chromaffin cell
a modified postganglionic neuron
For somatic neurons, what neurotransmitter is released and what receptor is it bound to
acetylcholine, binds to nicotinic receptors (for skeletal muscles)
