Nervous System and Neuron Excitability parts 1 & 2 Flashcards
The nervous system plays a major role/is responsible for what (5)?
- Maintaining homeostasis
- Sensations
- Behaviors
- Memories
- Initiation of all voluntary movements
When stimuli cause variables to deviate from their set points, neurons respond by forming _______. The ability to form these is called ______.
electrical signals (graded and action potentials)
electrical excitability
What are the two types of electrical signals neurons can form?
Graded potentials
Action potentials
Electrical excitability is measured in what?
Action potentials (because electrical excitability is the ability to produce action potentials in response to stimuli)
Explain the difference between graded potentials and action potentials.
Graded potentials - “tiny potentials” that build up to an action potential; goes shorter distances
Action potentials - longer distances; electrical excitability is measured in action potentials
Action potentials communicate with other ____, ____, and ____ to regulate organ activity and restore homeostasis.
neurons, muscles, and glands
Regional specialization results in _______
predictable symptoms
Collectively, the ______ of the body constitute the nervous system.
Nervous tissue
The nervous system has a mass of ____ which constitutes about ___ of total body weight.
2 kg (~4.5 lbs); 3%
T/F The nervous system is the smallest and most complex of the 12 body systems
T
What are the two main subdivisions of the nervous system and their components?
- CNS - brain and spinal cord ONLY
- PNS - ALL nervous tissue OUTSIDE of the CNS: nerves and sensory receptors (I.e. cranial n. is part of the PNS - it is a NERVE that branches FROM the CNS, but is not part of it)
part of the CNS located in the skull
brain
part of the CNS that is connected to the brain and is enclosed by the bones of the vertebral column
spinal cord
What are the 4 functions of the CNS?
- Processes incoming sensory information (input)
- Thoughts
- Emotions
- Memories
Where do most signals that stimulate the muscles and glands originate?
CNS
What are nerves?
Bundles of axons that lie OUTSIDE the brain and spinal cord
_____ pairs of cranial nerves emerge from the _____
12; brain
____ pairs of spinal nerves emerge from the ______
31; spinal cord
Structure that monitors changes in the internal and external environment
sensory receptor (I.e. touch receptors in skin, olfactory/smell receptors in nose, stretch receptors in stomach wall/organs)
What are the subdivisions of the PNS and their functions?
- Afferent (Arrives to CNS) - conveys input INTO the CNS from the sensory receptors in the body (I.e., somatic senses and special senses)
- Efferent (Exits CNS) - conveys output FROM CNS to Effectors (muscles and glands)
What are the subdivisions of the Efferent NS and their functions?
- Somatic NS - coveys output from the CNS to the skeletal muscles ONLY (voluntary control)
- Autonomic NS - conveys output from the CNS to the smooth muscle, cardiac muscle, and glands (involuntary control)
Which branch of the nervous system is specific for voluntary control?
Somatic NS (branch of the Efferent NS which is a branch of the PNS)
Which branch of the nervous system is specific for involuntary control?
Autonomic NS (branch of the Efferent NS which is a branch of the PNS)
Conveys output from CNS to cardiac muscle, smooth muscle, and glands
Autonomic NS
Conveys output from CNS to the skeletal muscle
Somatic NS
Conveys input into the CNS from sensory receptors such as somatic and special senses
Afferent NS
What are the 3 subdivisions of the Autonomic NS and their functions?
- Sympathetic NS - supports exercise or emergency “fight or flight”
- Parasympathetic NS - supports “rest and digest” functions
- Enteric NS - nerves in the wall of the GI tract
Which branch of the Autonomic NS innervates its effectors?
Both sympathetic and parasympathetic
How do the sympathetic and parasympathetic NSs function together?
Opposing actions - 1 “revs up” while the other “revs down”
What are the 3 basic functions of the nervous system?
- Sensory - sensory receptors detect external/internal stimuli
- Integrative - CNS processes sensory information by analyzing it and making decisions for appropriate responses (integration)
- Motor - after integration (decision of appropriate response is made), an appropriate motor response is elicited (motor info conveyed from CNS through cranial and spinal nerves of PNS to effectors (muscles and glands) where a response (muscle contraction or gland secretion) occurs
What are the two principal types of cells of the nervous system?
- Neurons - nerve cells
- Neuroglia
The basic functional unit of the nervous system:
neuron/nerve cell
5 examples of neuron functions:
- Sensing
- Thinking
- Remembering
- Controlling muscle activity
- Regulating glandular secretions
Main INPUT portion of the neuron
dendrites
control center of the neuron
cell body/soma (“brain” of the neuron)
Cluster of cell bodies in the CNS = ?
Nucleus
Cluster of cell bodies in the PNS = ?
Ganglion
OUTPUT portion of neuron
axon
Bundle of axons in the PNS
Nerve (nerves are NEVER part of CNS)
Bundle of axons in CNS
Tract
Single, long process that extends from the cell body of a neuron and functions to generate and propagate actions potentials
axons
Short, highly branched processes that extend from the cell body and receive signals from other neurons/environment
dendrites
Dendrites receive signals/input from ____ and ____
other neurons; environment
In a neuron, structure that contains organelles and directs protein synthesis (of enzymes, membrane proteins, organelles, etc.) as well as other cellular activities; also receives signals from other neurons
cell body of neuron
Function of the axon:
generates and conducts action potentials
cone-shaped process where axon leaves the cell body
axon hillock
Axon hillock is also called the ______, why?
“trigger zone’; because it activates/”triggers” action potentials (area where lots of Na+ channels rush into cell causing depolarization)
side branches that extend off the axon
axon collateral
function of the axon collateral?
“talks” to other neurons
The end of an axon along with its collaterals
axon terminal
Axon terminals swell into synaptic end bulbs and contain _____ that house ______
synaptic vesicles; neurotransmitters
the chemical messengers of the nervous system
neurotransmitters
site of communication between a neuron and target cell (other neuron, muscle fiber, gland cell)
synapse
T/F Axonal transport uses ATP
T
Term referring to the movement of substances along the microtubule within an axon toward the axon terminal
Anterograde
Term referring the the movement of substances along the microtubule within an axon back toward the cell body
retrograde
What molecule is involved in moving substances anterograde along the microtubule of an axon?
Kinesin
What molecule is involved in transporting substances along the microtubule in an axon retrograde?
Dyneins
What substances may be moved anterograde by kinesins?
organelles and synaptic vessicles
What substances may be moved retrograde by dyneins?
- membrane vesicles
- cellular materials to be recycled
- Trophic chemicals (NGF)
- Harmful agents (toxins)
How would a toxin be carried into the CNS in a neuron?
retrograde transport
What does release of a tetanus toxin in a wound cause?
toxin is carried to CNS by retrograde transport => activation of neurons that stimulate the muscle to contract leading to prolonged muscle spasms (tetanus)
What is the cause of delay between release of toxin in nervous system and symptoms?
takes time for toxin to travel
Wounds in what area of the body are most susceptible to more rapid infection?
head/neck
Where are interneurons located?
located ENTIRELY in the CNS between the sensory and motor neurons
literally means “nerve glue”
neuroglia
Neuroglia make up about ____ the volume of the CNS
1/2
Which is NOT a function of neuroglia?:
- provides structural support
- transmits action potentials
- nourishment
- protection
- facilitates neurotransmission
- maintains homeostasis of interstitial fluid
transmits action potentials
What can neuroglia cells do that neurons cannot which contribute to formation of tumors by neuroglia cells and difficulty/inability for neurons to heal?
multiply and divide
brain tumors = _____
Gliomas
neuroglia of PNS
Schwann cells
Neuroglia found in CNS:
- Oligodendrocytes
- Astrocytes
- Microglia
- Ependymal cells
most numerous glial cell
astrocytes
neuroglial cell which maintains blood brain barrier
astrocytes
Responsible for forming and maintaining myelin sheath around axons in CNS
Oligodendrocytes
How do oligodendrocytes contribute to the difficulty to heal damaged neurons?
secrete inhibitory protein after nerve injury
remove cellular debris and phagocytize microbes and damaged nervous tissue
microglia - phagocyte of the nervous system
produces and assists in the circulation of CSF; line ventricles of the brain and central canal of the spinal cord
Ependymal cells
What contributes in the difficulty for a neuron (CNS) to heal?
Astrocytes rapidly react to damaged neural tissue by proliferation (creates scar - a physical barrier to regeneration)
Oligodendrocytes secrete inhibitory protein after nerve injury
Absence of growth stimulating cues from fetal development
Function of Schwann cells:
form myelin sheaths around axons of PERIPHERAL neurons
Participate in axon regeneration (PNS)
Myelin sheaths are multilayer coverings composed of _____ and _____
lipids; proteins
Function of myelin sheaths are to:
- insulates axon
- increases speed of the conduction of APs
What 2 types of neuroglia produce myelin sheaths?
- Oligodendrocytes in CNS
- Schwann cells of PNS
Gaps in myelin sheath =
Nodes of Ranvier
Each Schwann cell wraps ___ axon segment between 2 nodes
1
term for “sheath of Schwann” that contains the cytoplasm and nuclei of Schwann cells which lie OUTSIDE the myelin sheath
Neurilemma
Schwann cells wrap about ____ of a single axon’s length by spiraling many times around the axon (as many as ___ layers)
1 mm; 100
How can neurilemma be used to regenerate axons?
neurilemma form a regeneration tube through which the re-growing axon re-establishes its original connection
each oligodendrocyte puts forth about ___ broad flat processes that spiral around CNS axons to form myelin sheath
15
T/F Nodes of Ranvier are absent when oligodendrocytes form myelin sheath on the axon of a neuron in the CNS
F - they are present, but are fewer in number
term for myelinated axons
white matter
term for unmyelinated axons
gray matter
Where can white matter be found?
brain and spinal cord; myelinated axons
Where can gray matter be found?
brain and spinal cord
neuronal cell bodies
dendrites
unmyelinated axons
axon terminals
neuroglia
What does multiple sclerosis do/cause and where?
Auto immune disease that causes progressive destruction of myelin sheaths of CNS
Multiple regions in the myelin sheaths deteriorate to scleroses
Myelin sheath destruction = slowing the short-circuiting of APs
What is the difference between plasticity and repair?
Plasticity - ability to change throughout life (sprouting dendrites, new protein synthesis, changes in synaptic contacts)
Repair - regeneration after damage is LIMITED (need intact cell body and Schwann cell for regeneration)
Graded potentials and action potentials are deviations of _____
Membrane potential (Voltage)
Nerve AP results in a ____
nerve impulse
Production of action potentials depend on 2 basic features of the plasma membrane of excitable cells:
- presence of specific types of ion channels
- resting membrane potential
ion channel with gates that randomly alternate between open and closed positions
leak channels
What are leak channel important for?
establishing the resting membrane potential
opens or closes in response to a specific ligand (chemical) stimulus
ligand-gated channel
Ligand channels participate in generation of ________
graded potentials
opens or closes in response to mechanical stimulation (touch, pressure, tissue stretching, and vibration)
mechanically-gated channels
Mechanically gated channels participate in generation of ________
graded potentials
opens in response a change in membrane potential (voltage)
Voltage gated channels
Voltage-gated channels are responsible for the generation and conduction of ______
action potentials
Functions of ion channels:
Causes changes in membrane permeability
- ions can flow
- resting membrane potential changes
- allows for electrical communication
Ion channels are common in excitable tissues such as:
muscle and nervous tissue
What is membrane potential? What are its units?
Voltage/electrical potential difference that exists across the plasma membrane (charges along PM); volts (V) or mV
Voltage is also known as ______
electrical potential difference
The presence of the plasma membrane creates a(n) _______ distribution of positive and negative charges.
unequal
____ cells display a resting membrane potential.
Unstimulated
What is Resting Membrane Potential?
the voltage/electrical potential difference that exists across the plasms membrane of excitable cells (nervous and muscle) under resting conditions
Generally, membrane potential will exhibit more ____ charges on the outside (side of ECF) and _____ charges on the inside (side of the cytosol) of the membrane.
positive; negative
Describe Ohm’s law and its relationship to membrane potential.
I = V/R
I = current/flow of charged particles
V = voltage/electrical potential difference
R = Resistance/hindrance to flow of charges
Increasing voltage = decrease in resistance
Increasing resistance = decrease in voltage
- V and R are inversely proportional
Voltage at RMP = ___
-70 mV
In the plasma membrane, there are more _____ leak channels than ____ leak channels
K+; Na+; leak channels important for establishing the RMP
In general, which ion is the plasma membrane most permeable to at resting membrane potential? Why?
K+ - has more leak channels for K+ than Na+
What effect does an ion have when the plasma membrane is more permeable to that particular ion?
that ion has a greater influence on the resting membrane potential
Which ion has the greatest influence on resting membrane potential? Why?
K+; plasma membrane is more permeable to K+ due to having more K+ leak channels
What are the 3 determinants of the RMP?
- Unequal distribution of ions in the ECF and cytosol - want more Na+ outside (ECF) and more K+ inside
- Differences in membrane permeability (more permeable to K+ at RMP due to more K+ leak channels)
- Action of the Na+/K+ pump also contributes to the generation of the RMP (maintains unequal ion distribution)
An inside-_______ membrane potential is reached upon a greater K+ concentration gradient (not considering electrical gradient for K+ or Na+ electrochemical gradient)
Negative
An Inside-______ membrane potential is reached with a greater K+ concentration gradient along with a weaker K+ electrical gradient going in the opposite direction (K+ only cell)
negative (more negative)
When concentration and electrical gradient for K+ are equal in strength and are going in opposite directions, _____ potential is reached (K+ only cell)
Potassium Equilibrium potential (Ek)
At what voltage is potassium equilibrium potential?
-90 mV
What occurs at the K+ leak channel when a potassium equilibrium potential is reached (K+ only cell)?
K+ ion will go down its concentration gradient and another K+ ion will go down its electrical gradient simultaneously
An inside-_______ membrane potential is reached upon a greater Na+ concentration gradient (not considering electrical gradient for Na+ or K+ electrochemical gradient)
positive
An Inside-______ membrane potential is reached with a greater Na+ concentration gradient along with a weaker Na+ electrical gradient going in the opposite direction (Na+ only cell)
positive (more positive)
When concentration and electrical gradient for Na+ are equal in strength and are going in opposite directions, _____ potential is reached (Na+ only cell)
Sodium equilibrium potential (ENa)
At what voltage is Na+ equilibrium potential?
+60 mV
What occurs at the Na+ leak channel when a Na+ equilibrium potential is reached (Na+ only cell)?
Na+ ion will go down its concentration gradient and another Na+ ion will go down its electrical gradient simultaneously
____ - the point at which there is no net flow of an ion
Equilibrium potential
At equilibrium potential, the electrical and chemical gradient are ___ and ___.
equal and opposite
What equation is used to calculate equilibrium potential?
What is the equilibrium potential for K+? for Na+?
Nernst equation (Ex = 61/z(always is 1) log([X] out from cytosol/[X] in from ECF)
-90 mV for K+; +60 mV for Na+
What equation is used to calculate membrane potential and takes into account ion permeabilities?
Goldman-Hodgkin-Katz equation
Vm = 61log((Pk[K+ out] + PNa [Na+ out]) / (PNa[K+ in] + PNa[Na+ in])
What result should be obtained after using Goldman-Hodgkin-Katz equation?
-70 mV
T/F Graded potentials always are excitatory.
F - will not always build up to a response/action potential
Graded potentials are generated from ____ and ___ gated channels
ligand-gated; mechanically-gated
Graded potentials experience a ___ deviation from RMP
small (less than 10 mV difference)
Depolarizing graded potentials makes the membrane potential ______ polarized and therefore have a ___ charge
less; less negative
Hyperpolarizing graded potentials makes the membrane potential ____ polarized and therefore have a _____ charge
more; more negative
______ occur when stimulus causes mechanically or ligand-gated channels to open or close
Graded potentials
Where are mechanically-gated channels located?
Dendrites of sensory neurons (stimulus deforms membrane - I.e., pressing fingers against a table)
Where are ligand-gated channels located?
Dendrites AND cell bodies of interneurons and motor neurons
Graded potentials experience ______, a bidirectional movement from stimulus site
Local current flow
T/F Graded potentials and axons participate in local current flow - the bidirectional movement from stimulus site
F - only graded potentials participate in local current flow; axons go in one direction => towards their terminals
What are primary differences between graded and action potentials?
Graded potentials:
- along dendrites (mechanically and ligand-gated channels)
- small deviation from RMP
- local current flow - bidirectional movement from stimulus
- decremental conduction- gradual “dying out” from loss of charges through leak channels
- can vary in amplitude
- amplitude of GPs decrease as distance from point of origin increases
- ONLY USEFUL FOR SHORT DISTANCE COMMUNICATION
- GPs can be added together (SUMMATE) to generate an action potential
Action Potentials:
- along axon
- Voltage-gated channels
- move in one direction towards axon terminals
- threshold at -55 mV
- all-or-nothing principle (AP generated if stimulus causes potential to reach threshold)
- does NOT vary in amplitude (no such thing as a “strong AP), but a suprathreshold stimulus can cause for multiple APs to be generated
- LONG DISTANCE
When do graded potentials occur?
when stimulus causes mechanically or ligand-gated channels to open or close
Amplitude of GP ____ as distance from point of origin _______; what does this mean?
decreases; increases; GPs are only useful for SHORT distances
What is decremental conduction?
The gradual “dying out” of graded potentials from loss of charges through leak channels
____ - when two or more graded potentials add together, increasing the amplitude of the potential and therefore has the potential to reach threshold if combined graded potentials are strong enough
Summation of graded potentials
____ and ____ graded potentials can summate
1 Depolarizing GP and 1 hyperpolarizing GP
threshold = ____ mV
-55 mV
How is an action potential generated?
stimulus must be strong enough to depolarize the membrane to threshold (-55 mV)
Will a subthreshold stimulus cause an AP?
no (stimulus must cause depolarization to -55 mV)
Will a suprathreshold stimulus cause an AP?
yes because it caused depolarization to threshold (-55 mV)
T/F A suprathreshold stimulus will produce a stronger AP than a stimulus that just reached threshold
F - no such thing as a “strong AP”; an AP is just an AP and nothing else (all-or-nothing); a suprathreshold stimulus CAN produce more than 1 AP all of the same strength (because there are no APs that vary in strength)
What are the 3 phases to an AP?
- Depolarizing phase - less polar, less negative
- Repolarizing phase - more polar, more negative
- After hyperpolarizing phase - returning back to RMP at -70 mV
What occurs during the depolarizing phase of an AP?
- Rising phase of an AP - less negative
- rises until the MP reaches +30 mV
- Caused by opening of voltage-gated Na+ channels
What is it called when the depolarizing phase reaches between 0-30 mV?
overshoot
How many Na+ ions flow across membrane during depolarization of an axon?
~10,000 Na+ ions
What occurs during the repolarization phase?
- Falling phase of an AP - more negative
- becomes more negative until it reaches -70 mV (may continue to become more negative during hyperpolarization (-90 mV))
- Caused by opening of the voltage-gated K+ channels
- voltage-gated Na+ channels are inactivating
What occurs during after-hyperpolarization phase?
- After RMP is reestablished, undershoot (-90 mV) is observed
- Voltage-gated K+ channels remain open, voltage-gated Na+ channels are in resting state
Depolarization and most of the repolarization phase are part of the _______ period
absolute refractory period
Then end portion of repolarization and after-hyperpolarizing phase are part of the _____ period
relative refractory period
