Neurophysiology of Nerve Conduction Flashcards
The functional/structural unit of the nervous system is a
neuron
Depending on the structures and functions, neurons take
different forms and classifications
Cell body (soma)
keeps the cell running
Dendrite
receives info from another neuron via nerve terminal and send impulse to cell body
Axon
sends impulses away from cell body
Nerve and muscle are _____ tissues but the properties of nerves also include _______.
excitable, conductivity
_____ can initiate action potentials and conduct/transmit impulses/signals
nerves
Cell membrane is composed mainly of a
lipid bilayer of phospholipids
______ are found in the lipid bilayer that have different functions that protrude through
protein molecules
______ moieties are also attached to the protein molecules. (glycoprotein)
carbohydrate
There are _____ differences between the EC & IC fluids
concentration
The cell membrane has _____
selective permeability
Ionic charge between the 2 sides create an _________
electrical potential difference
The _____ of the cell is more _______ during resting electrical membrane potential
outside, more positive
The diffusion of Na and K ions, and the pumping function of the Na/K ATPase largely contribute to
Resting membrane potential
Nerves are also able to
self propagate
__ can be used for direct measurement of the membrane potential
Microelectrode
The _____ in the cell membrane serve as components of the transport process for molecules and ions across the cell membrane.
protein molecules
provide watery pathways
channel/pore proteins
bind specific substances to be transported
carrier proteins
Can cross cell membrane without transporters or ion channels by simple diffusion
lipid soluble substances
Substances can leave and enter cells using
simple diffusion, facilitated diffusion, active transport
Membrane conductance refers to # of
channels that are open in a membrane
The rate at which ions move across a membrane depends on
1) # of open channels and 2) net force
Channels are divided into 3 groups
1) ungated channels
2) voltage-gated channels
3) ligand-gated channels
Have no gates and are always open
ungated channels
Gates open and/or close in response to a membrane voltage change
voltage-gated channel
Example of a voltage-gated channel
Na channels in excitable cells
_____ are part of protein conformation forms/shapes in the cell membrane.
Channels
Conformational changes in channel molecules ________ gates guarding them
open and close
Two types of gating
1) Voltage-gating
2) Ligand-gating (chemical gating)
Upon opening of gates, ions move down concentration gradients which means
from high to low concentrations
3 ways substances can leave cells
1) simple diffusion
2) Facilitated diffusion (carrier mediated)
3) Active transport (both carrier-mediated and energy-dependent)
This process is carrier mediated
Facilitated disffusion
Molecule binds to ____ to be transported in facilitated diffusion and involves a conformational change
carrier protein
The molecule is released ____ in facilitated diffusion
inside
Examples of facilitated diffusion
transport of glucose and most amino acids
_____ involves diffusion of substances against electromechanical gradient “uphill movement”
active transport
Active transport needs ____ and a _____
ATP, carrier protein
Examples of primary active transport
1) sodium potassium pump for transport of Na and K ions outward and inward
2) calcium pump in SR of skeletal muscle
NA-K/ATP pump
3Na from inside to outside, 2 K from outside to inside, + ATP used
The Na-K/ATP pump is present in ___ cells
all
The voltage (charge) difference across cell membrane when the cell is at rest
Resting membrane potential
Resting membrane potential is due to
unequal distribution of charged particles (ions).
Resting membrane potential exists in ____ cells
all
The outside of the cell contains excess ____ and is relatively _____
Na, positive
The inside of the cell contains excess ______ and is relatively ________
K, negative
With excess Na outside and K inside, the cell is said to be ______ but with no impulse transmission
polarized
Na/k ATPase pump maintains high NA outside and K inside the cell by pumping
3 Na and 2 K against their concentration gradients
___ leaks back outside the cell more easily than ___ leaks in, further contributing the electrical potential difference
K, Na
The magnitude of membrane potential mostly depends on the distribution and permeability of ions like Na and L being at _____ in most nerves and ___ in muscle
-70 mV, -90 mV
Establishment of resting membrane potential in nerve fibers occurs when
1) the membrane potential is caused entirely by K+ diffusion alone
2) When the membrane potential is caused by diffusion of both sodium and potassium
3) When the membrane potential is caused by diffusion of both sodium and potassium ions plus pumping of both ions by the Na/K pump
There is also additional contribution of _____ to the potentials
ion leak
Resting membrane potential
-90 mv
Nerve action potential generated in ____ tissues and is stimulated by
excitable tissues, electrical, chemical or physical stimuli.
Polarized state of the membrane becomes _________ as Na channels open, and Na ions enter the cell.
depolarizes
The membrane potential decreases with ______ conductance of Na
increased
When potential decreases with Na entering the cell the potential becomes ____ at which point the Na channel is inactivated
+40 mv
K channel gets activates to stop the influx of NA and allow the exit of K. This efflux causes
repolarization
K exiting slows down after depolarization followed by a faster K exit which makes the membrane more negative, which is called
hyperpolarisation
The axon develops an AP of the stimulus is at the threshold or above
all or none law
Any ___ of stimulus above threshold does not alter pattern of response.
increase
The time interval during which the nerve fiber does not respond to a second stimulus is known as
absolute refractory (nerve is still in excitatory phase)
When a stronger stimulus can produce a response close to the end
relative refractory period
If not interrupted, this phase leads to the return of normal excitability or polarized state/RMP.
relative refractory period
Due to the inability of many negatively charged molecules to pass through the membranes, the deficit of positive ions (K) on the inside of the membrane leaves an excess of impermeant negative ions. These are responsible for the negative charge inside the cell.
Non-diffusible anions
This pump behaves like the Na-K pump and regulates the IC concentration of calcium in many cells.
Calcium pump
Voltage gated calcium channels are usually involved in
smooth and cardiac muscle
The initial spike of a cardiac AP is
Na channel activation (fast channels)
The plateau in a cardiac ap is due to
1) slow opening of the voltage gated calcium channels
2) slowed/delayed activation of voltage-gated potassium channels
Rhythmical AP in intestinal smooth muscle is similar to those recorded int he rhythmical control od the
heart
When stimuli are below threshold required for eliciting an AP
acute subthreshold potentials
Velocity of conduction in nerve fibers varies from
0.25 m/sec to 100 m/sec
Approximate rate of conduction for most fibers
1 m/s for unmyelinated, 10-100 m/sec for myelinated
impulses travel by self-excitation and propagation
unmyelinated fiber
directly related to the square roots of diameter of the nerve fiber
conduction of velocity
____ fibers are myelinated
large fibers
Factors causing ______ sufficiently can set off automatic regenerative opening f the channels
N ions to diffuse inward
The functional significance of the schwann cell is to form
myelin
Myelin serves as support for the axon and
a tube for nerve regeneration in the event of damage or degeneration.
General structure of LA molecules
aromatic group, ester/amide, and amine group
LA block and close ______ bu interacting with an intracellular domain of the channels.
Na channels
By blocking impulse transmission along sensory nerve fibers, LAs ____ pain
reduce/block
T or F: LA are analgesics
F-They are not analgesics, they only block pain.
Other membrane stabilizers that decrease nerve excitability include
high extracellular calcium ions and some other drugs
The _____ form binds to the sodium channel in the open state which prolongs the sodium channel inactivation state
ionized form
Sodium entry is blocked during
Sodium inactivation state
As anesthetic progressively develops in a nerve, the…
1) threshold for electrical excitability gradually increases
2) the rate of rise of the action potential declines
3) impulse conduction slows
all leads to nerve conduction
nerve fibers with _______ diameters are affected first
smaller
Transient and reversible in the following order
autonomic function, temperature, blocking of pain, touch, pressure, motor function.
Loss of autonomic function causes
vasodilation
Depending on the local tissue concentrations of LA, there may be ________ or_________
inhibitory (lower doses) or excitatory (higher doses)
____________ is used as a desensitizing agent for tooth pain.
potassium nitrate
Potassium nitrate provides protection against
painful sensitivity like cold, heat, acids, sweets, or contact
Potassium nitrate works by
- decreasing the ability of the nerve fibers in the dental pulp to re-polarize
- decreasing the fluid flow decreasing the level of the activity of dental sensory nerves and preventing or reducing the sensation signals from reaching the brain
Synaptic transmission is ____ in nature
chemical
Neurotransmitters can be
excitatory or inhibitory
Synaptic transmission is initiated by entry of ___ in to the nerve terminal
Ca
Ca ions coming into the nerve channel helps release of
neurotransmitters from the presynaptic vesicles
The neurotransmitters released from the presynaptic terminal are released via
exocytosis
The presynaptic nerve terminal is rich in ____ which is needed for synthesis of the neurotransmitter.
mitochondria
The event following the interaction of the NT on the ______ receptor depends on the nature of the NT.
postsynaptic
Synthesis of acetylcholine starts with acetyl CoA+ choline, involving the enzyme
choline actyltransferase
Ach is stored in vesicles released by exocytosis and broken-down by
acetylcholinesterase
Ach acts on M receptors on effector tissue to produce response. An example is
saliva secretion
Ach involved with
autonomic cholinergic
Autonomic adrenergic involves
NE
Synthesis of for autonomic adrenergic starts with the uptake of
tyrosine and phenylalanine
NE is stored in vesicles, released by exocytosis, and broken-down by enzymes…
MAO and COMT
____ is a major terminating mechanism for NEs action (about 80%)
Uptake1 (U1)
NE acts on the receptors __ and ___ at the effector site
alpha and beta
alpha activation causes _____ by an agonist like EP
vasoconstriction
At the NMJ, the arrival of the AP at the somatic nerve terminal causes Ca influx into the nerve. This is followed by the release of ____ from its vesicle into the synaptic space/cleft.
Ach
The Ach by activating its receptors on muscle fibers across the synapse, leads to
muscle contraction
On the inside surface of the neural membranes are linear
dense bars.
Each side of the protein bars are ____ that penetrate the membrane as voltage gated calcium channels.
protein particles
Voltage gated calcium channels allow for the _____ into the nerve ending for the release of ______-
influx of Ca, Ach
Events of NMJ for muscle contractino
1) Nerve AP
2) Release of Ach
3) binding of Ach with receptor
4) Activation of receptor
5) sodium influx into SKM fibers
6) muscle AP and SR channel opening
7) Ca2+ release
8) contraction
Examples of other sensory receptor mediated responses
muscle spindle, golgi tendon organ, baroreceptor, chemoreceptors
Excitation from anterior motor nucleus and ____ help with proper function of muscles.
continuous sensory feedback to the nervous system
_____ are located in the muscle and sense changes in muscle length and rate of change of length
muscle spindles
_____ are located in tendons and give information about tension
golgi tendon organs
______ give rise to axons that exit the cord via the ventral roots and pass in peripheral nerves to innervates skeletal muscle
anterior horn motor neurons
Spinal cord ventral horn ____ neurons are alpha or gamma neurons
motor
____ large, give rise to myelinated axons, conduct AP rapidly
alpha
____ smaller, give rise to small axons, conduct slowly
gamma
Interneuron cells contribute to ____ and _____ in the spinal cord
motor and sensory
There are ___ interneuron than motor neurons
30x more
Interneurons have relatively high excitability and receive inputs as incoming
sensory info or as signal descending from higher centers in the brain and help processing info.
Interneuron cells connect adjacent segments of the cord and help
modulate signals
Large skeletal muscle fibers called extrafusal fibers
alpha motor neurons
very small intrafusal muscle fibers in muscle spindles
gamma motor neurons
Muscle spindles detect muscle ____, while tendon organ detects muscle _____
length, tension and also stabilizes contractile forces
