Neurophysiology Flashcards
What is membrane potential maintained by?
Membrane potential is maintained by nonconducting neuron’s plasma membrane, typically - 70 mV
What is resting membrane potential determined by?
RMP is determined primarily by the membrane permeability to K+ and Na+
What is the membrane more permeable to?
K+
Why is the inside of the cell negatively charged?
there are more proteins inside the cells, which carry negative charges
What does the sodium-potassium exchange pump do?
Stabilize the RMP; the passive and active mechanisms are in balance
What is the equilibrium potential?
the transmembrane potential at which there is no net movement of a particular ion across the cell membrane
electric potential = concentration potential
When does transmembrane potential rise or fall?
In response to temporary changes in membrane permeability resulting from opening or closing specific membrane channels
What are the two types of membrane channels?
passive channels (leak channels) and active channels (gated channels)
What is a characteristic of passive channels?
they are always open
What are the characteristics of active channels?
open or close in response to specific stimuli
What are the three states of active channels?
- close but capable of opening
- open (activated)
- closed and incapable of opening (inactivated)
What are the three classes of gated channels?
chemically regulated channels, voltage-regulated channels, mechanically regulated channels
How do chemically regulated channels work?
Open in presence of specific chemicals at the binding site.
Where are chemically regulated channels found?
Found on neuron cell body and dendrites
How do voltage-regulated channels work?
respond to changes in transmembrane potential, have activation gates (opens) and inactivation gates (closes). Characteristic of excitable membrane
Where are voltage-regulated channels found?
found in neural axons, skeletal muscle sarcolemma, and cardiac muscle
How do mechanically reguated channels work?
they respond to membrane distortion
Where are mechanically regulated channels found?
found in sensory receptors (touch, pressure, vibration)
What are graded potentials?
changes in transmembrane potential that can’t spread far from site of stimulation (also called local potentials)
How is magnitude related to graded potentials?
The magnitude is proportional to the magnitude to the stimulus (open more channels) –> graded
How is a graded potential produced?
Any stimulus that opens a gated channel produces a graded potential
What is a graded potentials excitation?
when a stimulus triggers the opening of additional Na+ channels, allowing the membrane potential to move toward zero (depolarization). The effect spreads passively owing to local currents and decreases with distance
What is a graded potentials inhibition?
When a stimulus triggers the opening of additional K+ channels, increasing the membrane potential (hyperpolarization)
What is a graded potentials repolarization?
it restores the normal RMP after depolarization by channels and ion pumps
What is action potential?
propagated changes in transmembrane potential that affect an entire excitable membrane and are link graded potentials at cell body with motor end plate actions
What happens when initiating action potential?
the initial stimulus is a graded depolarization of axon hillock large enough (10 to 15 mV) to change resting potential (-70 mV) to threshold level of voltage-regulated sodium channels (-60 to -55 mV)
What is the all or none principle?
If a stimulus exceeds threshold amount, then the action potential is the same no matter how large the stimulus (action potential is either triggered or not)
What are the four steps in the generation of action potentials?
- depolarization to threshold (-60 mV)
- activation of voltage regulated Na+ channels
- inactivation of Na+ channels, activation of K+ channels
- return to normal permeability
What happens during the activation of voltage regulated Na+ channels?
rapid depolarization, Na+ ions rush into cytoplasm, inner membrane changes from negative to positive
What happens during the inactivation of Na+ channels, activation of K+ channels
happens at +30 mV, inactivation gates close (Na+ channel activation), voltage-gated K+ channels open, repolarization
What happens during return to normal permeability?
K+ channels will begin to close when membrane reaches normal resting potential (-70 mV), K+ channels finishing closing when membrane is hyperpolarized to -90 mV, and when transmembrane potential returns to resting level – the action potential is over
What is an absolute refractory period?
brief period of stimulus resistance
What is a relative refractory period?
will only respond to a very strong stimulus
What is the propagation of action potentials?
the movement of action potentials generated in the axon hillock. This happens along the entire length of an axon. This is also a series of repeated actions, not a passive flow
What are the 2 methods of propagating action potentials?
continuous propagation and saltatory propagation
What is continuous propagation?
the local current depolarizes the next segment; the cycle repeats. This occurs on an unmyelinated axon and is always forward. This is slow (1 m/s)
What is saltatory potential propagation?
it leaps from node to node and occurs on a myelinated axon. This a rapid movement and uses proportionately less energy
Overall summary of graded potentials:
- depolarizing or hyperpolarizing
- no threshold value
- amount of depolarization or hyperpolarization - depends on intensity of stimulus
- passive spread from site of stimulation
- effect on membrane potential decreases with distance from stimulation site
- no refractory period
- occurs in most cell membranes
Overall summary of action potentials:
- always depolarizing
- must depolarize to threshold before action potential begins
- all-or-none phenomenon: all stimuli that exceed threshold with produce identical action potentials
- action potential at one site depolarizes adjacent sites to threshold
- propagated across entire membrane surface without decrease in strength
- refractory period
- occur only in excitable membrnaes of specialized cells such as neurons and muscle cells
How do local anesthetics work?
they block the voltage-gated sodium channels which prevents sensory nerves from depolarizing and also prevents transmission of the signal –> prevent generation of action potential –> no sensitivity
What is the synapse?
the area where a neuron communicates with another cell
What is a presynaptic cell?
has the synaptic terminal and sends a message. This also contains synaptic vesicles and releases neurotransmitters
What is a postsynaptic cell?
It receives the message
What is a synaptic knob?
a round structure which occurs where the post synaptic cell is another neuron
What are the two post synaptic cell junctions?
neuromuscular junction and neuroglandular junction
What is synaptic activity?
action potentials (nerve impulses)
How are action potentials transmitted?
they are transmitted from presynaptic neuron to postsynaptic neuron (or other postsynaptic cell) across a synapse
What are the two types of synapses?
electrical synapses and chemical synapses
Where are electrical synapses found?
they are rare, found in the brain and eye
How do electrical synapses work?
They are cells joined by gap junctions and work quickly and efficiently. The action potential will always be propagated to the next cell
How do chemical synapses work?
presynaptic cells release neurotransmitters across a tiny gap
What are neurotransmitters?
- are chemical messengers
- are released at presynaptic membrane
- affect receptors of postsynaptic membrane
- are broken down by enzymes
- are reassembled at synaptic knob
What are the two classes of neurotransmitters?
excitatory neurotransmitters and inhibitory neurotransmitters
How do excitatory neurotransmitters work?
- influx of sodium
- cause depolarization of postsynaptic membranes
- promote action potentials
How do inhibitory neurotransmitters work?
- away from threshold
- cause hyperpolarization of postsynaptic membranes (towards refractory period)
- suppress action potentials
What are cholinergic synapses?
This includes acetylcholine (ACh) which is released at all neuromuscular junctions involving skeletal muscle fibers, many synapses in the CNS, all neuron to neuron synapses in the PNS, all junctions of the parasympathetic divisions of the ANS
What is synaptic fatigue?
the synapses remains inactive until ACh has been replenished
How do chemical synapses work?
the synaptic terminal releases a neurotransmitter that binds to the postsynaptic membrane. This produces temporary, localized change in permeability or function of postsynaptic cell. These changes affect the cell, depending on the nature and number of stimulated receptors
What are the three general regions of the brain?
hindbrain, midbrain, and forebrain
What are the parts of the hindbrain?
medulla oblongata, pons, and cerebellum
What are the parts the midbrain?
short portion of brainstem rostral to pons (around where oculomotor nerves emerge)
What are the two parts of the forebrain?
diencephalon and telencephalon
What makes up the diencephalon?
epithalamus, thalamus, hypothalamus (where the pituitary attaches)
What does the telencephalon consist of?
cerebral hemispheres (frontal, parietal, temporal, occipital)
What is the ventral root of the spinal cord?
contains axons of motor neurons and it carries motor information out of the spinal cord
What does the dorsal root of the spinal cord do?
contains axons of sensory neurons and carries sensory information into the spinal cord
What does the dorsal root ganglia contain?
it contains cell bodies of sensory neurons
What is the spinal nerve of the spinal cord?
a single mixed nerve on each side where the dorsal and ventral nerve roots join together
What is white matter?
myelinated and unmyelinated axons
What carries information between the brain and spinal cord?
ascending and descending tracts
What is gray matter?
cell bodies and neurons and neuroglia and unmyelinated axons. Gray horns contain sensory and motor nuclei
What are the functions of the spinal cord?
tracts that provide conduction routes to and from the brain.
What are ascending tracts and descending tracts?
tracts are both structural and functional organizations of nerve fibers (bundles of axons)
What does the spinal cord serve as?
the integrator, or reflex center, for all spinal reflexes
What are reflexes?
are rapid, automatic responses to stimuli
What is a neural reflex?
an automatic, involuntary motor response by the nervous system that helps preserve homeostasis by rapidly adjusting the functions of organs or organ systems. the response shows little variability
What is the reflex arc?
the neural wiring of a single reflex
What are the 5 steps involved in a neural reflex?
- the arrival of stimulus and activation of a receptor
- the activation of a sensory neuron
- information processing
- the activation of a motor neuron
- a response by an effector
What is the autonomic nervous system?
the ANS is a subdivision of the nervous system that regulates involuntary (visceral) effectors (cardiac muscle, smooth muscle, glandular epithelial tissue)
What systems does the ANS coordinate?
cardiovascular
respiratory
digestive
urinary
reproductive (parasympathetic and sympathetic)
What is the somatic nervous system?
the SNS is a subdivision of the nervous system that regulated voluntary (motor) effectors (muscle) and coordinates voluntary movements
What are the 5 effects of the parasympathetic division (rest or restore)
- decrease metabolic rate
- decrease heart rate and blood pressure
- increases secretion by salivary and digestive glands
- increases motility and blood flow through the digestive tract
- stimulates urination and defecation
What are the 7 effects of the sympathetic division (fight or flight)
- heightens mental alertness
- increases metabolic rate
- reduces digestive and urinary functions
- activate energy reserves
- increases respiratory rate and dilation of respiratory passageways
- increases heart rate and blood pressure
- activate sweat glands
How is the sympathetic nervous division organized?
- preganglionic fibers synapses in ganglia near spinal cord
- preganglionic fibers are short
- postganglionic fibers are long
How is the parasympathetic nervous division organized?
- preganglionic fibers synapse in ganglia close to (or within) target organs
- preganglionic finers are long
- postganglionic fibers are short
What is the organization differences between parasympathetic and sympathetic divisions?
- most vital organs receive instructions from both
- two divisions commonly have opposing effects
