Neurophysiology: Neurons And ANS Flashcards
who developed the NIssl stain
German neurologist Franz Nissl
when was the nissl stain eveloped
late 19th century
what did the nissl stain show
The stain was a basic dye. it stained clumps of material surrounding the nuclei- called Nissl bodies
who developed the golgi stain
Camillo golgi
when was the golgi stain developed
1873
the golgi stain was developed from»>
silver reagents used in photography
what did the golgi stain show
Golgi stain shows neurons have at least 2 distinguishable parts: a central region that contains the cell nucleus and numerous thin tubes that radiate away from the central region called neurites
what did golgi propound from what he saw in his stain
He concluded that the neurites of different cells are fused together to form a continuous reticulum, or network, similar to the arteries and veins of the circulatory system.
whose research brought about the neuron doctrine
Santiago Ramon Y. Cajal
when was the neuron doctrine brought
1939
what was Cajal’s observation on the neuron
cajal said that the neurons were individual units (they existed as discrete entities). That is, neurons communicate by contact not continuity
when did golgi and cajal win the noble prize
1906
when was the neuron doctrine proved, and why?
The Neuron Doctrine was not proved until the development of in the 1950s. Neurons primarily communicate with one another at contacts called synapses (the exceptions being gap junctions).
the brains are composed of 2 cell types
-Neurons
-Glial cells
what are the glial cells
They outnumber the neurons 10:1. They insulate, support, and nourish injuries. They also remove degeneration debris
what are the glial cells of the CNS
-Astrocytes
-Oligodendrocytes
-Ependymal cells
-Microglia
what are the glial cells of the PNS
-Schwann cells
-satellite cells
what are the astrocytes
They are glial cells in the CNS that:
-maintain the blood-brain barrier
-provide structural support
-regulate ions
-regulate nutrients and dissolved gas concentrations
-They absorb and recycle neurotransmitter from scar tissue
what are the oligodendrocytes
They myelinate the axons of the CNS and provide structural framework
what are the ependymal cells
they line the ventricles of the brain and the central spinal canal. They participate in the production regulation and monitoring of CSF
what are the microglial cells
Remove cell debris, wastes and pathogens by phagocytosis
what are the satellite cells
they surround the cell bodies in the ganglia and regulate, the O2, CO2, nutrients and neurotransmitter levels around those neurons in the ganglia
what are the schwann cells
They surround all the axons in the PNS, myelinate them and take part in the process of repair after injury
Draw a neuron
check the book.
what are the differences between the neuron and the common cell
-Nissl bodies: they are the organelles containing the ribosomes.
-Mitochondria: they are numerous in neurons because energy is required to maintain the resting membrane potential
-There is a neuronal membrane
-Cytoskeleton are; microtubules, neurofilaments, microfilaments.
-Dendrites
-Axon
comment on the microtubules of a neuron
they are 20nm, made of a polymer protein called tubulin
comment on neurofilaments
they are 10nm, made of glial fibrillary acidic protein
comment on microfilaments
they are 5nm, made of protein actin
comment on the dendrites
👉The dendrite is the branched process of neurons and it is
branched repeatedly.
👉Dendrite may be present or absent. If present, it may be one or many in number.
👉Dendrite has Nissl granules and neurofibrils.
👉Dendrite transmits impulses towards the nerve cell
body(the receiving portion).
👉Usually, the dendrite is shorter than axon.
comment on the axons
👉It conducts impulses away from the cell body
👉It has no nissl bodies
👉it joins the soma at a cone shaped elevation- the axonal hillock
👉The first part of the axon is the initial segment
👉Most electrical impulses arise from the junction of the axonal hillock and the initial segment, it is called the TRIGGER ZONE
comment on alzheimers disease
👉 Alzheimer’s disease is a progressive neurodegenerative
disease.
👉It is due to degeneration, loss of function and
death of neurons in many parts of brain, particularly:
-cerebral hemispheres,
-hippocampus and
-pons.
👉There is a reduction in the synthesis of most of the
neurotransmitters, especially acetylcholine.
👉Synthesis of acetylcholine decreases due to lack of enzyme
choline acetyltransferase.
👉Norepinephrine synthesis decreases because of degeneration of locus ceruleus.
👉It results in memory loss, such that the patient may not even remember family members
👉Over time, cognitive functions are lost, and in the final stages of the disease the patient can no longer communicate
👉The diagnosis is made through the patients declining cognitive abilities in mental examinations (dementia)
who first described Alzheimer’s diseases
It was first described in 1907 by the German physician A. Alzheimer.
what year was alzheimer’s discovered
1907
by 2030, how many people are projected to have alzheimer’s
14million
why is norepinephrine production affected in alzheimer’s disease
locus ceruleus degenration
why is acetylcholine production affected in alzheimer’s disease
the enzyme choline acetyltransferase
acording to the number of dendrites and axons, what are te classes of neurons
👉Unipolar
👉Bipolar
👉multipolar
👉pseudounipolar
draw the 4 types of neurons (according to number of dendrites/axons)
check your booklet
comment on unipolar neurons
👉These are neurons with only one pole.
👉from that single pole, both the dendrite and axon arise
👉This type of neuron is only present in the embryonic stage of humans.
are there unipolar neurons in human
no
what neurons are in human, instead of unipolar neurons
pseudounipolar neuron
what is a pseudounipolar neuron
👉A pseudounipolar neuron is a type of sensory neuron found in the dorsal root ganglia of the spinal cord.
👉They have a single process that splits into 2 branches, but unlike unipolar neurons, the single process is actually a fusion of two processes that arise from opposite sides of the cell body, which is at one side.
👉One branch carries sensory information from the periphery to the central nervous system, while the other branch extends to the periphery and acts as an axon.
where is the pseudounipolar neuron seen
dorsal root ganglia of the spinal cord
comment on the bipolar neuron
👉they are neurons with 2 poles,
👉the dendrite arises from one pole, the axon from the other pole
👉they are the retina, inner ear and olfactory bulb
comment on multipolar neurons
👉they have numerous poles,
👉one gives rise to the axon, many others give rise to the dendrites
based on function, what are the classifications of neurons
👉Afferent (sensory) neurons
👉Efferent (motor) neurons
👉Interneurons
comment on interneurons
👉They function as integrators and signal changers.
👉They act to integrate groups of sensory and afferent neurons into reflex circuits
👉They lie entirely in the CNS and account for 90% of all neurons
👉The number of interneurons between specific afferent and efferent neurons varies according to the complexity of the action they control.
👉Interneurons {millions} are involved in memories such as when you smell a perfume or song and it evokes memories
comment on efferent (motor neurons)
👉They transmit information out of the CNS to effector cells, particularly muscles, glands, neurons and other cells
👉Their Cell bodies have multiple dendrites and
👉a small segment of the axon is in the CNS but most of the axon is in the PNS
👉Generally, each motor neuron has a long axon and short dendrites.
comment on the afferent (sensory neurons)
👉They transmit information into the CNS from receptors at their peripheral endings
👉They have single processes from the cell body split into a long peripheral process (axon) that is in the PNS and a short central process that enters the CNS
👉Generally, each sensory neuron has a short axon and long dendrites
draw a diagram to show the classification of neurons (according to function)
check the book
what is voltage
It is the measure of potential energy between two points generated by a charge separation
what is membrane potential
It is the voltage difference between the inside and outside of a cell
what is resting membrane potential
👉it is the potential difference recorded across the cell membrane at rest.
➡️Causes:
👉80% caused by selective permeability of the cell membrane to K+. The K+ diffuses out of the cell & Na+ diffuses into the cell according to the concentration gradient. The K+ permeability is 50-75 folds more than Na+
👉20% is caused by the Na+/K+ pump. It is an active process that needs energy taken from ATP. This is very important to maintain the concentration gradient across the cell membrane
what are the causes of resting membrane potential
👉80% caused by selective permeability of the cell membrane to K+. The K+ diffuses out of the cell & Na+ diffuses into the cell according to the concentration gradient. The K+ permeability is 50-75 folds more than Na+
👉20% is caused by the Na+/K+ pump. It is an active process that needs energy taken from ATP. This is very important to maintain the concentration gradient across the cell membrane
80% of resting membrane potential is attributed to:
👉80% caused by selective permeability of the cell membrane to K+
20% to resting membrane potential is attributed to:
Na+/K+ pump
what keeps Na/K concentrations different across the cell
the sodium/potassium pump which is dependent on ATP
when the electrode is outside the cell, the record reference potential is recorded as
0mV
when the electrode is in the cell, the record reference potential is
it drops to -70mV (resting membrane potential)
what is equilibrium potential
it is the membrane potential that exactly opposes the concentration of the ion that the cell is permeable to.
Eion = ENa, ECl, EK .
so, for instance, what would potassium equilibrium potential be defined as
Potassium equilibrium potential (Ek) is the membrane potential at which the chemical and electrical gradients are equal in magnitude and opposite in direction, resulting in no net movement of K+
equilibrium is calculated using:
👉Nernst equation
👉Goldman equation
what is the equilibrium potential of sodium
+60mV
what is the equilibrium potential of potassium
-90mV
What ion drives resting membrane potential
Potassium (K+)
What is Nernst equation used for
👉Use to calculate the membrane potential of an ion at equilibrium
👉Represents the electrical potential necessary to maintain a certain concentration gradient of a permeable solute
state the nernst equation
E = (61/z) * log([ion]outside/[ion]inside)
what does the value of 61 in nernst equation mean
The value 61 in the Nernst equation refers to the constant (RT/zF) at room temperature (25°C
what is Goldman’s equation used for
👉Used to calculate overall membrane potential when multiple ions are involved.
👉Incorporates permeability of each ion.
state the goldmans equation
Em = (60mV * log((P[K+]o + P[Na+]o + P[Cl-]i) / (P[K+]i + P[Na+]i + P[Cl-]o))
-Em= membrane potential
What would happen to the resting membrane potential of a cell poisoned with a substance, that is an inhibitor of the Na –K – ATPase
👉Inhibition of the Na-K ATPase pump would lead to an accumulation of sodium ions inside the cell and a depletion of potassium ions inside the cell.
👉This would cause the inside of the cell to become more positively charged, leading to depolarization of the membrane potential.
👉The degree of depolarization would depend on the severity and duration of the inhibition, as well as the initial state of the resting membrane potential.
👉Depolarization of the membrane potential can have a range of effects on cellular function, including:
- changes in ion channel activity,
- alterations in synaptic transmission, and
- changes in gene expression.
- In severe cases, depolarization can lead to cellular dysfunction or death.
comment on the concept of excitability
👉All living cells have a resting membrane potential due to the presence of ion pumps and leak channels in the cell membrane.
👉This difference in charge can be measured as potential energy- measured in millivolts.
👉In addition, however, some cells have another group of ion channels that can be gated (opened or closed) under certain conditions. Such channels give a cell the ability to produce electrical signals that can transmit information between different regions of the membrane.
👉This property is known as Excitability and such membranes are called excitable membranes
what cells exhibit excitability
👉all neirons
👉muscle cells
👉some endocrine cells (e.g beta cells of the islets of langerhans)
👉some immune cells
👉some reproductive cells
what are the 2 forms that excitability occurs
👉action potential
👉graded potential
give 10 differences between graded potential and action potential
Action potentials and graded potentials are both types of electrical signals that occur in neurons, but they have several key differences. Here are 10 differences between action potentials and graded potentials:
- Definition: An action potential is an all-or-nothing electrical signal that is generated when a neuron depolarizes to a certain threshold. A graded potential is a small, variable change in membrane potential that can be either depolarizing or hyperpolarizing.
- Magnitude: Action potentials are typically the same size and duration regardless of the strength of the stimulus that triggered them. Graded potentials vary in magnitude depending on the strength of the stimulus.
- Threshold: Action potentials have a specific threshold that must be reached in order to be generated. Graded potentials do not have a specific threshold and can be generated by any strength of stimulus.
- Location: Action potentials are generated at the axon hillock and propagate down the axon of the neuron. Graded potentials can occur anywhere on the neuron, including the dendrites, cell body, and axon.
- Duration: Action potentials are very brief, typically lasting only a few milliseconds. Graded potentials can last for varying lengths of time depending on the strength of the stimulus.
- Direction: Action potentials always travel in one direction, from the cell body down the axon to the axon terminal. Graded potentials can travel in any direction, depending on the location of the stimulus.
- Amplitude: Action potentials have a fixed amplitude that does not vary with distance from the cell body. Graded potentials have a variable amplitude that decreases with distance from the site of stimulation.
- Summation: Action potentials do not summate or add together. Graded potentials can summate, meaning that multiple graded potentials occurring close together in time can add together to create a larger signal.
- Refractory period: Action potentials have a refractory period during which they cannot be generated again. Graded potentials do not have a refractory period and can be generated repeatedly.
- Role: Action potentials are used for long-distance communication within the nervous system, allowing neurons to transmit signals over long distances. Graded potentials are used for short-distance communication within the neuron, allowing neurons to integrate information and make decisions about whether or not to generate an action potential.
does the graded potential summate?
yes, but action potential doesn’t
do graded potentials last longer than action potential?
yes they do, depending on the strength of the stimulus. action potentials are only for a few milliseconds
do action potentials travel in any direction
no they don’t, they only travel down the axon. graded potentials though travel in any direction
do graded potentials have a fixed amplitude
no they don’t, their amplitude depends on their distance to the cell body. it ios action potential that has a fixed amplitude
do graded potentials have a refractory period
no they don’t, that is action potential. graded potentials can be generated repeatedly
do graded potentials have a specific threshold
no they don’t, they can be transmitted by any strength of stimulus. Action potentials though have a threshold
are graded potentials generated in the axonal hillock only
nahh fam, that is action potential. graded potentials are generated anywhere on the neuron (dendrites, cell body, axon)
what are the major factors contributing to membrane potential
👉The concentration of ions across the membrane: Normally, sodium (Naᶧ), Chloride (Cl⁻), and calcium (Ca²ᶧ) are more concentrated in the extracellular fluid than in the intracellular fluid, while potassium (Kᶧ) is more concentrated in the intracellular fluid than in the extracellular fluid.
👉Membrane permeability to these ions: The resting cell membrane is much more permeable to Kᶧ than to Naᶧ or Ca²ᶧ. This makes Kᶧ the major ion contributing to the resting membrane potential.
comment on the ‘concentration of ions across the membrane’ factor that contributes to membrane potential
Normally, sodium (Naᶧ), Chloride (Cl⁻), and calcium (Ca²ᶧ) are more concentrated in the extracellular fluid than in the intracellular fluid, while potassium (Kᶧ) is more concentrated in the intracellular fluid than in the extracellular fluid.
comment on ‘membrane permeability to these ions’ factor that contributes to membrane potential
The resting cell membrane is much more permeable to Kᶧ than to Naᶧ or Ca²ᶧ. This makes Kᶧ the major ion contributing to the resting membrane potential.
what does it mean to say that a membrane is depolarized
The membrane is depolarized when its potential becomes less negative i.e more positive (closer to zero) than the resting level.
what is an overshoot
Overshoot refers to a reversal of the membrane potential polarity, that is when the inside of a cell becomes positive relative to the outside
what is repolarization
When a membrane potential that has been depolarized is returning toward the resting value, it is repolarizing
what is hyperpolarization
The membrane is hyperpolarized when the potential is more negative than the resting level.
a large stimulus on graded potential will…
create a strong graded potential
a small stimulus on graded potential will
create a weak graded potential
what is graded potential
👉Graded potential is a mild local change in the membrane potential that develops when stimulated in receptors, synapses or neuromuscular junction.
👉It is also called graded membrane potential, graded depolarization or
local potential.
👉It is nonpropagative and characterized by mild depolarization or hyperpolarization.
👉In most cases, the graded potential is responsible for generating an action potential.
👉However, in some cases the graded potential hyperpolarizes the membrane potential (more negativity than resting membrane potential) and inhibits the generation of action potential (as in inhibitory synapses)
List some types abi examples of graded potentials
- End plate potential in neuromuscular junction
- Electronic potential in nerve fibers
- Receptor potential
- Excitatory postsynaptic potential
- Inhibitory postsynaptic potential
what is end plate potential in a neuromuscular junction
👉The end-plate potential is a type of graded potential that occurs at the neuromuscular junction, which is the synapse between a motor neuron and a muscle fiber.
👉It is a depolarization of the muscle fiber caused by the release of acetylcholine from the motor neuron, which binds to nicotinic acetylcholine receptors on the muscle fiber and allows positively charged ions to enter.
👉The magnitude of the EPP depends on:
-The amount of ACh released by the motor neuron,
-The sensitivity of the nicotinic Ach receptors on the muscle fiber, and
-The number of nAChRs that are activated.
👉The End plate potential can vary in size and duration, but is typically around 40-50 mV in amplitude and lasts for several milliseconds.
👉The End plate potential is important for initiating muscle contraction by triggering an action potential in the muscle fiber.
