in-class quiz review - neurophysiology

7/29/2019 In-Class Quiz Review - Neurophysiology

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Waqas A. Gil

Pathophysiology In-class Quiz - Review

Ch. 10Neurophysiology

Understand the functions and components of nervous systemo Functions: Sensory input (collection), Integration (computes everything), Control (coordinates

action/reaction), Homeostasis (ensures balance), & Mental Activity.

o Components:Brain, spinal-cord, nerves, & sensory receptors.o Sub-divisions:

i. Central Nervous System (CNS): Brain (+ brain-neurons) & Spinal cord only Interneurons: Connect 1 neuron to another within the CNS.

ii. Peripheral Nervous System (PNS): Everything else neuronally-connected. Sensory receptors: Nerve endings or separate, specialized cells that detect:

o Temperature, pain, touch, pressure, light, sound, & odors. Nerve: Bundle of axon/sheaths that connects CNS to receptors, muscles, & glands.

Cranial nerves: Originate from the brain

12 pairs Spinal nerves: Originate from the spine 31 pairs Ganglion: Collection of neuronal cell bodiesoutside the CNS (similar to nerves)

o Serves as a secondary relay-center that can process senses w/out the brain. Plexus: Extensive network of axons or neuron cell bodies, also located outside CNS Divisions of PNS:

a) Sensory (Afferent) pathway: From receptors CNSb) Motor (Efferent) pathway:From CNSMuscles/glands (effectors)

i. Somatic: CNSSkeletalmuscle (walking) Voluntary, 1-neuron system that uses Synapse (quicker).

ii. Autonomic: CNSSmooth muscle (cardiac muscle, sweat glands) Involuntary, 2-neuron system that uses Ganglions (slower).

Understand neuronal parts, types, and associated cellso Neurons: Nerve-cells with the unique ability to send/receive

electricalsignals, and are made up of:

Cell body: aka Soma (Nucleus, etc.) Dendrites: Sensory-input (collection) Axons: Sensory-output (conduction away from body) Nissl Substances:Rough ERs needed for protein-

production for cell-maintenance [Pic: Dark granulations

(top-right)]

Trigger-zone:Converges dendritic electrical potentialsinto 1 that flows down the axon.

Schwann-cell: Form myelin sheaths around axons between theNodes of Ranvier.


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Classifications of Neurons:

Functional classification: Sensory (Afferent): Action potentials towardthe CNS Motor (Efferent): Action potentials away from the CNS Interneurons (Association): within CNS from one neuron to another

Structural classification: Multipolar: Motor neurons w/ several dendrites & an axon (mostneurons in CNS). Bipolar: Sensory neurons with 1 dendritic protrusion & an axon (retina & nose). Unipolar: 1 neuron that divides into 2 branches, 1 of which extends to the periphery

and has dendrite-like sensory receptors

o Glial Cells: akaNeuroglia that work to support & protect neurons. The types of glial cells are: Make up the majority of the brain (no electrical signals)CNS

a. Astrocytes: Cover neurons, vessels, and pia-mater& utilize microfilaments/tight-junctions tohelp regulate brain-fluid composition. They hold neurons in place, provide them w/

nutrition (O2), maintain homeostasis & signal transmission and help form the:

Blood-Brain barrier:Protects neurons from toxins and regulates nutrient/wasteexchange b/w neurons & blood in the brain.This is important b/c the brain takes 20%

of cardiac-output (10x more than anything else), so an ion imbalance here is fatal.

o Found in Endothelial cells and utilizes gap junctionso Lipophilic substances (ethanol, nicotine, penicillin) can getpastthis barrier.

Reactive Astrocytosis: Proliferation of astrocytes during inflammation, which is good(for protection) and bad (b/c it doesnt allow neurons to repair in areas of replication).

b. Ependymal Cells: Line brain-ventricles and the spinal cords central canal, whilst forming: Choroid Plexuses:Secrete CSF w/in ventricles, which is moved around by cilia.

c. Microglia: Inflammatory Macrophages Phagocytize necrotic tissue, microorganisms, andforeign substances that invade the CNS (destroy pathogens).

d. OligoDendrocytes: Form myelin sheaths around 1 or moreaxons (electrical insulation) bywrapping several times b/w Nodes of Ranvier (important for Somatic system).


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PNS

e. Schwann Cells: Wrap around 1 axonseveraltimes to form a phospholipid myelin sheathf. Satellite Cells: Surround neuron cell bodies in sensory ganglia (provide support and nutrients).

Organization of Nervous Tissueo White matter: Myelinated axons. Nerve tracts propagate action potentials within the CNS.o Gray matter: Integrates unmyelinated axons, cell bodies, dendrites, & neuroglia. In brain: Gray (outer cortex + inner nuclei); White (deeper tissueMedulla). In spinal cord: White (outer area); Gray (deeper tissue).

Understand permeability characteristics of plasma membrane including channels and their properties Cells produce action potentials, which are electrical properties that result from ionic concentration

differences across plasma membranes (affected by relative permeability of membrane).

Lipid bilayers, due to their hydrophobicity, helpseparate charged ions on either side.o Electrical Potential is defined as the netcharge across a plasma membrane, so although there may

be positive/negative charges on both sides, an unequalratio will lead to an electrical gradient.

o Chemical gradient is the netconcentration of ions across a membrane, which alters theconcentration gradient. Energy flows down the concentration gradient.

Usually, it is the chemical gradient which drives the electrical gradient through ionic charges. Creating these gradients is aslow process of creating stored energy, which we can tap into.

o Electrochemicalgradients (combining of the 2) give a more accurate description of membrane pot. Resting membrane potential, establishment, changes, and determinants

o Resting membrane potential(EM) is the net charge/voltage across the membrane when the cell is atrest, meaning closest to its homeostatic values (Potential Difference: -70 to -90 mV). Ex.) If the outside = 0 mV, but EM = -70 mV,

this infers that the inside of the cell is 70 mV

more negative than the outside.

Several ions (K+, Na+, Cl-, Ca2+) worktogether to establish the resting membrane

potential, but its mainly Na+/K+-pumps and

K+ leak-channels that maintain that

homeostatic potential.

o Depolarization: The potential difference becomessmaller, & Na+rushes into cell, K+ out, causing it to become less negative (rise).

o Hyperpolarization: The potential difference becomesgreater, &the cell will lose Na+ and gain K+ as needed to get back to resting pot

o Afterpotential: A temporary phenomenon where the loss of Na+ andgain K+ is so quick, that there is aslighthyperpolarization, but the

K+ leak-channels quickly bring it back to resting membrane potential

o Hyperpolarization:An exaggerated repolarization event (or IPSP)that lowers the overall resting membrane

potential to a value lower than -70 mV


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Local potential, action potential, refractory periodo Local Potentials: Are measurablegradedpotentials that move in a decrementalfashion, but they are

not the same thing as action potentials. Summation of graded-potentials can reach threshold.

o Action Potential: Electrical properties as a result of ionicconcentration differences across a membrane that triggers a

depolarization event, which is a temporary, yet intense shift of

intracellular polarity (makes internal environment much more

positive), which propagates the electrical signal all the way downthe axon to its target (CNS or muscle/gland).

All-or-none principle refers to the necessity of graded-potentials to reach threshold before an action-potential

will occur (like a camera flash, you either have one or

you dont).

o Refractory Period: Temporary insensitivity to further stimulation. Absolute:Complete insensitivity during the depolarization/repolarization phase.

Cause: Na+ channels already open and stimulated, so a new action potential cannotpropagate, since relative concentration ratios are temporarily locked in place.

This explains why APs propagate un idirectionally. Relative: Slightinsensitivity, where a stronger-than-threshold stimulus must be induced

for another AP to initiate.

Ion-exchange and linked disorders: Na+/K+-pumps: Use ATP to pump out3Na+ ions and pump in2

K+ ions, thus making the cell lose1 positive charge, overall. These

are Voltage-gatedchannels that are closed until threshold is met

K+ leak-channels: Are always open and help extra K+ ions exit thecell to help maintain gradients.

Cl- leak-channels: Are also always open, but Cl-mostly exists in its salt form as NaCl.


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o Hyperkalemia: Too much K+ in the blood and ECF, thus leading to K+ staying inside the cell, insteadof leaving through the leak channels as it does in normal cases to maintain the -70mv resting

potential. This will eventually lead to the resting potential to increase (cell becomes less negative,

like an emphasized form of EPSP).

o Hypernatremia:Too much Na+ in the blood (usually induced by dehydration). This will not affectthe membrane potential, because since theres no Na+ leak-channels, theres no way for Na+ activity

to change since its physiological activity is ATP-driven, not concentration-driven.

o Hypercalcemia: Too much Ca2+ in the blood, which can lead to decreased neuronal excitability.

Gated Ion-channels:

Ligand-gated: Open/close in response to

ligands (like Acetylcholine) binding to receptor

proteins.

Voltage-gated: Open/close in response to smallvoltage changes across the cell membrane.

(Step 1 of 2) (Step 2 of 2)

Neuronal conduction and modulation of neuronal conductiono Positive Cooperativity: The depolarization of one voltage-gated channel after another, with the

previous one influencing the next one.

o Propagation refers to the ability of neurons to mobilize this electrochemical gradient byinstantaneously depolarizing 1 part of the axon after another, thus causing a domino-effect of

depolarization, which in the grand scheme, is seen as an electrical charge running along the axon.

o The action-potentials will jump from oneNode of Ranvierto another, making it faster. Therefore,myelinated axons propagate action-potentials much quickerthan unmyelinated axons.

o Nerve Fiber Types: Myelinated (faster propagation) vs. Unmyelinated (slower propagation)a) Type-A:Heavilymyelinated fibers conduct APs the fastest (15-120 m/s)

Provides that instant, sharp pain incurred from injury Motor neuronsb) Type-B:Lightly myelinated, so propagation is a bit slower (3-15 m/s) ANS

Leads to that dull, continuous pain that settles in a few seconds after sharp pain.c) Type-C:Non-myelinated conduct APs the slowest ( 2 m/s) ANS


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o Synapse: The junction b/w 2 cells where APs from a cell cancause an AP in another cell:

a) Presynaptic Terminal: AP travels down towards thesynaptic cleft, where it attracts Ca2+ ions, which help

release neurotransmitters (acetylcholine) from vesicles.

They then diffuse out of the synapse and enter the

synaptic cleft where they bind to postsynaptic receptors.

b) Synaptic Cleft:Open space b/w pre & postsynapticterminals, where neurotransmitters bind to ligand-gated

channels, potentially leading to the 2nd AP propagation.

c) Postsynaptic Terminal: Becomes depolarized w/ Na+as ligand-gated channels are activated, and if threshold

is reached, it will fire the 2nd AP.

Neurotransmitters and neuromodulators Neurotransmitters: Can be excitatory or inhibitory.o Acetylcholine: A neurotransmitter commonly associated with

Ligand-gated Na+ channels in synaptic terminals.

o Acetylcholinesterasebreaks down: Acetylcholine Acetyl-CoA + Choline, after they

unbind from their post-synaptic receptors. The choline is

recycled back into the pre-synaptic terminal.

o Norepinephrine is released in a similar fashion, except insteadof being broken down within the pre-synaptic region (like

acetylcholine), MAO will break down norepinephrine once it

returns into the presynaptic terminal.

o Neuromodulators: Chemicals produced by neurons thatmodulate APs. Some act by increasing/decreasing the amount

of neurotransmitter released by the presynaptic neuron.

EPSP: Raises the resting membrane potential to make itnaturally more depolarized, thus making future action-

potential easierto reach (Endorphins)

IPSP:Lowers the resting membrane potential to make itnaturally less depolarized, thus making future action-

potential harderto reach (Hyperpolarization).

Presynaptic Inhibition and Facilitation:o Axoaxonic synapses: Axon of one neuron synapses with the

presynaptic terminal of another (like many CNS synapses).

o Presynaptic inhibition: Reduction in neurotransmitter releasefrom presynaptic terminal (Endorphins can inhibit pain senses).

o Presynaptic facilitation: Amount of neurotransmitter releasedfrom presynaptic terminal increases (Glutamate facilitating

nitric oxide production).


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Summationo Spatial-summation: Each dendrite is receiving a different stimulus, so the relative amount of

stimulus at each dendrite is considered agradedpotential. It is only called an action-potentialafter

the trigger-zone region of the neuron converges all these stimuli into one, leading to their

summation, which can create an action-potential. (left pic)

o Temporal summation: Dendrite is receiving 2 stimuli, in quick succession, at thesame part of thedendrite, thus leading to summation and the propagation of an action-potential. (right pic)

Neuronal Pathways and Circuitso Convergent pathways: Many converge & synapse withsmallernumber of neurons.

Ex. Synthesis of data in brain.o Divergent pathways: Small # of presynaptic neurons synapse with large # of postsynaptic neurons.

Ex. Important information being transmitted to many parts of the brain.o Oscillating circuit: Outputs cause reciprocal activation

Ex. Sleep cycle, body-pain being induced with no injury

in-class quiz review - neurophysiology

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