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Bio 273 > Unit 2 - Neurophysiology - (Course Notes) Important Terms and Concepts > Flashcards

Unit 2 - Neurophysiology - (Course Notes) Important Terms and Concepts Flashcards

1
Q

CNS

A

-made up of the Brain and Spinal Chord
-greatest variety of neurotransmitters

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2
Q

PNS

A

-nervous system outside the brain and spinal cord
-consists of sensory (afferent) neurons and motor (efferent) neurons
-efferent branch sends signals OUT to the other organ systems (effectors/targets)
-two main types of neurotransmitters: acetylcholine and norepinephrine/epinephrine

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3
Q

Neuron

A

-generate and transmit electrical impulses Two types of signals:
-Short distance (graded potential)
-Long distance (action potential)

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4
Q

Dendrite

A

-slender processes that receive information
-transmit electrical signals toward the soma
-location of graded potentials (along with cell body)

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5
Q

Axon Terminal

A

The end of the axon, the connection between the neuron and other cells

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6
Q

Myelin

A

An insulating layer that forms around nerves, made up of many layers of plasma membrane. Membranes are part of specialized glial cells that wrap around the axon of a neuron (called Schwann cells in PNS, and oligodendrocytes in CNS)

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7
Q

Node of Ranvier

A

-gaps formed between the myelin sheath where the axons are left uncovered
-concentrated with voltage-gated Na+ channels
-action potentials jump from one node to the next

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8
Q

Saltatory Conduction

A

-action potentials jump from one node to the next
-results in faster conduction down the length of the axon compared to unmyelinated axons

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9
Q

Synapse

A

The points of contact between neurons where information is passed from one neuron to the next, most often form between axons and dendrites, consist of a presynaptic neuron, synaptic cleft, and postsynaptic neuron

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10
Q

Postsynaptic Neuron

A

Integrates all the signals it receives to determine what happens next, transmits the signal toward the synapse

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11
Q

Somatic Division

A

-controls skeletal muscles (its only effector/target)
-a single neuron carries information from the CNS to the effector
-causes ONLY muscle excitation, cannot inhibit muscle function

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12
Q

Neuromuscular Junction

A

-the synapse between a somatic motor neuron and a skeletal fibre
Has 3 components:
1. pre-synaptic axon terminal (filled with neurotransmitter vesicles that contain ACh)
2. Synaptic cleft
3. Post-synaptic membrane of skeletal muscle fibre
-membrane is modified into a motor endplate
-contains nicotinic ACh receptor channels

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13
Q

Depolarization

A

-a decrease in membrane potential
-cell membrane bodies become LESS negative (e.g. -70 mV to +30 mV)
-brings membrane potential closer to the threshold potential

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14
Q

Repolarization

A

Returning back to resting membrane potential shortly after the depolarization phase of an action potential

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15
Q

“All-or-none”

A

Describes action potentials for long distance transmission, do not diminish in strength over distance

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16
Q

Neurotransmitter

A

Endogenous chemicals that allow neurons to communicate with each other throughout the body
Create two types of responses in postsynaptic cell:
1. Direct responses - fast synaptic potential, does not last long, response via interaction with an ion channel
2. Indirect responses - slow synaptic potential, longer lasting response. Uses G proteins via 2nd messenger response system

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17
Q

Antagonist

A

since sympathetic and parasympathetic axons release different neurotransmitters the two elicit antagonistic responses from the target tissue

Sympathetic axons release norepinephrine (NE)
Parasympathetic axons release acetylcholine (ACh)

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18
Q

Norepinephrine

A

-amine derived from a single amino acid
-tyrosine is converted to norepinephrine
-called “catecholamines”
-synthesized in axon terminal & packaged into vesicles
-neurons that secrete norepinephrine are called “adrenergic”
-released by most post-ganglionic sympathetic neurons onto adrenergic receptors
Two classes of adrenergic receptors (both coupled to G proteins): ɑ (alpha) and β (beta)

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19
Q

Epinephrine

A

-amine derived from a single amino acid
-tyrosine is converted to epinephrine
-called “catecholamines”
-synthesized in axon terminal & packaged into vesicles

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20
Q

Acetylcholine (ACh)

A

-synthesized from choline & acetyl CoA, catalyzed by enzyme choline acetyl transferase (CAT)
-synthesized in axon terminal & packaged into vesicles
-neurons are “cholinergic” if they secrete ACh or have receptors
-degraded by “acetylcholinesterase”
-released by ALL pre-ganglionic neurons (both branches) onto cholinergic nicotinic receptors
-released by most post-ganglionic parasympathetic neurons onto cholinergic muscarinic receptors

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21
Q

Acetylcholinesterase

A

-found on presynaptic or postsynaptic membrane or both
-Choline is actively transported back into the presynaptic axon terminal to be used again

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22
Q

Muscarinic Cholinergic Receptor

A

-a type of cholinergic receptor that couples with G proteins to generate a slow response
-may close or open different ion channels
-may be excitatory or inhibitory
-stimulated by ACh & muscarine, agonists
-ACh is primary ligand

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23
Q

Nicotinic Cholinergic Receptor

A

-a type of cholinergic receptor operate via ion channels to generate a fast response, always excitatory
-acetylcholine (ACh) is released by ALL pre-ganglionic neurons [sympathetic and parasympathetic] onto cholinergic nicotinic receptors
-stimulated by ACh & nicotine, agonists
-located on motor end plates (skeletal muscle) and sympathetic/parasympathetic ganglia

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24
Q

Adrenergic Receptor

A

-receptors for epinephrine and norepinephrine
ɑ1 (alpha one) - found on most tissue, response NE>E
β1 (beta one) - heart muscle and kidney, response NE=E
β2 (beta two) - blood vessels & smooth muscle, E>NE

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25
Receptor Types (ion vs. GPCR)
Adrenerigic receptors act via G proteins -β1 & β2 receptors stimulate cAMP production -ɑ1 receptors increase Ca2+ levels in the cytoplasm
26
Events at the Synapse
1. Action potential depolarizes the axon terminal in presynaptic cell 2. Depolarization triggers opening of voltage-gated Ca2+ channels in presynaptic cell membrane 3. Calcium signals synaptic vessels to release neurotransmitter 4. Neurotransmitter then diffuses across synaptic cleft and binds to receptors on postsynaptic cell membrane 5. Binding of neurotransmitter initiates a response in post synaptic cell
27
Glial Cell
-many different kinds of glial cells are found in the CNS -associated with neurons -communicate with each other and nearby neurons using electrical and chemical signals (no electrical signals over long distances) -help neurons through nerve impulse conduction and by maintaining the microenvironment around neurons
28
Soma (cell body)
-contains nucleus and biosynthetic machinery -centre of chemical processes (which keeps cell functioning and alive) -location of graded potentials (along with dendrites)
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Axon
-cytoplasmic extension that sends out information -transmit electric signals away from soma
30
Initial Segment (trigger zone)
-action potential starts in the trigger zone -also known as the integration centre of the neuron -location is different in various kinds of neurons
31
Schwann Cell
PNS glial cells -a special glial cell wrapped around axons -forms myelin (made of membrane) -myelin acts as an electrical insulator
32
Graded Potential
-can initiate cell action potential if sum of these potentials reaches the threshold potential -come from various areas on the soma and dendrites of the neuron -spatial summation (space), temporal summation (time)
33
Afferent Neuron
-sensory -receive information from receptor cell -transmit sensory info “to” the CNS -cell bodies located outside CNS -long cytoplasmic extensions transmit info to cells (interneurons) within the CNS -trigger zone adjacent to the receptor
34
Efferent Neuron
-Motor neurons that receive information from the interneurons -Cell bodies are located in the CNS -Cytoplasmic extensions transmit information by sending signals out to the other organ systems (effectors/targets) -trigger zone is the axon hillock and initial segment (first part of the axon)
35
Efferent Branch of PNS
Divided into two main parts: 1. Autonomic division - 2 neuron chain -innervates smooth and cardiac muscle, glands, some adipose tissue -sometimes called "involuntary division" 2. Somatic division - single neuron -innervates skeletal muscle -sometimes called "voluntary division"
36
Autonomic Division of PNS
Branches of Autonomic Division: 1. Sympathetic - (fight or flight) -prepares for physical activity and stress 2. Parasympathetic - (rest and digest) Structure of Autonomic Division: -both branches share same general structure, two-neuron chain between CNS and effector -synapses between these neurons are in cell clusters known as "autonomic ganglia" Cells leading from CNS to ganglion are preganglionic Cells leading from the ganglion to the effector are postganglionic ## Footnote Sympathetic axons release norepinephrine (NE) Parasympathetic axons release acetylcholine (ACh)
37
Neuroendocrine Tissue
Adrenal gland two parts: 1. Adrenal cortex - secretes steroid hormones 2. Adrenal medulla - associated with the sympathetic division, modified sympathetic ganglion -Chromaffin cells (special cell type) secrete epinephrine which then travels in the blood
38
Targets of Autonomic Pathway
1. Innervates - smooth & cardiac muscle, exocrine and endocrine glands, and adipose tissue 2. Synapse structure - different from model synapse -axon ends with swollen areas at distal ends called a "Varicosity" which contains vesicles with neurotransmitter to be released into interstitial fluid (tissue fluid), varicosity is not always at the end of the axon
39
Interneuron
-located inside CNS -make up 96% of all neurons -transmit signals within CNS (either laterally to spinal chord, or vertically to the brain) -integrate info from afferent neurons -transmit signals to efferent neurons -trigger zone is the axon hillock and initial segment (first part of the axon)
40
Threshold Potential
-minimum depolarization necessary to trigger an action potential
41
Hyperpolarization
-an increase in membrane potential -cell membrane potential becomes MORE negative
42
Oligodendria (oligodendrocytes)
-CNS version of Schwann cell -wrap around axons -form myelin to insulate CNS axons
43
Astroglia (astrocytes)
-star shaped cells -contract blood vessels and neurons -maintain neuron microenvironment -helps maintain homeostasis in ECF around neurons
44
Ependymal Cell
-epithelial cells that produce CSF -create create a selectively permeable barrier between compartments of the brain
45
Action Potential
-travel long distances along neurons without decreasing in strength because of Na+ channel's positive feedback loop -depolarization in one area causes depolarization in the region next to it (and so on) -wave of depolarization travels down the axon -once threshold is reached, action potential is generated identical to the previous action potential -can't go backwards because areas of depolarized membrane are in refractory periods
46
Absolute Refractory Period
-lasts approx. 1 millisecond -No action potential can be triggered no matter how large the stimulus
47
Relative Refractory Period
-a large (suprathreshold) stimulus is required to bring forth an action potential during the relative refractory period
48
IPSP (inhibitory post synaptic potentials)
-hyperpolarizing graded potentials make the membrane potential more negative (farther away from the threshold potential) -decrease the chance of exciting the axon to fire (inhibit the cell from reaching the threshold move farther away from action potential)
49
EPSP (excitatory post synaptic potentials)
-a depolarizing graded potential that increases the chance of axon firing (action potential firing after threshold is reached)
50
Myelin Sheath
Allows electrical impulses to transmit quickly and efficiently along the nerve cells
51
Satellite Cells
-PNS glial cell, non-myelinating Schwann cells -support soma (the nerve cell body)
52
Nuclei
cluster of cell bodies in the CNS
53
Ganglia
cluster of cell bodies in the PNS
54
Tract
a bundle of axons in the CNS forming a pathway
55
Nerves
a bundle of axons in the PNS forming a pathway
56
Pseudounipolar Neuron
-somatic sensory neurons -axon and dendrites fuse during development into a single process
57
Bipolar Neuron
-smell/vision sensory neurons -contain a single axon and dendrite
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Multipolar Neuron
-CNS and Efferent -single axon process -two or more dendrites
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Microglia
-small specialized immune cells -remove damaged cells and foreign invaders (like macrophage)
60
Nervous System
61
Electrical Principals
-human body is electrically neutral -cell membrane is an electrical insulator, allows for the separation of electrical charge -difference in change inside and outside creates electrical gradient -ICF has net (-) charge, ECF has net (+) charge -Na+, Ca+, Cl- higher in ECF -K+ higher in ICF (anions, large negatively charged intercellular proteins are higher in ICF) -ion channels allow electrical charge to move through the membrane -easier for K+ to move passively due to large number of passive leak channels (compared to Na+ in ECF)
62
Excitable tissue (nervous & muscle)
-use rapid changes of membrane potential (electrical difference inside & outside the cell measured in mV, millivolts) when excited -allows neurons to conduct an electrical signal -allows muscle cells to contract
63
Equilibrium Potential (Eion)
-membrane potential that exactly opposes the concentration gradient of an ion -electrical and chemical forces acting on the ion are equal and opposite -for any single ion you can calculate the electrical potential of the cell needed to generate equilibrium state if the concentration gradient is known using the Nernst Equation
64
Nernst Equation
z= electrical charge of ion 61 is 2.303 RT/F at 37 °C -equilibrium potential for K+ in a typical neuron is approx. -90mV -equilibrium potential for Na+ is approx. +60mV -Nernst equation looks at what the membrane potential would be is the membrane was only permeable to one ion -in living systems there are multiple ions that contribute to membrane potential in a cell
65
Goldman-Hodgkin-Katz (GHK) equation
-predicts membrane potential using multiple ions -considers the membrane permeability of each ion
66
Selective Ion Channels (in neurons)
4 major types: 1. Na+ channels 2. K+ channels 3. Ca2+ channels 4. Cl-channels
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Graded Potentials
-started by ions entering the cell from the EFC -amplitude of the potential is proportional to the strength of the triggering event -travel only short distances -lose strength due to: current leak and cytoplasmic resistance
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Refractory Period
-during hyperpolarization phase there is a period called the "refractory period" Made of two parts: Absolute refractory period and Relative refractory period
69
Voltage-gated Sodium Channels
Two gates that regulate movement during action potential: 1. Activation gate-closed at resting membrane potential to prevent Na+ influx 2. Inactivation gate-ball and chain of amino acids on cytoplasmic side of membrane (open at resting membrane potential, closes much slower) -depolarizing stimulus has to reach -55 mV to stimulate the entire channel and trigger action potential -activation gate opens, Na+ enters the cell causing further depolarization -positive feedback loop causes more voltage-gated Na+ channels to open -inactivation gate closes (short delay), prevents further influx of Na+ and ends (+) feedback loop (at peak of action potential)
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Voltage-gated Potassium Channels
-neurons also have voltage-gated K+ channels in their membranes -K+ channels are slower to open than Na+ channel -depolarizing to threshold (-55 mV) triggers opening of K+ channel -full opening is around +30 mV for K+ channels Note: very few ions move across the membrane during a single action potential, the concentration gradient remains essentially unchanged after one action potential

Bio 273 (25 decks)

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