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Histo > Basic Neuronal Synapse > Flashcards

Basic Neuronal Synapse Flashcards

1
Q

General Nerve Classification

A

Nerve fibers classified by the size of the fiber

Includes motor and sensory neurons

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2
Q

A-fibers

A

medium to large nerve fiber; myelinated

Aa, Ab, Agamma, Adelta–largest to smallest

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3
Q

C-fibers

A

small fiber, unmyelinated

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4
Q

Sensory Nerve Classification

A

Organized from largest to smallest

Ia : Muscle spindle primary ending (muscle stretch)
Ib: Golgi tendon organ: (muscle tension)

II: Muscle spindle secondary ending
III: Small, myelinated: (crude touch, sharp p!)
IV: Unmyelinated C-fibers: (dull, aching pain and temp)

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5
Q

Motor Neurons: (largest to smallest)

A

Alpha motor neuron
Gamma motor neuron
C-motor neuron

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6
Q

Alpha Motor Neuron

A

Extrafusal muscle fibers (skeletal muscle fibers)

Muscle fiber contraction

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7
Q

Gamma Motor Neuron

A

Intrafusal muscle fibers (muscle spindle)

Generate muscle response to sensory input from muscle spindles; control muscle spindle length

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8
Q

C-motor neuron

A

Autonomic nervous system fibers to smooth muscle

sympathetic and parasympathetic

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9
Q

Factors affecting NCV

A 
Membrane myelination
Neuron fiber diameter
Temperature 
Cold – decreases NCV
Heat – increases NCV
Pharmacological agents: most decrease NCV
Pathological processes: decrease NCV
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10
Q

Neuronal Synapses

A

Synapses are where neurons communicate with other neurons
axon terminal of one neuron that is adjacent to the dendrites of another neuron
consists of pre-synaptic neuron and post-synaptic neuron

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11
Q

Pre-synaptic neuron

A

releases neurotransmitter chemicals from the axon terminal

NTs bind to post-synaptic neuron and cause a change in MB permeability

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12
Q

Components of synapse

A

axon terminal
synaptic vesicles
synaptic cleft
post-synaptic receptors

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13
Q

Axon terminal

A

pre-synaptic neuron

Contains numerous synaptic vesicles and mitochondria

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14
Q

Synaptic vesicles

A

Contain neurotransmitters

Vesicles fuse with pre-synaptic membrane for exocytosis of contents

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15
Q

Synaptic cleft

A

Space between neurons that is maintained by reversible binding between membrane proteins of synaptic cells

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16
Q

Post-synaptic receptors

A

Protein receptors on membrane of post-synaptic neuron

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17
Q

Synaptic Sites: Axodendritic

A

Axon to dendrites and spines (most common type)

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18
Q

Synaptic Sites: Axosomatic

A

Axon to cell body synapse

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19
Q

Synaptic Sites: Axoaxonic

A

Axon to axon synapse

Most often occur at the initial segment or at the axon terminal of post-synaptic neuron

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20
Q

Synaptic Sites: Dendrodendritic

A

Dendrite to dendrite synapse

Occur infrequently and are typically reciprocal connections (synaptic communication in both directions)

21
Q

Chemical Synapse

A

Release of neurotransmitter (NT) molecules into synaptic cleft

NT is released from the pre-synaptic terminal

NT binds to specialized receptors on the post-synaptic membrane

Each type of neurotransmitter has specific receptors on the post-synaptic membrane

Different NTs and their respective receptors have different effects on the post-synaptic cell

22
Q

Electrical Synapse

A

Synapse that consists of gap junctions between adjacent cells

Gap junctions allow free passage of ions:

Any polarity change in one cell is easily passed to the adjacent cell

Allows synchronization of polarity changes among numerous adjacent cells
Abundant in connections between smooth muscle and cardiac muscle cells
Also contained within mammalian CNS

The easy transmission of changes in membrane potential between cells is important in contraction of:

Myocardium, smooth muscle of GI tract, and glandular epithelium

These synapses allow for coordinated contraction of smooth and cardiac muscle tissue

23
Q

Electrical Synapses components:

A

Gap Jxn
fast transmission
common in smooth and cardiac muscle

24
Q

Chemical Transmission of AP

A
  1. AP reaches the pre-synaptic terminal
  2. Change in membrane potential opens voltage-gated Ca 2+ channels to allow Ca 2+ to flow into the terminal
  3. Ca 2+ interacts with vesicles to cause vesicle fusion and exocytosis of neurotransmitter
  4. Neurotransmitter binds to receptor site on post-synaptic membrane
  5. Receptor is activated and creates channel opening in post-synaptic membrane
25
Q

Synaptic Transmission: Post Synaptic processing of NT

A

Neurotransmitter degradation/removal must occur to clear the cleft for new signal transmission
NTs bind receptor, cause action and are released from receptor
Diffusion – molecule unbinds from receptor and simply “floats” away from cleft
Re-uptake - pre-synaptic terminal removes neurotransmitter and recycles it
Enzymes – chemically degrade neurotransmitters

26
Q

Post-synaptic Response: potentials

A

Receptor-activated channels open to allow ion influx into post-synaptic cell

Amount of transmitter released (and bound) determines how many of these receptors/channels will be activated

Ion flux results in local potential change called:
Post-Synaptic Potential or graded potentials

Post-synaptic potentials are short-lived (milliseconds) changes in membrane potential

27
Q

Excitatory Post-Synaptic Potential (EPSP)

A

Influx of Na+ and Ca 2+ results in local depolarization–moves closer to threshold

28
Q

Inhibitory Post-Synaptic Potential (IPSP)

A

Influx of Cl- results in local hyper-polarization

further away from threshold

29
Q

Neuronal Intergration

A

The post-synaptic membrane contains thousands of transmitter-gated channels that create EPSPs or IPSPs

Post-synaptic neurons compute (integrate) numerous EPSPs and IPSPs = (summation)

Integration/summation occurs in order to determine whether the overall set of stimuli creates enough depolarization to reach threshold for the post-synaptic neuron

Excitation of post-synaptic neuron requires numerous EPSPs to provide enough polarity change to reach action potential threshold

30
Q

Spatial summation

A

Summation of all the EPSPs that are occurring simultaneously on neuron

31
Q

Temporal summation

A

Summation of EPSPs at the same synapse when they occur in rapid succession
Within 3-15 milliseconds of each other

32
Q

Divergence

A

Process by which a signal from a single neuron is transmitted to a large number of post-synaptic neurons

Allows amplification of a signal from one neuron to many neurons

33
Q

Convergence

A

Process by which multiple signals from different neurons excite a single post-synaptic neuron

Allows summation of input of several neurons

34
Q

Presynaptic Fxn

A

Functions of the pre-synaptic terminal can be affected by axoaxonal synapses it receives
Axoaxonal synapses alter NT release from axon terminal

35
Q

Presynaptic inhibition

A

Axoaxonal synapse causes anion (Cl-) channel opening

Reduces the positive charge of the presynaptic cell, and reduces the amount of NT released

36
Q

Presynaptic Facilitation

A

Axoaxonal synapse slows K+ channel opening of pre-synaptic neuron
Prolongs depolarization and increases NT release

37
Q

Characteristics of Neurotransmitters

A

Chemicals contained in vesicles in the pre-synaptic terminal

Released into synaptic cleft as mode of transmission of signals between neurons

Neurotransmitters are either excitatory or inhibitory

Most cells produce only one neurotransmitter

Most receptors bind only one particular NT
Some NTs can bind to more than one receptor

As a rule, no 2 NTs bind the same receptor but the same NT may bind to many different receptors- each different receptor that a NT binds to is called a receptor subtype receptors often named by their agonists

38
Q

Acetylcholine: Neurotransmitter

A

Excitatory NT
Major NT of the ANS and the neuromuscular junction
Utilizes nicotinic receptors at the neuromuscular junction

Utilizes muscarinic receptors at several areas of CNS and in the heart PNS (parasympathetics system)

39
Q

Receptor Blockade

A

Curare: blocks nicotinic receptors (creates paralysis)
Atropine: blocks muscarinic receptors (increase heart rate)
BoTox: blocks nicotinic receptors (creates paralysis)

40
Q

Glutamate: NT

A

Major excitatory neurotransmitter of CNS

Utilizes three different receptors with variable locations within the CNS
AMPA, NMDA, Kainate

Released in large quantities in cerebral injury and/or pathology
Excess excitation can have deleterious effects on neurons and CNS function:
Epilepsy
Cerebrovascular accident (CVA)
Seizures

41
Q

GABA: NT

A

Major inhibitory neurotransmitter of CNS
Utilizes GABAa and GABAb receptors
A receptors: open Cl- channels

B receptors: use intracellular messenger to affect gene transcription and ultimately neuron function
Important in long-term memory/learning

Barbituates and benzodiazepenes (anti-anxiety, anti-depressants)
Bind to GABAa receptor and lengthen duration of channel opening when GABA is bound

42
Q

Catecholamines: NT

A

Dopamine, serotonin, norepinephrine, epinephrine

43
Q

Dopamine

A

Inhibitory NT with receptors throughout CNS
Involved with motor function, memory, mood and emotions

Important function of maintaining smooth, controlled movements

Lack of dopamine leads to Parkinson’s disease

Excess dopamine associated with schizophrenia

44
Q

Serotonin (5-HT)

A

(5-hydroxytryptamine)

Inhibitory NT associated with mood (euphoria), emotion, sleep

45
Q

LSD

A

Agonist of serotonin (binds serotonin receptor

46
Q

Prozac

A

Inhibits reuptake of serotonin; allows it to be longer acting at synapses

47
Q

Tryptophan

A

Molecular precursor to serotonin

48
Q

Norepinephrine

A

noradrenaline

49
Q

Epinephrine (adrenaline)

A

Major NTs of the autonomic nervous system

Both have excitatory and inhibitory functions

Function of these NTs is dependent on which receptor type they bind

Use adrenergic receptors:
Alpha 1 and alpha 2 receptors
Beta 1 and beta 2 receptors

Histo (12 decks)

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