Moderate sized diameters and myelinated, therefore moderately fast Speeds up to 15 m/sec. Found in ANS & visceral organs

Nervous Tissue Lecture 4 Flashcards by a w

What are the factors that influence the speed of propagation?

Amount of myelination
Axon diameter
Temperature

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How are nerve fibers classified based on propagation speed?

A fibers (Very fast)
B fibers (Moderately fast)
C fibers (Slowest)

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What are the characteristics of A fibers?

Largest diameter axons and myelinated, therefore FASTEST
Speeds up to 130 m/sec.
Associated with touch, pressure, proprioception, some pain, and temperature sensations
Conduct APs to skeletal muscles

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Describe B fibers.

Moderate sized diameters and myelinated, therefore moderately fast
Speeds up to 15 m/sec.
Found in ANS & visceral organs

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What are the characteristics of C fibers?

Smallest diameters with no myelination, therefore SLOWEST
Slowest of the 3 fibers.
Found in reproductive, urinary, excretory, digestive neurons, nociceptors from skin and viscera

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What is the site of communication between two neurons or a neuron and an effector cell?

Synapse

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What are the terms used to describe neurons before and after the synapse, and the connections between an axon and a dendrite/cell body?

Pre-synaptic neuron
Post-synaptic neuron/cell
Axo-dendritic (connection between an axon and a dendrite)
Axo-somatic (connection between an axon and a cell body)

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What type of synapse contains gap junctions and what are its advantages?

Electrical synapses
Advantages: Faster communication, synchronization, allows a large number of neurons or muscle fibers to produce action potentials in unison

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What is the most abundant type of synapse and what are its advantages?

Chemical synapses
Advantages: Can modulate response, can be excitatory or inhibitory

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What are the steps involved in chemical synapses?

Arrival of action potential at the pre-synaptic neuron’s synaptic end bulb
Membrane depolarization opens voltage-gated Ca2+ channels, allowing Ca2+ influx
Ca2+ stimulates exocytosis of synaptic vesicles containing neurotransmitters (NTs)
NTs diffuse across the synaptic cleft and bind to receptors on the post-synaptic membrane
Binding of neurotransmitters to receptors opens ligand-gated channels, allowing ion flow
Ion flow generates a graded potential (post-synaptic potential)
Signal ends when NT is broken down by an enzyme and recycled, diffuses out of the synaptic cleft, or taken back into pre-synaptic neuron.

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What is the process involved in the integration of information in a single neuron?

Single neuron may receive information from thousands of synapses, both excitatory and inhibitory.
Axon hillock integrates all stimuli and determines the rate of action potential generation at the initial segment.
The sum of all excitatory and inhibitory effects at any given time determines the effect on the postsynaptic neuron.

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What happens during synaptic fatigue and what are its consequences?

Neurotransmitters are usually reabsorbed and recycled.
After extended stimulation, the supply of neurotransmitter may not keep up with demand.
Synapse is unable to function until ACh (acetylcholine) is replenished.
Inability to function leads to synaptic fatigue.

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What are the two types of neurotransmitter receptors?

Ionotropic receptors (Ligand-gated receptors)
Metabotropic receptors (G-protein coupled receptors)

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What are the characteristics of ionotropic receptors?

Neurotransmitter receptor connected directly to an ion channel
Can be excitatory or inhibitory

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How do metabotropic receptors function?

Uses a messenger protein (G Protein) to open certain ion channels
Usually inhibitory
Acetylcholine (ACh) can be excitatory at some synapses (ionotropic) and inhibitory at others (metabotropic)

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What are the two major categories of neurotransmitters?

Small-Molecule Neurotransmitters
Peptide Neurotransmitters

What are the functions of acetylcholine?

Excitatory neurotransmitter at NMJ
Excitatory between pre-ganglionic and post-ganglionic neurons of the autonomic nervous system (ANS)
Inhibitory neurotransmitter in cardiac muscle in response to parasympathetic NS

What are examples of excitatory and inhibitory amino acid neurotransmitters?

Excitatory: Glutamate and aspartate
Inhibitory: Gamma-aminobutyric Acid (GABA) (CNS), Glycine (NMJ)

What are examples of biogenic amine neurotransmitters?

Epinephrine and norepinephrine
Dopamine (DA)
Serotonin (5-HTP)

What are the functions of nitric oxide as a neurotransmitter?

Potent vasodilator
Excitatory neurotransmitter in the brain
Important in generating and maintaining an erection

What are characteristics of peptide neurotransmitters?

Found in CNS and PNS
Both excitatory and inhibitory
Usually bind to metabotropic receptors
Many are also hormones

How can the effects of neurotransmitters be modified?

NT synthesis can be stimulated or inhibited
NT release can be enhanced or blocked
NT receptors can be activated or blocked
NT removal can be stimulated or inhibited

What are neural circuits?

Functional groups of neurons that process specific types of information.

What are the different types of neural circuits?

Simple
Diverging
Converging
Reverberating
Parallel after-discharge

Describe a simple neural circuit.

The simplest type of neural circuit where a presynaptic neuron stimulates a single postsynaptic neuron, which then stimulates another, and so on (very rare).

What is a diverging neural circuit?

A single neuron stimulates multiple neurons, leading to signal amplification.

Explain a converging neural circuit.

Multiple neurons stimulate a single neuron, allowing for summative effects.

What characterizes a reverberating neural circuit?

Similar to simple circuits, but branches from later neurons synapse with earlier ones, causing reverberation backwards. For example, coordinated movement, short-term memory, and breathing.

Describe a parallel after-discharge neural circuit.

In this circuit, a single presynaptic neuron stimulates multiple neurons, which all synapse back to a common postsynaptic cell

What is neuroplasticity?

Neuroplasticity refers to the capability of the nervous system to adapt and change based on experience. changes can include: * sprouting of new dendrites * synthesis of new proteins * alterations in synaptic contacts with other neurons.

Define neuroregeneration.

Neuroregeneration is the capability of neurons to replicate or repair themselves. In the peripheral nervous system (PNS), mild to moderate damage to neurons often allows for the recovery of nerve function, facilitated by the protective sheath called the neurolemma. However, the central nervous system (CNS) lacks regenerative capabilities.

What is neurogenesis?

Neurogenesis refers to the birth of new neurons from undifferentiated stem cells.

What changes occur when there is damage to an axon?

When an axon is damaged, changes occur in both the cell body and the distal portion of the axon. Chromatolysis involves Nissl body degranulation in the neuron as part of repair, while Wallerian degeneration is the degeneration of the distal axon and its myelin sheath.

How do Schwann cells respond to axonal injury?

Schwann cells multiply and form a regeneration tube at the injured site, guiding new axon growth from the proximal area. Axons usually grow at a rate of approximately 1.5 mm per day.