Nerve Cell A&P Pt.3 Flashcards
What diameter axons propagate nerve impulses faster: Larger diameter or smaller diameter?
Larger.
What are the 3 categories of nerve fiber diameters?
- A fibers.
- B fibers.
- C fibers.
How wide are A fibers?
5-20 um.
Are A fibers myelinated or unmyelinated?
Myelinated.
What type of refractory period do A fibers have?
Brief absolute refractory periods.
How quickly do A fibers conduct nerve impulses?
12-130 m/sec. .
What types of sensory neuron axons contain A fibers?
Those associated with touch, pressure, joint position, and some thermal sensations (rapid temperature change).
What type of motor neuron axons contain A fibers?
Those that conduct impulses to skeletal muscle.
How wide are B fibers?
2-3 um.
Are B fibers myelinated or unmyelinated?
Myelinated.
How rapidly do B fibers conduct nerve impulses?
~15 m/sec. .
What type of refractory period do B fibers have?
Absolute refractory periods that are longer than in A fiber.
What types of sensory neuron axons contain B fibers?
Those sending nerve impulses from the viscera to the brain and spinal cord.
What types of motor neuron axons contain A fibers?
All autonomic ones that extend from the brain and spinal cord to autonomic ganglia.
How wide are C fibers?
0.5-1.5 um.
Are C fibers myelinated or unmyelinated?
Unmyelinated.
How rapidly are nerve impulses conducted in C fibers?
0.5-2 m/sec. .
What type of refractory period do C fibers have?
Absolute refractory period, longest of the three fiber types.
What types of sensory neuron axons contain C fibers?
Those associated with pain, touch, pressure, temperature from skin (gradual temperature change), and pain impulses from viscera.
What types of motor neuron axons contain A fibers?
Autonomic ones that extend from the autonomic ganglia to the glands, heart, and smooth muscle.
What are 3 motor functions of B and C fibers?
- Pupil constriction and dilation.
- Heartrate decrease and increase
- Urinary bladder contraction and relaxation.
What is the pre-synaptic neuron?
The neuron sending the signal.
What is the post-synaptic neuron?
The neuron receiving the signal.
What does the term axodendritic refer to?
The movement or communication of something from the axon of one neuron to the dendrite of another neuron.
What does the term axosomatic refer to?
The movement or communication of something from the axon of one neuron to the soma of another neuron.
What does the term axoaxonic mean?
The movement or communication of something from the axon of one neuron to the axon of another neuron.
What are the 2 types of synapse?
- Chemical.
- Electrical.
Which synapse is faster: chemical synapse or electrical synapse?
Electrical synapse.
How are signals communicated through an electrical synapse?
Gap junctions.
What 3 kinds of tissues utilize electrical synapses?
- Visceral smooth muscle.
- Cardiac muscle.
- Embryo.
What feature of an electrical synapse allows for its use in the heart?
Synchronized messaging, allowing the heart to beat as one unit.
What is the synaptic cleft?
The space between the pre- and post-synaptic neurons that allows for indirect communication.
What is the synaptic cleft filled with?
Interstitial fluid.
What does the nerve impulse in the presynaptic neuron cause to occur when it reaches the dendrites and telodendria?
It causes the release of neurotransmitters.
What happens after the binding of the neurotransmitters to the post-synaptic neuron?
A postsynaptic signal (a type of graded potential) is produced.
What do the neurotransmitters do once released?
They diffuse through the synaptic cleft and bind to receptors on the plasma membrane of the postsynaptic neuron.
What do presynaptic cells covert electrical signals into?
Chemical signals.
What do postsynaptic cells convert electrical signals into?
Chemical signals.
When the nerve impulse reaches the synaptic end bulb of the pre-synaptic axon, what voltage-gated channels are opened?
Ca2+ by depolarization.
Which direction does Ca2+ flow through the open voltage-gated Ca2+ channels?
Into the cell membrane.
What does the change in membrane potential in the synaptic end bulb trigger?
The exocytosis of synaptic vesicles.
What do the vesicles merge with to release the neurotransmitters into the synaptic cleft?
Plasma membrane.
What specific type of channels do the neurotransmitters bind to on the postsynaptic plasma membrane?
Ligand-gated channels.
What does the binding to ligand-gated channels allow for the influx of?
Na+, K+, or Cl-.
What does the influx of ions cause to form?
A postsynaptic potential.
What occurs when enough Na+ has entered the cell membrane?
Depolarization has reached the threshold, triggering an AP.
What are the 2 potentials that neurotransmitters could induce in the post-synaptic cell?
- Excitatory.
- Inhibitory.
What induces excitatory potential or excitatory post synaptic potentials (EPSP)?
Depolarization.
What ion(s) causes EPSP?
Na+ moving through open cation channels.
What induces inhibitory potential or inhibitory post synaptic potentials (IPSP)?
Hyperpolarization.
What ion(s) causes IPSP?
Cl- moving through open anion channels and some K+.
What are the 3 ways neurotransmitters are removed?
- Diffusion.
- Enzymatic degradation.
- Uptake by cells.
How does diffusion remove neurotransmitters?
They diffuse away from the synaptic cleft, likely into the post-synaptic cell.
How does enzymatic degradation remove neurotransmitters?
Enzymes breakdown the neurotransmitters in the synaptic cleft.
ex: Acetylcholinesterase
How does uptake by cells remove neurotransmitters?
The neurotransmitters are moved back to the presynaptic neuron for reuse in a process called reuptake.
ex: Norepinephrine.
How many synapses does the typical CNS neuron receive input from?
1-10K.
What is summation?
The process of integrating neuron inputs that occurs in the trigger zone.
In EPSPs, what is the correlation between the level of summation and the chance of the threshold being achieved?
Positive.
What are the 2 types of summation?
- Spatial.
- Temporal.
What is spatial summation?
When a build-up of neurotransmitters in several presynaptic end bulbs are simultaneously released.
What is temporal summation?
When a build-up of neurotransmitters is released by one presynaptic end bulb 2+ times in rapid succession.
Can spatial and temporal summation occur at the same time?
Yes.
Are postsynaptic neurons only connected to one presynaptic neuron?
No, they are connected to multiple neurons that are potentially releasing conflicting neurotransmitters.
What ultimately determines the effect of neurotransmitters on the postsynaptic neuron?
The sum of all the excitatory and inhibitory neurotransmitters.
What is required for a EPSP to occur?
The total excitatory potential must be greater than the total inhibitory potential, but less than the threshold.
What is required for a nerve impulse to occur?
The total excitatory potential must be greater than the total inhibitory potential and the threshold must be reached.
What is required for an IPSP to occur?
The total inhibitory potential must be greater than the total excitatory potential.
What 3 things occur as a result of IPSP achievement?
- Membrane hyperpolarization.
- Inhibition of postsynaptic neuron.
- Inability to generate nerve impulses.
What are Renshaw cells?
Inhibitory neurons in the spinal cord that prevent excess skeletal muscle contraction.
How do Renshaw cells complete their function?
They release glycine at inhibitory synapses with somatic motor neurons.
What does strychnine poison bind to?
Glycine receptors.
What does strychnine poison cause to occur?
The excitation/inhibition balance in the CNS to be disturbed by allowing for uninhibited generation of nerve impulses by motor neurons.
What do skeletal muscles look like in an individual that has ingested strychnine?
Fully contracted and unable to relax.
