Conduction Velocity and Neuronal Synapses Study Guide

Question 1

Once an action potential is generated, they are _____________ of stimulus intensity.

Answer 1

alike and independent

Question 2

A strong stimulus is indicated to the central nervous system by a _________ of impulses.

Answer 2

higher frequency

Question 3

What are the 2 types of refractory periods? In terms of the ion channels, what is happening in the 1st type of refractory period that prevents the generation of 2nd action potential? How about in the 2nd type of refractory period?

Answer 3

• absolute refractory period: 1 AP is already being generate, and it starts with the opening of the Na+ channels and lasts until they reset, which ensures that each AP is all or none, and enforces 1 way transmission of nerve impulses
• relative refractory period: most Na+ channels have returned to their resting state, some K+ channels are still open, and repolarization is occurring. This follows the absolute refractory period

Question 4

Is a 2nd action potential truly prevented from forming in the 2nd type of refractory period?

Answer 4

No – however the threshold for AP generation is elevated – only an exceptionally strong stimulus can stimulate an AP

Question 4

Be ready to identify the 2 types of refractory periods on a graphical tracing of an action potential.

Answer 4

draw out

Question 5

The rate of AP propagation depends on what 2 factors? How do these factors alter conduction velocity?

Answer 5

• Axon diameter: larger diameter fibers have less resistance to local current flow and faster impulse conduction
• Degree of myelination: presence of myelination dramatically increases speed of propagation

Question 6

continuous conduction

Answer 6

slower conduction; occurs in unmyelinated axons, voltage-gated channels in the membrane are immediately adjacent

Question 6

saltatory conduction

Answer 6

faster conduction – about 30x faster. Occurs only in myelinated axons. Voltage gated NA+ channels are located at the myelin sheath gaps, APs are generated at the gaps, and electrical signals appear to jump rapidly from gap to gap. Myelin sheaths insulate and prevent leakage of charge

Question 7

Define multiple sclerosis. What does it have to do with myelin sheaths? How does this generally impact nervous system function?

Answer 7

• An autoimmune disease that primarily affects young adults, causing visual disturbances, weakness, loss of muscular control, speech disturbances, and incontinence
• Myelin sheaths in the CNS are destroyed when the immune system attacks myelin. APs are slower.

Question 8

Make a table/chart for group A, B, and C nerve fibers. Compare them based on diameter, whether myelin is present, and the rate at which they transmit impulses.

Answer 8

draw out

Question 9

Explain paresthesia.

Answer 9

Both cold and continuous pressure can interrupt blood circulation. This hinders the delivery of oxygen and nutrients to neuronal processes. Without oxygen and nutrients, neurons are unable to conduct impulses and paresthesia occurs.
- Fingers going numb when holding ice
- Foot going numb when you sit on it

Question 10

Neurons are connected at ________.

Answer 10

synapses

Question 11

What are the 2 most common types of synaptic connections? Define these types – what is connecting?

Answer 11

• Axodendritic: between the axon terminals of one neuron and the dendrites of another
• Axosomatic: between the axon terminals of one neuron and the soma (cell body) of another

Question 12

What are the 2 main types of synapses? Which of these is by far the more common in the human body?

Answer 12

• Axon terminal of presynaptic neuron - contains synaptic vesicles filled with neurotransmitter
  Receptor region on postsynaptic neuron’s membrane (typically on dendrite or cell body) – receives neurotransmitter
• Two parts are separated by fluid filled synaptic cleft

Question 13

What is synaptic delay? What causes it?

Answer 13

the time needed for neurotransmitter to be released, diffuse across the synapse, and bind to receptors (can take anywhere from 0.3-5.0 ms)
- Cause: transmission across the chemical synapse is the rate-limiting step of neural transmission

Question 14

How are impulses transmitted across electrical synapses? What kind of cell junction facilitates this?

Answer 14

Neurons are electrically coupled – joined by gap junctions that connect the cytoplasm of adjacent neurons

Question 15

Define EPSP. How does neurotransmitter binding create this type of graded potential?

Answer 15

excitatory postsynaptic potentials – neurotransmitter binding opens chemically gated channels – allows simultaneous flow of Na+ and K+ in opposite directions. Na+ influx is greater than K+ influx, which results in local graded potential depolarizations called EPSPs

Question 15

Fully define neuronal integration.

Answer 15

The summation of many different EPSPs and IPSPs at a specific axon’s initial segment

Question 16

Define IPSP. How does neurotransmitter binding create this type of graded potential?

Answer 16

• inhibitory postsynaptic potentials – neurotransmitter binding opens chemically gated channels which allows entrance / exit of ions that cause hyperpolarization
• Makes postsynaptic membrane more permeable to K+ or Cl-
  
  • K+ moves out of the cell
  • Cl- moves into the cell
• Reduces the postsynaptic neuron’s ability to produce an AP – moves neuron father away from threshold (more negative)

Question 17

What are the two types of summation? Define and create an example of each type of summation. How is each type of summation able to create an AP?

Answer 17

• Temporal summation: 1 or more presynaptic neurons transmit impulses in rapid fire order
  
  • The 1st impulse produces ESPS and before it can dissipate another EPSP is triggered and adds on top of the 1st impulse, creating an AP
• Spatial summation: postsynaptic neuron is stimulated by many different terminals simultaneously
  
  • Many receptors are activated and each produces EPSPs which then add together, creating an AP

Question 18

What are the 2 parts of a chemical synapse? What separates these parts?

Answer 18

• Axon terminal of presynaptic neuron - contains synaptic vesicles filled with neurotransmitter
• Receptor region on postsynaptic neuron’s membrane (typically on dendrite or cell body) – receives neurotransmitter
• Two parts are separated by fluid filled synaptic cleft