Nerve Impulses and Synapses

Question 1

What are the 3 overlapping functions of the nervous system?

Answer 1

1. Sensory Input: sensory information to monitor body
2. Integration: processes and interprets information
3. Motor output: activates a response in the body

Question 2

Membrane potential changes when:

Answer 2

• Concentrations of ions across membrane change
• Membrane permeability of ions changes

Question 3

What is the resting membrane potential?

Answer 3

Approximately 70mV (inside negative)

Question 4

What is depolarization?

Answer 4

A decrease in membrane potential. Inside the membrane becomes less negative. Promotes nerve impulses.

Question 5

What is hyperpolarization?

Answer 5

An increase in membrane potential. Inside the membrane becomes more negative. Reduces nerve impulses.

Question 6

What are graded potentials?

Answer 6

Short lived, localized changes in membrane potential. The stronger the stimulus, the stronger the voltage change and farther the current flows.

Question 7

What are action potentials?

Answer 7

Brief, long-distance signals that only occur in muscle cells and axons of neurons. They do not decay over distance.

Question 8

How are stimulus intensitys coded?

Answer 8

The strength of a stimulus is depicted by the frequencey of action potential impulses.

Question 9

What is conduction velocity of action potential impulses dependent on?

Answer 9

Axon diameter and degree of myelination.

Question 10

What are the 2 types of conduction?

Answer 10

Continuous conduction: slow conduction in nonmyelinated axons
Saltatory conduction: occurs in myelinated axons and is about 30x faster.

Question 11

What are the 3 groups of fibers?

Answer 11

Group A fibers: largest diameter, myelinated somatic sensory and motor fibers of skin, skeletal muscles and joints. Transmit at 150m/s
Group B fibers: Intermidiate diameter, lightly myelinated, transmit at 15m/s
Group C fibers: smallest diameter, unmyelinated, trasnmit at 1m/s

Note: B/C group fibres prodominately serve viceral organs.

Question 12

What is a synapse?

Answer 12

A juction that mediates information transfer from one neuron to another or an effector cell.

Question 13

What are the presynaptic and postsynaptic neurons?

Answer 13

The presynaptic neuron conducts impulses toward the synapse and the postsynaptic neurons conducts impulses away from the synapse.

Question 14

What are the most common synapse connections?

Answer 14

Axodendritic synapses (between axon endings and dendrites of another neuron) and Axosomatic synapses (between axon endings and cell body of another neuron)

Question 15

What are the less common synapse connections?

Answer 15

Axoaxonal, Dendrodendritic and Somatodendritic synapses.

Question 16

What are the 2 types of synapses?

Answer 16

1. Electrical synapses: much less common than chemical synapses.
2. Chemical synapses: convert the electrical signals to chemical signals (neurotransmitters) to travel acorss the synapse to the postsynaptic cells.

Question 17

What is the space between two neurons in a chemical synapse called?

Answer 17

The synaptic cleft is a fluid-filled space approximately 30-50 nm wide. The axon terminal of the presynaptic neuron contains synaptic vesicles which hold neurotransmitter molecules. The receptor region of the postsynaptic neuron sits on the other side of the synaptic cleft.

Question 18

What are the steps of chemical synapses?

Answer 18

1. Action potential arrives at axon terminal.
2. Voltage-gated Ca2+ channels open and Ca2+ enters the axion terminal.
3. Ca2+ entry causes synaptic vesicles to release neurotransmitter by exocytosis.
4. Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.
5. Binding of neurotransmitter opens ion channels, creating graded potentials.
6. Neurotransmitter effects are terminated.

Question 19

What are the ways the postsynaptic slate is reset?

Answer 19

Reuptake: astrocytes/presynaptic terminal stores or destroys neurotransmitter with enzymes.
Degradation: by enzymes associated with the postsynaptic membrane or present in the synaptic cleft.
Diffusion: away from the synapse.

Question 20

What is the difference between excitatory versus inhibitory neurotransmitters?

Answer 20

Excitatory cause depolarization and inhibitory cause hyperpolarization. Some neurotransmitters exert both effects depending on the specific receptor types with which they interact.

Question 21

What happens when excitatory neurotransmitters bind to receptors?

Answer 21

Chemically gated channels allows flow of Na+ and K+ in opposite directions. This results in a local net graded potential depolarization called EPSP. EPSPs trigger AP if EPSP is of threshold strength.

Question 22

What happens when inhibitory neurotransmitters binds to receptors?

Answer 22

Makes postsynaptic membrane more permeble to K+ and Cl-. K+ moves out of cell, Cl- moves into cell. This reduces postsynaptic neuron’s ability to produce an action potential. (makes potential more negative, farther from threshold).

Question 23

What are direct action neurotransmitters?

Answer 23

Neurotransmitter binds driectly and opens ion channels. Promotes rapid responses. Examples are ACh and amino acids.

Question 24

What are indirect action neurotransmitters?

Answer 24

Acts through intracellular second messengers, usually G protein pathways. Broader, longer-lasting effects similar to hormones. Examples are amines, neuropeptides and dissolved gases.

Question 25

What are the 2 common neurotransmitter receptors?

Answer 25

Channel-linked receptors: mediate fast synaptic transmission.
G protein-coupled receptors: which oversee slow synaptic responses.

Question 26

Explain neuronal pools

Answer 26

A presynaptic input fiber ditruputes synapses to multple postsynaptic neurons. Postsynaptic neurons in the discharge zone are more likely to reach threshold and generate APs, while neurons in the facilitated zone recieve less and usually only approach the threshold.

Question 26

What is serial processing?

Answer 26

Input travels along one pathway to specific destinating to produce a specific response. Common in reflexes.

Question 26

What is parallel processing?

Answer 26

Input travels along several pathways, one stimulus promotes numerous responses.

Question 26

What is a diverging circuit?

Answer 26

One input, many outputs.

Question 26

What is a converging circuit?

Answer 26

Many input, many outputs.

Question 26

What is a reverberating circuit?

Answer 26

An ocillating circuit, controls rythmic activity.

Question 26

What is a parallel after discharge circuit?

Answer 26

One input goes along many parallel arrays that converge on a single output. The inputs reach the output cell at different times causing a burst of impulses called an after discharge.