Organization of the Nervous System, Synapses and Transmitters

Question 1

What is enclosed in the CNS?

Answer 1

Encephalon (brain, brainstem, cerebellum), spinal cord

Question 2

What is enclosed in the PNS?

Answer 2

Peripheral nerves ( sensory & motor)

Question 3

What is the function of the autonomic nervous system?

Answer 3

It controls the autonomic functions of the body like the heart rate, respiratory rate, digestion, urination.

Question 4

What is the difference between the sympathetic and parasympathetic nervous systems?

Answer 4

Sympathetic increases the activity of the autonomic functions
Parasympathetic decreases the activity of the autonomic functions

Question 5

What are the three major levels of organization in the CNS?

Answer 5

Cortical Level
Subcortical Level
Spinal Cord Level

Question 6

What does the spinal cord level contain?

Answer 6

• Walking circuits (central pattern generator)
• Circuits for reflexes that control movement
• Circuits for body support against gravity
• Circuits for reflexes that control organ functions

Question 7

What is the Subcortical Level?

Answer 7

Contains the brainstem (medulla & pons), mesencephalon, hypothalamus, thalamus, cerebellum, and basal ganglia
Controls subconscious body activities like arterial pressure, respiration, equilibrium, feeding reflexes, body temp…

Question 8

What is the Cortical Level?

Answer 8

the superficial layer of the gray matter
It never functions alone
Place of the most complicated and sophisticated functions of the NS: info processing, memory storage, thought processing, decision making

Question 9

What is the somatosensory system?

Answer 9

transmission of somatic info from receptors to CNS
Info transmitted to:
- spinal cord
- reticular substance (brainstem & mesencephalon)
- Cerebellum
- thalamus
- cerebral cortex

Question 10

What percentage of all sensory info is discarded by the brain as being irrelevant and unimportant?

Answer 10

99%

Question 11

What does the motor system do?

Answer 11

Controls body activities

Question 12

What are the three components of a neuron?

Answer 12

Dendrites: receives signals
Cell body: process signals
Axon: signal propagation and output

Question 13

what are the four types of neurons?

Answer 13

Unipolar: one process ( dendrites & axon on the same side)
Bipolar: one main dendrite & one main axon
Multipolar: several dendrites, 1 axon
Pseudo-unipolar: one process (develops from bipolar)

Question 14

Explain Neuronal Communication

Answer 14

Info is transmitted within the neuron by action potentials (electrical signals)
APs start at the axon hillock and propagate along the nerve until it comes to the fiber’s end
Info is communicated between neurons by synapses (chemical signals)

Question 15

What is the role of Ca++ in neuronal communication?

Answer 15

Ca++ enters the cell and causes neurotransmitters to be released from vesicles. The amount of neurotransmitters released is directly related to the # of Ca++ ions that enter

Question 16

What is a neurotransmitter (Ligand)?

Answer 16

It is a chemical substance synthesized in the presynaptic terminal and released in the synapse by the arrival of an AP. By diffusing across a synapse the neurotransmitter causes the transfer of an AP to another nerve or muscle fiber

Question 17

What are the two types of neurotransmitters?

Answer 17

Excitatory (dopamine, serotonin, acetylcholine, norepinephrine glutamate) and inhibitory (GABA)

Question 18

What are the steps of neurotransmitter release?

Answer 18

AP arrives at the presynaptic terminal
Local depolarization opens voltage-gated Ca++ channels and Ca++ ions flow out into terminal
Ca++ ions trigger the fusion of synaptic vesicles with the presynaptic membrane
Release of the transmitter into the synaptic cleft (exocytosis)

Question 19

What are the two types of receptors on the postsynaptic membrane that bind the neurotransmitter released from the presynaptic terminal?

Answer 19

1) ionotropic receptor: ion channels

2) Metabotropic receptor: second messenger activator

Question 20

What are the two types of ion channels that make up the ionotropic receptors?

Answer 20

Cation channels allow cations to pass. they excite (depolarize) the postsynaptic neuron

Anion channels allow anions to pass. They inhibit (hyperpolarize) the postsynaptic neuron

Question 21

What are metabotropic receptors?

Answer 21

Metabotropic receptor is a protein structure that causes prolonged changes in the neurons ( seconds to months) by activating substances inside the postsynaptic neuron.

Question 22

What is the most common type of second messenger activator ( metabotropic receptor)?

Answer 22

G-Proteins. It is a protein complex attached to the interior side of the receptor protein. the binding of the transmitter on the receptor activates the G-protein which initiates a a cascade of events leading to alteration in cellular activity. (alpha-subunit detaches from complex and triggers these events)

Question 23

Why do we need Metabotropic receptors for?

Answer 23

Memory, learning

Question 24

What is the difference between ionotropic and metabotropic receptors in terms of transmission speed?

Answer 24

Ionotropic: fast synaptic transmission
Metabotropic: Slow synaptic transmission

Question 25

What is the excitatory postsynaptic potential (EPSP)?

Answer 25

the membrane potential moves towards less negative values. Increased permeability to Na+ and/or Ca++ (more positivity inside)
caused by the activation of excitatory receptors

Question 26

What is the inhibitory postsynaptic potential (IPSP)?

Answer 26

the membrane potential moves towards more negative values ( < Vm, hyperpolarization)
Increased permeability to Cl- and K+ ( more negativity inside)
Caused by the activation of inhibitory receptors

Question 27

What are the characteristics of Postsynaptic potentials?

Answer 27

• sub-threshold potentials ( below threshold of AP)
• summation of different PSPs ( spatial & temporal)
• EPSPs increase the likelihood of AP (signal transmission)
• IPSPs decrease the likelihood of AP (no signal transmission)

Question 28

What is the principle of spatial summation?

Answer 28

When a postsynaptic neuron is only excited by a single presynaptic terminal, it will likely never induce an AP. However, when many presynaptic terminals excite the same postsynaptic neuron their respective EPSPs can add up (summate) and reach threshold to generate an AP

Question 29

What is the principle behind temporal summation?

Answer 29

If the same presynaptic terminal fires rapidly enough, the discharges can add up to one another and reach threshold for AP

Question 30

Describe the generation of Action Potentials on Postsynaptic neurons

Answer 30

APs do not begin on soma or dendrites (near synapses) but rather at the initial segment of the axon called the axon hillock. Soma and dendrites have few voltage-gated Na+ channels which are necessary for the generation of AP.
Electrical signals propagate from dendrites and soma to the axon hillock through electronic conduction

Question 31

What is synaptic plasticity?

Answer 31

It is the ability of a synapse to strengthen or weaken over time, in response to increases or decreases in its activity

Question 32

What does synaptic plasticity result from?

Answer 32

Change in the number of neurotransmitters released
Change in the number of postsynaptic receptors
Change in the response of the postsynaptic neuron to neurotransmitter

Question 33

What are the types of synaptic plasticity?

Answer 33

Synaptic enhancement: increase in the efficacy of the synapse
Synaptic depression: decrease in the efficacity of the synapse
Short-term plasticity: lasts from few ms to min
Long-term plasticity: lasts from hours to months