Chapter 2: Synapse

Question 1

Synapse:

Answer 1

specialized gap between neurons.

Question 2

Sherrington

Answer 2

studied reflexes (automatic muscular responses to stimuli) and introduced the term synapse

Question 3

Reflex arc:

Answer 3

the circuit from sensory neuron to muscle response

Question 4

6. Temporal summation:

Answer 4

Repeated stimuli within a brief time having a cumulative effect.

Question 5

Presynaptic neuron:

Answer 5

The neuron that delivers the synaptic transmission.

Question 6

Postsynaptic neuron:

Answer 6

The neuron that receives the message.

Question 7

Graded potential:

Answer 7

Either depolarization (excitatory) or hyperpolarization (inhibitory) of the postsynaptic neuron.

Question 8

excitatory postsynaptic potential (EPSP)

Answer 8

A graded depolarisation which occurs when Na+ ions enter the postsynaptic neuron.

• EPSPs are not action potentials: The EPSP’s magnitude decreases as it moves along the membrane.
• A quick sequence of EPSPs combine to exceed the threshold and produce an action potential

Question 9

Spatial summation:

Answer 9

Several synaptic inputs originating from separate locations exerting a cumulative effect on a postsynaptic neuron.

a. For example, pinching one point does not produce a reflex but pinching two points at once does.
b. This happens because the two points activated separate sensory neurons, whose axons converged onto a neuron in the spinal cord.
c. Spatial summation critical to brain functioning

Question 10

Inhibitory postsynaptic potential (IPSP):

Answer 10

A temporary hyperpolarization of a postsynaptic cell (this occurs when K+ leaves the cell or Cl- enters the cell after it is stimulated).

Question 11

Spontaneous firing rate:

Answer 11

The ability to produce action potentials without synaptic input (EPSPs and IPSPs increase or decrease the likelihood of firing action potentials).

Question 12

The Discovery of Chemical Transmission at Synapses

• T.R. Elliott (1905):
• Otto Loewi (1960):

Answer 12

1. T.R. Elliott (1905): Suggested that the sympathetic nerves stimulate muscle by releasing adrenaline or a similar chemical. However, the evidence was not convincing and most scientists continued to belief that synapses communicated electrically.
2. Otto Loewi (1960): Fluid from a stimulated frog heart was transferred to another heart. The fluid caused the new heart to react as if stimulated.
3. Lead to the conclusion that synaptic transmission depends on chemical rather than electrical stimulation.
4. This discovery revolutionized our understanding and led to research developing psychiatric drugs.

Question 13

neurotransmitters:

Answer 13

a. Chemicals that are released by one neuron at the synapse and affect another neuron

Question 14

Categories of neurotransmitters include:

Answer 14

Amino acids
Monoamines
Acetylcholine
Neuropeptides (chains of amino acids)
Purines
Gases (such as nitric oxide, which dilate nearby blood vessels, increasing blood flow to nearby brain areas)

Question 15

Catecholamines (dopamine, epinephrine, and norepinephrine):

Answer 15

Three closely related compounds containing a catechol and an amine group.

Question 16

Synthesis of Transmitters

Answer 16

Neurons synthesize neurotransmitters (from amino acids) from precursors derived originally from food.

Question 17

Vesicles:

Answer 17

Tiny nearly spherical packets that store high concentrations of neurotransmitters near the presynaptic terminal
- Nitric oxide is an exception to this rule, as neurons do not store nitric oxide for future use.

Question 18

MAO (monoamine oxidase):

Answer 18

break down transmitters into inactive chemicals because it is possible for a neuron to accumulate excess levels of a neurotransmitter
- The first antidepressant drugs that psychiatrists discovered were MAO inhibitors, by blocking MAO they increased the brain’s supply of serotonin, dopamine and norepinephrine

Question 19

exocytosis:

Answer 19

When an action potential reaches the axon terminal, the depolarization causes voltage-dependent calcium gates to open. As calcium flows into the terminal, the neuron releases a neurotransmitter into the synaptic cleft within 1-2 milliseconds

Question 20

A neurotransmitter can have two types of effects when it attaches to the active site of the receptor:

Answer 20

ionotropic (faster but shorter effect) or metabotropic (slower but longer effects) effects.

Question 21

Ionotropic effects:

Answer 21

• Sodium and potassium channels along an axon are transmitter-gated or ligand-gates channels. When the neurotransmitter attaches, it opens a channel.
• Well suited to conveying visual and auditory information along with anything else that needs to be updated ASAP

Question 22

Metabotropic Effects:

Answer 22

when the neurotransmitter attaches to the receptor, it alters the configuration of the rest of the receptor protein, enabling a portion of the protein inside the neuron to react with other molecules. Activation of the receptor by the neurotransmitter leads to activation of G-proteins, which are attached to the receptor.
- These synapses are better for more enduring effects such as taste, smell and pain

Question 23

G-proteins:

Answer 23

A protein coupled to the energy-storing molecule guanosine triphosphate (GTP)

Question 24

Second messenger:

Answer 24

Chemicals that carry a message to different areas within a postsynaptic cell; the activation of a G-protein inside a cell increases the amount of the second messenger.
- A metabotropic synapse, by way of its second messenger, influences activity in much or all of the cell and over longer time

Question 25

Neuropeptides/ neuromodulators:

Answer 25

b. Whereas the neuron synthesizes most other neurotransmitters in the presynaptic terminal, it synthesizes neuropeptides in the cell body and then slowly transports them to other parts of the cell.
c. Whereas other neurotransmitters are released at the axon terminal, the neuropeptides are released mainly by dendrites, and also by the cell body and the sides of the axon.
d. They are better for hunger, thirst and other long-term changes in behaviour and experience

Question 26

Hallucinogenic drugs:

Answer 26

Drugs that distort perception.

i. Many hallucinogenic drugs like lysergic acid diethylamide (LSD) resemble serotonin and bind to serotonin type 2A (5-HT2A) receptors.
ii. These drugs provide stimulation at inappropriate times or for longer than usual durations.

Question 27

A drug that chemically resembles a neurotransmitter:

Answer 27

can bind to its receptor.

Question 28

Nicotine:

Answer 28

Compound found in tobacco.

i. Stimulates the nicotinic receptor (a type of acetylcholine receptor) in both the central nervous system and neuromuscular junction of skeletal muscles.
ii. Can also increase dopamine release by attaching to neurons that release dopamine in the nucleus accumbens.

Question 29

Opiate drugs:

Answer 29

Derived from, or chemically similar to those derived from, the opium poppy.

i. Familiar opiates include morphine, heroin, and methadone.
ii. Opiate drugs exert their effects by binding to the same receptors as endorphins.

Question 30

Inactivation and Reuptake of Neurotransmitters

Answer 30

a. Neurotransmitters need to be inactivated because they may continue to excite or inhibit the receptor. Neurotransmitters are inactivated in different ways.
b. Acetylcholine is broken down by the enzyme acetylcholinesterase (AChE); the two components are reabsorbed and recycled.
c. Serotonin and the catecholamines (i.e., dopamine and norepinephrine) are taken up by the presynaptic neuron. This process is called reuptake; it occurs through specialized proteins called transporters.
d. Some serotonin and catecholamine molecules are converted into inactive chemicals by enzymes such as COMT (converts catecholamines) and MAO (converts both catecholamines and serotonin).
e. Stimulant drugs, including amphetamine and cocaine, inhibit the transporters for dopamine, thus decreasing reuptake and prolonging dopamine’s effects.

Question 31

Methylphenidate (Ritalin):

Answer 31

Stimulant drug often prescribed for attention- deficit/hyperactivity disorder.

i. Works like cocaine by blocking reuptake of dopamine at presynaptic terminals.
ii. The effects of methylphenidate are much longer lasting and less intense as compared to cocaine, yet also come with a risk of addiction.

Question 32

Autoreceptors:

Answer 32

Presynaptic receptors sensitive to the same neurotransmitter they release. Detect the amount of transmitter released and inhibit further synthesis and release (that is, they provide negative feedback).

Question 33

Electrical Synapses

- Gap junction:

Answer 33

A few special-purpose synapses operate electrically because it is faster than chemical transmission (somewhat confirming Sherrington’s hypothesis).
- Gap junction: In an electrical synapse, the membrane of one neuron comes into direct contact with the membrane of another.

Question 34

a hormone:

Answer 34

chemical that is secreted primarily by glands but also by other cells and is conveyed by blood to other organs whose activity it influences
- Unlike neurotransmitters, which are released directly to another neuron, hormones convey messages to any organ that can receive them.

Question 35

Endocrine glands:

Answer 35

produce hormones

Question 36

Protein hormones and peptide hormones:

Answer 36

composed of chains of amino acids
- Protein and peptide hormones bind to membrane receptors and activate a second messenger within the cell—exactly the same process as at a metabotropic synapse.

Question 37

Hormones secreted by the brain control the secretion of other hormones.

Answer 37

a. The pituitary gland is attached to the hypothalamus and consists of two distinct glands, the anterior pituitary and the posterior pituitary, which each produce different hormones.
b. The posterior pituitary is composed of neural tissue like the hypothalamus. Two hormones, oxytocin and vasopressin (also known as antidiuretic hormone), are released from the posterior pituitary. However, both of these hormones are synthesized in the hypothalamus.
c. The anterior pituitary, composed of glandular tissue, synthesizes six hormones.
d. The hypothalamus controls the release of these six hormones by secreting releasing hormones that stimulate or inhibit the release of other hormones.
- The hypothalamus maintains fairly constant circulating levels of certain hormones through a negative feedback system