MNSR 15

Question 1

What are the four main categories of chemical messengers used in intercellular communication and what is their significance?

Answer 1

The four main categories of chemical messengers are hormones, neurotransmitters, paracrine substances, and autocrine substances. They are essential for coordinating reflexes and local homeostatic responses as they enable cells to communicate by secreting these messengers into the extracellular fluid.

Question 2

Define hormone

Answer 2

A substance secreted by cells in one part of the body that passes to another part where it is effective, in very small concentrations, in regulating the growth or activity of the cells.

Question 3

How do hormone levels in the blood change, and what prompts these changes?

Answer 3

Hormone levels in the blood vary constantly, rising and falling in response to specific stimuli. For example, insulin levels increase when blood glucose levels rise.

Question 4

What role do hormones play in the regulation of bodily functions?

Answer 4

Hormones act as long-term regulators of a wide range of physiological activities, often playing a crucial role in homeostasis, such as the regulation of plasma calcium levels by the parathyroid gland.

Question 5

Why do hormones only affect specific cells in the body?

Answer 5

Hormones only influence cells that possess the appropriate receptors for them. These receptors are specific proteins that, when bound by their hormone, initiate a response within the cell.

Question 6

Hormones are usually secreted directly into the bloodstream by the…

Answer 6

endocrine glands.

Question 7

Hormones are transferred to the site of action, or…

Answer 7

target organ

Question 8

Hormones are usually complexed with (transported by)…

Answer 8

plasma proteins

Question 9

Some hormones are produced by neurons:

Answer 9

Pass down the axon to the nerve endings
Released into special capillary networks near the target organ
Known as neuro-hormones (neurosecretion)
e.g. serotonin

Question 10

Tissue hormone examples include:

Answer 10

Kinins
- Bradykinin (Blood vessel dilation)

Prostaglandins
- Prostaglandin H2 (Inflammatory mediator)

Hormones of the GIT
- Gastrin (Gastric acid secretion)
- Secretin (Regulation of pH in duodenum)
- Cholecystokinin (Digestion of fat & protein).

Adipose tissue
- Adiponectin (glucose regulation and fatty acid catabolism )
- Resistin (inflammation/obesity/T2DM?)

Question 11

What is endocrine signaling?

Answer 11

Hormones act on target cells distant from site of synthesis

e.g. Adrenocorticotrophic Hormone – stimulates release of steroids

Question 12

What is paracrine signaling?

Answer 12

Signalling molecules act on neighbouring cells

e.g. Serotonin – helps regulate wide range of activities including mood and social behavior, appetite and digestion, sleep, memory and body temperature

Question 13

What is autocrine signaling?

Answer 13

Signalling molecules act on same cells to amplify signals

e.g. The cytokine interleukin-1, an inflammatory cytokine which induces fever

Question 14

What is a peptide hormone?

Answer 14

Long/ short chains of amino acids
eg. vasopressin, oxytocin

Question 15

What is an amino acid derived hormone?

Answer 15

Derived from amino acids (tryptophan or tyrosine)
eg. adrenaline

Question 16

What are steroid hormone?

Answer 16

Derivatives of cholesterol
eg. testosterone, estrogen, cortisol

Question 17

What are fatty acid derivatives?

Answer 17

Derived from arachidonic acid
eg. prostaglandins

Question 18

A nerve cell (neuron) has a fibrous projection called an…

Answer 18

axon that reaches toward the next neuron.

Question 19

A nerve impulse is…

Answer 19

a wave of
electrical charge sweeping
from neuron to neuron.

Question 20

There is a gap called a…

Answer 20

synapse between one neuron and next.

Question 21

Neurotransmitters move across the synapse…

Answer 21

across the synapse.

Question 22

Neurotransmitter – what are they?

Answer 22

Also calledchemical transmitterorchemical messenger,
Are chemical agents released byneurons(nerve cells).

Cause stimulation of neighbouring neurons ormuscleorglandcells.

Allow signals to be passed from onecellto the next throughout the nervous system.

Question 23

Neurotransmitters are:

Answer 23

Synthesized by neurons
Stored in vesicles, typically located in theaxon’s terminal end (presynaptic terminal)

Question 24

When anerveimpulse arrives at the presynaptic terminal of one neuron, the neurotransmitter molecules are…

Answer 24

released through the presynaptic membrane and into the synaptic cleft. In milliseconds, they travel across the synaptic cleft to the postsynaptic membrane of the adjoining neuron, where they then bind to receptors.

Question 25

The activation of receptorscauses…

Answer 25

either the opening or closing of membraneion channels in the second cell, and this alters the cell’s permeability.

Question 26

In many instances, this change in permeability causes ______; the cell then produces its own_______, thereby initiating an electrical impulse.

Answer 26

depolarization, action potential

Question 27

There are various types of neurotransmitters classified by their chemical and molecular properties including:

Answer 27

Amino acids e.g. glutamate, glycine, γ-aminobutyric acid (GABA);

Amines e.g. dopamineandserotonin, acetylcholine

Peptides e.g.somatostatin, opioids, metenkephalin, Tyr-Gly-Gly-Phe-Met)

Purines e.g. ATP

Some gaseous substances, e.g.nitric oxide, can also act as neurotransmitters

Question 28

How do neurotransmitters work?

Answer 28

Neurotransmitter molecules are released from vesicles of one neuron, travel across the synapse, and find receptors in the next neuron.

Question 29

The ___ neuron is the neuron before synapse: the ___ neuron is the neuron on other side.

Answer 29

presynaptic, postsynaptic

Question 30

What is the name of the neurotransmitter in the autonomic nervous system?

Answer 30

Acetylcholine

Question 31

Main job of acetylcholine is to…

Answer 31

carry a signal from nerve cells to muscle cells.

Question 32

When acetylcholine has done its work, the enzyme __ helps to hydrolyse it.

Answer 32

acetylcholinesterase

Question 32

How does acetylcholine work?

Answer 32

When a motor nerve cell gets the proper signal from the nervous system, it releases acetylcholine into its synapses with muscle cells. There, acetylcholine opens receptors on the muscle cells, triggering the process of contraction.

Question 33

List how acetylcholine works in a summary.

Answer 33

1. Synthesis of acetylcholine (ACh) from acetyl CoA and choline.
2. Storage of ACh in pre-synaptic vesicles
3. Release of Ach into the synapse
4. ACh binds to and activates receptors
5. Inactivation by enzymatic breakdown of ACh by acetylcholinesterase (AChE) located in synapse

Question 34

What initiates the production of Nitric Oxide (NO) in the nervous system?

Answer 34

The process begins with the release of glutamate, a neurotransmitter, which crosses the synapse and interacts with receptors on the postsynaptic neuron, leading to the opening of Ca²⁺ ion channels.

Question 35

How does calcium ion influx lead to the production of NO?

Answer 35

The influx of Ca²⁺ ions binds to calmodulin, which then activates nitric oxide synthase (NOS). Activated NOS converts arginine to NO and citrulline.

Question 36

What is the significance of NO’s ability to diffuse through neurons?

Answer 36

NO diffuses to numerous neurons in the vicinity due to its solubility in water and lipids, activating guanylate cyclase, which leads to cyclic GMP production and results in changes to the postsynaptic response to stimuli and causes vascular relaxation.

Question 37

How does NO act as a retrograde messenger and what is its effect on the presynaptic neuron?

Answer 37

NO diffuses back to the presynaptic neuron and affects it by potentially activating the release of more glutamate. This characteristic of NO classifies it as a retrograde messenger, meaning it can modulate the activity of the neuron that originally released the neurotransmitter.