Neurons & Hormones

Question 0

What are the two control systems?

Answer 0

The nervous and hormonal systems.

Question 1

What is the function of control systems in metazoans?

Answer 1

+To monitor the external environment
+To control internal functions - effector systems
+To respond to perceived changes.

Question 2

What are the differences in control systems between invertebrate phyla?

Answer 2

In invertebrates, there is considerable overlap in the structure and functions of the systems. In some phyla they are a single control system.

Question 3

What are the differences in the control systems of vertebrates?

Answer 3

Vertebrates have evolved highly defined linking points, for example the pituitary glands and the pineal glands embedded in the brain.

Question 4

What is the pituitary gland and what is its function?

Answer 4

The pituitary gland is a hormonal gland at the base of the brain. It has multiple functions including the regulation of hormones that effect growth, stress, blood pressure, the thyroid, and some reproductive functions.

Question 5

What is the pineal gland and what is its function?

Answer 5

An endocrine gland that start off as aa light sensitive organ and has links to SAD. It produces melatonin, which affects sleep patterns in both circadian rhythms and seasonal patterns.

Question 6

What is the ‘Neuroid’ system and which phyla is it found in?

Answer 6

A lack of defined nervous system with no specialised nerve cells. This is found in the Porifera.

Question 7

Describe the nerve system of the Porifera.

Answer 7

They have no defined nervous system. However, there is evidence of conduction of electrical impulses (0.26cm/s) that shut down choanacyte pumping, for example when something noxious is encountered.

Question 8

What is epithelial conduction?

Answer 8

This is where the whole of the epithelium acts as a single receptor organ at 3-35cm/s. Found in the hydromedusan Sarsia sp & the urochordate Oikopleura sp.

Question 9

What are nerve nets and in which phyla are they found?

Answer 9

Interconnected neurons lacking a brain or any form of cephalisation. They are most characteristic of cnidarians but are also found associated with nerve cords of other phyla, e.g. in the molluscan foot, echinoderm arms and even the gut of vertebrates.

Question 10

What are the conduction speeds of a nerve net?

Answer 10

10-100cm/s.

Question 11

What are nerve nets in the cnidarians like?

Answer 11

They have several layers of nets that communicate with each other, but the method of communication varies within the phylum. In the Anthozoa and Scyphozoa the neurons within each net are linked with symmetrical bidirectional chemical synapses, meaning communication is chemical between cells, and they have both emitters and receptors. In the Hydrozoa neurons have direct electrical coupling which allows division of nerve nets. In all three taxa they nets are linked by polarised chemical synapses.

Question 12

What are the nerve systems found in Invertebrates?

Answer 12

The central nervous & peripheral systems.

Question 13

What is the function of the Central Nervous System (CNS)?

Answer 13

1) acts as the destination for inputs from the peripheral system.
2) coordinates the consequent motor control.

Question 14

What is the peripheral system?

Answer 14

Sense organs and the nerve tracts from them.

Question 15

What is the basic structure of the CNS?

Answer 15

A pair of cerebro–pleural ganglia (CPG) connected to paired, solid nerve cords, usually ventral.

Question 16

What is the structure of the CNS in ascidian ‘tadpole’ larvae and vertebrate chordates?

Answer 16

The CNS consists of a single ganglionic structure connected to a dorsal, hollow neural tube.

Question 17

What are unmyelinated axons and where are they found?

Answer 17

Neurons without a myelin sheath around the axon. All invertebrates have unmyelinated axons, but they are also found in the grey matter of vertebrate brains.

Question 18

What are the three main types of neuronal forms?

Answer 18

Monopolar, bipolar and multipolar.

Question 19

What are monopolar neurons?

Answer 19

Neurons that connect the CNS to effectors (muscles).

Question 20

What are bipolar neurons?

Answer 20

Peripheral sense cells whose axons connect to the CNS.

Question 21

What are multipolar neurons?

Answer 21

They connect the CPG and stretch receptors.

Question 22

What are stretch receptors?

Answer 22

Mechanoreceptors responsive to the distension of various organs and muscles, as well as the carotid artery where they measure blood pressure.

Question 23

What are giant axons?

Answer 23

Axons found in giant squid, polychaetes and insects. They evolved to facilitate rapid movements, as the speed of conduction in unmyelinated neurons is roughly proportional to the square root of the axonal diameter.

Question 24

What are myelinated neurons?

Answer 24

Neurons with a myelin (protein) sheath around them.

Question 25

Why are myelinated neurons better than unmyelinated?

Answer 25

They increase the speed of conduction as the action potential will ‘jump’ between nodes (saltatory conduction).
Also, since the ionic currents are confined to the nodes of ranvier, fewer ions ‘leak’ across the membrane, which saves metabolic energy (nervous system uses approx 20 percent of metabolic energy).

Question 26

How are action potentials generated?

Answer 26

By the sequential operation of sodium–potassium pumps.

Question 27

What is transported in and out during the sodium–potassium pump?

Answer 27

3 sodium (Na plus) out and 2 potassium (K minus) in, powered by ATP.

Question 28

How does an action potential propagate?

Answer 28

The neuotransmitters open one Na gate, which allows Na in. This changes the voltage outside the axon, allowing more voltage gated channels to open as more Na move in and K move out.

Question 29

What is synaptic transmission?

Answer 29

Communication between nerves via synapses.

Question 30

What is the size of the synaptic cleft?

Answer 30

Around 100nm.

Question 31

What are the two major classes of neurotransmitters?

Answer 31

Cholinergic transmitters (acetylcholine) and Adrenergic transmitters (nor–adrenaline, octopamine and various neuropeptides.)

Question 32

What is used to prevent prolonged and damaging depolarisation in the post–synaptic neurone?

Answer 32

Enzymes, such as cholinesterase, are released into the cleft immediately after transmitter release. Nerve gases & some insecticides work b blocking this enzymatic cleanup.

Question 33

What are the benefits of synaptic transmission?

Answer 33

They ensure the flow of impulses is in one direction, as the vesicles containing transmitter are only in the pre–synaptic neurone and the receptors only in the post one.
They allow integration & summation?

Question 34

What is integration of a synaptic transmission?

Answer 34

An impulse travelling down a neurone may reach a synapse with several post–synaptic neurones, all going different locations. This allows the impulse to be dispersed. It can work in reverse, with several impulses converging at a synapse.

Question 35

What is spatial summation?

Answer 35

Several pre–synaptic neurons converge at a synapse with a single post–synaptic neuron.

Question 36

What is temporal summation?

Answer 36

There is only one pre and post–synaptic neurons but the frequency of impulses reaching the synapse is important.

Question 37

What is good about summation?

Answer 37

They allow the grading of nervous response – if the stimulation affects too few presynaptic neurons or the frequency is too low, there is no impulse transmission.
They allow the filtering out of continual unnecessary or unimportant background stimuli, as if a neuron is constantly stimulated the synapse will not be able to renew its supply of transmitter fast enough to continue passing the impulse across the cleft.

Question 38

What does synaptic fatigue do?

Answer 38

Place an upper limit on the frequency of depolarisation.

Question 39

What are the hormonal systems of polychaetes like?

Answer 39

Hormonal substances are produced in neurosecretory cells in the CPG and these are carried to target sites by neurosecretory axons. The best known mechanism is the hormonal control of epitoky in nereids.

Question 40

What is the CPG?

Answer 40

Cerebro–pleural ganglia.

Question 41

What are the hormonal systems of the molluscs like?

Answer 41

They have a similar means of delivering neurohormones as the polychaetes, & a no. off neuroendocrine control mechanisms have been identified, such as osmoregulation, oogenesis and development of the reproductive system.

Question 42

What effect did the antifouling agent TBT have on gastropods?

Answer 42

They caused a crash in gastropod populations by mimicking the neurohormone responsible for penile morphogenesis. All the females developed male genitalia superimposed on top of female genitalia – blocking the oviduct & causes it to burst, killing females of secondary infection – IMPOSEX.

Question 43

What is the hormonal systems of the Crustaceans like?

Answer 43

They are more complex – they have neuro–secretory systems similar to those sen in annelids and molluscs but also true endocrine organs, the X–organ and sinus gland, that function by releasing hormones into the haemolymph.

Question 44

What are the hormonal systems of Echinoderms like?

Answer 44

Spawning can be induce in mature starfish by injecting extracts of radial nerves into the body cavity. The nerves contain a peptide hormone, gonad stimulating substance, that in turn causes the release of meiosis–inducing substance into the follicles that in turn induces the production of maturation–promoting factor. This is an example of an endocrine cascade mechanism.

Question 45

What were pheromones first called when they were discovered?

Answer 45

Ecto–hormones.

Question 46

What are pheromones?

Answer 46

Chemical factors that trigger a social response, usually in members of the same species, though there is evidence of pheromonal control in symbiotic and parasitic relationships.

Question 47

What two aspects of reproduction are pheromones associated with?

Answer 47

Co–ordination of spawning aggregations, e.g. nereid polychaetes.
Larval site–selection and metamorphosis, e.g. echiurans and Crepidula sp.

Question 48

How is larval site selection controlled by pheromones?

Answer 48

The larvae chose sites by detecting pheromones from previously settled larvae.

Question 49

How is metamorphosis in echiurans affected by pheromones?

Answer 49

The echiurans males are dwarf males. The first settler is a full sized female, other settlers become dwarf males via the nephridiopore – a sac in the nephridium which is there to hold them where they develop into testes that are nourished by the female. Reproduction is easier, as the females are sessile.