locomotion & nervous systems

Question 1

What does a nervous system do

Answer 1

CONDUCT INFORMATION in a directed way through the body via electrical and/or chemical signals, and cells specialized for these functions

Question 2

what does the nervous system allow

Answer 2

• Coordination (especially of muscles)
• Sense organs

Question 3

what do neurons do and what do they consist of

Answer 3

conduct impulses over long distances
- Consist of an axon (long fibre), a nucleated cell body (soma) and shorter extensions (dendrites)

Question 4

who has unipolar neuron’s and what are they

Answer 4

invertebrates
Single process (axon) splits into two branches:
-One transmits to the cell body
-One transmits from the cell body

Question 5

what do Cnidaria and Ctenophora have for a nervous system

Answer 5

• do not posses brains or central nervous systems
• Network of multipolar nerve cells (nerve net) that conducts slowly in all directions

Question 6

what are nerve nets

Answer 6

diffuse networks of neurons, connected by chemical or electrical synapses or syncytial contacts
- In more complex forms, neurons are grouped into loose nerve tracts or plexuses
- Sometimes >1 distinct nerve nets

Question 7

how are cnidarian neurons different to other animals’

Answer 7

they lack polarity so conduction occurs in both direction

Question 8

what kind of neurons do Scyphozoans have

Answer 8

pacemaker neurons - rhythmical activity to generate swimming

Question 9

what kind of germ layers do cnidarians and Ctenophora have

Answer 9

Diploblast, but musculo-epithelial cells can extend into mesoglea from both endoderm and ectoderm

Question 10

nervous system characteristics in echinoderms

Answer 10

No brain
Simple radial nervous system
Modified nerve net

Question 11

nervous system characteristics in bilateral animals

Answer 11

• polarised locomotion
• accumulation of sensory receptors at the front CEPHALISATION (to form head, brain etc)
• Typically one or more ganglia (sing. ganglion)

Question 12

what is a ganglion

Answer 12

group of neuronal cell bodies, connected by synapses
- Ganglia = integrating centres for the nervous system

Question 13

what are the 3 neurons and their functions

Answer 13

• Sensory (afferent) neurons: Convey information from body -> CNS
• Interneurons: convey signals from one neuron to another
• Efferent Neurons: Convey information from CNS -> effector organs (ex. motor neurons)

Question 14

what is the Central nervous system (CNS) and what does it contain

Answer 14

• Aggregation of neuronal components organised into longitudinal or ring-like nerve cords, normally near the midline
• Includes the cell bodies and dendrites of motor neurons
• All interneurons

Question 15

what does the Peripheral Nervous System (PNS) do

Answer 15

• carries sensory information from the periphery to CNS and motor signals back
• Synapses between neurons (as opposed to those made by neurons onto muscles) are relatively rare
• Motor signal from the CNS is modified in PNS to produce a finely tuned response

Question 16

what does the Connection between CNS and PNS allow

Answer 16

coordination of action, when there could be a conflict between signal and motor requirements

Question 17

nervous system characteristics in annelids

Answer 17

CNS, including brain, and PNS
- In segmented (metameric) invertebrates the layout of the nervous system largely reflects the degree of body segmentation
- Each body segment = innervated by a corresponding segment of the CNS
- Anterior ganglia above (supraesophageal ganglion = brain) and below the oesophagus, linked by nerve loops (called commisures)
- Brain provides simple coordination between sensory input and motor output
- Suboesophageal ganglion is the first of a chain of segmental ganglia along the double ventral nerve cord

Question 18

what is the brain called in annelids

Answer 18

supraesophageal ganglion

Question 19

what are the nerve loops that link the supraesophageal ganglion above and below the oesophagus in annelids

Answer 19

commisures

Question 20

what kind of animals have a hydrostatic Skeleton

Answer 20

soft-bodied (flexible)

Question 21

how is the force of muscular contraction transmitted in soft-bodied animals aka ones with a hydrostatic Skeleton

Answer 21

via internal pressure
- A small decrease in diameter causes a large increase in length to keep a constant volume
- Water = incompressible: a sealed bag can change shape but not volume

Question 22

what happens when Antagonistic circular muscle is contacted

Answer 22

goes longer
- Contractions take different forms – allows different motion and activity

Question 23

what happens when Antagonistic longitudinal muscle is contacted

Answer 23

goes fatter/wider
- Contractions take different forms – allows different motion and activity

Question 24

explain connective tissue fibres in annelids / soft bodied animals

Answer 24

Body walls are often reinforced with layers of connective tissue fibres that control and limit shape change
- Straight lines (orthogonal) results in kinks
- Helical pattern allows it to bend - better

Question 25

explain hydrostatic skeleton in sea stars + urchins

Answer 25

• tube feet are controlled by radial nerve that runs down each arm (form of hydrostatic skeleton)
• Ampulla muscles force water into tube feet
• Postural muscles moves tube feet around – can also retract terminal plate for suction

Question 26

explain hydrostatic skeleton in gastropods, acoelomate worms with a muscular foot

Answer 26

• Circular muscle contraction extends the anterior end followed by longitudinal contraction – allows them to dig (burrow very well)
• Force themselves into sand, expand to form anchor, contract body to bring themselves down

Question 27

explain the wave motion in errant polychaetes

Answer 27

Waves of contraction are propagated alternately along the sides, producing an “S”-shape, and backwards force, pushing the animal forwards

Question 28

Disadvantages of hydrostatic skeletons

Answer 28

• Soft bodies – vulnerable to predation
• Skeleton requires hydration (no problem for marine vertabrates, possibly problem for intertidal animals)
• Inefficient:
  i. large part of body exposed to friction
  ii. entire body needs to be moved, not just locomotive parts – requires more energy + muscle
• Much harder for nervous control, precise control difficult

Question 29

explain the parapodia in polychaetes

Answer 29

• More efficient to move small part of your body (parapodia) than your entire body
• Bundles of muscle fibres act against the hydrostatic skeleton of the compartmentalised coelom
• Each segment is controlled individually, with parapodia on each side working alternately
• During locomotion, each parapod performs two strokes: effective (backwards) and recovery (forwards)

Question 30

explain muscular attachment in arthropods

Answer 30

exoskeleton (not hydrostatic one)

Question 31

nervous system characteristics in arthropods

Answer 31

• fusion of ganglia, especially at head (reduces conduction distance)
• Brains usually well developed, leading to elaborate behaviour

Question 32

arthropod legs characteristics

Answer 32

• Bundles of striated muscle attached to the inner surface of the exoskeleton
• composed of a series of segments connected by flexible joints / hinges that only go in one plane – but a series of them allows a lot of control

Question 33

what are the swimming legs + walking legs called in decapods

Answer 33

Pleopods
Pereopods

Question 34

Disadvantages of an exoskeleton

Answer 34

• need to moult – vulneralbility + energy costing
• imposes a maximum size limit: the animal relies on a hydrostatic skeleton post-moult
• Weight of animal and resulting stress produced when moving would require heavy skeletal walls
• When the animal moulted, the new skeleton would collapse under the animal’s weight before it could harden

Question 35

Gastropoda nervous system characteristics

Answer 35

• Paired anterior “cerebral” ganglia
• Paired pleural ganglia innervating the lining of the mantle cavity
• Paired pedal ganglia, innervating the foot
• Visceral ganglia
• Commisures connecting right and left sides

Question 36

cephalopod nervous system characteristics

Answer 36

Greatest number of derived neuronal characters:
- Well-developed sensory organs, esp eyes
- Ganglia condensed into a brain
- Stellate ganglia
- Chromatophore system under nervous control
- Giant axons

Question 37

what are the 3 muscle types that work against each other in cephalopods

Answer 37

• longitudinal (axially running along the length of the arm)
• radial (transversal)
• oblique muscles (diagonally surrounding the arm)

Question 38

what is Muscular-hydrostatic support also used in cephalopods to do

Answer 38

• create substantial pressure in the suckers
• support and actively bend fins
• create movement of the beak

Question 39

what are giant axons typically used for

Answer 39

escape reactions

Question 40

what animals have giant axons

Answer 40

Annelids, cephalopods, arthropods

Question 41

what also increases conduction speeds along axons of relatively small diameter

Answer 41

myelin
- Conduction velocity of action potential is greatly increased

Question 42

what allows squid to have near simultaneous
contraction of its mantle

Answer 42

Combining axons of different diameters

Question 43

what does Reynolds number explain

Answer 43

what kind of conditions an animal lives in when it’s in water (increases with size of animal)
- Describes relationship between inertial forces + viscous forces – can think of it as a ratio between these two

Question 44

what classes as low Re

Answer 44

lower than 1,000-2,000 - means the animal lives in very different environment

Question 45

what does it mean If Re is high

Answer 45

• inertial forces are dominating (or viscous forces = very low) - continue moving after thrust
• thrust usually powered by muscles (often return to their original state through elasticity in the tissue rather than antagonistic force)

Question 46

what does it mean If Re is low

Answer 46

viscous forces are dominating (or inertial forces = very low) - animal comes to a stop very quickly e.g. copepod
- these animals use cilia or flagella for thrust

Question 47

what animal has the lowest cost of transport of all metazoans

Answer 47

scyphozoans