locomotion & nervous systems Flashcards
What does a nervous system do
CONDUCT INFORMATION in a directed way through the body via electrical and/or chemical signals, and cells specialized for these functions
what does the nervous system allow
- Coordination (especially of muscles)
- Sense organs
what do neurons do and what do they consist of
conduct impulses over long distances
- Consist of an axon (long fibre), a nucleated cell body (soma) and shorter extensions (dendrites)
who has unipolar neuron’s and what are they
invertebrates
Single process (axon) splits into two branches:
-One transmits to the cell body
-One transmits from the cell body
what do Cnidaria and Ctenophora have for a nervous system
- do not posses brains or central nervous systems
- Network of multipolar nerve cells (nerve net) that conducts slowly in all directions
what are nerve nets
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
how are cnidarian neurons different to other animals’
they lack polarity so conduction occurs in both direction
what kind of neurons do Scyphozoans have
pacemaker neurons - rhythmical activity to generate swimming
what kind of germ layers do cnidarians and Ctenophora have
Diploblast, but musculo-epithelial cells can extend into mesoglea from both endoderm and ectoderm
nervous system characteristics in echinoderms
No brain
Simple radial nervous system
Modified nerve net
nervous system characteristics in bilateral animals
- polarised locomotion
- accumulation of sensory receptors at the front CEPHALISATION (to form head, brain etc)
- Typically one or more ganglia (sing. ganglion)
what is a ganglion
group of neuronal cell bodies, connected by synapses
- Ganglia = integrating centres for the nervous system
what are the 3 neurons and their functions
- 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)
what is the Central nervous system (CNS) and what does it contain
- 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
what does the Peripheral Nervous System (PNS) do
- 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
what does the Connection between CNS and PNS allow
coordination of action, when there could be a conflict between signal and motor requirements
nervous system characteristics in annelids
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
what is the brain called in annelids
supraesophageal ganglion
what are the nerve loops that link the supraesophageal ganglion above and below the oesophagus in annelids
commisures
what kind of animals have a hydrostatic Skeleton
soft-bodied (flexible)
how is the force of muscular contraction transmitted in soft-bodied animals aka ones with a hydrostatic Skeleton
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
what happens when Antagonistic circular muscle is contacted
goes longer
- Contractions take different forms – allows different motion and activity
what happens when Antagonistic longitudinal muscle is contacted
goes fatter/wider
- Contractions take different forms – allows different motion and activity
explain connective tissue fibres in annelids / soft bodied animals
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
explain hydrostatic skeleton in sea stars + urchins
- 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
explain hydrostatic skeleton in gastropods, acoelomate worms with a muscular foot
- 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
explain the wave motion in errant polychaetes
Waves of contraction are propagated alternately along the sides, producing an “S”-shape, and backwards force, pushing the animal forwards
Disadvantages of hydrostatic skeletons
- 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
explain the parapodia in polychaetes
- 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)
explain muscular attachment in arthropods
exoskeleton (not hydrostatic one)
nervous system characteristics in arthropods
- fusion of ganglia, especially at head (reduces conduction distance)
- Brains usually well developed, leading to elaborate behaviour
arthropod legs characteristics
- 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
what are the swimming legs + walking legs called in decapods
Pleopods
Pereopods
Disadvantages of an exoskeleton
- 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
Gastropoda nervous system characteristics
- 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
cephalopod nervous system characteristics
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
what are the 3 muscle types that work against each other in cephalopods
- longitudinal (axially running along the length of the arm)
- radial (transversal)
- oblique muscles (diagonally surrounding the arm)
what is Muscular-hydrostatic support also used in cephalopods to do
- create substantial pressure in the suckers
- support and actively bend fins
- create movement of the beak
what are giant axons typically used for
escape reactions
what animals have giant axons
Annelids, cephalopods, arthropods
what also increases conduction speeds along axons of relatively small diameter
myelin
- Conduction velocity of action potential is greatly increased
what allows squid to have near simultaneous
contraction of its mantle
Combining axons of different diameters
what does Reynolds number explain
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
what classes as low Re
lower than 1,000-2,000 - means the animal lives in very different environment
what does it mean If Re is high
- 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)
what does it mean If Re is low
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
what animal has the lowest cost of transport of all metazoans
scyphozoans
