nervous system

Question 1

define the nervous system and understand how it responds to environmental factors.

Answer 1

nervous system-Produce effective responses to a stimulus from the environment

environment can be either external or internal
External stimuli
* Light
* Temperature
* Chemical
* Touch Vibration
Internal stimuli
* Chemical (pH, ions, molecules)
* Blood pressure
Temperature

Question 2

To describe the basic structure of a neuron, to understand that neurons have variable morphology and that structure is related to function.

Answer 2

The neurone is the basic cell type of the nervous system

Cell body (soma) – size and shape
Dendrites – number, branching and length
Axon – length, diameter, branching, myelinated or unmyelinated
Synaptic terminals – number and structure
Synaptic transmission – chemical or electric

Question 3

To describe the characteristic features of interneurones.

Answer 3

Located between neurones and form a connection between other neurones.
Found in both invertebrate and vertebrate nervous systems.
May be local or send their axons for long distances within a nervous system (projection interneurones).
Increase the number of synapses – and therefore the complexity of neuronal circuits.
AKA relay neurones, association neurones or connector neurones.

Question 4

To understand and give examples of invertebrate nervous systems (hydra, sea anemone, corals, jelly fish, star fish).

Answer 4

HYDRA
Hydra – an example of a freshwater invertebrate
A simple nerve net with no central nervous system.
Permits movement of the body and tentacles in water.
Action potentials (AP) can be conducted in all directions (AP
conduction is bidirectional).

SEA ANEMONE/CORAL
Slow but co-ordinated movements of polyps.
Tentacles (catching prey).
Body movements (defence).
Tentacles/oral disc 4000x more sensitive than the ‘column’.

JELLYFISH
More complex nerve nets
Spontaneous rhythmic activity (slow state and startle)
Contractions of the margin of the ‘bell’ produce a propulsive force forwards

STARFISH
A modified nerve net with control of limb movements coordinated by the neural ring.
The radial nerves can control the movements of each limb individually.
Movement and feeding = complex movements.

Question 5

To state and understand the main consequences of cephalisation in invertebrates.

Answer 5

Evolution of bilaterality (bilateral symmetry = mirror image on both sides) leads to cephalisation (cephalic = of, or in the head)

consequences:
1. Increase in number of nerve cells.
2. Concentration of nerve cells into ganglia; ganglia into brains, nerves into nerve cords.
3. Development of functional speciality:
AFFERENT neurons – towards the CNS.
EFFERENT neurons – away from CNS.
4. Localisation of specific functions in different parts of the nervous system.
5. Development of interneurones and more complex synaptic contacts.
6. Development of head bearing sense organs.
7. Development of a ventral nerve cord.

Question 6

To state and understand the main consequences of segmentation in invertebrates.

Answer 6

A segment is a unit of anatomical structure that can be repeated along the length of an animal

consequences:
1. Development of segmental ganglia with sufficiently complex neural circuitry to control locomotion in individual segments
2. Coordination of movement (and/or limb movement) between adjacent segments
e.g. in annelid worms or earth worms

Question 7

To describe the invertebrate nervous systems of arthropods.

Answer 7

Arthropods have connectives = ganglia joined by connecting nerves
Arthropods also have an autonomic nervous system (ANS) which innervates the viscera of the body.

segmental ganglia in arthropods:
Co-ordination of movement in walking/running and flying by:
Receiving sensory information from a defined part of a body segment whose activity it regulates directly.
Activating dorsal/ventral or left/right limb muscles appropriately in response to stimuli.
Using central pattern generators (CPGs) – repeated rhythmic motor output independent of sensory stimulation.
Interconnections between segmental ganglia (connectives) can propagate activity along the length of the ventral nerve cord – and along the length of the animal – coordinated by the ‘brains’.

Question 8

To describe the invertebrate nervous systems of molluscs, including octopus as an example.

Answer 8

molluscs: Organised into ganglia:
Buccal-feeding
Cerebral-coordination
Pleural-respiration
Pedal-movement
Parietal-‘peripheral’
Visceral-organs

octopi:
Exhibit ‘human-like’ intelligence (when observed in captivity):
Gets food, clears the front of its den and arranges rocks in order to cover the entrance before going to sleep (foresight, planning, use of tools).
Opens childproof caps on pill bottles (persistence, thinking).
Blowing jets of water from the funnel to send a pill bottle to the other end of the
tank where the water flow sends it back - repeatedly (playing).
Recognise their human ‘caretakers’ by moving towards them and squirting water
at them (memory, affection).
Solving difficult problems using objects of differing colours and shapes (thinking).

Question 9

Explain the difference between vertebrate and invertebrate photoreceptors and transduction

Answer 9

verterbrate:
-rods and cones
-photoreceptive opsin molecules
-light hyperpolarises

verterbrate phototransduction:
DARK:
* Similar between vertebrates and invertebrates but with some striking differences
* In the dark, Sodium (Na+) and calcium (Ca2+) ion channels are kept open by high levels of cGMP
* The photoreceptor is depolarised (receptor potential) increasing transmitter release but these receptors do not produce action potentials
LIGHT:
* Light activates transducin to break down cGMP into GMP
* Ion channels close hypolarising the cell and reducing transmitter release

Invertebrate light transduction:
Shares many principles with the vertebrate system but differs in detail
Light activates phopholipase C to break down PIP2 to IP3 and DAG
By an unknown mechanism this opens ion channels in the membrane causing the photoreceptor to depolarise but there are no action potentials

Question 10

4 classes of photoreceptors

Answer 10

• At low light levels only rods are active and we have no colour perception
• Red light can help dark adapt
• In bright light cones sensitive to red, green and blue light give us colour perception
• Not all vertebrates have 3-colour (trichromatic) vision. Many mammals (such as dogs) do not, while brightly coloured tropical fish do. Some animals may see things we do not

Question 11

visual processing in lower vertebrates

Answer 11

• Reptiles, amphibians and fish have small rudimentary forebrains
• There is no visual processing in the forebrain in these animals
• Instead this takes place mainly in the visual part of the midbrain (the optic tectum)
• Mammals also have visual areas in the midbrain but these are involved only in visual reflexes – turning to look at new objects appear in the visual fields

Question 12

Understand the difference between rods and cones in the vertebrate retina

Question 13

compound eyes

Answer 13

• Insects and crustacea have compound eyes made up of photoreceptor units each with its own lens (may vary in sensitivity)
• Because of their bulbous shape, they can provide nearly all round vision
• Receptor units in different parts of the eye can have different properties (e.g. different sensitivity to colour or light polarization (eg bees)

Question 14

what is the flys visual field focused on

Answer 14

• Computational resources in the invertebrate nervous systems are limited have - e.g. the fly brain contains only around 250,000 neurones
• They therefore have only a limited behavioural repetoire, but the small number of tasks they can carry out, they do well
• We have seen how they can use polarised light for navigation and colour vision to find flowers (food sources)
• The visual system is also tuned to recognise such features as……..
  a) movement (which may indicate danger or mating displays)
  b) looming (approaching) objects e.g. for collision avoidance when flying
  c) visual field slippage – indicates movement relative to the ground an also turning

Question 15

Understand the significance of simple eyes in the invertebrates

Answer 15

• Smaller than compound eyes
• Many receptors under a single lens
  Hunting spiders have only simple eyes but these are distributed around the head to provide a wide field of view
  Insects with compound eyes usually have three simple eyes (ocelli) arranged in a triangular pattern
  When flying, these eyes act as a horizon detector so that the insect can maintain a stable flight path

Question 16

Explain the nature of infra-red vision in snakes

Answer 16

This only works because snake body temperature is much lower than mammalian prey, so the receptor is in kept cool
It is part of the somatosensory system and does not receive signals from the eyes, confirming that snakes see infrared by detecting heat, not light

• In snakes, the forebrain is primative and visual processing is carried out in the midbrain optic tectum
• The infrared “vision” of the pit organs also maps onto the optic tectum so that the two types of information are superimposed
• This is not a unique form of mapping. In owls, auditory and visual maps of the world also overlap in the optic tectum so that their fine directional hearing augments visual input which may be poor at night.
• In theory the pit organ could detect photons like the mantis shrimp eye but it does not
• The receptor (TRPA1) is like the one in our skin and mouth that detects both noxious heat and chemical heat sensation e.g. chilli powder (capsaicin)
• In rattle snake this becomes sharply active at 28oC
• Rat snake does not have effective infrared “vision”

Question 17

Explain the basic elements and function of the vertebrate ear

Answer 17

pinna
external ear canal
ear drum
middle ear-inner ear
within inner ear: organ of corti:(cochlea)
tectorical membrane
hair cells, nerve cells and basilar membrane

Question 18

auditory pathways

Answer 18

auditory nerve
medulla
mid…
thalamus
auditory cortex

Question 19

tonotopy

Answer 19

Because how far the travelling wave travels depends on frequency, there is a tonotopic relationship (position codes frequency) that is seen
not only here but throughout the auditory pathways
This is one way the nervous system can make sense of auditory input. Tonotopy is maintained all the way to the auditory part of the brain

Question 20

Understand the similarities and differences between this and the insect “ear”

Answer 20

insect hearing:
The tympanum (thin cuticle) plays the same role as the eardrum in the vertebrates that vibrates more than normal cuticle(in the leg)

behaviour:
Bat calls are much higher frequencies than cricket mating calls (Ultrasound pulses)
* Bats use echolocating calls for navigation and catching prey
* Their call frequencies are typically 25-100kHz
* When hunting, they can detect insect wing movements as well as judging how far away they are (size, species)
Moths use auditory systems to detect predators and take evasive action

antennal hearing in mosquitos:
Male mosquitos use hearing to find detect females by the humming of their wingbeats
The airborne vibrations are detected by the antenna
The antenna resonates at the female wingbeat frequency e.g. 360-400Hz – it is not a general hearing organ but only used for this purpose
The airborne vibrations are detected by Jonston’s organ at the base of the antenna. Active processes in the sensory neurones amplify the signal making it extremely sensitive at this frequency

Question 21

Describe the modalities of human taste and receptor cell responses

Answer 21

1. Sweet. Indicates source of energy and ripeness(fruit)
2. Salt. Vital dietary component
3. Bitter. Poisonous plants/fruits/insects
4. Sour(acid) indicates spoilage of foods
5. Umami(glutamate). “Meaty” taste (MSG)

Question 22

Describe the basic cellular responses involved in mammalian olfaction

Answer 22

binding of odour molecules causes a G protein subunit to stimulate adenylyl cyclase (amplification)

this increases levels of cAMP which opens ion channels in the cell membrane causing it to depolarise which causes an action potential to be generated

The G protein coupled taste receptors (sweet and umami) operate in a similar manner

• Mammals have up to 1000 odour receptor genes that allow discrimination of around 10,000 odours
• Olfactory receptor neurones that respond to the same odour send their axons to the same glomerulus
• Genetic diversity in receptors

Question 23

 Compare taste and olfaction in vertebrates with that of invertebrates

Answer 23

olfaction similar between mammals and insects-convergent evolution

insects:
antenna -airborne odours
palps/proboscis-mouthparts for food
food odours-flowers, carrion
pheremones- molecules released by one sex to attract the other eg. moths, pheremone receptors can be activated by a single molecule

antennae have a range of different sensory hairs not only olfactory - but also very long fine hairs (airflow) and short(tactile) to pick up odours