Sensing and Reacting

Question 1

How many stages of Information processing by the nervous system are there and what are they?

Answer 1

• 3 stages:
  1) Sensory input
  2) Integration
  3) Motor Output

Question 2

How does the first stage of information processing work?

Answer 2

Input: Sensory neurons
» Transmit information about external stimuli (eg, light, touch, smell) or internal conditions (eg, blood pressure, muscle tension)

Question 3

How does the second stage of information processing work?

Answer 3

Integration: Interneurons

» Integrate multiple sensory inputs taking into account context and experience

Question 4

How does the last stage of information processing work?

Answer 4

Output: Motor neurons

» Then transmit signal to muscle cells, causing them to contract → movement

Question 5

What is the difference between the CNS and the PNS

Answer 5

In animals with a brain, integration occurs in the Central Nervous System (CNS) (= brain), while the neurons that carry information in and out of the CNS are the Peripheral Nervous System (PNS)

Question 6

Draw the CNS and PNS diagram

Answer 6

book

Question 7

What is a neuron and what is its structure?

Answer 7

• A neuron is a nerve cell
• Cell body contains all organelles (including nucleus)
• Cells has several branched extensions
  » Many dendrites, which receive signals from other neurons
  » A single axon, which transmits signal to other cells
  » Axons ends in multiple synapses, where chemical messengers (neurotransmitter) pass information to receiving cell

Question 8

Draw a diagram of a neuron

Answer 8

book

Question 9

what are ATP pumps

Answer 9

• ATP pumps in the cell membrane pump Na+ out and K+ in, producing a concentration gradient

Question 10

What are Passive Channels?

Answer 10

Passive channels allow K+ ions to equalise, but there are no open Na+ channels → net ion flow creates a charge difference across the membrane called “membrane potential”

Question 11

What are gated ion channels?

Answer 11

• The membrane also contains gated ion channels
  » Gated Na+ channels, which open in response to stimulus
  » Voltage gated channels, which open when membrane potential reaches a particular threshold

Question 12

What is action potential

Answer 12

• An action potential is a series of sudden changes in the voltage, or equivalently the electric potential, across the plasma membrane. Action potentials, or nerve impulses, allow long-distance signalling in the nervous system

Question 13

What are the first three steps in the transition of information from a neuron?

Answer 13

1) The ATP pumps and Passive channels create “membrane potential”
2) The Voltage gated channels open in response to the “membrane potential”
3) When the stimulus is strong enough, all voltage gated ion channels open → rapid depolarization (“action potential”), followed by return to normal

Question 14

What is step four of the transition of information from a neuron?

Answer 14

4) After the Wave of depolarization (“action potential”) is released it travels down the axon
» Special coating (“myelin sheath”) allows the depolarisation wave to travel faster

Question 15

What are steps 5 and 6 of the transition of information from a neuron

Answer 15

5) When depolarisation wave reaches the end of the axon (“synapse”), it causes it to release vesicles filled with chemical (“neurotransmitter”) into the intercellular space (“synaptic cleft”)
6) Neurotransmitter opens gated Na+ channels on the next neuron → depolarise cell membrane of that neuron → action potential

Question 16

How does the brain integrate the overall input of a sensory organ?

Answer 16

Neurons have many synapses from other neurons → integrate overall input

Question 17

What is the nervous system?

Answer 17

• Nervous systems = network of neurons + supporting cells (“glial cells” which nourish the nerve cells)

Question 18

What is the difference in nervous systems in vertebrates and invertebrates?

Answer 18

» Invertebrate nervous systems range from simple nerve nets to CNS
» Vertebrates have a CNS (integration) and PNS (input/output)

Question 19

What are the different types of sensory inputs?

Answer 19

• Our brains commonly receive sensory stimuli from our visual, auditory, olfactory (smell), gustatory (taste), and somatosensory (touch) systems.

Question 20

What are the general different types of sensory receptors?

Answer 20

Sensory receptor can be
» A neuron itself, or
» Specialised cells that releases neurotransmitters upon detecting specific stimuli
• External (eg, heat, light, pressure, chemicals)
• Internal (eg, blood pressure, body position)

Question 21

What is the signal transmission in neurons?

Answer 21

Neurons produce action potential (AP)
» All APs are exactly the same amplitude; intensity of stimulus can be transmitted by increasing frequency of APs or the number of cells involved

Question 22

What are the different stimulus that animals can detect and what are their speciefic receptors called?

Answer 22

- Electromagnetic receptors:
» Light, magnetic fields, electric fields
- Mechanoreceptors:
» Physical environment (touch)
» Gravity
» Sounds
- Thermoreceptors:
» Heat
- Chemoreceptors:
» Taste, smell
- Pain receptors:
» Detect extreme stimuli

Question 23

What do electromagnetic receptors do?

Answer 23

Detect electromagnetic energy
» Electric fields: aquatic animals only (sharks, fish, lampreys, platypus)
» Magnetic fields: migratory animals (birds, whales, bees)
» Light
• Presence: light detecting organ in invertebrates
• Movement: compound eye in insects
• Colour: single-lens eye in vertebrates

Question 24

What do Mechanoreceptors do and how do they work?

Answer 24

Sense physical deformation caused by mechanical energy such as pressure, touch, stretch, motion and sound
- Typically ions channels linked to “hairs” (cilia) that extend outside the receptor cell

Question 25

What are Chemoreceptors and what do they do?

Answer 25

• Diverse group of receptors
  » Up to 1000 genes in humans (~3% of total # of genes!)
• Respond to chemical stimuli and can be:
  » Specific for individual kinds of molecules
  • Most animals: O2, CO2, glucose, amino acids
  • In insects: pheromones (maybe in other animals, but no conclusive evidence)
  » General, responding to total solute concentration
  • Receptors in brain detect osmolarity of blood and stimulate thirst when osmolarity increases

Question 26

What are Thermoreceptors

Answer 26

Detect hot and cold

» eg snakes detect infrared radiation (heat) emitted by warm preys

Question 27

What are Pain receptors (“nociceptors)

Answer 27

• Nociceptors detect extreme stimuli that can damage animal tissues
  » Mechanical
  » Chemical
  » Thermal
• Nociceptive pathways trigger defensive reactions → withdraw from danger

Question 28

What is motor out put

Answer 28

A function in the nervous system which processes and Interprets sensory input and then makes decisions

Question 29

What is Vertebrate skeletal muscle

Answer 29

• Each muscle fibre is a single cell with multiple nuclei
  » Derived from embryonic cells that fused to form one muscle cell
• Inside this cell are bundles of myofibrils
  » Made up of thin (actin) and thick (myosin) filaments

Question 30

What is actually happening during muscle contraction?

Answer 30

• During muscle contraction, the filaments slide past each other
  » Filaments themselves do NOT contract, but the overall effect is a shortening of the sarcomere (and thus of the whole muscle fibre)
  » “We move our bodies by shortening (contracting) our muscles”

Question 31

How does Nervous control of muscle tension work?

Answer 31

• There are Motor neurons synapses on muscle fibres
• The Action potential in motor neuron causes a neurotransmitter release at the synapse. This then causes Ca2+ release inside muscle fibre which causes the myosin to slide up actin filament

Question 32

How do we create movement?

Answer 32

• Muscle + skeleton = movement
• Muscles can only exert force by contracting, not by extending
• Skeletal systems transform contraction into locomotion

Question 33

What are the three functions of the skeletal systems?

Answer 33

• Protection
• Support
• Locomotion

Question 34

What are the different types of skeletons?

Answer 34

» Hydrostatic (fluid based, no bones; flatworm, nematodes …)
» Exoskeleton (on the outside; molluscs, arthropods)
» Endoskeleton (needles, plates, cartilage, bone on the inside)

Question 35

What are the pros and cons of a Hydroskeleton?

Answer 35

Pros:
- Fluid shape, fit into odd shapes
passages
- Quick regeneration

Cons:

• Not as much strength (lifting capacity)
• Fragile (effect of Puncture)

Question 36

What are the pros and cons of an exoskeleton?

Answer 36

Pros:
- Strong protection

Cons:

• Requires regular moulting
• No flexibility
• Cannot be repaired

Question 37

What are the pros and cons of an Endoskeleton?

Answer 37

Pros:

• Can repair itself when damaged
• Grows as the animal grows

Cons:
- Soft tissues are exposed

Question 38

What is movement?

Answer 38

• Movement is the hallmark of animals
  » Even sessile animals move, eg sponges beat their flagella to generate water currents
• Friction and gravity oppose motion, so animals must expend energy to move
• Amount of energy is reduced by animal body plan

Question 39

What are the different modes of movement on land and what is required for animals to do so?

Answer 39

• Crawling, walking, running, hopping
• On land:
  » Must be able to support itself and move against gravity → need powerful muscles and strong skeletal support
  » Air poses relatively little resistance → no need for streamlined shape

Question 40

What is required for animals to move in water?

Answer 40

In water:
» Animals are relatively buoyant, so overcoming gravity not as big a deal
» However, water is much denser, so drag (friction) is a major problem
- Thus, sleek fusiform shape (like a torpedo) is a common adaptation of fast swimmers

Question 41

What is required for animals to fly?

Answer 41

• Active flight only in a few animal groups:
  » Insects
  » Reptiles (incl. birds)
  » Mammals (bats)
• For flying:
  » Must generate enough lift to overcome the downward force of gravity!
• Thus, specialised wing shapes (for maximum lift) and adaptations to lessen the weight

Question 42

What are the adaptions that enable birds to fly

Answer 42

• Honeycombed “hollow” bones
• Air sacs
• Young develop outside of body
• No urinary bladder
• No teeth
• Efficient circulatory system
• Powerful flight muscle
• Wing shape adapted to flight mode
  » Gliding, agility, speed …

Question 43

What are the adaptions that enable bats to fly?

Answer 43

Skeletal adaptations