1a - Evolutionary History of the Brain

Question 1

What are the key functions of the brain?

Answer 1

1. Using sensory input to guide movement (takes input from sense organs and produces outputs by muscles)
2. Using sensory input to regulate internal organs (producing outputs to organs)

Question 2

What is the
1. Cortex
2. A Gyrus
3. A Sulcus

Answer 2

Cortex: covers most of the surface of the brain
–> Check you can divide the cortex lobes (lateral view)

Gyrus - ridges in the brain

Sulcus - gaps between the ridges

*beneath the cortex there are many brain regions associated with a variety of functions - these regions are LOOSELY ASSOCIATED with specific functions

Question 3

How can the brain be divided into three main parts?

Answer 3

1) Forebrain - uses current sensory input and past experience to make (and communicate) decisions

2. Midbrain - uses current sensory input to direct movement
3. Hindbrain - maintains the current state; controls mouth

Question 4

What are the two ways in which the brain sends messages to the body?

Answer 4

1. Through the NERVOUS SYSTEM
   - Electrical signals
   - Rapid
   - Costly communication (organism has to pay upkeep costs)
   - Network structure determines which cells receive the messages
2. Through the VASCULAR SYSTEM (uses chemical signals - hormones)
   - Slower but cheaper communication (vascular system already exists)
   - Membrane receptors determine which cells receive the messages

Question 5

A Brief History of Life: Key events that impacted how our brains came to be: Describe…
1. Prokaryotic Cells (3.5-2 billion years ago)
2. Eukaryotic Cells (2 billion years ago)

Answer 5

1. Prokaryotic Cells
   - membrane regulates contents
   - cytoplasm contains molecules
   - flagella regulates movement
   - DNA allows protein production
2. Eukaryotic Cells
   - much more efficient and compartmentalised cell
   - DNA packaged inside central nucleus
   - mitochondria performs phagocytosis
   - microtubule network allows complex structure
   - cilia and microvilli provide specialised sensing areas

–> Phagocytosis and Secretion: the founding principles for intercellular communication

Question 6

A Brief History of Life: Key events that impacted how our brains came to be: Describe…
3. Metazoa - The founding principles for intercellular communication (635 million years ago)
4. Bilateria (555 million years ago)

Answer 6

3. Metazoa
   - Cells stick together after division (MULTICELLULAR)
   - differentiated tissues, digestive chamber, intracellular signalling and sensory cells
4. Bilateria
   - complete digestive tract with seperate mouth and anus
   - front end had concentration of visual, olfactory, and taste sensors
   - muscle
   the first bilaterally symmetrical organisms

Question 7

A Brief History of Life: Key events that impacted how our brains came to be: Describe…
5. Chordates 535 million years ago)
6. Vertebrates (525 million years ago)

Answer 7

5. Chordates
   - much more efficient movement
   - have a tail and notochord
   - neural tube for communication along body (nerve cord)
6. Vertebrates
   - bone cranium and vertebrae
   - first group with tripartite brain (recognisable fore,mid,hind brains)

Question 8

A Brief History of Life: Key events that impacted how our brains came to be: Describe…
7. Jawed Fishes (430 million years ago)
8. Mammals (225 million years ago)

Answer 8

7. Jawed Fishes
   - teeth: more energy
   - eye muscles: for movement
   - three semi-circular canals
   - cerebellum to control stabilisation and gaze
8. Mammals
   - differentiated teeth (more efficient digestion)
   - sensory innovations
   - extended parental care (learning)

Question 9

A Brief History of Life: Key events that impacted how our brains came to be: Describe…
9. Primates (60 million years ago)
10. Homo (2 million years ago)

Answer 9

9. Primates
   - thumbs for grasping
   - binocular vision
   - colour vision (trichromatic)
10. Homo
    - rapid brain expansion (unclear why:)
    o Expensive Tissue (better food)
    o Social Brain (complex social relationships = better brain)
    o Mating Mind (bigger brain more attractive)

KEY: Several of the major evolutionary changes in the brain were linked to changes in motor control and digestive efficiency

Question 10

Comparative Neuroanatomy: What does brain evolution depend on? What does the size of shared brain regions tell us about different animals?

Answer 10

Great variation in sizes of different brain regions in animals
–> Shared ancestry - studying animals can help us understand how our brains work
–> natural selection will favour enlargement of brain region only if it enhances survival or reproduction
–> Thus brain evolution depends on an animal’s ANATOMY and ECOLOGY

Size of a cortical area is related to the importance of information it processes