1. UNIT 3 – BEHAVIOUR, POPULATION & ENVIRONMENT
Chapter 25 - Brain

2. Brain Composed of billions of neurones
Human brain size has increased greatly over millions of years
3x larger than ape brain
Higher mental faculty areas (centres) far more developed in humans
E.g sight, hearing, intelligence, speech
Humans are the dominant species due to complex internal organisation

3. Cerebrum Split by a cleft into 2 hemispheres
Left hemisphere controls right body side (& vice versa)
Hemispheres connected by corpus callosum
Grey matter – mainly nerve cell bodies
White matter – mainly nerve cell fibres
Convoluted surface increases surface area
Distinct areas -
Sensory: receive info from sense organs
Association: analyse & interpret info
Motor: send motor impulses to effectors

4. Localisation of function
Hemispheres divided into distinct regions
Regions are duplicated in both hemispheres
Speech area is only exception (90% in left hemisphere)
Somatosensory, visual & auditory areas receive separate impulses
All are interconnected
- allow for sophisticated perception of a situation
Also allows for a sophisticated response
Memory, creativity, imagination, consicence etc
– higher mental functions (uncharted)

5. Motor area Consists of motor neurones
Send out impulses – voluntary movement of skeletal muscles
Size of motor area relates to number of motor endings in the body part
Larger the area = more mobility
E.g lips, hands have large areas
Shown by motor homunculus
Similar properties for sensory areas

6. Studying the brain Electroencaphalogram (EEG):
Records cerebrum’s electrical activity
Brain wave patterns indicate mental activity
Abnormal EEG’s often accompany personality problems
Doesn’t show specific regions of brain
Brain scans:
Visual images – can indicate metabolic activity
E.g speech involves ‘language’ areas – these have high metabolic activity when speaking
Abnormalities also identified

7. Split-brain issues Visual pathways – normal:
Each eye receives light from both sides of a field of view
Hemispheres receives info of about half the visual field
Info is shared between hemispheres via corpus callosum
Abnormal (‘split brain’):
Corpus callosum cut (operations etc.)
No info exchange - only half the info at each hemisphere
Patient will only say what they see on side of motor speech area
Patient will point to image on the same hemisphere that controls their hand

8. Evidence from brain injuries
Injuries allow for identifying what certain brain regions do
Frontal lobes – planning, goal setting & personality
Spike through head
Wife or hat…
Shrapnel wounds – often cause partial paralysis
Lesions – indicative of speech impairment
Stroke – lack of blood flow to a brain region
- brain cell death, loss of function