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

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

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

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)

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

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

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

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