Unit 3: Behaviour, Populations and

environmentChapter 25: The Brain

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Higher Human Biology

Learning Intentions

To examine the workings of the brain and the nervous system.

Success Criteria

1. Outline the structure of the human brain with reference to;a. Sizeb. The cerebrum and its convoluted

surfacec. Localisation of function in discrete

areas of the cerebrumd. The relationship between size of a

discrete are and the function carried out

e. The importance of the corpus callosum in transferring information between two hemispheres

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VARIABLESThe brain is a very

complex organ not fully understood by

scientists

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FYI: The BrainFYI: The Brain• Weighs 1300 - 1400g

• Made up of about 100 billion neurons.

• “The most complex living structure on the universe” Society for Neuroscience

• Makes us who we are.

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“We are like chameleons, we take our hue and the colour of our moral character,

from those who are around us.”

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• John Locke was an influential philosopher from the 17th century. He has provided many important ideas and bases on philosophy, one of which was his theory of personal identity. Locke believed all true knowledge came from the senses and human experience.

• Basically each of us are a combinations of all the experiences we ever had and how we perceive these experiences. This can only happen with a brain to perceive, process, store, these experiences

“No man's knowledge here can go beyond his experience”.

The brain & size of the brain

• The brain is a large organ composed of billions of nerve cells (neurones).

• Compared with other animals, the human brain is disproportionally large, relative to body size.

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Why is it appropriate to say the weight of the brain determines intelligence?

Animal Wt. of Brain Brain/Body wt ratioWhale 15 lbs 1/10000Elephant 3 lbs 1/1000Human 3 lbs 1/50

• The human brain is more developed and has a larger weight in proportion to total body weight.

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Evolution of the Brain: Fossil evidence

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Increase in Brain SizeFossil evidence has shown that the human brain has increased in capacity (volume of skull occupied by the brain) over a fairly rapid evolutionary timescale.

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Apes

• When compared with the brains of modern apes, the human is found to be approximately three times larger.

• Humans have much larger centres responsible for higher mental faculties such as intelligence, speech, hearing and sight.

• An apes area controlling speech is so small and poorly developed it is impossible to teach an ape to speak.

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Image source: http://www.nature.com

Ape BrainsApe BrainsCompared to the brain of modern apes the human brain is about 3 times larger. Humans have much larger centres responsible for higher mental faculties such as intelligence, speech, hearing and sight.

An apes area controlling speech is so small and poorly developed it is impossible to teach an ape to speak..

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Dominant SpeciesCompared to other animals humans are physically weak.

However humans have become a dominant species on earth because the human brain has:• a larger size• complex internal development• complex organisation19/04/23 12Mrs Smith Ch25 The Brain

Brain Structure:~ Revision

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Cerebrum Structure

• Controls conscientious thought, voluntary actions, determines personality etc

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The Cerebrum:The Cerebrum:localisation of functionlocalisation of function

The cerebral hemisphere has several distinct regions each with a particular function.

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Cerebrum: Cerebrum: Con’tCon’t

• Largest part of human brain• Split into 2 halves called cerebral hemispheres 2 sides of the brain are

joined by the corpus callosum - a large

bundle of nerve fibres. This allows information to be transferred from one

side to the other.

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Each side of the brain controls the other side of the body

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• inner cerebrum • made of nerve cell fibres

• surface of cerebrum• made of nerve cell bodies

Cerebrum: Grey and white matter

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Cerebrum

Cerebrum: Convolution • The cerebrum’s surface

is convoluted (folded) to give it a large surface area allowing many cell bodies to be close together.

• This maximises the potential for interconnections and the transmission of messages.

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Task: Torrance-TYK pg 206 Qu 1-4

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The cerebrum has 3 main types of functional area, which are all discrete (they have their own function):

• Sensory• Association• Motor

View the Scholar animation: http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=2ba96ae7-1eff-e695-8b5d-5f08e2cc8533

Discrete Functional Areas

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Roles of the 3 discrete functional areas

Sensory areasReceive info as sensory impulses from body’s receptorse.g. touch receptors in skin and thermoreceptors in hypothalamus

Motor areas

Receive info from

association areas &

send motor impulses to

the effectors

e.g. muscles

Association areas

Analyse & Interpret sensory impulses

e.g. Make decisions

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Association areas

Somatosensoryassociation area

Visualassociation area

Premotorassociation area

Auditoryassociationarea19/04/23 27Mrs Smith Ch25 The Brain

Speech

Each region of the left cerebral hemisphere is duplicated on the right cerebral hemisphere except speech.

Each person only has one speech area. In 90% of people this is in the left cerebral hemisphere.

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Interconnections in the BrainInterconnections in the Brain Tiny nerve fibres interconnect the different areas of the brain. Messages constantly pass between them.

Sensory area

Association area

Motor area

This allows the human brain to cope with

several sensory impulses at once (sophisticated

perception)

They then cause more exchange of impulses

between cerebral areas allowing a sophisticated

responsee.g.

channel flicking

e.g. singing & dancing19/04/23 30Mrs Smith Ch25 The Brain

Motor Area• The motor area is one of the largest

regions of each cerebral hemisphere.

• Each motor area consists of motor neurons which sends out impulses to bring about voluntary movement of skeletal muscles

• However, the size of the part of the motor area is not in proportion to the actual size of the body part.

The size of the motor area is in proportion to the number of

nerve endings in the body part19/04/23 31Mrs Smith Ch25 The Brain

Discovery of the motor area Discovery of the motor area

In 1870, Hitzig and Fritsch electrically stimulated parts of a dog's motor cortex. Depending on what part of the cortex they stimulated, a different part of the body contracted. When they destroyed this same small area of the cortex, the corresponding part of the body became paralysed.

They concluded that every part of the body has a particular region of the primary motor cortex that controls its movement.

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MOTOR OR SENSORY AREA ALLOCATED TO A PARTICULAR BODY PART IS FOUND TO BE IN RELATIVE

PROPORTION TO ITS MOBILITY/SENSORY. E.G. THE MORE MOBILE A PART THE LARGER THE MOTOR AREA.

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Who is Homunculus?

• Imaginary human whose body parts have been drawn in proportion to – Mobility and fine motor

control– Sensory perception

• The more control needed of a task, the larger the area of the brain that is required

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The motor area of the left cerebral hemisphere

MOTOR HOMUNCULUS

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Motor homunculus—larger parts of the brain control larger parts of the body such as the hand and mouth, which require a lot of “motor” or motion “signals.” That is, if the human body were to be built in proportion to its motor significance because of the brain power needed to “motor” them, the hands and mouth would be proportionally bigger.

"This model shows what a man's body would look like if each part grew in proportion to the area of the cortex of the brain concerned with its movement."

View the Scholar animation: http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=8af4bea2-600b-deeb-baec-d7517d578e46

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SENSORY HOMUNCULUS

The sensory area of the left cerebral hemisphere

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Sensory homunculus—Similar to motor homunculus but it tells the brain how much power is needed for sensory perception of different body parts.

"This model shows what a man's body would look like if each part grew in proportion to the area of the cortex of the brain concerned with its movement."

Mrs Smith Ch25 The Brain

Cerebellum

• Attached to underside of brain

• Unconscious fine control of voluntary muscle movement and balance

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Medulla Oblongata

• Connects brain to spinal cord

• Unconscious co-ordination of basic functions – breathing, heart rate, digestion, reflex actions

Medulla oblongata

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Studying the Brain• The evidence that there is localisation of

brain functions (i.e. that different parts of the brain have different functions) include:

A. Electroencephalograms (EEG’s)

B. Brain Scans• Cat Scan• fMRI Scan

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Brain ScansBrain ScansSpeech involves several specific

regions of the brain.

These show up in brain scans

as areas of high metabolic

activity. FYI: You DON’T need to know the names of these areas!!

View the Scholar animation: http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=c622c31f-213c-2853-d6e0-e311a44d055f 19/04/23 40Mrs Smith Ch25 The Brain

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A record of the cerebrum’s electrical activity. Electrodes are placed on the different regions of the scalp. They detect impulses which are displayed on a monitor. Different brain wave patterns show different levels of mental activity.

ElectroencephalogramsElectroencephalograms Studying the Brain- EEG

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The more densely packed the spikes, the higher the level of electrical activity in the brain.

EEGs can show abnormal patterns that indicate a problem (e.g. dense spikes are shown during epileptic attacks), but the EEG doesn’t show the area of the brain responsible.

EEGs are not very precise because they reflect the activity of many brain cells.

Epilepsy

Infants, Sleepin

g adults

Children, Sleeping adults

EEG wave patternsEEG wave patterns

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This brain scan shows a tumour in pale blue.

Image source: www.sciencemuseum.org.uk

Studying the Brain: Brain ScansCAT SCANS

• Often referred to as CAT (Computer Assisted Tomography) scans.

• These give a clear image of the brain without any surgery

• used mainly to diagnose abnormalities

• Can indicate areas of high metabolic activity – so can be used to determine which part of the brain is responsible for certain actions and emotions.19/04/23 44Mrs Smith Ch25 The Brain

• Brain scans provide pictures of very active parts of the brain

• The parts of the brain which are active show up as brightly coloured areas

• The following diagrams show four fMRI (functional magnetic resonance imaging) brain scans obtained during a visual memory task.

Studying the Brain: Brain ScansfMRI SCANS

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Scan 1

In scan 1, a subject is asked to remember a face. Areas at the rear of the brain that process visual information are active during this task, as is an area in the frontal lobe.

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Scan 2In scan 2, the subject is asked to "think about this face." The hippocampus is activated. The hippocampus was already known to be important for memory, but these results show that this part of the brain is specifically active during the time when we are remembering new information.

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Scans 3 and 4• In scans 3 and 4, the subject was asked to compare

another face to the remembered face. Some of the same visual areas are activated as during the initial memory task, but other areas, such as part of the frontal lobe, are involved in making a decision about the memory.

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Split-brain studies

• Split brain happens when a person’s corpus callosum has been cut.

• Because of this exchange of information between cerebral hemispheres doesn’t occur.

• Learn more.............• http://www.nobelprize.org/educational/medicine/split-brain/

background.html • Play the split brain game.................• http://www.nobelprize.org/educational/medicine/split-brain/

index.html

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Split Brain StudiesSplit Brain Studies Visual Pathways – Normal situationVisual Pathways – Normal situation

• Each cerebral hemisphere only receives half the information of the visual field.

• Everything to the left Is represented by the right cerebral hemisphere

• Everything to the right is represented by the left cerebral hemisphere.

When the corpus callosum is intact both hemispheres perceive all information from both eyes as each hemisphere quickly communicates so the whole picture is in view19/04/23 50Mrs Smith Ch25 The Brain

Normal Visual PathwayNormal Visual Pathway

Information passed across

corpus callosum

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View the Scholar animation: http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=a3d7028a-e33c-5447-e177-1457682f9206

Split Brain Studies Split Brain Studies Visual Pathways – Abnormal situationVisual Pathways – Abnormal situation

• If the corpus callosum is cut (e.g. during surgery required due to intractable epilepsy), exchange of information is prevented because the corpus callosum does not connect the 2 cerebral hemispheres.

• So each hemisphere only perceives half of the information. The right hemisphere only gets information from the left eye & vice versa.

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Abnormal Visual PathwayAbnormal Visual Pathway

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Because the speech area is only found in the left hemisphere.

If a person with a split-brain (severed corpus callosum) is….

a) shown an object with their right eye open and left eye closed, they will be able to say the name of the object

b) shown an object with their left eye open and right eye closed they will be able to use the object (e.g. a spoon), write the name of the object, but NOT say the word!

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Watch this!!!! http://www.youtube.com/watch?v=ZMLzP1VCANo

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• See Scholar – Split Brain Studies

http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=a3d7028a-e33c-5447-e177-1457682f9206

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Blind Spot

• Because each eye has an optic nerve at the back, there is an area of the retina which has no light sensitive neurones. This area is called the blind spot.

• To find out about your blind spot, go to:http://serendip.brynmawr.edu/bb/blindspot1.html

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Task:

• Look around. Do you see a blind spot anywhere? Maybe the blind spot for one eye is at a different place than the blind spot for the other (this is actually true), so you don't notice it because each eye sees what the other doesn't. Close one eye and look around again. Now do you see a blind spot? Hmm. Maybe its just a little TINY blind spot, so small that you (and your brain) just ignore it. Nope, its actually a pretty BIG blind spot.

• LET’S PROVE IT!!!

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Try this!!

• Close your left eye and stare at the cross mark in the diagram with your right eye. Off to the right you should be able to see the spot. Don't LOOK at it; just notice that it is there off to the right (if its not, move farther away from the computer screen; you should be able to see the dot if you're a couple of feet away). Now slowly move toward the computer screen. Keep looking at the cross mark while you move. At a particular distance (probably a foot or so), the spot will disappear (it will reappear again if you move even closer). The spot disappears because it falls on the optic nerve head, the hole in the photoreceptor sheet.

• So, as you can see, you have a pretty big blind spot, at least as big as the spot in the diagram. What's particularly interesting though is that you don't SEE it. When the spot disappears you still don't SEE a hole. What you see instead is a continuous white field (remember not to LOOK at it; if you do you'll see the spot instead). What you see is something the brain is making up, since the eye isn't actually telling the brain anything at all about that particular part of the picture.

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Brain Injury Studies

Studies for brain injuries include:

• Phineas Gage – frontal lobe determines personality.

• A man with visual agnosia mistook his wife for a hat.

• Soldiers with shrapnel wounds

• People with brain lesions

• Stroke sufferers

Brain damage is usually caused by: Tumours, disease or accidents

Studying this damage has allowed experts to learn more about the way the brain works.

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Damaged frontal lobe

• In 1848 an accident happened to a railroad worker.

• A rod entered beneath his left eye and through the top of his head.

• He survived and eventually returned to work...... BUT....

• He changed personality becoming ill-tempered, unreliable and could no longer stick to a plan.

• This is because our FRONTAL LOBES are required in planning, goal setting and personality.

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Wife or Hat?

• A musician of great ability developed a problem in later life.

• He no longer recognised people or objects and failed to remember the past visually.

• He would chat to furniture thinking it was a person.

• On one occasion he reached out, took hold of his wife’s head and tried to lift it to put it on, thinking it was a hat.

• HE HAD A PROBLEM WITH HIS VISUAL ASSOCIATION CENTERS

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Shrapnel wounds

• Experts studied soldiers blinded or paralysed be cause of shrapnel.

• There findings provided early evidence that the rear of the cerebrum is responsible for vision and the area we call the MOTOR AREA controls movement.

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The cost of war: Washington Post 04/10/2010

• http://voices.washingtonpost.com/blog-post/2010/10/traumatic_brain_injuries_18000.html

• Robert Warren, three weeks after leaving Afghanistan, could not remember the name of the country he was just in. Shrapnel tore into his skull and a chunk of it had to be removed. "That country," he called Afghanistan, unable to grasp the right word.

• A piece of shrapnel pierced John Barnes's brain, tearing through his frontal lobe, the region in charge of decision making, reason and morality. As a result, Barnes exhibits impulsive behaviour and is unable to live on his own

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Lesions

• Lesions are small regions of damage.

• The location of the brains language centres is verified by the fact that lesions in these areas give rise to speech defects.

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Strokes

Stroke suffers often loose the function of part of their brain (sometimes permanent) , by matching the area of the brain affected to the lost bodily function experts can identify which parts of the brain are responsible for which bodily functions.

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Task: Torrance-TYK pg 211 Qu’s 1-4

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Task: Torrance AYK pg211/212 Qu’s 1-6

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Task: Can you answer these?

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Task: Can you answer these?

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More Questions

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Answers

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Even more Questions

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Answers

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And Again!!

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Answer Again!!

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Essay style Questions Scholar

Describe the appearance of the human brain, commenting on localised structures and their functions (10)

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ANSWER: Describe the appearance of the human brain, commenting on localised structures and their functions (10)

79

Each numbered point is worth 1 mark. The information in brackets is not a required partCorrect facts (8 marks) •The brain consists of a central core, including medulla and cerebellum.•The medulla controls unconscious activities such as peristalsis and rates of breathing and heartbeat.•The limbic system, including the hippocampus, is found in above the medulla.•The outer layer of the brain is called the cerebrum or cerebral hemispheres.•Conscious activities are co-ordinated by the cerebrum.•The outer surface of the cerebrum (cortex) is folded to increase the numbers of connections possible between neurones.•A visible cleft in the cerebrum is the location of the somatosensory area.•Sensory messages are received in the latter part of the cleft and motor responses are sent out by the frontal part.•The areas allocated are directly proportional to the degree of sensation and control required.•Large areas are devoted to the lips and hands, particularly the fingers.•The right side of the brain controls the left side of the body and vice versa.•The corpus callosum is a massive bundle of nerves that transfers information across the cerebral hemispheres.

Coherence (1 mark) One mark is given if at least 5 relevant points provided.Relevance (1 mark) It causes glycogen to be (rapidly) converted to glucose (not 'converts') One mark is deducted if a detailed explanation of negative feedback control is given.19/04/23 Mrs Smith Ch25 The Brain

Humour: Toddler brain

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Humour: Teenage brain

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Humour: Adult brain

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Humour: Canine brain

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Humour: Feline brain

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