BioKnowledgy A.2 The human brain

A.2 The human brain

The image shows several different regions of the human brain and within each region the areas that have been attributed to different functions.

By Chris Paine

http://www.bioknowledgy.info/

Essential idea: The parts of the brain specialize in different functions.

https://askabiologist.asu.edu/sites/default/files/resources/articles/nervous_journey/brain-regions-areas.gif








UnderstandingsStatement Guidance

A.2.U1 The anterior part of the neural tube expands to form the brain.

A.2.U2 Different parts of the brain have specific roles.

Although specific functions can be attributed to certain areas, brain imagery shows that some activities are spread in many areas and that the brain can even reorganize itself following a disturbance such as a stroke.

A.2.U3 The autonomic nervous system controls involuntary processes in the body using centres located mainly in the brain stem.

A.2.U4 The cerebral cortex forms a larger proportion of the brain and is more highly developed in humans than other animals.

A.2.U5 The human cerebral cortex has become enlarged principally by an increase in total area with extensive folding to accommodate it within the cranium.

A.2.U6 The cerebral hemispheres are responsible for higher order functions.

A.2.U7 The left cerebral hemisphere receives sensory input from sensory receptors in the right side of the body and the right side of the visual field in both eyes and vice versa for the right hemisphere.

A.2.U8 The left cerebral hemisphere controls muscle contraction in the right side of the body and vice versa for the right hemisphere.

A.2.U9 Brain metabolism requires large energy inputs.

Applications and SkillsStatement Guidance

A.2.A1 Visual cortex, Broca’s area, nucleus accumbens as areas of the brain with specific functions.

A.2.A2 Swallowing, breathing and heart rate as examples of activities coordinated by the medulla.

A.2.A3 Use of the pupil reflex to evaluate brain damage.

A.2.A4 Use of animal experiments, autopsy, lesions and fMRI to identify the role of different brain parts.

A.2.S1 Identification of parts of the brain in a photograph, diagram or scan of the brain.

Image of the brain should include the medulla oblongata, cerebellum, hypothalamus, pituitary gland and cerebral hemispheres.

A.2.S2 Analysis of correlations between body size and brain size in different animals.

http://i-biology.net/

A.2.U1 The anterior part of the neural tube expands to form the brain.

Development of the brain

In a mammalian embryo, the neural tube is initially a straight, linear structure running the length of the rear-side.

Most of the neural tube eventually becomes the spinal cord, but as early as the fourth week the anterior end develops into three distinct bulges known as the primary vesicles. The vesicles continue to develop and form the fore, mid and hind sections of the brain.

http://thebrain.mcgill.ca/flash/d/d_09/d_09_cr/d_09_cr_dev/d_09_cr_dev_3a.jpg

Fact: the human brain contains an estimated 86 billion neurons

http://onlinelibrary.wiley.com/doi/10.1002/cne.21974/abstract;jsessionid=EC9F44A0305DF8852C37DA27A1D5D433. f02t03



http://onlinelibrary.wiley.com/doi/10.1002/cne.21974/abstract;jsessionid=EC9F44A0305DF8852C37DA27A1D5D433.f02t03

http://onlinelibrary.wiley.com/doi/10.1002/cne.21974/abstract;jsessionid=EC9F44A0305DF8852C37DA27A1D5D433.f02t03

A.2.U9 Brain metabolism requires large energy inputs.

Metabolism of the brain

http://www.the-scientist.com/images/December2012/brain_640x360.jpg

The energy demands of the brain are high: they account for at least 20% of a human adult’s energy consumption.

Studies indicate have linked higher cognitive functions to increased glucose demand.

• Synthesise neurotransmitters• carry out the active transport needed

to maintain resting potential.

Cell respiration produces the ATP that is constantly required by neurons to:



A.2.S1 Identification of parts of the brain in a photograph, diagram or scan of the brain. A.2.U2 Different parts of the brain have specific roles.

Functions of the human brain

Edited from: http://old-ib.bioninja.com.au/_Media/brain_med.jpeg

front

- can you label and annotate the diagram?

http://old-ib.bioninja.com.au/_Media/brain_med.jpeg







front







Coordinates unconscious functions, such as movement and balance.

Act as the integration centre for highly complex functions, such as learning, memory and emotion.

Controls automatic and homeostatic activities, such as swallowing, digestion and vomiting, and breathing and heart rate.

Produces and secretes hormones regulating many body functions, e.g. such as ADH

Maintains homeostasis via coordination of the nervous and endocrine systems, produces hormones secreted by posterior pituitary




Identifying brain function – autopsy and animal experiments

Animal experiments can take different approaches to investigating brain function. Commons approaches are:• Autopsy, dissection of the brain• Stimulating regions of the brain with electrodes and

then observing behaviour and movement – e.g. Ferrier work with dogs and monkeys

• Lobotomy - removing regions of the brain and observing impairment of brain function, e.g. Flourens’ experiments on pigeons

Animals are used rather than humans as the methods are highly invasive and potentially cause permanent damage.

Experimental results have limited validity as there are differences between human and animal brains. The most valid comparisons use primates as they are more closely related to humans.

What are the ethical considerations that need to be made before proceeding with an animal experiment?

What benefits could arise from the seemingly cruel experiment above?

Animal experimentation has lead to many advances in science and medicine, particularly in neurobiology and treatment of neurological disorders such as multiple sclerosis

Monkey feeds itself with a robotic arm

https://youtu.be/jOkpn0BN2HE

Find out more about the study of brain function in the 19th century: http://www.cerebromente.org.br/n01/frenolog/frenloc.htm



http://www.cerebromente.org.br/n01/frenolog/frenloc.htm

http://www.cerebromente.org.br/n01/frenolog/frenloc.htm



Identifying brain function - lesions Lesions are abnormal areas in brain tissue caused by accidents or present from birth

Presence of a lesion is usually associated with damaged and loss of function in the affected area.

Complex functions often involve multiple brain areas making results difficult to interpret. Also brain plasticity, to a degree functions to be re-organised into undamaged areas.

https://commons.wikimedia.org/wiki/File:BrocasAreaSmall.png

In 1861, a French physician named Broca heard of a patient who had a 21-year progressive loss of speech and paralysis, but not a loss of comprehension nor mental function. Broca predicted the presence of a lesion in the frontal lobe of the left cerebral hemisphere (later known as Broca’s area). After Leborgne’s death, Broca confirmed the presence of the lesion by autopsy. The finding was confirmed by further autopsies and more recently by fMRI.

https://www.dnalc.org/view/1112-Broca-s-Area-Primary-Functions-.html








Identifying brain function - fMRI

https://youtu.be/Cwda7YWK0WQ

fMRI and autism research

https://commons.wikimedia.org/wiki/File:FMRI_scan_during_working_memory_tasks.jpghttp://www.medicalland.gr/wp-content/uploads/2015/02/-lung-screening-e1428992181862.jpg

Measurements can be made in real-time so regional brain activity can be correlated with a stimulus. Also the sequencing of brain activity, e.g. language comprehension followed by production can be observed.

fMRI is the primary tool used in modern research. It measures changes in blood flow through the brain. This can indicate which regions of the brain are most active.

fMRI works because oxyhaemoglobin responds differently to a magnetic field than (deoxygenated) haemoglobin. Computers interpret the results to produce coloured brain activity images (different colours often represent different levels of activity).

The procedure is non-invasive and can be performed without injury, but it is an indirect measure and not all brain activity is detected.

This is a tool for medicine as well as being used in research. For example ADHD and dyslexia can diagnosed and stroke recovery can be monitored.



https://commons.wikimedia.org/wiki/File:FMRI_scan_during_working_memory_tasks.jpg

https://commons.wikimedia.org/wiki/File:FMRI_scan_during_working_memory_tasks.jpg

http://www.medicalland.gr/wp-content/uploads/2015/02/-lung-screening-e1428992181862.jpg

http://www.medicalland.gr/wp-content/uploads/2015/02/-lung-screening-e1428992181862.jpg

A.2.U3 The autonomic nervous system controls involuntary processes in the body using centres located mainly in the brain stem. A.2.A2 Swallowing, breathing and heart rate as examples of activities coordinated by the medulla.


A.2.U3 The autonomic nervous system controls involuntary processes in the body using centres located mainly in the brain stem. A.2.A2 Swallowing, breathing and heart rate as examples of activities coordinated by the medulla.

The autonomic nervous system The autonomic nervous system controls unconscious processes using the medulla oblongata.

The autonomic nervous system is part of the peripheral nervous system, which consists of all the nerves outside the central nervous system.

There are two distinct parts to the autonomic nervous system: sympathetic and parasympathetic. These two parts have contrary effects, e.g. parasympathetic nerves cause an increase in blood flow to the gut, during digestion and absorption of food, whereas the sympathetic nerves cause a decrease in blood flow.


Activities coordinated by the medulla – breathing and heart rate

Stimulus: blood pH falls as CO2 concentration increasesReceptor:

Nerves: sympathetic nerves stimulate …Responses: the Intercostal muscles and diaphragm (lung muscles)

to increase the rate and size of contractions: increasing the rate and depth of ventilation.heart’s pacemaker (sino-atrial node) to increase the heart rate

breathing and heart rate centres in the medulla oblongata contain chemoreceptors in their blood vessels.

https://commons.wikimedia.org/wiki/File:Ergospirometry_laboratory.jpg

Stimulus: blood pH rises as CO2 concentration decreases*Receptor:

Nerves: parasympathetic nerves stimulate …Responses: the Intercostal muscles and diaphragm (lung muscles)

to decrease the rate and size of contractions: decreasing the rate and depth of ventilation.heart’s pacemaker (sino-atrial node) to decrease the heart rate

breathing and heart rate centres in the medulla oblongata contain chemoreceptors in their blood vessels. *




Activities coordinated by the medulla – swallowing

*

The first phase of swallowing, the passing of food from the mouth to the pharynx, is voluntary and therefore controlled by cerebral cortex, not the medulla.

Stimulus: bolus of food touches the walls of the pharynxReceptor: touch receptors in the walls of the pharynxNerves: Response: contraction of muscles in the pharynx and esophagus (peristalsis)

http://swm.synology.me/pixacts/wp-content/uploads/apple1.jpg

parasympathetic nerves send impulses via the swallowing centre in the medulla oblongata




The pupil reflex – assessing brain damage

https://youtu.be/E2XzBaOOX8g

http://library.med.utah.edu/kw/animations/hyperbrain/parasymp_reflex/reflex.html

Stimulus: Bright lightReceptor: photoreceptors on the retina detect potential damaging levels of lightCoordination: Sensory neurons in the optic nerve send impulses to the medulla oblongata. Relay and then motor neurons direct the impulse to the iris muscles.Effect: Radial muscles relax and circular muscles contract to constrict the size of the pupil

The pupil reflex originates in the brainstem and is under the control of the autonomic nervous system

Test your pupil reflex

Detailed exploration of the pupil reflex

http://old-ib.bioninja.com.au/_Media/pupil-reflex_med.jpeg









The pupil reflex – assessing brain damage


Failure of the pupil reflex indicates the damage to medulla oblongata (brain stem).

The brain stem controls basic automatic brain functions. If the brain stem fails then the organism can no longer function and it is unlikely that higher order brain functions persist. Therefore brain stem death is used to test for whole brain death.

Following brain stem death life support can sustain other parts of the body, but it is very unlikely that a recovery can be made.

Many countries accept brain stem death as the legal definition of death. After brain death doctors may seek consent to recover functional organs for donation to those that need them.

What is your opinion on organ donation:• Should doctors be allowed to interrupt the grieving process to ask for permission from relatives?• Or should doctors have the legal right to collect organs without needing to seek permission from

relatives?



A.2.U5 The human cerebral cortex has become enlarged principally by an increase in total area with extensive folding to accommodate it within the cranium.

Enlargement and folding of the cerebral cortexThe cerebral cortex, which consists of the two cerebral hemispheres, is the outer layer of neural tissue in humans and other mammals. It is very thin (2 – 4 mm) and contains the neurons key to controlling complex behaviour.

The folds in the cortex enabling a large increase in surface area, without increasing the size of the cranium (skull).

Through evolution the human cranium has increased in size and the folding has become more extensive. Both changes allowed an increase in the number of neurons present in the cortex controlling complex behaviour, folding being the key change.

Left shows brain images to scale, right shows the folding, but images are not to scale.

http://thebrain.mcgill.ca/flash/i/i_05/i_05_cr/i_05_cr_her/i_05_cr_her_1a.jpg




Correlations between body size and brain sizeIs there a relationship between the size of an animal and the size of it's brain?

Can you suggest reasons for a causal link between body size and brain size?

https://commons.wikimedia.org/wiki/File:Brain-body_mass_ratio_for_some_animals_diagram.svg





There is a strong correlation (despite outliers such as the Alligator). Note the logarithmic scales, this relationship is not directly proportional.


• The larger the animal the larger the brain required to monitor and control it’s processes.

• Brain size is limited by the metabolism of the animal.

n.b. when groups of animals, e.g. primates, are examined the correlation becomes very weak. Other factors, such as evolution and the ecological niche occupied, seem to have more effect on brain size than body size.




n.b. when groups of animals, e.g. primates, are examined the correlation becomes very weak. Other factors, such as evolution and the ecological niche occupied, seem to have more effect on brain size than body size.



There is a strong correlation (despite outliers such as the Alligator). Note the logarithmic scales, this relationship is not directly proportional.


• The larger the animal the larger the brain required to monitor and control it’s processes.

• Brain size is limited by the metabolism of the animal.

Discuss whether there a relationship between the size

of an animal's brain and “behavioural complexity”




A.2.U4 The cerebral cortex forms a larger proportion of the brain and is more highly developed in humans than other animals.

Evolutionary development of the cerebral cortex

http://thebrain.mcgill.ca/flash/a/a_05/a_05_cr/a_05_cr_her/a_05_cr_her_1a.jpg

The cerebral cortex, which is only present in mammals, varies greatly as to it’s proportion of the brain’s mass. For instance in shrews it is 20% of the mass, whereas in humans it accounts for 80%.

In mammals certain brain areas, such as the cerebellum, which coordinates muscle movement have remained a constant proportion compared to the overall size of the brain.

The image shows evolutionary changes in the prefrontal cortex (the most forward region of the cerebral cortex).

The cerebral cortex linked to the development of complex behaviours, but changes in the connections between the neurons, not just the number of neurons, is also key to behaviour development.



A.2.U6 The cerebral hemispheres are responsible for higher order functions.

https://commons.wikimedia.org/wiki/File:Blausen_0215_CerebralHemispheres.png

The hemispheres act as the integration centres for highly complex functions, such as learning, memory and emotion.

Cerebral hemispheres

Higher order functions rely on input both from stimuli and and memories.

Sophisticated processes, such as reasoning, planning, self-awareness and morality, rely on a complex network of neurons. It is estimated that there are 1014 synapses in the brain.

Due to the huge complexity of these neural networks how these functions work is only partially understood.



A.2.U7 The left cerebral hemisphere receives sensory input from sensory receptors in the right side of the body and the right side of the visual field in both eyes and vice versa for the right hemisphere. AND A.2.U8 The left cerebral hemisphere controls muscle contraction in the right side of the body and vice versa for the right hemisphere.

http://mercercognitivepsychology.pbworks.com/f/1385067467/Left-or-Right-Brain-Marketer.jpg




WRONG





Left and right cerebral hemisphere functions

http://faculty.pasadena.edu/dkwon/chap%209%20accessible/chapter%209%20accessible%20web%20page_files/images/image38.

png

Some functions are limited to a particular hemisphere, but most brain functions are bilateral, they are dealt with by both sides of the brain.

It is however true that the brain is “cross-wired”:• The right side of the brain receives stimuli from

the left side of the body (and vice-versa)• The left visual field from both eyes is processed

by the right side of the brain (and vice-versa)• The left side of the brain controls movement,

muscle contraction, on the right side of the body (and vice-versa)

This explains why stroke victims lose sensation and/or the ability to move limbs on one side of the body as a stroke may cause a brain damage to a single hemisphere.

Review: A.3.U6 The information from the right field of vision from both eyes is sent to the left part of the visual cortex and vice versa.


A.2.A1 Visual cortex, Broca’s area, nucleus accumbens as areas of the brain with specific functions.

Localised functions of the cerebral hemispheres

• Visual cortex processes stimuli received by light-sensitive rod and cone cells in the retina. The stimuli from both eyes are combined to allow distance, speed and size to be judged.

https://commons.wikimedia.org/wiki/File:Brain_stem_normal_human.svg

• Broca’s area is involved in both language comprehension, but is most strongly associated with language production. If damaged a person has trouble forming words and sentences to express their thoughts.

• Nucleus accumbens are pleasure and reward centres. Selective stimuli, e.g. food and sex, cause the release of the neurotransmitter dopamine by the nucleus accumbens. Dopamine causes feelings of well-being and pleasure. The feeling of pleasure can also act as a reinforcement during learning.

Certain regions of the cerebral hemispheres are specialised to carry out certain functions, for example:







Coordinates unconscious functions, such as movement and balance.

Acts as the integration centre for highly complex functions, such as learning, memory and emotion.

Controls automatic and homeostatic activities, such as swallowing, digestion and vomiting, and breathing and heart rate.

Produces and secretes hormones regulating many body functions, e.g. such as ADH

Maintains homeostasis via coordination of the nervous and endocrine systems, produces hormones secreted by posterior pituitary

n.b. brain imagery (MRI) has shown that some activities are

spread across several areas. Following brain injuries, e.g. a

stroke, the brain can, to a degree, reorganise functions into

undamaged areas.




Functions of the human brain - can you label the MRI image?

http://images.radiopaedia.org/images/3892/250f2c53630e8ed64750391d0ae46f.jpg




Functions of the human brain - can you label the MRI image?

Cerebral hemisphere

CerebellumMedullaoblongata

Pituitary gland

Hypothalamus




Nature of science: Use models as representations of the real world - the sensory homunculus and motor homunculus are models of the relative space human body parts occupy on the somatosensory cortex and the motor cortex. (1.10)

Sensory homunculus

https://lh6.googleusercontent.com/-lZ5sI2Mcgdo/T-Bx6O8pY-I/AAAAAAAAEKE/Bc5m9vWDgdM/w800-h800/1.images_brain_map_final_MotorSensoryCortex-L.png

A cortical homunculus is a physical representation of the human body, located within the brain.

Can you compare and contrast the importance of different body parts in the gaining of stimuli and responding to it?

How useful is this model?

What are the limitations of this visual approach?

Cortical homunculi

This neurological "map" gives a sense of the proportions of the sensory and motor cortex devoted to different parts of the body.

Motorhomunculus



Bibliography / Acknowledgments

http://ib.bioninja.com.au/


Education

BioKnowledgy A.2 The human brain