The Human BrainHL Only

• E.5.1. Label, on a diagram of the human brain, the medulla oblongata, cerebellum, hypothalamus, pituitary gland and cerebral hemisphere.

Label the brain

• E.5.2 Outline the functions of each of the parts of the brain listed in E.5.1

• The brain is the most complex organ in the body.• Weighs about 1.4 kg• Contains over 100 billion neurones with thousands of synapses• New connections made daily• Regulates & monitors unconscious body processes• Receives & interprets information from our senses• Controls voluntary movement

• E.5.3 Explain how animal experiments, lesions and fMRI (functional magnetic resonance imaging) scanning can be used in the identification of the brain part involved in specific functions.

Brain Lessions

• Accidents to the brain, stroke and tumours can damage specific parts of the brain, the damaged area is a lesion. From the position of the lesion, we can determine functions of that part of the brain by observing what the patient can no longer do.

Broca’s area

• The most famous study is of a region known as Broca’s area, in the 1860’s. One patient, Leborgne, could only speak one word. Lelong could only speak a few words.

Broca’s area

• When they died, Broca examined their brains• Lesions were found in the same area• Deduced this region was responsible for language

– Broca’s area – interferes with localization– Wernicke’s area – affects the ability to put words into sentences

• fMRIs have confirmed this• Brain divided into left & right hemispheres• Connected by the corpus callosum• Not the same functions

Right & Left Hemisperes

Right Hemisphere

• Specializes in receiving & analyzing information from all of our senses

• Problem identifying faces• Problems locating an object

correctly in space• can’t identify melodies

Left Hemisphere

• Important for all forms of communication

• Difficulty speaking• Difficulty doing complicated

movements of the hands/arms

• Deaf people with damage here – can’t use sign language

fMRI

How do we know about the functions of the brain?• “Brain Mapping” – uses radio waves & a strong magnetic field

(not Xrays)• Can see the blood flow in the brain as it occurs• Increased blood flow to regions of the brain is detected and

overlayed on a brain map• Allows us to see which sections of the brain are most active

during particular tasks

fMRI

• Studies have been used to discover the functions of various regions of the brain

• To show differences and similarities between groups of people and are a useful diagnostic tool in medicine

Animal Experiments

• Are often controversial• Have led to many advances in science• Key to 19th century discoveries

Animal Studies

Studies involved dissection of human brains (post-mortem) –compared to animal

specimens Removal of sections of animal brains - to observe impaired

function (Flouren – exp. on pigeons. Removal of the cerebellum led to its discovery as the movement centre of the brain)

Electrical stimulation of living primate and dog brains in order to observe movement and actions in the body

Animal Studies

• One type of animal experiments is to expose animal models to addictive substances in controlled situations.– Want more and more of the substance– Spend lots of time and energy getting it– Keep taking it despite adverse conditions– Have withdrawal symptoms on withdrawal of the substance– Go back to the substance when stressed– Go back to the substance with another exposure to that substance

To test if a chemical meets the criteria for addiction

1. An animal is trained to press a lever to get a reward2. The animal is given an injection of the addictive substance. The

lever must automatically give the injection if it is pushed by the animal. (self-administration)

3. In order for this to be a controlled experiment, 2 levers must be available, one which gives the substances & one that doesn’t

4. If the substance is ‘reinforcing’, the animal will seek to repeat the experience by pushing that lever much more frequently

Animal Experiments

• E. 5.4 Explain sympathetic and parasympathetic control of the heart rate, movements of the iris and flow of the blood to the gut

Sympathetic & Parasympathetic control

Cardiac muscleSmooth muscle

Antagonistic

Target Sympathetic Parasympathetic

Heart rate Increase heart rate Decrease in heart rate

Blood vessels Decreases diameter of major arteries therefore increasing blood pressure

Increases diameter of major arteries therefore decreasing blood pressure

Flow of blood to intestines (gut)

Decreased flow to intestines Increased flow to intestines

Iris movement Iris muscles cause pupil to dilate

Iris muscles cause pupil to constrict

Heart Rate

Gut Blood Flow

Iris Control

• E.5.5 Explain the pupil response

Pupil Reflex

Pupil Reflex

Cranial reflexCranial reflex

Not spinal cord reflex

Not spinal cord reflex

• E.5.6 Discuss the concept of brain death and the use of the pupil reflex in testing for this.

Determining Brain Death

• We can artificially maintain the body using ventilation & circulation

• Brain stem controls heart rate, breathing rate and blood flow

What is the definition of brain death?

What is the definition of brain death?

That time when a physician has

determined that the brain and brain

stem have irreversibly lost all

neurological function.

That time when a physician has

determined that the brain and brain

stem have irreversibly lost all

neurological function.

Coma vs Brain Death?

Coma• Profound or deep state of

unconsciousness• Still have neurological signs

– No eye-opening– Unable to follow instructions– No speech or other forms of

communication– No purposeful movement

Brain Death• Must perform a toxicology

test• Examination

– Movement of extremities– Eye movement– Corneal reflex– Pupil reflex– Gag reflex– Respiration response

Spinal reflexes may still function – knee jerk

Spinal reflexes may still function – knee jerk

• E.5.7 Outline how pain is perceived an dhow endorphins can act as painkillers.

Perception of Pain

• Stimulus: Pressure, heat or penetration (nocioreceptors)– Housed in the skin, muscles, bones, joints & membranes around

organs• Impulse: relayed to brain via spine• Perception: in cerebral cortex leads to feelings of pain• Function: pain acts as a ‘stop’ signal to prevent more damage to

the body– Muscles stop the action causing the pain stimulus– Alerts the autonomic nervous system if the pain requires change in

heart rate or breathing– Can direct other brain cells to release pain-suppressing endorphins

Pain is in the Brain!

Endorphins

• First discovered by scientists studying opium addiction• Found receptors for opiates, morphine & heroin in brain cells• Morphine & heroin bound to the brain receptors because they

were mimicking endorphins• Endorphins are CNS neurotransmitters with pain-relieving

properties• They are small peptides which bind to opiate receptors & block

the transmission of impulses at synapses involved in pain perception

Endorphins