The Human Brain HL 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.

When they died, Broca examined their brains 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 Left 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 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

How do we know about the functions of the brain? 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 An animal is trained to press a lever to get a reward 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) In order for this to be a controlled experiment, 2 levers must be available, one which gives the substances & one that doesn’t 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 Central Nervous System Brain & Spinal Cord Peripheral Nervous System Somatic & Autonomic

Cardiac muscle Smooth muscle PNS (involuntary) Autonomic sympathetic parasympathetic (voluntary) Somatic From senses to muscles Cardiac muscle Smooth 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 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 That time when a physician has determined that the brain and brain stem have irreversibly lost all neurological function. What is the definition of brain death?

Profound or deep state of unconsciousness Coma vs Brain Death? Coma Brain Death 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 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

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

Stimulus: Pressure, heat or penetration (nocioreceptors) 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