Topic A.2 – The human brain

The anterior part of the neural tube expands to form the brain. The neural tube goes on to form all the parts of the brain. However, the anterior region expands much more rapidly, resulting in the cerebral hemispheres and brain structures. Parts of the adult brain that are important are: Medulla oblongata Cerebral Cortex Sulci/Gyri Left Hemisphere Right Hemisphere Visual Cortex Broca’s Area Nucleus accumbens Cerebellum Hypothalamus Pituitary gland

The autonomic nervous system controls involuntary processes in the body using centers located in the medulla oblongata. The medulla oblongata contains neurons that coordinate many of the muscles of the mouth, throat and larynx, and as such, regulates the swallowing reflex and the peristalsis that moves food down the esophagus, and not the windpipe. The medulla also controls the heart beat by constantly sending out cardio- inhibitory signals. During exercise, the medulla stops sending these signals, thereby allowing the heart rate to increase. The medulla plays a large role in the monitoring of blood carbon dioxide, which controls the respiration rate. High CO 2 levels increase the rate, and low CO 2 levels lower the rate.

Application: Visual cortex, Broca’s area, nucleus accumbens as areas of the brain with specific functions. Visual Cortex Area of the brain that receives visual information and passes on to the visual association area, which processes the information. Broca’s Area Responsible for speech and language. People with tumors or damage in this area of the brain have a severely limited capacity to communicate Nucleus accumbens The center of the reward circuit of the brain, dealing primarily with dopamine and serotonin, which operate oppositely with respect to desire. Dopamine = Desire Serotonin = Desire Visual Cortex

The cerebral cortex forms a larger proportion of the brain and is more highly developed in humans than other animals. Correlated with our additional development time as an embryo, our cerebral cortex is much larger than our animal counterparts. This has to do with neural migration This simple table demonstrates the increase in brain size (E) with respect to body size (S). How can ants and birds have a higher ratio than us? Not to be outdone, humans created a second index, in which incorporates the average brain size for animals of that type and we call this the Encephalization Quotient (EQ). Notice…..humans are way at the top.

The human cerebral cortex has become enlarged principally by an increase in total area with extensive folding to accommodate it within the cranium. These folds in the brain allow for a much higher surface area for neuronal connections. This allows for increased interactions between lobes of the brain, and leads to the complexity of our senses. Wow….grammar Brain metabolism requires large energy input. At rest, the brain uses approximately 20% of the body’s energy, while accounting for only 2% of your body mass. If your diet is 2000 kcal/day, then that is over 400 kcal! You are basically eating a whole meal each day, just to fuel your brain. This, when converted into electrical power, is about 19.4 watts/day, which is pretty efficient when you consider the supercomputers that compete with the human brain often run on ~750 servers, each with over 1000 watts powering them.

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. This allows us to partition the amount of sensory information coming to any on part of the brain at any time. Here you can see the two eyes connected to the brain by the optic nerves. The left visual field is giving information to the right side of the primary visual cortex and vice versa. fMRI is used as a way to identify the areas of the brain that are active, with respect to certain actions. Areas of high activity allow us to determine the function of different parts of the brain.

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. Roger Sperry carried out many different experiments that confirmed what we believed to be the functions of each of the hemispheres. This lead to a series of revelations on how instrumental the corpus callosum is in our daily function. We used to treat the some types of epilepsy through the severing of the corpus callosum in order to stop seizures.

The role of experimentation in determining the role of the areas of the brain. Outline the ability of each of the following methods of analysis on determining the role of different brain areas: -Lesions -Pupil Reflex -Animal Experiments -Autopsy Give an example experiment of the method you are investigating and describe how the results lead to greater understanding of certain areas of the brain.

Application: Use of animal experiments, autopsy, lesions and fMRI to identify the role of different brain parts. Self-administration experiments are one of the most common types of animal experimentation, in which mice can choose what type of food to eat. This is useful to determine whether a substance is addictive, and whether it would have withdrawal symptoms as well. Results from such an experiment shown to the right. (A)Adolescent rats self-administered nicotine combined with acetaldehyde with increasing frequency, but did not with any variable alone. (B)Adult rats did not have any preference. (C)Total intake was greatest in the youngest group of animals.

Application: Use of the pupil reflex to evaluate brain damage. The pupil reflex is the reflex within the eyes that causes the pupil to widen or narrow in response to changes in light. This is often used as a marker for brain activity in individuals that are non-responsive, as a method of determining whether brain death has occurred. If there is no movement in the pupil, along with no response to a variety of other tests, then it can be determined that the individual is “brain dead” The pathway of the pupil reflex is: 1.Optic nerve receives messages from retina 2.Optic nerve connects with pretectal nucleus of the brainstem 3.Message is sent to the Edinger- Westphal nucleus, back to the eye 4.At the synapse with the ciliary ganglion stimulates the muscle of the iris to contract

Challenge Questions Draw and annotate a diagram of the human brain. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ Explain why the brain metabolism requires a large input of energy. ___________________________ ___________________________ ___________________________ ___________________________ ___________________________ ___________________________ ___________________________ __________________________ Describe how an fMRI is used to identify the role of different brain parts. _________________________ _________________________ _________________________ _________________________ _________________________ _________________________ _________________________ _________________________ State the specific function of each of the following: Broca’s area, nucleus accumbens, visual cortex. _________________________ _________________________ _________________________ _________________________ _________________________ _________________________ Explain how folding has allowed the cerebral cortex to become more highly developed in humans than in other animals. _________________ _________________ _________________ _________________ _________________ After this subunit, can you do each of these?