Characteristics of the Brain
By Renee Cohen
Is your computer a chemical factory? Even the most sophisticated computer network will never have the ability to carry out the functions that control so many human processes, including movement, emotions and language. That’s why we carry this computer around with us all the time – our brains.
Like the computer we use for producing transcripts, our brain also sends electrical signals from cell to cell along circuits, which process, store and retrieve information. In the simplest description, the brain of all vertebrates is partitioned into three main sections: the forebrain, midbrain and hindbrain. In humans, the three sections of the brain are more commonly called the cerebrum, cerebellum and brain stem. The grayish-pink organ is protected by a cushion of fluid and the bones of the cranium, and has 12 cranial nerves, numbered in the order in which they exit the brain through the skull. Together, the nerves, cerebrospinal fluid and the chemical mechanisms of the brain support metabolism, reproduction, coordination, excretion and the integration of all other bodily systems.
The hardware of the brain, its anatomy, resembles a giant soft walnut, weighing approximately three pounds. The brain grows from a slender stalk of the spinal cord, upward and sideways until it fills the skull. Traditional wisdom holds that the brains of humans adapted, forming a neocortex, resulting in an increased capacity for learned, complex behavior, which is less developed in other vertebrates. And no mammals, except human beings, have such an intricately folded cerebral surface, increasing the functional areas of the brain.
As in all cells, many complex chemical processes occur within the neurons of the brain. Electrically charged atoms, or ions, such as sodium and potassium, are maintained in varying concentrations inside the neuron and surrounding fluids. As cell membranes selectively allow ions to enter and leave the cells, an electric charge, or a nerve impulse, transmits messages to other systems, causing a reaction.
In the use of language, the brain's centers of vision and hearing enable us to understand spoken and written words. When reading, the vision center will convert impulses from the eyes into an image of a word. That visual image is then transformed in its associated sound pattern, which is then interpreted. When we wish to convey a thought, an impulse is sent to the brain, which issues instructions for the necessary muscular movements. The motor cortex orders the proper movements of the lips, tongue and other organs of speech, while the cerebellum is alerted to coordinate the movements, enabling the use of a human voice.
The sense of smell has its own private connection to the brain. This unique mainline may explain the ability of odors to evoke very powerful human memories. Although smell and taste are thought to be interlinked, they are actually independent of one another. Taste buds are restricted to the moist membranes of the walls of the mouth, throat and tongue, while the olfactory epithelium is situated high in the nasal cavity. The chemoreceptor cells involved in smell affect the behavior and physiology of many species. Phernomes, or chemical signals, can trigger extraordinary responses, most often from other members of the same species. A single molecule of a phernome can excite a receptor cell, and only a few molecules are needed to elicit a behavioral response.
The network of blood vessels that supply the brain are constantly pumping. While the human brain is only two percent of total body weight, it uses about 20 percent of the oxygen content of the entire body while at rest. Three to five minutes without oxygen is the longest the brain can last before serious injury occurs.
As with all biochemical reactions, the functions of the brain are highly temperature sensitive. The metabolic pathways are a series of chemical reactions that only occur when the conditions are regulated within specific limits. All vertebrates gain energy from the environment as food and heat, and they release energy during activity, growth, reproduction and waste production. The brain senses the conditions inside and outside of the body, analyzes the information and produces the necessary reactions.
While the mechanisms that control learning and thought processes may never be fully understood, scientists have made some inroads in explaining the phenomena. The encephalization quotient of any animal is the ratio of brain to body size. There is a certain amount of brain tissue needed to support each of the bodily functions. As brain size increases, it is able to operate in a more complex manner. Based on brain size alone, the largest whales would be the most intelligent animals on earth. Along with chimpanzees and other apes, the brains of whales and dolphins resemble the human brain more closely than the brain in any other species of animals.
The computers we buy and use on a daily basis are continually upgraded and result in increased capacity. So too is the evolution of mammals and the increasing complexity of societies leading to more intricate structures of the brain, and therefore, more circuits within the spinal cord and between the spinal cord and the brain. As humans continue to evolve, it is worthwhile to examine how other species have grown, adapted and used strategies of self-preservation.
Next month in this column, we will explore some of the behaviors of whales and dolphins, those marine mammals with our closest level of intelligence.
Characteristics of the Brain Exam
1. Mammals have _____ cranial nerves, numbered in the order in which they exit the brain through the skull. A) 10 B) 12 C) 14 D) 16
2. The hindbrain in humans is the area responsible for: A) vision B) sense of smell C) balance and vibration detection D) muscular control.
3. The senses of smell and taste are: A) interlinked in the brain B) situated in the midbrain C) independent of one another D) affected by surrounding fluids.
4. The muscles of speech are ordered to move by the A) motor cortex B) cerebellum C) medulla D) pituitary gland.
5. Reflex actions A) always involve the brain B) sometimes involve the brain C) never involve the brain D) usually involve the brain stem.
6. Pathways for electrical signals in the brain can be compared to A) radio waves B) computer circuits C) microwaves D) electrocardiograms.
7. Evolution and increasing complexity of human societies require better forms of A) communications B) transportation C) coordination D) concentration.
8. Other mammals with nearly the same encephalization quotient as humans are A) chimpanzees B) elephants C) birds D) whales and dolphins.
9. Based on brain size only, ________ would be the most intelligent animals on earth. A) rats B) dolphins C) whales D) humans
10. Electrically charged atoms are A) protons B) neutrons C) neurons D) ions.
11. Nerve impulses transmit messages for A) reactions B) perceptions C) coordination D) all of the above.
12. The human brain weighs approximately A) three pounds B) five pounds C) eight pounds D) 12 ounces.
13. The cerebrum is the A) smallest portion of the brain B) largest portion of the brain C) upper end of the spinal cord D) outermost portion of the brain.
14. Simple animals, such as worms, have A) no brains B) multiple small brains C) brains consisting of small groups of nerve cells D) brains without a brain stem.
15. Phernomes are A) chemical signals B) small animals C) sensory receptors D) behaviors.
16. Drugs can cause reactions in the brain that are A) temporary B) permanent C) mood altering D) all of the above.
17. Brain disorders include all but which of the following A) Down’s syndrome B) epilepsy C) asthma D) multiple sclerosis.
18. Biochemical reactions are sensitive to A) temperature B) hyperactivity C) hormones D) chromosomes.
19. Neurotransmitters affect all of the following except A) emotions B) thought processes C) judgment D) physique.
20. The folds and indentations on the brain A) are fluid-filled B) increase its surface area C) regulate emotions D) play a role in mental illness.