Ch. 9 The Central Nervous System

Language Is the Most Elaborate Cognitive Behavior

"Wernicke's area" at the junction of the parietal, temporal and occipital lobes and "Broca's area" in the posterior part of the frontal lobe, close to the motor cortex Receptive aphasia: person is unable to understand sensory input; if damage occurs to Wernicke's area, a person may have difficulty understanding spoken or visual information; the person's own speech may be nonsense because the person is unable to retrieve words Expressive (Broca) aphasia: result of damage to Broca's area; people with Broca aphasia understand simple, unambiguous spoken and written language but have difficulty interpreting complicated sentences with several elements linked together; deficit in short-term memory; these people have difficulty speaking or writing in normal syntax; their response to a question to a question may consist of appropriate words strung together in random order; mechanical forms of aphasia occur as a result of damage to the motor cortex

Fig 9.11 The limbic system

*Cingulate gyrus is emotions and memory

Learning Is the Acquisition of Knowledge

-Associative learning: occurs when two stimuli are associated with each other (ex. Pavlov's experiment in which he simultaneously presented dogs with food and range a bell; over time, the dogs came to associate the sound of the bell with food and begin to salivate in anticipation of food whenever the bell was rung) -Nonassociative learning: is a change in behavior that takes place after repeated exposure to a single stimulus; type of learning includes habituation and sensitization, two adaptive behaviors that allow us to filter out or ignore disruptive stimuli i) Habituation: an animal shows a decreased response to an irrelevant stimulus that is repeated over and over; these responses allow us to filter out stimuli that we have evaluated and found to be insignificant (ex, a sudden loud noise may startle you, but if the noise is repeated over and over again, your brain begins to ignore it) ii) Sensitization: opposite of habituation; and the two behaviors combined help increase an organism's chances for survival; exposure to a noxious or intense stimulus causes an enhanced response upon subsequent exposure; is adaptive because it helps us avoid that food again, PTSD is the maladaptive form of sensitization (ex. people who become ill while eating a certain food may find that they lose their desire to eat that food again)

Neural Tissue Has Special Metabolic Requirements

-neurons require a constant supply of oxygen and glucose to make ATP for active transport of ions and neurotransmitters -15% of the blood pumped by the heart goes to the brain and is distributed through the excessive cerebral vascular system -the brain uses about 1/5 of the body's oxygen supply -under normal conditions, the only energy source for neurons is glucose, which is one reason that blood glucose homeostasis is critical -by some estimates, the brain is responsible for about half of the body's glucose consumption -if glucose homeostasis fails, progressive hypoglycemia (low blood glucose levels) leads to confusion, unconsciousness, and eventually death *diabetes: hypoglycemia and the brain understanding

Three layers of membrane

-collectively called the "meninges," lie between the bones and tissues of the CNS Three Layers (outer to inner order): 1) dura mater 2) arachnoid membrane 3) pia mater

The Cerebrum is the Site of Higher Brain Functions

-composed of two hemispheres connected primarily at the "corpus callosum" -this connection ensures that the two hemispheres communicate and cooperate with each other -each cerebral hemisphere is divided into 4 lobes: frontal, parietal, temporal, and occipital Cerebral cortex: is the outer layer of the cerebrum; within these layers are where our higher brain functions arise Basal ganglia: second region of cerebral grey matter; are involved in the control of movement Third region is the limbic system (which surrounds the brain stem); major areas of the limbic system are the amygdala and cingulate gyrus, which are linked to emotion and memory, and the hippocampus, which is associated with learning and memory

Gray Matter

-consists of unmyelinated nerve cell bodies, dendrites, and axons -cell bodies are assembled in an organized fashion in both the brain and the cord -clusters of cell bodies in the brain and spinal cord are known as nuclei

The Blood-Brain Barrier Protects the Brain

-final layer of protection for the brain is a functional barrier between the interstitial fluid and the blood -necessary to isolate the body's main control center from potentially harmful substances in the blood and from blood-borne pathogens such as bacteria

Pons (2nd region of brain stem)

-is a bulbous protrusion on the ventral side of the brain stem above the medulla and below the midbrain -primary function is to act as a relay station for information transfer between the cerebellum and cerebrum, the pons is often grouped with the cerebellum -also coordinates the control of breathing along with centers in the medulla

Alzheimer's Disease

-is a progressive neurodegenerative disease of cognitive impairment that accounts for about half the cases of dementia in the elderly -characterized by memory loss that progresses to a point where the patient does not recognize family members -over time, even the personality changes, and in the final stages, other cognitive functions fail so that patients cannot communicate with caregivers

White Matter

-mostly myelinated axons and contains very few neuronal cell bodies -color comes from the myelin sheaths that surround the axons -bundles of axons that connect different regions of the CNS are known as tracts *tracts in the CNS are equivalent to nerves in the PNS

Physiological Functions Exhibit Circadian Rhythms

-primary "clock" resides in networks of neurons located in the suprachiasmatic nucleus (SCN) of the hypothalamus, with secondary clocks influencing the behavior of different tissues. -simple interpretation of how the biological clock works is that clock cycling results from a complex feedback loop in which specific genes turn on and direct protein synthesis. -the SCN clock has intrinsic activity that is synchronized with the external environment by sensory information about light cycles received through the eyes -circadian rhythms in humans can be found in most physiological functions and usually correspond to the phases of our sleep-wake cycles (ex. body temperature and cortisol secretion) -melatonin is sometimes called the "darkness hormone" because its secretion increases in the evening -disruption of circadian rhythms, such as occurs with shift work and jet lag, can have detrimental effects on mental and physical health

The Brain Stem Is the Oldest Part of the Brain

-the "brain stem" is the oldest and most primitive region of the brain and consists of structures that derive from the embryonic midbrain and hindbrain

The Cerebellum Coordinates Movement

-the "cerebellum" is the second largest structure in the brain -the specialized function of the "cerebellum" is to process sensory information and coordinate the execution of movement -sensory input into the cerebellum comes from somatic receptors in the periphery of the body and from receptors for equilibrium and balance located in the inner ear -also receives motor input form neurons in the cerebrum

Medulla (1st region of brain stem)

-the "medulla oblongata," frequently just called the medulla, is the transition from the spinal cord into the brain proper -its white matter includes ascending somatosensory tracts that bring sensory information to the brain, and descending corticospinal tracts that convey information from the cerebrum to the spinal cord -about 90% of corticospinal tracts cross the midline to the opposite side of the body in a region of the medulla known as the pyramids -as a result of this crossover, each side of the brain controls the opposite side of the body *gray matter in the medulla includes nuclei that control many involuntary functions, such as blood pressure, breathing, swallowing and vomiting

Midbrain (3rd region of brain stem)

-the "midbrain," or mesencephalon, is a relatively small area that lies between the lower brain stem and the diencephalon -primary function of the midbrain is control of eye movement, but is also relays signals for auditory and visual reflexes

Memory Is the Ability to Retain and Recall Information

1) Memory: the ability to retain and recall information; very complex function 2) Short-term memory: limited storage area that can hold only about 7 to 12 pieces of information at a time; these items disappear unless an effort, such as repetition, is made to put them into a more permanent form 3) Working memory: special form of short-term memory processed in the prefrontal lobes; devoted to keeping track of bits of information long enough to put them to use in a task that takes place after the information has been acquired 4) Long-term memory: a storage area capable of holding vast amounts of information; associated with limbic system 5) Consolidation: the processing of information that converts short-term memory into long-term memory; can take varying periods of time Long-term memory can be divided into 2 types that are consolidated and stored using different neuronal pathways 1) Reflexive (implicit) memory, which is automatic and does not require conscious processes for either creation or recall, involves the amygdala and the cerebellum; information stored here is acquired slowly through repetition (also can be called procedural memory because it generally concerns how to do things) 2) Declarative (explicit) memory, requires conscious attention for its recall; creation generally depends on the use of higher-level cognitive skills such as inference, comparison, and evaluation; neuronal pathways involved in this type of memory are in the temporal lobes; deal with knowledge about ourselves and the world around us that can be reported or described verbally

The Cerebral Cortex is Organized into Functional Areas

Cerebral cortex serves as an integrating center for sensory information and a decision-making region for many types of motor output Three specializations: 1) Sensory areas (aka sensory fields), which receive sensory input and translate it into perception (awareness) 2) Motor areas, which direct skeletal muscle movement 3) Association areas (association cortices), which integrate information from sensory and motor areas and can direct voluntary behaviors Cerebral Lateralization (aka cerebral dominance) -Language and verbal skills tend to be concentrated on the left side of the brain, with spatial skills concentrated for the right side. -The left brain is the dominant hemisphere for right-handed people, and it appears that the right brain is dominant hemisphere for many left-handed people

Why Do We Sleep?

Sleep is defined as an easily reversible state of inactivity characterized by lack of interaction with the external environment Some explanations that have been proposed include to conserve energy, to avoid predators, to allow the body to repair itself, and to process memories Some of the newest research indicates that sleep is important for clearing waste out of the cerebrospinal fluid, particularly some of the proteins that build up in degenerative neurological diseases such as Alzheimer's Good evidence supporting the link between sleep and memory

The Diencephalon Contains the Centers for Homeostasis

The "diencephalon," or "between-brain," lies between the brain stem and the cerebrum Composed of two main sections, the thalamus and the hypothalamus, and two endocrine structures, the pituitary (adenohypophysis [anterior pituitary] & neurohypophysis [posterior pituitary) and pineal (secretes melatonin) glands 1)Thalamus -occupies most of the diencephalon -receives sensory fibers from the optic tract, ears, and spinal cord as well as motor information from the cerebellum -projects fibers to the cerebrum, where the information is processed -often described as relay station because almost all sensory information from lower parts of the CNS passes through it 2)Hypothalamus -center for homeostasis and contains centers for various behavioral drives, such as hunger and thirst -output form the "hypothalamus" also influences many functions of the autonomic division of the nervous system, as well as a variety of endocrine functions

Moods Are Long-Lasting Emotional States

i) Moods -are similar to emotions but are longer-lasting, relatively stable subjective feelings related to one's sense of well-being -difficult to define at a neurobiological level ii) Depression -is a mood disturbance that affects nearly 10% of the US population each year -characterized by sleep and appetite disturbances and alterations of mood and libido that may seriously affect the person's ability to function at school or work or in personal relationships -antidepressants known as selective serotonin reuptake inhibitors (SSRIs) and serotonin/norepinephrine reuptake inhibitors (SNRIs) slow down the removal of serotonin and norepinephrine