Psychology Chapter 4.3-4.5: The Brain and Nervous System PDF

**The Brain** 4.3.01 The Forebrain, Midbrain, and Hindbrain The brain can be described as comprising three major regions: the forebrain, the midbrain, and the hindbrain. The **forebrain** (prosencephalon) contains the cerebrum, the brain\'s two hemispheres. Major forebrain structures include the...

**The Brain** 4.3.01 The Forebrain, Midbrain, and Hindbrain The brain can be described as comprising three major regions: the forebrain, the midbrain, and the hindbrain. The **forebrain** (prosencephalon) contains the cerebrum, the brain\'s two hemispheres. Major forebrain structures include the olfactory bulbs (discussed in more detail in Lesson 12.3), the basal ganglia (a collection of nuclei involved in initiating voluntary movements), and the [pineal gland](javascript:void(0)). The pineal gland releases melatonin, a hormone that causes sleepiness, when it is dark (see Lesson 13.2). The forebrain also includes several brain structures that contribute to emotion, memory, and motivation. These structures are sometimes collectively referred to as the limbic system (Figure 4.16). Limbic structures include: The **amygdala** is involved in aggression and emotions such as fear. Researchers have shown that electrical stimulation of the amygdala leads to displays of fear and aggression, whereas damage to the amygdala can result in a lack of fear. The **hypothalamus** releases hormones and controls the pituitary gland\'s hormone release; it coordinates many bodily processes such as hunger, growth, and the fight-or-flight stress response, as is discussed in Lesson 4.5. The **hippocampus** is involved in learning and memory, such as the formation of explicit/declarative memories (ie, memory for facts and events that can be intentionally recalled) (Lesson 19.3 covers the biological underpinnings of memory in further detail). Damage to the hippocampus (eg, brain trauma caused by a head injury) can result in amnesia: severe memory loss. The **thalamus** contributes to sensation and perception; it is responsible for processing and relaying sensory information and directly receives information from all the senses except olfaction. **Figure 4.16** Limbic structures. A diagram of a brain Description automatically generated Chapter 4: The Nervous and Endocrine Systems 30 The **midbrain** (mesencephalon) is an area of the brainstem that connects the brain and the spinal cord. The superior and inferior colliculi, structures located in the midbrain, serve important sensory functions; the superior colliculus processes visual information, and the inferior colliculus processes auditory information. In addition, the midbrain contains two areas with large numbers of dopaminergic neurons: the substantia nigra (SN) and the ventral tegmental area (VTA). The SN projects axons to the basal ganglia and plays an important role in voluntary movements. Parkinson\'s disease, a progressive neurodegenerative disease, is marked by the death of dopaminergic neurons in the SN and results in impaired movement (see Concept 29.2.01). The VTA projects to different parts of the forebrain (eg, prefrontal cortex, nucleus accumbens) and plays an important role in reward. Finally, the **hindbrain** (rhombencephalon) is made up of the cerebellum and the lower part of the brainstem, including the medulla, pons, and reticular formation (Figure 4.17). The brainstem region closest to the spinal cord is the **medulla**, which controls critical functions such as breathing and heart rate. The **pons** lies above the medulla and regulates sleeping, waking, and dreaming. The **reticular formation** is a series of neurons that spans the entire brainstem and contributes to consciousness and wakefulness. Located behind the brainstem, the **cerebellum** is responsible for coordinating voluntary movements, posture, and balance. Specifically, the cerebellum integrates visual, vestibular, and kinesthetic information to maintain balance and posture, coordinate complex movements, and execute precise fine motor movements. The cerebellum is also critical for motor learning, which occurs when an organism repeatedly practices a motor task (eg, swimming). **Figure 4.17** Hindbrain structures.  Chapter 4: The Nervous and Endocrine Systems 31 4.3.02 Lobes of the Brain The **cerebral cortex** is the outermost portion of the brain. The cortex can be divided into the frontal, temporal, parietal, and occipital lobes (Figure 4.18). **Figure 4.18** Lobes of the brain. The frontal lobe is responsible for higher-order processes (eg, planning, decision-making, personality, judgment). The **prefrontal cortex** is an area of the frontal lobe that contributes to decision-making, personality, and memory. Voluntary muscle movements also involve the frontal lobe. The frontal lobe\'s **motor cortex** relays motor commands from the motor cortex to the skeletal muscles. The regions of the body requiring more motor control (eg, the hands) occupy a greater area of the motor cortex. The temporal lobe contains the **auditory cortex**, an area primarily responsible for processing auditory stimuli based on input from the ears (see Lesson 11.2). The temporal lobe also contains structures involved in learning and memory (eg, the hippocampus), as well as areas involved in language (eg, Wernicke\'s area). The parietal lobe is responsible for proprioception (awareness of one\'s body position in space) and somatosensation (eg, perception of touch, pain, temperature). Specifically, somatosensory information is processed in the parietal lobe\'s [somatosensory cortex](javascript:void(0)). The more sensitive regions of the body (eg, fingers, tongue) occupy a greater area of the somatosensory cortex. See Chapter 12 for more information on the role of the parietal lobe in somatosensation and proprioception. The occipital lobe is located in the back of the cerebral cortex and is responsible primarily for visual processing. The occipital lobe\'s **visual cortex** receives and processes input from the eyes. Visual processing is discussed in more detail in Lesson 10.2. A diagram of the brain Description automatically generated Chapter 4: The Nervous and Endocrine Systems 32 4.3.03 Lateralization The brain\'s right and left hemispheres are each specialized for certain processes; this specialization is known as **hemispheric lateralization**. Each hemisphere is responsible for contralateral control of the body; the left hemisphere controls touch and movement on the right side of the body, and vice versa. In the majority of people, the right hemisphere is crucial for visuospatial processing. In contrast, the left hemisphere in most people is specialized for language functions, including writing, speech production (Broca\'s area), and language comprehension (Wernicke\'s area). These language centers are shown in Figure 4.19. **Figure 4.19** Language centers in the brain. The **corpus callosum** is a bundle of myelinated axonal projections connecting the right and left hemispheres of the brain, allowing the two hemispheres to communicate. Severing the corpus callosum is sometimes used to treat severe epileptic seizures. Individuals with a severed corpus callosum (\"split-brain\") experience disrupted communication between the two hemispheres. In famous experiments, Roger Sperry and Michael Gazzaniga demonstrated that information presented to a split-brain patient\'s left visual field is processed in the right hemisphere; without interhemispheric communication, the patient is unable to express what is seen verbally but would be able to draw it with the left hand (Figure 4.20). **The Spinal Cord** 4.4.01 The Spinal Cord The **spinal cord** is a structure in the central nervous system that facilitates the brain\'s communication with the peripheral nervous system (PNS). While the spinal cord relays messages between the PNS and the brain, information processing also occurs in the spinal cord. The spinal cord contains tracts of white matter (myelinated axons) and gray matter (cell bodies and dendrites) as discussed in Concept 4.1.01. In the context of the sensory and motor systems, the spinal cord\'s afferent (ascending) tracts send sensory signals toward the brain, and efferent (descending) tracts carry motor commands away from the brain. The organization of the spinal cord is illustrated in Figure 4.21. **Figure 4.21** Information relayed through the spinal cord. In addition to transmitting sensory and motor information to the brain, some spinal cord neurons are responsible for processing information. An example of this is a **spinal reflex**. The neural process of receiving and acting on sensory information in this reflex arc involves the following steps:  1.Somatosensory receptors in the skin are stimulated by something painful (eg, a prick from a sharp needle). 2.Afferent sensory neurons relay this information to spinal interneurons (neurons in the spinal cord that integrate sensory and central nervous system inputs). 3.Spinal interneurons process the sensory information before it travels to the brain and directly stimulate efferent motor neurons. 4.Efferent motor neurons relay motor commands to the skeletal muscles, causing the muscles to respond (eg, pull the hand away from the needle). The steps of this reflex are shown in Figure 4.22 **The Endocrine System** 4.5.01 Components of the Endocrine System In addition to the nervous system, the body also communicates through the **endocrine system**. In contrast to neural communication wherein cells communicate by forming synapses with nearby cells, endocrine communication is a slower form of long-distance cell-to-cell communication. The endocrine system regulates physiological activity through the secretion of **hormones**, chemical messengers that travel throughout the body via the bloodstream. Hormones then bind receptors in target tissues to elicit specific responses (eg, altering cellular function). Hormones affect the function of diverse and distant tissues because hormone receptors can be found on various cell types throughout the body. Any cell with the correct receptor is capable of responding to the hormone. Hormones are regulated by a brain structure called the hypothalamus. The **hypothalamus** serves important functions for both the nervous and endocrine systems by processing inputs from the cortex and sensing the plasma concentration of numerous hormones. In response to these inputs, the hypothalamus controls body-wide endocrine function by releasing hormones and regulating hormone release from the **pituitary gland**, an endocrine organ located below the hypothalamus (see Figure 4.23). **Figure 4.23** The hypothalamus and pituitary gland. A diagram of the brain Description automatically generated Chapter 4: The Nervous and Endocrine Systems 37 Together, the hypothalamus and the pituitary gland regulate hormone release from the rest of the endocrine system\'s glands. An overview of the endocrine system is shown in Figure 4.24. **Figure 4.24** The endocrine system. 4.5.02 Impact of the Endocrine System on Behavior Hypothalamic and pituitary hormones coordinate many bodily processes, such as growth, blood pressure, core body temperature, appetite, sleep, and the stress response. The hypothalamus has several nuclei (collections of neuronal cell bodies) with specialized functions. One of these nuclei is the **suprachiasmatic nucleus**, which is the area that regulates circadian rhythms, cycles in physiological activity or behavior that occur over 24-hour intervals (eg, the sleep/wake cycle). Another hypothalamic nucleus, the [ventromedial nucleus](javascript:void(0)), regulates hunger and satiety.  The pituitary gland can be divided into two separate lobes, the **anterior pituitary** and the **posterior pituitary**. The two lobes release distinct hormones involved in regulating different bodily processes. One example is oxytocin, a hormone released by the posterior pituitary gland that is involved in pair bonding, reproductive behavior, labor, and lactation. The hypothalamus and pituitary also impact behavior by affecting endocrine glands throughout the body. For example, during stress, the hypothalamus releases a hormone that causes the pituitary gland to release adrenocorticotropic hormone (ACTH), a stress hormone. ACTH travels in the bloodstream to the adrenal glands (endocrine organs on top of the kidneys), where it causes the release of additional stress hormones (eg, cortisol) that help activate the body to deal with the stressor ( A diagram of a brain Description automatically generated **Behavioral Genetics** 5.1.01 Adaptive Value of Traits and Behaviors **Adaptive value** refers to the extent to which a trait or behavior helps an organism survive and reproduce. Traits and behaviors that are innate (ie, unlearned) result from genetic influences; babies are born with many **reflexes** (eg, feeding reflexes like suckling and rooting) that are preprogrammed behaviors which help them survive. An additional example is the research finding that infants prefer human faces and human speech, suggesting that this innate preference has evolved. This is an adaptive behavior because recognition of these stimuli confers a survival advantage: faces and speech convey important social information (eg, emotion) and contribute to the pair-bonding process between infant and caregiver. Conversely, behaviors that are learned (ie, nongenetic) result from observation and experience. They can change over time with practice or environmental demands. For example, feeding oneself with utensils (eg, spoon, chopsticks) is a learned behavior. Most human behaviors involve both genetic and environmental contributions, falling along the continuum from innate to learned (Figure 5.1). **Figure 5.1** Continuum of human behavior. 5.1.02 Interaction of Heredity and Environmental Influences Physical and social development are influenced by both heredity and the environment. **Heredity**, sometimes referred to as nature, describes genetic influences on development (eg, genes coding for eye color). In contrast, the **environment**, sometimes referred to as nurture, describes all nongenetic influences (eg, parenting styles). Many traits are a result of the interaction of nature and nurture. For example, an individual\'s height is determined by both the genetic information passed down from their biological parents as well as the influence of their environment, such as the nutrition they received as a child. Because heredity and the environment both impact traits and behavior in significant ways, researchers use twin studies and adoption studies to estimate the relative contribution of genetic versus environmental factors. Although they are rare, **twin adoption studies** can help clarify the role of heredity and the environment for complex human traits.  Identical (monozygotic) twins raised together share the same genes and an extremely similar environment (eg, same household, same schools, similar experiences), so it is not possible to determine if similar traits are the result of genetics, environment, or a combination of the two. However, if identical twins are each adopted and raised apart, traits that they share are most likely determined by genetics, whereas traits that are more similar to those of their adoptive families are most likely determined by environmental influences (see Figure 5.2)