Chapter 4: The Brain and Behavior

Neurons

• Neurons: are the basic building blocks of the nervous system
• Dendrites: specialized receiving units like antennae that collect messages from neighboring neurons and send them on to the cell body
• Axon: which conducts electrical impulses away from the cell body to other neurons, muscles, or glands
• Resting Potential: internal difference of around 70 millivolts (mV)
• Action Potential: An electrical shift, which lasts about a millisecond (1/1,000 of a second, also called a nerve impulse
• Myelin Sheath: a whitish, fatty insulation layer derived from glial cells during development

How Neurons Communicate

• Synaptic Space:  a tiny gap between the axon terminal and the next neuron
• Neurotransmitters: chemical substances that carry messages across the synaptic space to other neurons, muscles, or glands.
  • Acetylcholine
  • Excitatory at synapses involved in muscular movement and memory
  • Norepinephrine
  • Excitatory and inhibitory functions at various sites; involved in neural circuits controlling learning, memory, wakefulness, and eating
  • Serotonin
  • Inhibitory or excitatory; involved in mood, sleep, eating, and arousal, and may be an important transmitter underlying pleasure and pain
  • Dopamine
  • Excitatory; involved in voluntary movement, emotional arousal, learning, memory, and experiencing pleasure or pain
  • GABA(gamma-aminobutyric acid)
  • Inhibitory transmitter in the motor system
  • Endorphin
  • Inhibits transmission of pain impulses (a neuromodulator)
• Synaptic Vesicles: chambers within the axon terminals
• Receptor Sites: large protein molecules embedded in the receiving neuron’s cell membrane
• Reuptake: in which the transmitter molecules are taken back into the presynaptic axon terminals
• Neuromodulators: have a more widespread and generalized influence on synaptic transmission
• Psychoactive Drugs: chemicals that produce alterations in consciousness, emotion, and behavior

The Nervous System

• Sensory Neurons: carry input messages from the sense organs to the spinal cord and brain
• Motor Neurons: transmit output impulses from the brain and spinal cord to the body’s muscles and organs
• Interneurons: perform connective or associative functions within the nervous system
• Peripheral Nervous System: contains all the neural structures that lie outside of the brain and spinal cord
• Somatic Nervous System: consists of sensory neurons that are specialized to transmit messages from the eyes, ears, and other sensory receptors, and motor neurons that send messages from the brain and spinal cord to the muscles that control voluntary movements
• Autonomic Nervous System: which senses the body’s internal functions and controls the glands and the smooth (involuntary) muscles that form the heart, the blood vessels, and the lining of the stomach and intestines
• Sympathetic Nervous System: has an activation or arousal function, and it tends to act as a total unit.
• Parasympathetic Nervous System: is far more specific in its opposing actions, affecting one or a few organs at a time. In general, it slows down body processes and maintains a state of tranquility.
• Homeostasis: a delicately balanced or constant internal state
• Central Nervous System: contains the brain and the spinal cord, which connects most parts of the peripheral nervous system with the brain
• Electroencephalograph: measures the activity of large groups of neurons through a series of large electrodes placed on the scalp
• Computerized Axial Tomography (CT or CAT) scans: use X-ray technology to study brain structures
• Magnetic Resonance Imaging (MRI): creates images based on how atoms in living tissue respond to a magnetic pulse delivered by the device.
• Positron-Emission tomography (PET) Scans: measure brain activity, including metabolism, blood flow, and neurotransmitter activity.
• Functional MRI (fMRI): which can produce pictures of blood flow in the brain taken within seconds of one another

The Hierarchical Brain: Structures and Behavioral Functions

• Hindbrain: is the lowest and most primitive level of the brain
• Brain Stem: support vital life functions
• Medulla: plays an important role in vital bodily functions such as heart rate and respiration
• Pons: lies just above the medulla and carries nerve impulses between higher and lower levels of the nervous system.
• Cerebellum: concerned primarily with muscular movement coordination, but it also plays a role in learning and memory
• Midbrain: contains clusters of sensory and motor neurons
• Reticular Formation:  acts as a kind of sentry, both alerting higher centers of the brain that messages are coming and then either blocking those messages or allowing them to go forward
• Forebrain: the brain’s most advanced portion from an evolutionary standpoint
• Cerebrum: consists of two large hemispheres, a left side, and a right side
• Thalamus: has sometimes been likened to a switchboard that organizes inputs from sensory organs and routes them to the appropriate areas of the brain
• Hypothalamus: plays a major role in many aspects of motivation and emotion, including sexual behavior, temperature regulation, sleeping, eating, drinking, and aggression
• Amygdala: organizes motivational and emotional response patterns, particularly those linked to aggression and fear
• Cerebral Cortex: a 1/4-inch-thick sheet of gray (unmyelinated) cells that form the outermost layer of the human brain
• Somatic Sensory Cortex: receives sensory input that gives rise to our sensations of heat, touch, and cold and to our senses of balance and body movement (kinesthesis)
• Wernicke’s area:  in the temporal lobe, is primarily involved in speech comprehension
• Bronca’s Area: in the frontal lobe, is mainly involved in the production of speech through its connections with the motor cortex region that controls the muscles used in speech

Hemispheric Lateralization: The Left and Right Brains

• Corpus Callosum: a neural bridge consisting of white myelinated fibers that acts as a major communication link between the two hemispheres and allows them to function as a single unit
• Lateralization:  the relatively greater localization of a function in one hemisphere or the other
• Aphasia: the partial or total loss of the ability to communicate

Plasticity in the Brain: The Role of Experience and the Recovery of Function

• Neural Plasticity: refers to the ability of neurons to change in structure and function
• Neurogenesis: The production of new neurons in the nervous system
• Neural Stem Cells: immature “uncommitted” cells that can mature into any type of neuron or glial cell needed by the brain

Interactions with the Endocrine System

• Endocrine System: consists of numerous hormone-secreting glands distributes throughout the body

• Hormones: chemical messengers that are secreted from its glands into the bloodstream

• Adrenal Glands: twin structures perched atop the kidneys that serve, quite literally, as hormone factories, producing and secreting about 50 different hormones

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