Psychology -Unit 3 – Chapter 2

     Neuroscience and Behavior

Neural Communication

In reality, everything psychological is simultaneously biological. Viewing each person as a biopsychosocial system lets us study behavior from multiple levels of analyses. At the biological level, neurons and other cells compose organs, which form larger systems (digestions, circulation, information processing). At the social-cultural level, people live in specific times and places and are subject to specific environmental and social-cultural influences. At the psychological level, people's thoughts and emotion interact with their biology and personal history to produce that unique individual. Scientists gain much from their study of neural processes in other mammals and in relatively simple animals because humans and other animals have similar neural systems.

The body's circuity, the nervous system, consists of billions of individual cells called neurons. Neurons send signals through their axon, which is sometimes encased in a myelin sheath. Neurons receive signals from other cells through their branching dendrites and their cell body. If the combined signals are strong enough, the neuron fires, transmitting an electrical impulse (the action potential) down its axon, by means of a chemistry-to-electricity process in which ions are exchanged. The neuron's reaction is an all-or-none response.

When action potentials reach the end of an axon (the axon terminals), they stimulate the release of neurotransmitters. These chemicals messengers carry a message from the sending neuron across a synapse to receptor sites on a receiving neuron. The sending neuron, in a progress called reuptake, then normally absorbs the excess neurotransmitters molecules in the synaptic gap. The receiving neuron, if the signals from that neuron and others are strong enough, generates its own action potential and relays the message to other cells.

Each neurotransmitter travels a designated path in the brain and has a particular effect in behavior and emotions. Acetylcholine, one of the best-understood neurotransmitters, affects muscle action, learning, and memory. The endorphins are natural opiates released in response to pain and exercise.

Drugs and other chemicals affect communication at the synapse. Agonists, such as some of the opiates, excite by mimicking particular neurotransmitters or by blocking their reuptake. Antagonists, such as curare, inhibit a particular neurotransmitters release or block its effect.

The Nervous System

One major divisions of the nervous system is he central nervous system (CNS), which consists of the brain and spinal cord. The other is the peripheral nervous system (PNS), which consists of the neurons that connect the CNS to the rest of the body by means of nerves (bundles axons of the sensory and motor neurons). Sensory neurons carry incoming information from sense receptors to the CNS, and motor neurons carry information from the CNS out to the muscles and glands. Interneurons communicate within the CNS and between sensory and motor neurons.

The peripheral nervous system has two main divisions. The somatic nervous system enables voluntary control of the skeletal muscles. The autonomic nervous system, (picture) through its sympathetic and parasympathetic divisions, controls our involuntary muscles and glands.

Reflex pathways are automatic inborn responses to stimuli, and they do not rely on conscious decisions made in the brain. A single sensory neuron, excited by some stimulus (such as a flame), passes a message to an interneuron in the spinal cord. The interneuron activates a motor neuron, causing some muscle reaction (such as jerking away from the heat source). In contrast, neural networks, found in the brain, are clusters of many neurons that together share some special task. These complex networks strengthen with use, learning from experience. Each neural network connects with other networks performing different tasks.

The Endocrine System

The endocrine system is a set of glands that secrete hormones into the bloodstream. These chemical messengers travel through the body and affect other tissues, including the brain. Some hormones are chemically identical to neurotransmitters. The endocrine system's master gland, the pituitary, influences hormones release by other glands. In an intricate feedback system, the brains hypothalamus influences the pituitary gland, which in turn influences the brain.

The Brain

Clinical observations have long revealed the effect of damage to various areas of the brain. But MRI scans now reveal brain structures, and EEG, PET, and fMRI (functional MRI) recordings reveal brain activity. By surgically lesioning or electrically stimulating specific brain areas, recording the brain surface electrical activity, and by displaying neural activity with computer-aided brain scans, neuroscientists explore the connections among brain, mind, and behavior.

The brainstem is the oldest part of the brain and is responsible for automatic survival functions. Its components are the medulla (which controls heartbeat and breathing), the pons (which helps coordinate movements), and the reticular formation (which affects arousal). The thalamus, the brain's sensory switchboard sits above the brainstem. The cerebellum, attached to the rear of the brainstem, coordinates muscle movement and helps process Sensory information.

Between the brainstem and cerebral cortex is the limbic system, which is linked to emotions, memory, and drives. One of its neural centers, the amygdala, is involved in various bodily maintenance functions, pleasurable rewards, and the control of the hormonal systems. The hypothalamus sits just above the pituitary (the “master gland”) and controls it by stimulating it to trigger the release of hormones. The hippocampus, also part of the limbic system, processes memory.

The cerebral cortex is the thin surface layer of interconnected neurons covering the brain's hemisphere. The human brain's cortex is larger than that of the other animals, and it enables learning, thinking, and the other complex forms of informations processing that makes us uniquely human.

Some areas of the brain serve specific functions. One such area is the motor cortex, an arch-shaped region at the rear of the frontal lobe that controls voluntary movements. Another is the sensory cortex, a region at the front of the parietal lobes that registers and processes body sensations. In these regions, body parts required precise control (in the motor cortex) or those that are especially sensitive (in the sensory cortex) occupy the greatest amount of space. Most of the brains cortex – the major portion of each of the four lobes – is devoted to uncommitted association areas, which integrate information involved in learning, remembering, thinking, and other higher-level functions.

Language results form the integration of many specific neural networks performing specialized subtasks. When you read aloud, your brain's visual cortex registers words as visual stimuli, the angular gyrus transforms those visual representations into auditory codes, Wernicke's area interprets those codes and sends the message to Broca's area, which controls the motor cortex as it creates the pronounced words.

If one hemisphere is damaged early in life, the other will pick up many of its functions. This plasticity compensate for damaged ones after a stroke or other brain injury.

Clinical observations long ago revealed that the left cerebral hemisphere is crucial for language. Split-brain research (experiments on people with a severed corpus callosum) has confirmed that in most people the left hemisphere is the more verbal, and that the tight hemisphere excels in visual perception and the recognition of emotion. Studies of healthy people with intact brains confirm that each hemisphere makes unique contributions to the integrated functioning of the brain.

About 10% of us are left-handed. Almost all right-handers process speech in the left hemisphere, as do more than half of all left-handers. This remainder of let-handers split about evenly in processing language in the right hemisphere or in both hemispheres. The percentage of lefters decreases sharply with age, from about 15% at age 10 to less than 1% at age 80. This decline may reflect a higher risk of accidents. 

-----------------------------------------------------------------------------------------------------------------

 This is not a summary made in my own words,  because it's a lot of info and I was scared that I would do it wrong. These are the learning outcomes all put together. Next will come next weekend and in my own words again.  If you're confused with something then let me know and I can go into it with more details and examples.