NEUROSCIENCE - THE NERVOUS SYSTEM

• Everything psychological is simultaneously biological
• Plato correctly located the mind in one’s head, whereas Aristotle believed it was in the heart
• German physician Franz Gall invented phrenology—bumps on the skull indicated mental ability.  Later this emerged phrenological society that traveled giving skull readings
• Biological psychologists –
•  a branch of psychology concerned with the links between biology and behavior. (some biological psychologists call themselves behavioral neuroscientists, neuropsychologists, behavior genticists, physiological psychologists, or biopsychologists)

NEURAL COMMUNICATION

• The body’s information system is built of billions of interconnected cells called neurons
• To understand our behavior, we need to study how these biological, psychological, and social-cultural systems work and interact
• Because information systems of animals operate similarly to that of human’s, we can study relatively simple animals like squids and sea slugs to see how our neural systems operate

Neurons

• Our body’s neural information system is complexity built from simplicity, made from neurons, or nerve cells, the building blocks
• Neuron –
• a nerve cell; the basic building block of the nervous system
• each consists of a cell body and branching fibers
• Dendrite –
• the bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body
• Axon –
• the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles
• *Axons speak, dendrites listen*
• Motor neurons which control muscles, are the neural system’s giant redwoods
•  Myelin sheath –
• a layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next
• Neural impulses travel from 2mph to 200mph, but that’s still 3 million times slower than electricity through a wire
• A neuron fires an impulse when it receives signals from sense receptors stimulated by pressure, heat, or light, or by chemical messages from neighboring neurons      
• Action potential –
• a neural impulse; a brief electrical charge that travels down an axon. the action potential is generated by the movement of positively charged atoms in and out of channels in the axon's membrane
• The chemistry-to-electricity process involves the exchange of electrically charged atoms, called ions
• The positive-outside/negative-inside state is called the resting potential
• The axon’s surface is very selective about what it allows in, it’s selectively permeable
• The neuron is a miniature decision-making devise that performs some complex calculations
• It receives signals on its dendrites
• Excitatory, like pushing a neuron’s accelerator
• Inhibitory, pushing its brake
• Threshold –
• The level of stimulation required to trigger a neural impulse

How Neurons Communicate

• Neurons interweave so intricately that even with a microscope it’s hard to see where they start
• Spanish anatomist, Santiago Ramon y Cajal, describes gaps between individual nerve cells and conclude that the individual neurons must function as independent agents
• British physiologist Sir Charles Sherrington noticed that neural impulses were taking an unexpectedly long time to travel a neural way
• Synapse –
• The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or cleft
• When the action potential reaches the terminals at an axon’s end, it triggers the release of chemical messengers, called neurotransmitters
• Neurotransmitters –
• Chemical messengers that traverse the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse
• Excess neurotransmitters are reabsorbed by the sending neuron in a process called reuptake

How Neurotransmitters Influence Us

• As researches discovered dozens of different neurotransmitters, they began to examine what influences they have on everything we do
• Acetycholine (Ach) –
• a neurotransmitter that enables learning and memory and also triggers muscle contraction
• Candace Pert and Solomon Snyder discovered that the morphine, an opiate drug that elevates mood and eases pain, bound to receptors in areas linked with mood and pain sensations
• Researchers soon confirmed that the brain contains several types of neurotransmitter molecules similar to morphine
• Endorphins –
• “morphine within” – natural, opiatelike neurotransmitters linked to pain control and to pleasure
• * runner’s high or the painkilling effects of acupuncture

How Drugs and Other Chemicals Alter Neurotransmission

• One problem with flooding the brain with opiate drugs like heroin and morphine is that the brain may stop producing its own natural opiates
• Mood-altering drugs, from alcohol to nicotine to heroin, share a common effect: they trigger unpleasant, lingering aftereffects
• Various drugs affect the communication at the synapse
• Agonists excite.  An agonist molecule may be similar enough to the neurotransmitter to mimic its effects or block the reuptake
• Antagonists inhibit.  It can be a drug molecule that inhibits a neurotransmitter’s release.  It also may be similar enough to the natural neurotransmitter to block its effect
• Neurotransmitter research is leading to new drugs to alleviate depression, schizophrenia, and other disorders
• A blood-brain barrier enables the brain to fence out unwanted chemicals circulating in the blood, making it hard to invent new drugs

The Nervous System

• To live is to take info from the world and the body’s tissues, to make decisions, and to send back info and orders to the body’s tissues
• Nervous system –
• The body’s speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous system
• Central nervous system (CNS) –
• The brain and spinal cord
• Peripheral nervous system (PNS) –
• The sensory and motor neurons that connect the CNS to the rest of the body
• The axons carrying this PNS info are bundled into electrical cables called nerves
• Nerves –
• Neural “cables” containing many axons.  These bundled axons, which are part of the PNS, connect the CNS with muscles, glands, and sensory organs
• Info travels in the nervous system through three types of neurons:
• Sensory neurons –
• Neurons that carry incoming info from the sense receptors to the CNS
• Motor Neurons –
• Neurons that carry outgoing info from the CNS to the muscles and glands
• Interneurons –
• CNS neurons that internally communicate and intervene between the sensory inputs and motor outputs

The Peripheral Nervous System

• The PNS has two components: somatic and autonomic
• Somatic nervous system –
• The division of the PNS that controls the body’s skeletal muscles.  Also called the skeletal nervous system
• Autonomic nervous system –
• The part of the PNS that controls the glands and the muscles of the internal organs (such as the heart).  Its sympathetic division arouses; its parasympathetic division calms
• **a dual system: sympathetic and parasympathetic**
• Sympathetic nervous system –
• The division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations
• Lie detection machines measure such stress responses
• Parasympathetic nervous system –
• The division of the autonomic nervous system that calms the body, conserving energy
• Decreases heartbeat or lowers blood sugar

The Central Nervous System

• The tiny billions of neurons in our body that “talk” to one another to carry out our basic human needs still baffle scientists today
• How does this neural machinery organize itself into complex circuits capable of learning, feeling, and thinking?

The Spinal Cord and Reflexes

• The CNS’s spinal cord is an info highway connecting the PNS to the brain
• Ascending fibers send up sensory info, descending fibers send back motor-control info
• Reflex –
• A simple, automatic, inborn response to a sensory stimulus, such as the knee-jerk response
• Pain reflexes, like touching a flame, are pathways with activity excited by the heat and travel via sensory neurons to the interneurons in your spinal cord who activate motor neurons in the arm
• Since the simple pain reflex pathway runs through the spinal cord and out, your hand jerks from the flame before your brain tells it to
• If the spinal cord is severed, no pain or pleasure would be felt
• **To produce bodily pain or pleasure, the sensory info must reach the brain**

The Brain and Neural Networks

• The other part of the CNS, the brain, receives info, interprets it, and decides responses (like a computer)
• Every act you make requires several thousand computations to make it happen
• A grain-of-sand-sized speck of your brain has 100,000 neurons and 1 billion “talking” synapses
• Neural networks –
• Interconnected neural cells.  With experience, networks can learn, as feedback strengthens or inhibits connections that produce certain results.  Computer simulations of neural networks show analogous learning
• To understand this, Stephen Kosslyn and Olivier Koenig invite us to “think about why cities exist; why don’t people distribute themselves across the countryside?”
• **Neurons that fire together wire together
• Open the brain and you’ll see no arrows that tell you where one network begins and ends