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Chapter 4

PS101 Chapter Notes - Chapter 4: White Matter, Oboe, Axon Terminal

Course Code
Lawrence Murphy

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The Brain: Source of Mind and Self
The Nervous System: A Basic Blueprint
Function of nervous system- to gather and process information, produce responses to stimuli,
and coordinate the workings of different cells
Nervous system has billions of cells, divided into two main parts: the central nervous system and
the peripheral (outlying) nervous system
The Central Nervous System
Central Nervous System (CNS): the portion of the nervous system consisting of the brain and the
spinal cord
Receives, processes, interprets, and stores incoming sensory information- information about
tastes, sounds, smells, colour, pressure on the skin, the state of internal organs, and so on
Sends out messages to muscles, glands, and internal organs
Spinal cord: a collection of neurons and supportive tissue running from the base of the brain
down the centre of the back, protected by a column of bones (spinal column)
o Extension of brain
o Acts as bridge between brain and parts of body below neck
Spinal cord produces some behaviours on its own without any help from brain
o Spinal reflexes
o Touching a hot iron, pull hand away before brain has had chance to register
o Nerve impulses bring message to spinal cord (hot!), and the spinal cord immediately
sends out command via other nerves, telling muscles in arm to contract and pull hand
away from iron
o Reflexes above neck (sneezing & blinking) involve lower part of brain, not spinal cord
Neural circuits underlying many spinal reflexes linked to neural pathways that run up and won
spinal cord, to and from brain
o Because of connections, reflexes can be influenced by thoughts and emotions
Erection (inhibited by anxiety or distracting thoughts, initiated by erotic
o Some reflexes can be brought under conscious control (may be able to keep knee from
jerking when tapped)
Men can learn to voluntarily delay ejaculation (spinal reflex)
The Peripheral Nervous System
Peripheral Nervous System (PNS): all portions of the nervous system outside the brain and spinal
cord; it includes sensory and motor nerves
o Handles central nervous system’s input and output
Like receiver to radio
Sensory nerves carry messages from special receptors in skin, muscles, and other internal and
external sense organs to spinal cord which sends them to brain
Nerves put us in touch with outside world and activities of own bodies
Motor nerves carry orders from central nervous system to muscles, glands, and internal organs
o Enable us to move, cause glands to contract and secrete substances including hormones
Peripheral nervous system divided into somatic (bodily) nervous system and autonomic (self-
governing) nervous system

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Somatic Nervous System: the subdivision of the peripheral nervous system that connects to
sensory receptors and to skeletal muscles; sometimes called the skeletal nervous system
o Consists of nerves that are connected to sensory receptors (cells that let you sense the
world) and also to skeletal muscles that permit voluntary action
o Somatic system active when feeling bug on arm or turning light off or writing name
Autonomic Nervous System: the subdivision of the peripheral nervous system that regulates the
internal organs and glands
o Regulates functioning of blood vessels, glands and internal (visceral) organs- bladder,
stomach, heart
o Autonomic system active when you see someone you have a crush on and your heart
pounds, hands get sweaty, and cheeks feel hot
o Divided into two parts
Sympathetic Nervous System: the subdivision of the autonomic nervous system that mobilizes
bodily resources and increases the output of energy during emotion and stress
o Acts like accelerator of car, mobilizing body for action and output of energy
o Makes you blush, sweat, breathe more deeply, pushes up heart rate and blood pressure
o Whirls into action when in situation that requires flight, flee, or cope
Parasympathetic Nervous System: the subdivision of the autonomic nervous system that
operates during relaxed states and that conserves energy
o More like brake, doesn’t stop body but slows things down and keeps them running
Two parts work together, but in opposing ways, to adjust body to changing circumstances
o If have to jump out of way of speeding motorcyclist, sympathetic nerves increase heart
rate, after, parasympathetic slow down again and keep rhythm regular
Neuropsychologists and other scientists study the brain because it is the bedrock of
consciousness, perception, memory, and emotion
The function of the nervous system is to gather and process information, produce responses to
stimuli, and coordinate the workings of different cells. Scientists divide it into the central
nervous system (CNS) and the peripheral nervous system (PNS). The CNS, which includes the
brain and spinal cord, receives processes, interprets, and stores information and sends out
messages destined for muscles, glands, and organs. The PNS transmit information to and from
the CNS by way of sensory and motor nerves
The peripheral nervous system consists of the somatic nervous system, which permits sensation
and voluntary actions, and the autonomic nervous system, which regulates blood vessels,
glands, and internal (visceral) organs. The autonomic system usually functions without conscious
control. The autonomic nervous system is further divided into the sympathetic nervous system,
which mobilizes the body for action, and the parasympathetic nervous system, which conserves
Communication in the Nervous System
Nervous system made of neurons: cells that conduct electrochemical signals; the basic unit of
the nervous system; also called a nerve cell
o Brain’s communication specialists, transmit information to, from, and within CNS
Neurons held in place by glia: cells that support, nurture, and insulate neurons, remove debris
when neurons die, enhance the formation and maintenance of neural connections, and modify
neuronal functioning ; also called glial cells (from Greek word for “glue”)

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o Make up 90% of brain’s cells
o Communicate chemically with each other and other neurons; without glial cells, neurons
could not function properly
o Help determine which neural connections get stronger or weaker, suggests that they
play a vital role in learning and memory
Neurons building blocks of nervous system though in structure, more like snowflakes than
blocks, exquisitely delicate and differing from one another greatly in size and shape
o In a giraffe, neuron that runs from spinal cord to hind leg may be 3 metres long
o In human brain, microscopic ~100 billion
The Structure of the Neuron
Three main parts: dendrites, a cell body, and an axon
Dendrites: a neuron’s branches that receive information from other neurons and transmit it
toward the cell body; means “little tree” in Greek
o Act like antennas, receiving messages from as many as 10 000 other nerve cells and
transmitting these messages toward the cell bod
o Also do preliminary processing of messages
Cell Body: the part of the neuron that keeps it alive and determines whether or not it will fire
o Shaped like sphere or pyramid, contains biochemical machinery for keeping neuron
o Plays key role in determining whether the neuron should “fire”- transmit a message to
other neurons- depending on inputs from other neurons
Axon: a neuron’s extending fibre that conducts impulses away from the cell body and transmits
them to other neurons; means “axle” in Greek
o Commonly divide at the end into branches called axon terminals
o Dendrites and axons give each neuron a double role: a neuron is first a catcher, then a
Myelin Sheath: a fatty insulation that may surround the axon of a neuron
o Made up of glial cells
o Constrictions in this covering, called nodes, divide it into segments, with make it look
like a string of sausages
o One purpose is to prevent signals in adjacent cells from interfering with each other
o Another is to speed up conduction of neural impulses
Nerve: a bundle of nerve fibres (axons and sometimes dendrites) in the peripheral nervous
o Human body has 43 pairs of peripheral nerves; one nerve from each pair is on the left
side of the body and the other is on the right
o Most of these nerves enter or leave the spinal cord, but 12 pairs in the head, the cranial
nerves, connect directly to the brain
Neurons in the News
Severed axons in spinal cord can regrow if treated with certain nervous system chemicals
Neurogenesis: the production of new neurons from immature stem cells
Stem Cells: immature cells that renew themselves and have the potential to develop into
mature cells; given encouraging environments, stem cells from early embryos can develop into
any cell type
o Stem cells involved in learning and memory seem to divide and mature throughout
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