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Chapter 2

Chapter 2 the biology of the mind.doc

Course Code
PSY 1101
Najwa Haddad

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Chapter 2: The Biology of the Mind
∑ The Nervous System
1) Function and Structure
Nervous System:
-Central Nervous System (CNS): brain, spinal cord
-Peripheral Nervous System (PNS): all nerves in the body (motor, sensory, etc.)
-these 2 systems have different tasks, but any behaviour requires integration of the CNS
and PNS
-the NS is a communication network
-it receives info from the senses
-organizes and integrates info and analysis in a meaningful manner
-uses new and existing information to send out messages to muscles and glands,
allowing for production of behaviours and produces movement
-it creates conscious experience (awareness, perceptions, feelings, etc.)
-everything psychological is physiological
2) Neurons
A. Basic Function and Structure of the Neuron
-neurons are the basic unit of communication in the nervous system
-1 trillion neurons in the body
-there are 10 000 types of neurons in the body, all categorized into 3 major types
-the 3 major types correspond to 3 major functions of the NS
a) Sensory Neurons
-receives information from sensory organs and sends information to CNS via nerves
b) Interneurons
-only found in CNS
-communicates with other neurons
-carries messages between neurons
-organizes and integrates information
-has the most complex job
c) Motor Neurons
-carries messages from the brain and spinal cord to muscles / glands via nerves

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The Basic Structure
a) Cell Body (soma)
-contains the nucleus and DNA; it manufactures everything the neuron needs to
survive and grow
b) Dendrites
-thin, tube-like structures
-increases surface area of soma
-receives information from other neurons
c) Axon
-carries action potential (electrical impulse / nerve impulse) to axon branches
d) Axon Branches
-knob-like structure at the end of the axon branches called terminal buttons / axon
e) Myelin Sheath
-some axons are covered in myelin sheath (a fatty-like substance)
-provides insulation to the axon
-speeds up transmission of action potential
-20x faster than axons without myelin sheath
-multiple sclerosis (myelin sheath is destroyed)
f) Synapse
-where neurons meet to communicate with each other
g) Synaptic Cleft / Gap
-tiny gap between 2 neurons at the synapse
h) Pre-Synaptic Neuron
-neuron that is sending a message to another neuron
i) Post-Synaptic Neuron
-neuron that receives message from another neuron
B. Communication
B1. Communication Within a Neuron
-the brain is made up of 80% water
-water inside the cell is called intracellular fluid
-water outside the cell is called extracellular fluid
-water contains dissolved chemicals in it (kind of like sea water)
-Na+, Cl-, K+, A- (proteins, anions)
-dissolved chemicals have + or - charges
-Na+, Cl-, K+ are found in different concentrations inside and outside the cell

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-A- found only inside the cell
-the membrane of the neuron is porous
-ions can flow in and outside of cell
-selectively permeable (ions cannot move freely)
-membrane determines what / when ions cross
-when the neuron is at rest, the neuron is not firing
At Rest:
Inside Outside
-higher [K+] -higher [Na+]
-overall, more negative ions -overall, more positive ions
-negatively charged (@ -70 mV) -positively charged
-membrane is polarized (- on the
inside; + on the outside)
-even at rest, the neuron still receives messages from neurons; the messages are either
excitatory or inhibitory
-inhibitory messages:
-tells neurons not to fire
-changes the concentration of ions
-membrane becomes hyperpolarized (more negative)
-e.g.: -70 mV to -76 mV as a result of inhibitory messages
-the neuron is therefore less likely to fire
-excitatory messages:
-tells neuron to fire
-changes the concentration of ions
-membrane becomes depolarized (less negative)
-e.g.: -70 mV -> -63 mV -> -60 mV
-the neuron is therefore more likely to fire
-when the membrane is at the threshold is excitation (~ -50 mV) the neuron fires
Inside Outside
+ ions outnumber - ions <----- <------ large # of Na+ (moves to the
inside of the cell)
positively charged negative ions outnumber positive
ions (negatively charged)
+40 mV
membrane is depolarized
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