This lecture provides an overview of the physiology and complexity of the human brain and the nervous system. We will briefly examine the biological basis of behavior.
2. The Human Brain
The adult brain weighs about 3
pounds.
The brain is soft β feels like a
ripe pear.
Protected by the skull, the
meninges and cerebrospinal
fluid.
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3. Neurons: The Brainβs
Communicators
ο The brain contains about 100 billion neurons, or
neural cells.
ο There are more than 15 times as many neurons in the
brain as there are people on Earth!
ο Each neuron receives, processes, and transmits
messages to thousands of others.
ο There are about 160 trillion neural connections in the
human brain!
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4. Structure of a
Typical Neuron
β the βreceiversβ. They
receive stimulation from other neurons
β contains the nucleus and is
responsible for the life processes of the
cell
β a long, narrow tube that carries
the neural impulse toward the terminal
branches.
- the
βsendersβ. They contain chemicals that
neurons use to communicate with each
other.
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5. Communication Within Neurons
ο When a neuron is at rest, there is an uneven
distribution of ions across the cell membrane.
ο There are more negative ions inside than outside the
neuron.
ο The difference in charge is about -70 millivolts.
ο When a neuron is sufficiently stimulated, a tiny wave
of electricity (an action potential) is generated and
travels along the axon to the terminal branches.
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6. Communication Within Neurons
ο When an action potential occurs we can describe it as
the neuron βfiring.β
ο During an action potential, positively charged particles
flow rapidly into the neuron and then just as rapidly
flow out.
ο Neurons can fire as rapidly as 100 to 1000 times per
second!
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7. Communication Between Neurons
β’ When the action potential reaches the terminal button, it
triggers the release of chemicals known as neurotransmitters
into the synapse.
β’ The neurotransmitters bind to specific receptor sites on
neighbouring neurons, stimulating them.
β’ Different receptor sites recognize different types of
neurotransmitters.
β’ Communication between neurons is halted by reuptake of
neurotransmitters.
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10. The Divisions of the Nervous
System
ο The nervous system can be
divided into two parts:
ο The central nervous
system (CNS) - made up
of the brain and spinal
cord.
ο The peripheral nervous
system (PNS) β consists
of neurons that lie outside
the CNS.
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12. The Central Nervous System
ο The central nervous system can be divided into
different sections:
ο Brain
ο Cerebral cortex
ο Basal ganglia
ο Limbic system
ο Cerebellum
ο Brain stem
ο Spinal cord
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13. The Cerebral Cortex
ο The uppermost and largest area of the
brain is the cerebrum.
ο The outer surface of the cerebrum is
the cerebral cortex.
ο The cortex is divided into two halves
known as cerebral hemispheres.
ο The two hemispheres are connected
by the corpus callosum.
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14. The Cerebral Cortex
ο The cerebral cortex is the part of the brain primarily
responsible for processes such as thinking,
remembering, planning and analyzing sensory
information.
ο Each hemisphere of the cerebral cortex is divided into
four regions called lobes:
ο Frontal
ο Parietal
ο Temporal
ο Occipital
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16. The Cerebral Cortex
ο Frontal lobes:
ο Assist in movement, speech production and memory.
ο They oversee and organize most other brain functions.
ο Contain the primary motor cortex which controls
movements, and the prefrontal cortex, which is
responsible for thinking, planning and language.
ο The prefrontal cortex also contributes to mood,
personality and self-awareness.
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17. The Cerebral Cortex
ο Parietal lobes:
ο Contain the primary somatosensory cortex which
processes information related to touch.
ο Integrate vision and touch
ο Temporal lobes:
ο Contain the primary auditory cortex which is
responsible for hearing.
ο Allows us to understand language.
ο Stories memories of our past.
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18. The Cerebral Cortex
ο Occipital lobes:
ο Contain the primary visual cortex, which is responsible
for vision.
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19. Basal Ganglia
ο A set of structures buried deep inside the brain that
help to control movement.
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20. Limbic System
ο A set of interconnected brain regions devoted to
emotion, motivation, smell and memory.
ο Included in the limbic system are the amygdala and
hippocampus.
ο The amygdala plays a role in fear, anger and
excitement.
ο The hippocampus plays a role in memory, especially
spatial memory, and helps us to convert short term
memories to long term memories.
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22. The Brain Stem
ο Consists of several structures, including:
ο Reticular activating system β plays a role in arousal
ο Cerebellum β plays a role in balance and coordination
ο Pons β involved in sleep and dreaming
ο Medulla β controls vital functions, such as breathing,
heart rate and blood pressure.
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23. The Spinal Cord
ο Extends from the brain stem to the lower back.
ο Conveys information between the brain and the rest of
the body.
ο Made up of sensory neurons which carry information
toward the brain and motor neurons which carry
motor commands from the brain to the body.
ο The spinal cord also consists of interneurons which
connect sensory and motor neurons.
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25. The Peripheral Nervous System
ο The peripheral nervous system is divided into:
ο The somatic nervous system β controls voluntary
movement.
ο The autonomic nervous system β controls involuntary
actions of our internal organs and glands.
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26. The Peripheral Nervous System
ο The autonomic nervous system, in turn, consists of
two divisions:
ο The sympathetic nervous system β mobilizes the fight-
or-flight response.
ο The parasympathetic nervous system β active during rest
and digestion.
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27. Neuroplasticity
ο Refers to the brainβs ability to change throughout life.
ο Neuroplasticity occurs:
ο 1β During the early stages of life: when the immature
brain organizes itself.
ο The network of neurons in the brain changes in four
primary ways:
ο Growth of dendrites and axons
ο Synaptogenesis: formation of new synapses
ο Pruning: death of certain neurons and removal of connections
that arenβt useful.
ο Myelination: formation of the myelin sheath
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28. Brain Plasticity (Neuroplasticity)
ο 2β Through adult-hood: whenever something new is
learned and memorized.
ο 3β In case of brain injury: to compensate for lost
functions or maximize remaining functions.
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29. βIf the human brain were so
simple that we could
understand it, we would be so
simple that we couldnβtβ
-Emerson Pugh, The Biological
Origin of Human Values (1977)
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