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The Nervous System Part 2
By the end of this class you should
understand:
• The functions of the autonomic nervous
system
• The three major regions of the brain and their
general functions
• The layers of protection around the central
nervous system
• The functions of sleep, memory and the limbic
system
Brief Disclaimer:
• I am massively oversimplifying everything
there is to say about the brain
• There are entire upper-division courses
dedicated solely to the study of the brain
– Feel free to take some! They’re awesome!
• I will now cover in 1 hour what could
reasonably take 40…
Peripheral Nervous System
• The peripheral nervous system
is highly organized by function
– Sensory neurons bring
information to the CNS
– Motor neurons bring information
from the CNS to the organs of the
body
• The CNS is composed of
interneurons that connect to
each other and process
information
Somatic vs. Autonomic
• Somatic motor neurons
are voluntary
– They innervate (attach to)
skeletal muscles
• Autonomic motor
neurons are involuntary
– They innervate the heart,
liver, digestive organs
– They also innervate glands
that release hormones
Autonomic Nervous System
• The autonomic nervous system is further
subdivided into two branches:
– Sympathetic nervous system
– Parasympathetic nervous system
• These two branches work against each other
– Sympathetic: “fight or flight”
– Parasympathetic: “rest and digest”
Autonomic Nervous System
Sympathetic vs. Parasympathetic
• Sympathetic nervous system increases blood
flow to muscles, heart and lungs
– Response to fear and to exercise
• Parasympathetic nervous system increases
blood flow to liver, kidneys and digestive
organs
– Dominates before/during/after eating food unless
blocked by sympathetic
Autonomic Neurotransmitters
• Sympathetic nerve fibers
release neurotransmitters
called norepinephrine
– One of its major functions is to
stimulate the adrenal glands to
release a hormone called
epinephrine
– The resulting hormone rush is
more commonly known as
adrenaline
• Parasympathetic nerve fibers
release acetylcholine, the same
as somatic motor nerves
Brain vs. Body
• People often believe that the
brain and the body are separate
– The “car” model of brain activity
• The reality is that the brain’s
state, including emotions, is
affected by the body and in turn
affects the body
– The sympathetic nervous system
activates even when you are
looking at someone attractive or
get excited about something
Central Nervous System
• The central nervous
system processes
incoming information
from all sensory
neurons
– Most of this processing
is done in the brain
– The spinal cord does
some processing, as in
reflexes
Brain Regions
• Forebrain
– Site of conscious and
emotional processing of
information
• Midbrain
– Reflexive processing and
control of senses
• Hindbrain
– Controls basic motor and
homeostatic functions
– Common to all vertebrates
Brain Regions
Parts of the Forebrain
• The cerebral cortex
– AKA the cerebral hemispheres
– Made of five lobes (only three covered here)
– Dedicated to processing sensory information,
making decisions, and creating emotions
• The diencephalon
– Responsible for regulating the brain’s and the
body’s activity
• Thalamus and hypothalamus
Cerebral Cortex
• Frontal lobes
– Site of active decisions and
short-term memory
– Hyperdevelops during puberty,
responds to social input, is not
fully mature until the mid-20s
• C.f. Teenager behavior and Phineas
Gage
• Occipital lobes
– Dedicated entirely to processing
visual information
• Parietal lobes
– Initiates voluntary movement
and sensation of touch
Diencephalon
• The thalamus is a major
component of the brain
situated directly below the
cerebral cortex
– All sensory information comes
through the thalamus before
reaching the cerebral cortex
• Exception: sense of smell has direct
line to limbic system!
• The hypothalamus is the body’s
thermostat for hunger, thirst,
and temperature
– Also controls activity of the
autonomic nervous system
Midbrain
• The midbrain has many functions we take for granted
–
–
–
–
Regulates wakefulness
Creates visual reflexes
Coordinates senses with movement of head
Processes unconscious reflexes related to standing and
moving
Hindbrain
• The hindbrain has two regions
– Cerebellum: coordinates timing on firing of motor neurons and
helps store muscle memory
– Brain stem: attaches to spinal cord and sends and receives
information, also manages breathing and heart rate
• The hindbrain is often called the “reptilian brain” since
even the simplest vertebrates have a similar brain
CNS Protection
• The entire central
nervous system has
four layers of
protection:
– Bone (skull and
vertebral column)
– Cerebrospinal fluid
(helps protect and
support weight)
– Meninges
(connective tissue
layers)
– Blood-brain barrier
Blood-Brain Barrier
• The most common type of neuroglial
cell in the CNS is called the astrocyte
• Astrocytes tightly seal the blood
vessels entering the CNS and only
permit vital nutrients to pass
through
– Restrict access of bacteria and toxins
• Anything that affects the brain must
be able to diffuse through astrocyte
cell membranes
– What chemicals can diffuse through a
cell membrane?
Selected Functions of the Brain
• Sleep
– A period of unconsciousness during which brain
activity changes and regenerates the brain
– Without sleep, death will occur within two weeks
• Emotion
– Activity in the limbic system in response to stimuli
– In constant back-and-forth communication with the
frontal lobe (consciousness)
• Memory
– Created and processed in the frontal lobe, there are
many types of memory
Sleep
• There are two types of sleep:
– Rapid-Eye Movement sleep (REM
sleep)
– Non-Rapid-Eye Movement sleep
(Non-REM or NREM sleep)
• REM sleep is most vital to brain
function
– Most dreams occur during REM
sleep
– During REM sleep, body is
paralyzed
• Sleepwalking occurs during NREM
dreams
Limbic System
• Limbic system produces
emotions in response to
stimuli such as sex
hormones, stress hormones,
hunger hormones, body
senses, and information from
the frontal lobe
– Essentially a parallel
consciousness
– Animals with no frontal lobe
activity (including infants)
behave solely on limbic
information
Types of Memory
• Short-term memory can only retain a few pieces of
information at a time
• If the information is repeated, emphasized or attached
to other information it may be stored in long-term
memory
– One aspect of sleep is the process of reorganizing memory
• The frontal lobe also stores motor memory in
collaboration with the cerebellum
• The limbic system also has its own limbic memory for
retaining emotional information (for example, trauma)
See you next week!
• Also next week’s lab will be the nerve lab!
• Come prepared to cut up some sheep brains!
– Morning lab will start approx. an hour late, sorry!