Download The Nervous System Part 2

The Autonomic Nervous System
Motor Neurons
• Motor neurons are signaled
by other neurons
(interneurons) and send
signals to other organs
(muscles/glands)
– Also called efferent neurons
• Motor neurons fall into two
categories: somatic and
autonomic
– Receive information from
different portions of the brain
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
– Also increases alertness but reduces memory
access (don’t freak out on exams!)
• 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 norepinephrine onto
target glands and organs
– One of its major functions is to
stimulate the medulla of 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
Autonomic Activity
• When norepinephrine or
acetylcholine is released onto
target organs, they exhibit a
stimulatory or inhibitory effect
depending on what the organ’s
function is
• The heart’s pacemaker cells are
stimulated by norepinephrine and
inhibited by acetylcholine
– Which neurons release which onto
the heart?
– Again note these neurons are
controlled by the limbic system, NOT
the frontal lobe
Adrenaline Rush
• Epinephrine is a hormone in
the bloodstream that affects
most organs, and is broken
down over time by the liver
– This is not an immediate
process!
• The sympathetic nervous
system outranks the
parasympathetic nervous
system as a result
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!
Pupil Dilation
• Pupil dilation is stimulated by the
sympathetic nervous system
– Allows more light in, enables seeing
at a distance and in poor lighting
more effectively
• As a result, your pupils dilate when
you are excited, attracted to
someone/something, or sexually
aroused
– This is why poker players wear
shades!
– Also why you should wear
sunglasses when buying an
expensive car
Have an awesome spring break!
• Optional (0-point) quiz will be on blackboard
for you to assess your learning!
– Recommendation: take it at the end of spring
break to get yourself back into school gear
• Midterm grades will be available by the end of
spring break!