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11-Jun-15
Control Systems
How the Human Body Communicates
with Itself
Control Systems
Two of the 11 human body systems are involved
with control of the body:
The NERVOUS SYSTEM
• Uses a combination of electrical and chemical
signals to communicate information along
specialized cells (neurons).
The ENDOCRINE SYSTEM
• Glands secrete chemicals (hormones) in the
bloodstream to communicate information to
target cells.
Neurons
Neurons are the cells that carry
messages between parts of the body.
body.
• A nerve is a bundle of neurons.
Sensory neurons carry messages to the
brain from the body.
Motor neurons carry messages from
the brain to the body.
Interneurons connect motor and
sensory neurons.
How a neuron works
A resting neuron uses active transport to
pump sodium (Na
(Na+) ions out of the cell and
pump potassium (K
(K+) into the cell.
K+ ions also naturally leak across the
membrane more easily than Na+ ions.
This process creates the resting potential – a
net electrical difference across the cell
membrane. There is a positive charge outside
the axon and a negative charge inside.
Neuron structure
The Nervous System
The nervous
system consists of
your brain, spinal
cord, and a large
network of nerves
that branch
throughout your
body.
Neuron structure, cont’d
Most of the neuron is the cell body.
body.
From the cell body are many
branched extensions called dendrites
dendrites..
• Dendrites carry nerve impulses to the
cell body.
Neurons have a long fiber that carries
impulses from the cell to another –
this is called an axon
axon..
How a neuron works, cont’d
The cell remains at resting potential until
a stimulus reaches the cell, either from
another neuron or the environment.
Channels in the membrane open to allow
Na+ ions to enter the cell. The inside of
the cell temporarily becomes more
positive. This is called the action
potential..
potential
Refer to fig. 3535-7, pg. 899.
How a neuron works, cont’d
Soon after the action potential passes a
point on the axon, the cell returns to
resting potential and is ready to receive
another impulse.
This is an “all“all-or
or--none” process
process..
The following website illustrates the
process:
http
http://www.phschool.com/atschool/phbio/active
://www.phschool.com/atschool/phbio/active
_art/nerve_impulse/index.html
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The synapse
Neurons are separated by narrow gaps
called synapses.
synapses.
When the action potential reaches the
end of the axon it must pass to the next
neuron.
The neuron before the synapse (pre
(pre-synaptic neuron) releases chemicals
called neurotransmitters in response to
the action potential.
Divisions of the Nervous System
The human nervous system is made
up of two parts:
parts:
Central nervous system
• Brain and spinal cord
Peripheral nervous system
• All the other neurons throughout the
body
Peripheral Nervous System
Divided into sensory division and
motor division.
The motor division is further
divided:
• Somatic system: regulates activities
under conscious control & reflex arcs
• Autonomic system: controls organ
systems not under conscious control.
The synapse, cont’d
The neurotransmitters find receptacles
on the post
post--synaptic neuron, which then
trigger an action potential (AP) in that
cell
cell..
The cell passes the AP along its own
axon, reaching another synapse, which
releases neurotransmitters that cross the
synapse to the next neuron, etc.
Central nervous system
The brain has various regions responsible
for different functions. Major ones are:
• Cerebrum
Cerebrum:: voluntary actions, judgment,
learning. It is divided into two
hemispheres.
• Cerebellum
Cerebellum:: coordinates and balances
muscles for efficient movement
• Brain stem:
stem: connects brain and spinal
cord; controls involuntary functions like
breathing, heart rate, blood pressure, etc.
etc.
Comparing Nervous Systems
Central nervous system, cont’d
• Thalamus:
Thalamus: receiving point for most
sensory info.
• Hypothalamus
Hypothalamus:: coordinates nervous &
endocrine systems
Spinal cord: Relays info between
brain and rest of body.
• Also responsible for reflexive actions.
The Endocrine System
While the nervous system
functions like a landline
telephone system with
specific receivers of
information, the endocrine
system is used to
communicate with many
receivers at the same time,
like a radio broadcast.
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Glands
The endocrine system uses chemicals
released into the blood (hormones
(hormones)) to
communicate between parts of the body.
An organ that releases hormones is called
a gland.
gland. The gland releases the hormones
into the blood stream so they can then
reach the target cells.
cells.
Target cells have receptors on their cell
membranes for the hormone.
Endocrine glands, cont’d
Parathyroids: Four glands that work with
Parathyroids:
the thyroid gland to manage calcium levels
in the body (important for many
processes)
Adrenals:: Glands on top of each kidney
Adrenals
that prepare the body to deal with stress.
• Responsible for the “fight“fight-or
or--flight” response.
Pancreas: Secrete the hormones insulin
Pancreas:
and glucagon,
glucagon, for managing blood sugar
levels.
Control of endocrine system
The endocrine system is managed by
feedback mechanisms.
It is responsible for controlling
metabolism, maintaining water
balance, reproductive systems, and
many other important functions in
the body.
Endocrine glands, cont’d
Endocrine glands
Pituitary: Secretes hormones that
Pituitary:
regulate many body functions,
including the function of other
endocrine glands.
Hypothalamus:: Controls pituitary
Hypothalamus
function; handles interaction of
endocrine and nervous systems.
Thyroid:: Regulates body’s metabolism.
Thyroid
Glands of the endocrine system
Reproductive glands:
glands: AKA gonads;
responsible for producing gametes
(sperm and eggs) as well as sex
hormones.
• Ovaries: produce estrogen and
progesterone.
• Testes: produce testosterone.
More information
Refer to text sections 3535-2 & 3535-3
for nervous system info.
Refer to text sections 3939-1 & 3939-2
for endocrine system info.
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