Download Neurons are the cells that carry messages between parts of the body

6/9/2014
How the Human Body Communicates
with Itself
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
The nervous system
consists of your brain,
spinal cord, and a
large network of
nerves that branch
throughout your
body.
◦ Glands secrete chemicals (hormones) in the bloodstream
to communicate information to target cells.
Neurons are the cells that carry
messages between parts of the 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.
Most of the neuron is the cell body.
From the cell body are many branched
extensions called 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.
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.
Refer to fig. 35-7, pg. 899.
A resting neuron uses active transport to
pump sodium (Na+) ions out of the cell and
pump potassium (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.
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-or-none” process.
The following website illustrates the process:
http://www.phschool.com/atschool/phbio/active_ar
t/nerve_impulse/index.html
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Neurons are separated by narrow gaps called
synapses.
When the action potential reaches the end of the
axon it must pass to the next neuron.
The neuron before the synapse (pre-synaptic
neuron) releases chemicals called
neurotransmitters in response to the action
potential.
The human nervous system is made
up of two parts:
Central nervous system
◦ Brain and spinal cord
Peripheral nervous system
◦ All the other neurons throughout the
body
Divided into sensory division and
motor division.
The motor division is further divided:
The neurotransmitters find receptacles on the postsynaptic neuron, which then trigger an action
potential (AP) in that 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.
The brain has various regions responsible
for different functions. Major ones are:
◦ Cerebrum: voluntary actions, judgment,
learning. It is divided into two
hemispheres.
◦ Cerebellum: coordinates and balances
muscles for efficient movement
◦ Brain stem: connects brain and spinal
cord; controls involuntary functions like
breathing, heart rate, blood pressure, etc.
◦ Thalamus: receiving point for most
sensory info.
◦ Hypothalamus: coordinates nervous &
endocrine systems
Spinal cord: Relays info between brain
and rest of body.
◦ Also responsible for reflexive actions.
◦ Somatic system: regulates activities under
conscious control & reflex arcs
◦ Autonomic system: controls organ systems
not under conscious control.
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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The endocrine system uses chemicals released
into the blood (hormones) to communicate
between parts of the body.
An organ that releases hormones is called a
gland. The gland releases the hormones into the
blood stream so they can then reach the target
cells.
Target cells have receptors on their cell
membranes for the hormone.
Parathyroids: Four glands that work with the
thyroid gland to manage calcium levels in the body
(important for many processes)
Adrenals: Glands on top of each kidney that
prepare the body to deal with stress.
◦ Responsible for the “fight-or-flight” response.
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.
Reproductive glands: AKA gonads; responsible for
producing gametes (sperm and eggs) as well as sex
hormones.
Pituitary: Secretes hormones that
regulate many body functions,
including the function of other
endocrine glands.
Hypothalamus: Controls pituitary
function; handles interaction of
endocrine and nervous systems.
Thyroid: Regulates body’s metabolism.
◦ Ovaries: produce estrogen and
progesterone.
◦ Testes: produce testosterone.
Pancreas: Secrete the hormones insulin and
glucagon, for managing blood sugar levels.
Refer
to text sections 35-2 & 35-3
for nervous system info.
Refer
to text sections 39-1 & 39-2
for endocrine system info.
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