Download Nervous System Structure

Biology 12
Imagine you are
on a beach. What
do you feel? What
do you see?
Smell?
 You can recreate
the experience of
being at the
beach without
any external
stimuli.
 How is this
possible?

 What
is pain? What is pleasure?
What are thoughts?
 We know the brain is made up of
cells but how does the miracle of
the mind emerge from this mass
of cells?
 The human Nervous System is a
whole that is far greater than the
sum of its parts.

“...from the brain, and from the brain
only, arise our pleasures, joys,
laughter and jests, as well as our
sorrows, pains griefs and tears.
Through it, in particular, we think,
see, hear... Eyes, ears,
tongue, hands and feet act in
accordance with the discernment of
the brain.”
 Hippocrates
 Much
of what we know about the
brain is drawn from inferences.
 There remain many unanswered
questions... This makes
neuroscience so fascinating!
1.
2.
3.
Receive sensory messages that provide
information about the external environment
Organize that information and integrate it
with other, already stored information in
useful ways.
Use the integrated information to send out
messages to the muscles and glands to
produce organized movements and adaptive
secretions
4. Provide the basis for what we call conscious
experience – the stream of perceptions,
thoughts and feelings that make up our
mental life!
Brain
Central Nervous
System
Spinal Cord
Somatic Sensory
Neurons
Nervous System
Sensory (Afferent)
Division
Visceral Sensory
Neurons
Peripheral Nervous
System
Motor (Efferent)
Division
Autonomic
Nervous System
(Involuntary)
Somatic Nervous
System (Voluntary)
Sympathetic
Nervous System
Parasympathetic
Nervous System
The brain + the spinal cord
 The center of
integration and control
 The nervous system outside of
the brain and spinal cord
 Consists of:
 31 Spinal nerves
 Carry info to and from the
spinal cord
 12 Cranial nerves
 Carry info to and from the
brain
• Can be divided
into:
– Sympathetic
Nervous
System
• “Fight or Flight”
– Parasympathetic
Nervous System
• “Rest and Digest”
These 2 systems are antagonistic.
Typically, we balance these 2 to keep
ourselves in a state of dynamic balance homeostasis.


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organs of our body, such as the heart,
stomach and intestines, are regulated by the
autonomic nervous system (ANS).
part of the peripheral nervous system
controls many organs and muscles within the
body.
functions in an involuntary, reflexive manner.
For example, we do not notice when blood
vessels change size or when our heart beats
faster.
1. In emergencies that cause stress and
require us to "fight" or take "flight" (run away)
2. In non-emergencies that allow us to "rest"
and "digest."
Muscles
◦ in the skin (around hair follicles; smooth
muscle)
◦ around blood vessels (smooth muscle)
◦ in the eye (the iris; smooth muscle)
◦ in the stomach, intestines and bladder
(smooth muscle)
◦ of the heart (cardiac muscle)
Glands

It is a nice, sunny day...you are taking a nice
walk in the park.

Suddenly, an angry bear appears in your
path.
Do you stay and fight OR do you turn
and run away?
 These are "Fight or Flight" responses.
 In these types of situations, your
sympathetic nervous system is called
into action - it uses energy - your
blood pressure increases, your heart
beats faster, and digestion slows
down.

 The
sympathetic nervous system
originates in the spinal cord.
Neurons lead to the "target" either a muscle or a gland.
 Adrenalin
is involved in the
activation of this system.
 So…
 This
is why you may pee when
you are surprised by a bear?
 This tid-bit will impress your
friends!
You fight off the bear and the danger
is over.
 This calls for "Rest and Digest"
responses. Now is the time for the
parasympathetic nervous to work to
save energy - your blood pressure
decreases, your heart beats slower,
and digestion can start.

 Sympathetic
changes are detected
by polygraphs to help determine
when someone is lying!
 These two systems are
antagonists – they are opposites
of each other.

http://itc.gsw.edu/faculty/gfisk/anim/autono
micns.swf


The neuron is the
basic functional
unit of the nervous
system.
Function: Send
impulses to and
from the CNS and
PNS and the
effectors
(muscles/glands)

Dendrite  Fine hair-like extensions on the
end of a neuron.
◦ Function: receive incoming stimuli.

Cell Body or Soma  The control center of
the neuron.
◦ Function: Directs impulses from the dendrites to
the axon.

Nucleus  Control center of the Soma.
◦ Function: Tells the soma what to do.


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Axon Pathway for the nerve impulse
(electrical message) from the soma to the
opposite end of the neuron.
Myelin Sheath  An insulating layer around
an axon. Made up of Schwann cells.
Nodes of Ranvier  Gaps between schwann
cells.
◦ Function: Saltatory Conduction (Situation where
speed of an impulse is greatly increased by the
message ‘jumping’ the gaps in an axon).
Dendrites receive the nerve impulse
and carry it toward the cell body,
which contains the nucleus.
 The axon carries the impulse from the
cell body toward the synaptic
knobs/terminals where it will be
transferred to other neurons.


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Myelinated neurons carry nerve
impulses faster than unmyelinated
ones because the impulse jumps from
one node of Ranvier to the next,
instead of traveling along the whole
length of the axon.
This is called saltatory conduction

1.
2.
3.
There are 3 types of neurons.
Sensory Neurons 
Neurons located near receptor
organs (skin, eyes, ears).
 Function:
receive incoming stimuli from the
environment.
Motor Neurons  Neurons located near effectors
(muscles
and glands)
 Function:
Carry impules to effectors to initiate a
response.
Interneurons  Neurons that relay messages between
other neurons such as sensory and motor neurons.
(found most often in Brain and Spinal chord).

Carries impulses from receptors e.g pain
receptors in skin to the CNS( brain or spinal
cord)


Carries impulses from sensory nerves to
motor nerves.
Responsible for integration

Carries impulses from CNS to effector e.g.
muscle to bring about movement or gland to
bring about secretion of hormone


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Nerves  Collections
of neurons that are
joined together by
connective tissue.
Responsible for
transferring impulses
from receptors to CNS
and back to effectors.
http://www.youtube.co
m/watch?feature=play
er_embedded&v=xRkP
Nwqm0mM
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Specialized receptors (light, sound, taste,
touch) react to a stimulus and generate nerve
impulses in the sensory neurons near them.
The sensory neurons carry the impulse to the
spinal cord and then to the brain where
interneurons interpret the sensory
information
The interneurons send out impulses to motor
neurons which elicit a response by an effector
(muscle or gland)


The simplest neural pathway is called
a reflex arc and it does NOT involve
the brain
The pathway is: receptor, sensory
neuron, interneuron in spinal cord,
motor neuron, effector
The fact that the ‘decision’ is made in
the spinal cord saves the time that it
would take the nerve impulse to travel
through the many circuits of the brain.
 Reflexes are often so fast they are
involuntary
 Reflexes are important mechanisms
that are important in maintaining
homeostasis


http://www.sumanasinc.com/webcontent/ani
mations/content/reflexarcs.html

Label the handout placing the components of
the reflex arc in the spinal nerve.