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Nervous System
Components: Brain, spinal cord, nerves,
sense organs, and associated structures.
Functions:
Works with endocrine system to coordinate
body activities.
Integrates and processes information from
sense organs.
Sends signals (instructions) to muscles and
glands.
Responds to internal stimuli.
Homeostatic Role:
Regulates most organ activities along with
endocrine system.
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Human Nervous System
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Functions of Nervous Tissue
1. Sensory Input: Conduction of signals from
sensory organs (eyes, ears, nose, skin, etc.)
to information processing centers (brain and
spinal cord).
2. Integration: Interpretation of sensory signals
and development of a response. Occurs in
brain and spinal cord.
3. Motor Output: Conduction of signals from
brain or spinal cord to effector organs
(muscles or glands). Controls the activity of
muscles and glands, and allows the animal to
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respond to its environment.
Nervous System Allows Us to Respond to Our Environment
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Cells of Nervous Tissue
1. Neuron: Nerve cell. Structural and functional
unit of nervous tissue.
Carry signals from one part of the body to another.
2. Supporting cells: Nourish, protect, and
insulate neurons.
There are roughly 50 supporting cells for every
neuron.
In humans, Schwann cells wrap around the axons of
neurons, forming a myelin sheath that is essential
for transmission of nerve impulses.
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Neuron Structure
Cell body : Contains nucleus and most
organelles.
Dendrites: Extensions that convey signals
towards the cell body.
Short, numerous, and highly branched
Axon: Extension that transmits signals away
from the cell body to another neuron or
effector cell.
Usually a long single fiber.
Axon is covered by a myelin sheath made up of
many Schwann cells that are separated by small
spaces (Nodes of Ranvier).
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Structure of the Neuron
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Neuron Structure
Myelin sheath and nodes of Ranvier greatly speed up
nerve impulses, which jump down axon from node to
node.
Speed of signal
Myelinated axon 100 meters/second
Unmyelinated axon
5 meters/second
Multiple sclerosis: A disease in which a person’s
immune system destroys the myelin sheaths on their
neurons.
• Loss of muscle control
• Impaired brain function
• Death
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Neurons and Synapses
Types of Neurons
Sensory
Motor
Interneurons
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Sensory Neurons
INPUT From sensory organs to the
brain and spinal cord.
Drawing shows a
somatosensory
neuron
Brain
Sensory
Neuron
Spinal
Cord
Vision, hearing,
taste and smell
nerves are cranial,
not spinal
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Motor Neurons
OUTPUT From the brain and spinal
cord To the muscles and glands.
Sensory
Neuron
Brain
Spinal
Cord
Motor
Neuron
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Interneurons
Interneurons
carry
information
between other
neurons only
found in the
brain and
spinal cord.
Brain
Sensory
Neuron
Spinal
Cord
Motor
Neuron
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Structures of a neuron
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The cell body
Contains the cell’s Nucleus
Round, centrally
located structure
Contains DNA
Controls protein
manufacturing
Directs metabolism
No role in neural
signaling
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Dendrites
 Information
collectors
 Receive inputs
from neighboring
neurons
 Inputs may number
in thousands
 If enough inputs
the cell’s AXON
may generate an
output
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Dendritic Growth
 Mature neurons
generally can’t
divide
 But new dendrites
can grow
 Provides room for
more connections
to other neurons
 New connections
are basis for
learning
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Axon
The cell’s output
structure
One axon per cell,
2 distinct parts
tubelike structure
branches at end
that connect to
dendrites of other
cells
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Myelin sheath
 White fatty casing
on axon
 Acts as an electrical
insulator
 Not present on all
cells
 When present
increases the speed
of neural signals
down the axon.
Myelin Sheath
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How neurons communicate
Neurons communicate by means of an
electrical signal called the Action
Potential
Action Potentials are based on
movements of ions between the
outside and inside of the cell
When an Action Potential occurs a
molecular message is sent to
neighboring neurons
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Neuron to Neuron
 Axons branch out
and end near
dendrites of
neighboring cells
 Axon terminals are
the tips of the
axon’s branches
 A gap separates the
axon terminals from
dendrites
 Gap is the Synapse
Dendrite
Axon
Cell
Body
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Synapse
 axon terminals
contain small
storage sacs
called synaptic
vesicles
Sending
Neuron
Axon
Terminal
Synapse
vesicles contain
neurotransmitter
molecules
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Neurotransmitter Release
 Action Potential causes vesicle to
open
 Neurotransmitter released into
synapse
 Locks onto receptor molecule in
postsynaptic membrane
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Locks and Keys
 Neurotransmitter
molecules have
specific shapes
 Receptor molecules have
binding sites
 When NT binds to
receptor, ions enter
positive ions (Na+ )
depolarize the neuron
negative ions (Cl-)
hyperpolarize
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Some Drugs work on
receptors
 Some drugs are
shaped like
neurotransmitters
 Antagonists : fit the
receptor but poorly
and block the NT
e.g. beta blockers
 Agonists : fit
receptor well and
act like the NT
e.g. nicotine.
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Summary
 3 types of neurons
 The cell membrane
 Ion movements
 Action potentials
 Synapse
 Neurotransmitters
 Receptors and ions
 Agonists and
antagonists
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In this experiment you are required to say the color of the
word, not what the word says. For example, for the word,
RED, you should say "Blue."
Green
Red
Blue
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