Download The Nervous System

The Nervous System
Nervous System
• Three basic functions
– Sensation
• gather information
– Integration
• process information
• use of multiple sources of
information.
– Response
• coordinated action
appropriate to
environment
EK3E2: Animals have nervous systems that detect external
and internal signals, transmit and integrate information, and
produce responses.
a. The neuron is the basic structure of the nervous system that reflects
function.
1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin
sheath that acts as an electrical insulator.
2. The structure of the neuron allows for the detection, generation, transmission
and integration of signal information.
3. Schwann cells, which form the myelin sheath, are separated by gaps of
unsheathed axon over which the impulse travels as the signal propagates along the
neuron.
The neuron is the basic structure of the
nervous system that reflects function.
1. A typical neuron has a cell body, axon and dendrites. Many axons
have a myelin sheath that acts as an electrical insulator.
2. The structure of the neuron allows for the detection, generation,
transmission and integration of signal information.
3. Schwann cells, which form the myelin sheath, are separated by gaps
of unsheathed axon over which the impulse travels as the signal
propagates along the neuron.
Rat Cortical Neuron
Primary rat hippocampal
neurons
Hippocampal Neuron
Neurons are similar to other cells in the body
because:
1. Neurons are surrounded by a cell membrane.
2. Neurons have a nucleus that contains genes.
3. Neurons contain cytoplasm with organelles
4. Neurons carry out basic cellular processes such as
protein synthesis and energy production.
However, neurons differ from other cells in the
body because:
1. Neurons have specialized extensions called
dendrites and axons. Dendrites bring information to
the cell body and axons take information away from
the cell body.
2. Neurons communicate with each other through an
electrochemical process.
3. Neurons contain some specialized structures (for
example, synapses) and chemicals (for example,
neurotransmitters).
Neuron Trivia
Neurons are the oldest and longest cells in
the body! You have many of the same neurons
for your whole life. Although other cells die
and are replaced, many neurons are never
replaced when they die. In fact, you have
fewer neurons when you are old compared to
when you are young. On the other hand, data
published in November 1998 show that in one
area of the brain (the hippocampus), new
neurons CAN grow in adult humans.
Neurons can be quite large - in some
neurons, such as corticospinal neurons (from
motor cortex to spinal cord) or primary
afferent neurons (neurons that extend from
the skin into the spinal cord and up to the
brain stem), can be several feet long!
Neuron Anatomy
• Soma/Cell Body: is the metabolic
center of the neuron, contains the
Nucleus and Mitochondrion.
• Dendrites: convey incoming messages
to the cell body.
• Axon: generates nerve impulses and
topically conduct them away from the
cell body myelinated by either
oligodendroglia in CNS or Schwann
cells in PNS. Each neuron has only one
axon.
• Axon Hillock: a cone like region from
where an axon arises.
• Presynaptic terminals: The swollen,
distal end of an axon; contains a
neurotransmitter substance within
synaptic vesicles. Also called synaptic
ending or synaptic bouton.
• Synapse: Specialized junctions with
other cells that are along the length or
at end of an axon.
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Axons
Take information away
from the cell body
Smooth Surface
Generally only 1 axon per
cell
No ribosomes
Can have myelin
Branch further from the
cell body
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Dendrites
Bring information to the
cell body
Rough Surface (dendritic
spines)
Usually many dendrites
per cell
Have ribosomes
No myelin insulation
Branch near the cell body
Neuron Anatomy
Neurons can also be classified by the
direction that they send information:
• Sensory (or afferent)
neurons: send information
from sensory receptors (e.g.,
in skin, eyes, nose, tongue,
ears) TOWARD the central
nervous system.
• Motor (or efferent) neurons:
send information AWAY from
the central nervous system to
muscles or glands.
• Interneurons: send
information between sensory
neurons and motor neurons.
Most interneurons are located
in the central nervous system.
EK3E2: Animals have nervous systems that detect external
and internal signals, transmit and integrate information, and
produce responses.
b. Action potentials propagate impulses along
neurons.
1. Membranes of neurons are polarized by the
establishment of electrical potentials across the
membranes.
2. In response to a stimulus, Na+ and K+ gated channels
sequentially open and cause the membrane to become
locally depolarized.
3. Na+/K+ pumps, powered by ATP, work to maintain
membrane potential.
How neurons
conduct impulses:
• Membrane potential (as
seen in muscle cells)
• K+ diffuses out of neurons
faster than Na+ diffuses in,
• Na-K pump moves 3Na+
back out for 2K+ back in
• Cl-, phosphate, protein
anions balance cations
• “Resting potential” ~ -70mV
• Nerve Impulse
• Action Potential Exercise
Voltage Gated
Channels and
the Action
Potential
Rate of conduction
• Unmyelinated axons
– Action potential
propagates at 2-3
meters per
second (m/sec)
• Saltatory Conduction
• Action Potential occurs only
in nodes,
– "leaps" from node to node
– Ion attraction and diffusion
stimulate new A.P. in each node
– Saltatory conduction much
faster than continuous
conduction in unmyelinated
fibers.
• up to 100 m/sec
EK3E2: Animals have nervous systems that detect external
and internal signals, transmit and integrate information, and
produce responses.
c. Transmission of information between neurons
occurs across synapses.
1. In most animals, transmission across synapses involves chemical
messengers called neurotransmitters.
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Acetylcholine
Epinephrine
Norepinephrine
Dopamine
Serotonin
GABA
2. Transmission of information along neurons and synapses results in a
response.
3. The response can be stimulatory or inhibitory.
How does impulse get from cell to cell?
Chemical synapses, 2
•Axon (& A.P.) ends short of
– “Gap junctions,” tiny holes
connect cytoplasm of adjacent
next cell,
cells
•Synaptic knob (axon end)
– A.P. continuous from cell to cell
releases chemical transmitter
Electrical synapses
Neurotransmission
• When Action Potential
reaches synaptic knob,
– Synaptic vesicles unite with
membrane,
– Release neurotransmitter,
– Neurotransmitter diffuses
across synaptic cleft,
– Neurotransmitter binds to
receptors in postsynaptic
membrane,
– Chemically gated channels
open
• Chemical Signals
• Mouse Party
Synapse
• Neurotransmitter can't remain in cleft (would continue to
stimulate uncontrollably)
– ACh removed by acetylcholinesterase (AChE)
– Acetate & choline reabsorbed by axon end, resynthesized to ACh
– Other neurotransmitters taken back by axon or diffuse away
Neurotransmitters may be …
• Excitatory
– depolarize postsynaptic
membrane
– Excitatory Postsynaptic
Potential (EPSP)
• Inhibitory
– hyperpolarize
postsynaptic membrane
– Inhibitory Postsynaptic
Potential (IPSP)
• Reward Pathway
• Reflex Arc
EK3E2: Animals have nervous systems that detect external
and internal signals, transmit and integrate information, and
produce responses.
d. Different regions of
the vertebrate brain
have different
functions.
LO 3.43 The student is able to construct an explanation, based on scientific theories
and models, about how nervous systems detect external and internal signals,
transmit and integrate information, and produce responses.
LO 3.44 The student is able to describe how nervous systems detect external and
internal signals.
LO 3.45 The student is able to describe how nervous systems transmit information.
LO 3.46 The student is able to describe how the vertebrate brain integrates
information to produce a response.
LO 3.47 The student is able to create a visual representation of complex nervous
systems to describe/explain how these systems detect external and internal
signals, transmit and integrate information, and produce responses.
LO 3.48 The student is able to create a visual representation to describe how
nervous systems detect external and internal signals.
LO 3.49 The student is able to create a visual representation to describe how
nervous systems transmit information.
LO 3.50 The student is able to create a visual representation to describe how the
vertebrate brain integrates information to produce a response.
Resources
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Action Potential Tutorial
A&P Text, 2
Essential Study partner Links
Parts of a Neuron Review
Anatomy Drill
Body Smart Nervous System
Campbell’s Activity Quiz
Human A&P Lessons
Cerebral Commando
Synaptic Transmission Tutorial
Drugs, Brains & Behavior
Parts of the Brain, 2
Video Quiz - Making Brain Cells
Video Quiz - ALS Lost Nerve Power
Video Quiz - Wild Young Brains
Video Quiz - Vanishing Brain
Video Quiz - Meth and the Brain
Video Quiz - Paralysis Push
Resting Membrane Potential
Action Potential (Biological Psychology)
A&P Chapter 8
A&P Chapter 14
Function of the Neuromuscular Junction