Nervous System

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Transcript Nervous System

Cells of the Nervous System
• Neurons – cells that send signals within
the body
• Supporting cells:
– Glial cels – glue neurons together,control
extra-cellular environment of cell
– Astrocytes contribute to the blood brain
– Schwann cells : forms myelin sheath in
PNS, loss of myelin sheath results in MS
Membrane Potential
• All mammalian cells have a negative
resting potential
• What factors help maintain this negative
resting potential?
• Neurons have ionic channels in the
membrane that allows the membrane
potential to change
• How is the resting potential maintained
in a neuron if there are ionic channels
that allow for diffusion of ions?
The Action Potential
• Neurons have gated channels that
allows for a change in the resting
• Different stimuli open different channels:
• Excitatory stimulus opens the Na+
channels and leads to depolarization
• Inhibitory stimulus opens K+ channels
and leads to hyper-polarization
What is happening with the gated channels at rest?
What do you notice about the response of these
gates to the excitatory stimulus?
Why is there no sodium entering the cell anymore?
Use your knowledge of the timing of these gates to
understand why there will be no response to a new
stimulus during this phase of the action potential.
Propagation of the Action
• Generated at the axon hillock
• What is the “all or none” concept
associated with an action potential?
• How is it that you can feel different
degrees of stimulus when action
potentials are generated in an all or
none fashion?
• How is it that an action potential moves
in only one direction?
Speed of Propagation
• How is the speed of propagation of an
action potential regulated?
• Larger diameter axons conduct faster
action potentials
• Saltatory conduction…..
The Synapse
What is a synapse?
The space between neurons
Presynaptic cell = transmitting cell
Postsynaptic cell = receiving cell
Electrical synapse – action potential spreads
directly via gap junctions
• How is an action potential propagated
between synpases that do not use gap
junctions to directly send the impulse?
• Chemicals called neurotransmitters are used
• What channel is opened by an excitatory
• Na+
• What channels is opened by an inhibitory
• K+
• How is the regulation of the postsynaptic
membrane’s gated channels different from the
gated channels found along the axon?
• These channels are chemically sensitive gates
as opposed to voltage sensitive gates
• Neurotransmitters:
– Can cause IPSP or EPSP
– Are discharged from synaptic vessicles
– Are rapidly removed by enzymes
• Acetylcholine – found at neuromuscular
– Cholinesterase = enzyme that removes
ach from synapse
• Epinephrine
• Norepinehrine
• Dopamine – too much associated with
schizophrenia, too little associated with
Parkinson's disease
• Serotonin – associated with learning, sleep
and moodiness
– LSD binds to serotonin receptors and is a
• GABA – inhibitory neurotransmitter
• Endorphins – natural analgesic in brain
• Some neurons release gas molecules such
as NO and CO (Viagra stops an enzyme
that slows NO effects on erectile tissue)
• Nerve gas, malathion destroys
• DDT increases permeability to Na+
• Tetrodotoxin – found in puffer fish and
red tide toxin
– Blocks Na+ channels
• Botulin – prevents release of ach
• Curare – blocks ach receptor
Functional Organization of the
Nervous System
Neuronal Circuits
• Reflex cause an automatic response does not
invovle the brain
• Ganglion = a cluster of nerve cell bodies found
outside of the CNS
• Interneurons – neurons that integrate sensory
input with motor output
• Interneuron branches can carry signals to
different parts of spinal cord or brain
– Convergent circuits bring information from different
– Divergent circuits send information to different regions
The Brain
• Brainstem: automatic
– Medulla oblongata
controls homeostatic
functions, and conducts
data to other parts of the
– Pons – helps medulla
with regulation
– Midbrain – integration of
sensory information from
auditory and visual
• Cerebellum:
movement and
• Hand-eye
coordination uses
cerebellar function
• Diencephalon –
intrgrating centers:
– Thalamus –
sensory input and
motor output center,
integration to other
brani centers
– Hypothalamus –
hormonal regulation
of anterior pituitary
and production of
posterior pituitary
Cerebrum most complex
integration center: thought
Note the cell
body that is
connected to
the axon. This
will be part of
a ganglion to