Download Lecture_31_2014_noquiz

Monday April 14, 2014.
Nervous system and biological electricity IV
1. Exam 2 results
2. Lab this week
3. Review of the synapse
4. The connectome
5. Vertebrate nervous system
6. Mapping the brain
This week in Lab
Lab philosophy and Scientific literacy
An example of why this is important
Lab philosophy and Scientific literacy
• Lab is designed to illustrate science as:
– A creative process
– Challenging
– An interactive and social activity
Dropping grades in lab
ACTION POTENTIAL TRIGGERS RELEASE OF
NEUROTRANSMITTER
Na+ and K+
channels
Presynaptic
membrane
(axon)
Postsynaptic
membrane
(dendrite or
cell body)
Action
potentials
1. Action potential arrives;
triggers entry of Ca2+.
2. In response to Ca2+, synaptic
vesicles fuse with presynaptic
membrane, then release
neurotransmitter.
3. Ion channels open when
neurotransmitter binds; ion
flows cause change in
postsynaptic cell potential.
4. Ion channels will close as
neurotransmitter is broken
down or taken back up by
presynaptic cell (not shown).
Excitatory vs. Inhibitory Synapses
• Excitatory synapses cause the post-synaptic cell
to become less negative triggering an excitatory
post-synaptic potential (EPSP)
– Increases the likelihood of firing an action potential
• Inhibitory synapses cause the post-synaptic cell
potential to become negative triggering an
inhibitory post-synaptic potential
– Decreases the likelihood of firing an action potential
Postsynaptic Potentials Can Depolarize or Hyperpolarize
the Postsynaptic Membrane
Postsynaptic potentials can depolarize or hyperpolarize the
postsynaptic membrane.
Depolarization,
Na+ inflow
Hyperpolarization, K+
outflow or Cl– inflow
Excitatory
postsynaptic
potential
(EPSP)
Resting potential
Inhibitory
postsynaptic
potential
(IPSP)
Depolarization and
hyperpolarization
stimuli applied
EPSP  IPSP
Neurons Integrate Information from Many Synapses
Most neurons receive information from many other neurons.
Axons of
presynaptic neurons
Dendrites of
postsynaptic neuron
Cell body of
postsynaptic neuron
Axon
hillock
Axon of postsynaptic cell
Excitatory synapse
Inhibitory synapse
Neurons Integrate Information from Many Synapses
Postsynaptic potentials sum.
Action potential
Threshold
Resting
potential
Neurotransmitters
• More than 100 neurotransmitters are now
recognized, and more will surely be discovered.
• Acetylcholine is important and one of the first ones
discovered because its involvement in muscle
movement.
• Dopamine and serotonin hugely important for
many behaviors.
• The workhorses of the brain are glutamate, glycine,
and γ-aminobutyric acid (GABA).
Neurotransmitter Transport
Proteins/Reuptake
Neurotransmitters must be stopped. They have to be broken
down and recycled by the neuron.
E.g., Acetylcholine is broken down by acetylcholine esterase.
Drug companies often target these 'reuptake' proteins for
drug therapies.
‘The Connectome’
• Sebastian Seung
• Biophysicist/neurophysiologist
@ MIT.
• http://www.ted.com/talks/seb
astian_seung
Mini-Brain/Nervous System Lecture
Central Nervous System = brain and spinal cord
(interneurons)
Peripheral Nervous System = all other parts of
nervous system besides brain & spinal cord
- includes motor neurons and sensory neurons
The Functions of the PNS Form a Hierarchy
Central nervous system (CNS)
Information processing
Peripheral nervous system (PNS)
Sensory
information
travels in
afferent division
Somatic
nervous
system
Most information
travels in
efferent division,
which includes…
Autonomic
nervous system
Sympathetic
division
Parasympathetic
division
Neurons vs. Nerves
• Neuron = a cell that is specialized for the transmission
of nerve impulses. Typically has dendrites, a cell body,
and a long axon that forms synapses with other
neurons. Also called a nerve cell.
• Nerve = A long, tough strand of nervous tissue
typically containing thousands of neurons wrapped in
connective tissue; carries impulses between the
central nervous system and some other part of the
body.
Sciatic Nerve
The sciatic nerve is this huge nerve that leaves
your lower back (and spinal cord) and runs the
length of your leg.
There are many different types of neurons.
Some are myelinated, some are not.
Smaller nerves branch off of the sciatic nerve.
The sciatic nerve responsible for innervating
muscles, skin, etc. in the leg.
It contains both motor neurons and sensory
neurons (i.e. messages go both way).
There are some neurons that originate at the
top and have axons that run the whole way to
your foot. In other words, there are axons that
are about 1 meter long.
How Does Information Flow through the Nervous System?
The brain integrates sensory information and sends signals
to effector cells.
Sensory neuron
CNS (brain
 spinal cord)
Sensory receptor
Interneuron
Motor neuron
(part of PNS)
Effector cells
How Does Information Flow through the Nervous System?
When reflexes occur, sensory information bypasses the
brain.
Spinal cord
Interneuron
Motor neuron
Sensory
receptor
Effector cells
Sensory neuron
Brain Parts
The brain is made up of four distinct structures.
Inside view
Cerebrum
Diencephalon
Information
relay and control
of homeostasis
Brain stem Information relay
and center of autonomic control
for heart, lungs, digestive system
Conscious
thought,
memory
Cerebellum
Coordination
of complex
motor patterns
Functional Mapping
Paul Broca
Studied the brain of a person who could
hear and comprehend, but not speak.
Found a lesion on one part of the brain.
First to claim that different parts of the
brain did different things.
Brain Lesion
Brain Mapping – Electrical Stimulation
• In treating people with severe seizures,
doctors electrically stimulate the brain to find
the area where the seizure originates from.
• The idea is to remove this part of the brain
with removing as little as possible from other
adjoining areas. Doctors still do this today.
• Based on electrical stimulation of conscious
patients, we know that different parts of the
brain do different things.
Brain Mapping – fMRI
Mapping of Brain to Anatomical Parts
Specific Brain Areas Have Specific Functions
Genitals
Teeth
Jaw
Tongue
Intra-abdominal
Leg
Hip
Trunk
Cross section through area responsible for sense of touch
and of temperature
Left
hemisphere