Transcript Neurons, Synapses and Signaling

Neurons, Synapses and
Signaling
Chapter 48
Warm Up Exercise
 What types of cells can receive a nerve signal?
Nervous Organization
 Neurons- nerve cells.
 Brain- organized into clusters of neurons, called
ganglia.
 Central Nervous System- includes the brain and the
spinal cord.
 Peripheral Nervous System- all of the neurons
extending from the brain and the spinal cord.
Types of Neurons
 Sensory Neurons- transmit information from the
senses to processing centers in the brain or
ganglia.
 Interneurons- neurons in the brain that analyze
and interpret sensory input.
 Motor Neurons- transmit signals for muscle and
gland activity.
Neuron Structure and Function
 Cell Body- contain the organelles and nucleus.
 Dendrites- branched extensions that receive
signals from other neurons.
 Axon- extension from the cell body that transmits
signals to other cells.
 Synapse- junction between neurons.
 Neurotransmitters- chemical messengers that
pass information between neurons.
 Glial Cells- supporting cells that insulate the
axons of neurons and regulate fluid surrounding
neurons.
Neuron
 Insert image
 kl
Ion Pumps and Resting Potential
 Membrane Potential- the difference in voltage
between the inside and outside of the cell
membrane.
 Resting Potential- the membrane potential of a
resting neuron is -60 to -80 mV.
 Formed by a high concentration of K+ ions inside the
cell, and high Na+ ions outside the cell.
Sodium-Potassium Pumps
 Sodium-Potassium Pumpsmaintain resting potential in
the cell membrane.
 Transport 3 Na+ ions out for
every 2 K+ ions in. In
addition to the SodiumPotassium pump, ions diffuse
across the concentration
gradient. Many K+ channels
are open, allowing for a large
amount of K+ to move out of
the cell, few Na+ channels are
open allowing little flow
inside, leading to a negative
membrane potential inside.
Warm Up Exercise
 Explain how a nervous response is transmitted
through a series of neurons?
 How does the sodium-potassium pump maintain a
membrane gradient?
Ion Gated Channels
 Ion Gated Channels- ion channels that open or
close in response to stimuli.
 The opening and closing of ion gated channels alters
the membrane potential.
 Hyperpolarization- an increase in the magnitude
of the membrane potential.
 Depolarization- a reduction in the magnitude of
the membrane potential.
Graded and Action Potentials
 Graded Potential- a shift in the membrane
potential; is a response to hyperpolarization or
depolarization
 Action Potential- a massive change in membrane
voltage, caused by depolarization.
 Action potentials can be regenerated to spread along
the axon at a constant magnitude.
Graded Potentials and Action Potentials
 kk
Voltage Gated Ion Channels
 Voltage-Gated Ion Channels- open and close
when the membrane potential passes a particular
level.
 Action potentials occur when depolarization increases
the membrane potential to a certain level, called the
threshold.
 kk
Warm Up Exercise
 Explain what happens in hyperpolarization and
depolarization? Which ions move in which
direction?
 Describe what happens in an action potential.
Action Potentials
 Refractory Period“downtime” when a
second action potential
cannot be initiated.
 Occurs because of the
inactivation of the
sodium channelsduring the falling
phase and early part
of the undershoot.
Action Potentials
 Saltatory Conduction- how the action potentials
jumps from node to node along the axon.
Communication With Other Cells
 Electrical Synapses- contain gap junctions which allow
electrical currents to flow from one neuron to the next.
 Chemical Synapses- release a chemical
neurotransmitter between cells.
 INSERT DIAGRAM
Chemical Synapse
 Presynaptic neuron synthesizes neurotransmitter and
packages in synaptic vesicles. The arrival of action
potential at axon/synaptic terminal depolarizes plasma
membrane, opening voltage-gated channels, which allow
Ca2+ to diffuse into the synaptic terminal, which forces
vesicles to fuse with membrane causing the release of
neurotransmitter into the synaptic cleft.
Neurotransmitters diffuse across the cleft and binds to
and activates a specific membrane receptor (called a
ligand-gated ion channel).
Ligand-Gated Ion Channels
 Ligand-Gated Ion Channel- located in
postsynaptic cell- binding of neurotransmitter to
this receptor opens the channel and allows specific
ions to diffuse across the postsynaptic membrane,
resulting in a postsynaptic potential.
 Excitatory Postsynaptic Potential (EPSP)- occurs
when channel is permeable to both Na+ and K+.
Causes depolarization.
 Inhibitory Postsynaptic Potential (IPSP)- occurs
when channel is permeable to either K+ or Cl-.
Causes hyperpolarization.
Summation of Action Potentials
 Temporal Summation- two EPSP’s occur at a single
synapse in rapid succession- in this case the EPSP’s add
together.
 Spatial Summation- two EPSP’s produced simultaneously
at different synapses on the same postsynaptic neuronEPSP’s added together.
Exit Slip
 In multiple sclerosis, myelin sheaths harden and
deteriorate. How would this affect the nervous
system function?
Warm Up Exercise
 What is meant by the term saltatory conduction?
 Explain the difference between an electrical and
chemical synapse.
 Discuss how a presynaptic cell transmits a
chemical impulse once it receives the action
potential near the axon terminal.
Neurotransmitters
 Acetylcholine- causes the opening of potassium
channels in cardiac muscle membrane. Leads to
hyperpolarization, which reduces the rare at which
the heart pumps (inhibitory).
 Dopamine and Serotonin
 Epinephrine and Norepinephrine
Organization of Human Brain
 Cerebrum- the center for voluntary movement,
learning, emotion, memory, etc.
 Divided into right and left hemispheres, connected by the
corpus callosum.
 Cerebellum- coordinates movement and balance.
Organization of Human Brain
 Diencephalon
 Thalamus
 Hypothalamus
 Pineal Gland
 Pituitary Gland
 Brainstem- receives signals
from sensory neurons
 Midbrain
 Pons
 Medulla Oblongata
 INSERT DIAGRAMS