Transcript Nervous System

Neurons- The matter of the
nervous system
Chapter 7: Pgs 120-133
The Nervous system controls the
entire body
• It is the interface
between stimulus and
response
• Allows animals to interact
with their environment
• Brain and spinal cord:
central nervous system
(CNS)
• Other nerves: peripheral
nervous system (PNS)
The nervous system is the interface
between stimulus and response
The Neuron is the base unit of the
nervous system
Neurons are large cells supported by a
variety of glial cells
• Human neurons can be
1m in length
• Potentially thousands of
glial cells support a
single neuron
• Provide nutrition,
support, insulation
• Schwann cells are an
example
Schwann cells are glial cells which
protect neurons with myelin
The 3 kinds of neurons
work together to
interface between
stimulus and response
• The reflex arc is the
simplest neural circuit
• Consists of
– 1 sensory neuron
– 1 interneuron
– 1 motor neuron
The synapse is
the connection
point between
neurons
• Vesicles sit in
axon terminals,
loaded with
neurotransmitte
rs
Some important neurotransmitters
• AcetylcholineNeuromuscular
• Dopamine-Exitatory
• Norepinephrine
• GABA- Inhibitory
• Serotonin-Regulatory
Many Drugs copy the action of
neurotransmitters
• Methamphetamine is
structurally similar to
dopamine
• Dopamine involved in
learning and reward
systems
Dopamine
Methamphetamine
Many synapses make complex
information processing possible
• Cell interactions form
logic circuits
• AND, NOT, etc. gates are
formable
• Human Brain: 100
billion neurons
• Up to 10,000 synaptic
connections/neuron
Which one of the following
statements is false?
A) Sensory neurons convey signals from the CNS to
sensory receptors.
B) Motor neurons convey signals from the CNS to
effector cells.
C) Interneurons integrate data and relay
appropriate signals to other interneurons or to
motor neurons.
D) The PNS includes nerves and ganglia.
E) The CNS consists of the brain and spinal cord.
The Nerve impulse
The nervous system runs on electricity
• Current- The movement of charge (electrons
or ions)
• Voltage- potential energy stored in a charge
disparity over distance
• Nervous system uses ions (Na+, K+, Cl-, Ca++)
to send signals from one neuron to another
At rest, neurons must be ready to
respond in milliseconds
Water behind a dam is stored
potential energy
Charge and concentration
gradients hold potential chemical
energy
Neurons have a resting membrane
potential
• Negatively charged
• Keeps the neuron
poised for instant action
• -70mV
• Maintained by constant
active transport of ions
Pumps maintain gradients, channels
activate cells
• Which of the following statements about the
sodium-potassium pump is false?
• A) It is a membrane protein.
• B) It keeps the concentration of sodium low
inside the cell.
• C) It moves sodium across the membrane and
into the cell.
• D) It helps maintain the resting membrane
potential.
• E) It actively transports potassium into the cell
Two kinds of ion channels
Ligand-gated ion channels
open when bound to a ligand
(a neurotransmitter)
Voltage gated ion channels
open when the voltage in the
cell changes
Neurons can respond in milliseconds,
giving us quick reflexes
Neurotransmitters are the chemical
signals with which neurons
communicate across a synapse
• Neurotransmitters bind
to gated ion channels in
the cell membrane of
the next neuron
• Binding opens the ion
channel
• Hydrolysis or reuptake
removes the
neurotransmitter
The Nerve Impulse step by step
Step 1- depolarization causes
vesicles to fuse
Step 2- Fused vesicles release
neurotransmitter into the synapse
Step 3- Neurotransmitters open gated
sodium channels, depolarizing cell
Step 5- Voltage-gated sodium channels
pass the signal down the axon
Voltage-gated channels sit at nodes of
Ranvier, making the signal travel faster
Step 6- Change in voltage at the
axon terminal passes the signal on
Step 7- Potassium channels are opened, repolarizing the cell for its next response
Step 8- Ion balance is restored using active
transport- the Na+/K+ pump
What is the functional unit of the
nervous system?
•
•
•
•
•
A) dendrite
B) cell body
C) neuron
D) axon
E) synapse
Depolarization is the activation event
• Depolarization is
caused by opening of
gated sodium
channels
• When depolarized,
neurons respond in
milliseconds
Action potentials normally travel
along an axon
• A) toward the cell body.
• B) away from the cell body.
• C) in either direction, depending on the needs
of the animal.
• D) away from the synapse.
• E) from axons into dendrites.
Step 0.5: Vesicles were marched down
the axon previously by kinesin
Antidepressants can block reuptake of
neurotransmitters
• SSRI- “Selective
Serotonin Reuptake
Inhibitors”
• Prozac, Paxil, Zoloft,
etc.- all SSRI’s
Sarin nerve gas is an
Acetylcholinesterase Inhibitor
• How does it work?
• How does it kill people?
The reflex arc is the most basic neural
circuit
The Ganglion splits the signal to notify
the brain
The human brain has 3 major regions
Higher thought is compartmentalized
to the cerebrum
Regions of the cerebral cortex are
themselves compartmentalized
A homonculus shows the area of the
brain devoted to regions of the body