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6.5
Nervous System
What is the nervous system?
A network of specialized cells that
communicate information about an animal's
surroundings and itself
Nervous system processes this information
and causes reactions in other parts of the body
Specialized cells called neurons
What are the two main sections
of the nervous system?
Central Nervous System—
Brain and spinal cord
Peripheral Nervous System—
Composed of nerves that
branch from the CNS and
connect the CNS to the rest of
the body
How do the CNS and PNS work together
to transmit signals and responses?
The CNS receives impulses from the nerves of
the PNS
CNS interprets impulses
Transmits the corresponding signals back to
the origin through the PNS
Thus controlling the functions of the entire
body
Along what route are nerve impulses
relayed to and from the CNS?
Nerve impulses are conducted
from receptors to the CNS by sensory neurons
within the CNS by relay neurons
from the CNS to effectors (muscles) by motor
neurons
Be able to draw this motor neuron.
Cell body
Nucleus
Dendrite
Axon
Myelin sheath
Node of Ranvier
Axon terminals /
synaptic knobs
Identify the components
of this motor neuron.
Cell body
Nucleus
Dendrite
Axon
Myelin sheath
Node of Ranvier
Axon terminals /
synaptic knobs
Resting Potential and Action Potential
Resting potential—
the membrane potential of a neuron membrane
when not conducting an impulse
What is the resting potential of a resting neuron?
a resting neuron has a resting potential of about -70
millivolts
Action potential—
is the state of the cell membrane while conducting
an impulse
Impulse Transmission
In resting neurons, there exists an imbalance of ions inside and
outside of the cell membranes.
The cytoplasm just inside the membrane is negative in charge,
and the fluid just outside the membrane is positive. The
membrane is said to be polarized.
Like a flashlight battery, the difference in electrical charge
carries potential energy, which can be measured as a voltage
An action potential is triggered when a nerve impulse triggers
voltage-gated sodium channels to open, and sodium ions rush
into the cell, reversing the charges
Now the cytoplasm just inside the membrane becomes positive
in charge, and the fluid just outside the membrane becomes
negative.
Very quickly, the sodium channels close, while voltage-gated
potassium channels open, allowing potassium ions to rapidly
diffuse out. The plasma membrane returns to being positive on
the outside and negative on the inside, and the potassium
channels close
Action Potential and
Impulse Transmission Diagram
Synaptic Transmission
nerve impulse travels to end of the neuron
this causes synaptic vesicles to fuse with membrane
the vesicles release neurotransmitter molecules into
synaptic cleft
these neurotransmitter molecules bind to receptors on
next neuron
this causes ion channels to open on that neuron
sodium ions rush in, changing the polarity of the
membrane, and an action potential is triggered in the
receiving cell
Synaptic Transmission Diagram
IB Exam Question
1. Outline the general organization
of the human nervous system.
The nervous system is divided into two main parts:
the central nervous system (CNS), and the peripheral
nervous system (PNS)
The organs of the CNS are the brain and the spinal
cord
The PNS is composed of nerves that branch from the
CNS and connect the CNS to the rest of the body
The CNS receives impulses from the nerves of the PNS
and interprets them, and transmits the corresponding
signals back to the origin through the PNS, thus
controlling the functions of the entire body
Both the CNS and PNS is composed of specialized
cells called neurons that carry rapid electrical impulses
IB Exam Question
2. Draw a labelled diagram to show the
structure of a motor neuron and indicate with
an arrow the direction of the nerve impulse.
Drawing must contain
nucleus;
cell body;
axon;
dendrites;
myelin sheath;
node of Ranvier;
synaptic knob;
IB Exam Question
3. Define resting potential and
action potential.
(2 marks)
Resting potential is the membrane potential of
a neuron membrane when not conducting an
impulse.
Action potential is the state of the cell
membrane while conducting an impulse
IB Exam Question
4. In a nerve impulse, what happens at the
site following the highest point of the action
potential?
(1 mark)
A.
B.
C.
D.
Voltage-gated sodium ion channels open
and Na+ is pumped in.
Voltage-gated sodium ion channels open
and Na+ diffuses out.
Voltage-gated potassium ion channels open
and K+ is pumped out.
Voltage-gated potassium ion channels open
and K+ diffuses out.
Correct answer: D
IB Exam Question
5. Explain how a nerve impulse passes
along a non-myelinated neuron (axon).
In resting neurons, there exists an imbalance of ions inside and
outside of the cell membranes.
This is called the “resting potential” and represents potential energy!
The cytoplasm just inside the membrane is negative in charge, and
the fluid just outside the membrane is positive. The membrane is said
to be polarized.
Like a flashlight battery, the difference in electrical charge carries
potential energy, which can be measured as a voltage
A resting neuron has a resting potential of about -70 millivolts.
An action potential is triggered when a nerve impulse triggers
voltage-gated sodium channels to open, and sodium ions rush into
the cell, reversing the charges
Now the cytoplasm just inside the membrane becomes positive in
charge, and the fluid just outside the membrane becomes negative.
Very quickly, the sodium channels close, while voltage-gated
potassium channels open, allowing potassium ions to rapidly diffuse
out. The plasma membrane returns to being positive on the outside
and negative on the inside, and the potassium channels close
IB Exam Question
6. What is the role of active transport in the
transmission of nerve impulses by
neurones?
(1 mark)
A.
Propagates an action potential by pumping
sodium ions across the membrane out of the
neurone.
B.
Propagates an action potential by pumping
sodium ions across the membrane into the
neurone.
C.
Initiates the action potential needed for the
transmission of an impulse by pumping calcium
ions out of the endoplasmic reticulum.
D.
Establishes the resting potential needed for the
transmission of an impulse by pumping sodium
and potassium ions across the membrane.
Correct answer: D
IB Exam Question
7. Explain the principles of synaptic
transmission.
(6 marks)
nerve impulse travels to end of the neuron;
this causes synaptic vesicles to fuse with membrane;
the vesicles release neurotransmitter molecules into
synaptic cleft;
these neurotransmitter molecules bind to receptors on
next neuron;
this causes ion channels to open on that neuron;
sodium ions rush in, changing the polarity of the
membrane, and an action potential is triggered in the
receiving cell