AP Biology
I. Nervous System Notes
1. General information: passage of information occurs in two ways:
Nerves - process and send information fast (eg. stepping on a tack)
Hormones - process and send information slowly (eg. growth hormone etc)
2. Major components of the nervous system: Two major divisions
The central nervous system (CNS) - made up of the spinal cord and brain
The peripheral nervous system (PNS) - made up of the cranial and spinal nerves
3. Neurons
a) Definition - neurons are the cells which make up the nervous system. They consist of an axon, 2
or more dendrites and a cell body containing a nucleus.
b.) Types of Neurons
i. Sensory neurons - send information from the sense organs (outside) to the C.N.S. They have long
dendrites and short axons. The diagram above shows a picture of a sensory neuron.
Be able to label sensory receptors, myelin sheath, Schwann cells, Node of Ranvier, axon, dendrite,
cell body and nucleus in the diagram of a sensory neuron above
ii. Motor neurons - send information from the C.N.S to the muscles. Causing the muscles to move.
They have short dendrites and long axons. The diagram below show a diagram of a motor neuron
Be able to label effector, myelin sheath, Schwann cells, node of ranvier, axon, dendrite, cell body and
nucleus in the diagram of the motor neuron above
iii. Interneurons - connect different neurons together, send information between
neurons. They have short dendrites and short axons.
4. Myelin sheath - is a sheath that surrounds the axon. It is like a bunch of sausages joined together.
The sausages are the Schwann cells and the spaces between the sausages the nodes of ranvier.
The myelin sheath increases the speed of the nerve impulse because the nerve impulse jumps from
one Node of Ranvier to the next (the node is the depression between the Schwann cells that make
up the myelin sheath. The myelin sheath also insulates axon preventing the nerve impulse from
"shorting" out.
5. Reflex arc - Be able to label the kinds of neurons and their parts, in the two diagrams of reflex
arcs in the diagrams below and be able to describe how a reflex arc works
The correct order of a reflex arc is: sensory receptor --> sensory neuron-->Spinal cord (CNS) -->
motor neuron --> effector (muscle or gland)
5. The Nerve Impulse
A. Passage of a nerve impulse within a Neuron
i. Resting potential - polarized membrane
-higher concentration of potassium ions (K+) inside the axoplasm (axoplasm = cytoplasm of the axon)
than outside and a higher concentration of sodium ions (Na+) outside the axoplasm than inside.
-membrane of the axon impermeable to sodium ions (Na+) (Sodium gates are closed)
-membrane permeable to potassium ions (K+),
-potassium ions (K+) diffuse from a high concentration inside the axon to a lower concentration
outside the axon according to the law of diffusion. (they are slightly more permeable that Na+ ions)
-sodium ions (Na+) diffuse from a high concentration outside the axon to a lower concentration inside
the axon according to the law of diffusion.
- sodium/potassium pump located in the membrane of the axon, pumps potassium ion (K+ ions) from
the outside of the axoplasm to the inside and sodium ions (Na+) from the inside of the axon to the
outside
- The axoplasm is negatively charged because of large negatively charged ions located there.
- the area outside the axoplasm is positively charged because of the excess (Na+) and (K+) ions.
- (-60)mV membrane potential difference
b. Threshold stimulus - in order for a nerve to depolarize it much reach a threshold level of stimulus,
the level at which an action potential is generated
ii. Action potential
a. Upswing - depolarized membrane
-membrane is permeable to Sodium ions (Na+) (Sodium gates are open)
-sodium ions move into the axoplasm making the axoplasm more positive.
-Outside the axoplasm becomes more negative as the sodium ions move into the axoplasm.
-Inside the the axoplasm becomes more positive
-membrane potential changes from -60mV to +40 mV
b. Downswing - repolarization
-Sodium gates close, potassium gates open
-potassium ions diffuse from inside the axoplasm to outside. The movement of (K+) ions to the
outside causes
the polarity to change back to positive and the loss of (K+) ions on the inside causes the polarity to
change
back to negative .
-membrane potential changes from +40mV to -60 mV
c. Recovery phase
-Even though the polarity and membrane potential (voltage) of resting potential has been
reestablished, The sodium and potassium ions are in the wrong places (eg. the sodium on the inside
and the potassium on the outside). The Sodium/Potassium pumps re-establishes the resting potential
configuration of sodium ions on the outside and potassium ions on the inside during this time.
d. Refractory period
As soon as the action potential has move on, the axon undergoes a refractory period. At this time the
sodium gates are unable to open. This ensures that the action potential cannot move backwards and
always moves down an axon to the axon branches
B. Transmission of a Nerve Impulse Between two Different Neurons (across the Synapatic cleft)
-presynaptic means anything before the synapse and postsynaptic means anything after the synapse.
Therefore the cell transmitting the nerve impulse is called the presynaptic cell and the cell receiving
the information is called the postsynaptic cell.
-nerve impulses reaching the presynaptic ending cause calcium ions to interact with contractile
proteins. These proteins pull the synaptic vesicles (containing neurotransmitters) to the inner surface
of the presynaptic cell membrane.
-the synaptic vesicles merge with the presynaptic cell membrane (like in exocytosis) and
neurotransmitters are released into the synaptic cleft (the small space between the neur
-the neurotransmitters diffuse across the cleft and fit into receptor sites on the postsynaptic cell
membrane in a lock and key manner. (Inhibitor substances stop the impulse because they can fit into
the receptor sites and block the normal neurotransmitter.)
-this generates an action potential in the postsynaptic membrane and the nerve impulse continues on
-after their release the neurotransmitters are quickly broken down by enzymes such as cholinesterase
or reabsorbed by the presynaptic ending.
The diagram below represents a synaptic knob (terminal knob) of an axon. Be able to identify parts A
( the synaptic vesicles) and B (the postsynaptic membrane), substance X (neurotransmitters) and the
other parts of the synapse
This is a close up view of the vesicles that contain the neurotransmitters and the receptor sites that
the neurotransmitters fit into
7. Differences between the Sympathetic and Parasympathetic systems
The autonomic nervous system, part of the PNS is made up of two divisions: the sympathetic and
parasympathetic systems.
Characteristic
Sympathetic
Parasympathetic
When functioning?
emergencies
normal/everyday
Digestive system
inhibits/slows down
promotes
Pupil
dilates
constricts
Heartbeat
accelerates
retards
Breathing rate
increases
Neurotransmitter
norepinephrine
retards
acetylcholine
8. Parts of the brain
a. Medulla oblongata - Contains the centres for heartbeat, breathing and blood pressure. It also
contains the reflex centers for vomiting, coughing, sneezing, hiccuping and swallowing
b. Thalamus - It is the relay centre for sensory impulses travelling upwards from other parts of the
cord and the brain to the cerebrum. It receives all sensory impulses (except for smell) and channels
them to appropriate regions of the cerebrum
c. Cerebrum - The area responsible for consciousness.
d. Cerebellum - It functions in muscle co-ordination, integrating impulses received from the higher
centres to ensure that all the skeletal muscles work together to produce a smooth and graceful
motions. it is also responsible for maintaining muscle tone, and transmitting impulses that maintain
posture.
e. Hypothalamus - Is concerned with homeostasis or the constancy of the internal environment.
Contains the centers for hunger, thirst, body temperature, water balance and blood pressure. It
controls the pituitary gland and links the nervous and endocrine glands.
f. Corpus callosum - is a connection between the two cerebral hemispheres. This allows the two
hemisphere to share information. Severing the Corpus callosum can cause severe epileptic seizures.
Be able to labeled the parts of the Brain below
II. Nerve Quiz Questions
1. What is the function/definition of the following:
a. dendrite b. axon c. cell body d. myelin sheath e. Schwann cell
2.. What kind of neuron transmits impulses
a. towards the C.N.S.
b. away from the C.N.S
3. Name the two divisions of the peripheral nervous system.
4. Name 2 characteristics of motor neurons
5. Name 2 characteristics of sensory neurons
6. Name the parts that make up the the C.N.S.
7. What is the name of the sheath that covers some neurons
8. What is the space between two successive neurons called
9. What do synaptic endings store
10. Name of the nerves which link the brain with the body
11. What is the correct order of occurance for a reflex action
12. List 4 characteristics of resting potential
13. List the conditions during upswing of an action potential
f. node of Ranvier
14. List the conditions during downswing of an action potential
15. Describe how impulses are transmitted between two successive neurons.
16. The sympathetic nervous system functions during times of?
17. The parasympathetic nervous system functions during times of?
18. Name a neurotransmitter of the sympathetic nervous system?
19.) Name a neurotransmitter of the parasympathetic nervous system?
20. The nervous system is made up cells called?
21. What is the definition of an interneuron?
22. What is the definition of a synapse
23. What is the function of Acetylcholinestersase (AChE)
24. What is a neurotransmitter?
25. What kind of neuron transmits impulses within the C.N.S.
26. Be able to identify parts of different neurons from a diagram.
27. The brain part injured if irregularities in heartbeat and respiration occur is the:
28. The brain part injured if a person shows a lack of muscle co-ordination.
29. The major function of the cerebral cortex would be to control of:
30. The part of the brain that controls mental concentration and the solving of complex problems.
31. The part of the brain that controls homeostasis is the:
32. Know the parts of the brain from a diagram
III. Nerve subjective questions
1. List the differences between the following:
a. sensory neuron/motor neuron
b. interneuron/sensory neuron
c. depolarization/repolarization
d. interneuron/motor neuron
e. acetylcholinesterase/adrenalin
f. spinal/cranial nerves
g. adrenalin and acetycholine
h. autonomic and somatic nervous systems
2. Describe the events that occur during resting potential
3. Describe, in detail, what occurs during the passage of a nerve impulse between 2 neurons.
4. Explain why a nerve impulse can only travel in one direction.
5. Explain how a chemical could disrupt the transmission of a nerve impulse
6. Describe the chemical and physical events that occur during action potential
7. Define reflex. Describe the sequence of events during a reflex action
8. Describe the physical and chemical events happening to the nerve membrane and what is
happening inside and outside the nerve axon during the following: a. resting potential b. action
potential
9. Describe the changes that would occur in the: membrane surrounding the axon; distribution and
kinds of ions inside and outside the membrane and; polarity inside and outside the axon, during the
following.
a. An action potential is generated and travels down an axon
b. After the action potential has passed and resting potential is being re-established
10. Be able to identify the parts of a neuron from a diagram and their functions
11. List 4 differences between the Central and Peripheral nervous systems.
12. List 4 difference between the sympathetic and parasympathetic nervous systems
13. From a diagram of the brain or Neuron recognize the parts and describe their functions
IV. Nerve Vocabulary
Acetylcholinesterase (AChE) (same as cholinesterase)
action potential (upswing)
action potential (downswing)
axon
axoplasm
cell body
central nervous system
cerebellum
cerebrum
cerebral cortex
corpus callosum
dendrite
depolarization
effectors
hypothalamus
interneuron
medulla oblongata
motor neuron
myelin sheath
neurotransmitter
parasympathetic nervous system
peripheral nervous system
pituitary gland
polarization
postynaptic membrane
presynaptic membrane
reflex arc
refractory period
repolarization
resting potential
sensory neuron
sodium/potassium pump
somatic nervous system
spinal nerves
sympathetic nervous system
synaptic cleft
temporal lobe
thalamus