Download UNIT 9 – EXCRETORY SYSTEM

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Chapter 12 Nervous System Written Assignment KEY
1. Describe, in correct order, the events that occur during the transmission of a nerve
impulse (action potential) as it travels from point X to point Y. (6 marks)
_____________________________________________________________________________The
neuron is at resting potential when the voltage is -70mV and there is a greater concentration of
sodium ions outside the neuron and greater concentration of potassium ions inside the neuron.
When there is stimulation of the neuron (either due to neurotransmitters or receptors),
depolarization begins when the sodium gates open and sodium rushes into the neuron by diffusion. If
enough sodium enters the neuron for the potential to go up past threshold, a full depolarization
continues to +30 mV.
Repolarization begins when the sodium gates close and the potassium gates open to allow a
rush of potassium out of the neuron. The potential decreases to -70mV or less.
Refractory is when the sodium-potassium pumps actively transport sodium back out and
potassium back into the neuron to restore the ion distribution and resting potential.
This action potential occurs from X to Y at the nodes of Ranvier which speed up the
transmission of the impulse along the neuron.
2. Describe the process that occurs to transmit an action potential between two neurons as
shown in the picture below.
(6 marks)
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When the action potential reaches the axon bulb the following occurs to transmit the action potential
to the next neuron.
1. Calcium gates open and calcium rushes into the bulb
2. The vesicles carrying neurotransmitter (NT) are pulled towards the pre-synaptic
membrane
3. Exocytosis of the NT occurs into the synaptic cleft
4. NT diffuses across the cleft to the post-synaptic membrane
5. The NT attaches to receptors on the sodium gates causing them to open
6. Sodium rushes into the next neuron initiating depolarization (as long as threshold is met)
and the action potential continues
3. Compare and contrast motor and sensory neurons.
(4 marks:)
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Sensory Neuron
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Cell body outside CNS
Long myelinated dendrite
Short partially myelinated axon
Carries impulses towards CNS
Motor Neuron
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Cell body inside CNS
Short unmyelinated dendrites
Long myelinated axon
Carries impulses away from
CNS
4. a) Name the “fight-or-flight” division of the nervous system, identify the hormone involved,
state the source of this hormone and give three effects that the hormone has on the body.
(6 marks)
division name: _sympathetic__
hormone: _norepinephrine (epinephrine or adrenalin)__
source gland:_adrenal gland (adrenal cortex)__
3 effects:
i)__increased heartrate_____
ii)__decreased digestion/peristalsis_____
iii)__pupils dilate_____
b) Name the “relaxed or digestive state” division of the nervous system, identify the hormone
involved, and give three effects that the hormone has on the body.
(5 marks)
division name: __parasympathetic ___
hormone: __acetylcholine__
3 effects on body:
i)______decreased heartrate_______
ii)____increased digestion/peristalsis____
iii)___pupils constrict_________
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5. Label and describe functions of the structures in the brain diagram below.
SEE CLASS NOTES FOR FUNCTIONS
(11 marks)
1. __cerebrum – thinking, processing senses, decision making, personality, emotions
2. __corpus callosum – connects the right and left hemispheres of cerebrum
3. __ventricle – produces and stores the cerebrospinal fluid
4. ____hypothalamus – controls/regulates the homeostasis; water balance, hunger,
thirst, temperature, sleep, reproductive hormones
5. _thalamus – sorts incoming sensory stimuli to appropriate areas of the cerebrum
6. __pituitary gland – secretes hormones and is stimulated by the hypothalamus
7. ___pons – helps the medulla oblongata functions and involved in head relfexes
8. ___medulla oblongata – regulates heart rate and breathing
9. ____spinal cord – carries messages (action potentials) to and from the brain
10. ____cerebellum – controls motor movements, balance, posture, muscle tone and
learning new motor skills
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11. __midbrain – relay station for allowing communication between the cerebellum, brain
stem, and cerebrum
6. Describe a simple reflex arc naming all structures in the pathway. (5 marks)
1. sensory receptors detect change in external or internal environment
2. action potential carried along sensory neuron towards CNS
3. action potential transmitted through interneuron in spinal cord or brain but does not go to higher
brain centres for processing until after the reflex
4. action potential continues on motor neuron away from CNS toward effector
5. effector receives impulse and a coordinated response occurs to complete the reflex