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. 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) 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:) Sensory Neuron Motor Neuron Cell body outside CNS Long myelinated dendrite Short partially myelinated axon Carries impulses towards CNS 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
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 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