life science chapter 21 the nervous system
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The Nervous SystemThe Nervous System
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Neuron – working unit of the nervous system
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Axon – carries messages away from the cell body
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dendrites – receive the messages and send them to the cell body
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Terminal Bud – send messages to other neurons
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3 types of neurons
• Sensory neurons – send info to the spinal cord or brain
• Interneurons – send info out of brain and spinal cords to the motor neurons
• Motor neurons – send info from brain and spinal cord to muscles or glands
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Sensory neuron (hand)
Motor neuron
(arm)
Interneuron
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Synapse
• Small space in between neurons
• Neurotransmitters are released in the synapse and starts an impulse in the next neuron
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Synapse
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Divisions of the Nervous System
CNS – central nervous system – brain and spinal cord
PNS – peripheral nervous system – all the nerves outside the CNS
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Central Nervous System
• Brain 100 billion neurons
• 3 major parts
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1. Cerebrum
• Divided into hemispheres
• Memory is stored
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Cerebrum
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2. Cerebellum
• Under the cerebrum
• Coordinated voluntary muscle movements
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3. Brainstem
• Connects the brain to the spinal cord
• Made up of the – Mid brain– Pons– Medulla
• Controls homeostasis of heart, breathing, blood pressure, involuntary muscle movements
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Peripheral Nervous System
• 2 divisions of the peripheral nervous system
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Peripheral
Nervous System
Somatic
Nervous System
Skeletal Muscle
Autonomic
Nervous System
Heartrate, breathing, digestion, salivary glands
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Reflex
• Involuntary response to a stimulus
• Involves a pathway called a (reflex arc) over which impulses travel
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Reflex arc
1. Impulse is sent to the spinal cord
2. Impulse passes to an interneuron in the spinal cord which immediately relays the impulse to motor neurons
3. Motor neurons transmit the impulse to muscles in your arm
4. Your arm pulls back (Without thinking!)
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Steps of a reflex arc1. Receptor
2. Sensory neuron
3. Interneuron (spinal cord)
4. Motor neuron
5. Effector – “response”
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Your Endocrine System
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Endocrine system
• System of glands that release their products into the blood stream and broadcast messages throughout the body
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Hormones
• Affect specific tissues called target cells
Target cells – control activities in parts of the body other than right around the gland
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Glands of the Endocrine System
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Hypothalamus• Part of the brain
• Produces hormones that influence the pituitary gland
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Pituitary Gland• “Master Gland”
• Secretes numerous hormones
• Growth-stimulating Hormone
• Hormones to control specific glands
• Thyroid Stimulating Hormone (TSH)– Tells thyroid to produce thyroxine
• The Follicle Stimulating Hormone– Stimulates activity in the ovary and testes
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Thyroid Gland• Located in the neck
• Makes thyroxine
• Regulates metabolism
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Parathyroid Glands• Embedded in the thyroid gland• Secrete parathormone• Controls the metabolism of calcium• Necessary for nerve function,
blood clotting, and proper growth of teeth and bones
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Adrenal Glands• Two glands located on top of the
kidneys
• Each gland has 2 distinct regions
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Adrenal Cortex• Secretes two types of steroid hormones
1. promotes the conversion of body fat and protein into glucose
2. promotes the reabsorbtion into the blood stream of sodium and chloride ions by the kidney tubules
– This affects the water balance and maintains BP
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Adrenal Medulla• Secretes adrenalin in times of
emergency
• Increases the blood sugar level
• Speeds heart and breathing rates
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Islets of Langerhans• Located in the pancreas
• Secrete insulin and glucagon
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Insulin• Helps take glucose into cells
• Lowers blood sugar levels by taking it out of the blood and storing it in the liver and muscle cells
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Glucagon• Stimulates the release of sugar
from the liver
• Raises blood sugar level
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Gonads• Sex glands• Testes • Secrete testosterone – develop male
secondary sex characteristics• Ovaries• Secrete estrogen - develop female
secondary sex characteristics
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Endocrine Control• Negative feedback system
• Controls the amount of hormone an endocrine gland produces
• Works like a thermostat in your house
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Negative feedback system
Start: 1. Hormone level low
2. Hormone production increases
3. Hormone level high
4. Hormone production slowed down
End: 5. Hormone level low
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Endocrine Feedback System of TSH
Hypothalamus
Pituitary Gland
Thyroid
Stimulating
Hormone
Thyroid Gland
Thyroxin
stimulates
Inhibits
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Endocrine System Disorders
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Goiter• Enlargement of the thyroid gland
• Results in not being able to make thyroxine
• Often associated with iodine deficiency in the diet
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Diabetes• Insulin deficiency
• Results in an elevated blood sugar level
• Also an inability of the body to store the sugar glycogen in the liver
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