Divisions of The Nervous System

Parasympathetic Neurons Bases of Comparison Sympathetic Neurons Parasympathetic Neurons Effect Active body function “fight or flight” Normal activity “rest and digest”   Neurotransmitter Noradrenalin Acetylcholine Restoring enzyme Monoamine oxidase Acetylcholinesterase SAME Function automatically (involuntary) Serve all internal organs   Serve all internal organs 

Fight or Flight Adrenal Glands Sudden simultaneous release of noradrenalin from all the sympathetic neurons (as in times of fright) has a critical effect.

It causes the release of the hormone adrenalin from the interior of the adrenal glands located on top of the kidneys. The noradrenalin and the adrenalin initiate and sustain what is known as the ‘Fight or Flight” response.

They prepare the body to respond to danger in the following ways: 1. Increase heart rate so that more blood is supplied to the body more quickly. Widen air passageways so that more air can be exchanged with each breath.

3. Sudden contraction of some muscles to tense the body up for action 3. Sudden contraction of some muscles to tense the body up for action. Included in this is the contraction of the diaphragm. A scared person will gasp, inhaling suddenly.

The iris of the eye contracts thus widening the pupil to maximize visual alertness. 5. Increased blood flow to the skeletal muscles so they are more able to act. 6.  Decreased digestive activity, circulation and control.

Brain:   Medulla Oblongata -Brain Stem (bottom of the brain) -Pathway between brain and spinal cord -Controls: Vomiting, coughing, sneezing, hiccoughing, swallowing. -Controls: Heartbeat rate, breathing, and blood pressure.

Cerebellum -Butterfly shaped -Rear, lower portion of the brain -Second largest portion of the brain -Controls: Muscle co-ordination (smooth graceful motions) muscle tone, balance and posture.

Hypothalamus -Located just above the pituitary gland. -Controls: The pituitary gland and production of hormones Hunger, thirst, sleep, body temp, water balance, and BP. Maintains homeostasis by controlling endocrine system (more later)

Thalamus -Above the hypothalamus -Controls: Relay station for information going to the cerebrum. Channels info to appropriate place and prevents sensory overload.

Cerebrum -Largest part of the brain -Controls: Conscious thought Perceives sensory information Initiates movements -Contains 2 hemispheres (Right and left) -Memory

Parts: 1. Frontal Lobe- Conscious thought 2.  Parietal Lobe – Temperature, Touch and Pain 3.  Temporal Lobe – Hearing and smelling 4.  Occipital Lobe – Vision

Corpus Callosum -Holds the hemispheres of the Cerebrum together -Conducts impulses from one side of the brain to the other.

Neuroendocrine Control There is an association between nerve tissue and the body’s hormones (endocrine = hormonal). This association is between the hypothalamus (below the thalamus) and the pituitary gland.  

It can be seen that there are two lobes of the pituitary gland: an anterior and a posterior lobe. Both of these extend down from the hypothalamus.

As blood passes through the hypothalamus , its composition and temperature stimulate various homeostatic responses. Homeostasis is the process of keeping the body conditions the same ie temperature, blood glucose levels, blood pressure etc. Those responses involve the release of hormones, which are chemical messengers traveling through the blood to affect other organs.

The anterior pituitary releases six major hormones that range in effect from bringing about reproductive changes to skeletal growth. The posterior pituitary releases two hormones.  

Unit P Unit O Unit P Unit H

Hormonal Control and Negative Feedback help to Maintain Homeostasis   Negative feedback mechanisms act like a thermostat in the home. As the temperature rises (deviation from the ideal normal value), the thermostat detects the change and triggers the air-conditioning to turn on and cool the house. Once the temperature reaches its thermostat setting (ideal normal value), the air conditioning turns off.

The thyroid gland secretes thyroxin (which controls the metabolic rate) into the bloodstream. Low levels of thyroxin are detected by the hypothalamus in the brain to release a hormone (TRH - thyroid releasing hormone) that acts on the pituitary gland to release thyroid-stimulating hormone (TSH) into the blood.

TSH acts on the thyroid, causing it to increase production of thyroxin TSH acts on the thyroid, causing it to increase production of thyroxin.  Once the levels of thyroxin are restored, these levels no longer stimulate the receptors in the brain/hypothalamus and so no more TSH is released.   

Quick Review Questions

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D Hypothalamus would NOT make ADH (antidiuretic hormone) and would NOT send it to the posterior pituitary gland. ADH would NOT be released which would cause the collecting duct in the nephron in the kidneys to be relatively impermeable to water. The urine would be more dilute and less water would be taken back into the body. Did I trick anyone? … haha? 

3 Regions of The Brain

The forebrain consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system). The midbrain consists of the tectum and tegmentum. Acts as a relay station between cerebrum, spinal cord and cerebellum. The hindbrain is made of the cerebellum, pons and medulla. Often the midbrain, pons, and medulla are referred to together as the brainstem.

What makes humans distinctive in animal world? Is it the size of brain?

Not really … (elephant and whales are larger) Has to do with the size, increase in the folds of the cortex and the cortex’s ratio of the brain’s total weight. (i.e. In shrews, the cortex accounts for 20% of the brain's weight, and in humans, it accounts for 80%!) The increased folds, enable a larger cortical surface area to fit inside the cranial vault, allow for a better organization of complex behaviours.