Guyton Chapter 58 Behavioral And Motivational Mechanisms Flashcards
Nerve signals in the brain stem activate the cerebral part of the brain in two ways - which ways?
- By directly stimulating a background level of neuronal activity in wide areas of the brain
- By activating neurohormonal systems that release specific facilitory or inhibitory hormone like neuro transmitter substances into selected areas of the brain.
Control of cerebral activity by continuous excitatory signals from the brain stem. What is the central driving component of this system?
An excitatory area located in the reticular substance of the pons and mesencephalon. This area is also known by the name bulboreticular facilitory area.
The signals passing through the thalamus are of two types. Name them and their characteristics.
One type is rapidly transmitted action potentials that excite the cerebrum for only a few milliseconds. These originate from large neuronal cell bodies that lie throughout the brain stem reticular area. Their nerve endings release acetylcholine which serves as an excitatory agent.
The second type of excitatory signals originates from large numbers of small neurons spread throughout the brain stem reticular excitatory area. These pass through the thalamus but through small slowly conducting fibers that synapse mainly in the intralaminar nuclei of the thalamus and in the reticular nuclei over the surface of the thalamus.
Describe if norepinephrine, dopamine and serotonin are excitatory or inhibitory?
Norepinephrine - excitatory
Serotonin - inhibitory
Dopamine- excitatory in some areas but inhibitory in some areas
Describe the locus ceruleus and the norepinephrine system:
Small area located bilaterally and posteriorly at the juncture between the pons and mesencephalon.
Nerve fibres from this area spread throughout the brain and they secrete norepinephrine that generally excites the brain to increased activity (inhibitory effects in a few brain areas).
Describe the location and effects of substantia nigra and the dopamine system.
It lies anteriorly in the superior mesencephalon and it’s neurons send nerve endings mainly to the caudate nucleus and putamen of cerebrum where they secrete dopamine. The dopamine is believed to act as an inhibitory transmitter in the basal ganglia but in some other areas of the brain, it’s possibly excitatory.
What is the raphe nuclei and the serotonin system?
Are several raphe nuclei in the midline of the pons and the medulla.
Many of the neurons in these nuclei secrete serotonin. They send fibers into the diencephalon and a few fibers to the cerebral cortex.
What is the gigantocellular neurons of the reticular excitatory area and the acetylcholine system?
Reticular excitatory area of the pons and mesencephalon. The fibres from these large cells divide into two branches. One passes upward to the higher levels of the brain and the other passing downward through the reticulospinal tracts into the spinal cord.
Acetylcholine is secreted at their terminals and is mostly excitatory.
What is one of the most central elements of the limbic system?
Hypothalamus
What is an important route of communication between the limbic system and the brain stem?
The medial forebrain bundle which extends from the septal and orbitofrontal regions of the cerebral cortex downward through the middle of the hypothalamus to the brain stem reticular formation.
Describe the 3 pathways that the hypothalamus and its closely allied structures send output signals to:
- Backward and downward to the brain stem mainly into the reticular areas of the mesencephalon, pons, and medulla and from these areas into the peripheral nerves of the autonomic nervous system.
- Upward toward many higher areas of the diencephalon and cerebrum especially to the anterior thalamus and limbic portions of the cerebral cortex.
- Into the hypothalamic infundibulum to control or partially control most of the secretory functions of both the posterior and the anterior pituitary glands.
What is the limbic cortex composed of?
A ring of cerebral cortex in each side of the brain 1. Beginning in the orbitofrontal area on the ventral surface of the frontal lobes, 2. Extending upward into the subcallosal gyrus, 3. Then over the top of the corpus callosum onto the medial aspect of the cerebral hemisphere in the cingulate gyrus and finally 4. Passing behind the corpus callosum and downward onto the ventromedial surface of the temporal lobe to the parahippocampal gyrus and uncus.
What is the medial forebrain bundle?
An important route of communication between the limbic system and the brain stem. It extends from the septal and orbitofrontal regions of the cerebral cortex downward through the middle of the hypothalamus to the brain stem reticular formation.
Where does the hypothalamus send output signals to?
- Backward and downward to the brain stem mainly into the reticular area of the mesencephalon, pons and medulla and from these areas into the peripheral nerves of the autonomic nervous system.
- Upward toward many higher areas of the diencephalon and cerebrum especially to the anterior thalamus and the limbic portions of the cerebral cortex.
- Into the hypothalamic infundibulum to control or partially control most of the secretory functions of both the posterior and anterior pituitary glands.
How does stimulation in the posterior and lateral hypothalamus increase the arterial pressure and heart rate?
Increases the arterial pressure and heart rate.
