Flashcards in Chapter 58 Deck (45):
What are the 2 ways the cerebrum can be excited from the reticular formation?
1. rapidly transmitted action potential
2. neurohormonal excitatiory signals that can build up
How does the rapidly tranmitted AP excite the cerebrym from the reitcular formation?
i. This excitatory signal excites the cerebrum for milliseconds with ACh
ii. Originates from large neuronal cell bodies that lie throughout the brainstem
iii. Activate thalamus first which then activates the cerebral cx
How do neurohormonal excitatory signals, that are built up, excite the cerebrum?
i. This excitatory signal is able to build up progressively for seconds to minutes
1. These signals are important for controlling longer-term background excitability levels of the brain
ii. Originates from small neurons in brainstem reticular excitatory area
iii. Pass to thalamus via small slow conducting fibers which synapse mainly in the intralaminar nuclei of the thalamus and in the reticular nuclei over the surface of the thalamus
The gigantocellular nucleus sends descending cholinergic projections to create the excitatory portion of which tract?
These neurons in the reticulospinal tract send ascending cholinergic projections via the thalamus to the entire cortex and other parts of the brain to control what?
the level of excitability
What if you lesion this tract?
What are the input signals to the brainstem reticular formation excitatory area?
a. The excitatory area of the brainstem (and so the whole brain) is determined by the number and type of sensory signals that enter the brain from the periphery
i. Ex: pain signals increase activity in the excitatory area, so they excite the brain to attn.
What happens if u have a lesion above CN V where it exits the pons?
the level of activity of the brainstem excitatory area diminishes
What happens if u have a lesion below CN V where it exits the pons?
this leaves sensory input from the face and oral regions to the excitatory area, which is enough sensory input to the excitatory area to allow for brain stimulation, which avoids coma
What is the excitatory loop between the cerebral Cx and the reticular formation?
a. Again, the Reticular Excitatory Area of the Brainstem is what stimulates the cerebral cx. But what also happens is the cerebral cx sends feedback signals to the reticular excitatory area exciting it.
b. So whenever the cerebral cx is excited it will send feedback signals to the reticular excitatory area, and the reticular excitatory area will send still more excitatory signals back to the cx, this is a positive feedback loop.
Whaat is the reson for this loop?
c. The reason for this loop is to maintain the level of excitation of the cerebral cx or even enhance it leading to the Awake Mind
What is the role of the thalamus in the excitatory response?
a. First remember that the reticular excitatory area of the brainstem sends input to the thalamus first, and it is the thalamus that directly activates the cerebral cx. Also the inputs between the thalamus and cx reverberate, that is the thalamus excites the cx and the cx sends input to the thalamus and excites it.
i. It is this reverberating back forth that may lead to long-term memories
b. Figure 57-2 shows the thalamus mapped on the cerebral cx, stimulation of specific point in the thalamus will activate a specific region of the cx.
c. The thalamus may also function to call forth specific memories from the cortex or to activate specific thought processes, but this is unproven
In additional to relaying information to various parts of the brain, the thalamus controls the sequence of activation for any task by modulating which input to the relevant areas of the Cx?
What is the role of reticular inhibitory neurons ?
c. The reticular inhibitory area can inhibit the reticular excitatory area of the upper brain stem and thereby decrease activity in the superior portions of the brain as well
Which NT does the reticular inhibitory neurons use?
What is the location, NT, primary target and effect of locus ceruleus?
i. Location of release: the locus ceruleus is located bilaterally and posteriorly at the juncture between the pons and mesencephalon and sends nerve fibers all over brain
ii. NT released: NE
iii. Primary target: excites brain to increase activity
iv. Effect: brain excitation and REM sleep
What is the location, NT, primary target and effect of the substantia nigra?
i. Location of release: anteriorly in the superior mesencephalon
ii. NT released: Dopamine
iii. Primary target: caudate nucleus and putamen of the cerebrum
iv. Effect: inhibitory in basal ganglia
What is the location, NT, primary target and effect of the raphe nuclei
i. Location of release: raphe nuc is located in the midline of the pons and medulla, and send fibers to diencephalon and cerebral cx and down cord
ii. NT released: Serotonin
iii. Primary target: diencephalon, cerebrum, and cord
iv. Effect: normal sleep patterns when released in diencephalon and cerebrum, also pain suppression in cord
What is the location, NT, primary target and effect of the gigantocellular nuclei?
i. Location of release: the gigantocelluar (giant cells) are located in the reticular excitatory area of the pons and mesencephalon, and send fibers up to higher brain levels and down the RST into the cord.
ii. NT released: ACh
iii. Primary target: brain and cord
iv. Effect: excitatory leading to acutely awake and excited nervous system
What is the fxn of the limbic system?
a. The limbic system is the neuronal circuitry that controls emotional behavior and motivational drives, it also controls many internal conditions of the body (temp, osmolality of fluids), and drives us to eat and drink, and controls body weight.
What are the 3 outputs of the hypothalamus?
1. Backward and downward into the reticular areas of the mesencephalon, pons and medulla (brain stem)into peripheral nerves of the ANS
2. Upward towards many higher areas of the diencephalon and cerebrum, especially to the anterior thalamus and limbic portions of the cerebral cortex
3. Into the hypothalamic infundibulum to control or partially control most of the secretory functions of both the posterior and anterior pituitary gland
How does the hypothalamus regulate BP?
Stimulation in the posterior and lateral hypothalamus increases the arterial pressure and heart rate
Stimulation in the preoptic area causes decrease in arterial pressure and heart rate
These effects are transmitted through specific cardiovascular control center in the reticular regions of the pons & medulla.
How does the hypothalamus regulate body temp?
Preoptic area is concerned with regulation of body temperature.
An increase in the temperature of the blood flowing through this area increases the activity of temperature-sensitive neurons and vice versa.
How does the hypothalamus regulate body water?
1. By creating the sensation of thirst
Thirst center is located in the lateral hypothalamus when fluid electrolytes become too concentrated in this center that will cause you to become thirsty
2. By controlling the excretion of water into the urine
Supraoptic nuclei becomes stimulated when body fluids become too concentration
How does the hypothalamus regulate feeding?
1. Lateral hypothalamic area: associated with hunger
Damage to lateral hypothalamic area on both sides of the hypothalamus causes you to lose desire for food (causes lethal starvation)
2. Ventromedial nuclei-satiety center opposes the desire for food. If this area is destroyed bilaterally you have huge appetite, resulting in obesity.
3. Mammillary bodies- control feeding reflexes such as licking the lips and swallowing.
How does the hypothalamus regulate the anterior pituitary?
The anterior pituitary gland receives its blood supply mainly from blood that flows first through the lower part of the hypothalamus and then through then through the anterior pituitary vascular sinuses and as it courses through, it releases excitatory or inhibitory hormones to control specific anterior pituitary hormones.
So what happens if we stimulate the lateral N?
Causes thirst and eating
Increases the general level of activity and can cause rage and fighting
Bilateral lesion will decrease drinking and eating almost to zero lethal starvation
Makes one VERY passive with loss of most of its overt drives
So what happens if we stimulate the vetnromedial N?
Opposite of lateral: satiety (satisfaction), decreased eating and tranquility
Bilateral lesion will cause one to drink and eat excessively, hyperactivity and extreme rage
So what happens if we stimulate the periventricular N?
Located immediately adjacent to the third ventricle
Fear and punishment reactions
Which nuclei are associated with the sex drive?
Several areas of the hypothalamus especially the most anterior and most posterior portion
Where is the major reward system for the hypothalamus?
Major reward center is located long the course of the medial forebrain bundle, especially in the lateral and ventromedial nuclei of the hypothalamus.
Where is the major punishment center?
Most potent area for punishment is in the central gray area surrounding the aqueduct of Sylvius (cerebral aqueduct) extending upward into periventricular zone of hypothalamus and thalamus.
Where is the major rage center?
STRONG stimulation of the punishment center of the brain especially in the periventricular zone of the hypothalamus and in the lateral hypothalamus.
What happens if the reward or punishment center is tranquilized?
Cholorpormazine, a tranquilizer inhibits both reward and punishment center thus decreasing the affective reactivity (numbed) of the animal so it is presumed that it suppresses many of the important behavioral areas of the hypothalamus and its associated regions of the limbic system.
What is the fxn of the hippocampus in memory?
Hippocampus provides the drive that causes translation of short-term memory into long term memory. It transmits some signal that makes the mind rehearse the new information over and over again until permanent storage takes place.
Lesions of the hippocampus cause anterograde amnesia of what type of memories?
What is the role of the amygdala for behavioral responses?
Amygdala is believed to make the person’s behavioral response appropriate for each occasion.
Stimulation of amygdala mediated through hypothalamus causes what Sx?
1. Increase or decrease in arterial pressure
2. Increase or decrease in heart rate
3. Increase or decrease in GI motility and secretion
4. Defecation or micturition
5. Pupillary dilation or constriction (constriction is more rare)
7. Secretion of various ant pituitary hormones
Especially Gonadotropins and adrenocorticotropic hormones
What type of involuntary movements can occur with stimulation of the amygdala?
1. Tonic movement (raising the head or bending the body)
2. Circling movements
3. Occasionally clonic, rhythmical movements
4. Movements associated with olfaction and eating (licking, chewing & swallowing)
Bilateral lesions of the amygdala can cause what syndrome?
Kluver Bucy syndrome
What are the Sx of Kluver Bucy syndrome?
1. Not afraid of anything
2. Has extreme curiosity of about everything
3. Forgets rapidly
4. Has a tendency to place everything it its mouth and sometimes even tries to eat solid objects
5. Often has a sex drive so strong that it tries to have sex with young animal, wrong sex or different species
What is the main fxn of the limbic Cx?
Association area for control of behavior
What are the Sx of lesion to the anterior Cx?
What are the Sx of lesion to the posterior orbital frontal Cx?
Bilateral- insomnia associated with intense motor restlessness, keeps on moving around