Chapter 58 Flashcards
What are the 2 ways the cerebrum can be excited from the reticular formation?
- 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?
reticulospinal
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?
coma
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?
gigantocellular input
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?
serotonin
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?
- Backward and downward into the reticular areas of the mesencephalon, pons and medulla (brain stem)into peripheral nerves of the ANS
- Upward towards 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 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?
- 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 - By controlling the excretion of water into the urine
Supraoptic nuclei becomes stimulated when body fluids become too concentration
