16

Question 1

Reticular formation formed

Answer 1

formed of a large number of diffuse neurons (sensory and
motor) in the brain stem..

Question 2

Reticular formation extend upward lower to ?

Answer 2

extend upward extend upward to the thalamus, sub thalamus, hypothalamus & cerebral cortex.

•The lower end continues with the inter-neurons of the spinal cord.

Question 3

Functions of R.F.:

Answer 3

1- Support the body weight against gravity:
2-Reticular Activating system (RAS):

3-Neurohormonal Control of Brain Activity

Question 4

Support the body weight against gravity:
The reticular nuclei are divided into two major groups:

Answer 4

(1) Pontine reticular nuclei.
(2) Medullary reticular nuclei.

These two sets of nuclei function mainly antagonistically to each other, with the pontine exciting the antigravity muscles supporting the body against gravity without any signals from higher levels of the brain.

The medullary nuclei relax these same muscles, so that under normal conditions body muscles are not abnormally tense.

Question 5

Reticular Activating system (RAS):?

receives impulses from:

Answer 5

is a part of the reticular formation which is essential for the initiation and maintenance of consciousness through polysynaptic system of nerve fibers that extend upward from the brain stem.

receives impulses from: receives impulses from: Special senses & somatic sensations.

Impulses from RAS pass diffusely to the whole cerebral cortex controlling its overall activity.

Question 6

Connections of RF

Main inputs of reticular formation:

Main out puts of reticular formation:

Answer 6

Main inputs of reticular formation:
1- from all sensory pathways:
2- From cerebellum, basal ganglia & cerebral cortex.
3- From vestibular nucleus.

Main out puts of reticular formation:
1- To the Spinal cord (Reticulospinal tracts):
ventral (facilitatory) & lateral (inhibitory).
2- To the cerebral cortex (RAS):
arise from facilitatory R.F. & terminate diffusely in all areas of cerebral cortex.
3- To the cerebellum:

Question 7

R.A.S is activated by:

Answer 7

R.A.S is activated by:
1- Sensory signals specially pain.
2- Sympathomimetics: E. & N.E. secreted during stress.
3- Impulses from cerebral cortex:
a- limbic lobe: inability of sleep by emotional reaction.
b- motor cortex: voluntary movement resist desire
to sleep.

Question 8

Reticular Excitatory Area of the Brain Stem

Answer 8

The central driving component of this system is an excitatory area located in the reticular substance of the pons and mesencephalon.

•This area → facilitatory signals downward → spinal cord → to maintain the tone in the antigravity muscles and to control spinal cord reflexes.

•This area also → signals in the upward direction. → the thalamus, → to all regions of the cerebral cortex as well as to multiple subcortical areas.

•The Cerebral Cortex send Feedback Signals To Increase Activity of the Excitatory Area.

•The Thalamus act as a distributing center for the excitatory area

Question 9

Neurohormonal systems in the brain stem
Include :

Answer 9

1. Norepinephrine system,
   2.Dopamine system, and
   3.Serotonin system.
   4.The Gigantocellular neurons of the reticular excitatory area and the acetylcholine system

Question 10

Other Neurotransmitters Secreted in the Brain

Answer 10

1. Enkephalins,
2. Gamma-aminobutyric acid,
3. Glutamate,
4. Vasopressin,
5. Adrenocorticotropic hormone,
6. Histamine,
7. Endorphins,
8. Angiotensin II, and
9. Neurotensin.

Question 11

Acetyl Choline System from

Answer 11

Gigantocellular neurons of the reticular excitatory area
fibers from these large cells divide immediately into two branches, one passing upward to the higher levels of the brain and the other passing downward through the reticulospinal tracts into the spinal cord.

Question 12

Dopamine system from

Answer 12

(The substantia nigra)
•It lies anteriorly in the superior mesencephalon, and its neurons send nerve endings mainly to the caudate nucleus and putamen of the cerebrum, where they secrete dopamine.

• They send their endings into more ventral areas of the brain, especially to the hypothalamus and the limbic system.

•The dopamine is believed to act as an inhibitory transmitter in the basal ganglia, but in some other areas of the brain it is possibly excitatory.

Question 13

Serotonin system from

Answer 13

Midline Raphe Nuclei)

Many of the neurons in these nuclei secrete serotonin. They send fibers into the diencephalon and a few fibers to the cerebral cortex; still other fibers descend to the spinal cord.
•The serotonin secreted at the cord fiber endings has the ability to suppress pain.
•The serotonin released in the diencephalon and cerebrum almost certainly plays an essential inhibitory role to help cause normal sleep

Question 14

Norepinephrine from

Answer 14

Locus Cerulus)
•Small area located bilaterally and posteriorly at the juncture between the pons and mesencephalon.
•Nerve fibers from this area spread throughout the brain.
•The norepinephrine generally excites the brain to increased activity. However, it has inhibitory effects in a few brain areas
•This system probably plays an important role in causing dreaming, thus leading to a type of sleep called rapid eye movement (REM) sleep.