Activating driving systems of the brain.

1. ACTIVATING-DRIVING
SYSTEMS OFTHE BRAIN
Presented By:
Muhammad SanaUllah

2. ACTIVATING-DRIVING
SYSTEMS OFTHE BRAIN
• Without continuous transmission of nerve signals from the
lower brain into the cerebrum, the cerebrum becomes useless.
Nerve signals in the brain stem activate the cerebral part of the
brain in two ways:
• (1) by directly stimulating a background level of
neuronal activity in wide areas of the brain and
• (2) by activating neurohormonal systems that release
specific facillitatory or inhibitory hormone-like
neurotransmitter substances into selected areas of the
brain.

4. RETICULAR EXCITATORY AREA OFTHE
BRAIN STEM
Is an excitatory area located in the reticular substance of the pons and
mesencephalon. (also called bulboreticular facilitory area).
Transmits facillitory signals downward to the spinal cord to
maintain tone in the antigravity muscles and to control levels of activity of
the spinal cord reflexes.
It also sends a profusion of signals in the upward direction.
Most of these go first to the thalamus, where they excite a different set
of neurons that transmit nerve signals to all regions of the
cerebral cortex, as well as to multiple subcortical areas.

5. THE SIGNALS PASSINGTHROUGHTHE
THALAMUS ARE OFTWOTYPES.
• One type is rapidly
transmitted action potentials
that excite the cerebrum for
only a few milliseconds
• From large neuronal cell
bodies
• Acetylcholine is the
neurotransmitter
• Second type of excitatory
signal originates from small
neurons spread throughout
the brain stem reticular
excitatory area.
• slowly conducting fibers
synapse mainly in the
intralaminar nuclei of the
thalamus
• longer-term background
excitability level of the brain

6. • The signals passing through the thalamus are of two types.
• 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 the neurotransmitter substance
acetylcholine, which serves as an excitatory agent, lasting for only a few
milliseconds before it is destroyed.

7. The second type of excitatory signal originates from large numbers of
small neurons spread throughout the brain stem reticular
excitatory area.
These are slowly conducting fibers that synapse mainly in the intralaminar
nuclei of the thalamus and in the reticular nuclei over the surface
of the thalamus.
The excitatory effect of these is especially important for
controlling longer-term background excitability level of the brain.

8. EXCITATION OFTHE
EXCITATORY AREA BY
PERIPHERAL SENSORY SIGNALS
Excitability of brain stem &
in turn cerebrum
depend on the number and
type of sensory signals from the periphery
Pain signals in particular increase activity in this
excitatory area and therefore strongly excite the
brain to attention.

9. INCREASED ACTIVITY OFTHE
EXCITATORY AREA CAUSED BY
FEEDBACK SIGNALS RETURNING
FROMTHE CEREBRAL CORTEX
• Signals are sent from the cortex to the brain stem
excitatory area, which in turn sends still more excitatory
signals to the cortex.
• This is a general mechanism of positive feedback
that allows any beginning activity in the cerebral
cortex to support still more activity, thus leading to
an "awake" mind.

10. A RETICULAR INHIBITORY AREA
IS LOCATED INTHE LOWER
BRAIN STEM
• This is the reticular inhibitory area, located medially
and ventrally in the medulla.
• This area can inhibit the reticular facilitory area of the
upper brain stem and thereby decrease activity in the
superior portions of the brain as well.
• One of the mechanisms for this is to excite serotonergic
neurons; these in turn secrete the inhibitory
neurohormone serotonin at crucial points in the
brain.

11. In addition to these areas there are different
neurohormonal systems

12. NEUROHORMONAL SYSTEMS INTHE
HUMAN BRAIN

13. The locus ceruleus and the norepinephrine system.
The locus ceruleus is a small area located bilaterally and posteriorly at the
juncture between the pons and mesencephalon. Nerve fibers from this
area spread throughout the brain, they secrete norepinephrine.
The norepinephrine generally excites the brain to increased activity.
However, it has inhibitory effects in a few brain areas because of inhibitory
receptors at certain neuronal synapses.
This system probably plays an important role in causing dreaming, thus
leading to a type of sleep called rapid eye movement sleep (REM sleep).

14. The substantia nigra and the dopamine system
They secrete dopamine. Other neurons located in
adjacent regions also secrete dopamine, but 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.

15. The raphe nuclei and the serotonin system.
In the midline of the pons and medulla are several thin nuclei called the
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 suppress pain,
& in the diencephalon and cerebrum almost certainly plays an essential inhibitory
role to help cause normal sleep.

16. The gigantocellular neurons of the reticular excitatory area and
the acetylcholine system.
• The 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.
• The neurohormone secreted at their terminals is acetylcholine.
• In most places, the acetylcholine functions as an excitatory
neurotransmitter.Activation of these acetylcholine neurons leads to an
acutely awake and excited nervous system.

17. OTHER NEUROTRANSMITTERS
AND NEUROHORMONAL
SUBSTANCES SECRETED INTHE
BRAIN
enkephalins, gamma-aminobutyric acid, glutamate,
vasopressin, adrenocorticotropic hormone, α-
melanocyte stimulating hormone (α-MSH),
neuropeptide-Y (NPY), epinephrine, histamine,
endorphins, angiotensin II, and neurotensin

18. norepinephrine excites the brain to increased
activity/inhibit certain areas
(dreaming)rapid eye movement sleep
(REM sleep).
dopamine. inhibitory transmitter in the basal
ganglia/excitatory in certain areas
The raphe nuclei and the serotonin system
suppress pain,
cerebrum almost certainly plays an
essential inhibitory role to help
cause normal sleep.
The gigantocellular neurons of
the reticular excitatory area
and the acetylcholine system
Activation of these
acetylcholine neurons leads to
an acutely awake and excited
nervous system.