Activating Driving System in the Brain Flashcards
How is Brain Activity Controlled
Brain activity is controlled by two mechanism:
- The Reticular Activiating System(RAS)/ Reticular Formation
- Activation of Neurohormonal Systems for the release of Neurotransmitter substances
These two activiating systems for cortical activity always operates together and cannot be entirely seperated from one another
The Reticular Activating System(RAS)/Reticular Formation:
Direct stimulation of background levels of activity:
The reticular excitatory area in the brain stem
The reticular inhibitory area in the brain stem
Activation of neurohormonal systems for the release of neurotransmitter substances
Excitatory or inhibitory neurotransmitter hormonal agents:
Norepinephrine system Dopamine system Serotonin system Acetylcholine system Orexin system
The Function of the Reticular Activating System(RAS)/Reticular Formation
The RF is responsible for arousal and the maintenance of awareness.
It is a complex, polysynaptic wickerwork of small neurons occupying the central part of the brain stem.
It reaches from the medulla upwards through the pons and midbrain to the thalamus.
Some of the reticular neurons receive synapses from collaterals, lemniscal system, visual, auditory, and olfactory systems.
The Reticular Excitatory Area in the Brainstem(Bulboreticular Faciliatory Area)
It is located in the pons and midbrain.
Ascending (reticulofugal) fibers radiate from the RAA via the non-specific projection nuclei of the thalamus to diffuse cortex areas.
The RAA receives descending (reticulopetal) fibers from all these cortical areas, as well as collaterals from all the sensory tracts.
Impulse discharged from the RAA to the cortex is essential for wakefulness and
perception.
Damage to the RAA causes permanent coma and the inability to perceive sensory stimuli.
Signals passing through the thalamus can be:
Fast-conducting action potentials from large
neuron cell bodies that excite the cerebrum for only milliseconds (excitatory – releasing
acetylcholine), or
Slow-conducting action potentials from small cell bodies that control the longer-term background excitability level of the brain.
The Reticular Excitatory Area in the Brainstem(Bulboreticular Faciliatory Area):
The activity of the RF depends on:
- Impulses from the peripheral receptors- when the sensory receptors are stimulated effectively, the RAS discharges impulses to alert the cortex.
- Impulses from the aroused cortex, in turn, can stimulate the RAS.
The Reticular Inhibitory Area in the Brainstem:
It is located medial and ventral in the medulla.
This area inhibits the reticular excitatory area in
the brain stem and superior portions of the brain (one of the mechanisms: serotonin release -
inhibitory neurotransmitter).
The Reticular Inhibitory Area in the Brainstem:
The activity of the RF is affected by:
Anesthetic agents-Suppress RAS
Lesions-Unconsciousness/coma
Adrenaline and Noradrenaline- Alert RAS
Alcohol-Suppresses RAS
The Function of the Neurohormonal Systems:
Aside from direct control of brain activity by nerve signals from the reticular areas in the brain stem,
brain activity can also be controlled by neurohormonal systems, which can either be excitatory or inhibitory
Diseases/Conditions of Neurotransmitter Systems
Parkinson’s disease
Huntington’s disease
Depression
Schizophrenia
Alzheimer
Parkinson’s disease:
Loss of neurons in the substantia nigra whose axons secrete dopamine in the caudate nucleus and putamen.
Huntington’s disease:
Loss of GABA-secreting neurons and acetylcholine-secreting neurons.
With abnormal motor patterns that are observed.
Depression:
Diminished activity of the norepinephrine and serotonin systems
Schizophrenia:
Possible exaggerated function of part of the dopamine system
Alzheimer:
Premature aging of the brain. Amyloid plaques in widespread areas of the brain
Electroencephalogram
An electroencephalogram (EEG) is a test used to evaluate the electrical activity in the brain. It
measures the electrical activity of the brain through direct measurement - placement of electrodes on
the surface of the skull.
Types of EEG Waves
Alpha waves:
Beta waves:
Theta waves:
Delta waves:
Alpha waves:
α-rhythm (adults: awake, eyes closed)
Rhythmical
Normal awake adults in rest
Disappear during sleep
Beta waves:
β-rhythm (adults: awake, eyes open)
Higher frequency, asynchronous
Seen during mental activity
Theta waves:
φ-rhythm (children)
Children
Emotional stress in adults
Brain disorders
Delta waves:
δ-rhythm (predominant in sleep)
Very low-frequency waves
Very deep sleep
Infancy
Organic brain disease
Definition of Sleep
Sleep is defined as unconsciousness from which the person can be aroused by sensory or other stimuli.
It is distinguished from a coma, which is unconsciousness from which the person cannot be aroused.
Stages of Sleep
Awake
Slow Waves Sleep
Rapid Eye Movement(REM) Sleep
Slow-Wave Sleep/Non REM
Deep, restful
A decrease in peripheral vascular tone and vegetative functions
A decrease in BP, respiratory rate, BMR
Consolidation of dreams in memory does not occur
Rapid Eye Movement Sleep (REM) / Paradoxical sleep
After 90 min, last for 20 minutes -associated with dreaming
Episodically (5-30 minutes) during sleep (25%) of sleep time, every 90 minutes
Vivid dreaming
Difficult to arouse
Depressed muscle tone with irregular movements
High levels of brain activity
Irregular heart rate and respiratory rate
Theories: Mechanism that can cause Sleep
- Passive theory of sleep – earlier theory, the fatigue of the RAS.
- Sleep is caused by an active inhibitory process – below the mid pontine level of the brain, some
centers that cause sleep by inhibiting parts of the brain. - Stimulation of the raphe nuclei in the lower half of the pons and medulla. Raphe neurons secrete
serotonin, a major transmitter substance associated with the production of sleep. Problem with
this theory – serotonin levels low during sleep.
Theories: Mechanisms that can cause REM sleep
Acetylcholine is secreted by large neurons in the upper brain stem reticular formation.
Function of Sleep
Restore the natural balance among neuronal centers.
Driving Systems of the Brain
Limbic System
Hypothalamus
Limbic System Definition
The entire neuronal circuitry that controls emotional behavior and motivational drives.
OR
The limbic lobe and all the cortical and subcortical areas
Function of the Limbic System
Intimately involved with behavior, emotion, motivation, many vegetative functions of the brain. It is also
concerned with the affective aspects of sensations (pleasant/unpleasant).
Behavior-
Emotion-
Motivation –
Function of the Limbic System:
Behavior
Primitive behavioral reactions are essential for survival (hunger, thirst, temperature changes, and danger).
Chemical substances and drugs can influence behavior (antidepressants, sedatives).
Function of the Limbic System:
Emotion
Cognition (awareness of feeling and the physical expression thereof).
Function of the Limbic System:
Motivation
So-called reward and punishment centers in the limbic system and hypothalamus.
Reward and Punishment Functions of the Limbic System
The reward and punishment centers are important controllers of our bodily activities, our drives, our
aversions, and our motivations.
Reward Centers:
In the lateral and ventral nuclei of the hypothalamus, septum, amygdala, certain areas of the
thalamus, basal ganglia.
Punishment Centers:
In the central grey area surrounding the aqueduct of Sylvius in the mesencephalon, periventricular zones of hypothalamus and thalamus, amygdala, and the hippocampus.
Functions of the Hippocampus
Numerous indirect connections with many portions of the cerebral cortex and the basic structures of the limbic system.
The additional channel through which incoming sensory signals can lead to appropriate
behavioral reactions. The hippocampus is a critical decision-making neural mechanism, determining the importance and type of importance of the incoming signals.
Consolidation of long-term memories of the verbal or symbolic type.
Stimulation can cause almost anyone of the behavioral patterns.
Functions of the Amygdala
Behavioral awareness area that operates at a semi-conscious level. Help pattern the person’s
behavioral response so that it is appropriate for each occasion.
Function of Limbic Cortex
The limbic cortex functions as a cerebral association area for control of behavior.
The Communication Pathways of the Hypothalamus with all levels of the Limbic System
The hypothalamus sends out signals:
Downward: Brain stem (reticular areas) and autonomic nervous system
Upward:
Higher areas
Infundibulum:
Control secretory functions of the posterior and anterior parts of the pituitary gland.
The function of the Hypothalamus:
The hypothalamus is responsible for the:
Controls vegetative and endocrine functions of the body
Controls aspects of emotional behaviour
Vegetative and Endocrine control functions of the Hypothalamus:
Cardiovascular regulation
Increases (post./lat. Hypothalamus) / decreases (preoptic area) in arterial pressure and heart
rate
2. Regulation of Body Temperature
Increase/decrease in the activity of temperature-sensitive neurons (preoptic area)
3. Regulation of Body Water
• Thirst sensation (thirst center in the lateral hypothalamus, sensitive to changes in electrolyte
concentration)
• Controlling water excretion (supraoptic nucleus – fibers to posterior pituitary for ADH release
to cause water reabsorption)
4. Regulation of Uterine Contractility and Milk Ejection by the Breasts
Oxytocin released by neurons in the paraventricular nucleus:
• Increased uterine contractility (for labor)
• Contraction of myoepithelial cells surrounding alveoli in breasts (reflex signal from nipple to
hypothalamus)
5. Gastrointestinal and Feeding Regulation
• Hunger area (lateral)
• Satiety center (ventromedial nucleus)
• Feeding reflexes (mamillary bodies)
6. Control of Endocrine Hormone Secretion by the Anterior Pituitary Gland
Anterior pituitary blood supply from the hypothalamus into vascular sinuses:
Releasing and inhibitory hormones from hypothalamic nuclei (medial basal nuclei:
periventricular, ventromedial, arcuate) axons to the median eminence anterior
pituitary
Vegetative and Endocrine control functions of the Hypothalamus:
Cardiovascular regulation
Regulation of Body Temperature
Regulation of Body Water
Regulation of Uterine Contractility and Milk Ejection by the Breasts
Gastrointestinal and Feeding Regulation
Control of Endocrine Hormone Secretion by the Anterior Pituitary Gland:
Vegetative and Endocrine control functions of the Hypothalamus:
Cardiovascular Regulation
Increases (post./lat. Hypothalamus) / decreases (preoptic area) in arterial pressure and heart rate.
Vegetative and Endocrine control functions of the Hypothalamus:
Regulation of Body Temperature
Increase/decrease in the activity of temperature-sensitive neurons (preoptic area)
Vegetative and Endocrine control functions of the Hypothalamus:
Regulation of Body Water
Thirst sensation (thirst center in the lateral hypothalamus, sensitive to changes in electrolyte concentration)
Controlling water excretion (supraoptic nucleus – fibers to posterior pituitary for ADH release
to cause water reabsorption)
Vegetative and Endocrine control functions of the Hypothalamus:
Regulation of Uterine Contractility and Milk Ejection by the Breasts
Oxytocin released by neurons in the paraventricular nucleus:
Increased uterine contractility (for labor)
Contraction of myoepithelial cells surrounding alveoli in breasts (reflex signal from nipple to hypothalamus)
6.
Vegetative and Endocrine control functions of the Hypothalamus:
Gastrointestinal and Feeding Regulation
Hunger area (lateral)
Satiety center (ventromedial nucleus)
Feeding reflexes (mamillary bodies)
Vegetative and Endocrine control functions of the Hypothalamus:
Control of Endocrine Hormone Secretion by the Anterior Pituitary Gland
Anterior pituitary blood supply from the hypothalamus into vascular sinuses:
Releasing and inhibitory hormones from hypothalamic nuclei (medial basal nuclei: periventricular, ventromedial, arcuate) ->axons to the median eminence ->anterior pituitary
Emotional, behavioral functions of the hypothalamus
and associated limbic structures
Lateral hypothalamus – thirst, eating, increased level of activity, rage/fighting
Ventromedial nucleus – satiety, decreased eating, tranquillity
Periventricular nuclei – fear/punishment reactions
Anterior/posterior portions of the hypothalamus - sexual drive
