Reticular Formation

I will use RS' as short name for Reticular formation on some of the items. Answer Multiple choice before Identification.

Reticular Formation

Reticular Formation

Set of interconnected nuclei that are located throughout the brainstem, resembles a net (reticular) that is made up of nerve cells and nerve fibers.

Median Column

• Raphe Nuclei

• Intermediate-sized neuron

• Place of synthesis of Serotonin

Medial Column

• Gigantocelluclar Reticular Nuclei

• Large neurons

• Motor coordination

Lateral Column

• Parvocellular Reticular Nuclei

• Small neurons

RS’ Control of Skeletal Muscle

• Influence the activity of the Alpha and Gamma motor neuron.

• Maintains balance, reflex, and muscle tone.

• Vital in maintaining the tone of antigravity muscles during standing.

RS’ Control of Somatic & Visceral Sensation

• Influence the ascending pathways passing the supraspinal levels.

• Can either be facilitatory or inhibitoy

• Vital in “Gating Mechanism” in pain perception control.

RS’ Control of Autonomic Nervous System

• Higher control of the ANS from the Cerebral cortex, Hypothalamus, and other subcortical nuclei.

• Can be exerted by the reticulobulbar and reticulospinal tract.

RS’ Control of the Endocrine System

• Either directly or indirectly through the hypothalamic nuclei,

• Can influence the synthesis or release of releasing or release-inhibiting factors and thereby control the activity of the hypophysis cerebri

RS’ Influence on the Biologic Clock

• By means of its multiple afferent and efferent pathways to the hypothalamus, the RS probably influences the biologic rhythms.

RS’ Control of Facial Expression

• Control of facial expression with association to emotion.

  • The descending tracts are separate from the corticobulbar fibers.

    • Means that a person that suffered a stroke that involves the corticobulbar fibers and exhibit facial paralysis on the lower part of the face is still able to smile symmetrically.

RS’ Reticular Activating System

• Arousal and the level of consciousness are controlled by the reticular formation.

• Multiple ascending pathways carrying sensory Information to higher centers are channeled through the reticular formation.

  • This information is projected to different parts of the cerebral cortex, causing a sleeping person to awaken.

• Incoming pain sensations strongly increase the activity of the reticular formation, which, in tum, greatly excites the cerebral cortex

Acetylcholine and Norepinephrine

Main Excitatory Neurotransmitter of the RAS

Alert, Lethargic, Obtunded, Stupor, Coma

Level of Alertness (Most to Least alert)

Reticular Activating System

• AKA: Ascending Arousal System

• Responsible for arousal, sleep, and level of consciousness

• Contains circuits that originate from several areas of the midbrain including the midbrain reticular formation and ascend to the cerebral cortex and thalamus

Alert

Normal level of consciousness

Lethargic

• Severe drowsiness

• Can be aroused by moderate stimulation and would drift back to sleep

Obtunded

• decreased alertness, slower psychomotor responses

• needs repeated stimulation to maintain attention and response to environment.

Stupor

• Sleep like state but not unconscisous with little to no spontaneous activity

• Moan only response

Coma

• Cannot be aroused, no response to stimuli.

Limbic System

• Group of structures that lie in the border zone between the cerebral cortex and the hypothalamus.

• Involved in the control of Emotion, Behavior, Long term memory.

Paleomammalian System

Other name for the Limbic system

Border/Margin

Meaning of Limbic

Anterior Thalamic Nucleus

• Receives input from mamillary bodies

• Involved in memory processing

Mamillary Bodies

• Receives signal from the hippocampus via fornix and projects to the thalamus

• Internal structure of limbic system

Hypothalamus

Regulates number of autonomic processes.

Cingulate Gyrus

• Location: Immediately above the corpus callosum

• Integral part of the limbic system Involve in emotional functions and processing, learning and memory.

• Manifestation: depression and schizophrenia.

Parahippocampal Gyrus

Lies between the hippocampal fissure and the collateral sulcus.

Hippocampus

• Play a certain role in the consolidation of new memories.

• Concerned with converting recent memory to long term memory.

  • Lesion: unable to store long term memory

  • Memory of remote past events before the lesion developed is unaffected.

Anterograde Amnesia

• Difficulty in learning new information

• most common in TBI

Amygdaloid Body

• resembles an almond

• Situated partly Anterior and partly Superior to the tip of the Inferior horn of Lateral Ventricle

Fornix

• a white matter structure connecting the hippocampus with the other brain structure particularly the mammillary bodies and septal nuclei.

Nucleus Accumbens

• Involved in reward, pleasure, and addiction

• Play a role in sexual arousal and a "high" derived from certain recreational drugs

Septal Nucleus

• A set of structure that lie in front of the lamina terminalis considered as “pleasure zone”

Amygdala

• Location: deep within the temporal lobe and related with several emotional processes

• Responsible for sexual desire.

KLÜVER BUCY SYNDROME

Affectation of the Amygdala that would represent as hypersexuality.

Medial temporal lobe of the brain

Location of the Hippocampal formation

Hippocampus (Contrib to HF)

• Curved elevation of gray matter

• Resembles a sea horse in coronal section

• The convex ventricular surface is covered with ependyma, beneath which lies a thin layer of white matter called the Alveus

• The alveus, consists of nerve fibers that originated in the hippocampus and unite medially to form a bundle called the fimbria

• Molecular Layer: superficial, consists of nerve fibers and scattered small neurons

• Pyramidal Layer: consists of large pyramidal shaped neurons

• Polymorphic Layer: inner layer

Layers of the Hippocampus

Dentate Gyrus

Narrow, notched band of gray matter that lies between the fimbria of the hippocampus and the parahippocampal gyrus, also has 3 layers like the hippocampus.

Parahippocampal Gyrus

Lies between the hippocampal fissure an collateral sulcus

Alveus

• Consists of a thin layer of white matter that lies on the superior or ventricular surface of the hippocampus

• Composed of nerve fibers that originate in the hippocampal cortex

• The fibers unite on the medial border of the hippocampus to form a bundle called the FIMBRIAE.

Mammillothalamic Tract

• Provides important connections between the mammillary body and the anterior nuclear group of the thalamus

Striata Terminalis

• Arises from the posterior aspect of Amygdaloid Nucleus

• Is a bundle of nerve fibers that runs posteriorly in the roof of the inferior horn of the lateral ventricle on the medial side of the tail of the caudate nucleus

Schizophrenia

Sx:

• Chronically disordered thinking

• Blunted Affect

• Emotional Withdrawal

• Paranoid delusions

• Auditory Hallucinations

• Through research it has been found that the inhibition of limbic dopamine receptors using a pharmacologic agent may lessen the symptoms of schizophrenia.

Temporal Lobe Dysfunction

• Acoustic and olfactory experience may precede a temporal lobe epilepsy

• Olfactory Aura: unpleasant odor

• Post-seizure a patient may not be aware of what happened during the seizure.

• Patient is often confused, anxious, and docile and may perform automatic or complicated movements (undressing in public or driving a car)

Hypersomnia and Apnea

• Excessive daytime sleepiness and recurrent apnea during sleep may occur.

• Affected patients are apt to be obese middle-aged men who snore loudly.

Narcolepsy

• Intermittent episodes of uncontrollable sleep.

• Sudden transient loss of muscle tone in the extremities or trunk (cataplexy) may occur.

• Pathologic muscle weakness during emotional reactions may also occur.

• Sleep paralysis - the inability to move in between sleep and arousal

• Hypnagogic hallucinations may occur at the onset of sleep.

• Sleep attacks happen without warning and may last from minutes to hours.