Reticular excitatory area

1
Reticular excitatory area

• General area/system for control of the overall
  level of excitation of the brain
• in reticular formation of pons midbrain
• diffuse stimulation of cerebrum via thalamus
• rapid short lasting from magnocellular releasing
  ACH
• long lasting from many small nuclei (spatial
  summation from many small nuclei
• transmits excitatory signals to cord
• maintain tone of antigravity muscles
• control activity of reflexes

2
Reticular Excitatory Area

• If inactivated the brain activity reduced (coma
  is likely)
• stimulated by
• peripheral sensory signals
• cut brain stem mid pons (above entry CN V)-coma
• cut brain stem below entry CN V- coma unlikely
• cerebral cortex thalamus
• reverberating signals

3
Wakefulness

• Promoted by pontomesencephalic cells located in
  the locus ceruleus and dorsolateral pontine
  tegmentum
• dopaminergic cells
• noradrenergic cells
• Caudal mesencephalic cholinergic cells
• Oral pontine reticular formation
• glutaminergic cells
• Posterior hypothalamic neurons containing
  histamine

4
Wakefulness (cont)

• Caudal mesencephalic (cholinergic) and cells of
  the oral pontine reticular formation
  (glutaminergic) in the laterodorsal and
  pedunculopontine tegmental nuclei produce tonic
  cortical activation wakefulness primarily
  through ascending projections to the thalamus
  (via a dorsal pathway)
• These neurons also communicate with the
  hypothalamus and basal forebrain (via a ventral
  pathway)

5
Wakefulness (cont)

• Thalamocortical projections from primarily
  glutamate containing neurons in the midline,
  intralaminar and medial thalamic nuclei provide
  widespread neocortical innervation
• Basal forebrain (basal nucleus of Meynert
  substantia innominate is another major
  cholinergic arousal area and project to the cortex

6
Reticular inhibitory area

• Located in medulla in reticular formation
• inhibits the reticular excitatory area via
  serotonergic projections

7
Neurohormonal control

• Norepinephrine system (locus ceruleus)
• most widespread-generally stimulatory
• Dopamine system(sub. Nigra, arcuate, VTA)
• can /-, neuroendocrine control, behavior
• Serotonin system (raphe nuclei)
• usually inhibitory, induction of sleep, pain
  control, mood
• Acetylcholine system (gigantocellular)
• usually excitatory (part of reticular excitatory)

8
Other neurotransmitters and neurohormonal
substances associated with brain function

• enkephalins
• glutamate
• ACTH
• endorphins
• neurotensin
• substance P
• histamine

• GABA
• vasopressin
• epinephrine
• angiotensin II
• vasoactive intestinal peptide
• neuropeptide Y

9
Neural circuit associated with Emotion

• Papez circuit- (1937)
• anatomic basis for connections of limbic system
  with higher cortical areas (bidirectional)
• emotions reach consciousness thought
• higher cognitive function affect emotions
• Cortex, cingulate gyrus, hippocampal formation,
  amygdala, mammillary body, hypothalamus, thalamus
• these structures are functionally and
  anatomically related

10
Limbic system

• Hypothalamus
• Cingulate gyrus
• Subcallosal gyrus
• Orbitofrontal cortex
• Septum area
• Paraolfactory area

• Anterior thalamic nuclei
• Amygdala
• Hippocampus
• Portions of basal ganglia
• Parahippocampal gyrus
• Uncus

11
Limbic System
Prefrontal Cortex
Association Cortex
Cingulate gyrus
Ant. Thalamic nuclei
Mammillothalamic tract
Fornix
Hippocampal formation
Mamillary body
Hypothalamus
Amygdala
Bold arrows are the original Papez Circuit
later extended by Paul MacLean
12
Two Basic Emotional States

• Arousal
• Steep tropistic gradient
• Fight-Fright-Flight
• Associated with sympathetic functions
• Increased energy expenditure
• Feeling of general excitement
• Conservation
• Inactivity/stupor
• Rest and Digest
• Associated with parasympathetic functions
• Apathy, tiredness, weakness
• Decreased muscle tone
• in the extreme-depression or pressed to the ground

13
Hypothalamus

• Major output pathway one of the central
  elements from the limbic system
• Functions
• behavior control (reward and punishment)
• control of vegetative functions (ANS)
• body temperature
• osmolality
• motivational drives
• thirst hunger
• endocrine control (anterior pituitary)
• immune system effects via pituitary and ANS

14
Hypothalamic control of vegetative functions

• cardiovascular regulation
• regulation of body temperature
• regulation of body water
• regulation of uterine contractility milk
  ejection
• gastrointestinal and feeding regulation

15
Behavior functions of Hypothalamus

• lateral hypothalamus
• thirst, eating, increased level of activity,
  rage, fighting
• ventromedial nucleus
• satiety, tranquility
• periventricular nucleus or central gray
• fear punishment reactions
• extreme anterior posterior regions
• sexual drive

16
Reward Punishment function

• Reward centers (positive reinforcement)
• located along the course of the medial forebrain
  bundle especially in the lateral and VM nuclei of
  hypothalamus
• here will cause a behavior to be repeated
• Punishment centers (negative reinforcement)
• central gray around aqueduct of Sylvius in
  mesencephalon extending into periventricular
  zones of hypothalamus thalamus
• here will cause a behavior to cease

17
Endogenous opiate receptors

• Lowest density in the cerebral cortex
• Highest density in the amygdala hypothalamus
• A third area enriched with neuropeptide receptors
  in the dorsal horn of the spinal cord (should be
  included as part of the limbic system- Pert)

18
Kluver-Bucy Syndrome

• Bilateral ablation of the amygdala
• Excessive tendency to examine objects orally
• Loss of fear (tame)
• Excessive sexual drive
• Changes in dietary habits