Diencephalon Flashcards
Chapter 17 Epithalamus Subthalamus Thalamus
Which grew faster during fetal development?
Telencephalon grows faster than interbrain during fetal development.
Diencephalon is almost entirely hidden from view.
The diencephalon forms almost all the walls of which ventricle
The III ventricle
The Diencephalon contains all of the
Thalamus-Named Structures
The diencephalon lies
From the posterior commissure, extending rostrally to the interventricular foramen of monro
Pineal Gland is the size of
a grain of rice
The diencephalon has five (5) divisions
Hypothalamus, Thalamus, Epithalamus, Subthalamus,, Metathalamus
The Metathalamus is made of
Medial Geniculate (auditory/nucleus pathway) Lateral Geniclate body(optic pathway/visual nucleus)
The functions of the Hypothalamus
3.Instrumental in maintaining ‘internal homeostasis’
2.Needs are signaled by ‘hunger and thirst’, eating behaviors
1.Produces strong responses to ‘emotional changes’, defensive
Regulation of ‘sleep-wake’ cycles
4.’Endocrine’ regulation, growth, metabolism, reproduction
How many nuclei are in the Hypothalamus
9 nuclei in the Hypothalamus
What structures make up the Hypothalamus?
Structures include:
1-‘optic chiasm’
2-Tuber cinerium-hypothalamus region bounded by mammillary bodies
3-Infundibulim-stalk arising from pituitary gland (sella tursica)
4-“Fornix fibers” from temporal hippocampus–mamillary bodies
5-9 nuclei in mesial or lateral zones
What do the Fornix fibers do?
Divide the hypothalamus into medial and lateral zones
What are the three regions of the medial zone of the hypothalamus
The medial zone has three rostral-caudal regions
- suprachiasmatic (supraoptic)
- Tuberal(infundibular, intermediate, paraventricular)
- Mamillary
9+ nuclei in medial or lateral zones
nuclei located on ‘suprachiasmic’, ‘tubera’l, and ‘mamillary’ regions
What is the chief regulator of the ANS and endocrine system?
Hypothalamus
Why is the hypothalamus is essential for survival?
Because of its intergration of behaviors with visceral functions
1. Maintaining Homeostasis
How does the hypothalamus help maintain homeostasis
1.Adjustment of body temperature
2.metabolic rate
3.blood pressure
4.water intake and excretion
digestion
What part of the hypothalamus in sensitive to temperature increase
the Anterior hypothalamus
What part of the hypothalamus is sensitive to temperature decreases
Posterior hypothalamus
The parasympathetic response to Blood Pressure is
Decrease BP
Thy sympathetic response to Blood Pressure is
Increase BP
How does the Hypothalamus control water intake and excretion
drinking and thirst centers; renal water reabsorption
Hypothalamic function
1. control of Eating, Reproduction and defensive behavior
Satiety & feeding centers (stimulation of appetite vs.
starvation)
– Sexual stimulation by regulating sex hormones
– Sympathetic stimulation & limbic system
Hypothalamus Function
2. Emotional expression of pleasure, rage, fear, and
aversion
– Limbic system & ANS
– Drive & motivation
Hypothalamus Function
- Regulation of circadian rhythms in a 24 hour cycle,
i. e. our biological clock – day-night rhythms
– Sleep & wakefulness cycles
Hypothalamus Function
4. Endocrine regulation of growth, metabolism, and
reproductive organs
1– Anterior pituitary = adrenocortico-, thyro-, & gonadotrophic
hormones
2– Posterior pituitary = water metabolism & milk ejection reflex
Hypothalamic
Endocrine Functions
1• These functions are carried out by
hypothalamic regulation of pituitary gland
secretions, and by
2• Efferent neural connections with the cortex, limbic system, brain stem, and spinal cord.
Hypothalamus and Pituitary
1• Hormone production by adenohypophysis is controlled by chemicals synthesized in anterior hypothalamic cells (from ventromedial and infundibular nuclei) 1– Luteinizing hormone [LH] • Final ripening of ovarian follicle -- progesterone secretion 2– Follicle-stimulating hormone [FSH] • Promotes follicular maturation -- estrogen (estradiol) secretion
Hypothalamus and Pituitary
1• Neurohypophyseal hormones elaborated in ‘Supraoptic’
and ‘Paraventricular’ nuclei –Hypothalamohypophseal pathways
1– Antidiuretic hormone (ADH, Vasopressin)
• Reabsorption of water from the kidneys à
water metabolism, in response to increased
plasma osmolality; i.e. controls water excretion
2– Oxytocin
• Causes lactation and uterine contraction
• Anterior hypothalamus (“Preoptic” area and A Nucleus) function
Regulates parasympathetic responses and heat loss;
sensitive to increases in blood temperature
• Slows heart rate, vasodilation, lowers BP, Increases
peristalsis, bladder contraction, increases sweating
• Posterior hypothalamus (Posterior and L Nuclei)
Sympathetic response
• Cardiac acceleration, increase BP, cease peristalsis
& sweating, dilation of pupils, heat conservation
(vasoconstriction and shivering)
Lateral zone
– Feeding and hunger center
• lesion = loss of hunger
– Drinking and thirst
• lesion = abolishes thirst
Ventromedial nucleus
– Satiety center; lesion = hyperphagia (over eating)
Pituitary and Pineal Glands: 4 commissures
- Corpus callosum
- Anterior commissure
- Posterior commissure
- Habenular commissure [H]
Epithalamus major structure is the
Pineal Gland
The Pineal Gland is
- an endocrine gland innervated by sympathetic fibers
- –believed to help regulate circadian rhythms
- Pre-puberty gonadal influence with melatonin production.
Pineal Gland believed to help regulate circadian rhythms by
• Monitors length of day and seasons
• Influence secretions of the pituitary – adrenal -
parathyroid glands, and islets of Langerhans
(pancreas)
– Pre-puberty gonadal influence with melatonin
production
- Light decreases melatonin production
- Melatonin depresses gonadal function
- Pineal tumor causes precocious (early) puberty
Epithalamus – 2 Nuclear Groups
Pineal Body and Habenular Nucleus
Pineal body (epiphysis)
- Has anti-gonadotrophic activity (pre-puberty)
2.– Tendency to calcify (brain sand) with aging, so useful
as marker on x-ray film as a midline/median structure
Habenular nucleus
1– [L.] frenulum; fibrous band – used to be thought to be
the stalk of the pineal gland
2– ‘Primitive cerebral function’, fibers part of the
olfactory system (smell) and limbic system (emotions)
3– Dorsal Longitudinal Fasciculus (DLF) connects
hypothalamus to habenular cells to midbrain relating
data from viscera
Pineal gland positions with Ca++ concretions (brainstand) help neurosurgeon with brains tissue displacement
A Epidural hemotoma
C Pineal Gland
Note:Ventricular Diaplacement
Epithalamus hardens and surgeons use it as a place marker for where brain tissue should be in relation to it
Subthalamus is located
Superior to the substantia Nigra of the midbrain
The subthalamus is often associated with the
Basal Nuclei (ganglia) functions as part of the basal nuclei
The function of the subthalamus
involved in regulation of motor control
–influences motor activity through the globus pallidus and substantia nigra
Subthalamus
1.The ML, spinothalamicT, TrigeminothalamicT run sensory fasciculi “through the subthalamus”–to terminate in the VP nucleus of the Thalamus.
(lesion in subthalamus effect on sensory pathways that run through this area)
Dentato-rubro-thalamic (cortico) fibers
Dentate-cerebellum
rubro-red nuceleus of the midbrain
Dentato-rubro-thalamic fibers -
prerubral area (fields of Forel) - thalamic
fasciculus -VL nucleus of thalamus
Prerubral fasciculi (Fields of Forel)
Prerubral fasciculi (Fields of Forel) (part of subthalamus)
– Efferent fibers of globus pallidus;
substantia nigra connections
Zona Incerta
part of the subthalamus a continuation of midbrain
reticular formation
The external globus pallidus (GABA) has a inhibitatory affect on the
Subthalamic Nucleus
glu
The subthalamic nucleus has an excitatory effect on the
Internal Globus Pallidus
GABA
Hemiballismus
Throwing of the limbs of one side of the body
- Uncoordinated swinging of limbs and jerky movements
- -usually due to CVA involving subthalamic Nucleus
With time hemiballismus turns into
Chorea
The subthalamic nucleus is deeply involved in the
Extrapyramidal Systems
Ischemic lesions in the Subthalamus lead to
Very intense movement disorders
The majority of the Diencephalon is
The Thalamus 4/5
The Thalamus is the
the final subcortical Relay station from which all sensory information is relayed to the Cerebral Cortex
The thalamus is called
The gateway to the Cerebral Cortex
The thalamic rediations project to
- Premotor and motor frontal cortex
- P_O_T association cortex
- Limbis System Structures
Thalamus has how many nuclei
• 12+ different nuclei in tiers or groups
– Caudal half ->somatosensory to P-O-T
association cortex
– Rostral half -> pre-motor & motor F cortex and
limbic system
A function of the thalamic nuclei
Processing of correlation, direction, and
interpretation occurs here, but not conscious
interpretation of most peripheral sensory stimuli
– Exception is some low level pain appreciation
VPL–Ventral posterolateral (sensory) thalamic nuclei
DCML and Spinothalamic have 2 synapses here
VPM-ventral posteromedial
(sesory) thalamic nuclei
Trigiminal Sensory
synapses here
Medial Geniculate (thalamic nuclei)
auditory tract
Lateral Geniculate (thalamic nuclei)
optic tract
Intralaminar Nuclei
related to the Reticular formation ARAS–ascending reticular activating system
Incoming Thalamic Sensory Pathways
- Lateral lemniscus–Auditory
- Medial Lemniscus(DCML)–All except pain and temperature
- Spinal Leminscus(spinothalamic)-Pain and Temprature
- Trigeminal leminscus-All sensory related to the face
- Optic Tract
- Auditory Fibers in inferior brachium
- Ascending Reticular Formation
- Cerebellar Pathways
- Hypothalamic pathways
- Basal Nuclei Connections
- Substantia Nigra connections
Thalamic Functions
“executive Assistant” to cerebral hemispheres, receiving specific sensory input for general sense
- -Relay station from which all sensory information reaches the cerebral cortex
- -Categories for specific nuclei
What are the categories for specific thalamic Nuclei
- Relay Nuclei
- Association Nuclei
- Nonspecific Nuclei
The Relay Nuclei of the Thalamic Nucleus
1.Conveys information from sensory systems, basal ganglia and cerebellum
2.Sensory and motor
A. Sensory
- VPL – VPM -> Somatosensory
– MGB -> Auditory
– LGB ->Visual
B. Motor
• VA-VL -> transfer basal nuclei and cerebellar activities to
motor cortex
EX. Motor Planning Area
The association nuclei of the thalamic nucleus
1• Process emotional and some memory
information
2• Integrates different types of sensation
3• Limbic and P-O-T cortex
A. Pulvinar
• Widely related to P-O-T association cortex
• Collaborates with cerebral cognitive functions
• Ex: Complex visual and language functions
EX. Sensory integration-complex visual and language functions
B. A-MD
• Projections to prefrontal cortex to process “limbic
system” input
• Integrates emotional and motivational stimuli (moods)
Ex. Arouses cortex and maintains
The Non-specific thalamic nuclei
• Regulates consciousness, arousal, and attention A-CM-Reticular • Arouses cortex and maintains waking state – EX. Lesion = lethargy
Metathalamus
1• Lateral geniculate body
– Visual pathway to occipital lobe
2• Medial geniculate body
– Auditory pathway to temporal lobe
Thalamic Syndrome
• Caused by PCA vascular or tumor lesion à leads to
“Thalamic Pain Syndrome [of Dejerine-Roussy”
SIgns and Symptoms of the Thalamic Syndrome
usually an ischemic vascular lesion–sometimes a tumor
1– Internal capsule injury with transitory hemiparesis
and homonymous hemianopia
2– Loss of ipsilateral deep (visceral) sensation and
contralateral impairment of superficial sensation
3– Pain threshold decreased contralateral, but once
reached – sensations are exaggerated, perverted
and disagreeable
4• Pin prick causes severe burning sensation
5• Spontaneous burning or knife-like pain; hard to
manage
6– Position sense, proprioception sense frequently
affected
7– There may be emotional instability with
spontaneous/forced crying or laughing
Subcortical Structures
Subcortical White fibers
• Subcortical White Matter
1– “Projection”
connect subcortical structures-cerebral cortex-through internal capsule-spinal cord, brainstem, basal ganglia and thalamus
2– “Commissural”
Connect homologous areas of cerebral hemispheres
3– “Association fibers”
connect cortical fibers within one hemisphere (adjacent gyri)
short association fibers-connect one or two gyri within a lobe
long association fibers- connect many gyri to many gyri
MLF, ILF, SLF
Subcortical Structures Basal Nuclei (Ganglia)
• Basal Nuclei [Ganglia]
– Vital for normal motor function
– Function to sequence movements, regulate muscle
tone and muscle force, and select and inhibit specific
motor synergies
– Less well understood: its role in awareness of body
orientation in space, memory for location of objects,
ability to change behaviors as task requirements
change, and motivation
