Subcortical Grey Matter
Rahul's Noteblog
Notes on Neurology
Subcortical Grey Matter
• Thalamus and epithalamus (pineal gland).
• Hypothalamus, limbic system and pituitary gland.
• Basal ganglia.
THALAMUS – Relay station for sensory impulses
The thalamus is part of the diencephalon. Other components of the diencephalon include the hypothalamus, subthalamus and epithalamus.
Two wedge-shaped or ovoid (egg) structures composed of grey matter and joined together by the interthalamic adhesion.
Form the lateral walls of 3rd ventricle.
The internal medullary Y-shaped lamina consisting of white matter divides the thalamus into three portions and 25 nuclei (thalamic organization).
a. Lateral nuclear mass.
b. Mediodorsal nuclear mass.
c. Anterior nuclear mass.
The reticular nucleus is also separated from the thalamus by the external medullary lamina.
Identifiable Macro Components:
1. Interthalamic adhesion (joins two thalami).
2. Pulvinar (posterior surface).
3. Lateral (i.e. for vision) and medial geniculate bodies (latter for auditory impulses).
4. Lateral surface beveled by internal capsule.
5. Various nuclei and internal medullary Y-shaped lamina.
6. Ventral posterior nucleus (associated with taste, touch, pressure, vibration, heat, cold, pain).
Function of Thalamic Nuclei: Major synaptic relay station.
1. Specific or relay nuclei: Have specific connections with the motory or sensory areas of the cerebral cortex. (Ventral anterior nucleus, ventral lateral nucleus, ventral posterior nucleus, medial and lateral geniculate nucleus). Crude appreciation of subconscious sensation. Vague awareness of sleep and level of consciousness.
2. Association nuclei: Reciprocally connected to the association areas of the cerebral cortex.
3. Non-specific nuclei: Intralaminar and reticular nuclei.
4. Principal somatosensory relay nuclei (ventrobasal complex of nuclei) are concerned with taste sensation, vestibular relay, auditory, visual, motory and limbic relay. Initial autonomic response to pain.
Summary: Principal relay station for sensory impulses that reach the cerebral cortex from the spinal cord, brainstem, cerebellum and cerebrum. Crude appreciation of pain, temperature and pressure. Essential role in the acquisition of knowledge (= cognition).
Nuclear Connections
1. Afferent: To motor and prefrontal cortex, sensory cortex, visual and auditory cortex.
2. Efferent: From globus pallidus, cerebellum, spinal lemnisci and optic tracts.
3. Cerebral connections: Are via fanlike thelamic projections to the anterior, superior, posterior and inferior peduncles.
Dysfunction: Tumour infiltration or ischaemia due to thrombosis may result in the thalamic syndrome which is characterized by a lowered threshold to pain, temperature and touch.
Location of Primary Sensory and Association Areas of the Human Cerebral Cortex:
• Primary sensory area (posterior to central sulcus)
• Sensory association area (behind the primary area)
• Visual association area
• Primary visual area
• Wernicke’s area
• Primary auditory area
• Broca’s area (motor, speech): Area 44. Left cerebral hemisphere.
Epithalamus: Consists of the pineal gland, habenula and stria medullaris. (Latter are part of the limbic system).
PINEAL GLAND: Attached to roof of the 3rd ventricle.
Production: Melatonin. Secretion is regulated by sunlight and stimulation of the activity of the suprachiasmatic nucleus in the hypothalamus. Melatonin regulates day/night cycle. It also may regulate onset of puberty. Also contains neuroactive peptides. (TRH, LHRH) and somatostatin. Associated with mechanisms that regulate circadian rhythm. Body rhythms and onset of puberty. There is an association between light, the pineal gland and depression.
Clinical Application: Often the pineal becomes calcified. Useful in radiology to determine shift of the midline by a space-occupying lesion. Mainly replaced today by the use of CT-scans of the brain. Phototherapy, which acts like sunlight to inhibit melatonin secretion, is effective in the treatment of “winter depression”.
HYPOTHALAMUS
General: Part of the diencephalon and sited at the lower part of the lateral wall and floor of the third ventricle. Located below the thalamus and weighs about 4 grams. Separated macroscopically from the thalamus by the hypothalamic sulcus and lies in front of the interpeduncular nuclei. There are prominent neural connections (portal hypophyseal vessels) with the posterior lobe of the pituitary (hypothalamohypophyseal tract) and vascular connections with the anterior lobe i.e. hypothalamic control of the pituitary.
Regions:
1. Mammillary region (includes mammillary bodies).
2. Tuberal region (tuber cinereum, and infundibulum).
3. Supraoptic region (superior to optic chiasm).
4. Preoptic region.
Important Hypothalamic Regulatory Functions: Homeostasis
1. Temperature regulation (thermoregulation).
2. Neuroendocrine hormonal control of: Catecholamines, vasopressin, oxytocin, TSH, ACTH, FSH, LH, prolactin, GH (by releasing and inhibiting hormones RH/IH) ie regulation of hormonal release from the pituitary gland (hypophysis) ie control of the pituitary gland.
3. Appetite control (thirst, hunger) ie eating and drinking (saiety and feeding centre)
4. Sexual behaviour, blood circulation.
5. Defense reactions (fear, rage); sleep wake cycle, aggression, pleasure, defense mechanisms ie regulator of emotional and behavioural patterns.
6. Anterior hypothalamus: regulates parasympathetic functions.
7. Posterior hypothalamus: regulates sympathetic functions.
8. Supraoptic and paraventricular nuclei are the principle producers of oxytocin and vasopressin (ADH).
9. Regulation of diurnal rhythms and states of consciousness - especially the suprachiasmatic nucleus that establishes patterns of sleep.
Afferent and Efferent Hypothalamic Connections:
1. Connections with limbic system, nuclei of the midbrain tegmentum, thalamus, lenticular nucleus, mammillary nuclei, reticular parts of midbrain.
2. Tracts: Medial forebrain bundle, fornix, stria terminalis, mammillary peduncle, rhinohypothalamic fibres, etc.
Hypothalamic Relations:
1. Superior: Hypothalamic sulcus.
2. Inferior: Optic chiasm, tuber cinereum, mammilary bodies, median eminence and infundibulum.
3. Anterior: Lamina terminalis.
4. Posterior: Midbrain tegmentum.
5. Medial: 3rd ventricle.
6. Lateral: Internal capsule.
Hypothalamic Nuclei:
1. Anterior: supraoptic, preoptic, suprachiasmatic, paraventricular.
2. Middle (tuberal): infundibular, lateral, dorsal, dorso and ventromedial, posterior.
3. Posterior: Mammilary, posterior.
LIMBIC SYSTEM (Limbic means “border”) – EMOTIONAL OR SMELL BRAIN i.e. control basic emotional drives
General: Formerly called the rhinencephalon. Limbic lobes consist of limbic cortical tissue sited around the hilum of the cerebral hemispheres (allocortex) associated with the amygdala, cingulate gyrus, certain thalamic nuclei, mammillary bodies of hypothalamus, hippocampus, olfactory bulbs, cingulate and parahippocampal gyri and septal nuclei.
Limbic system (“border”):
Prev: Rhinencephalon (“emotional brain”)
Site: Limbic cortex Assoc: Amyg/Cing/subthal nucleus/ mamm bod/hypohtal/hypocamp/olf bulb/septal
Function:
• Emotional aspects of behaviour and memory
• Pleasure and pain
• Olfactory
• Biol rhyth / sexual behaviour
• Emotion (rage, fever, motivation)
Associations:
• Brainstem/hypothal/thal/BG/hypocamp/CC
Functions: Chiefly governs emotional aspects of behaviour and memory (“emotional brain”). Associated with pleasure and pain sensations. Olfaction, control of biologic rhythms (circadian or diurnal rhythms), sexual behaviour, hunger and emotions (rage, aggression, fear, motivation). Sometimes called the “emotional” brain.
Connections:
1. Hippocampus (ie subiculum, hippocampus and dentate gyrus) is connected to the mammilary bodies by the fornix.
2. Mammilothalamic tract of Vicq d’ Azur connects the mammilary body to the thalamic nuclei (stria medullaris thalami) and habenular nucleus.
Summary: Limbic system governs emotional aspects of behaviour.
PITUITARY GLAND (Hypophysis Cerebri)
Sited: Pituitary fossa in the sella turcica of the sphenoid bone saddled between the middle and posterior clinoid processes. Pituitary stalk penetrates the diaphragma sella. Sella is lined with dura. Regulated by the hypothalamus (releasing or inhibiting hormones).
Divisions:
1. Neurohypophysis (downgrowth of diencephalon): Secrete ADH (vasopressin) and oxytocin.
2. Adenohypophysis (consists of pars anterior, intermedia and tuberalis). Secretes tropic hormones (GH, ACTH, TSH, FSH, LH, prolactin). Releasing hormones or factors of hypothalamus control pituitary function (ie CRF, TRF, GHRF, FSHRF, LRF).
Blood Supply: Internal carotid artery branches (hypophysial artery); portal vessel. The pituitary portal system is an intricate venous network and channels connecting the hypothalamus and anterior pituitary gland.
Embryology: Ectoderm origin.
1. Anterior lobe: from Rathke’s pouch (stomodeum).
2. Posterior lobe: diencephalon, neuro-ectoderm diverticulum.
BASAL NUCLEI (Ganglia) – The control of movements
The term, corpus striatum is frequently used, and includes two structures (caudate nucleus and lentiform nucleus). The striatum refers to caudate nucleus and putamen.
Components: Large nuclei at the base of the cerebral hemispheres
1. Caudate nucleus - C-shaped and consists of a head, body and tail. Tail communicates with the amygdaloid nucleus (influences movement, endocrine and feeding functions).
2. Lentiform nucleus: consists of the putamen and globus pallidus (latter is further divided into an internal and external division) (paleostriatum). Separated from the thalamus by the internal capsule.
3. Amygdaloid nucleus: Associated with limbic and olfactory systems (see 1).
4. Claustrum: thin sheet of grey matter between lentiform nucleus and insula. Function unclear. Extreme capsule lies lateral and external capsule medially.
5. Corpus striatum refers to caudate and lentiform nuclei.
6. Neostriatum refers to the caudate nucleus and putamen.
7. Subthalamic nucleus.
8. Substantia nigra (pars compacta).
Projections: Afferent and efferent pathways (to thalamus and cortex). A failure of the nigrostriatal pathway is associated with Parkinson’s Disease and the release of dopamine.
Functions
1. Part of the “extrapyrmidal system”. Modulation of motor outflow.
2. Connections:
a. Cerebral cortex: motor and premotor areas (motor control) - control of movement. Smoothing of voluntary actions.
b. Thalamic and subthalamic nuclei.
c. Cerebellum.
d. Substantia nigra.
e. With limbic system.
Dysfunction: Results in dyskinesias ie rigidity, rapid and aimless movements, tremor, chorea, ballism and athetosis; Parkinson’s disease.
3. Putamen processes sensorimotor data and the caudate nucleus integrates fibres destined for the prefrontal cortex association areas.
4. Putamen and globus pallidus: Motor activity integration.
5. Globus pallidus: major efferent nucleus with projections to the thalamus, hypothalamus and midbrain. Regulates muscle tone for specific, intentional body movements.
6. Acts in concert with the cerebral cortex and corticospinal system.
7. Putamen circuit: Connections include sensory and motor cerebral cortex, globus pallidus, thalamus, subthalamus and substantia nigra. Important for performing learned patterns of movement ie writing, cutting paper, hammering nails, throwing a ball.
8. Caudate circuit: Important for cognitive control of motor activity. Neural connections include globus pallidus, thalamus and cerebral cortex.
9. Important for the timing and scaling functions.
10. Associated with important specific neurotransmitter pathways.
a. Dopamine pathway (subst. nigra to caud. nucleus and putamen).
b. Gamma-aminobutyric acid (GABA) pathway (Caud. nucleus to subst. nigra.)
c. Acetylcholine pathway (Cortex to the caudate nucleus and putamen).
d. Norepinephrine, serotonin and enkephalin pathways. Multiple pathways connect the ganglia with the cerebrum.
Amygdaloid Body and Temporal Lobe:
Amygdala functions:
• Behavioural and emotional function
• Fear, irritability, anger
• Cats: furious defensive reaction and aggressive noises and gestures and sympathetic +++
• Damage in man also affects hippocampus and visual association cortex of the temporal lobe mixture of behavioral and cognitive disturbances.
Temporal lobe epilepsy:
• Anxiety states (inappropriate activity of amygdala)
• Depression
• Schizophrenia
Temporal Lobe Destruction:
Monkey: Bilateral temporal lobe excision
Klüver-Bucy Syndrome
• Docility
• Lack of emotional responses (i.e. fear or anger)
• Increased, inappropriate sexual activity / drive
• ¯ performing tricks or tasks (unable to do new learning)
• ¯ recognition of objects - compensates by exploring objects with its mouth. This is termed visual agnosia or psychic blindness = loss of visual association cortex for formed images. Associated with excessive eating.
Amygdaloid Complex*
• Gray mass in temporal lobe
• 2-3 nuclei (two main nuclear massas)
• Afferent fibres: olfactory, diencephalon, hypothalamus
• Peptides: somatostatin, ENK, SP, CCK, NT, VIP
• Projections to cerebral cortex (F, ins, T, O, somatosensory), basal ganglia
• Function: "olfactory," higher cognitive and motivational function, behaviour, defence reaction, fear, confusion, disturbance of awareness, amnesia. Removal ® placcidity, decrease in aggression and assaultive behaviour, ¯ emotional excitability, normalise social behaviour; integrator of autonomic and visceral functions
* Essential for correlation of emotional expression and meaningful behaviour
Amygdalar Function:
• Modulates hypothalamus (due to vast connections)
• Damage: ~ hypothalamus (aphagia or hyperphagia)
• Subjective feelings
• Emotions (fear: pupils, adrenalin, HR)
• Damage: ¯ agression; tame, placid
• Memory deficit
Anatomy of Memory*:
• Posterior temporal lobes (long term memory storage)
• Hippocampus (+ parahippocampal areas)
• Rhinal cortex* (entorhinal) profound amnesia
• Diencephalon (anterior, dorsomedial nuclei and mammillary bodies1 of the hypothalamus? Thalamus? Amygdala)
* Recognition and declarative memory short- and long memory
1 Korsakoff’s syndrome (ante- and retrograde)
Anatomy of Memory 2:
Hippocampus*
• Spatial memory (going down a maze)
• Working memory or relational memory
* Temporal lobe: declarative and procedural memory
* Working memory resides in multiple brain locations especially prefrontal cortex (= problem solving; planning behaviour)
Anatomy of Memory 3:
Types of Memory and Amnesia
• learning
• declarative memory
• procedural memory
• short-term memory
• long-term memory
• consolidation
• working memory
• retrograde amnesia
• anterograde amnesia
• transient global amnesia
Additional Reading:
Basic Neurology
1. Peripheral Nervous System
2. Central Nervous System
3. The Ventricular System
4. The Spinal Cord
5. The Brain Stem
6. The Cerebellum
7. Visual Pathways
8. Diencephalon
9. Basal Ganglia
10. Cerebral Cortex
11. The Limbic System
12. Sleep Disorders
13. Autonomic Nervous System
14. Cranial Nerves and Parasympathetic Ganglia
15. Cells of the Nervous System
16. Cerebrospinal fluid
17. Additional short notes on Cerebrum
18. Functions and Diseases of Cerebrum
19. Subcortical Grey Matter
20. Notes on The Spinal Cord
21. Regulation of Heart Rate by Autonomic Nervous System
22. Action Potentials, Axon Conduction, and Neuromuscular Junction
Related Topics
1. Nervous System Disorders
2. Histology of Nervous Tissue
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Page accessed on: July 29, 2010, 11:04 am.