DIENCEPHALON - 123seminarsonly.com€¦ · Diencephalon • between cerebral hemispheres and...

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DIENCEPHALON

..Central core of the forebrain

..Consists of three paired structures –

---------- --thalamus, --------hypothalamus, -------epithalamus..Encloses the third ventricle

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Diencephalon

• between cerebral hemispheres and brainstem• surrounds third ventricle

• thalamus• hypothalamus• optic tracts• optic chiasm• infundibulum• posterior pituitary• mammillary bodies• pineal gland

11-32

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Thalamus

• Paired, egg-shaped masses that form the superolateral walls of the third ventricle

• Connected at the midline by the intermediate mass• Nuclei project and receive fibers from the cerebral

cortex• Final relay point for ascending sensory information• Coordinates the activities of the cerebral cortex

and basal nuclei

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Grey matter nucleus of thalamusSubdivisions of the Thalamus Medial nuclear group, lateral nuclear group, anterior nuclear group Internal medullary lamina Intralaminar nuclei Midline thalamic nuclei Thalamic reticular nucleus

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Relay Nuclei

Most of thalamus consists of relay nuclei.Relay nuclei receive inputs from pathways, process the input and send it on to a particular region of cerebral cortex.All sensory modalities except for olfaction have a relay in the lateral thalamus that projects to a specific region of cerebral cortex.

Ventral posterior lateral nucleus (VPL): somatosensory relay from body (C2 and below)Ventral posterior medail nucleus (VPM): somatosensory relay from cranial nervesLateral geniculate nucleus: visual relayMedial geniculate nucleus: auditory relayVentral lateral nucleus: motor relays from cerebellum and basal gangliaAnterior nuclear group: limbic connections to cingulate gyrus

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Intralaminar Nuclei

Unlike relay nuclei, their main inputs and outputs are from the basal ganglia.Caudal intralaminar nuclei: including large centromedian nucleus; involved mainly in basal ganglia circuitryRostral intralaminar nuclei: reciprocal connections with basal ganglia; connections with ascending reticular activating system

Reticular Nucleus

Only nucleus of thalamus not projecting to cerebral cortex.Inputs from other thalamic nuclei and cortex and projects to other thalamic nuclei.Inhibitory control of other thalamic nucleiAlso may function in alertness & attention

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Hypothalamus

• Located below the thalamus, it caps the brainstem and forms the inferolateral walls of the third ventricle

• Mammillary bodies– Small, paired nuclei bulging anteriorly from the

hypothalamus– Relay station for olfactory pathways

• Infundibulum – stalk of the hypothalamus; connects to the pituitary gland– Main visceral control center of the body

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--optic part

--tubersl part

--mamillary part

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Optic part:

1. Supraoptic nucleius

2. Paraventrical nucleus

Tuberal part:

3. Ventromeddial nucleus

4.Dorsomedial nucleus

5.Tuberal nucleus

Mamillary part

6.Posterior nucleius

7.Lateral nucleus

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Functions

1. Endocrine control: regulate secretion of TSH, ACTH, STH, LH ,FSH

2. Neurosecretion; supraoptic and paraventricular nuclei produce ADH and oxytocin

3. Controls autonomic function, Regulates blood pressure, rate and force of heartbeat, digestive tract motility, rate and depth of breathing, and many other visceral activities

4. Produces emotions and behavioral drives

5. Regulates feelings of hunger and satiety

6. Regulates sleep and the sleep cycle

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Epithalamus

• Most dorsal portion of the diencephalon; forms roof of the third ventricle

• Pineal gland – extends from the posterior border and secretes melatonin– Melatonin – a hormone involved with sleep

regulation, sleep-wake cycles, and mood

• Choroid plexus – a structure that secretes cerebral spinal fluid (CSF)

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Cerebral Hemispheres

• Form the superior part of the brain and make up 83% of its mass

• Contain ridges (gyri) and shallow grooves (sulci)

• Contain deep grooves called fissures

• Are separated by the longitudinal fissure

• Have three basic regions: cortex, white matter, and basal nuclei

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Deep sulci divide the hemispheres into five lobes:Frontal, parietal, temporal, occipital, and insula

Three fissure: 1.Central sulcus( sulcus of Roando) – separates the frontal and parietal lobes

2. Parieto-occipital sulcus – separates the parietal and occipital lobes

3. Lateral sulcus – separates the parietal and temporal lobes

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FRONTAL LOBE--PRECENTRAL SULCUS : is in front of & parallel to the central sulcus

--precentral gyrus: between precentral and c entral sulcus;

-- Superior & inferior frontal sulci : divide remaining front lobe into SUPERIOR, MIDDLE & INFERIOR.

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PARIETAL LOBE--POSTCENTRAL SULCUS : is behind & parallel to central sulcus, bound the POSTCENTRAL GYRUS.

--Interparietal sulcus extend from middle of the postcentral sulcus, divide into SUPERIOR & INFERIOR PARIETAL lobules.

--inferior parietal lobule have SUPRAMARGINAL GYRUS & ANGULAR GYRUS, respectively

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TEMPORAL LOBE:

--superior & inferior temporal sulci divide the laeral surface of temporal lobe into SUPERIOR , MIDDLE & INFERIOR TEMPORAL GYRI.

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OCCIPITAL LOBE

-Calcarine sulcus: continues for a short distance over the occipital pole & joins the parieto-occipital sulcus. The cortex on both sides of calcarine sulcus

represents the striate cortex.

CINGULATE gyrus: is seperated from the corpus callosum by the callosal sulcus.

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The cortex – superficial gray matter; accounts for 40% of the mass of the brain

Each hemisphere acts contralaterally (controls the opposite side of the body)

The three types of functional areas are:--------Motor areas – control voluntary movement-------Sensory areas – conscious awareness of sensation-------Association areas – integrate diverse information

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MOTOR AREA:Located in the precentral gyrusComposed of pyramidal cells whose axons make up the corticospinal tractsAllows conscious control of precise, skilled, voluntary movements

BRODMANN’S …4, giant pyramidal dell of Betz present here.

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PREMOTOR AREA:Located anterior to the precentral gyrusControls learned, repetitious, or patterned motor skillsBrodmann;s area..6

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SENSORY AREA:Located in the postcentral gyrus, this area:

Receives information from the skin and skeletal musclesBRODMANN;S area..3,1.2Associate sensory area

Located posterior to the primary somatosensory cortexIntegrates sensory informationForms comprehensive understanding of the stimulusDetermines size, texture, and relationship of parts

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VISUAL AREA:Primary visual (striate) cortex

Seen on the extreme posterior tip of the occipital lobeMost of it is buried in the calcarine sulcusReceives visual information from the retinasBROADMANN’S AREA…17

Visual association areaSurrounds the primary visual cortexInterprets visual stimuli (e.g., color, form, and movement)

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ACOUSTIC AREA:Primary auditory cortex

Located at the superior margin of the temporal lobeReceives information related to pitch, rhythm, and loudnessBRODMANN’ AREA:…41, 42

Auditory association areaLocated posterior to the primary auditory cortexStores memories of sounds and permits perception of soundsWernicke’s area: which is nearby Broca's area but in the temporal lobe, right next to the auditory cortex. This is were we understand the meaning of speech, and damage to this area will leave you with receptive aphasia, meaning that you will be unable to understand what is being said to you

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Broca’s areaLocated anterior to the inferior region of the premotor areaPresent in one hemisphere (usually the left)A motor speech area that directs muscles of the tongueIs active as one prepares to speak

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TheCerebr

alCortex

FronFrontaltal

LobeLobe

HigherHigherIntellectualIntellectualFunctionsFunctions

PrimaryPrimaryMotorMotorAreaArea

PremotorPremotorAreaArea

SpeechSpeechMotorMotorAreaArea

leglegtrunktrunkarmarm

handhandfaceface

tonguetongue

ParieParietaltal

LobeLobePrimaryPrimarySensorySensory

AreaArea

SensorySensoryAssociationAssociation

AreaArea

OccipiOccipitaltal

LobeLobe

PrimaryPrimaryVisualVisualAreaArea

VisualVisualAssociationAssociation

AreaArea

TempTemporaloralLobeLobe

MemoryMemory

PrimaryPrimaryAuditoryAuditory

AreaArea

LanguageLanguageComprehensionComprehension

& Formation& Formation

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INTERNAL STRUCTURE

BASAL GANGLIA : consistsCorpus striatum

Lentiform nucleus( putamen & globus pallidus) Caudate nucleus

Claustrum Amygdaloid body

FunctionFunctionRegulate voluntary Regulate voluntary movementmovementIntegrative or just a Integrative or just a relay station?relay station?

PathologyPathologyMovement disorders Movement disorders (e.g. Parkinson’s)(e.g. Parkinson’s)

Neostriatum: caudate + putamen

Paleostriatum: globus

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The limbic system has three functions:• It mediates the sense of smell• It mediates emotional behaviour• It plays an important role in memory.

Limbic system include the amygdala, the Limbic system include the amygdala, the hippocampus and the fornixhippocampus and the fornix

Recall that the amygdala is for emotion Recall that the amygdala is for emotion regulation,and perception of odorregulation,and perception of odor

Hippocampus and fornix are important for Hippocampus and fornix are important for learning and memorylearning and memory

Structures on medial and basal Structures on medial and basal surfaces of cerebral hemispheressurfaces of cerebral hemispheresCingulate gyrus + Cingulate gyrus + parahippocampal gyrus + parahippocampal gyrus + hippocampal formation + fornix + hippocampal formation + fornix + amygdala + septum + mammillary amygdala + septum + mammillary bodiesbodies

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Cingulate gyrus

Para-olfactoryarea

Hypothalamus

Uncus

AmygdalaPara-hippocampalgyrus

Hippocampus

Mamillary bodies ofhypothalamus

Fornix

Thalamus

Anterior nucleus of thalamus

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Three connective tissue membranes external to the CNS – dura mater, arachnoid mater, and pia mater

Functions:-Cover and protect the CNS-Protect blood vessels and enclose venous sinuses-Contain cerebrospinal fluid (CSF)-Form partitions within the skull

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BLOOD SUPPLY OF BRAIN & SPINAL CORD

Brain recive the blood from vertebral artery and internal carotid artery

Subclavian

Vertebral

Thyrocervical

Transversecervical

Deep cervical

Suprascapular

Ascendingcervical

Inf. thyroid

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Blood supply to brain

• Brain is supplied by:– Internal carotid

Aa. – Basilar A. (formed

by fusion of vertebral Aa.)

– Together they contribute to the Circle of Willis that sends branches to supply cerebral hemispheres

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Venous Drainage• Internal Jugular

– Brain• External Jugular

– Scalp, face• Vertebral

– cervical vertebrae, spinal cord, neck muscles

• Dural sinuses– Veins in brain to

Internal Jugular

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Ventricles of the Brain

• Arise from expansion of the lumen of the neural tube

• The ventricles are:– The paired C-shaped lateral ventricles – The third ventricle found in the diencephalon– The fourth ventricle found in the hindbrain dorsal

to the pons

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Ventricles of the Brain

Figure 12.5

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Flow of CSF• Choroid plexus

• Ventricles

• Subarachnoid space through lateral and median apertures of 4th ventricle

• Blood of dural sinuses via arachnoid villi

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There are four cavities in the brain, called ventricles. The ventricles are filledwith cerebrospinal fluid (CSF), which provides the following functions:

1---- Absorbs physical shocks to the brain 2-----Distributes nutritive materials to and removes wastes from nervous tissue3---- Provides a chemically stable environment

There are four ventricles:------ Each of two lateral ventricles occupies a cerebral hemisphere. -----The third ventricle is connected by a passage (interventricular foramen)to each of the two lateral ventricles. -----The fourth ventricle connects to the third ventricle (via the cerebralaqueduct) and to the central canal of the spinal cord (a narrow, centraltube extending the length of the spinal cord). Additional openingsin the fourth ventricle also allow CSF to flow into thesubarachnoid space.

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Blood-Brain Barrier (BBB)Selective Permeability:

Substances that can pass include oxygen, glucose, carbon dioxide, alcohol, anesthetics & water Substances that can not pass include medications such as many antibiotics & systemic chemotherapy agents. • Brain capillary

endothelium less permeable, tightly joined

• Toxins cannot penetrate

• O2 & glucose pass through

• Lipid soluble substances pass

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Major Functions

1. Sensory perception2. Voluntary control of movement3. Language4. Personality traits5. Sophisticated mental events, such as thinking memory, decision making, creativity, and self-consciousness

1. Inhibition of muscle tone2. Coordination of slow, sustained movements3. Suppression of useless patterns of movements

1. Relay station for all synaptic input2. Crude awareness of sensation3. Some degree of consciousness4. Role in motor control

1. Regulation of many homeostatic functions, such as temperature control, thirst, urine output, and food intake2. Important link between nervous and endocrine systems3. Extensive involvement with emotion and basic behavioral patterns

1. Maintenance of balance2. Enhancement of muscle tone3. Coordination and planning of skilled voluntary muscle activity

1. Origin of majority of peripheral cranial nerves2. Cardiovascular, repiratory, and digestive control centers3. Regulation of muscle reflexes involved with equilibrium and posture4. Reception and intergration of all synaptic input from spinal cord; arousal and activation of cerebral cortex5. Role in sleep-wake cycle

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

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