Brainstem and diencephalon II

Done by:

-Haneen omar

- Adonia haddad

The slides are included in this sheet (bold) but pictures aren’t a continuation of

the last lecture, sorry for any mistakes

slide 32:

Reticular Formation

• Scattered nuclei in medulla, pons & midbrain

• Lateral one third have small cells

(parvocellular)

– Receive sensory inputs and cortical inputs

• Medial two thirds have large cells

(magnocellular)

Output to spinal cord, brainstem nuclei, thalamus, hypothalamus & cerebral

Cortex.

reticular formation: collection of cells all over the brainstem (specially medulla

and pons)

Roughly collected nuclie (it’s not collected in away like the other nucleus , so

when it’s stained the sections are not that clear )

in order to understand the function of the reticular formation you have to know

that it links different systems with each other :

different informationحلقة وصل بسبب وجود

it’s located in the brain stem and has other connections with other nuclie in :

1)brainstem 2)SC 3)other areas in brain … ( makes coordination between them)

توزيعها ووظيفتها مختلف عليها بعد ومعلوماتها ال تزال غامضة

Reticular formation is be distributed as columns: (from midline)

-lateral one third --- Receive afferent reticular information --- make little

reorganization

From the lateral part the information will go towards the:

-medial two third --- make analysis of data --- give efferent outputs to other

structure in the neuroaxis

Magnocells are the largest cell body in the nervous tissue (150micron) so when

they’re stained we can see them by naked eye (large because it receives inputs

from all over the body --- huge analysis --- and give outputs to all over the

neuroaxis )

Slide 33:

Reticular Formation Functions

• The reticular formation modulates (excite or

inhibit) the activities of:

– Sensory systems – e.g. pain

– Motor systems – e.g. muscle tone, segmental

reflexes, eye movements

– Autonomic systems – e.g. respiration, blood

pressure, cardiac function

– Consciousness – e.g. vital centers in the

brainstem, awareness, attention & arousal

the function of reticular formation is mostly modulation ( coordination) ---

excitation or inhibition or it can block

functionsرح تشتغل بكل ال

-sensory : according to function can excite or inhibit

-motor system: makes toning and works on plexuses in spinal cord toward the

cerebellum and basal ganglia

-autonomic system: projection toward the spinal cord and regulation of spinal

cord plexuses (modulate(toning) autonomic function like urination and

evacuation)

Mostly ascending excitatory and descending inhibitory pathway)it’s not clear in

records so I took it from the internet)

- consciousness :alert and awake --- ascending tracts -- coordination of different

systems stimuli عشان تصحصح

-every part of the brain will contribute with a certain percentage with other parts

in brain (circuits --- every circuit has a connection with other circuits – very

complicated)

اذا ما ارتبطو مع بعض بصير خلل)يجب وجود تداخل بينهم(

Brain has centers --- every group of centers gives nucli --- every nuclei has a

function (IN a form of circuit)

Every neuron has an axon and every axon has up to hundreds of collaterals that

gives hundred of copies to every circuit ) every circuit will receive a copy from info

and it will deals with it in a different way from other circuits )

reflexes ofوال بتعمل perception for sensory stimuliوال بتعمل motot initiationهيه ما بتعمل

autonomic functions وال شو بتعمل؟ بتعمل ....…modulation and toning حلقة وصل بوصلها كلstimuli

system ...modulation of other circuitsما يحصل لكل الوتطلع على كل

فقط systemمعين مش معناها انها بتستفرد بهذا ال systemب nucleusلما نحكي

Slide 34:

Organization of Reticular Formation

• Reticular formation organized

into three longitudinal columns

– Midline raphe group

– Parasagittal medial zone

– Parasagittal lateral zone

Same as what has been mentioned before :

Midline raphe and medial zone --magnocellular

lateral zone --- parvocellular

Neural cells aren’t either excitatory or inhibitory (wrong idea) --- the neural cell

can be excitatory and inhibitoty at the same time – depends on the

type/time/intensity of the stimuli : a cell respond to a certain stimuli in a certain

way , at the same time this exact cell will respond (in a certain nucleus) in a

different way according to other stimuli different from the first one(from

another organ) .

functionتتغير ال stimuliاذا شغلت اكثر من

Slide35:

Organization of Reticular Formation

• Fourth set of nuclei that have

common cerebellar

projections (precerebellar

reticular nuclei)

Coordination of muscle

contraction

– Paramidian reticular nucleus of

the medulla

– Lateral reticular nucleus of the

medulla

– Reticulotegmental nucleus of

the pons

another Column of reticular formation is the fourh set of nuclie , it is related to

cerebellum and the function of it (modulation of motor system)

precerebellar reticular nuclei --- group of nuclie ( see the slide فرعاتهم) ت .. make

connection with cerebellum

معلوم عنهم القليل

Slide36:

Raphe Nuclei

• Serotonin projecting cells

• Rostral group (upper pons &

midbrain)

– Project to cerebellum, cerebrum

(cortex, basal ganglia, limbic system)

– Involved in the regulation of

forebrain activity

• Sleep, memory processing, mood

• Caudal group (lower pons &

medulla)

– Receives nociceptive input from

brainstem & spinal cord

•Involved in the regulation of pain

Raphe nuclie is at the midline – uses serotonin as it’s neurotransmitter and

divided to:

- rostral group : function related to sleeping/mood/memory processing/ alertness

-caudal group: it’s sensory (pain modulation) and it has another functions

(modulation autonomic functions in SC)

(what connects between the two of them is the neurotransmitter)

Neurotransmitters are important --- because functional classifications are

according to the neurotransmittesr function(neurophysiology)

Slide37:

Medial Reticular Zone

• The effector part of the reticular formation

– Provides most of the ascending & descending projection

• Most inputs come from the lateral reticular zone (sensory somatic

& visceral)

• Ascending projections form the Ascending Reticular Activating

System (ARAS)

– Alter the levels of consciousness & state of attention

• Conscious activities of the cerebral cortex require excitatory influences from

the ARAS

• Descending projections regulate muscle tone, spinal reflexes &

motor activity through

– Medial (pontine) reticulospinal tract

• ↑ muscle tone spinal reflexes

– Lateral (medullary) reticulospinal tract

• ↓ muscle tone spinal reflexes

The most important part of it is the ascending tract ---receive inptuts from

different stimuli systems (sensory and motor)

ARAS is responsible for consciousness and alert , it has a role in coordination of

unconscious sleep

تبعك شغال حتى وانت غايب عن الوعي sensoryال

Descending projections we will talk about them more when we reach the

descending tracts but for now you have to know this:

- medial tract : comes from pontine nuclie --- excitatory to spinal reflexes

-lateral tract : comes from medulla --- inhibitory of spinal reflexes

(opposite to each other – modulation of spinal reflexes

Add to them that they are not only motor but also sensory (somatic and

auotonomic)

Slide 38:

Medial Reticular Zone

• Locus ceruleus in pons

– contain norepinephrine &

extensive projections

throughout CNS

– Ascending projections are part

of the ARAS

• Involved in the mood, memory

and regulation of motor activity

locus ceruleus use the norepinephrine neurotransmitter , it contributes with ARAS

and it is involved with other functions --- it has a role in nocturnal enuresis In

Children (modulation of motor autonomic system)

slide39:

Lateral Reticular Zone

• Receives extensive afferents to mediate

cranial nerve reflexes and visceral functions

• Output is mainly to medial zone

• Other projections

– Pedunculopontine nucleus (acetylcholine neurons)

• Projects to the substantia nigra, subthalamic nucleus,

motor cortex, & medial zone

– All have important motor control functions

Like we said before lateral zone receives info (afferents) andt i organise all

sensories that arrives then they go to medial zone for further processes

Another nuclei --- pedunculopontine nucleus that uses the neurotransmitter

Acetylcholine

Coordinator center --– gives sensory info to -basal ganglia nuclie (modulation of

motor system// initiator) --- gives info to(modulate) - motor cortex --- gives

direct orders to motor system .

Slide 40:

Go and see the picture

Different nuclie use different neurotransmitter (specific distribution of

neurotransmitter for specific functions)

Serotonine --- mood and depression (psychological)

Dopamine--- motor (substantia nigra) … will talk about it later on in basal ganglia

Acetylcholine --- ARAS ( awareness and alertness)

Slide41:

The doctor said again >> projections and neurotransmitters >> check the picture

The Diencephalon

The diencephalon (“interbrain”) is the region of the vertebrate neural tube that

gives rise to posterior forebrain structures. It lies above the midbrain between the

lower parts of the 2 cerebral hemispheres.

#Third ventricle lies b/w the 2 halves of diencephalon.

It is made up of four distinct components: the thalamus, the subthalamus, the

hypothalamus, and the epithalamus.

All these components of diencephalon are located medial to the cerebrum and

lateral to third ventricle.

Subthalamus lies directly above midbrain, under the thalamus and posterior to

hypothalamus and located near the substantia nigra . It may be considered as a

part of diencephalon structurally ( mostly lies within the entity of diencephalon)

but functionally is connected directly to basal ganglia. All fibers directed from

basal ganglia to thalamus pass through the subthalamus.

Hypothalamus is a region of the forebrain located below the thalamus, in front of

subthalamus, forming the basal portion of the diencephalon.

Epithalamus is the dorsal posterior segment of the diencephalon.

Thalamus is a large oval mass of gray matter, located at the center of

diencephalon, forms the upper 2/3 of lateral wall of the third ventricles and

considered as a relay station for sensory and motor signals to the cerebral cortex.

Each of these component has right and left sides.

# Thalamus and hypothalamus form the lateral walls of third ventricle .

Thalamus: Structure

From medial to lateral:

–Medial n.

• Dorsomedial n.

–Anterior n.

Internal medullary lamina

Intralaminar n.

–Lateral n.

External medullary lamina

–Reticular n.

Internal capsule

On transverse section of thalamus , we found 3 nuclei ; medial , lateral and

anterior.

Anterior n. is considered as only one nucleus, mostly related to the limbic system.

Medial n. considered as a group of nuclei , the most important one is the

dorsomedial nucleus.

Lateral n. also considered as a group of nuclei, divided into dorsal and ventral.

Reticular n. has a connection with the reticular formation that we talked about it

previously.

As we know, thalamus is a mass of grey matter separated by fibers of white

matter which are :

1. internal medullary lamina separated b/w medial, ant. & lateral n. . The major

nucleus within these fibers is the intralaminar n. .

Also, there is 2. the external medullary lamina separated b/w lateral and reticular

n.

After the reticular n. there is the internal capsule, then we will find the basal

ganglia.

Subdivided into:

-Dorsal tier • Lateral dorsal (LD) • Lateral posterior (LP) • Pulvinar (Pu)

-Ventral tier • Ventral anterior (VA) • Ventral lateral (VL) • Ventral posterior

(VP)

–Ventral posterolateral (VPL)

–Ventral posteromedial (VPM) • Posterior nucleus (Po)

–Medial & lateral geniculate nuclei.

If we take a sagittal section of lateral nucleus we will note that is subdivided into

dorsal and ventral tiers .

The dorsal one is subdivided from ant. To post. Into LD, LP & Pu and they can be

noticed superiorly

The ventral one is also subdivided into VA, VL, VP & Po .

VP involves VPL & VPM , both are considered as relay stations for sensory tracts .

Po could be found or could be absent.

Also there are medial and lateral geniculate nuclei (most posterior & inferior) ,

have a direct connection with sup. & inf. Colliculi . Lateral to visual and medial to

auditory.

# The doctor said that you should read the 2 tables quickly.

# In non specifc nuclei , most projections are toward association cortex.

• Location << Hypothalamus is located inferior and medial to thalamus.

• Boundaries –Lamina terminalis –Hypothalamic sulcus. –3rd ventricle

“The left and right lateral walls of the third ventricle are divided by an

anteroposterior depression known as the hypothalamic sulcus which separates

the thalamus (superiorly) from the hypothalamus (inferiorly). The superior part of

the lamina terminalis is directly anterior to it, while the supraoptic and

dorsomedial nuclei are at inferiorly and posteriorly related, respectively.

Superiorly: there is the hypothalamic sulcus, the thalamus, the choroid plexus of

the third ventricle and the fornix.

Inferiorly : (from anterior to posterior), there is the supraoptic recess and crest,

the pituitary stalk and gland and tuber cinereum.

Posteriorly: the mammillary bodies, posterior perforated substance, cerebral

peduncle and the cerebral aqueduct of Sylvius can be found.”

Divisions

–In coronal section

• Periventricular (also can be found paraventricular nucleus) • Medial > Fornix (

separates the medial from lateral ) • Lateral

Divisions

–In sagittal section (from anterior to posterior)

–Chiasmatic ( most anterior one , supraoptic)

–Tuberal (middle) ( above the intermediate)

–Mamillary (posterior) ( above or at the level of mammillary bodies )

Functions of hypothalamus :

Inputs from

- Neuronal influences

- Hormonal influences

Outputs to

- Autonomic

- Limbic ( emotions and mood)

- Endocrine

Please return to the final 4 slides

“The limbic system – also known as the circle of Papez (or Papez’s Circuit) is

considered to be the epicenter of emotional and behavioral expression.

The limbic lobe refers to a specific group of anatomical structures found in the

forming a rim region of the cortex on the medial aspect of cerebral hemisphere

around the corpus callosum. It also includes cingulate and parahippocampal gyri.

These structures also have interdependent functional similarities associated with

the formation of memories and the expression of a variety of emotions.

ior surface of inferThe parahippocampal gyrus is more readily appreciated on the

the temporal lobe of the cerebrum.”

Good luck