the$brain$divisions$con/nued$ - sweethumananatomy.weebly.com · diencepalon$–the$thalamus$...

The Brain divisions con/nued Review: The brain has four major divisions:

1) Cerebrum

2) Diencephalon. The diencephalon is further divided into the thalamus, hypothalamus, epithalamus

3) Cerebellum

4) Brainstem, including the medulla oblongata, pons, and midbrain We have explored the Cerebrum

now we move on to the Diencephalon!

Diencepalon – the Thalamus

*Diencephalon – Gray MaHer areas deep in brain.

*Surrounded by the cerebral hemispheres & encloses the third ventricle.

*Consists of 3 structures: 1.  Thalamus 2. Hypothalamus 3. Epithalmus

Diencephalon loca/on in the brain

Diencephalon Loca/on in the third ventricle ( circled by the blue line)

* *

Thalamus MRI

-‐Spinal cord-‐-‐-‐-‐-‐-‐-‐Spinal Cord

Func/ons of the diencepalon structures:

Thalamus-‐ Greek word meaning-‐ “inner room”, is a large oval mass of gray maHer. Cons/tutes nearly 80% of the diencephlon. The thalamus receives all sensory messages from the spinal cord (except those from the olfactory receptors) prior to being directed to the cerebrum's sensory areas. The func/on of the thalamus is to relay the incoming impulses to precise loca/ons within the cerebral lobes for interpreta/on.

The thalamus is the gateway to the cerebral cortex

Diencephalon -‐ hypothalamus Lying just beneath the thalamus, the hypothalamus forms the floor of the third ventricle. The hypothalamus contains olfactory centers and is the main integra/on hub for controlling the viscera (internal organs). It supplies input to areas in the medulla and spinal cord that control ac/vi/es such as heart rate, respira/on, and fat metabolism.

The hypothalamus regulates body temperature, controls appe/te, water balance and plays a part in emo/onal and sexual responses. The hypothalamus is the BRIDGE BETWEEN THE NERVOUS AND ENDOCRINE SYSTEMS. It produces various hormones and regulates the pituitary gland.

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hypothalamus

pituitary gland

medulla-‐-‐-‐

Hypothalamus

Diencephalon –the epithalamus The third structure of the diencephalon is the epithalamus. It is the most dorsal por/on of the 3 structures and forms the roof of the 3rd ventricle which contains the vascular choroid plexus (site of CSF produc/on).

Extending from its posterior boarder is the pineal gland or body. pineal, “pine cone shaped.”

The pineal gland secretes the hormone melatonin, and along with the hypothalamic nuclei helps regulate sleep-‐wake cycle.

choroid plexus in epithalamus

-‐-‐-‐-‐pineal gland thalamus-‐-‐-‐

hypothalamus

Diencephalon-‐recap

* *

chornoid plexus in epithalamus

*

*


1) Cerebrum


3) Cerebellum

4) Brainstem, including the medulla oblongata, pons, and midbrain We have explored the Cerebrum, and

Diencephalon. on to the Cerebellum

Cerebellum

CEREBELLUM “small brain” The cerebellum is the second largest division of the brain and is the reflex (i.e. unconscious) center for muscular coordina/on and refinement of movements.

Injury or disease of the cerebellum can cause impaired muscle coordina/on. When the human cerebellum is impaired any ac/vity necessita/ng fine motor coordina/on, such as threading a needle, becomes prac/cally impossible.

Cerebral Cortex

Cerebellum pons

medulla oblongata

transverse cerebral fissure

Located dorsal to the pons and medulla.

Cerebellum con/nued Accounts for 11% of brain mass

It protrudes under the occipital lobes of the cerebral hemispheres from which it is separated by the transverse cerebral fissure

It has 2 cerebellar hemispheres which are connected by the vermis “worm”.

transverse cerebral fissure

⏎ vermis

Cerebellum con/nued Like the cerebrum the cerebellum has a thin ouHer layer of gray maHer (cerebellar cortex) and a thick deeper layer of white maHer.

The tracts of white maHer have a dis/nct paHern called the Arbor Vitate (“tree-‐ life”)

The principal func9on of the cerebellum is coordina9ng skeletal muscle contrac9ons by recrui9ng precise motor units within the muscles. Impulses for voluntary muscle movement originate in cerebral cortex but are coordinated by the cerebellum

Cerebellar ataxia-‐gross lack of coordina/on of muscular movements

Another classic finding of alcohol intoxica/on is ataxia, Ataxia is responsible for the observa/on that drunk people are clumsy, sway back and forth, and oeen fall down. It is probably due to alcohol's effect on the cerebellum.

hHp://www.youtube.com/watch?v=5eBwn22Bnio


1) Cerebrum


3) Cerebellum

4) Brainstem, including the medulla oblongata, pons, and midbrain We have explored the Cerebrum,

Diencephalon. and Cerebellum, last division of brain to explore is the Brainstem

Brain Stem-‐ composed of the midbrain, pons & medulla

region of midbrain

-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐Pons

-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐Medulla

-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐spinal cord

. The brain stem looks like a stalk supporJng the cerebrum. It has three subdivisions: the medulla, pons, and midbrain.

The medulla, in the lower porJon of the brain stem anterior to the cerebellum, runs uninterrupted with the spinal cord.

The pons, a large mass of fibers, is superior to the medulla.

Located just above the pons, the midbrain is the hub of visual and auditory reflexes Ventral view of the human brain

cerebellum

Midbrain (aka Mesencephalon)

midbrain-‐aka mesencephalon

Running through the midbrain is the *cerebral (mesencephalic) aqueduct which connects the 3rd and 4th ventricles.

pons

midbrain %

hypothalamus

thalamus

4th ventricle

*

Midbrain con/nued

*Corpora Quadrigemina represents two pairs of rounded knobs on the upper surface of the

midbrain & mark the loca/on of four nuclei, which are called collec/vely the "corpora quadrigemina”. The superior pair, the superior colliculi, are visual reflex centers. the inferior pair, the inferior colliculi, are responsible for auditory reflexes.

sagiHal sec/on

*

*

midbrain

midbrain con/nued.

1.Pineal gland 2.Superior colliculi 3.Inferior colliculi 4.Cerebral aqueduct 5.Midbrain 6.Cerebellum 7.Fourth ventricle 8.Pons

Brain stem-‐Pons

The pons is the bulging brain stem region wedged between the midbrain and medulla. dorsally it forms part of the anterior wall of the 4th ventricle.

The Pons is the bridge between the midbrain and medulla

The pons func/ons as a relay sta/on, connec/ng neuronal pathways from the spinal cord, cerebrum, and cerebellum. It contains nuclei that relay impulses from the cerebrum to the cerebellum.

Brain MRI Pons outlined

Brain Stem-‐ The medulla The medulla, in the lower por/on of the brain stem, anterior to the cerebellum, runs uninterrupted with the spinal cord.

It blends impercep/bly into the spinal cord at the level of the foramen magnum of the skull.

The medulla consists of vital nuclei and white maHer that form all the descending and ascending tracts communica/ng between the spinal cord and various parts of the brain.

Anterior view-‐human brain

PONS

Medulla

cerebellum

spinal cord

Brain stem-‐medulla

The medulla is crucial as an autonomic role in maintaining body homeostasis. Neuron cell bodies in the medulla control respira/on, heartbeat, and blood pressure. Other reflex centers in the medulla control ac/ons such as swallowing, coughing, and vomi/ng. Sounds like the hypothalmus? The overlap is easily explained. The hypothalmus exerts its control over many visceral func/ons by relaying its instruc/ons to the medulla, which carries them out. The hypothalmus is the boss, the medulla does what it’s told.

Anesthesia and medullary depression The info below is taken from Dr. Cliff Swanson-‐Professor of Anesthesiology dated 1999. This is what he has to say about the drug propofol. (Medica/on given to Michael Jackson)

“The biggest dosage problem with propofol is that if too much is given, too quickly, even if it is the "right" amount in terms of the total dose but is just administered too quickly, you end up with a pa/ent that is not breathing very well, or may stop breathing, called apnea. So long as this side effect is expected, and the medical professional is prepared to deal with it, it does not present a problem.

Generally speaking we talk about there being four stages of anesthesia. 4) Medullary depression -‐ This stage refers to the lower centers of the brain. Those that are responsible for all the things you don’t have to think about like keeping your heart going, blood pressure regula/on, and all the other body func/ons that maintain us in a normal state of health which normally happen automa/cally. The trick in anesthesia is to stay in the area of surgical anesthesia without straying into medullary depression.

In par/cular how close we are to crossing over into medullary depression because you can give, and give anesthe/c, and eventually knock out the func/oning of the centers in the brain that maintain all this other necessary func/ons, like blood pressure regula/on, breathing, and then you have a dead pa/ent.”

green outline-‐diencephalon blue outline-‐brain stem

DecussaJon of pyramids in medulla-‐ Where the projec/on fiber tracts cross over. Reason why the right side of the brain controls the lee side of the body.

What structures do you recognize?

Diencephalon Summary Diencephalon Region

DescripJon General FuncJons

Thalamus Two egg shaped bodies that surround the third ventricle

Relays sensory informa/on to cerebral cortex, relays informa/on for motor ac/vites; informa/on filter. “Gateway to the Cerebral Cortex”

Hypothalamus Below thalamus, forms floor of 3rd ventricle

Controls automa/c centers for heart rate, blood pressure, respira/on, diges/on; hunger center, thirst center; regula/on of body temp; produc/on of emo/ons; Bridge between the N.S and the Endocrine System (controls pituitary gland).

Epithalamus Located on roof of 3rd ventricle; choroid plexus found here (forms CSF); includes the pineal gland

Pineal gland makes hormone melatonin which regulates day-‐night cycles

Brain Stem summary

Bain stem region DescripJon General FuncJon

Medulla oblongata

Between spinal cord & pons Respiratory control center; cardiovascular control center This is the area that was affected by the “sleeping” drugs given to Michael Jackson!

Pons Between medulla and midbrain; buldges out as a widen region in brain stem

relays informa/on from cerebrum to cerebellum “bridge”. Or you could say Pons is the middle man between big brain and liHle brain

Midbrain Between diencephlon and pons; includes corpora quadrigemnia and cerebral aqueduct

Visual and auditory reflex centers; provides pathway between brain stem and cerebrum

Know these summaries!

Guess who’s brain?

the$brain$divisions$con/nued$ - sweethumananatomy.weebly.com · diencepalon$–the$thalamus$...

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