The brainy brain: Oh the complexities of the human brain

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Okay, so let’s talk about the brain. First thing anyone needs to know is the 7 major regions of the brain:

1. Cerebrum

2. Cerebellum

3. Diencephalon

4. Basal Ganglia

5. Midbrain*

6. Pons*

7. Medulla Oblongata*

brain major regions

Notice the last three (5-7) are actually a part of the brainstem which ultimately becomes the spinal cord once it exits the foramen magnum, which is basically a hole in the occipital bone.

The basal ganglia isn’t as visible as the other regions when looking right at the brain model, to see it clearly you have to look at a transverse cut of the brain:

transverse cut of brain BASAL GANGLIA

Okay so before we can go into detail about why you should even care about any of this we have to go over a few more basic ideas so it can all come together in the big picture.

The brain has several coverings, called meninges which mainly serves as a protective covering for the amazing organ that basically makes you, YOU! In the brain we have:

1. Dura mater

2. Arachnoid mater

3. Pia mater

The dura mater is the most superficial layer of meninges and there are two layers of the dura mater. Dura mater literally translates as “tough mother” so we can safely assume this layer is the most durable layer in the meninges.

The arachnoid mater is the middle layer which forms a loose brain covering and is separated from the dura mater by a narrow cavity toward the subdural space. Beneath the arachnoid membrane is subarachnoid space. In this portion weblike extensions secure the arachnoid to the last layer, the pia mater.

The pia mater clings tightly to the brain and contains many tiny blood vessels to serve the brain.

So the next thing you need to know are the ventricles of the brain:

Ventricles of brain

So lets talk about what we’re looking at. At the superior part of the highlighted structure, we see two C shaped structures that are known as the Lateral ventricles (ventricles 1 and 2) they are separated by the septum pellucidum and are located in each of the cerebral hemispheres. These two ventricles connect to the interventricular foramen, which connects the lateral ventricles to each other and to the third ventricle.  As you can see, the third ventricle is located medially to the lateral ventricles and the cerebral aqueduct (which is just inferior to the third ventricle) connects the third to the fourth ventricle. The fourth ventricle, the most inferior of the ventricles is located between the pons and the cerebellum and median and lateral apertures connect the fourth ventricle to the subarachnoid space that surrounds the brain.

So now that we know all of that we can talk about the Cerebrospinal fluid. This is another protective aspect of the brain and it flows through the brain via the ventricles.

Starting at the lateral ventricles and working its way to the interventricular foramen (which we learned connects the lateral ventricles to each other and the third ventricle) so it seems natural that the next location the CSF would flow to would be the third ventricle which then makes its way to the, you guessed it, cerebral aqueduct which of course goes to the fourth ventricle. At this point it can go one of three ways 1) through the central canal, 2) through the medial aperture, or 3) the lateral aperture.The medial and lateral apertures go to the subarachnoid space then to the arachnoid villi and then the venous sinuses (blood)

Lateral ventricles –> interventricular foramen –> third ventricle –> cerebral aqueduct –> fourth ventrical –> medial or lateral apertures –> subarachnoid space –> arachnoid villi –> venous sinuses (blood)

Cerebrospinal fluid is created by the ependymal cells of the choroid plexus which filter blood plasma and use pumps to get the correct ion concentrations.

So now we move on to the major lobes, which are different from the major regions and are all located in the cerebrum:

1. Frontal

2. Parietal

3. Temporal

4. Occipital

major regions cerebrum

Birds eye view flow chart (excludes temporal bone)

Frontal lobe –> precentral gyrus –> central sulcus –> post central gyrus –> parietal lobe –> parieto-occipital sulcus –> occipital lobe –> transverse cerebral fissure –> cerebellum –> pons –> medulla oblongata

Fissures:

The longitundinal fissure separates the two cerebral hemispheres

Central sulcus separates the frontal lobe from the parietal lobe

Lateral sulcus separates the temporal lobe with the parietal and frontal lobes.

 

Functional areas of the cerebral cortex:

1. Primary motor cortex- located in the precentral gyrus and controls the voluntary movement of the skeletal muscles

2. Premotor cortex- located in the frontal lobe just anterior to the precentral gyrus, its responsible for repetitive movements and plans movements this is the area of the brain responsible for typing, playing a musical instrument, etc.

3. Broca’s area- unilateral, usually on the left cerebral cortex which lies anterior to the inferior region of the premotor cortex which controls the movements necessary to speak.

4. Primary somatosensory area- located in the postcentral gyrus and is responsible for spatial discrimination which means its identifies the region of the body being stimulated.

5. Sensory association cortex- posterior to the somatosensory area and integrates sensory input (temperature, pressure, etc) relayed to it via the primary somatosensory cortex, this is what allows us to figure out what things are without your sight (feeling for your keys in your purse)

6. Primary visual cortex- located at the posterior tip of the occipital lobe which recieves and processes visual inputs from the retina

7. Association area- covers much of the occipital lobe and receives and processes visual inputs, this is what puts all the info from the visual cortex together.

8. Primary auditory cortex- located in the temporal lobe and receives and processes sound

9. Association cortex-  located in the temporal lobe and receives and processes sounds received from the auditory cortex

10. Prefrontal cortex- anterior portion of frontal lobe which is responsible for our intellect, cognition, memory and personality

So now lets talk about lateralization and cerebral dominance.

Lateralization

Left: language, math and logic

Right: visual spacial skills, intuition, emotion, artistic skills, musical skills and creativity

Cerebral is determined by the hemisphere that is dominant for language which is usually the left and which has greater control over language, math and logic.

 

Commissural Fibers connect the hemispheres to each other and run horizontally ex/ corpus callosum

Association fibers connect different parts of the same hemisphere and run horizontally

Projection fibers connect the cerebral cortex to the lower brain and spinal cord, may carry impulses to the lower brain and spinal cord and run vertically

Diencephalon and subdivisions

Location of diencephalon- surrounds the third ventricle

subdivisions of the diencephalon are the thalamus, hypothalamus, and epithalamus

The thalamus receives and integrates sensory input and sends the information to the cerebral cortex

Hypothalamus is the main visceral control center of the body

epithalamus includes the pineal gland (endocrine)

 

Major regions of brain stem

Midbrain coordinates the head and eye movements with visual tracking of an object. Its linked to the basal ganglia and contains motor tracts on their way to the spinal cord.

Pons acts as a relay station between the motor cortex and the cerebellum it contains neurons from higher centers on their way to the spinal cord

Medulla oblongata works where motor tracts cross over, the right side controlling the left side and the left controlling the right. This contains important visceral motor nuclei which control hiccuping, vomiting, swallowing, coughing and sneezing as well as cardiovascular and respiratory functions

 

Cerebellum coordinates sensory input from the motor cortex to produce smooth coordinated movement, its also responsible for predicting sequences of events to produce coordinate movement, word association and puzzle solving, it consists of 2 hemispheres the superficial being gray matter and the deep layer white, located posterior to the pons and medulla.

 

Limbic system:

its located on the medial aspect of each cerebral hemisphere and diencephalon includes the hippocampus, amygdala and other structures. This is the emotional center of the brain, although the amygdala and hippocampus play a role in memory as well.

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