1. What Does the Brainstem Do?

The brainstem serves as a communication point between the body, the spinal cord, and the brain through ascending and descending sensory and motor pathways [1].

Ascending pathways are groups of nerve fibers that bring sensory and motor information from the body (peripheral nervous system) to the brain through the spinal cord, while descending pathways work in the opposite way.

Ascending and descending pathways are also known as ascending and descending tracts of the spinal cord.

The brainstem also contains most cranial nerve nuclei (group of neurons), and therefore, is involved in the processing of efferent (coming from) information of the head.  

As the brainstem is made of the midbrain, pons, and medulla, it performs its functions through these structures.

2. What Does the Midbrain Do?

Midbrain or mesencephalon is the most rostral part (top) of the brainstem, found just below the cerebral cortex and above the pons. It is involved in vision, hearing, sleep, wakefulness, temperature regulation, alertness (arousal), and motor control [2]. 

It is composed of the tectum, the tegmentum, and cerebral peduncles, and receives blood supply from the basilar artery, superior cerebellar artery, and posterior cerebellar artery.

The tectum is divided into the superior colliculi that contain nuclei (group of neurons) involved in visual (vision) reflexes and the inferior colliculi involved in auditory (hearing) reflexes.

The tegmentum is divided into the substantia Negra where dopamine is released to the basal ganglia, and the red nucleus, which is involved, together with the cerebellum, in movement coordination.

The cerebral peduncles are paired structures separated by the interpeduncular cistern (Filled with cerebrospinal fluid) that connects the brainstem to the thalami (plural of the thalamus).

Lesions affecting the midbrain such as infarct, tumor, hemorrhage, or infections, can result in neurological disorders, including Benedikt syndrome, Claude syndrome, Weber syndrome, or Nothnagel syndrome.

These neurological disorders are characterized by palsies (paralysis) and ataxia (movement incoordination).

3. What Does the Pons Do?

The pons or pons Varolii is the structure of the brainstem located between the midbrain and the medulla (Medulla oblongata) and serves as a relay between the cerebral hemispheres and the cerebellum [3].

It is divided into the basilar part of the pons (Basis pontis) and the pontine tegmentum and receives blood supply from branches of the superior cerebellar artery and the pontine branches of the basilar artery.

The basilar part of the pons contains the pontine nuclei (cluster of neurons) that relay motor information coming from the motor cortex in the frontal lobe to the cerebellum. This activity is mediated by the corticofugal fibers.

The pontine tegmentum contains nuclei involved in sleep and wakefulness, breathing, and alertness.

It also contains nuclei of the cranial nerves, trigeminal (V), abducens (VI), facial (VII), and vestibulocochlear (VIII), and therefore, is also involved in the functions of these trigeminal nerves.

Lesions affecting the pons such as infarct, hemorrhage, tumors, or infections, can lead to the following neurological disorders:

• Gasperini Syndrome
• Facial Colliculus Syndrome
• Millard-Gubler Syndrome
• Brissaud-Sicard Syndrome
• Raymond Syndrome
• Foville Syndrome
• Marie-Foix Syndrome
• Locked-In Syndrome
• Tuberculosis Rhombencephalis

These neurological disorders are characterized by palsies (paralysis), ataxia, and symptoms associated with alterations in the function of some cranial nerves, such as loss of taste, loss of pain, temperature sensations on the face, or hearing loss.

4. What Does the Medulla Do?

The medulla (Medulla oblongata) is the part of the brainstem located between the pons and the spinal cord. It is responsible for the body’s involuntary functions (autonomous nervous system) such as cardiovascular function, heart rate, breathing, sleep-wake cycle, vomiting, sneezing, and swallowing [4].

The medulla is composed of the ventral medulla and the medulla tegmentum and receives its blood supply from the posterior inferior cerebellar artery (PICA), the anterior spinal artery, and branches of the distal vertebral artery.

The ventral medulla contains the olive, the pyramidal tracts, and the rootlets (nerve fibers) of the cranial nerve IX (Glossopharyngeal nerve) and XII (Hypoglossal nerve).

The olive is involved in movement coordination and in sound perception, while the pyramidal tracts are involved in the movement of muscles, and the rootlets of cranial nerve IX and XII carry away information from the central nervous system (brain and spinal cord) to the tongue, pharynx, larynx, parotid gland, and sinus.

The medulla tegmentum contains the inferior olivary nuclei and the nuclei of the cranial nerves IX to XII.

Lesions affecting the medulla oblongata such as infarct, hemorrhage, tumors, or degeneration, lead to the following neurological disorders:

• Babinski-Nageotte Syndrome
• Opalski Syndrome
• Wallenberg Syndrome
• Déjerine syndrome
• Wallerian Degeneration
• Demyelinating lesions
• Hypertrophic Olivary Degeneration
• Brainstem Glioma
• Syringobulbia

These neurological disorders manifest with symptoms such hemiparesis/hemiplegia, paralysis of parts of the body (e.g., tongue, soft palate, the pupil of the eye), ataxia, sensory deficits, and slurred speech.

5. What Are the Developmental Anomalies of the Brainstem?

Developmental anomalies of the brainstem are disorders that are originated during embryonic development of the brainstem [4].

The main known developmental disorders of the brainstem are Möbius syndrome (congenital facial diplegia syndrome) and axonal guidance disorders.

5.1. What Is Möbius syndrome?

Möbius syndrome or congenital facial diplegia syndrome is due to the underdevelopment or absence of the nuclei of the abducens cranial nerve (VI) and the facial cranial nerve (VII) resulting in paralysis of one side (unilateral) or both sides (bilateral) of the face muscles [5].

5.2. What Are Axonal Guidance Disorders of the Brainstem?

This group of disorders is associated with abnormal white matter tracts in the brainstem such as ectopic white matter tracts or anomalies in their location [6].

These disorders result in disorders such as horizontal gaze palsy, Joubert syndrome, progressive scoliosis, and pontine tegmental cap dysplasia [4].

Conclusion

The brainstem is made of the midbrain, pons, and the medulla oblongata and plays an essential role in communicating information between the body, the spinal cord, the cerebellum, and the brain.

This information includes instruction related to vision, hearing, sleep, wakefulness, temperature regulation, alertness (arousal), motor control, and the autonomous nervous system.

Lesions such as those caused by trauma, hemorrhage, tumors, or infections can affect the different parts of the brainstem (midbrain, pons, and the medulla oblongata) resulting in paralysis of parts of the body, ataxia, and sensory deficits.

The post What Is the Brainstem? appeared first on .

1. Internal Carotid Arteries

Internal carotid arteries consist of the left internal carotid artery and the right internal carotid artery which run along the inner side of the front of the neck towards the brain.

Internal carotid arteries originate from the common carotid arteries at the level of the thyroid cartilage. Common carotid arteries generate both internal and external carotid arteries.

• What Happens If There Is a Stroke in Internal Carotid Arteries?

A stroke affecting the internal carotid arteries will result in a lack of blood supply to the areas controlling vision, speech, and sensations.

2. Vertebral Arteries

Vertebral arteries consist of the left vertebral artery and the right vertebral artery which run along the back of the neck toward the skull where they both merge to form the basilar artery.

The basilary artery is responsible for the supply of blood to the brainstem, cerebellum, the posterior part of the brain, and also the upper part of the spinal cord.

Vertebral arteries are originated from the subclavian arteries that originate from the aortic arch (left subclavian artery) and the brachiocephalic artery (right subclavian artery).

• What Happens If There Is a Stroke in Vertebral Arteries?

A stroke affecting the vertebral arteries will result in a lack of blood supply to the areas controlling muscle movements and coordination, speech and vision, and alertness.

3. What Is the Circle of Willis?

The circle of Willis is formed by the meeting of the internal carotid arteries and the vertebral arteries at the base of the brain.

From the circle of Willis 3 major arteries are originated: the anterior cerebral artery (ACA), the middle cerebral artery (MCA), and the posterior cerebral artery (PCA).

4. What Does the Anterior Cerebral Artery Supply?

The anterior cerebral arteries (left and right) are connected by the anterior communicating artery and supply blood to the frontal lobes and the superior parietal lobes of the brain through their cortical and central branches.

The cortical branches of the anterior cerebral arteries supply blood to:

• The olfactory cortex, gyrus rectus and medial orbital gyrus through its orbitofrontal branches
• The corpus callosum, the cingulate gyrus, the medial frontal gyrus, and the paracentral lobule through its frontal lobe branches
• The praecuneus through its parietal branches. 

The central branches of the anterior cerebral arteries supply blood to the deep cerebral structures such as the rostrum of the corpus callosum and surrounding structures.

• What Happens If There Is a Stroke in Anterior Cerebral Arteries?

A stroke affecting the anterior cerebral arteries will result in a lack of blood supply to the areas controlling thinking, decision-making, and muscle strength of the legs [2].

5. What Does the Middle Cerebral Artery Supply?

The middle cerebral artery supplies blood to the cerebrum, the anterior temporal lobes, and the insular cortices through their cortical and central branches.

The cortical branches of the middle cerebral artery supply blood to the orbital, frontal, temporal, and parietal parts of the cerebral cortex.

The central branches of the middle cerebral artery supply blood to the deep structures of the brain such as the basal ganglia, and the caudate nucleus.

• What Happens If There Is a Stroke in Middle Cerebral Arteries?

A stroke affecting the middle cerebral arteries will result in the following symptoms:

· Hemiplegia (Paralysis on one side of the body)

· Blindness (the left or right side)

· Language problems, such as impairment in the ability to form words and sentences or understanding what others are saying.

· Changes in sensation

6. What Does the Posterior Cerebral Artery Supply?

The posterior cerebral artery supplies blood to the occipital lobes at the back of the brain and the posteromedial temporal lobes through their cortical and central branches.

The cortical branches include the thalamoperforating arteries, the thalamogeniculate arteries, the posterior choroidal arteries.

• The thalamoperforating arteries supply blood to the midbrain and the thalamus.
• The thalamogeniculate arteries supply medial and lateral geniculate nucleus and the pulvinar nuclei of the thalamus.
• The posterior choroidal arteries supply blood to the choroid plexus and the posterior part of the thalamus.

The central branches include the temporal branches, the occipital branches, the parieto-occipital artery, and the calcarine artery.

• The temporal branches supply blood to the uncus, and the parahippocampal, medial and lateral occipitotemporal gyri.
• The occipital branches supply blood to the cuneus, lingual gyrus, and posterolateral surface of the occipital lobe.
• The parieto-occipital artery supplies blood to the precuneus and cuneus.
• The calcarine artery supplies blood to the cuneus and lingual gyrus.

• What Happens If There Is a Stroke in Posterior Cerebral Arteries?

A stroke affecting the anterior cerebral arteries will result in a lack of blood supply to the areas controlling vision [3].

7. What Is a Stroke?

A stroke is the interruption of blood supply to the brain causing the death of brain cells. The longer is the lack of blood supply the more damage is caused to the brain.

The causes are associated with any event that causes the interruption of blood supply to the brain. The main causes are the following:

• Ischemic stroke which is due to a blockage of an artery (e.g., Atherosclerosis).
• Hemorrhagic stroke due to the bursting of an artery causing hemorrhagie that leads to significant loss of blood.

A transient ischemic attack is when the interruption of the blood supply is temporary.

Conclusion

The brain is supplied by the internal carotid arteries and the vertebral arteries that form the circle of Willis where the anterior cerebral arteries, middle cerebral arteries, and posterior cerebral arteries branch out to supply the different parts of the brain.

A stroke in one of these arteries or its branches will have specific symptoms that are associated with the control of specific functions within the body.

There are certain conditions that increase the risk of stroke including diabetes, hypertension (high blood pressure), high cholesterol levels in the blood, and irregular heartbeats.

The post What are the arteries that supply blood to the brain? appeared first on .

• Regulation of motor movements (directed movements and reflexes)
• Balance control

However, functional imaging studies indicated its potential involvement in cognition, including working memory, executive functioning (e.g., attention, reasoning, and problem-solving), time perception, language, and emotional processing [1].

1. What Is the Structure of the Cerebellum?

The cerebellum contains almost 80% of the brain neurons and consists of two lateral hemispheres involved in the control of quick and finely coordinated movements of the arms.

The lateral hemispheres are separated by a narrow midline zone, known as the vermis, involved in coordinating the movements of the trunk and legs [2].

The cerebellum is divided into 3 lobes, the anterior lobe, the posterior lobe, and the flocculonodular lobe.

The anterior lobe is separated from the posterior lobe by the primary fissure and the posterior fissure from the flocculonodular lobe by the posterior fissure.

the flocculonodular lobe is involved in maintaining equilibrium and coordinating the movements of the eye, head, and neck.

The cerebellum has an outer layer of intricately folded grey matter (accordion-like structure) known as the cerebellum cortex that surrounds a layer of white matter known as the arbor vitae.

The arbor vitae surrounds 3 pairs of nuclei (compact groups of specialized neurons) that form the center of the white matter.

These pairs of nuclei are known as fastigial (deep nuclei), interposed, and dentate nuclei.

The cerebellar cortex is made of 3 layers: the molecular layer (outer layer), the Purkinje layer (middle layer), and the granular layer (deep layer).

The molecular layer is made of dendritic arborizations from the Purkinje cells in the Purkinje layer and fibers from the granule layer.

The Purkinje layer is made of neurons known as Purkinje cells involved in movement coordination.

The granule layer is made of granule neurons which role is unknown.

2. What Causes Cerebellum Disorders?

They are several disorders that can affect the cerebellum:

• Ischemia or stroke of the cerebellar artery (cerebellar stroke) results in reduced or absent supply of blood to the cerebellum
• Tumors (e.g., medulloblastoma) or abscess in the cerebellum
• Alcoholism (alcoholic cerebellar degeneration)
• Thiamine (vitamin B1) deficiency
• Vitamin E deficiency
• Celiac disease
• Toxin exposure such as carbon dioxide, lithium, and heavy metals.
• Brain trauma
• Excessive consumption of certain drugs (e.g., sedatives and antiseizure medications).
• Cerebellar degeneration
• Congenital malformations
• Genetics
• Metabolic and endocrine disorders such as Wilson’s disease, hypothyroidism, and inherited metabolic disorders (e.g., mitochondrial disorders).

3. What Are Some of the Cerebellum Disorders?

Cerebellum disorders can be due to congenital malformations associated with inherited genetic mutations or acquired after birth [3].

3.1. Congenital Malformations

3.1.1. What Is Joubert Syndrome?

Joubert Syndrome is an inherited disorder of brain development that affects the cerebellar vermis and the brainstem.

This disorder may manifest with the following symptoms:

• Low muscle tone resulting in muscle weakness
• Intellectual disability
• Abnormal eye movements
• Ataxia (difficulty coordinating movements)
• Episodic breathing anomalies
• Distinctive facial features.

3.1.2. What Is Dandy-Walker Malformation?

Dandy-Walker malformation is a congenital malformation that affects the development of the cerebellum and the 4^th ventricle (space around the cerebellum).

This malformation during embryonic development results in the underdevelopment of the cerebellar vermis, cystic expansion of the 4th ventricle, and an enlargement of the base of the skull.

This disorder may manifest with the following symptoms:

• Ataxia
• Muscle weakness due to low muscle tone
• Mental retardation
• Seizures
• Enlarged head circumference

3.1.3. What Is Rhombencephalosynapsis?

Rhombencephalosynapsis is a congenital abnormality of the cerebellum characterized by the absence of the vermis.

This disorder may manifest with the following symptoms:

• Truncal and/or limb ataxia
• Head stereotypies (e.g., body rocking, head banging)
• Abnormal eye movements
• Delayed motor development

3.1.4. What Is Pontocerebellar Hypoplasia?

Pontocerebellar hypoplasia is a group of inherited degenerative disorders characterized by the underdevelopment (hypoplasia) of the pons and cerebellum.

This disorder may manifest with the following symptoms:

• Mental retardation
• Slow development
• Ataxia
• Nystagmus (involuntary eye movement)

3.1.5. What Is Cerebellar Hypoplasia?

Cerebellar hypoplasia is a congenital malformation characterized by the underdevelopment (hypoplasia) of the cerebellum.

This disorder may manifest with the following symptoms:

• Intellectual disability
• Seizures
• Bilateral spastic cerebral palsy (stiff and tight muscles reducing movement ability)
• Microcephaly
• Loss of hearing

3.1.6. What Are Spinocerebellar Ataxias?

Spinocerebellar Ataxias (SCA) are a group of genetic diseases (over 25 SCA) characterized by the degeneration of the spinal cord and cerebellum.

These disorders may manifest with the following symptoms:

• Poor coordination of the eyes
• Poor speech coordination
• Progressive Gait incoordination
• Poor hand coordination

3.2. Acquired Cerebellum Disorders

Acquired cerebellum disorders are characterized by cerebellar degeneration associated with ischemic or hemorrhagic stroke, which limits blood flow or oxygen to the cerebellum.

These acquired disorders can also be associated with Multisystem atrophy, cerebellar cortical atrophy, and olivopontocerebellar degeneration.

Transmissible spongiform encephalopathies, such as Creutzfeldt-Jakob disease, can cause inflammation in the brain, including the cerebellum.

Damages to the neurons’ myelin sheath during diseases, such as multiple sclerosis can also affect nerve cells of the cerebellum.

Chronic alcohol abuse can lead to temporary or permanent cerebellar damage that can cause cerebellar degeneration.

Finally, paraneoplastic disorders that are triggered by the body’s own immune system in response to cancers (e.g., lung, ovarian, lymphatic, or breast cancer) can result in the production of substances that cause immune system cells to attack neurons in the cerebellum leading to cerebellar degeneration.

Conclusion

Although the cerebellum plays an important role in the regulation of motor movements and balance control, little is known about its development.

Little is also known about the role of the cerebellum in cognition. Interestingly, using advanced imaging techniques, some studies indicated the cerebellum may have a potential role in working memory, executive functioning, time perception, language, and emotional processing.

This potential role of the cerebellum in cognition is less surprising when we consider that it is interconnected with brain networks involved in cognition such as the cerebrum, the thalamus, and the cerebral cortex.

However, more research on this topic will certainly uncover more details about the mechanisms by which the cerebellum contributes to cognition.

The post What Are the Main Functions of the Cerebellum? appeared first on .

Explicit Memories are long-term memories that are stored in the following brain structures:

• Hippocampus
• Neocortex
• Amygdala

Implicit Memories are long-term memories that are stored in the following brain structures:

• Basal Ganglia
• Cerebellum

Working Memory and short-term memory are stored in the following brain structure:

• Prefrontal Cortex

1. What Is Memory?

Memory is the faculty of processing, storing, and remembering experiences and knowledge. It is what makes us and what makes our identity.

Memories are processed, stored, and reactivated in specific neurons that interact with each other through synapses which are known as synaptic plasticity.

Memories are made stronger or weaker depending on dynamic interactions between these groups of specialized neurons.

Memory is divided into short-term memory or working memory and long-term memory which includes explicit and implicit memories.

2. What Does It Mean to Have an Explicit Memory?

Explicit memories are conscious memories that recall events that happen to us (episodic memories) or that recall general knowledge of the world (semantic memories).

They are formed and stored in a specific group of neurons found in the hippocampus, neocortex, and amygdala.

2.1. What Does the Hippocampus Do for Memory?

The hippocampus is the structure of the brain where episodic memories are formed and stored. It is situated in the temporal lobe of the brain.

In addition to its role in long-term memory, the hippocampus is also involved in learning, flexible and goal-oriented behavior, navigation, and spatial orientation.

The hippocampus is also one of the two areas of the adult brain where there is still the production of new neurons (hippocampal neurons) due to the presence of neural stem cells.

2.2. What Does the Neocortex Do for Memory?

The neocortex serves as a storage area for temporary memories provided by the hippocampus and that are stored in a form of semantic memories.

It is the largest part of the cerebral cortex and is also involved in sensory perception (perception of outside stimuli), spatial reasoning, language, and the planning, control, and execution of voluntary movement.

2.3. What Does the Amygdala Do for Memory?

The amygdala is an almond-shaped structure of the brain’s temporal lobe involved in the formation and storage of emotional and fear-associated memories.

In addition to its role in memory, the amygdala is also involved in emotional responses (e.g., fear and anxiety) and decision-making in response to external stimuli.

3. What is Implicit Memory?

Implicit memories are unconscious or automatic memories that do not require conscious or voluntary recall to influence our behavior.

Implicit memories are divided into priming memories and procedural memories:

• Priming Memories

A priming memory is an unconscious improvement or change in dealing with a stimulus because of a previous experience with the same or a related stimulus [2].

• Procedural Memories

Procedural memory is associated with performing tasks without being consciously aware of doing them. An example is the capacity of riding a bike even if we did not cycle for a long period.

Implicit memories are formed and stored in a specific group of neurons found in the basal ganglia and cerebellum.

3.1. What Does Basal Ganglia Do for Memory?

Basal ganglia are structures resting deep within the brain and are involved in the storage of procedural memories [3].

Basal ganglia are also involved in many functions of the brain, including cognition, emotion, procedural learning, conditional learning, habit learning, and control of voluntary motor movements.

3.2. What Does the Cerebellum Do for Memory?

The cerebellum is situated at the back of the brain and is involved in procedural memory but also in motor learning and classical conditioning.

In addition, the cerebellum is involved in controlling the body balance, coordination, movement, and motor skills.

4. What Is Working Memory?

Working memory is a temporary storage of a small amount of information ready for immediate mental use [4].

5. What Is Short-Term Memory?

Working memory is a temporary storage of a small amount of information without manipulation of the information stored [5].

Theoretical concepts differentiate between working memory and short-term memory as short-term memory is suggested to refer to the maintenance while working memory involves a combination of maintenance and manipulation of information.

However, correlational studies have not been able to separate between working memory and short-term memory [5].

Working memory and short-term memory are mediated by the prefrontal cortex.

4.1. What Does the Prefrontal Cortex Do for Memory?

The prefrontal cortex is situated at the front part of the frontal lobe and is involved in the storage of a small amount of information.

In addition, the prefrontal cortex is involved in many functions of the brain, including executive processes (differentiating between conflicting thoughts), information processing, attention, judgment, behavioral organization, and certain aspects of language and speech [6].

5. What Are the Types of Memory Loss?

Memory loss is known as amnesia which can be caused by head or emotional trauma, Alzheimer’s disease, brain tumor, alcoholism, seizures, encephalitis, or stroke [7]. There are several types of amnesia:

• Retrograde Amnesia
• Anterograde Amnesia
• Post-Traumatic Amnesia
• Transient Global Amnesia
• Dissociative Amnesia
• Infantile Amnesia

5.1. What Is Retrograde Amnesia?

Retrograde amnesia is the incapacity to recall events or information from the past.

5.2. What Is Anterograde Amnesia?

Anterograde amnesia is the incapacity to recall new events or information following an amnesia incident.

5.3. What Is Post-Traumatic Amnesia?

Post-traumatic amnesia is a state of confusion associated with to incapacity to recall new events or information immediately after a traumatic incident.

5.4. What Is Transient Global Amnesia?

Transient global amnesia is a temporary sudden and total loss of short-term memory.

5.4. What Is Dissociative Amnesia?

Dissociative amnesia is the incapacity to recall personal information following trauma or stress.

5.5. What Is Infantile Amnesia?

Infantile amnesia is the incapacity to recall events or information from childhood.

Conclusion

Memory is a complex process that involves several parts of the brain that process, store, and reactivate conscious and unconscious information from the past and when we need them. Without memories, it is impossible to know who we are, what we are doing, and what we are planning to do.

The post What Part of the Brain Controls Memory? appeared first on .