Brain Anatomy: Ventricles and Meninges

• The brain is one of the largest organs and coordinates body activities.

• It's the center for thought, memory, judgment, and emotion.

• Different brain parts control functions like temperature regulation and breathing.

• The brain is contained in the skull and weighs 1300-1400 grams.

• It consists of about 1000 billion neurons, each surrounded by about 10 glial cells.

• Neurons cannot multiply but glial cells can throughout life.

• The brain is covered by "Meninges" which includes the outer duramater, middle arachnoidmater, and inner piamater.

Ventricles of the Brain

• Cavities in the brain are called ventricles
• Ventricles are filled with cerebrospinal fluid (CSF).
• There are 4 ventricles in total.
• The 2 lateral ventricles are located in the two hemispheres of the brain.
• The 3rd ventricle lies between the hypothalamus and thalamus.
• The 4th ventricle is between the brain stem and cerebellum and is continuous with the spinal cord's central cavity.

Parts of the Brain

• Cerebrum.
• Cerebellum.
• Brain stem including the medulla, pons, and midbrain.
• Diencephalon including the thalamus, hypothalamus, epithalamus, and pineal gland.

Cerebrum

• It's the largest section of the brain.

• Located in the upper portion of the brain, it processes thought, judgment, memory, problem-solving, language, and imagination.

• The cerebral cortex, is the superficial layer of the cerebrum, and is 2-4 mm thick and contains billions of neurons.

• During embryonic development, the gray matter of the cortex enlarges faster than the deeper white matter, resulting in cortical folding.

• Folds are called "gyri" or "convolutions".

• The deepest grooves are called "fissures".

• The shallower grooves are called "sulci".

• The longitudinal fissure separates the cerebrum into right and left halves called "cerebral hemispheres", with each hemisphere having 4 lobes.

• The cerebrum is divided into left and right hemispheres are connected by the "corpus callosum".

• The left hemisphere controls the right side of the body

• The right hemisphere controls the left side of the body.

Lobes of the Cerebrum

• Frontal lobe: This is the most anterior portion of the cerebrum, located under the forehead, and is responsible for motor function, personality, and speech.
• Parietal lobe: The parietal lobe is located on the top of the head and receives and interprets nerve impulses from sensory receptors and interprets language.
• Occipital lobe: The most posterior portion of the cerebrum, located at the back of the head. It receives input from the eyes and controls vision.
• Temporal lobe: Located on the sides of the head above the ears. The temporal lobe controls hearing and smell.

Functions of Cerebrum

• Motor functions like control of voluntary movements.
• Sensory functions like perception of pain, temperature, touch, hearing, taste, and smell.
• Control of intelligence, speech, memory, and learning.

Cerebellum

• It is the second largest portion of the brain.
• The cerebellum is located beneath the posterior part of the cerebrum.
• A deep groove called the "transverse fissure" separates cerebrum to cerebellum.
• The cerebellum coordinates voluntary body movements and maintains balance and equilibrium.

Cerebellum External Structure

• The external surface, called cerebellar cortex, looks like a butterfly/ constricted area called vermis.

• The lateral wings/lobes are called cerebellar hemispheres that are interconnected by a narrow portion called vermis.

• Each hemisphere consists of lobes separated by deep fissures.

• The cerebellum lies in the posterior cranial fossa, inferior to the occipital lobes.

• The cerebellum is 10% of the weight of the entire brain.

• The cerebellum is 50% of neurons.

Divisions & Layers of Cerebellum

• Anterior lobe: Regulate subconscious aspects of skeletal muscle movements.
• Posterior lobe:.
• Flocculonodular lobe: Maintains equilibrium and balance (on the inferior surface).
• Cerebellar cortex: Superficial layer of cerebellum made of gray matter called “folia”.
• Arbor vitae: Deep to gray matter, white matter resembles a branch of a tree.
• Cerebellar nuclei: Even deeper white mater that are the region of the gray mater.

Functions of the Cerebellum

• Coordinate contractions of skeletal muscles.
• Regulate posture and balance.
• Role in cognition/learning from experiences and language processing.

Brain Stem

• Brain stem consists of the midbrain, pons, and medulla oblongata.
• It is continuous with the diencephalon superiorly.
• The brain stem is continuous with the spinal cord inferiorly.
• Posteriorly, the pons and medulla are separated by the fourth ventricle.
• Midbrain, pons and medulla are connected to the cerebellum by superior, middle and inferior cerebellar peduncles.

Midbrain

• The midbrain or mesencephalon extends from the pons to the diencephalon and is about 2.5 cm long.

• The midbrain acts as a pathway for impulses to be conducted between the brain and spinal cord.

• It is associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.

• The midbrain screens information before it reach high brain structure

• The anterior part of the midbrain is called "cerebral peduncles".

• The posterior part is called "Tectum".

• The tectum contains 4 rounded elevations/swellings.

• The 2 superior elevations are the superior colliculi that receives input from the retina and the visual cortex and participates in visual reflexes.

• The 2 inferior elevations are the inferior colliculi receives auditory fibers and relay nucleus of the thalamus.

• Tegmentum: motor neurons relay inhibitory signals for unwanted body movements.

Functions of Midbrain

• Serves important functions in motor movement, particularly movements of the eye, and in auditory and visual processing.
• Dopamine produced in the substantia nigra and ventral tegmental area plays a role in excitation, motivation.
• The midbrain helps to relay information for vision and hearing.

Pons

• Pons means bridge - connects the cerebellum to the rest of the brain.
• It lies between the midbrain above and the medulla below in front of the cerebellum.
• Contains nuclei that deals with respiration, swallowing, bladder control, hearing, equilibrium, eye ball movements, facial expressions, etc.
• Like the medulla, it also contains sensory and motor tracts.

Medulla Oblongata

• It is the lowermost part of the brain stem and continuation of the superior portion of the spinal cord.

• Situated at the base of the skull and extends to the inferior border of the pons, a distance of about 3 cm.

• Ascending and descending sensory and motor white matter tracts (nerves) connecting brain to spinal cord pass through medulla oblongata.

• Many regulatory centers are located here.

• The cardiovascular center regulates the heart rate, force of heartbeat, and diameter of blood vessels.

• The medullary rhythmicity center is responsible for maintaining the basic rhythm of breathing.

• The vasomotor center regulates blood pressure.

• Others functions include vomiting, swallowing, coughing, hiccupping, and sneezing.

• 5 pairs of cranial nerves originate from the nuclei located in the medulla oblongata.

Diencephalon

• Posterior part of the forebrain that connects the midbrain with the cerebral hemispheres.
• Encloses the third ventricle.

Thalamus

• Contain mass of nerve cells.

• Thalamus means "inner room" in Greek, as it is located deep in the brain at the top of the brainstem.

• The thalamus is called the gateway to the cerebral cortex, as nearly all sensory inputs pass through it to the higher levels of the brain.

• It makes up 80% of the diencephalon.

• Important relay station for all incoming sensory nerves from periphery/spinal cord.

• Information is relayed from the thalamus to cerebrum through thalamic nuclei.

• Median geniculate nucleus is related to hearing.

• Lateral geniculate nucleus is related to vision.

• Ventral posterior nucleus is related to taste and somatic sensations like touch, pain, pressure, cold, heat, vibration.

Hypothalamus

• It sits under the thalamus at the top of the brainstem.
• Controls the autonomic nervous system.
• It’s the center for emotional response and behavior.
• Regulates body temperature.
• Regulates food intake (appetite).
• Regulates water balance and thirst.
• Controls sleep-wake cycles.
• Controls the endocrine system.
• Controls CVS regulation (heart rate & BP).

Epithalamus & Pineal Gland

• Epithalamus is a small region superior and posterior to the thalamus.
• Consists of the pineal gland.
• The pineal gland is about the size of a pea and protrudes from the posterior midline of the 3rd ventricle.
• It's an endocrine gland that secretes the hormone "Melatonin".
• Darkness stimulates the pineal gland to secrets melatonin, which promotes sleepiness.

Cranial Nerves

• The 12 pairs of cranial nerves pass through the bones of the cranium and arise from the brain inside the cranial cavity.
• These nerves may be sensory (carrying impulse to the brain), motor (carrying impulse from the brain to periphery) or mixed (containing both sensory & motor fibers).