Brain Anatomy: Meninges, Gyri, and Sulci

Terminology

• Dura mater, the "tough mother", is the tough outer tissue layer.
• The dura mater covers and protects the brain and spinal cord and is closest to the skull
• Arachnoid mater lies between the superficial dura mater and the deeper pia mater, separated by the subarachnoid space.
• The arachnoid mater surrounds the brain
• Cerebrospinal fluid (CSF) flows in the subarachnoid space within a meshwork of trabeculae under the arachnoid
• Arachnoid villi are small protrusions that allow CSF to exit the subarachnoid space and enter the bloodstream through the dura mater into the venous sinuses
• Gyrus (pl. gyri) refers to the bumps or ridges on the cerebral cortex
• Gyri are on the surface of the cerebral cortex
• Gyri are grey matter which contains nerve cell bodies and dendrites
• Gyri increase the surface area of the brain contained within the skull to aid cognitive function
• Sulcus (pl. sulci), from the Latin word for furrow, is a depression or groove in the cerebral cortex that surrounds gyri
• Larger sulci are called fissures
• The longitudinal fissure is a deep groove between the left and right cerebral hemispheres connected at the bottom by the corpus callosum.
• It is also known as the interhemispheric or sagittal fissure.
• The transverse fissure separates the cerebrum and cerebellum

Brain Divisions

• Forebrain includes the telencephalon which is the cerebrum.
• Forebrain includes the diencephalon which is the thalamus and hypothalamus.
• Midbrain connects the forebrain and hindbrain
• Hindbrain contains the medulla, pons and cerebellum

Forebrain Lobes

• The frontal lobe is directly behind the forehead.
• The frontal lobe is the largest in the human brain
• The frontal lobe is typically the most common injury area in traumatic brain injury.
• The frontal lobe is involved in personality, emotional expression, problem-solving, memory, language, judgment, and sexual behaviors.
• The frontal lobe is the "control panel" of personality and communication ability.
• The temporal lobe is behind the ears, the second largest lobe
• The temporal lobe processes auditory information and encoding memory.
• It contains the primary auditory complex and assists in understanding language, memory acquisition, face recognition, object recognition, perception, retention of visual memory, language comprehension, and emotion association
• The parietal lobe handles sensory perception and integration
• The parietal lobe contains the primary somatic sensory cortex to transmit touch, pain, temperature, taste, hearing, sight, and smell
• The parietal lobe manages information processing, spatial orientation, coordination of movement, visual and speech perception and cognition
• The occipital lobe is at the back of the head and processes vision
• It supports visuospatial processing, determining distance/depth, color determination, object/face recognition, and memory formation
• The occipital lobe is under the parietal lobe and above the temporal

Types of Brain Damage

• Phineas Gage's frontal lobe damage produced personality changes like irreverence and impatience
• Reduced activity in the orbital cortex is associated with psychopathic tendencies
• Lobotomy, the destruction of connections between the prefrontal cortex and the rest of the brain, was previously used as a psychosis treatment to treat depression, bipolar disorder, schizophrenia, and PTSD
• Lobotomies lead to brain damage and are not considered effective

Ventricles of the Brain

• These transport and store cerebrospinal fluid (CSF)
• Lateral ventricles consist of left and right ventricles, separated by a septum, and are the two largest of these structures
• The third ventricle is a narrow funnel-shaped cavity in the brain midline, comprising the ventricular system's center
• The third ventricle communicates with the fourth ventricle

Sheep Brain Dissection

• Key structures: corpus callosum, arbor vitae, thalamus, hypothalamus, pons, medulla oblongata, pineal body, lateral ventricle

Corpus Callosum

• Described as the Latin term for "tough body."
• A large bundle of over 200 million myelinated nerves.
• Connects the halves of the brain.
• Facilitates communication between the right and left sides.
• Corpus callosotomy is a surgery to cut it to treat refractory epileptic seizures or when antiseizure medicines fail

Thalamus

• Part of the diecenphalon
• Important for sleep and arousal
• Relays motor and sensory signals to the cerebral cortex

Hypothalamus

• Region of the forebrain below the thalamus
• Coordinates the autonomic nervous system and the activity of the pituitary
• Controls nearly every hormonal system in the body, including body temperature, emotions, sleep, sex drive, childbirth, blood pressure/HR, thirst, hunger, and other homeostatic systems, and involved in sleep and emotional activity.

Pituitary Gland

• The 'master gland'
• Hormone signals initiated via hypothalamus are transmitted here
• Releases hormones that stimulate or suppress other endocrine glands in the body

Pineal Gland/Body

• A pea-shaped gland in the brain.
• Produces and regulates hormones, including melatonin.
• Plays a critical role in regulating sleep patterns and circadian rhythms and can be interrupted by light exposure.

Brainstem

• The superior colliculi are structures on the roof of the mammalian midbrain
• Integrates visual, auditory, and somatosensory spatial information, and initiates orienting movements of the eyes and head
• The inferior colliculi are part of the midbrain to serve as an auditory center in the body
• Its primary role is signal integration, frequency recognition, and pitch discrimination.
• The midbrain facilitates the signal transduction between the forebrain and body
• It has functions in motor movement, e.g eye
• Pons control respiratory rhythm of breathing and may be fundamental to rapid eye movement (REM) sleep
• It relays fibers from the cerebrum to the cerebellum, contains nuclei of four cranial nerves, and is passage to corticonuclear and corticospinal tracts
• The spinal cord transmits signals between the cord, higher brain structures, and controls autonomic activities like heartbeat and respiration

Cerebellum & Arbor Vitae

• Cerebellum occupies about 10% of the brain's volume but contains over 50% of the total number of neurons
• From vestibular receptors and proprioceptors modulate commands to motor neurons to compensate for shifts in body position or changes in load upon muscles which control posture, balance, coordination, and speech
• Cerebellum also results in smooth and balanced muscular activity, as well as learning motor behaviors.
• Arbor vitae transmits sensory and motor information to and from the cerebellum with the structure located deep in the cerebellum

Cranial Nerves

• Olfactory nerve is CN 1, and supports sense of smell
• Optic nerve is CN 2, and carries visual messages between eyes and brain and supports light and accommodation reflexes

Radiology

• Computer Tomography (CT) combines a series of X-ray images taken from different angles to create cross-sectional images.
• The magnetic resonance imaging (MRI) uses the body's natural magnetic properties to produce detailed images
• MRI indications include ischemia/infarct vascular anomalies, hemorrhage, infection, tumors/masses, trauma and diffuse axonal injuries, neurodegenerative disorders/dementias, and inflammatory conditions
• Positron emission tomography (PET) uses radioactive materials called radiotracers, a special camera, and a computer to evaluate organ and tissue functions
• PET may detect early indications of disease before any other test