Hemisphere Dominance

Overview of Cerebral Hemisphere Functions

The concept of hemisphere dominance refers to the specialization of certain functions in either the left or right cerebral hemisphere. Contrary to popular belief, there is no strict division such as "right-brained" or "left-brained" personalities.

• Both hemispheres are involved in basic functions such as analyzing sensory impulses and controlling muscles.

• Functional lateralization exists for some tasks, such as language skills, which are typically dominant in the left hemisphere for most people.

• The dominant hemisphere is often responsible for verbal, analytical, and computational skills.

• The nondominant hemisphere specializes in nonverbal functions, including visuospatial processing and emotional thought.

Additional info: Lateralization is also associated with handedness and may influence learning disabilities and recovery from brain injury.

Basal Nuclei (Basal Ganglia)

Structure and Function

The basal nuclei, also known as basal ganglia, are masses of gray matter located deep within the cerebral hemispheres, adjacent to the lateral ventricles. They play a crucial role in the subconscious control of skeletal muscle activity.

• Functions: Subconscious regulation of motor plans and inhibition of counteracting movements.

• Main components:

  • Caudate nucleus

  • Lentiform nucleus (composed of putamen and globus pallidus)

  • Substantia nigra (located in the midbrain)

Additional info: Dysfunction of basal nuclei is associated with movement disorders such as Parkinson's disease and Huntington's disease.

Limbic System

Location and General Functions

The limbic system is a set of structures lying along the border between the cerebral cortex and the diencephalon. It is essential for emotional processing, memory, and motivation.

• Functions:

  • Establishes emotional states

  • Links conscious functions with autonomic functions

  • Memory storage and retrieval

  • Motivation

Main Structures of the Limbic System

• Amygdala: Almond-shaped structure deep to the temporal lobe; involved in fear conditioning, social processing, and emotional significance of memories.

• Hippocampus: Critical for memory recall and integration of "what", "where", and "when" information.

• Fornix: C-shaped bundle of nerve fibers; major output tract from hippocampus to hypothalamus.

• Hypothalamus: Contains mammillary bodies, important for recall.

• Thalamus: Relay station for sensory and motor signals.

• Limbic lobe: Arc-shaped region of cortex, includes parts of the frontal, temporal, and parietal lobes, as well as the cingulate gyrus and parahippocampal gyrus.

Additional info: The limbic system is also involved in olfaction and instinctual behaviors.

Cerebellum

Structure and Function

The cerebellum is responsible for coordinating and modulating motor commands from the cerebral cortex, fine-tuning learned movement patterns, and maintaining balance.

• Contains 10% of brain volume but 50% of neurons.

• Divided into two hemispheres by the vermis.

• Two lobes: Anterior and posterior.

• Cerebellar cortex: Thin layer covering the cerebellum, about 1/4 the thickness of the cerebral cortex.

• Folia: Folds in the cortex, similar to gyri but less prominent.

Arbor Vitae and Peduncles

• Arbor vitae: "Tree of life"; white matter forms branching patterns visible in sectional view.

• Cerebellar peduncles: Three pairs (inferior, middle, superior) link the cerebellum to the brainstem, cerebrum, and spinal cord.

• Middle and inferior peduncles carry most input to the cerebellum.

• Damage can result in ataxia: Disturbance in muscle coordination.

White Matter Connections

Types of Fibers in the Cerebrum

White matter in the cerebrum consists of myelinated axons that connect different regions of the brain.

• Association fibers: Interconnect areas of cortex within a hemisphere.

  • Arcuate fibers: Shorter, small arcs

  • Longitudinal fasciculi: Connect distant cortical areas

• Commissural fibers: Connect the two hemispheres (e.g., corpus callosum, anterior commissure).

• Projection fibers: Link cerebral cortex to underlying structures; must pass through diencephalon and form the internal capsule.

Ventricles of the Brain

Structure and Connections

The brain contains four major ventricles, which are interconnected cavities filled with cerebrospinal fluid (CSF).

• 2 lateral ventricles: One in each hemisphere, separated by the septum pellucidum.

• 3rd ventricle: Located in the diencephalon; connected to each lateral ventricle via the interventricular foramen.

• 4th ventricle: Begins in the midbrain and extends to the superior portion of the medulla oblongata; connected to the 3rd ventricle via the cerebral aqueduct and narrows to become the central canal of the spinal cord.

Choroid Plexus and CSF Production

• Choroid plexus: Specialized ependymal cells and capillaries in each ventricle produce and maintain CSF.

• Functions:

  • Contain tight junctions for selective permeability

  • Uptake water and molecules from blood into cells

  • Produce about 500 mL of CSF per day; only 150 mL present at any time

  • CSF is replaced every 8 hours

Cranial Meninges

Layers and Functions

The cranial meninges are three protective layers that surround the brain and spinal cord, providing physical stability and shock absorption.

• Dura mater: Tough, outermost layer

• Arachnoid mater: Middle layer, contains arachnoid membrane and trabeculae; followed by the subarachnoid space, which allows CSF flow around the brain

• Pia mater: Innermost layer, attached directly to the brain and extends into every fold; connected by astrocytes

Dural Folds

• Inner layer of dura mater extends into the cranial cavity to stabilize and support the brain.

• Falx cerebri: Between hemispheres of the cerebrum; contains inferior and superior sagittal sinuses.

• Falx cerebelli: Between hemispheres of the cerebellum.

• Tentorium cerebelli: Separates cerebellum from the cerebrum.

Cranial Nerves

Overview and Mnemonics

Cranial nerves are twelve pairs of nerves that emerge directly from the brain, each with specific sensory, motor, or mixed functions.

• I - Olfactory

• II - Optic

• III - Oculomotor

• IV - Trochlear

• V - Trigeminal

• VI - Abducens

• VII - Facial

• VIII - Vestibulocochlear (Auditory)

• IX - Glossopharyngeal

• X - Vagus

• XI - Accessory (Spinal)

• XII - Hypoglossal

Mnemonic for order: "On Occasion Our Trusty Truck Acts Funny, Very Good Vehicle Any How"

Mnemonic for function (sensory, motor, both): "Brains Matter More"

Cranial Nerve Classification Table

Additional info: Each cranial nerve has a specific anatomical pathway and clinical significance in neurological examination.