Neuroanatomy and development

The cerebral hemispheres are the two halves of the brain, which are typically referred to as the left and right hemispheres. They are separated by a structure called the corpus callosum, a bundle of axons facilitates communication between the two halves. Each hemisphere is responsible for different functions and processes information in unique ways.

Cerebral Hemispheres

1.     Left Hemisphere: 

o   Primarily associated with language, analytical thinking, and logical reasoning.

o   In most people, it is responsible for speech production and comprehension.

2.     Right Hemisphere: 

o   Often linked to creativity, intuition, and spatial awareness.

o   Plays a significant role in recognizing faces, interpreting emotions, and processing music.

Lobes of the Cerebral Hemispheres

Each hemisphere is divided into four main lobes, each with specific functions:

1.     Frontal Lobe:

o   Located at the front of the brain.

o   Responsible for higher cognitive functions such as decision-making, problemsolving, planning, and reasoning.

o   Houses the primary motor cortex, which controls voluntary movements.

o   Involved in personality, behavior, and emotional regulation.

2.     Parietal Lobe:

o   Located behind the frontal lobe.

o   Spatial cognition

o   Processes sensory information related to touch, temperature, pain, and proprioception (awareness of body position).

o   Contains the primary somatosensory cortex, which is crucial for interpreting sensory data. o Integrates different sensory modalities

3.     Temporal Lobe:

o   Located beneath the frontal and parietal lobes (side of the head above ears).

o   Plays a key role in processing auditory information and is involved in learning formation.

o   Contains the primary auditory cortex.

4.     Occipital Lobe:

o   Located at the back of the brain.

o   Primarily responsible for visual processing.

o   Contains the primary visual cortex, which interprets input from the eyes and is essential for understanding visual stimuli.

Sulci and gyri are important anatomical features of the cerebral cortex in the brain. They contribute to the brain's surface area. Sulci (sulcus singular)

•       Definition: Sulci are the grooves or indentations found on the surface of the brain. They create a boundary between different regions of the cerebral cortex. Gyri (gyrus singular)

•       Definition: Gyri are the raised ridges or folds of tissue that lie between the sulci on the surface of the brain.

*You need to know the location of the 4 lobes, cerebellum and brain stem. Use the figure above to locate these regions.

Planes to examine the brain

1.     Horizontal Plane (or Transverse Plane, blue):

o   A horizontal plane that divides the brain into superior (top) and inferior (bottom) parts.

o   Allows for cross-sectional views, facilitating the study of brain structures in a topdown perspective.

2.     Sagittal Plane (green):

o   A vertical plane that divides the brain into left and right halves.

o   Useful for examining symmetry and lateralization of brain functions.

3.     Coronal Plane (or Frontal Plane, orange):

o   A vertical plane that divides the brain into anterior (front) and posterior (back) sections.

o   Helps visualize structures in a frontal view, useful for understanding regions of the brain in relation to one another.

Brain areas and function

In addition to the lobes, a sagittal view of the brain allows identification of the cerebellum (purple) involved in motor coordination, Brain stem (vital functions, light brown). The brain stem is subdivided into midbrain, pons and medulla. The midbrain is associated with vision, hearing, sleep and wakefulness, arousal, and temperature regulation. The pons is a connection point for cranial nerves, which help to sense the movement of the head and the mouth.

Below the cortex is the cingulate gyrus (dark brown). This area is involved in pain processing, emotional responsiveness, autonomic responses, and motor tone.

The corpus callosum (light orange) are axons connecting bother brain hemispheres.

Structures in the central part of the brain

The thalamus (green) located below the fornix is an area that acts as a sensory relay

(receives sensory inputs and sends them to cortex). The fornix (purple) are axons that exit the hippocampus (you can see the hippocamps in this sagittal plane but this region is critical for memory)

The hypothalamus (area below the thalamus, pink) controls stress, feeding, sleep, and regulates hormones. The hypothalamus is connected to pituitary gland (hormonal center of the brain) and pineal gland (a gland that releases melatonin involved in sleep/wake cycles).

You can see the pituitary and pineal gland in the schematic below:

Limbic system

The limbic system is a complex set of structures located deep within the brain, primarily associated with emotions, memory, and motivation. Here are the key structures of the limbic system:

1.     Amygdala: Involved in processing emotions, particularly fear and pleasure. It plays a crucial role in the formation of emotional memories.

2.    

Hippocampus: Essential for the formation of new memories and learning. It is involved in the consolidation of information from short-term to long-term memory.

4. Hypothalamus: Regulates various autonomic functions, including hunger, thirst, temperature control, and circadian rhythms. It also influences emotional responses through its connection to the endocrine system.

6. Mammillary Bodies: Part of the hypothalamus, they are involved in the processing of memory and learning, particularly related to the recognition of smell.  

Focus only on the structures I highlighted in the paragraph above

Basal ganglia

The basal ganglia are a group of nuclei located deep within the cerebral hemispheres of the brain. They play a crucial role in coordinating movement and are involved in various functions related to motor control, habit formation, and procedural learning. Here are the key components and functions of the basal ganglia (you do not need to identify the location of these structures for the exam): Caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra (contains dopamine cell bodies that degenerate in Parkinson’s disease). 

Specialized support systems to protect the brain

1.     Meninges, three layer protective membrane composed of dura mater (outer layer), arachnoid space (filled with CSF) and pia mater (inner layer)

2.     Ventricular system: a series of chambers filled with CSF. They act as shock absorber pillows. They also provide an exchange medium between blood and brain (lateral, third, and fourth ventricles). I will NOT ask you to identify the ventricles.

3.     Blood brain barrier: network of cells and blood vessels that act as a filter to protect the brain.

In addition to providing nutrients, blood vessels can also cause damage through strokes. A hemorrhagic stroke occurs when a blood vessel ruptures, while an ischemic stroke occurs when the vessel is obstructed.

4.     Glymphatic system

The glymphatic system is a network of vessels in the brain that facilitates the clearance of waste products and excess fluids. It is primarily active during sleep. Key Features

1.     CSF Flow: Utilizes cerebrospinal fluid (CSF) to remove metabolic waste, such as amyloid-beta and tau proteins.

2.     Perivascular Spaces: Operates through spaces surrounding blood vessels, allowing CSF to exchange with interstitial fluid to enhance waste removal.

3.     Aquaporin Channels: Relies on aquaporin channels in the feet of astrocytes to facilitate fluid movement. Clinical Importance

1. Neurodegenerative Diseases: Dysfunction is linked to conditions like Alzheimer’s disease, in which waste accumulation harms neurons.

Brain development

During development a neural tube develops first after gestation (25-35 days). Then, the tip of the tube starts to expand forming the forebrain, the middle portion forms the midbrain, and the last portion connecting the spinal cord the hindbrain (40 days). 50 days after gestation the forebrain develops into the telencephalon (cerebral hemispheres) and diencephalon. The telencephalon gives rise to the cortex, basal ganglia, and limbic system. The diencephalon develops into the thalamus and hypothalamus.  The hindbrain develops into the cerebellum, pons, and medulla