Brain C2

Human Anatomy: Brain Overview

Learning Objectives

• By the end of this section, students should be able to:

  • Identify the major parts of the embryonic and adult brains.

  • Identify the major functions associated with each brain structure.

Embryonic Brain Development

• The brain forms from the anterior neural tube.

  • The center of the tube forms ventricles and canals.

• Forebrain:

  • Largest and most elaborate part of the brain.

  • Retina buds off from the diencephalon.

• Major divisions of the embryonic brain include:

  • Myelencephalon

  • Metencephalon

  • Mesencephalon

  • Diencephalon

  • Telencephalon

  • Forebrain

  • Midbrain

  • Hindbrain

Brainstem

• Functions:

  • Basic survival functions.

  • Innervation of the face and head.

  • Reflexes involving the face and head.

  • Connection to the spinal cord.

• Components:

  • Midbrain

  • Medulla oblongata

  • Pons

• Note:

  • Part of the midbrain degenerates in Parkinson’s disease.

Midbrain Nuclei

• Structure:

  • Cell bodies (grey matter) are grouped in nuclei.

• Functions:

  • Nuclei have specific motor functions.

• Definition:

  • “Nucleus” refers to a group of neuron cell bodies in the central nervous system (CNS).

• Key nuclei include:

  • Red nucleus

  • Tectum

  • Reticular formation

  • Periaqueductal grey

  • Substantia nigra

Brainstem Nuclei

• Functions:

  • Send or receive signals via cranial nerves.

  • Control unconscious processes.

  • Relay sensory information about body position.

  • Tracts carry most voluntary motor output.

• Key components:

  • Pyramid

  • Inferior olive

  • Cranial nerve nuclei

  • Reticular formation

Cerebellum

• Functions:

  • Coordinates movement aspects:

  • Precision

  • Timing

  • Coordination

  • Skill development

  • Maintains posture and equilibrium.

  • Engaged in computation.

  • Involved in learning, emotion, and behavior.

• Description:

  • Often referred to as the "little brain", it consists of approximately 75% of the brain's neurons.

• Components:

  • Peduncles link the cerebellum to other brain regions (Superior, Middle, Inferior).

Thalamus

• Description:

  • A paired collection of nuclei that acts as a relay station for the cerebral cortex.

• Functions:

  • Almost all sensory information from the peripheral nervous system (PNS) passes through it.

  • Processes information that passes through, allowing for focused attention.

  • Exception: olfaction (sense of smell) bypasses the thalamus.

Hypothalamus and Epithalamus

• Hypothalamus:

  • Composed of a collection of nuclei.

  • Functions:

  • Controls the autonomic nervous system (ANS).

  • Regulates body temperature, hunger, thirst, and sleep (homeostasis).

  • Controls endocrine system functions.

  • Involved in emotion, motivation, and memory.

• Epithalamus:

  • Contains habenula (nucleus):

  • Involved in decision-making.

  • Pineal gland:

  • Regulates sleep/wake cycles.

Cerebral Anatomy

• Insula:

  • Associated with taste.

• Cerebral Structure:

  • Lobes Overview:

  • Parietal Lobe:

    • Functions: Sensation, spatial awareness, speech.

  • Occipital Lobe:

    • Function: Vision.

  • Frontal Lobe:

    • Functions: Executive function, movement, speech, and emotion.

  • Temporal Lobe:

    • Functions: Hearing, smell, memory, and emotion.

  • Key Sulci and Fissures:

  • Central Sulcus

  • Parieto-occipital Sulcus

  • Lateral Fissure

  • Longitudinal Fissure

  • Transverse Cerebral Fissure

Cerebral Cortex

• Description:

  • Outermost layer of grey matter.

• Functions:

  • Primary sensory cortex: Receives sensory information.

  • Sensory association areas: Assign meaning to sensory input.

  • Multimodal association areas: Integrate information from multiple sources.

  • Motor areas: Responsible for planning and executing movement.

  • Notably, cortical neurons are primarily interneurons.

Cerebral White Matter

• Types of Fibers:

  • Association fibers: Connections within the same hemisphere.

  • Commissural fibers: Cross between hemispheres (e.g., corpus callosum).

  • Projection fibers: Connect cortex to other parts of the CNS, or vice versa.

• Definition:

  • White matter consists mainly of axon bundles (tracts), predominantly myelinated.

Split Brain

• Concept:

  • Split-brain patients have undergone surgery to cut the corpus callosum, which is the main bundle of neuronal fibers that connects the two cerebral hemispheres.

• Experimental Analysis:

  • A word is flashed briefly to the right field of view, and patients report what they see, processed by the left hemisphere (verbal processing dominant).

  • When a word is flashed to the left field of view, it is processed by the right hemisphere, but because it cannot share information with the left hemisphere, the patient cannot verbally articulate the word but may be able to draw it.

• Diagram of visual fields:

  • Left hemisphere: Dominant for verbal processing.

  • Right hemisphere: Non-verbal responses, including drawing.

Deep Cerebral Nuclei

• Basal Nuclei (Ganglia):

  • Functions: Regulate voluntary movements (initiation, stopping, intensity management) and time passage perception.

• Basal Forebrain Nuclei:

  • Functions: Arousal, learning, memory, and motor control.

  • Note: Degeneration links to Alzheimer’s disease.

• Key components include:

  • Basal forebrain

  • Putamen

  • Thalamus

  • Caudate

  • Globus pallidus

Limbic System

• Functions:

  • Motivation, emotional regulation, learning, and memory.

  • The system comprises various brain regions linked by function rather than strict compartmentalization.

• Specific Functions:

  • The limbic system controls the four F's:

  • Fleeing, Fighting, Feeding, and Mating.

• Major components include:

  • Cingulate

  • Hippocampus

  • Amygdala

  • Hypothalamus

  • Septum

  • Fornix

Reticular Formation

• Description:

  • Network of nuclei in the brainstem with long axons.

• Functions:

  • Coordinates systems for consciousness, arousal, and alertness.

  • Differences noted between sleep and wake states encompass:

  • Muscle tone

  • Blood pressure

  • Body temperature

  • Respiratory rate

  • Sensory information processing

• Clinical Importance:

  • The reticular formation is a target for substances like anesthesia, alcohol, and tranquilizers.

  • Damage can result in irreversible coma.