The Brain and spinal cord

The Central Nervous System: The Brain and Spinal Cord

Overview of the Brain

• Contains approximately 100 billion neurons.

• Weighs about 1.6 kg in males and 1.45 kg in females.

  • Weight proportional to body size.

• Composed of two hemispheres and multiple lobes.

• Size of the brain does not correlate with intelligence; complexity is key to processing power.

Understanding Brain Function

• Question: How does the brain produce the mind?

• Current Understanding: The workings of the brain remain largely unknown.

Research Techniques

• Insights into brain function primarily derived from studies of accident or stroke victims.

• Imaging Techniques:

  • PET (Positron Emission Tomography): Visualizes brain activity.

  • MRI (Magnetic Resonance Imaging): Shows brain structure and function.

Major Subdivisions of the Brain

1. Cerebrum

2. Diencephalon

   • Thalamus

   • Hypothalamus

   • Epithalamus

3. Brain Stem

   • Midbrain (Mesencephalon)

   • Pons

   • Medulla Oblongata

4. Cerebellum

Cerebrum

• Largest brain part; responsible for higher mental functions.

• Divided into left and right cerebral hemispheres.

• Consists of neural cortex (gray matter) which facilitates conscious thought and intelligence.

Cerebellum

• Second largest part of the brain.

• Coordinates repetitive body movements.

• Features two hemispheres and is covered by cerebellar cortex.

Cerebellar Structure and Function

• Purkinje neurons play a major role in controlling motor activities initiated by the frontal motor cortex.

Diencephalon

• Located beneath the cerebrum and cerebellum.

  • Thalamus: Relays sensory information; involved in learning and memory.

  • Hypothalamus: Associated with hormone production, emotion, and autonomic functions.

    • Pituitary gland: Major endocrine gland connected to the hypothalamus.

Brain Stem

• Processes information between the spinal cord and the cerebrum or cerebellum.

  • Midbrain: Manages sight, sound, and related reflexes.

  • Pons: Involved in motor control.

  • Medulla Oblongata: Regulates autonomic functions (heart rate, blood pressure, digestion).

Protection and Support of the Brain

• The Cranial Meninges:

  • Comprising three layers:

    1. Dura mater

    2. Arachnoid mater

    3. Pia mater

  • Continuous with spinal meninges; provides protection against cranial trauma.

Cerebral Hemispheres and Lobes

• Each hemisphere divided into: frontal, parietal, temporal, and occipital lobes.

  • Contains centers for reasoning, movement, somatic sensing, hearing, and vision.

Structural Features:

• Central Sulcus: Divides frontal and parietal lobes.

• Precentral Gyrus: Primary motor cortex.

• Postcentral Gyrus: Primary somatosensory cortex.

• Other landmarks include parieto-occipital sulcus, lateral sulcus, and transverse cerebral fissure.

Cerebral Cortex

• Accounts for about 40% of the brain’s mass; thickness of 2-4 mm.

• Center of conscious thought containing neuron cell bodies and dendrites.

• Folds in the cortex increase surface area for processing.

General Functional Organization of the Cortex

• Three functional activity types:

  1. Motor

  2. Sensory

  3. Association

• Each hemisphere controls the opposite side of the body.

• No individual brain area works alone; consciousness involves multiple areas.

Specific Areas of the Cerebral Cortex

Motor Areas

• Premotor Cortex: Involved in learned, repetitive movements (e.g., playing piano).

• Language Areas:

  • Broca's Area: Speech production, only located in the left hemisphere.

Sensory Areas

• Primary Somatosensory Area: Localizes sensation points.

• Auditory Area: Processes pitch, rhythm, and loudness.

Frontal Lobes

• Responsible for functions like self-awareness, initiative, and planning ahead.

Frontal Lobotomy

• Procedure that disconnects frontal lobes leading to loss of strong emotional reactions.

• Previously used in psychiatry but now considered obsolete due to negative effects on behavior and planning.

Multimodal Association Areas

Anterior Association Area (Prefrontal Cortex)

• Involved in intellect, complex learning, personality, judgment, and planning.

Language Areas

• Wernicke’s Area: Involved in understanding language.

• Broca’s Area: Speech production.

Brain Lateralization

• Each hemisphere is dominant for specific activities:

  • Left Hemisphere: Language, math, logic (dominance in 90% of people).

  • Right Hemisphere: Creative skills, intuition, emotion, appreciation of art and music.

  • Most left-dominant individuals are right-handed.

Reversal of Hemispheric Dominance

• Occurs in about 10% of the population, often more common in left-handed males.

Functions of the Hypothalamus

• Controls the Autonomic Nervous System and homeostasis:

  • Emotion responses, body temperature, food intake, water balance, sleep-wake cycles.

  • Supports endocrine functions through the Pituitary gland.

Spinal Cord Functions

1. Controls reflex activities independently from the brain.

2. Conducts signals to and from the brain.

Spinal Cord Anatomy

• Located within the vertebral column and acts as a major reflex center.

Meninges and Meningitis

• The Spinal Meninges protect the spinal cord and contain blood supply. Continues from cranial meninges.

• Meningitis: Infection resulting from viruses or bacteria, causing inflammation of the meninges.

Gray Matter and White Matter

• Peripheral regions contain white matter (sensory and motor neurons).

• Central region contains gray matter (nerve cell bodies around the central canal).

Cross-Sectional Anatomy of the Spinal Cord

• Gray matter divided into horns; identifiable features include anterior median fissure, posterior medial sulcus, and gray commissure.

External Anatomy of the Spinal Cord

• Tapers and ends at conus medullaris (between L1 and L2).

• Filum terminale attaches the spinal cord to the coccyx.

• Cauda equina refers to the final pairs of spinal nerves at the end.

Anatomy of Spinal Nerves

• Each spinal cord segment connected by a pair of spinal nerves.

• Spinal nerves are surrounded by three connective tissue layers that include blood vessels.

Dermatomes

• Regions of the skin innervated by cutaneous branches of spinal nerves.

Homeostatic Imbalances of the Brain

Conditions

• Meningitis: Inflammation of the meninges (can be viral or bacterial).

• Encephalitis: Brain inflammation due to viral infections, often associated with bites from ticks or mosquitoes.

Traumatic Brain Injuries

• Concussion: Caused by blow to the head without visible damage; leads to cognitive problems.

• Contusion: Results from bleeding and visible bruising, with effects dependent on the injury location.

Spinal Nerves and Herpes Zoster

• Initial chickenpox infection by varicella zoster virus can later lead to herpes zoster (shingles).

Prions and Brain Diseases

• Prions: Misfolded proteins that cause diseases like mad cow disease and Creutzfeldt-Jacob disease.

• Discovered by Stanley Prusiner; he earned a Nobel Prize in 1997.

Characteristics of Prions

• Infectious agents characterized by two forms of PrP:

  1. Normal PrP: Functional and composed primarily of a-helices.

  2. Prion PrP: Causes disease and involves beta-sheets, converting normal proteins into the misfolded form.