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The Brain and spinal cord

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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.