Chapter 13

Protection and Support of the Brain

65. Three Cranial Meninges (from superficial to deep):

  • Dura Mater: Tough, outer layer; two layers (periosteal and meningeal); forms dural venous sinuses.

  • Arachnoid Mater: Middle, web-like layer; contains subarachnoid space filled with cerebrospinal fluid (CSF).

  • Pia Mater: Thin, innermost layer that directly adheres to the brain surface.

  • Functions: Protect brain, support vessels, contain CSF.

  • Comparison to Spinal Meninges: Similar layers, but spinal dura has only one layer and is separated from vertebrae by epidural space (absent in the cranium).

66. Cerebrospinal Fluid (CSF):

  • Functions: Buoyancy (reduces weight), protection (cushion), and environmental stability.

  • Production: By choroid plexuses (ependymal cells + capillaries) in ventricles.

  • Circulation: Lateral ventricles → interventricular foramen → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space (via apertures) and central canal.

  • Reabsorption: Through arachnoid villi into dural venous sinuses.

67. Blood-Brain Barrier (BBB):

  • Definition: Selective barrier formed by tight junctions between endothelial cells of capillaries, astrocyte feet, and a basement membrane.

  • Function: Protects the brain from harmful substances, but allows nutrients and some drugs through.

Cerebrum

68. General Functions & Structures:

  • Cerebrum: Responsible for thought, memory, sensation, voluntary movement.

  • Cerebral Cortex: Outer gray matter, site of conscious thought.

  • Cerebral Hemispheres: Left and right; connected by corpus callosum.

  • Gray Matter: Neuron cell bodies; in cortex and nuclei.

  • White Matter: Myelinated axons.

  • Fibers: Connect brain regions.

  • Gyri: Ridges (e.g., precentral gyrus).

  • Sulci: Shallow grooves.

  • Fissures: Deep grooves (e.g., longitudinal fissure).

9. Key Cortex Areas and Functions:

  • Precentral Gyrus: Primary motor cortex; controls voluntary movement.

  • Broca’s Area: Motor speech (usually in left hemisphere).

  • Postcentral Gyrus: Primary somatosensory cortex; processes touch, pressure, pain.

  • Primary Visual Cortex: Occipital lobe; vision.

  • Primary Auditory Cortex: Temporal lobe; hearing.

  • Olfactory Cortex: Temporal lobe; smell.

  • Prefrontal Cortex: Higher-level thinking, decision-making, personality.

  • Wernicke’s Area: Language comprehension (usually left hemisphere).

70. White Matter Fibers:

  • Association Fibers: Connect regions within the same hemisphere.

  • Commissural Fibers: Connect corresponding regions in opposite hemispheres (e.g., corpus callosum).

  • Projection Fibers: Connect cortex with lower brain regions or spinal cord (e.g., internal capsule).

Diencephalon

71. Thalamus:

  • Relay station for sensory impulses (except smell); directs info to appropriate cortex areas.

73. Hypothalamus:

  • Controls autonomic nervous system and endocrine system.

  • Regulates body temperature, hunger, thirst, circadian rhythms, emotions.

  • Produces hormones (e.g., oxytocin, ADH).

  • Maintains homeostasis.

Brainstem

74. Brainstem Functions:

  • Midbrain: Visual and auditory reflexes (e.g., turning head), motor control.

  • Pons: Coordinates movement and breathing; relays signals between cerebrum and cerebellum.

  • Medulla Oblongata: Regulates vital functions—heart rate, respiration, blood pressure, reflexes (e.g., coughing, swallowing).

Cerebellum

75. Functions of the Cerebellum:

  • Coordinates voluntary movements.

  • Maintains posture, balance, and muscle tone.

  • Adjusts motor commands for smooth execution.