Brain and Cranial Nerves - Part 1 Notes

Brain Statistics

  • The adult brain:
    • Contains almost 97% of the body’s nervous tissue.
    • Has about 100 billion neurons.
    • Receives 15% of the total blood flow per minute.
    • Average weight is 1.4 kg (3 lbs).
    • Volume is typically 1200 mL.

Cranial Meninges

  • Meningeal layers continuous with spinal meninges:
    • Dura mater
    • Arachnoid mater
    • Pia mater

Main Regions of the Brain

  • Cerebrum:
    • Conscious thought, intellectual functions, memory.
    • Regulates skeletal muscle contractions.
  • Diencephalon:
    • Thalamus: Relays sensory information.
    • Hypothalamus: Controls emotions, autonomic functions, and hormone production.
  • Brainstem:
    • Midbrain: Processes visual and auditory data; generates reflexive motor responses.
    • Pons: Relays sensory information; subconscious motor centers.
    • Medulla oblongata: Relays sensory information; autonomic centers for visceral function.
  • Cerebellum:
    • Coordinates complex motor patterns; adjusts output of motor centers.

Diencephalon

  • Epithalamus:
    • Contains the pineal gland, which secretes melatonin.
  • Thalamus:
    • Processes and relays information to the cerebral cortex.
  • Hypothalamus:
    • Main visceral control center.
    • Controls autonomic nervous system, emotional responses, body temperature, hunger and thirst, behavior, sleep-wake cycles, and endocrine system.
    • Involved in memory formation.
  • Pituitary gland:
    • Major endocrine gland, connected to hypothalamus.

Brainstem

  • Connects the spinal cord and the brain; maintains vital functions.
    • Midbrain: Processes sight and sound, maintains consciousness.
    • Pons: Relay between cerebellum and thalamus; subconscious motor control.
    • Medulla oblongata: Relays sensory information; autonomic functions.

Cerebellum

  • Coordinates body movements.
  • Maintains posture and equilibrium.
  • Involved in repetitive task learning.

Ventricles

  • Expansions of the brain’s central cavity.
  • Filled with CSF and lined by ependymal cells.
    • Lateral ventricles: Lie in the cerebral hemispheres.
    • Third ventricle: Lies in the diencephalon; communicates with lateral ventricles.
    • Fourth ventricle: Lies in the hindbrain; connects with the third ventricle.

Cerebrospinal Fluid (CSF)

  • Surrounds all exposed surfaces of CNS.
    • Supports the brain.
    • Cushions neural structures.
    • Transports nutrients, chemical messengers, and wastes.
    • Used to diagnose abnormalities.

Choroid Plexus

  • Produces CSF in each ventricle.
    • Specialized ependymal cells secrete CSF.

Cerebrum

  • 83% of the brain’s total mass.
    • Divided into left and right cerebral hemispheres.
    • Controls higher mental function.
    • Processes somatic sensory and motor information.
  • Fissures:
    • Transverse cerebral fissure: Separates the cerebral hemispheres from the cerebellum.
    • Longitudinal fissure: Separates the left and right cerebral hemispheres.
  • Sulci: Grooves that divide the cerebral hemisphere into lobes.
  • Gyri: Ridges of brain tissue.
  • Cerebral cortex:
    • Site of the “conscious mind”.
    • Composed of gray matter.
    • Divided into five lobes.

Lobes of the Cerebral Cortex

  • Frontal: Primary motor area.
  • Parietal: Somatosensory area.
  • Occipital: Vision.
  • Temporal: Hearing and memory.
  • Insula: Integration of visceral sensations, emotions, and interoception.

Cerebral Cortex Functions

  • Frontal Lobe: voluntary control of skeletal muscles
  • Parietal Lobe: conscious perception of touch, pressure, pain, vibration, taste and temperature
  • Occipital Lobe: Conscious perception of visual stimuli
  • Temporal Lobe: Conscious perception of auditory and olfactory stimuli
  • All Lobes: Integration and processing of sensory data; processing and initiation of motor activities

Cerebral Lateralization

  • Left Hemisphere:
    • Sensory and motor control of the right side of the body.
    • Speech, language, comprehension.
    • Analysis and calculations.
    • Recognition of words, letters, and numbers.
  • Right Hemisphere:
    • Sensory and motor control of the left side of the body.
    • Creativity.
    • Spatial ability.
    • Context/perception.
    • Recognition of faces, places, and objects.

Fibers

  • Myelinated axons that carry information within and between hemispheres.
    • Association fibers: Connect areas within one hemisphere.
    • Commissural fibers: Connect one hemisphere to another (e.g., corpus callosum).
    • Projection fibers: Connect the cerebrum to other parts of the CNS and spinal cord.

Precentral and Postcentral Gyri

  • Central sulcus divides frontal lobe from parietal lobe.
    • Precentral gyrus (frontal lobe): Primary motor cortex; initiates voluntary movement.
    • Postcentral gyrus (parietal lobe): Primary somatosensory cortex; processes sensory information.

Homunculus

  • Areas requiring fine motor control have larger representation.
  • Areas with high tactile sensitivity have larger representation.

Speech and Language

  • Wernicke’s area:
    • Located in the left temporal lobe.
    • Involved in speech comprehension.
    • Damage: fluent speech lacking clarity; difficulty understanding language.
  • Broca’s area:
    • Located in the left frontal lobe.
    • Controls motor aspects of speech and language processing.
    • Damage: slow, poorly articulated speech, no impairment in comprehension.

Speech Production

  • Wernicke’s area processes language, sends information to Broca’s area, which signals the motor cortex to produce speech.