lecture 15

• The brain is far more complex than the spinal cord
• The brain consists of roughly 20 billion neurons
• Embryology of the Brain

  1. CNS begins as a hollow neural tube

  2. Lumen of the tube (neurocoel) is filled with fluid

  3. Lumen of the tube will expand thus forming the various ventricles of the brain

  4. In the fourth week of development, three primary brain vesicles in the cephalic area of the neural tube enlarge to form: Prosencephalon, Mesencephalon, Rhombencephalon

  
• Embryology of the Brain

  1. Prosencephalon and rhombencephalon subdivide

  2. During the sixth week, the prosencephalon and rhombencephalon form secondary brain vesicles: Telencephalon, Diencephalon, Metencephalon, Myelencephalon

  
• The mesencephalon does not subdivide
• Medulla oblongata


  • Relays information to the thalamus and brainstem
  • Regulates heart rate, blood pressure, and digestion
• Pons


  • Relays information to the cerebellum and the thalamus
  • Regulates somatic and visceral motor centers

  
• Mesencephalon (midbrain)


  • Processes visual and auditory data
  • Maintains consciousness and alertness
  • Involved with reflexive somatic motor responses to stimuli
• Epithalamus


  • Contains the pineal gland
• Thalamus


  • Relays information to the cerebrum
  • Processes sensory information
• Hypothalamus


  • Involved in emotions, thirst, some habitual activity
  • Connects to the pituitary gland (hypophysis) via the infundibulum
• Cerebellum


  • Coordinates somatic motor function
  • Adjusts output of somatic motor centers resulting in smooth operation
• Cerebrum (telencephalon)


  • Conscious thought processes
  • Intellectual functions
  • Memory storage
  • Conscious regulation of skeletal muscle contractions
• The cerebrum consists of paired cerebral hemispheres separated by the longitudinal fissure

  
• The cerebrum contains sulci (grooves) and gyri (ridges)
• In the cerebrum and cerebellum, the white matter is covered by gray matter (cortex)
• Gray matter consists of cell bodies
• Ventricular System of the Brain

  • Four fluid-filled ventricles
  • Filled with cerebrospinal fluid (CSF)
  • CSF transports nutrients to the CNS and transports waste away from the CNS
  • CSF provides cushion for the CNS
• Lateral ventricles (ventricles 1 and 2)

  • Located in the cerebral hemispheres
  • Separated by a partition called the septum pellucidum
  • Main portion lies in the parietal lobes
  • Each has an anterior horn extending into the frontal lobe, a posterior horn extending into the occipital lobe, and an inferior horn extending into the temporal lobe
  • Each communicates with the third ventricle through the interventricular foramen
• Third ventricle


  • Communicates with the fourth ventricle through the cerebral aqueduct of the midbrain
• Fourth ventricle


  • Communicates with the central canal of the spinal cord
  • Numerous foramina in the roof communicate with the subarachnoid space of brain/spinal cord

  
• Protection of the brain

  • Bones of the skull
  • Cranial meninges
  • Cerebrospinal fluid
  • Blood brain barrier
  • Rich blood supply

  
• Cranial Meninges


  • Dura mater, arachnoid mater, and pia mater

  
• Dura Mater


  • Consists of two layers: periosteal cranial dura and meningeal cranial dura
  • Forms folds called falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae
• Arachnoid Mater


  • Contains projections called arachnoid granulations
  • Contains subdural space and subarachnoid space
  • Consists of weblike material underlining the arachnoid layer
• Pia Mater


  • Attached to the surface of the brain
  • Anchored to brain by processes of astrocytes
  • Follows the sulci and gyri of the brain
  • Helps to anchor the larger blood vessels of the cerebrum

  
• Blood Brain Barrier


  • Lining of the blood vessels consists of endothelial cells that are highly interconnected by tight junctions
  • Only lipid-soluble material can pass from the blood to the cells of the brain and spinal cord
  • Water-soluble material can only pass via the action of transport mechanisms
• There are four major regions within the brain where the blood brain barrier is different from the rest of the brain: hypothalamus, capillaries in the pineal gland, capillaries in the choroid plexus, and capillaries in the posterior lobe of the pituitary gland

  
• Cerebrospinal Fluid


  • Prevents contact of neural tissue with the surrounding bones
  • Provides support for the brain
  • Transports nutrients to the CNS tissue
  • Transports waste away from the CNS
• Formation of CSF


  1. Produced by the ependymal cells of the choroid plexus

  2. They actively transport nutrients, vitamins, and ions into the CSF

  3. They actively remove waste from the CSF
• Circulation of CSF


  1. CSF from the choroid plexus of the lateral ventricles flows through the interventricular foramen into the third ventricle, then into the cerebral aqueduct of the midbrain, then into the fourth ventricle

  2. Most flows into the subarachnoid space and a small amount enters the central canal of the spinal cord

  3. Flows around the brain and spinal cord, and eventually enters circulation via the arachnoid granulations

  
• Blood Supply to the Brain

  • Arterial blood reaches the brain via the internal carotid arteries and vertebral arteries
  • Venous blood leaves the brain mostly via the internal jugular veins
  • Circulatory disorders include cerebrovascular diseases such as cerebrovascular accident (CVA)
• Medulla Oblongata


  • All communication between the brain and spinal cord passes through it
  • Nuclei in the medulla oblongata are relay stations for sensory or motor pathways, associated with cranial nerves, and associated with the autonomic control of visceral organs

  
• Relay Stations in the Medulla Oblongata

  • Gracile nucleus and cuneate nucleus pass somatic sensory information to the thalamus
  • Solitary nucleus receives visceral sensation from the spinal nerves and cranial nerves
  • Olivary nuclei pass information from the cerebrum, spinal cord, diencephalon, and brainstem to the cerebellum

  
• Internal jugular veins


  Pathway by which blood leaves the brain
• Circulatory disorders


  • Cerebrovascular diseases such as cerebrovascular accident (CVA)
• Medulla oblongata


  • Continuous with the spinal cord to the brainstem
  • All communication between the brain and spinal cord passes through it
  • Contains nuclei that are relay stations for sensory or motor pathways
  • Contains nuclei associated with cranial nerves
  • Contains nuclei associated with the autonomic control of visceral organs

  
• Gracile nucleus and cuneate nucleus


  Pass somatic sensory information to the thalamus
• Solitary nucleus


  Receives visceral sensation from the spinal nerves and cranial nerves
• Olivary nuclei


  • Pass information from the cerebrum, spinal cord, diencephalon, and brainstem to the cerebellum
  • Create the olives (bulges on the medulla oblongata)