Ch3 pt 2: Anatomy of the CNS

• Spinal Cord

  • comprises of 2 different areas:
  • an inner H-shaped core of gray matter
  • a surrounding area of white matter
• Gray Matter

  composed of cell bodies and unmyelinated interneurons
• white matter


  • composed of myelinated axons
• It is the myelin that gives the white matter its glossy white sheen
• dorsal hornes


  two dorsal arms of the spinal gray matter
• ventral horns


  two ventral arms of the spinal gray matter
• Spinal nerves

  • pairs of spinal nerves are attached to the spinal cord--one on the left and one on the right--at 31 different levels of the spine
  • each of these 62 spinal nerves divides as it nears the cord, and its axons are joined to the cord via one of two roots: the dorsal root or the ventral root
• Dorsal root axons

  • whether somatic or autonomic, are sensory (afferent) unipolar neurons with their cell bodies grouped together just outside the cord to form the dorsal root ganglia
  • many of their synaptic terminals are in the dorsal horns of the spinal gray matter
• neurons of the ventral root

  • efferent multipolar neurons with their cell bodies in the ventral horns
  • those that are part of the SNS project skeletal muscles
  • those that are part of the ANS project to ganglia, where they synapse on neurons that project to internal organs
• Spinal Cord and the Dorsal and Ventral Roots

  A) Gray matter

  B) whiter matter

  C) dorsal root

  D) dorsal root ganglion

  E) spinal nerve

  F) ventral root

  G) ventral

  H) dorsal

  I) dorsal horn

  J) ventral horn

  K) unipolar sensory neuron

  L) multipolar motor neuron

  
• Early Development of the Brain

  • in the vertebrate embryo, the tissue that eventually develops into the CNS is recognizable as a fluid-filled tube
  • the first indications of the developing brain are three swellings that occur at the anterior end of this tube
  • these three swellings develop into the adult forebrain, midbrain, and hindbrain
  • before birth, the initial 3 swellings in the neural tube become 5
  • this occurs because the forebrain swelling grows into two different swellings, and so does the hindbrain swelling
• 5 swellings that compose the developing brain at birth (anterior to posterior)

  1. telencephalon
  2. diencephalon
  3. mesencephalon (midbrain)
  4. metencephalon
  5. myelencephalon

  *these swellings develop into the 5 divisions of the adult brain
• in higher vertebrates, the telencephalon (the left and right cerebral hemispheres) undergoes the greatest growth during development
• brain stem -> the rest of the divisions of the brain except telencephalon
• brain stem


  the stem on which the cerebral hemispheres sit
• the myelencephalon is often referred to as the medulla
• The Early Development of the Mammalian brain compared with an adult human brain

  A) Forebrain

  B) Midbrain

  C) Hindbrain

  D) Spinal Cord

  E) Telencephalon (cerebral hemispheres)

  F) Diencephalon

  G) Mesencephalon (midbrain)

  H) Metencephalon

  I) Myelencephalon (medulla)

  J) Spinal cord

  
• 5 Divisions of the Adult Human Brain

  A) Forebrain

  B) Telencephalon

  C) Diencephalon

  D) Midbrain

  E) Mesencephalon

  F) Hindbrain

  G) Metencephalon

  H) Myelencephalon

  
• Myelencephalon or medulla


  • most posterior division of the brain
  • composed of tracts carrying signals between the rest of the brain and the body
  • contains the reticular formation
• Reticular Formation


  • complex network of about 100 tiny nuclei that occupies the central core of the brain stem from the posterior boundary of the myelencephalon to the anterior boundary of the midbrain
  • named bc of its netlike appearance (reticulum means "little net")
  • the reticular formation is referred to as the reticular activating system bc parts of it seem to play a role in arousal
  • the various nuclei of the reticular formation are involved in a variety of functions (sleep, attention, movement, maintenance of muscle tone, and cardiac, circulatory, and respiratory reflexes)
• Metencephalon

  • houses many ascending and descending tracts and part of the reticular formation
  • These structures create a bulge, called the pons, on the brain stem’s ventral surface
  • 2 Major divisions: pons and cerebellum
• Cerebellum


  • little brain
  • large, convoluted structure on the brain stem’s dorsal surface
  • an important sensorimotor structure
  • cerebellar damage eliminates the ability to precisely control one’s movements and to adapt them to changing conditions
  • the fact that cerebellar damage also produces a variety of cognitive deficits (e.g., deficits in decision making and in the use of language) suggests that the functions of the cerebellum are not restricted to sensorimotor control
• Structures of the human myelencephalon (medulla) and metencephalon

  A) Pons

  B) reticular formation

  C) medulla

  D) cerebellum

  
• Mesencephalon


  • 2 divisions: tectum and tegmentum
• Tectum

  • dorsal surface of the midbrain
  • in mammals, it is composed of 2 pairs of bumps, the colliculi (inferior colliculi and superior colliculi)
  • inferior colliculi
  • posterior pair; have auditory function
  • Superior Colliculi
  • anterior pair; have a visual-motor function; to direct the body's orientation toward or away from particular visual stimuli
  • in lower vertebrates, the function is visual-motor and is often referred to as optic tectum
• tegmentum

  • division of the mesencephalon ventral to the tectum
  • contains three colorful structures of particular interest to biopsychologists: the periaqueductal gray, the substantia nigra, and the red nucleus
• Periaqueductal gray


  gray matter situation around the cerebral aqueduct
• cerebral aqueduct

  the duct connecting the third and fourth ventricles; has a role in mediating the analgesic (pain-reducing) effects of opioid drugs
• The substantia nigra (black substance) and the red nucleus are both important components of the sensorimotor system
• Diencephalon

  • composed of two structures: the thalamus and the hypothalamus
• Thalamus

  • is the large, two-lobed structure that constitutes the top of the brain stem
  • one lobe sits on each side of the third ventricle, and the two lobes are joined by the mass intermedia which runs through the ventricle
  • visible on the surface of the thalamus are white lamina (layers) that are composed of myelinated axons
  • comprises many different pairs of nuclei, most of which project to the cortex
• The most well-understood thalamic nuclei are the sensory relay nuclei
• Sensory relay nuclei


  • nuclei that receive signals from sensory receptors, process them, and then transmit them to the appropriate areas of sensory cortex
  • e.g., Lateral geniculate nuclei (visual), medial geniculate nuclei (auditory), and ventral posterior nuclei (somatosensory systems)
  • are not one-way streets, they receive feedback signals from the very areas of cortex to which they project
  • majority of them receive input from areas of the cortex and project to other areas of the cortex
• Hypothalamus


  • located below the anterior thalamus
  • regulation of motivated behaviors (e.g., eating, sleep, and sexual behavior)
  • exerts its effects in part by regulating the release of hormones from the pituitary gland, which angles from it on the ventral surface of the brain
  • other structures that appear on the inferior surface of the hypothalamus: optic chiasm and mammalary bodies
• pituitary gland

  • "snot gland"
  • was first fiscovered in a gelatinous state behind the nose of a cadaver and was incorrectly assumed to be the main source of nasal mucus
• Optic chiasm

  • point at which the optic nerves from each eye come together and then decussate (cross over to the other side of the brain)
  • the decussating fibers are said to be contralateral and the nondecussating fibers are said to be ipsilateral
• contralateral


  projecting from one side of the body to the other
• ipsilateral

  staying on the same side of the body
• mammillary bodies

  • often considered to be part of the hypothalamus
  • pair of spherical nuclei located on the inferior surface of the hypothalamus
• Human Diencephalon

  A) Right Thalamus

  B) Left Thalamus

  C) Bands of myelinated axons

  D) hypothalamus