ANATOMY OF THE BRAIN

• Central Nervous System (CNS)

  Composed of the brain and spinal cord
• Brain


  An organ roughly half the size of a loaf of bread that constantly controls behavior
• Spinal cord


  A bundle of nerves that leaves the brain and runs down the length of the back; transmits messages between the brain and the body
• Peripheral Nervous System (PNS)


  Branches out from the brain and spinal cord and reaches the extremities of the body
• Somatic Nervous System


  Specializes in the control of voluntary movements and the communication of information to and from the sense organs
• Sensory (Afferent) Neurons


  Transmit information from the perimeter of the body to the central nervous system and the brain
• Motor (Efferent) Neurons


  Communicate information in the opposite direction, sending messages from the brain and nervous system to the muscles and glands
• Autonomic Nervous System


  Concerned with the parts of the body that function involuntarily without our awareness
• Sympathetic


  Acts to prepare the body in stressful situations, engaging resources to respond to a threat
• Parasympathetic


  Acts to calm the body after an emergency situation has engaged the sympathetic division; provides a means of the body to maintain storage of energy sources
• The 12 Cranial Nerves

  • Olfactory: smell
  • Optic: visual acuity
  • Oculomotor: opening of eyelids, eye movement (upward/medial, upward/lateral, downward/lateral)
  • Trochlear: eye movement (downward/medial)
  • Trigeminal: facial sensation, chewing movements
  • Abducens: eye movement (lateral)
  • Facial: facial muscle movement (except chewing muscles) and eyelid closing
  • Vestibulocochlear: hearing and balance
  • Glossopharyngeal: taste on the posterior third of the tongue
  • Vagus: uvula (palate muscles) and swallowing
  • Accessory: shoulder shrug
  • Hypoglossal: tongue movement
• Protective layers from the scalp to the cerebral cortex

  • Dura mater (tough mother): outermost meninx
  • Arachnoid mater (spider-weblike membrane): the second layer of meninx and beneath it is the subarachnoid space which contains many blood vessels and cerebrospinal fluid
  • Pia mater (pious mother): adheres to the surface of the cerebral cortex
• Cerebrospinal fluid (CSF)


  Fills the subarachnoid space, the central canal of the spinal cord, and the cerebral ventricles of the brain
• Central canal


  A small central channel that runs the length of the spinal cord
• Cerebral ventricles


  The four large internal chambers of the brain: the two lateral ventricles, the third ventricle and the fourth ventricle
• CSF is continuously produced by the choroid plexuses -- network of capillaries (small blood vessels) that protrude into the ventricles from the pia mater
• Hydrocephalus


  A condition where the flow of CSF is blocked, resulting in a buildup of fluid in the ventricles and expansion of the entire brain
• Neurons


  Cells that are specialized for reception, conduction, and transmission of electrochemical signals
• Major external features of a typical neuron

  • Cell body
  • Dendrites
  • Axon
  • Axon terminals (terminal buttons)
  • Synapses
• Major internal features of a typical neuron

  • Endoplasmic Reticulum (ER)
  • Ribosomes
  • Golgi apparatus
  • Nucleus
  • Mitochondria
  • Microtubules
  • Synaptic vesicles
  • Neurotransmitters
• Nuclei


  (in the CNS) Clusters of cell bodies
• Ganglia


  (in the PNS) Clusters of cell bodies
• Tracts


  (in the CNS) Bundles of axons
• Nerves


  (in the PNS) Bundles of axons
• Oligodendrocytes


  Glial cells with extensions that wrap around the axons of some neurons of the CNS, forming myelin sheaths
• Schwann Cells


  Glial cells that comprise one myelin segment and can guide axonal regeneration in the PNS
• Microglia


  Smaller glial cells that respond to injury or disease by multiplying, engulfing cellular debris, and triggering inflammatory responses
• Astrocytes


  The largest glial cells that play a role in allowing the passage of some chemicals from the blood into CNS neurons and in blocking their chemicals
• Golgi Stain


  A neuroanatomical technique
• Neuroanatomical Techniques


  • Neurons are tightly packed and their parts are intricately intertwined
  • Preparing neural tissue in a variety of ways permits a clear view of different aspects of neuronal structure
  • Combining knowledge obtained from each preparation is the key to studying neuroanatomy
• Golgi Stain


  1. Exposing a block of neural tissue to potassium dichromate and silver nitrate

  2. Chemical reaction (silver chromate) stains and makes neurons visible
• Golgi Stain


  Allows seeing individual neurons in silhouette, but provides no indication of the number of neurons or the nature of their inner structure
• Nissl Stain


  • Penetrates all cells on a slide, but binds effectively only to structures in neuron cell bodies
  • Used to estimate the number of cell bodies in an area by counting Nissl-stained dots
• Electron Microscopy


  • Provides information about the details of neuronal structure
  • Limit of magnification in light microscopy is about 1,500 times, insufficient to reveal fine anatomical details
  • Greater detail can be obtained by coating thin slices with an electron-absorbing substance and passing a beam of electrons through the tissue
• Electron Microscopy


  • Scanning Electron Microscope captures neuronal structure in exquisite detail (3D)
  • Images are so detailed that they make it difficult to visualize general aspects of neuroanatomical structure
• Anterograde Tracing Methods


  1. Chemicals are injected and taken up by cell bodies, then transported forward along their axons to their terminal buttons

  2. Brain is removed, sliced, and treated to reveal the locations of the injected chemicals
• Retrograde Tracing Methods


  1. Chemicals are injected and taken up by terminal buttons, then transported backward along their cell bodies

  2. Brain is removed, sliced, and treated to reveal the locations of the injected chemicals
• Anterior - Posterior


  Anterior: toward the nose

  Posterior: toward the tail
• Dorsal - Ventral


  Dorsal: toward the surface of the back or top of the head

  Ventral: toward the surface of the chest or bottom of the head
• Medial - Lateral


  Medial: toward the midline of the body

  Lateral: toward the away from the midline, toward the body's lateral surfaces