Introduction to Neuroanatomy PDF

Introduction to Neuroanatomy Christopher von Bartheld Introduction to Neuroanatomy Purpose of this Session Many students have had little exposure to human neuroanatomy They feel overwhelmed by the pace and the amount of detail in the lectures and labs The terminology can be confusing It is easy to l...

Introduction to Neuroanatomy Christopher von Bartheld Introduction to Neuroanatomy Purpose of this Session Many students have had little exposure to human neuroanatomy They feel overwhelmed by the pace and the amount of detail in the lectures and labs The terminology can be confusing It is easy to lose sight of the big picture Students suggested that a very simple introduction to human neuroanatomy, early in the Block, would be helpful Introduction to Neuroanatomy Basic Organization (Big Picture) Sensory Input (ascending tracts) From receptor cells to cortex Motor Output (descending tracts) Additional motor components: basal ganglia and cerebellum What are the major highways you need to know Terminology: Multiple names for the same thing The Brain as a Black Box Input Output Brain sensory motor Basic Organization: Sensory Input, Motor Output Motor output: via cranial and spinal nerves Sensory input: multiple modalities Brain & Spinal Cord 12 cranial nerves 31 spinal nerves Sensory Systems: General Rule: “Three neurons to cortex” Cortex Receptor cell (optional) 1. Bipolar / ganglion cell 2. Sensory Nucleus 3. Thalamus Cortex Receptor Exception: Olfaction 3 2 1 Ganglion cell Thalamus “Gateway to cortex” Brainstem or Spinal cord Basic Organization: Motor Systems Cerebellum (for Comparison of Intended and Actual Movement and Corrections) Motor cortex Basal Ganglia (for Initiation of Movement) Motor Neuron (in Brainstem or Spinal cord) Muscle Organization of Motor Control Major CNS Pathways (“interstate highways”) Ascending: Dorsal columns, spinothalamic tract Ascending: Internal capsule (thalamus à cortex) Descending: Corticospinal tract, cerebral peduncle Other: Cerebellar peduncles Other: Corpus callosum Telencephalon (connects the two hemispheres) Diencephalon (Mesencephalon) (Metencephalon) (Myelencephalon) Definitions/Terminology CNS = brain and spinal cord PNS = cranial and visceral nerves and ganglia Definitions/Terminology Neurons neural circuits Glia oligodendrocytes, astrocytes, microglia Definitions/Terminology Afferents carry information to the CNS Efferents carry information away from the CNS Interneurons Definitions/Terminology Nucleus collection of neuronal cell bodies in white matter (not to be confused with: nucleus of any cell) Lamina/cortex when neuronal cell bodies are organized in layers Ganglion accumulation of neuronal cell bodies in the PNS Definitions/Terminology Nerves collection of nerve fibers in the PNS Tracts collection of nerve fibers in the CNS = tractus (“bundle”), fasciculus (“bundle”), funiculus (“filamentous stalk”), peduncle (“stalk”), lemniscus (“ribbon”), column, capsule, pyramid, corona (“crown”), fornix (“arch”), crus (“leg”) Because most axons are myelinated, these tracts appear “white” hence “white matter” BUT: Weigert myelin stain is black! Definitions/Terminology Some Examples of “major highways” Pyramids = Corticospinal fibers (from motor cortex to ventral horn in spinal cord) Lower part of pyramids – site of crossing fibers! Definitions/Terminology Other Examples of “major highways” Internal Capsule = ascending fibers going to, and descending fibers coming from the cerebral cortex Crus Cerebri or Cerebral Peduncle = Corticospinal and corticobulbar fibers at the level of the midbrain Anterolateral System = Spinothalamic tract (pain and temperature) Medial Lemniscus = 2nd major tract from spinal cord to thalamus (touch/vibration/proprioception “TVP” fibers) uses different path (via dorsal columns in spinal cord) Definitions/Terminology Commissure/Decussation crossing over of nerve tracts from one side to the other Implications for localization of symptoms - neurological deficits! IMPORTANT CONCEPT: RIGHT BRAIN (CORTEX) CONTROLS LEFT SIDE OF BODY AND VICE VERSA. STROKE IN LEFT BRAIN CAUSES LESIONS ON THE RIGHT SIDE OF BODY. Concept: Right Body is represented in Left Brain, and Left Body in Right Brain A stroke on the left side of the brain will cause weakness of the body on the right side Stroke in left side of brain This is because the representation of the body is crossed before it reaches the forebrain Weakness of right side LEARNING GOALS NEUROANATOMY Know about the basic organization of the brain and spinal cord Major components of brain organization: from spinal cord to cortex and back It takes 3 neurons to get to cortex (thalamus = gateway to cortex) Major tracts and principal organization of sensory and motor systems Sensory (Input) uses two distinct pathways: pain & temperature = one “highway”; touch, vibration, proprioception (“TVP”) uses another “highway” Motor (Output): corticospinal and corticobulbar tracts run through internal capsule, then brainstem Left side of world (also left side of your body) is represented in right brain, and vice versa Terminology can be tricky to navigate – several names for the same structure or pathway