Physiology

• Structures and substance protecting Spinal Cord

  • Bones
  • Meninges
  • CSF
  • Blood Brain Barrier
• Meninges

  • Dura mater
  • Arachnoid
  • Pia mater
• Meningitis


  Inflammation (viral or bacterial infection), serious threat to the brain
• Encephalitis


  Inflammation of the brain tissue
• Flow of CSF

  1. Directly proportional to outflow pressure

  2. Lumbar CSF pressure is normally 70 to 180 mm H2O

  3. At a pressure of 112 mm H2O, filtration and absorption are equal

  4. Below 68 mm H2O, absorption stops
• CSF formation

  1. Plasma is passively filtered across the choroidal capillary endothelium

  2. Secretion of water and ions across the choroidal epithelium provides for active control of CSF composition and quantity

  
• Functions of CSF

  • Provides buoyancy and protects the brain from concussion
  • Regulates cerebral blood flow through adjustment in CSF pressure
  • Maintains the saline composition in the nervous system
  • Supply nutrients to the nervous system
  • Serves as lymphatics of the CNS
  • Preserves homeostasis in the nervous system
• Hydrocephalus

  Accumulation of large amount of fluid (CSF) in the brain, leads to brain herniation in adult individual
• Types of hydrocephalus


  • External/communicating hydrocephalus
  • Internal/ noncommunicating hydrocephalus
• Blood Brain Barrier


  Barrier between the blood and CSF, both at choroid plexuses and tissue capillary membrane, except in some areas of hypothalamus, pineal gland and area postrema where substance diffuse with ease
• Composition of Blood Brain Barrier


  • Endothelial cells (tight junction)
  • Epithelial cells of the choroid plexus (tight junction)
  • Plial and arachnoid membranes
  • Footlike processes of astrocytes
• Causes of Blood Brain Barrier disruption

  • Infection
  • Trauma/injury
  • Tumors
  • Marked increases in blood pressure
  • Intravenous injection of hypertonic fluid
• Functions of Blood Brain Barrier

  • Maintains the constancy of the environment of the neurons in the CNS
  • Protects the brain tissue from endogenous and exogenous toxins in the blood
  • Prevents the escape of NTA into the general circulation
• Permeability of Blood Brain Barrier

  • Highly permeable (small and non polar): water, CO2, O2, L-dopa (dopamine), and 5-HT (serotonin)
  • Less permeable (small and large polar substances): glucose (GLUT1 55k and 45k), HCO3-, Na+, Cl- K+ (Na+K+Cl- cotransporter), H+ etc.
  • Impermeable: proteins, protein-bound substances
• Circumventricular organs


  • Posterior pituitary (neurohypophysis)
  • Area postrema
  • Organum vasculosum of lamina terminalis (OVLT)
  • Subfornical organ (SFO)
• Circumventricular organs

  • Permit polypeptide hypothalamic hormones to leave the brain without disrupting the blood-brain barrier
  • Permit substances that do not cross the BBB to trigger changes in brain function
• Normal brain blood flow is 50 -65 ml/ 100 gms. of brain tissue/ minute, around 750-900ml/min
• Brain is about only 2% of the body weight but receives 15% of resting cardiac output
• Blood flow is supplied by 4 large arteries, 2 carotid, 2 vertebral merge to become Circle of Willis this travel along the brain and give rise to plial arteries where it branch out to become penetrating arteries and arterioles
• Monroe Kelly Doctrine


  The volume of blood, spinal fluid and the brain in the cranium at anytime must be relatively constant, as brain tissue and spinal fluid are incompressible

  
• Several diseases are now known to be associated with localized or general changes in cerebral blood flow, as revealed by PET scanning and fMRI techniques
• Hemispheric specialization


  Differential role of the left or right brain side in processing a specific neuronal task or behavior, one hemisphere might be predisposed to adopt a function because of specific structural and/or computational characteristics

  
• Characteristics of Dominant Hemisphere


  • Concerned with categorization and symbolization
  • For sequential and analytical processes
  • Main language center (90%) - aphasia, expressing ideas in speech and writing, understanding printed and spoken words, center for calculation
• Characteristics of Non-Dominant Hemisphere


  • For visuospatial relations
  • Simple language comprehension
  • Stereognosis
  • Non-verbal ideation
  • Recognition of faces and musical themes
  • Identification of objects by their form
  • Appreciation of art/music/tones
  • Interpretation of body language
• Cerebral Cortex

  • Neocortex
  • Archicortex
  • Paleocortex

  
• Functions of Cerebral Cortex


  • Sensory perception
  • Motor function (planning and programming)
  • Information processing (memory and learning)
  • Expression of behavior (cognition, language and communication)

  
• Areas involved in motor function


  • Primary Motor Area
  • Premotor cortex
  • Supplementary motor cortex
  • Parietal lobe
  • Primary somatosensory area

  
• Supplementary Motor Area


  Involved in planning and programming motor sequences concerned with mental rehearsal of a planned movement
• Lesions in Supplementary Motor Area cause awkwardness in performing complex movement and difficulty with bimanual coordination
• Broca's area (Brodmann area 44, 45) is involved in speech production
• Somatotopic organization


  • Continues throughout the corticospinal and corticobulbar pathways
• Cortical areas that account for corticospinal tract neurons


  • Premotor cortex (29%)
  • Supplementary motor cortex (29%)
  • Parietal lobe (40%)
  • Primary somatosensory area (40%)

  
• Supplementary Motor Area


  Above the superior bank of cingulate gyrus, involved in planning and programming motor sequences concerned with mental rehearsal of a planned movement (bilateral)
• Lesion of Supplementary Motor Area


  Awkwardness in performing complex movement, Difficulty with bimanual coordination
• Other specialized cortical areas that control motor function

  • Broca's area
  • Voluntary Eye Movement Field / Frontal Eye Field
  • Head Rotation Area
  • Area for Hand Skills
  • Primary Somatosensory Area
  • Accessory Somatosensory Area
  • Primary Visual Area
  • Accessory Visual Area
  • Primary Auditory Area
  • Accessory Auditory Area

  
• Basal Ganglia


  Controls rate of voluntary movement, Enhance or decrease voluntary activity, Involved in planning and programming
• Components of Basal Ganglia


  • Caudate nucleus
  • Putamen
  • Globus pallidus
  • Subthalamic nucleus
  • Substantia nigra
• Basal Ganglia


  • Dopaminergic nigrostriatal projection from substantia nigra pars compacta to striatum, GABAergic projection from striatum to substantia nigra pars reticulata, Striatum projects to both GPe and GPi, GPe projects to subthalamic nucleus which projects to both GPe and GPi
• Main inputs to Basal Ganglia


  Excitatory corticostriate pathway from M1 and premotor cortex, Projection from intralaminar nuclei of thalamus to striatum (thalamostriatal pathway)
• Direct Pathway


  Enhances motor activity, Controls rapid motor activity, Decreased activity causes hypokinetic behavior