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 choroidalcapillary 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