Exam 2: Neurophysiology Part 3 - CSF, BBB, EEG Flashcards
Three layers that brain and spinal cord enveloped by
Dura mater - outermost layer
Arachnoid mater - middle layer
Pia mater - innermost layer
Dura mater
Thick layer of fibroblasts
Fuses with bone inner surface of skull bones
Arachnoid mater
Spider web like
thin layer of fibroblasts that trap CSF between it and pia mater
Pia mater
Single layer of fibroblasts
what is cerebrospinal fluid
clear fluid present in ventricles of brain, central canal of spinal cord, and subarachnoid space (brain and spinal cord)
CSF functions (4)
Cushion brain
Maintain consistent extracellular microenvironment for neurons and glial cells (homeostasis)
Waste control system for removal of potentially harmful cellular metabolites
Distribution medium for peptide hormones and growth factors that are secreted into the CSF
Where is CSF formed
most of CSF is formed by choroid plexuses located in each of the 4 ventricles at a constant rate
CSF flow
Lateral ventricles
Interventricular foramen (of Monroe)
Third ventricle
Cerebral aqueduct (of Sylvius) of midbrain
Fourth ventricle
Subarachnoid space through foramen of Luschka
Then on to the central canal of spinal cord or lateral aperture of fourth ventricle (foramen of Luschka)
What are the choroid plexuses
cauliflower like growth of capillaries covered by thin layer of ependymal cells that form a selective, tight junction barrier to the secretions of the leaky capillaries and to other surrounding fluids
What surrounds each choroid plexus
single layer of ependymal cells that have microvilli and tight junctions
relevant processes with CSF
Transport of Na (active), chloride, and bicarbonate into the ventricles via carriers and NaKATPase as primary active transporter
Water follows NaCl passively into the ventricle
Water leaves by osmosis
Metabolization of some potentially harmful waste products
Cl uses chlorine channels, HC3O uses bicarbonate channels
Na - H exchange is secondary active transport
Cl-Na exchange is secondary active transport
HC3O - Cl exchange is tertiary active transport
Hydration reaction
CO2 + H2O < — > H2CO3 < — > HCO3 + H
H2CO3 - carbonic acid
HCO3 - bicarbonate
Why does CSF need bicarbonate
Because it works as a buffer
Bicarb can accept 1 proton (H) to make carbonic acid and then convert it to CO2 and H2O
(Hydration reaction in reverse)
What causes CSF flow
CSF flows down a pressure gradient from site of formation at choroid plexuses through ventricular system and subarachnoid space into the venous system
What are the only organs that do not contain lymphatic vessels
Brain and spinal cord
What do brain and spinal cord use instead of lymphatic vessels
Glymphatic system
Glymphatic system
Countercurrent exchange system
Arteries and veins in the subarachnoid space have countercurrent flow, the CSF around those capillaries follow in same direction
CSF flows in same direction as artery in arterial perivascular space then goes into neural tissue via aquaporins then goes into venous perivascular space via aquaporins and follows veins away
where does CSF absorption into venous system take place
dura-lined venous sinuses within the skull
what happens when CSF reaches venous sinuses
leaves system - no backflow
process of CSF absorption
Most of fluid absorbed from subarachnoid space into dural sinuses through arachnoid villi
Absorption is pressure dependent an unidirectional
Constant absorption is important to remove waste and maintain pressure
Hydrocephalus
Increased CSF volume in skull
Often associated with increased ventricular volume and increased intracranial pressure
Non-communicating hydrocephalus
Normally caused by obstruction to CSF flow (narrow cerebral aqueduct or blocked exits from 4th ventricle)
Causes ventricular regions inside brain to expand at expense of surrounding brain tissue
Communicating hydrocephalus
Impairment of absorption (can be secondary to meningitis or hemorrhage)
Can increase CSF volume in subarachnoid space which increases pressure on outside surface of brain
what kind of cells are in blood capillaries and do they contain clefts
Endothelial cells
Do not contain clefts
Passage through intercellular clefts in brain capillaries
Blocked by tight junctions between endothelial cells
Exchange of solutes is highly selective –> small uncharged lipid soluble substances
Characteristics of BBB (7)
Few or no fenestrations
Pinocytosis uncommon in BBB
Tight junctions
Abluminal side - from one tight junction to other on brain side
Luminal side - from one tight junction to another on blood side
Specific carrier systems for uptake of solutes
Endothelium surrounded by pericytes and astrocytes
Molecules that can easily pass across capillary endothelium of BBB
Small, uncharged, lipid soluble, unbound plasma proteins
Ex - O2, CO2, ethanol, nicotine
Molecules that need specific carrier mediated transport mechanisms
glucose, amino acids
Don’t fit profile of small, uncharged, lipid soluble, etc.
Transport systems of BBB
GLUT MCT Amino acid transporters OATPs OCTs OATs
Pgd - MDRs (Multi drug resistance protein)
MRPs - multi drug resistance associated protein
What does ABC mean
ATP binding cassette
Protein that can hydrolyze ATP
Efflux pump Pgp
ABC
Membrane protein, ATP dependent
first identified in cancer cells as protein that provided resistance to anti cancer drugs
Luminal side of membrane
To prevent things from reaching brain
When bad things in blood go toward brain multi drug resistance protein sends it back to lumen of capillary
MDR1
Multi drug resistance 1
Protective system against external harmful substances, poissons, and medicaments
what happened when Pgp (MDR) knockout mice got ivermectin
Ivermectin was able to reach brain and killed the mice because MDR (Pgp) was not there to send it away
what is an EEG
electrophysiological recording based on volume conduction theory (same as in ECG, electromyogram)
spread of ionic currents within extracellular fluid that can be measured using electrodes on skin
EEG and BAER
EEG - record of spontaneous brain activity
Variation - sensory-evoked potentials
BAER - brainstem auditory evoked response –> record of artificially evoked activity in brainstem and auditory system after a click stimulus in ear
Cell types found in cerebral cortex (5)
Pyramidal cells Stellate cells Astrocytes Oligodendrocytes Microglia
Pyramidal cells
Projection neurons
dendrites project up toward pial surface of cortex, some extend horizontally from cell body
Generally excitatory
Axons of pyramidal cells are efferent fibers
Stellate cells
local circuit interneurons within cortex
either excitatory or inhibitory
Cortical neurons and basket cells
Basket cells project horizontally and make synapses with cortical neurons in level II and III
changes in voltage recordings
Positive direction - deflection is down
Negative direction - deflection is up
Frequency and amplitude in EEG
Frequency - deflections per second (number of AP)
Amplitude - strength of AP
More AP = competition = weaker/shorter AP
Less AP = less competition = stronger/longer AP
EEG of alert, relaxed, and sleeping dog
Alert - high frequency, low amplitude
Relaxed - low frequency, high amplitude
Sleeping - low frequency, very hig amplitude
Sensory receptors (7)
Mechanoreceptors - inner ear, skin, muscle spindle, Golgi tendon organ
Chemoreceptors - mouth, nose, large blood vessels, brain
Thermoreceptors - skin
Photoreceptors - eye
Electroreceptors - lateral line organ in fish
Magnetoreceptors - birds (location unknown)
Nociceptors - pain detection (located in most parts of body)
Mechanism of action - mechanoreceptors
Ion channel closed –> stretch –> ion channel open
Mechanism of action - chemoreceptors
Ion channel closed –> chemical stimulus attaches to thing next to channel –> causes something to bind to ion channel on inside of cell –> ion channel open
Mechanism of action - photoreceptors
Ion channel open when thin bound to it on inside of cell
Light –> goes through cell and hits photoreceptor –> things that were bound to ion channel on inside of cell now gone –> ion channel closed
Thermoreceptors and what sensory nerve fibers they are associated with
perception of temperature
associated with sensory nerve fibers:
pain fibers
cold fibers
warmth fibers
Mechanoreceptors of the skin (5)
Hair follicle terminal -Whiskers (vibrassae) Ruffini's corpuscle Meissner's corpuscle Merkel's corpuscle Pacinian corpuscle
Are nerve fibers of mechanoreceptors myelinated
Nerve fibers of mechanoreceptors are all myelinated
Adaptation and stimulus: Meissner
Adaptation - rapidly
Stimulus - touch and vibration
Adaptation and stimulus: Merkel
Adaptation - slowly
Stimulus - touch and pressure
Adaptation and stimulus: Pacinian corpuscle
Adaptation - rapidly
Stimulus - pressure and vibration
Adaptation and stimulus: hair follicle sensor (hairy skin)
Adaptation - rapidly
Stimulus - touch and vibration
Adaptation and stimulus: Ruffini corpuscle
Adaptation - slowly
Stimulus - pressure
Tonic receptors
Slow adapting receptors
Generator potential spikes at on stage and slowly goes down until off stage
AP (Sensory neuron) - lots at on stage, continue to have AP until off stage
Phasic receptors
fast adapting receptors
Generator potential spikes at both on stage and off stage, nothing in between though
AP (sensory neuron) - only at on stage and off stage, none in between
Viscerosensory receptors
Composed primarily of free nerve endings
Visceral organs are not sensitive to cutting, heat, or cold
secondary vs primary neurons
Secondary neurons - second order neurons - entirely in CNS
Primary neurons - first order neurons - in periphery
Spinothalamic tract
pain
fibers cross midline and travel to contralateral white matter and go to brain
Spinomedullary tract
proprioception
what are viscerosensory fibers carried by
sympathetic (nociception) and parasympathetic (physiological receptors) nerves
Are viscerosensory fibers part of ANS
No, not considered part of ANS
Structural component of autonomic nerves
Types of pain
Acute - fast, sharp, transmitted by A-delta fibers (fast conducting), low threshold
Chronic pain - slow, dull, transmitted by C fibers (slow conducting), high threshold
Referred pain - pain fibers from skin/internal organs have synapses on same neurons/segments of spinal cord (pain in one place causes pain in another place due to neurons being from same part of spinal cord)
Phantom pain - perception of pain in an amputated limb
Theories - ascending damage to peripheral nerves; increase in NT in spinal cord; reorganization of motor and sensory cortices
what are pain fibers
free nerve endings
withdrawal reflex
pain fibers on skin influence motor neurons in ventral horn of spinal cord via interneurons
withdrawal reflex example
Rear paw placed on something hot
Stimulate motor neurons innervating muscles of rear of thigh - flexion of knee joint
Inhibit motor neurons innervating antagonistic muscles in front of thigh
Results in retraction of paw
How is withdrawal reflex useful in assessing depth of anesthesia
use it to make sure animal won’t feel anything during surgery
Pinch between toes, if there is a “twitch” anesthesia not deep enough
treatment of pain involves (4)
Drugs that inhibit activation of nociceptors
aspirin, ibuprofen, NSAIDs - block synthesis of prostaglandins
Drugs that block impulse conduction in pain fibers
local anesthetics - block voltage gated Na channels
Drugs that block signal transmission in pain pathways in CNS
morphine and related substances
Via activation of body’s own pain-modulating system
gate cells in spinal cord stimulated from skin through massage, touch, warm, and cold compresses
