Neuropathology Flashcards
How is the Nervous System organized?
CNS
PNS
Brain and Spinal cord
Somatic and Autonomic Nervous System
What are the two components of the CNS?
Brain and Spinal Cord
What are the two components of the peripheral nervous system?
Cranial nerves
Spinal Nerves
What are the voluntary and involuntary PNS pathways?
Somatic (voluntary)
Autonomic (involuntary)
What is the name of the sensory somatic pathways?
Afferent
What is the name of the effector somatic pathways?
Efferent
What are the two branches of the autonomic nervous system?
Sympathetic
Parasympathetic
What are the tree types of afferent information that can be transmitted to the CNS?
Somatic sensory
Visceral Sensory
Special Sensory
What are the two types of efferent responses?
Somatic motor
Autonomic motor
What are the three components of a ANS reflex?
Sensory
Central integrator
Motor effector
What are the functions of the CNS?
Central control center
Integrates many incoming signals and coordinates appropriate outgoing neural signals
Carry out higher mental function (memory and learning)
What are the functions of the PNS?
Connect CNS with peripheral structures
Connective tissue provides protection and support making the PNA nerves more resilient
Consists of bundles of nerve fibers, connective tissue and blood vessels
If injury were to occur to both the CNS and PNS which is most likely to recover and why?
PNS, since protective connective tissue is present
How are spinal nerves named?
Named for their site of emergence from the vertebral column
At what point are spinal nerves no longer considered part of the CNS?
Once exited from the spinal cord are now part of the PNS
What component of the brain is the spinal cord an extension of?
The Medulla Oblongata
What bones make up the vertebral column?
7 Cervical 12 Thoracic 5 Lumbar 5 Sacral 1 Coccyx (4 fused)
Where do the nerves of the cauda equina originate?
Conus Medullaris
What components make up the cauda equina?
2-5 Lumbar nerve pairs
1-5 Sacral nerve pairs
Coccygeal nerves
What structures does the cauda equina innervate?
Pelvic organs
Lower limbs
PSNS innervation to bladder and internal/external anal sphincters
At what level does the spinal cord typically stop?
T12-L2
What is the length of the pre-ganglionic fibers in the SNS compared to the PSNS?
Sympathetic short
PSNS long
What is the neurotransmitter of the SNS?
NE
What is the neurotransmitter of the PSNS?
Ach
Where do SNS nerves originate?
Thoracic and Lumbar
Where do the PSNS nerves originate?
Cranial Sacral
What are the two types of cells of the nervous system?
Neurons and Supporting Cells
What are the components of a neuron?
Cell body
Dendrite
Axon
What name is used to describe a dense pack of cell bodies in the CNS?
Nucleus
What name is used to describe a dense pack of cell bodies in the PNS?
Ganglia or a Plexus
What is the purpose of a dendrite?
It catches impulses directed toward a cell body
What is the purpose of an axon?
It creates impulses away from the cell body
What is the name of the supporting cells in the CNS?
Neuroglial
What is the name of the supporting cells in the PNS?
Schwann
What type of cells are the majority in the brain?
Supporting cells
What increases the surface area for receiving incoming messages from other neurons?
Cytoplasm
At what point does electronic conduction occur?
Unmyelinated Axon
What type of conduction occurs in an myelinated axon?
Sultatory Conduction
What are the nodes of Ranvier?
Area of high density of VG Na channels that potentiate the AP along the axon
What are the benefits of Sultatory conduction?
Its fast
Energy efficient, only have Na/K ATP pumps at the nodes
What are the functions of the ependymal cells?
Moves CSF through the ventricles
Barrier between CSF and interstitial fluid
What type of cells produce myelin?
Oligodendrocytes
What are the functions of the astrocytes?
Regulate composition of interstitial fluid
Form supportive framework for the nerve cells
Provide glucose to and remove ammonia from the neurons
What is the equivalent to the macrophage in the CNS?
Microglia
What are the three layers of a nerve?
Epineurium
Perineurium
Endoneurium
How is a nerve organized?
Each axon is called a nerve fiber –> the nerve fiber aligns into a nerve bundle –> the nerve bundle runs together in a peripheral nerve
What can be considered a nerve fiber?
Axon or a dendrite
Where are nerves located?
In the peripheral nervous system, can be sensory or motor fiber
What terminology is used to describe a bundle of fibers in the CNS?
A nerve tract
What is considered the white matter of the CNS?
Composed mainly of myelinated nerve fibers which often extend the length of the spinal cord
What makes up the gray matter of the CNS?
Nerve cells bodies and non-myelinated nerve fibers
What is a tract?
Nerve fibers of the brain or spinal cord with common origin and destination (ascending or descending)
What type of information does an afferent neuron carry?
Conveys info from tissues and organs to CNS
Sensory receptors
What type of information does an efferent neuron carry?
Convey inför from he CNS out to the effector cells
Where are the cell bodies and dendrites of efferent neurons located?
Within the CNS, axons extend out to periphery
What is the purpose of an interneuron?
Connect afferent and efferent neurons within the CNS
Where are interneurons located?
Within the CNS
What factors does neuronal health, function and survival depend on?
Blood flow to the neurons
Waste removal from neurons
Fluid removal from the cranial vast
What waste needs to be removed from neurons?
Neurotransmitters need to be flushed away or dangerously high levels can accumulate
What consequences can occur if proper fluid removal from the cranial vault does not occur?
Increase ICP and reduce cerebral blood flow
What is the equation used to determine blood pressure?
delta p = Q x R –> BP = SV x HR x TPR
Where CO = Q
delta p = arterial pressure - venous pressure
TPR = resistance
At what distance from a capillary will a cell receive diffusion of nutrients?
50um
What values represent the normal cerebral blood flow curve?
60-160 MAP is able to be regulated
What metabolism is the brain highly dependent upon?
glucose metabolism
What type of cells are able to use lactic acid as fuel?
Cardia myocytes and brain cells
How does ATP affect neuron volume and function?
ATP is required for activation of pumps that regulate intracellular ion concentrations and thus intracellular volume
What is osmotic pressure?
The pressure that must be applied to a solution to prevent the net flow of water into it
What term is used to describe the number of molecules in a solution?
Osmoles
What is the osmolality of a solution?
The osmotic concentration of a solution expressed as osmoses of solute per kg of solution
How does neuronal ischemia cause cell death?
Ischemia –> anaerobic metabolism –> lactic acid
lactic acid accumulation/ pump dysfunction = cell swelling
Neuroexcitotoxicity = cell death
How does lactic acid accumulation cause cell swelling?
Intracellular H ion concentration increases = pH decrease
The Na/H exchanger moves H out Na in = cell swelling
How does neuroexcitatoxicity occur with lactic acid accumulation?
Increased intracellular Na concentration (Na/H exchanger) causes RMP to be less negative, closer to threshold and increase AP probability
How do glutamate levels increase with neuroexcitatoxicity?
Elevated Na brings neurons closer to threshold causes the release of glutamate from synaptic boutons
Glutamate waste accumulates due to reduced blood flow
What eight factors come into play with cerebral ischemia?
Cellular acidosis Cellular swelling Neuroexcitotoxicity Enzyme activation NO production Inflammation Apoptosis Necrosis
How does increased glutamate cause additional enzyme activation?
Glutamate causes Na/Ca influx into the cell
Ca is a powerful second messenger and activates additional enzymes
What enzymes are activated from neuronal ischemia?
Protease and Lipase –> digest cell inside out
Reactive oxygen species
Once mitochondrial injury occurs, what happens to the cell?
Mitochondrial depolarization induces apoptosis or necrosis
What is apoptosis?
Programmed cell death, the cell can’t recover and genetic transcription stops making proteins and shrinks
What occurs during cell necrosis?
Lyses open and its contents leak out causing injury to other cells
What cells release pro-inflammatory cytokines after becoming ischemic?
Neurons, glial cells and leukocytes
How do leukocytes augment ischemic injury?
Cause occlusion of microcirculation
Release proteolytic enzymes and free radicles
Why is waste removal from neuron so important?
Higher than normal concentrations of any substance will injure brain cells –> inflammation
What are the waste products of neurons?
CO2, lactic acid, neurotransmitters, hormones and other secreted substances
What contents are in the cranial vault?
Brain 80%
Blood 12%
CSF 8%
What occurs when there is excess volume in the cranial vault?
Increased ICP
How is CPP calculated?
CPP = MAP - ICP
What are the functions of the CSF?
Protects the brain
Where is CFS produced?
Choroid plexus
Where does CSF drain into the venous circulation?
Arachnoid villi where it enters into the sagittal sinus then into the jugular and into the SVC
What type of cranial bleed has the highest risk of plugging the arachnoid villi?
Subarachnoid bleed
Why is cerebral circulation required?
Waste product removal
Substrate delivery
Maintaining physiological environment
What percentage of CO does the brain receiver?
15%
How does CBF rain constant?
Autoregulation and other feedback mechanisms
What is the average CBF in an adult?
50mL/100g/min (750mL/min)
What part of the brain receives more CBF?
White matter 80mL/100g/m
Gray matter 20mL/100g/m
How does we calculate CBF?
CPP
R
What occurs on an EEG when there is only 20-25mL/100g/m of CBF?
Slowing
What occurs on an EEG when there is only 15-20mL/100g/m of CBF?
Flat
What occurs on an EEG when there is only 10mL/100g/m of CBF?
Irreversible brain damage
What is the normal ICP?
Less than 10mmHg
At what ICP will CPP and CBF be compromised?
Greater than 30mmHg
What is a normal CPP?
80-100
How is CBF related to CPP?
CBF is directly proportional to CPP
How does CPP change is a patients CVP is greater than their ICP?
CPP = MAP - CVP
Which artery carries majority of the blood to the brain?
Middle cerebral artery- 80%
What are the two types of auto regulation?
Myogenic and Metabolic
How does myogenic auto regulation function?
Intrinsic response of smooth muscle in arterioles to change in MAP
How does metabolic auto regulation function?
Metabolic demand exceeds CBF, metabolites released cause vasodilation
At what MAP is the BBB disturbed?
MAPs greater than 150-160 can result in disruption of the BBB and cerebral edema/hemorrhage
How do changes in the CPP affect cerebral vasculature?
Decreased CPP = vasodilation
Increased CPP = vasoconstriction
Where do pediatric patient’s MAP lie on the auto regulation curve compared to adults?
Its lower than adults making them more susceptible to changes in CBF if there is a reduction in MAP
How is the cerebral auto regulation curve affected by HTN?
Shifts to the right in chronic HTN, can be restored if compliant to treatment
Why does the changed cerebral auto regulation curve in chronic HTN patients affect anesthesia?
We drop BP with drugs, can fall below shifted auto regulation and cause issues with regulating CBF
How does metabolic auto regulation occur?
Too many byproducts sensed = vasodilation
Low metabolism = vasoconstriction
What parts of the ANS innervate the intracranial vessels?
Sympathetic fibers
Parasympathetic fibers
Non-cholinergic/ Non-adrenergic fibers
What is the relationship between CBF and PaCO2?
CBF is directly proportional to PaCO2 between 20-80mmHg
Below what PaO2 will vasculature and CBF be impacted?
PaO2 less than 60mmHg
How does body temperature affect CBF?
CBF changes by 5-7% per 1C
Hypothermia decreases CBF and CMR
Hyperthermia increases CBF and CMR
How does viscosity impact CBF?
Decreased viscosity can increase CBF
At what Hct is said to be optimal cerebral O2 delivery?
30%
How does anesthesia impact CBF?
Anesthetics increase CFB and decrease CMR (uncoupling)
What percentage of total body metabolism is used by the brain?
20%
What is the average CMRO in an adult?
3-3.8mL O2/100g/min
= 50mL/min
What area of the brain has the greatest CMRO?
Gray matter of the cerebral cortex
At what O2 partial pressure does a person become unconscious?
Less than 30mmHg, takes about 10 seconds
What is cerebral function dependent upon?
Continuous glucose supply, 90% glucose metabolized aerobically
What is the typical glucose consumption?
5mg/100g/min
=75mg/min
What cells form the junction between the cerebral vasculature endothelial cells which are nearly fused?
Astrocytes, responsible for BBB
What governs the movement of a substance past the BBB?
Size, charge, lipid solubility and protein binding
What is the BBB semi-permeable to ?
Electrolytes
What should not cross the BBB unless pathology is present?
Proteins
How do changes in plasma electrolyte concentrations affect the amount of fluid in the brain?
H2O moves freely across BBB, a change to plasma electrolyte concentrations produce a transient osmotic gradient between plasma and brain
How would hyper/hypo tonicity of the plasma affect fluid in the brain?
Hypotonicity plasma = net movement of H2O into brain
Hypertonicity plasma = net movement H2O out of brain
What drug can be given to brain water content?
Mannitol
How might a newborn develop Kernicterus?
If the child is jaundice and bile pigments enter the BBB, if untreated can cause brain damage or hearing loss
How do the ependymal cells move CSF through the ventricles?
They have cilia on apical surface which move CSF
What do the ependymal cells allow into the choroid plexus?
Allow for selective movement of water and electrolytes into the CSF
Where is the choroid plexus located?
3rd and 4th ventricles
How much CSF does a typical produce in one hour?
21mL/hr or 500mL/day
What is the typical CSF composition?
K Ca HCO3 and glucose are lower,
Na Cl and Mg are higher
Very low protein content and NO RBCs
What is the total volume of CSF in the cranium and spinal cord at any given time?
150mL
What is the normal pH and specific gravity of CSF?
SG: 1.002-1.009
pH: 7.32
What is the typical route of flow of CSF?
Lateral ventricles –> foramen of Monro –> 3rd ventricles –> aqueduct of Sylvius –> 4th ventricle –> enters subarachnoid space through the foramen of Magendie
What are the three meningeal layers around the brain and spinal cord?
Dura mater
Arachnoid mater
Pia mater
What factors affect CSF drainage?
Clogged Arachnoid villi
Increased CVP
If the contents of the cranial vault increase, what is the first compensatory mechanism?
Decreased CSF production and increased drainage
Why must an individual be laying lateral in order to get an accurate ICP measurement?
Gravity will have no affect in the lateral position
What is said about intracranial compliance when ICP is low?
High compliance when the ICP is low
What can conclusion can be made based on the ICP compliance graph?
Once we exceed a certain pressure (10mmHg) small changes in volume will elicit large changes in pressure
What can occur with sustained elevations in ICP?
Herniation of the brain (foramen magnum)
What part of the brain contains the cerebral cortex?
Forebrain
What are the functions of the cerebral cortex?
Participate in perception, the generation of skilled movements, reasoning, learning and memory
What are the major functions of the thalamus?
It is a synaptic relay station for sensory pathways on their way to the cerebral cortex
Participate in skeletal muscle coordination
Awareness
What structure of the brain is responsible for coordinated movements for posture and balance and participates in some learning?
Cerebellum
What are the three components of the brainstem?
Midbrain, Pons and Medulla Oblongata
What cranial nerves cell bodies are located in the brainstem?
III-XII
What type od stimulus is sensed by tactile messiness’ corpuscle?
Light touch
What type od stimulus is sensed by Merkle’s corpuscles?
Touch
What type od stimulus is sensed by free nerve endings?
Pain
What type od stimulus is sensed by pacinian corpuscle?
Vibration and deep pressure
What type od stimulus is sensed by ruffini corpuscle?
Warmth
What type of sensory stimulus crosses high?
Discriminating touch via dorsal column
What type of sensory stimulus crosses low?
Pain and temperature vis lateral column
What is the mechanism of skeletal muscle tone?
Stretch receptors send afferent information to the spinal cord (reflex) and cerebellum efferent messages are sent back.
Increased rate of afferent firing increases tone
Decreased rate of firing reduces motor tone
What is the significance of the bulboreticular area in relation to skeletal muscle tone?
Facilitates gamma motor neurons which will facilitate increased muscle tone
What modulates autonomic and somatic motor tone?
Sensory information