neurology Flashcards
Draw a nerve..
how are neurons classified?
in a number of ways..
by shape e.g. monopolor, bipolar, multipolar
or by size and myelination…
Aa- large myelinated fibres - 50-100m/s
Ab
Ag
Ad
B - smaller myelinated - 3-15m/s
C - v.small unmyelinated - 0.5 to 2 m/s
where are different types of neurons found?
bipolar - sense organs
monopolar - ANS
Aa - motor neurons, proprioception in muscle spindle
Ab - touch and pressure
Ag - motor to muscle spindle
Ad - spinothalamic , sharp pain and temp
B - Autonomic pre-ganglionic
C - dull pain and post ganglionic ANS
what is myelin and what is its purpose?
myelin is a form of insulation provided to neurons. it is formed from schwaan cells or oligodendrocytes wrapping around axons to create a fatty sheath.
this helps insulate neuronal transmission such that AP will travel further before needing to be propagated (at nodes of ranvier)
therefore results in faster transmission via saltatory conduction.
how does axon diameter affect speed of AP conduction?
the larger the diameter, the fast
this is because reduced S.A: V for ions to be lost during AP hence less need to propagate (which takes time)
what are glial cells?
these are specialised cells that support the nervous system in various ways.
e.g. oligodentrocytes (CNS) and schwaan cells (PNS) produce myelin and insulate neurons
e.g. microglial act as specialised macrophages in CNS
e.g. astrocytes - create BBB and provide structure support.
what is the resting membrane potential?
At rest cells have a charge difference inside and out. this is normally a negative charge inside with compared to outside. This resting membrane potential will vary on cell type but in neurons is -70mV, cardiac cells and skeletal cells is -90mV.
It is achieved through a number of mechanisms
* Na/K ATPase - 3Na out, 2K in
* negatively charged anions in the cell - donnan effect
* equilibrium potential for pottasium - as at rest the membrane is mostly permeable to pottasium.
how can the resting membrane potential be calculated?
The nersnt equation for pottasium can be calculated to estimate the membrane potential at rest. this is because the membrane is largely permeable to pottasium.
however this is just an estimation and for more accurate calculation the goldman Katz equation is needed that takes into account other ion permeabilities
state the nernst equation…
E = RT/zF ln [out]/[in]
R = 8.31j/k/mol - universal gas c.
T = temp in kelvin
z = ion valency
F = faradays constant
what is the relative ion conc of major ions intra and extra cellularly?
Na out 135-145
Na in 15
k out 3.5-5
k in 150
ca much smaller in than out.
what is the gibbs donnan effect?
describes the distribution of charged particles across the semi-permeable membrane.
It occurs when there are charged particles on one side that the membrane is impermeable to e.g. proteins.
leads to a driving force - electrochemical gradient for other ions that are permeable.
until and charge/conc balance is reached.
draw the neuronal action potential and describe the stages
An action potential is a rapid depolarisation, an all or nothing event seen when a threshold is reached after sitmulation. It is triggered and is regenerated for propagation down a neuron
resting membrane potential = -70mV
stimulus - causes depolarisation - e.g. ligand binding opens receptor ion channel.
threshold reached = -55mV
AP triggered - positive feedback of VG Na channels opening. all or nothing +30mV
VG K channels open - repolarisation
overshoot - hyperpolarisation
VG K channels close
resting membrane restored.
what is the refractory period? types?
refractory period describes a period of time following AP whereby it is impossible or difficult to produce another AP.
This is because of innactivation of VG Na channels immediately after they are activated.
Initially all of them will be innactive - impossible to stimulate - absolute
after some time, some will begin to recover - higher threshold needed to cause AP.
important to ensure unidirectional flow of AP
how does an action potential propagate?
depolarisation as ions spreads as current in cell.
causes further AP to be produced in next segment along.
behind in refractory.
in myelinated cells will travel to next node of ranvier where further VG Na channels found - saltatory conduction.
what affects the velocity of an action potential ?
diameter - wider, less SA:V for current to be lost
myelin - insulation from current being lost, promotes saltatory.
temperature - increases movement of ions
draw a compound action potential recorded over time…
within one nerve fibre are various axons each with different diameters/ degree of myelination so slightly different conduction velocities. hence different peaks seen as each depolarises at different speeds.
what determines the direction of the neuronal signal?
synape - receptors on one side , NT released from one side
Refractory period.
what is meant by orthodromic and antidromic conduction?
orthodromic - one direction
antidromic - if AP was stimulated in centre of a neuron it would travel in both directions.
what is axoplasmic flow?
NT are synthesised in cell bodies and transported to the synapse by axoplasmic flow.
can be anterograde - to the synapse
or retrograde - from synapse to cell body
describe the anatomy of the spinal cord..
From top to bottom:
Thin tubular structure that lies in the verebral canal. travels from foramen magnum and terminates at conus medularis (L1/2 in adults, L3 in paeds)
surrounded in meninges and CSF
tethered to coccyx by the filum terminale (strand of pia mater)
there is a dural sac containing spinal nerves (cauda equina that ends at S2
Transverse:
within the cord is grey and white matter - grey matter contains nuclei which are split into laminae and white matter contains ascending and descending myelinated tracts.
emerging:
along its length it emits pairs of spinal nerves that exit through intervertebral foramina. 8 Cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.
describe the organisation of spinal nerves..
at each level of the spinal cord emerges a pair of spinal nerves - left side and right side.
7 cervical - above
C8 below
12 thoracic - below
5 lumbar - below
5 sacral
1 cocyx
these are mixed nerves and contain both sensory and motor components. the sensory fibres enter the dorsal horn, ventral fibres leave anterior horn and these come together to form a spinal nerve.
supplies each dermatome/ myotome.
describe the blood supply to the spinal cord…
3 arteries that run whole length vertically -
2 x posterior spinal artery - 1/3 posterior portion,
1 x anterior spinal artery - 2/3 anteiror portion.
anterior spinal artery arises from R+L vertebral arteries that are from basilar artery.
posterior spinal artery = arises from posterior inferior cerebellar artery (branch of vertebral artery)
plus there is blood supply form the anterior and posterior segmental arteries at each level.
Artery for adamkiewicz is largest of these in lower thoracic upper lumbar region.
(adam cer vit ch)
describe the venous drainage of the spinal cord?
3 anterior
3 posterior veins
then into systemic segmental veins
Describe the anatomy of spinothalamic tract
carries pain, temp and crude touch / pressure
pain and temp in lateral, others in anterior.
1st order = Ad and C fibres enter spinal cord via dorsal horn, synapse in dorsal horn substantia gelatinosa
2nd order = cross over to contralateral cord. travel up in spinothalamic tract to the thalamus where they synapse with 3rd order
3rd order = travel to cortex via internal capsule
describe the anatomy of dorsal columns medial leminiscus pathway
carries info on fine touch, proprioception and vibration sense
1st order = Abeta - into dorsal horn and ascend ipsilaterally to the medulla where they synapse with 2nd order
2nd order = from medulla cross to contralateral side and synapse to thalamus
3rd order = thal to cortex via internal capsule
Fasciculus gracilis: Carries information from the lower body (below T6).
Fasciculus cuneatus: Carries information from the upper body (above T6).
tell me about the descending spinal pathways..
the descending pathways carry motor information from brain and brainstem to peripheries.
The major one is the corticospinal tract which is responsible for conscious movement
- starts in pre-central gyrus of motor cortex
- UMN leave motor cortex and travel to medulla via the internal capsule
- at medulla some fibres cross over and 10% remains ipsilateral. The 90% that crossed are called the lateral corticospinal tract and responsible for limb movement, the other 10% are the anterior corticospinal tract, responsible for posture.
- at the ventral horn the UMN synapse with LMN
- the lLMN leave ventral root and join spinal nerves to innervate muscles.
other descending tracts includ corticobulbar e.g. responsible for head and neck. Also rubrospinal and others.
what areas of the brain do you that are involved in movement?
primary motor cortex = pre central gyrus
basal ganglia = fine tuning amplitude
cerebellum = coordination
pre-motor areas = planning
can you explain why in a stroke there is forehead sparring…
the motor supply for the face is by the corticobulbar tract.
this originates in cortex where UMN emerge and synapse with LMN at CN nuclei.
Most of these have b/l innervation i.e. right and left cortex both synapse with R and L CN nuclei except for hypoglossal nerve and the top part of facial nerve.
therefore the facial nerve - upper branches will show weakness if one side of brain is gone. the rest of the face will have innervation by other side.
draw a pic to help
what are the effects of acute spinal cord injury ?
In the acute phase spinal shock is seen. which includes
* hypotension
* flaccid paralysis
* hyporeflexia
* pripism
* urinary retention
depending on place of injury ..
if above C3 - diaphragm innervation effected - respiratory paralysis
if above T8 - loss of intercostals, poor cough, reduced FRC
at any level - loss of sensation/ motor control below that point.
later spastic paralysis, and hyperreflexia - UMN signs.
draw and label cross section of spinal cord showing major pathways…
what is brown sequard?
this is the syndrome presenation seen when there is a hemisection of the spinal cord. i.e. one half is injured.
it results in loss of contralateral spinothalamic pathways below the lesion. and loss of ipsilateral corticospinal and dorsal columns below the region.
what is anterior spinal artery syndrome?
stroke in the anterior spinal artery results in ischaemia to 2/3 anterior cord.
hence - pain, temp, motor
sparing of dorsal columns - proprioception and fine touch + vibration
describe central cord syndrome?
this is where there is injury to the cente of the cord extending outwards e.g. syringomyelia (cyst in central canal)
this will effect spinothalamic tracts crossin the cord at that level
**it will also affect motor nerves upper >lower ** = hallmark sign
it will also affect some dorsal columns
what is cauda equina syndrome?
the cauda equina is a collection of spinal nerves that continues on after the spinal cord has ended (L2/3).
Compression of these nerves results in a syndrome of back pain, saddle paraesthesia, loss of anal tone, b/l leg weakness and loss bladder / bowel control
can be caused most commonly by L5/S1 disc prolapse but also tumours, abscess, trauma.
what happens to spinal cord in B12 deficiency?
subacute degeneration of the cord
lack of B12 means it cant act as a co-factor for methionine synthase which is required to replenish myelin
hence dordal columns and lateral columns are most effected
- loss of prop, vibration, fine touch
- plus loss of lateral corticospinal - spasticity
describe the anatomy and function of the BBB
The BBB is a physical barrier created between the blood and brain to protect the brain for chemical injury.
It consists of endothelial cells with tight junctions, basement membrane and astrocytes.
This results in a physical barrier making it hard for free flow of molecules between blood and brain
hence
* maintains extracellular environment of brain
* protects from harmful chemicals
* maintain local high conc of NT and prevents spread to systemic
describe methods of transport across BBB?
simple diffusion - CO2, O2, inhalation agents (lipid soluble stuff)
active transport - small ions - allows regulation of CSF composition
fasciliated diffusion - GLUT1 and aquaporin
pinocytosis - vesicle transport e.g. insulin
can you tell me any areas of the brain that fall outside the BBB?
pituitary
pineal
choroid plexus
median eminence of hypothalamus - osmoreceptors
area postrema
can you name any substances that cant cross BBB?
bile and ammonia
drugs - L dopa, mannitol
what is the function of CSF?
CSF is fluid found between pia and arachnoid layers i.e. within the subarachnoid space. In total around 150ml of fluid at any one time and 500ml is produced per day by choroid plexus cells.
it has a number of roles including
1. acting as a shock absorber by increasing boyancy
2. regulates ICP - can act as a buffer for pressure changes
3. helps maintain a constant chemical environment inc removal of waste
4. part of the mechanisms for respiratory control based on PaCO2 by producing H+
describe the production and path for CSF…
produced in lateral ventricles by choroid plexus
travels via foramen monro into 3rd ventricle
then via aqueduct of sylvius into 4th ventricle and then via 2 further foramen into the subarachnoid space whereby it is absorbed by archnoid granulations.
foramen mag-en-die (medial foramen)
foramen lushk - lateral
(also produced by 3rd and 4th ventricles choroid plexus)
how does the composition of CSF compare to plasma?
slightly more acidic - 7.32
more chloride
less protein, less glucose, less bicarbonate
same K, same Na , same osmolality
what is the opening pressure of the CSF?
10-15mmHg lying down
20-30mmHg sitting up
what problems can occur with CSF circulation?
if too much/ too little CSF is produced it can result in problems in intracranial pressure
production - too much e.g. choroid tumour. too little e.g. choroid plexus are under perfused
flow / obstruction - tumours, bleeding - pressure can build up
removal - infection/ damage to arachnoid granulations - pressure builds up
if pressure builds up it can result in hydrocephalus
what is hydrocephalus?
increased volume of CSF
can be as a result of increased production, obstruction to flow or decreased resorption
pressure can build up and increase size of ventricles and compress the brain.
can be classified by onset e.g. congential vs acquired.
aquired causes include tumours, SAH, meningitis with adhesions.
managed by ventricular drains / shunts
how can CSF be used for diagnostication…
sampling of CSF is useful in diagnostics.
The biochemistry, cellular counts and gram stain can be analysed for example a low glucose may suggest bacterial infection, high white cells could suggest autoimmunity or infection, bleeding/ xanthachromia could suggest SAH.
Draw the circle of willis
the circle of wilis describes the organisation of blod supply to the brain. there is a posterior and anterior circulation which anastomose
anteriro = internal carotid
posterior = vertebral arteries feeding basilar artery.
basilar artery central one come down - not labelled on diagram.
which areas of brain are suplied by which arteries?
anterior cerebral artery = frontal and parietal
middle cerebral artery = lateral surfaces - temporal lobe
posterior cerebral artery = temporal and occipital
vertebral artery = brain stem and cerebellum
describe the venous drainage of the brain…
brain parenchyema is drain via cerebral veins which drain into sagital sinuses. eventually all meet into transverse sinus then sigmoid sinus then into IJV.
superior and inferior saggital sinus drain cerebral and cerebellar cortices
the superior sagital sinus drains into the transverse sinus
the inferior sagital sinus drains into the straight sinus and then the transverse sinus
Explain the factors that influence cerebral blood flow
cerebral blood flow = cerebral perfusion pressure / cerebral vascular resistance. hence anything affecting these will alter CBF
CPP in turn is affected by MAP and ICP
hence overall - MAP, ICP, radius vasculature, viscosity of blood all will effect blood flow
cerebral blood flow is autoregulated and under influence of a nother of physiological variables to ensure blood flow meets demand.
- autoregulation. CBF is autoregulated between a MAP of 50-150mmHg. therefore is MAP drops, there will be vasodilation to maintain blood flow (myogenic response)
- PaCO2 - linear relationship until CO2 is high e.g. more than 10kpa or very low less than 3kpa. this is because CO2 causes vasodilation
- PaO2 - minimal effect until less than 8kpa and then exponential rise with drop in PaO2. again due to vasodilation effect of hypoxia.
- temperature also affects CBF - reduced temp, reduces O2 consumption and thus CBF due to coupling.
draw a curve to show how autoregulation may be different in HTN ?
shifts to the right
auto reg occurs over higher range e.g. 70-170mmHg
therefore need to maintain a MAP about 70 in anaesthesia in those with HTN
how do anaesthetic drugs affect CBF ?
volatile - increase CBF and reduce O2 consumption - uncoupling of flow metabolism coupling
N20 - increases both CBF and O2 consumption
NMBA = no effect
ketamine = rise in ICP, O2 consumption and CBP
benzos and IV inductions agents = reduce CBF and reduce O2 consumption
what is the monro kielle doctrine hypothesis?
brain is a closed box
composed of different compartments - brain tissue, blood, CSF.
for ICP to be maintained, these 3 compartments must be balanced, increase in one leads to compensation by decrease in another.
Eventually other compartments cant compensat and there is a sharp rise in pressure for small changes in volume.
once ICP increases CPP drops unless MAP is increased further. (CPP = MAP - ICP)
compensation occurs via - venous drainage and CSF drainage initially.
what is the vasodilatory cascade?
this occurs following reduction in ICP which results in a viscious cycle…
reduced MAP leads to fall in CPP
this causes vasodilation (via autoreg)
increase in blood volume
further fall in ICP and so on.
draw an intracranial pressure waveform..
measured via an ICP transducer e.g. ventricular drain or subarchnoid bolt
3 components - 1. pulse wave (split into 3)
- P1 = arterial pressure
- P2 = tidal wave - reflection of pulse on brain tisue
- P3 - dicrotic wave - venous pressure.
baseline = respiratory wave = varies with respiration
some wave patterns can suggest pathology = slow wave = type A , B and C
describe the physiology of the knee jerk reflex…
monosynaptic reflex arc that results in rapid contraction of quadricept in response to stretch of quadricep muscle.
at same time as monosynaptic reflex there is also inhibitory interneuron which inhibits biceps femoris = reciprical innervation.
similar stretch reflexes exist in many muscle groups and help to maintain posture and tone and prevent injury.
what is a polysynaptic reflex arc? or crossed extensor reflex
for example the withdrawal reflex in response to pain
Ad fibres carrying pain - synapse with motor neurons for withdawal and contralateral limb for stability. multiple motor neurons are involved to coordinate the whole withdrawal movement.
other inputs can over ride this.
label the following structures of one of the cranial nerves shown in the picture
- Vagus nerve.
- Superior laryngeal nerve.
- Internal laryngeal nerve.
- External laryngeal nerve.
- Recurrent laryngeal nerve.
describe the course of left and right vagus nerve within the thorax..
On the right side,
* passes across anterior to subclavian artery
* descends by the side of the trachea to root of lung to pulmonary plexus and oesophageal plexus
on left
* enters the thorax between the left carotid and subclavian arteries,.
* runs along the anterior surface of the oesophagus,
* it unites with the nerve of the right side in the oesophageal plexus
recurrent laryngeal nerve on the
left - hooks under the arch of the aorta, ascending to innervate the majority of the intrinsic muscles of the larynx. hence longer course.
right - hooks under subclavian
how does pressure, protein, glucose and WCC change in CNS infections (bacteria, TB, viral)
