11. Neurophysiology Flashcards
The membrane potential of a nerve fibre can be calculated by what?
The Goldman constant-field equation is required to calculate the value of the overall membrane potential as it takes into account sodium, chloride and potassium.
Nernst equation can be applied to calculate the membrane potential for this individual ion.
Compared to plasma, CSF contains:
A. Less sodium B. Lower osmolality C. More hydrogen ions D. A higher PCO2 E. More urea
A. True. Sodium concentrations are higher in the plasma.
B. False. Both have an osmolality of around 290 mOsmol/l.
C. True. CSF has a pH of 7.32.
D. True. 6.6kPa vs 5.3 kPa in plasma.
E. False. Urea concentrations are higher in the plasma.
What is the osmolality of CSF?
Both plasma and CSF have an osmolality of around 290 mOsmol/l.
What is CSF pH?
pH of 7.32.
CSF PCO2?
6.6kPa vs 5.3 kPa in plasma.
TRUE OR FALSE:
CBF - Blood flow in the grey matter may be twice that in the whites matter.
TRUE
CBF is proportional or inversely proportional to PaCO2?
It is directly proportional to PCO2 between the range of approx 2.5 and 10.5 kPa .
What percentage of cardiac output goes to the brain?
15-20%
How does acidosis affect CBF?
Vasodilation
Majority of CBF supply comes from which vessels?
MAJORITY: internal carotid arteries
SMALL FRACTION: vertebral arteries.
Knee jerk reflex due to what stimulation?
It is dure to stretching of muscle spindles in the quadriceps muscle, caused by a tap on the patellar tendon.
Knee jerk reflex involves a single interneurone, true or false?
False. It has a single synapse.
Knee jerk reflex: what is the afferent pathway? Efferent pathway?
AFFERENT: A gamma fibres.
EFFERENT: A delta motor neuron.
What is Westphal’s sign?
Westphal’s sign is the absence or decrease of the knee jerk reflex.
How long does it take to recover knee jerk reflex after transection of the spinal cord at T6?
Transection of the cord is followed by a variable degree of spinal shock where all reflexes are depressed or absent.
Recovery of reflexes may take up to 6 weeks.
Which aspect of the spinal cord is fine touch transmitted?
Fine touch is transmitted in the:
- > > > posterior white column in the
- > > > medial and lateral fasiculi,
- > > > connect to cuneate and gracile nuclei.
What is transmitted in the spinotectal tract?
The spinotectal tract transmits pain, temperature and touch sensation to the midbrain.
When the nerve cell membrane is depolarised:
Sodium permeability is raised until the resting membrane potential is restored? T/F
False.
The rise in sodium permeability is transient.
Resting membrane potential restored by an increase in potassium conductance.
What factors limit depolarisation speed in the nerve cell membrane?
Three factors limit depolarisation speed:
- The temporary opening of the sodium channels.
- Increasing intracellular electro-positivity the initial sodium gradient reduces.
- Finally there is an increase in potassium conductance.
In a complete cord transection, what is the first reflex to recover?
The first reflexes to return are flexor reflexes to touch and anogenital reflexes.
How long after a complete spinal cord transection are reflexes recovered?
Recovery of reflexes occurs at around 2 weeks, though can be delayed for up to 6 weeks.
What equipment can be used to estimate cerebral blood flow?
SCINTILLOGRAPHY
Cerebral blood flow can be estimated by the Kety method (an application of the Fick principle), Scintillography.
Doppler is a crude but readily available method.
T/F: A decrease in arterial pressure causes vasoconstriction of cerebral vessels.
False.
Autoregulation would have the opposite effect.
How many phases does an action potential have?
It has 5 phases.Phases 0,1,2,3 and 4.
What is the resting membrane potential of a nerve fibre?
- 70 mV
When is threshold potential reached?
Once membrane potential rises from -70mV to -55mV, threshold is reached.
What signs does Tonsillar herniation cause?
Tonsillar herniation causes:
- neck stiffness
- Cheyne-Stoke breathing.
The effect of hypocapnoea-induced cerebral vasoconstriction is maintained for how long?
6 to 10 hours.
What is the normal ICP?
5-15 mmHg
is the standard normal range, although it varies with arterial pulsation, respiration, coughing and straining.
Does ICP increase linearly with increasing cerebral blood volume?
No according to -> MUNRO-KELLIE DOCTRINE:
Initially, a change in volume of one brain compartment is accompanied = RECIPROCAL change in the other compartment.
Concerning ICP: Are the Lundberg B pressure waves normal findings?
False.
Lund A + B = failed compensatory mechanisms.
Lund C = pathological/ normal.
What are Lundberg A waves?
Lundberg A waves “or plateau waves” are steep increases in ICP lasting for 5 to 10 minutes.
They are always pathological and represent reduced intracranial hypertension indicative of early brain herniation.
What are Lundberg B waves?
Lundberg B waves are oscillations of ICP at a frequency of 0.5 to 2 waves/min and are associated with an unstable ICP.
Lundberg B waves are possibly
the result of cerebral vasospasm,
because during the occurrence of these waves,
increased velocity in the MCA can be demonstrated on transcranial Doppler.
What are Lundberg C waves?
Lundberg C waves are oscillations with a frequency of 4-8 waves/min.
They have been documented in healthy subjects and are probably caused by interaction between the cardiac and respiratory cycles.
The following are parasympathetic ganglia:
Select true or false for each of the following statements.
A. Ciliary ganglion B. Otic ganglion C. Stellate ganglion D. Gasserian ganglion E. Coeliac ganglion
A. Ciliary ganglion - T
B. Otic ganglion - T
C. Stellate ganglion - F
D. Gasserian ganglion - F
E. Coeliac ganglion - F
The stellate and coeliac ganglia are sympathetic ganglia.
The gasserian ganglion is the fifth cranial nerve ganglion.
The chemical mediator released at the following sites is acetylcholine:
Select true or false for each of the following:
A. Parasympathetic preganglionic neurones
B. Parasympathetic postganglionic neurones
C. Sympathetic postganglionic neurones which innervate the heart
D. Sympathetic preganglionic neurones
E. Sympathetic postganglionic neurones which innervate sweat glands
A. Parasympathetic preganglionic neurones
B. Parasympathetic postganglionic neurones
D. Sympathetic preganglionic neurones
E. Sympathetic postganglionic neurones which innervate sweat glands
ALL TRUE EXCEPT:
C. Sympathetic postganglionic neurones which innervate the heart.
Under what conditions is CBF auto regulation impaired?
Hypoxia, Hypercapnia
The C-fibres release which neurotransmitters in response to pain? Where?
The C fibres release glutamate and substance P principally
in laminae II and III.
A-delta fibres terminate where?
Dorsal horn
A-gamma fibres are what type of fibres?
Motor
Pathways for pain sensations include descending pathways in which column?
Dorsolateral columns
In the autonomic nervous system, what leads to vasodilation and vasoconstriction in terms of
- sympathetic
- parasympathetic system?
-»> Sympathetic:
Beta 1 stimulation - dilate
alpha 1 - constrict
-»> Parasympathetic:
In the presence of an intact endothelium parasympathetic stimulation leads to a dilatation via the actions of nitric oxide.
In the autonomic nervous system, all preganglionic neurones cholinergic?
True
How does the stellate ganglia stimulation affect the heart?
The paired stellate ganglia send POSTganglionic fibres to the heart.
Stimulation via the RIGHT leads to increased HEART RATE.
while via the LEFT leads to increased CONTRACILITY.
Post-ganglionic sympathetic nerves increase catecholamine release from the adrenal glands. True or false?
False.
Sympathetic nerves reaching the adrenals are pre-ganglionic.
What enzyme synthesises acetylcholine?
enzyme choline acetyltransferase
How does acetylcholine change membrane permeability in the heart/ other tissues?
- Ach raises the membrane permeability to Na, K, and Ca in most tissues.
- In the heart only K permeability is increased.
Where is acetylcholine a neurotransmitter?
- all parasympathetic postganglionic nerve endings
- all preganglionic neurones
- sympathetic supply to
- skeletal muscle
- blood vessels
- sweat glands
Which arteries is the circle of Willis formed from?
internal carotid and vertebral arteries only
Which artery to anterior and posterior spinal arteries branch from?
vertebral artery
The anterior cerebral artery supplies which part of the cerebral hemisphere?
superior and medial parts of the cerebral hemisphere
