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ED Primary Exam > Week 6 Physiology + Anatomy - Nervous System/Transmission + CNS Anatomy > Flashcards

Week 6 Physiology + Anatomy - Nervous System/Transmission + CNS Anatomy Flashcards

1
Q

Describe the synthesis of acetylcholine?

A

ACh synthesised in cytoplasm from acetyl-CoA and choline via choline acetyltransferase.

Transported into vesicles which then are directed to inner membrane, and associated with VAMPs and SNAPs which participate in fusion of the vesicle with membrane to release neurotransmitter

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2
Q

What sequence of events leads to release of ACh into synapse?

A
  1. Action potential arrives into nerve terminal
  2. Opening of voltage gated Ca2+ channels
  3. Calcium interacts with “Vesicle associated membrane proteins” and triggers fusion with terminal cell membrane
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3
Q

What is the effect of ACh in synaptic cleft, and how is its action terminated?

A

ACh binds to nicotinic or muscarinic receptors and cause downstream effect.

Action terminated by acetylcholinesterase enzymes in synaptic cleft

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4
Q

What is the precursor to tyramine in regards to catecholamine synthesis?

A

Phenylalanine

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5
Q

What are the steps involved in synthesis of adrenergic neurotransmitters?

A
  1. Adrenergic neurons transport precursor amino acid (tyrosine) into the nerve ending
  2. Tyrosine converted to dopa via tyrosine hydroxylase (rate limiting step) –> dopamine –> noradrenaline –> adrenaline

Dopa to dopamine via dopa decarboxylase
Dopamine to noradrenaline by dopamine betahydroxylase
Noradrenaline to adrenaline via PNMT

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6
Q

What sequence of events leads to release of adrenergic NT in synaptic cleft?

A

Similar to cholinergic:
1. Action potential arrival
2. Ca2+ influx via voltage gated channels
3. Vesicle fusion with neuronal cell membrane and release of neurotransmitters (along with ATP, dopamine-beta hydroxylase )

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7
Q

How is the action of adrenergic transmission terminated?

A

1) Diffusion away from receptor site (with eventual metabolism in plasma/liver, or metabolism via MAO and COMT

2) Reuptake into nerve terminal by NET

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8
Q

What is an indirectly acting sympathomimetic?

A

I.e. amphetamines, ephedrine - capable of releasing stored neurotransmitters from adrenergic nerve endings via calcium independent processes

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9
Q

What are the different subtypes of GABA Receptors?

A

A, B and C (C in retina only, A + B in CNS)

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10
Q

What type of receptor is GABA-A? Structure?

A

Ion channel receptor

Pentamer structure, 2xalpha, 2xbeta and 1x gamma subunits. Site of GABA binding allows increased Cl- conductance into cell

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11
Q

What type of receptors is GABA-B?

A

GPCR - increases K+ conductance (efflux) and inhibits Ca2+ influx into neurons via G inhibitory protein mechanism

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12
Q

What are the steps involved in synthesis of serotonin?

A

Tryptophan –> 5-HTP –> serotonin via hydroxylase reactions

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13
Q

Where is the highest concentration of serotonin in the body?

A

Platelets
GIT (enterochromaffin cells)
Brain stem raphe nuclei

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14
Q

How is effect of serotonin terminated?

A

Reuptake into nerve terminal

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15
Q

What are the different classes/types of serotonin receptors?

A

GPCR, except 5 HT-3

5HT3 - ligand gated ion channel, related to vomiting, site of action of ondansetron
5HT2A - platelet aggregation and smooth muscle contraction
5HT4 - peristalsis and secretion
5HT 6 + 7 (brain/CNS

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16
Q

What is the clinical triad of serotonin syndrome?

A

Cognitive: delirium, coma
Autonomic: HTN, tachycardia, diaphoresis
Neurological: myoclonus, hyper-reflexia

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16
Q

What are the basic components of a reflex arc?

A
  1. Sensor organ/component
  2. Afferent neuron
  3. Synapse
  4. Efferent neuron
  5. Effector
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17
Q

What is the classic example of a monosynaptic reflex arc?

A

Stretch reflex, i.e. patella reflex

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18
Q

What is the classic example of a poly synaptic reflex arc?

A

Withdrawal reflex (at least 1 interneuron between afferent and efferent neurons)

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19
Q

What is the stretch reflex?

A

When muscle spindle is stretched, it causes reflex contraction

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20
Q

What is the inverse stretch reflex?

A

When muscle stretched to a tension too great, Golgi tendon organ causes sudden relaxation of muscle

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21
Q

Describe steps in patellar reflex?

A
  1. Tapping of patella tendon causes spindles in quadriceps femoris to send afferent signals of stretch to spinal cord
  2. Sensory neuron synapses with the motor neuron in anterior horn of spinal cord at level, causing there to be stimulation of quadriceps to contract
  3. Sensory neuron also synapses with inhibitory interneuron which then causes relaxation of hamstring muscles to prevent antagonism
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22
Q

What are the steps of sensory transmission of vision?

A
  1. Stimulation of sensory neurons within the retina/fovea centralis
  2. Optic nerve
  3. Optic chiasm
  4. Optic tracts
  5. Lateral geniculate bodies
  6. Visual cortex
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23
Q

What is the purpose of the nystagmus reflex?

A

Also known as vestibule-ocular reflex, maintains ocular fixation with head movement

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24
Q

What are the ascending tracts of the spinal cord?

A

Dorsal Column - Medial Lemniscus
Spinothalamic (Lateral and anterior)
Spino-cerebellar

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25
Q

What is the role of the dorsal column, how many neurons involved, and where does it decussate?

A

Dorsal column = fine touch, vibration and proprioception.

3 neurons involved: 1st order, second order, third order

  1. First order neuron (peripheral sensory neuron) travels on ipsilateral side up the spinal cord to synapse in the medulla
  2. Second order neuron (in medulla) decussates and synapses in the thalamus, and is relayed onwards to terminate in sensory cortex
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26
Q

What is the role of the spinothalamic tract, how many neurons involved, and where does it decussate?

A

Comprised of anterior and lateral spinothalamic tracts.

Anterior = light touch and pressure
Lateral = pain and temperature

3 neurons involved.

Sensory neuron enters the spinal cord, ascend 1-2 vertebral levels, and synapse at the tip of the dorsal horn on ipsilateral side.

2nd order neurons decussate at that level of the spinal cord, and ascend the lateral/anterior spinothalamic tract to synapse in thalamus and then be relayed onwards to the cortex

27
Q

What is the role of the spinocerebellar tract?

A

Transmission of unconscious proprioceptive information to brain for regulating movement/posture

28
Q

What is ‘the motor pathway’?

A

Corticospinal tract

29
Q

What is the role of the corticospinal tract, how many neurons, and where does it decussate?

A

Supplies musculature of the body for voluntary control.

2 neurons in pathway, cortical descending neuron which decussates within medullary pyramids and then synapses in the anterior horn to the lower motor neuron (which will have an effect on skeletal muscle)

30
Q

What is the corticobulbar pathway? What is different about this type of innervation compared with corticospinal?

A

Tract for motor control of muscles of face and neck.

Lateral aspects of primary motor cortex, still upper and lower motor neuron.

Synapses within nuclei of cranial nerve ganglia.

Corticobulbar tracts have dual innervation (largely) to cranial nerve nuclei (i.e. facial nerve getting bilateral cortical innervation to upper half of face, but contralateral only to lower half of face)

31
Q

What type of lesion causes forehead sparing? Why?

A

UMN lesion

Dual innervation to facial nerve nuclei means that stroke/insult to one side of brain will cause weakness to lower half of face, but above level of eyes receives innervation from ipsilateral side of brain, and so forehead muscles preserved in stroke.

However if LMN lesion, no sparing as the effector neuron itself cannot transmit signal to muscle (Bell’s palsy)

32
Q

What are the features of complete cord transection?

A

Complete loss of sensation and paralysis below level affected

33
Q

What are the features of cord hemi-section? (Brown-Sequard Syndrome)?

A

Because hemisection will sever dorsal columns, corticospinal and spinothalamic tracts, it will cause:

  1. Complete sensory loss on ipsilateral side
  2. Complete motor paralysis on ipsilateral side
  3. Contralateral loss of pain/temperature sensation (due to fact that spinothalamic tract ascends 1-2 levels before decussating in the spinal cord and travelling in contralateral tract
34
Q

What is the difference in posturing between brain stem transection and cerebral cortex transection?

A

Brainstem transection = decerebrate posturing (extensor posturing)

Cerebral cortex transection = decorticate posturing (flexion of upper limb, extension of lower limbs)

35
Q

What are the 3 components of a ‘nerve’?

A
  1. Bundle of nerve fibres outside the CNS
  2. Connective tissue coverings that surround and bind nerve fibres together
  3. Blood vessels that nourish nerve fibres and their coverings
36
Q

What are the components of a ‘spinal nerve’?

A

The anterior and posterior nerve roots, which unite to form a mixed spinal nerve (with all branches subsequently carrying mixed sensory and motor fibres)

37
Q

What structure separates the frontal lobes from the parietal lobes?

A

Central sulcus

38
Q

What structure separates frontal and parietal lobes from temporal lobe inferiorly?

A

Lateral sulcus

39
Q

What structure separates the temporal/parietal lobes from occipital lobe posteriorly?

A

Parieto-occipital sulcus

40
Q

What is the diencephalon?

A

Epithalamus, dorsal thalamus and hypothalamus

41
Q

What is CSF vs plasma comparison for osmolality?

A

The same

42
Q

Where is CSF made?

A

Choroid plexuses of ventricular system of brain

43
Q

How much volume of CSF is there at any single point in time?

A

Approximately 150mL

44
Q

Describe the pathway of CSF from formation to reabsorption?

A
  1. CSF formed in lateral ventricles of brain
  2. Leaves vis inter ventricular foramina and enters 3rd ventricle of brain
  3. CSF passes via cerebral aqueduct into 4th ventricle of brain
  4. Exits 4th ventricle via medial and lateral apertures to enter subarachnoid space (flows over cerebellum superiorly to surfaces of cerebral hemispheres
45
Q

What are the arteries which provide blood supply to the brain?

A

Internal carotids - ACA and MCA

Vertebral - unite to form basilar artery which supplies PCA

46
Q

What is different about origins of the common carotid artery right vs left?

A

R common carotid is from brachiocephalic artery

L common carotid directly from arch of aorta

47
Q

From where does the vertebral arteries arise?

A

From the subclavian artery - the first branch from it

48
Q

What are the dural venous sinuses? What is their function?

A

Endothelium lined spaces between periosteal and meningeal layers of the dura mater

Large veins from surface of brain empty into these, and returns via internal jugular veins

49
Q

What is the confluence of sinuses?

A

Junction of sinuses from superior sagittal, inferior sagittal and transverse sinuses

50
Q

What foramen does the optic nerve travel in?

A

Optic canal

51
Q

What are the consequences of optic nerve lesion vs optic chiasm lesion vs optic tract lesion?

A

Optic nerve = monocular blindness

Optic chiasm = bitemporal hemianopia

Optic tract = homonymous hemianopia

52
Q

What CN transit the superior orbital fissure?

A

Oculomotor
Trochlear
Ophthalmic division of trigeminal
Abducens

53
Q

What 3 different foramen does the trigeminal nerve access?

A
  1. Superior orbital fissure (V1)
  2. Foramen rotundum (V2)
  3. Foramen ovale (V3)
54
Q

What CN access the internal accoustic meatus?

A

Facial nerve
Vestibulocochlear nerve

55
Q

Which cranial nerves transit the jugular foramen?

A

Glossopharyngeal
Vagus
Spinal accessory

56
Q

How is taste to the tongue distributed?

A

Anterior 2/3 is via the facial nerve
Posterior 1/3 is the glossopharyngeal nerve

57
Q

What are the features of cervical vertebrae?

A

Body = small, wider from side to side than AP
Vertebral foramen = large and triangular
Transverse processes = foramen for transit of vertebral arteries

58
Q

What are the features of thoracic vertebrae?

A

Body = heart shaped
Vertebral foramen = circular and smaller than cervical and lumbar
Transverse processes = articulations for ribs

59
Q

What are the features of lumbar vertebrae?

A

Body = kidney shaped, largest
Vertebral foramen = triangular, larger than thoracic, smaller than cervical
Spinous process short and blunt

60
Q

What are the unique features of the atlas?

A

Doesn’t have a body or spinous process

61
Q

What is the dens and its function?

A

Odontoid process of C2 which allows for rotation of C1 on C2 (allowing for rotation of the head)

62
Q

What are the layers traversed in a lumbar puncture?
Remember, ligament ligament ligament in the middle

A

Skin
Superficial fascia
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space
Dura
Arachnoid
Subarachnoid space

63
Q

Describe the anatomy of the sympathetic nervous system?

A

Short preganglionic fibres from CNS that leave spinal cord from spinal nerves

Then synapse in ganglia located in paravertebral or prevertebral sympathetic chain

Post ganglionic fibres from from sympathetic chain to directly innervate the target organ

64
Q

Describe anatomy of parasympathetic nervous system?

A

Parasympathetic preganglionic fibres leave CNS via cranial nerves

These tend to be long pre-ganglionic fibres that then terminate in parasympathetic ganglia within walls of innervated organ

ED Primary Exam (46 decks)

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