Neuroanatomy & Pathophysiology

Question 1

Descending motor tracts

Answer 1

Pyramidal:
Corticospinal
Corticobulbar

Extrapyramidal: 
Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal

Question 2

Ascending sensory pathways

Answer 2

Dorsal column-medial leminiscal pathway

Spinothalamic pathway

Question 3

Corticospinal tract

Answer 3

Somatic motor function
UMN: Primary motor cortex –> internal capsule –> Crus cerebri (brain stem) –> Decussation in high spinal cord –> descends in corticospinal tracts –> ventral horn of spinal cord –> synapse
LMN: ventral horn –> ventral spinal nerve –> target muscle

Question 4

Dorsal Column

Answer 4

Vibration, proprioception, light touch
1st order neurone: sensory organ –> dorsal spinal nerve –> dorsal horn –> ipsilateral dorsal column –> (fasciculus gracilis: LL, fasciculus cuneatus: UL) –> nucleus gracilis/cuneatus (in medulla) –> synapse
2nd order neurone: –> medial leminiscal –> thalamus (ventral posterior lateral nucleus) –> synapse
3rd order: –> somatosensory cortex

Question 5

Spinothalamic tract

Answer 5

Pain, temperature
1st order neurone: sensory organ –> dorsal spinal nerve –> dorsal horn –> synapse
2nd order neurone: –> decussation –> spinothalamic tract –> thalamus –> synapse
3rd order neurone: –> primary somatosensory cortex

Question 6

Corticobulbar

Answer 6

UMN: Primary motor cortex –> internal capsule –> crus cerebri –> exits at appropriate level of brainstem –> synapse
LMN: cranial nerve

Question 7

Brown-Sequard Syndrome

Answer 7

Ipsilateral loss of:
Motor (corticospinal tract)
Vibration, position, light touch (dorsal column)

Contralateral loss of:
Pain, temp (Spinothalamic tract)

Question 8

Anterior cord syndrome

Answer 8

Caused by disruption of anterior spinal artery
Loss of:
Motor function (corticospinal tracts)
Pain, temp (spinothalamic)
Autonomic dysfunction: low BP

Retained:
Vibration, position, light touch (dorsal column)

Question 9

Central cord syndrome

Answer 9

Loss of:

Motor (Corticospinal tract)

Question 10

UMN signs

Answer 10

Increased tone
Increased reflexes
Babinski +ve
Clonus
Weakness

Question 11

LMN signs

Answer 11

Decreased tone
Decreased reflexes
Weakness/flaccid paralysis
Fasciculations
Atrophy

Question 12

Components of neurone

Answer 12

Cell body
Dendrites
Axon
Axon terminal (synaptic terminal)

Question 13

Cell body of neurone

Answer 13

Holds nucleus

Many neural bodies grouped together:
CNS: nucleus
PNS: ganglion

Question 14

Axon of neurone

Answer 14

Long thin structure which carries action potentials
Coated in myelin. Formed by cells wrapping around axon. CNS: oligodendrocyte cells. PNS: Schwann cells.
Gaps in myelin known as nodes of Ranvier

Question 15

Structure of nerves

Answer 15

Nerve is group of fascicles

Fascicle is group of neurones

Question 16

Coverings of neurones

Answer 16

Endoneurium (covers axon)
Perineurium (surrounds fascicle)
Epineurium (surrounds entire nerve)

Question 17

Resting membrane potential

Answer 17

-50 to -75mV
Extracellular: high Na+ and Cl-
Intracellular: high K+
Na/K ATPase maintains gradients (3 Na for 2 K)

Question 18

Action potential: stages

Answer 18

Stimulus
Depolarisation
Repolarisation
Refractory period
Resting state

Question 19

Action potential: Depolarisation

Answer 19

Depolarisation of voltage-gated Na channels due to electrical stimulus.
Na ions rush back into cell.
Causes intracellular charge to become more positive

Question 20

Action potential: repolarisation

Answer 20

Once cell has depolarisated voltage gated K channels open
K ions move down electrochemical gradient out of cell.
As K+ moves out of cell, membrane potential becomes more negative and starts to approach resting potential

Question 21

Action potential: refractory period

Answer 21

Absolute refractory period: Na channels close after action potential
Relative refractory period: Na channels slowly come out of inactivation. Neurone can be excited with stimuli stronger than one normally needed.

Question 22

Propagation of action potentials

Answer 22

Nodes of Ranvier have high density of ion channels
Myelinated axons have increases membrane resistance and lower membrane capacitance
Electrical signals are conducted from one node to the next, called saltatory conduction

Question 23

Autonomic Nervous System

Answer 23

Sympathetic

Parasympathetic

Question 24

Autonomic: spinal cord distribution

Answer 24

SNS: thoracolumbar
PSNS: craniosacral

Question 25

Autonomic: preganglionic neurone

Answer 25

SNS: short PSNS: long

Question 26

Autonomic: Preganglionic neurotransmitter

Answer 26

SNS: Acetylcholine PSNS: Acetylcholine

Question 27

Autonomic: postganglionic neurone

Answer 27

SNS: long PSNS: short

Question 28

Autonomic: postganglionic neurotransmitter

Answer 28

SNS: Noradrenaline (Ach: sweat/chromaffin cells of adrenal medulla) PSNS: Acetylcholine

Question 29

Sympathetic nervous system

Answer 29

``` Spinal compents: T1-L2 Sympathetic chain: "Paravertebral" ganglia 4 neurones: Ascending/descending Post-ganglionic splanchnic Pre-ganglionic splanchnic Spinal nerves ```

Question 30

SNS: ascending/descending

Answer 30

Pre-ganglionic: Lateral horn of spinal cord --> ventral root --> white ramus communicans --> sympathetic ganglion --> ascend --> synapse Post-ganglionic: --> grey ramus communicans --> spinal nerve --> target organ e.g. Head and neck, lower abdomen/pelvic viscera

Question 31

SNS: post-ganglionic splanchnic

Answer 31

Pre-ganglionic: Lateral horn of spinal cord --> ventral root --> white ramus communicans --> sympathetic ganglion --> synapse Post-ganglionic: --> leaves directly e.g. cardiopulmonary splanchnics

Question 32

SNS: pre-ganglionic nerve

Answer 32

Pre-ganglionic: Lateral horn of spinal cord --> ventral root --> white ramus communicans --> sympathetic ganglion (does not synapse) --> peripheral ganglion --> synapse Post-ganglionic: nerve --> target organ E.g. Abdominopelvic splanchnic Celiac ganglion, superior mesenteric ganglion, artorenal ganglion, inferior mesenteric ganglion, superior hypogastric ganglion, inferior hypogastric ganglion

Question 33

SNS: travel with spinal nerve

Answer 33

Pre-ganglionic: Lateral horn of spinal cord --> ventral root --> white ramus communicans --> sympathetic ganglion --> synapse Post-ganglionic: --> grey ramus communicans --> spinal nerve --> target organ E.g. supply to skin

Question 34

PSNS: cranial origins, ganglions, effects

Answer 34

CN: III, VII, IX, X CNIII: Edinger-Westphal nucleus (midbrain) --> ciliary ganglion: pupil constriction CNVII: superior salivary nuclei (pons) --> greater petrosal nerve --> pterygopalatine ganglion: secretomotor (lacrimal, nasal, palatine) chorda tympani --> submandibular ganglion: secretomotor (submandibular, sublingual) CNIX: inferior salivary nuclei (medulla) --> lesser petrosal --> otic ganglion: secretomotor (parotid) CNX: dorsal motor nucleus --> plexuses Cardiac plexus Pulmonary plexus Myenteric plexus (Meissner's, Auerbach's)

Question 35

PSNS: sacral component

Answer 35

S2-4. Pelvic splanchnic nerves.

Question 36

Meninges

Answer 36

Superficial to deep: Dura mater Arachnoid mater Pia mater

Question 37

Dura mater

Answer 37

Outermost 2 layers: Periosteal layer (inner surface of bones on cranium Meningeal layer (continuous with dura mater)

Question 38

Dura mater: blood supply/drainage

Answer 38

Blood supply: middle meningeal artery (branch off maxillary, from external carotid), enters via foramen spinosum Dural venous sinuses (between layers of dura mater) drain into internal jugular vein

Question 39

Dura mater: dural reflections

Answer 39

``` Folds inwards to form 4 dural reflections Falx cerebri (separates L & R cerebral hemispheres) Tentorium cerebelli (separates occipital lobes from cerebellum, contains tentorial notch) Falx cerebelli (seperates R & L cerebellar hemispheres) Daiphagma sellae (covers hypophyseal fossa of sphenoid bone ```

Question 40

Arachnoid mater

Answer 40

Middle layer of meninges Avascular. Sub-arachnoid space beneath contains CSF Arachnoid granulations: Small projections of arachnoid mater into dura allow CSF to enter circulation via dural venous sinuses

Question 41

Pia mater

Answer 41

Deepest layer. Thin, tightly adhered to the brain and spinal cord. Only covering to follow contours of brain. Highly vascularised with vessels perforating through membrane

Question 42

Traumatic brain injuries

Answer 42

``` Extradural Subdural Subarachnoid Cerebral contusion Intra-cerebral haemorrhage Diffuse axonal injury ```

Question 43

Extradural haemorrhage

Answer 43

Bleeding between dura and skull 2% of head injuries. 20-30 years. M>F. Blunt force with linear skull fracture. Parietotemporal fractures most common. Middle meningeal artery most common due to fracture at pterion. Sx: Initial LOC. Lucid period. Further deterioration. Headache, nausea, low GCS. CT: hyperdense biconvex (due to dura's firm attachments to suture lines. Rx: >30cm3: surgical. <30cm3 with no red flags: conservative

Question 44

Subdural haemorrhage

Answer 44

Bleeding under dural. Between dural and arachnoid: subdural space. Tearing of bridging veins, vulnerable to decelerating injuries. RFs: increasing age, ETOH, epileptics, anticoag Sx: low GCS, headache, focal neurology. Chronic: weeks to present. CT: crescent-shaped collection. diffusely hyper dense: acute. hypodense: chronic Rx: trauma craniotomy/burr hole craniotomy

Question 45

Subarachnoid haemorrhage

Answer 45

Bleeding into space between arachnoid and Pia mater: subarachnoid space Spontanous (85% cerebral aneurysm) or traumatic. Sx: thunderclap headache, meningism CT: hyper attenuating material seen in subarachnoid space LP: elevated oxyhemoglobin/bilirubin Rx: nimodipine (CCB), neurosurgical intervention: coiling/clipping aneurysm