Session 4 Flashcards

1
Q

What are the components of the CNS?

A
  • Brain
  • Spinal cord
  • Cerebellum
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2
Q

What information do cranial nerves carry?

A
  • Sensory and motor information
  • Not all cranial nerves are mixed
  • Carry special senses e.g. taste, vision, smell
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3
Q

What is the forebrain?

A
  • Part of CNS that sits on top of the brainstem
  • Cerebrum and diencephalon
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4
Q

Describe the structure of the cerebrum

A
  • Largest portion of forebrain
  • Can be split into 2 symmetrical hemispheres
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5
Q

Describe the structure of the diencephalon

A
  • Hypothalamus sits in centre
  • Thalamus x2 sit on either side and act as relay stations for information coming up towards the brain
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6
Q

Describe the structure of the brainstem

A
  • Top = midbrain
  • Middle = pons (bulbous structure)
  • Bottom = medulla
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7
Q

What happens once the medulla passes through the foramen magnum?

A
  • It becomes the spinal cord
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8
Q

Which components of the brain make up grey matter?

A
  • Cortex
  • Sulci and gyri
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9
Q

Why is grey matter grey?

A
  • Due to high density of nerve cell bodies
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10
Q

What is the function of the grey matter of the brain?

A
  • Necessary for conscious awareness
  • All sensory menalities arise from grey matter and need to reach grey matter in order to be perceived
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11
Q

Describe the cortex of the brain

A
  • Grey matter
  • Outer surface of cerebrum
  • A few mm thick
  • Highest level at which motor system is represented
  • Conscious decisions to move body originate here
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12
Q

What is the function of the sulci and gyri?

A
  • Allows increase in surface area and the number of neurones that can be packed inside the brain
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13
Q

What are fissures?

A
  • Deep furrows into surface of cortex
  • Longitudinal fissure (falx cerebri found here)
  • Lateral fissures x2
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14
Q

Why is white matter white?

A
  • Colour is due to myelinated axons
  • White matter is densely packed with axons that arise from cell bodies in grey matter
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15
Q

What are the 4 key lobes of the hemisphere?

A
  • Frontal
  • Parietal
  • Temporal
  • Occipital
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16
Q

Which sulci/fissures delineate the different lobes of the hemisphere?

A
  • Central sulcus delineates frontal lobe from parietal lobe
  • Lateral fissure delineates temporal lobe from frontal and parietal lobes
  • Parieto-occipital sulcus delineates parietal lobe from occipital lobe
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17
Q

What is the corpus callosum?

A
  • White matter connecting the 2 hemispheres of the brain
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18
Q

What is the ventricle of the brain?

A
  • Cavity full of CSF
  • Normally covered by septum pellucidum
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19
Q

What terms do we use when describing the orientation of the brain?

A
  • Dorsal (superior surface of the brain)
  • Caudal (posterior surface of brain)
  • Ventral (inferior surface of brain)
  • Rostral (anterior surface of brain)
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19
Q

What terms do we use when describing the orientation of the brain?

A
  • Dorsal (superior surface of the brain)
  • Caudal (posterior surface of brain)
  • Ventral (inferior surface of brain)
  • Rostral (anterior surface of brain)
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20
Q

What are the components of the brainstem?

A
  • Midbrain
  • Pons
  • Medulla
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21
Q

What are the major functions of the midbrain?

A
  • Many centres and cranial nerve nuclei important for coordinating eye movement found here
  • Also important for coordinating reflexes of pupils
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22
Q

What are the major functions of the pons?

A
  • Important role in feeding trigeminal nerve involved in mastication
  • Contains centres for controlling sleep
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23
Q

What are the major functions of the medulla?

A
  • Contains important centres for CVS and the respiratory centre
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24
Why do pathologies involving the brainstem impact a significant number of functions?
- Brainstem contains lots of nervous tissue in a relatively small area
25
How do nerve signals enter the brainstem?
- Signals travel from forebrain to cranial or spinal nerves via the brainstem - Sensory information passes to forebrain via the brainstem to be conciously perceived
26
What behaviours are controlled by the frontal lobe?
- Voluntary motor control - Speech production - Social behaviour - Impulse control - Higher cognition (planning, thinking)
27
What behaviours are controlled by the temporal lobe?
- Language - Emotion - Long-term memory - Sense of smell - Hearing - Taste
28
What behaviours are controlled by the parietal lobe?
- Somatosensory perception - Spatial awareness
29
What behaviours are controlled by the occipital lobe?
- Visual perception
30
What behaviours are controlled by the cerebellum?
- Co-ordination and motor learning
31
What is the clinical significance of the uncus?
- Can be pushed through tentorial notch when intracranial pressure rises - uncal herniation - Uncus is located proximal to cranial nerve III - When uncus herniates, it pushes against this nerve, causing dysfucntion
32
What is the clinical significance of the uncus?
- Can be pushed through tentorial notch when intracranial pressure rises - uncal herniation - Uncus is located proximal to cranial nerve III - When uncus herniates, it pushes against this nerve, causing dysfunction
33
What is the uncus?
- Where we receive olfactory information
34
What is meant by a topographical representation of the brain?
- Specific parts of the body are mapped onto specific regions of the cortex - Certain parts of the body have greater representation in the cortex than others e.g. fingertips, tongue, lips - Mapping helps localise where lesions might be in the brain because lesions will cause very specific neurological dysfunction
35
Outline the route taken by motor pathways in the brain
- Primary motor cortex is responsible for motor control in contralateral side of the body - Pathways decussate (cross) to opposite side at level of lower medulla - I.e. motor control of the left arm is initiated in the right side of the brain
36
Outline the pathway taken by sensory pathways in the brain
- Sensory information comes into the primary somatosensory cortex - This pathway also crosses - I.e. sensory information felt in right arm reaches and is perceived by left somatosensory complex
37
What do we mean by the statement that spinal nerves are mixed?
- Spinal nerves contain some axons of motor neurones and some axons of sensory neurones
38
What is meant by the statement that cranial nerves have dual cortical control?
- Pathways connecting primary motor cortex with cranial nerves controlling the muscles of neck/face decussate to the opposite side - Crossing over occurs at level of nuclei onto which they synapse - Cortical control of muscles is contralateral - But most cranial nerves also have a back-up from the ipsilateral cortex
39
Give brief overview of the cranial nerves
- Supply tissues and structures if head and neck region including special sense organs - Part of peripheral nervous system (except CNS I and II) - Arise as pairs - Most are associated with the brainstem due to their nuclei location
40
What kinds of fibres are carried in the cranial nerves?
- Some are mixed with motor and sensory fibres - Some can be purely motor or sensory - 4 cranial nerves carry parasympathetic fibres - Nio sympathetic fibres
41
What can neurological signs of cranial nerve dysfunction arise due to?
- An injury or lesion involving 1. The cranial nerve during its route outside of the CNS 2. The brainstem where CN nuclei are located 3. The neurones within the forebrain/brainstem which connect other parts of the brain to cranial nerves
42
What is meant by 2 2 4 4?
- 2 cranial nerves arise from the forebrain - 2 cranial nerves arise from the midbrain - 4 cranial nerves arise from the pons - 4 cranial nerves arise from the medulla
43
List the names and numbers of all the cranial nerves
- I = olfactory nerve - II = optic nerve - III = oculomotor nerve - IV = trochlear nerve - V = trigeminal nerve - VI = abducens nerve - VII = facial nerve - VIII = vestibulocochlear nerve - IX = glossopharyngeal nerve - X = vagus nerve - XI = accessory nerve - XII = hypoglossal nerve
44
What is special about CN I and CN II?
- They arise as extensions of the forebrain
45
What can cause olfactory nerve lesions?
- Head/facial injury - shears olfactory neurones during passage through cribriform foramina - Anterior cranial fossa tumours - compresses olfactory bulb/olfactory tract - Parkinson's, Alzheimer's - Commonest cause for anosmia is a common cold
46
How do we test for olfactory nerve lesions?
- Absence or reduced sense of smell (anosmia/hyposmia) - Test one nostril at a time - Not routinely tested
47
Outline the passage of the olfactory nerve
- Olfactory receptors within olfactory mucosa - Olfactory nerves travel up through base of skull through cribriform foramina - Travel to right or left olfactory bulb
48
Why is the optic nerve affected by raised intracranial pressure?
- It carries an extension of the meninges
49
How is the optic nerve tested?
Pupillary size and response to light - CNII forms sensory/afferent limb of the pupillary light reflex - Visual acuity (Snellen chart) and visual fields - Ophthalmoscopy - can directly visualise part of optic nerve
50
What will a patient with an optic nerve lesion report?
- Blurred vision or complete absence of vision in the eye supplied by the affected optic nerve - On clinical examination, patient will have poor visual acuity, abnormalities in pupil size and response to light, evidence of pathology on ophthalmoscopy
51
Which diseases can cause optic nerve lesions?
- Optic neuritis - Anterior ischaemic optic neuropathy
52
What changes might you see on opthalmoscopy of a patient with an optic nerve lesion?
- Papilloedema - swollen optic disc seen in cases of raised intracranial pressure - Pale optic disc
53
Outline the route taken by the optic nerve
- Retinal ganglion cell axons converge at optic disc and form optic nerve - Optic nerve exits back of orbit via optic canal - Fibres from left and right optic nerve merge at optic chiasm (close to pituitary gland) - Continue as left and right optic tracts - Some fibres communicate from tract into brainstem to give information about light intensity and control pupil size - Some continue visual pathway
54
Which pathologies can cause optic nerve lesions?
- Retinal detachment - Optic neuritis - Pituitary tumour - compress optic chiasm - Strokes
55
Why can optic nerve lesions affect either one eye or both eyes?
- Depends on location of lesion along optic nerve - Pathology affecting a retina or an optic nerve on one side will cause blurring/visual symptoms in that one eye - Lesions involving optic chiasm onwards cause visual disturbances in both eyes
56
What do the oculomotor, trochlea and abducens nerve all have in common?
- Supply muscles in the orbital cavity that move the eyeball - Have commonality in route after exiting brainstem at different levels
57
What is the common route taken by the oculomotor, trochlea and abducens nerve?
- Cavernous sinus - Superior orbital fissure - Orbital cavity
58
How do we clinically test the oculomotor, trochlea and abducens nerve?
- Observe patient's resting gaze - Ask patient to perform a series of eye movements
59
What fibres make up the oculomotor nerve?
- Contains motor and parasympathetic fibres
60
What are the targets of the oculomotor nerve?
1. Somatic efferent fibres are motor - Travel to skeletal muscle - all extraocular muscles (except 2) - Also supply levator palpebrae superioris (opens eyelid) 2. Visceral efferent fibres are parasympathetic - Supply muscles inside the eyeball: ciliary muscle (controls thickness of lens) and sphincter pupillae
61
Explain how we clinically examine the oculomotor nerve
- Check eyelid position - supplies levator palpabrae superioris that keeps eyelid retracted - Eye movements - oculomotor nerve responsible for most muscles that move eyelid - Pupils and pupillary light reflex - parasympathetic fibres supply muscles controlling pupillary constriction
62
What suggests an oculomotor nerve lesion?
- Pt reports double vision - Ptosis - Abnormal position of eye - 'down and out' - Pupil may or may not be dilated - Signs arise due to involvement of somatic fibres
63
Where does the oculomotor nerve arise from?
- Midbrain - Has close relationship to tentorium cerebelli edge as it travels to cavernous sinus
64
How are parasympathetic fibres arranged in a mixed cranial nerve?
- Around the periphery
65
What are the pupil sparing oculomotor nerve lesions?
- Microvascular ischaemia - Risk factors include: age >50 years and diabetes/hypertension
66
What are pupil involving oculomotor nerve lesions?
- Compressive lesions - E.g. aneurysmal, head injury, uncal herniation
67
What is the function of the trochlear nerve?
- Supplies superior oblique muscle
68
What fibres make up the trochlear nerve?
- Motor only
69
How do we examine the trochlear nerve?
- Inspect resting gaze - subtle abnormal eye position - Test eye movements - pt will have difficulty moving eye downwards when eye is positioned inwards - Pt will also report double vision
70
Where does the trochlear nerve arise from?
- Dorsal midbrain
71
How do trochlear nerve lesions arise?
- Congenital or acquired - Acquired due to: - microvascular ischaemia (risk factors include age >50, diabetes, hypertension) - trauma (causes nerve to snap or stretch) - intracranial tumour
72
From where does the abducens nerve arise?
- Caudal pons - Takes a vertical upwards route to cavernous sinus - this makes it susceptible to stretch e.g. when intracranial pressure rises
73
What can result in abducens nerve lesions?
- Microvascular ischaemia (diabetes, hypertension) - Head injury, tumour - Raised intracranial pressure - results in false localising sign
74
Out of the oculomotor, trochlea and abducens nerve, which is most likely to be affected by raised ICP?
- Abducens nerve - Has upwards vertical route - Is fixed at point of brainstem exit and entry to cavernous sinus
75
What would you see on examination of a patient with abducens nerve lesion?
- Pt reports double vision - Abnormal eye position at rest (one eye moves inwards when pt tries to look ahead) - Difficulty/inability to move affected eye laterally