Clinical neuroanatomy Flashcards
Explain the visual system
- The contralateral visual field projects onto the temporal or lateral portion of the retina, the ipsilateral visual field projects onto the nasal or medial portion of the retina
- The optic nerve carriers all information from the ipsilateral eye
- Nasal retinal fibres cross in the optic chiasm
- The optic tract contains fibres from the contralateral visual field
- Optic radiations are the projections from the lateral geniculate body to the primary visual cortex
What leads to monocular vision loss?
A lesion to the optic nerve of one eye
what leads to a bitemporal hemianopia?
•A lesion to the optic chiasm leads to the loss of the nasal fibres from each side
What leads to a contralateral homonymous hemianopia?
- A lesion to the optic tract
* A lesion of the entire primary visual cortex
What leads to a contralateral superior quadrantanopia?
•A lesion to the Meyer loop
What leads to a contralateral inferior quadrantanopia?
A lesion to the optic radiations
Where is Broca’s area
Frontal lobe
What does a lesion to Broca’s area result in?
Expressive dysphasia - speech may be non fluent, can’t say what they want to but they understand what is being said
What does a lesion to Wernickes area result in?
- Receptive aphasia
* Cannot understand what is being said
Describe the structure of the brainstem
- Midbrain most superior
- Pons is kind of a bulge anteriorly
- Medulla is most inferior and in posterior to the pons, anterior to the cerebellum
When does the spinal cord end?
L1-2
What is the order of the meninges?
Pia around spinal cord then arachnoid then dura
What is the denticulate ligament?
- Extensions of the Pia mater the anchor the spinal cord to the dura
- The lateral denticulate ligaments separate the anterior and posterior roots
What does the anterior root carry?
Motor information
How does the anterior root exit the spinal cord?
Through the anterolateral sulcus
What does the posterior root carry?
Sensory information
How does the posterior root enter the spinal cord
Postero-lateral sulcus
Where does the dura extend to?
S2
What is the epidural space?
- True space between the dura and the vertebral periosteum
* Filled with fat and venous plexus
Fasciculus gracilis
- Sensory - fine touch, vibration, proprioception
* Ipsilateral lower limb
Fasciculus cuneatus
- Sensory fine touch, vibration, proprioception
* ipsilateral upper limb
Spinocerebellar tract
Proprioception from the limbs to the cerebellum
Lateral corticospinal tract
•Motor to ipsilateral anterior horn
Spinothalamic tract
•Pain and temperature from the contralateral side of the body
Anterior corticospinal tract
•Motor to ipsilateral and contralateral anterior horn
At what level of the spine do the fibres enter the fasciculus gracilis vs fasciculus cuneate
T6
Where do the fibres that have travelled in the fasciculus gracilis/cuneate terminate?
Nucleus gracilis and nucleus cuneatus in brainstem
Where do the fibres carrying sensory information (fine touch, birbaiton and proprioception) cross?
After they have terminated in the nucleus cuneatus and gracilis, secondary fibres cross the midline as internal arcuate fibres and form the medial lemniscus
Where does the medial lemniscus terminate?
In the VPL of the thalamus
What happens after the medial lemniscus terminates in the VPL?
Fibres project through the internal capsule and corona radiata to terminate in the primary somatosensory cortex
Explain the route of the sensory tract carrying light touch, vibration and proprioception
- Axons enter the spinal cord from the spinal ganglion and pass directly to the ipsilateral posterior column. (Caudal fibres below T6 = gracilis, rostral = cuneatus)
- Ascend then terminate in culceus gracilis and nucleus cuneatus
- From these nuclei, axons of secondary neurones cross the midline as internal arcuate fibres and form medial lemniscus
- in the rostral medulla, the fibres travel as the medial lemniscus adjacent to the midline
- In the caudal pons, the medial lemniscus flattens horizontally
- As the medial lemniscus continues to ascend through the rostral pons and midbrain it moves horizontally and laterally
Explain the route of the sensory tract carrying pain and temperature
- Axons enter the spinal cord from the spinal ganglion, travel up or down 1-2 segments in the lissauer tract then synapse in the posterior horn
- Axons of secondary neurones cross the midline in the anterior commissure and ascend as the anterolateral tract in the spinal cord
- Anterolateral tract ascends through the caudal medulla
- In the rostral medulla, the anterolateral tract lies between the inferior olivary nucleus and the nucleus of the spinal tract of the trigeminal nerve
- in the pons and midbrain, the anterolateral tract lies lateral to the medial lemniscus
- The anterolateral tract terminates in the VPL of the thalamus
- From the thalamus the fibres project through the internal capsule and corona radiate to terminate in the primary somatosensory cortex (post central gyrus)
Explain the route of the motor corticospinal tract
- Originates from the primary motor cortex
- Descending fibres form the corona radiata and converge to pass through the posterior limb of the internal capsule
- Corticospinal fibres descend through the middle three fifths of the crus cerebra in the anterior part of the midbrain
- In the pons, the fibres are broken up into many bundles
- The corticospinal tract descends as the pyramids in the anterior part of the medulla
- At the junction of the medulla and the spinal cord, most of the fibres cross the midline in the decussation fo the pyramids
- Crossed fibres = lateral corticospinal tract, uncrossed = anterior corticospinal tract
What fibres cross in the anterior white commissure?
- Pain and temperature fibres
* Anterior corticospinal tract fibres
Explain the spinal reflex of the hamstring
- Ia fibre from the muscle spindle senses stretching of the muscle
- Ia fibre synapses directly with an alpha motor neurone in the anterior horn and an inhibitory interneurone
- The alpha motor neurone to the extensor muscles are excited and the inhibitory interneurone inhibits the alpha motor neurone of the antagonist muscle
