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Neural Pathways Flashcards

1
Q

What are ascending tracts

A

Neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex.

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2
Q

What are the conscious tracts

A

Comprised of dorsal column-medial lemniscal pathways and the anterolateral system

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3
Q

What are the unconscious tracts

A

Comprised of the spinocerebellar tracts

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4
Q

What does the dorsal column medial lemniscal pathway carry

A

Sensory modalities of fine touch, vibration and proprioception

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5
Q

Where does the DCML travel in the spinal cord

A

Dorsal culmn

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6
Q

Where does the DCML travel in the brain stem

A

Medial lemniscus

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7
Q

How many groups of neurones are involved in the pathway

A

3 - first, second, and third order

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8
Q

What are first order neurones of the DCML

A

Carry sensory information from the peripheral nerves to the medulla oblongata

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9
Q

Where do signals from the upper limb travel through in DCML

A

T6 and above travel in the fasciculus cuneatus (lateral part of the dorsal column). They then synapse in the nucleus cuneatus of the medulla oblongata

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10
Q

Where do signals from the lower limb travel through in DCML

A

Below T6 - travel in the fasciulus gracilis (medial part of the dorsal column). They then synapse in the nucleus gracilis of the medulla oblongata

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11
Q

Explain second order neurones of the DCML

A

Begin in cuneate nucleus or gracilis. Decussate in medulla oblongata. Travel in the contralateral medial lemniscus to reach the thalamus

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12
Q

Explain third order neurones of the DCML

A

Transmit signals fro mthe thalamus to the ipsilateral primary sensory cortex of the brain. Ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex

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13
Q

What are the two anterolateral systems

A

Anterior spinothalamic tract - carries the sensory modalities of crude touch and pressure
Lateral spinothalamic tract - carries the sensory modalities of pain and temperature

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14
Q

Explain first order neurones of ALS

A

Arise from sensory receptors in the periphery -> spinal cord -> ascend 1-2 vertebral levels -> synapse at tip of the dorsal horn (substantia gelatinosa)

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15
Q

Explain second order neurones of ALS

A

From substantia gelatinosa -> thalamus. Fibres decussate within the spinal cord and then form two distinct tracts

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16
Q

What are the two tracts of the second order neurones of ALS

A

Crude touch and pressure fibres - enter anterior spinothalamic tract
Pain and temperature fibres - enter the lateral spinothalamic tract

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17
Q

What are the spinocerebellar tracts

A

Carry unconscious proprioceptive information.

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18
Q

What are the four pathways of the spinocerebellar tracts

A

Posterior spinocerebellar tract
Cuneocerebellar tract
Anterior spinocerebellar tract
Rostral spinoerebellar tract

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19
Q

What does the spinocerebellar tract do

A

Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum

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20
Q

What does the cuneocerebellar tract do

A

Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum

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21
Q

What does the rostral spinocerebellar tract do

A

Carries proprioceptive information from upper limbs to ipsilateral cerebellum

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22
Q

What do lesions in the DCML pathway cause

A

Loss of proprioception and fine touch. If lesion occurs in spinal cord, sensory loss will be ipsilateral

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23
Q

What causes DCML lesions

A

B12 deficiency and tabes dorsalis

24
Q

What do lesions in the anterolateral system cause

A

Impairment of pain and temperature sensation. Sensory loss will be contralateral

25
What is Brown-Sequard syndrome
Hemisection of spinal cord. Most often due to traumatic injury and involves both conscious pathways
26
What do lesions in the spinocerebellar tracts cause
Ipsilateral loss of muscle coordination. Unlikely to be damaged in isolation, likely to be additional injury to the descending motor tracts
27
What are the two groups of descending tracts of the CNS
Pyramidal - originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem. Responsible for voluntary control and the musculature of the body and face Extrapyramidal - originate in the brain stem, carrying motor fibres to the spinal cord. Responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion.
28
How are pyramidal tracts divided
Corticospinal - supplies musculature of the body | Corticobulbar - supplies the musculature of the head and neck
29
Where do corticospinal tracts receive input from
Primary motor cortex Premotor cortex Supplementary motor area Somatosensory area
30
Describe path of corticospinal tract before division
Cortex->internal capsule->crus cerebri of midbrain->pons->medulla->divides into lateral and anterior corticospinal tract
31
Describe path of anterior corticospinal tract
Decussate in medulla -> spinal cord -> terminates in ventral horn -> LMN to muscles of the body
32
Describe path of the lateral corticospinal tract
Remains ipsilateral -> spinal cord -> decussate and terminate in ventral horn of the cervical and upper thoracic segmental levels
33
Why is the internal capsule clinically signifcant
Located between thalamus and basal ganglia, it is susceptible to compression from haemorrhagic bleeds - capsular stroke. Cause lesion of the descending tracts
34
Describe the path of the corticobulbar tract
Primary motor cortex -> internal capsule -> brainstem -> terminate on the motor nuclei of the cranial nerves -> synapse with LMN
35
What are the exception to bilateral innervation rule
UMN for facial nerve have contralateral innervation, only affects muscles in the lower quadrant of the face UMN for hypoglossla only provide contralateral innervation
36
What are the ipsilateral innervation extrapyramidal tracts
Vestibulospinal and reticulospinal
37
What are the contralateral innervation extrapyramidal tracts
Rubrospinal and tectospinal
38
Describe pathway of vestibulospinal tract
Two pathways: medial and lateral. Arise from vestibular nuclei -> spinal cord -> remains ipsilateral
39
What does the vestibulospinal tract control
Balance and posture by innervating anti gravity muscles (flexors of the arm, extensors of the leg), via LMN
40
What does the medial reticulospinal tract do
Arises from pons and facilitates voluntary movements, and increases muscle tone
41
What does the lateral reticulospinal tract do
Arises from the medulla. Inhibits voluntary movements and reduces muscle tone
42
Describe the path and function of the rubrospinal tract
Red nucleus (midbrain)->decussate->descend in to spinal cord. Contralateral innervation. Fine control of hand movements
43
Describe the path of the tectospinal tract
Superior colliculus (midbrain), receives input from optic nerves -> decussate -> enter spinal cord -> termiante at cervical levels of the spinal cord.
44
What does the tectospinal tract coordinate
Movements of the head in relation to vision stimuli
45
Describes lesions in corticospinal tracts
If there is only a unilateral lesion, symptoms will appear on the contralateral side: Hypertonia Hyperreflexia Clonus Babinski - extension of the hallux in response to blunt stimulation of the sole of the foot Muscle weakness
46
Describe a lesion in the UMN for the hypoglossal nerve
Spastic paralysis of the contralateral genioglossus. Deviation of the tongue to the contralateral side (in LMN, tongue deviates towards the damaged side)
47
Describe a lesion in the UMN for the facial nerve
Spastic paralysis of the muscles in the contralateral lower quadrant of the face
48
What occurs in extrapyramidal tract lesions
Commonly seen in degenerative diseases, encephalitis and tumours. Result in various types of dyskinesias or disorders of involuntary movement
49
What muscles does the occulomotor nerve supply?
``` Superior rectus Inferior rectus Medial rectus Inferior oblique Levator palpebrae superior ```
50
What muscle does the trochlear nerve supply
Superior oblique
51
What muscles does the abducens nerve supply
Lateral rectus muscle | Retractor bulbi muscle
52
What are the characteristics of a CN III lesion
Affects mostt of extraocular muscles. Displaced laterally by lateral rectus and inferiorly by superior oblique. Down and out
53
What are the characteristics of a CN IV lesion
Paralyse superior oblique. Px to complain of diplopia, may develop head tilt away from site of lesion
54
What are the characteristics of a CN VI lesion
Paralyse lateral rectus. Adducted by resting tone of medial rectus
55
What is Horner's syndrome
Triad of symptoms produced by damage to the sympathetic trunk in the neck Parial ptosis Misosi Anhydrosis - on ipsilateral side of the face
56
What causes Horner's syndrome
Tumour of the apex of the lung (Pancoast tumour), aortic aneurysm or thyroid carcinoma

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