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Supporting Life > Neural Pathways > Flashcards

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
Q

What is Brown-Sequard syndrome

A

Hemisection of spinal cord. Most often due to traumatic injury and involves both conscious pathways

26
Q

What do lesions in the spinocerebellar tracts cause

A

Ipsilateral loss of muscle coordination. Unlikely to be damaged in isolation, likely to be additional injury to the descending motor tracts

27
Q

What are the two groups of descending tracts of the CNS

A

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
Q

How are pyramidal tracts divided

A

Corticospinal - supplies musculature of the body

Corticobulbar - supplies the musculature of the head and neck

29
Q

Where do corticospinal tracts receive input from

A

Primary motor cortex
Premotor cortex
Supplementary motor area
Somatosensory area

30
Q

Describe path of corticospinal tract before division

A

Cortex->internal capsule->crus cerebri of midbrain->pons->medulla->divides into lateral and anterior corticospinal tract

31
Q

Describe path of anterior corticospinal tract

A

Decussate in medulla -> spinal cord -> terminates in ventral horn -> LMN to muscles of the body

32
Q

Describe path of the lateral corticospinal tract

A

Remains ipsilateral -> spinal cord -> decussate and terminate in ventral horn of the cervical and upper thoracic segmental levels

33
Q

Why is the internal capsule clinically signifcant

A

Located between thalamus and basal ganglia, it is susceptible to compression from haemorrhagic bleeds - capsular stroke. Cause lesion of the descending tracts

34
Q

Describe the path of the corticobulbar tract

A

Primary motor cortex -> internal capsule -> brainstem -> terminate on the motor nuclei of the cranial nerves -> synapse with LMN

35
Q

What are the exception to bilateral innervation rule

A

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
Q

What are the ipsilateral innervation extrapyramidal tracts

A

Vestibulospinal and reticulospinal

37
Q

What are the contralateral innervation extrapyramidal tracts

A

Rubrospinal and tectospinal

38
Q

Describe pathway of vestibulospinal tract

A

Two pathways: medial and lateral. Arise from vestibular nuclei -> spinal cord -> remains ipsilateral

39
Q

What does the vestibulospinal tract control

A

Balance and posture by innervating anti gravity muscles (flexors of the arm, extensors of the leg), via LMN

40
Q

What does the medial reticulospinal tract do

A

Arises from pons and facilitates voluntary movements, and increases muscle tone

41
Q

What does the lateral reticulospinal tract do

A

Arises from the medulla. Inhibits voluntary movements and reduces muscle tone

42
Q

Describe the path and function of the rubrospinal tract

A

Red nucleus (midbrain)->decussate->descend in to spinal cord. Contralateral innervation. Fine control of hand movements

43
Q

Describe the path of the tectospinal tract

A

Superior colliculus (midbrain), receives input from optic nerves -> decussate -> enter spinal cord -> termiante at cervical levels of the spinal cord.

44
Q

What does the tectospinal tract coordinate

A

Movements of the head in relation to vision stimuli

45
Q

Describes lesions in corticospinal tracts

A

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
Q

Describe a lesion in the UMN for the hypoglossal nerve

A

Spastic paralysis of the contralateral genioglossus. Deviation of the tongue to the contralateral side (in LMN, tongue deviates towards the damaged side)

47
Q

Describe a lesion in the UMN for the facial nerve

A

Spastic paralysis of the muscles in the contralateral lower quadrant of the face

48
Q

What occurs in extrapyramidal tract lesions

A

Commonly seen in degenerative diseases, encephalitis and tumours. Result in various types of dyskinesias or disorders of involuntary movement

49
Q

What muscles does the occulomotor nerve supply?

A 
Superior rectus
Inferior rectus
Medial rectus
Inferior oblique
Levator palpebrae superior
50
Q

What muscle does the trochlear nerve supply

A

Superior oblique

51
Q

What muscles does the abducens nerve supply

A

Lateral rectus muscle

Retractor bulbi muscle

52
Q

What are the characteristics of a CN III lesion

A

Affects mostt of extraocular muscles. Displaced laterally by lateral rectus and inferiorly by superior oblique. Down and out

53
Q

What are the characteristics of a CN IV lesion

A

Paralyse superior oblique. Px to complain of diplopia, may develop head tilt away from site of lesion

54
Q

What are the characteristics of a CN VI lesion

A

Paralyse lateral rectus. Adducted by resting tone of medial rectus

55
Q

What is Horner’s syndrome

A

Triad of symptoms produced by damage to the sympathetic trunk in the neck
Parial ptosis
Misosi
Anhydrosis - on ipsilateral side of the face

56
Q

What causes Horner’s syndrome

A

Tumour of the apex of the lung (Pancoast tumour), aortic aneurysm or thyroid carcinoma

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