Neural Pathways Flashcards
What are ascending tracts
Neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex.
What are the conscious tracts
Comprised of dorsal column-medial lemniscal pathways and the anterolateral system
What are the unconscious tracts
Comprised of the spinocerebellar tracts
What does the dorsal column medial lemniscal pathway carry
Sensory modalities of fine touch, vibration and proprioception
Where does the DCML travel in the spinal cord
Dorsal culmn
Where does the DCML travel in the brain stem
Medial lemniscus
How many groups of neurones are involved in the pathway
3 - first, second, and third order
What are first order neurones of the DCML
Carry sensory information from the peripheral nerves to the medulla oblongata
Where do signals from the upper limb travel through in DCML
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
Where do signals from the lower limb travel through in DCML
Below T6 - travel in the fasciulus gracilis (medial part of the dorsal column). They then synapse in the nucleus gracilis of the medulla oblongata
Explain second order neurones of the DCML
Begin in cuneate nucleus or gracilis. Decussate in medulla oblongata. Travel in the contralateral medial lemniscus to reach the thalamus
Explain third order neurones of the DCML
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
What are the two anterolateral systems
Anterior spinothalamic tract - carries the sensory modalities of crude touch and pressure
Lateral spinothalamic tract - carries the sensory modalities of pain and temperature
Explain first order neurones of ALS
Arise from sensory receptors in the periphery -> spinal cord -> ascend 1-2 vertebral levels -> synapse at tip of the dorsal horn (substantia gelatinosa)
Explain second order neurones of ALS
From substantia gelatinosa -> thalamus. Fibres decussate within the spinal cord and then form two distinct tracts
What are the two tracts of the second order neurones of ALS
Crude touch and pressure fibres - enter anterior spinothalamic tract
Pain and temperature fibres - enter the lateral spinothalamic tract
What are the spinocerebellar tracts
Carry unconscious proprioceptive information.
What are the four pathways of the spinocerebellar tracts
Posterior spinocerebellar tract
Cuneocerebellar tract
Anterior spinocerebellar tract
Rostral spinoerebellar tract
What does the spinocerebellar tract do
Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum
What does the cuneocerebellar tract do
Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum
What does the rostral spinocerebellar tract do
Carries proprioceptive information from upper limbs to ipsilateral cerebellum
What do lesions in the DCML pathway cause
Loss of proprioception and fine touch. If lesion occurs in spinal cord, sensory loss will be ipsilateral
What causes DCML lesions
B12 deficiency and tabes dorsalis
What do lesions in the anterolateral system cause
Impairment of pain and temperature sensation. Sensory loss will be contralateral
What is Brown-Sequard syndrome
Hemisection of spinal cord. Most often due to traumatic injury and involves both conscious pathways
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
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.
How are pyramidal tracts divided
Corticospinal - supplies musculature of the body
Corticobulbar - supplies the musculature of the head and neck
Where do corticospinal tracts receive input from
Primary motor cortex
Premotor cortex
Supplementary motor area
Somatosensory area
Describe path of corticospinal tract before division
Cortex->internal capsule->crus cerebri of midbrain->pons->medulla->divides into lateral and anterior corticospinal tract
Describe path of anterior corticospinal tract
Decussate in medulla -> spinal cord -> terminates in ventral horn -> LMN to muscles of the body
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
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
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
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
What are the ipsilateral innervation extrapyramidal tracts
Vestibulospinal and reticulospinal
What are the contralateral innervation extrapyramidal tracts
Rubrospinal and tectospinal
Describe pathway of vestibulospinal tract
Two pathways: medial and lateral. Arise from vestibular nuclei -> spinal cord -> remains ipsilateral
What does the vestibulospinal tract control
Balance and posture by innervating anti gravity muscles (flexors of the arm, extensors of the leg), via LMN
What does the medial reticulospinal tract do
Arises from pons and facilitates voluntary movements, and increases muscle tone
What does the lateral reticulospinal tract do
Arises from the medulla. Inhibits voluntary movements and reduces muscle tone
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
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.
What does the tectospinal tract coordinate
Movements of the head in relation to vision stimuli
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
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)
Describe a lesion in the UMN for the facial nerve
Spastic paralysis of the muscles in the contralateral lower quadrant of the face
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
What muscles does the occulomotor nerve supply?
Superior rectus Inferior rectus Medial rectus Inferior oblique Levator palpebrae superior
What muscle does the trochlear nerve supply
Superior oblique
What muscles does the abducens nerve supply
Lateral rectus muscle
Retractor bulbi muscle
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
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
What are the characteristics of a CN VI lesion
Paralyse lateral rectus. Adducted by resting tone of medial rectus
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
What causes Horner’s syndrome
Tumour of the apex of the lung (Pancoast tumour), aortic aneurysm or thyroid carcinoma
