Flashcards in Session 4 - Pyramidal Tracts Deck (23)
What are the two main classes of descending tracts?
What do pyramidal tracts do?
Maintain somatic control of muscle by making direct (monosynaptic) contact with LMN supplying distal muscle of extremities
What are the two mains part of the pyramidal tract?
What are the two different part of the corticospinal tract?
Lateral and anterior
Outline the path of the corticospinal tract
Skeletal Muscle α-LMN
Lateral decussates in Medullary Pyramids
Anterior remains ipsilateral
Where does the corticotubular pyramid extend to?
Cranial Nerve Nuclei
What are extrapyramidal tracts?
Indirect contact (polysynaptic) with motor neurones, via regulation of ventral horn interneurons.
What is the difference in relationships with LMN's between pyramidal and extra-pyramidal systems
Pyramidal system has direct (monosynaptic) contact with lower motor neurones supplying the distal muscles of extremities (e.g. the hand)
The extra-pyramidal system has an indirect contact with the rest of the motor neurone pool.
Give three causes of upper motor neurone lesions
Spinal cord injury
Motor neurone disease
Give three causes of LMN lesions
Motor neurone disease
Give key signs of UMN lesions
+’ve Babinski sign
No muscle wasting
Give key signs of LMN lesions
Where does hypertonia, hyperreflexia and spastic paralysis come from in a UMN lesion?
Loss of descending inhibition of spinal reflexes
What is clasp knife reflex?
Increased tone gives resistance to movement, but when sufficient force is applied resistance suddenly decreases
What is clonus caused by?
Loss of descending inhibition leads to self re-excitation of hyperactive reflexes
What is a positive Babinski sign?
Scrape along lateral edge of foot and in towards great toe
Dorsiflexion of hallux, extension/flaring of toes (Loss of descending inhibition means the reflex is unable to be suppressed)
What is hypotonia caused by in LMN lesions?
Lack of LMN means muscle cannot contract to produce tone
Name the extra-pyramidal tracts
Rubrospinal and rubrobulbar tract
Where does the tectospinal tract arise and what does it do?
– Main inputs are from the superior and inferior colliculi in the midbrain; decussate in the midbrain
– Innervate Motor neurone pools of neck – coordinate eye-head movements, responses to visual & auditory stimuli
Where does vestibulospinal tract arise and what does it do?
– Originates from vestibular nuclei in the Pons; remain ipsilateral;
– Innervates motor-neurone pools of anti-gravity muscles - balance reflexes.
Where does reticulospinal tract arise and what does it do
– Widespread inputs, including from motor cortex, medulla oblongata, pons and midbrain
- remain ipsilateral
– Medullary (lateral tract) - Flexor reflex facilitation
- Extensor reflex inhibition
– Pontine (medial tract) - Extensor reflex facilitation
– Role in regulation of posture and rhythmic movements
Where does rubrospinal tract arise and what does it do?
– Originates from red nucleus (tegmentum of the mid-brain at superior colliculus), inputs include motor cortex
- Decussates at level of nucleus
– Control flexor tone in distal muscles, also tone of facial muscles