Lecture 7 - Motor System Flashcards
What are the 2 types of motor neurone?
Upper motor neurones (UMN)
Lower motor neurones (LMN)
Where are upper motor neurones located (UMN)?
Primary motor cortex (CNS only)
Where are Lower Motor Neurones located (LMN)?
Ventral horn of spinal cord and brainstem
What do Upper Motor Neurones synapse to?
Lower motor neurones
What do lower motor neurones synapse to?
Skeletal muscle
(Smooth muscle in sympathetic NS)
What part of the Lower Motor Neurones are located in the CNS?
LMN cell body + Proximal axon
What part of the Lower Motor Neurone is located in the PNS?
Distal axon of LMN
What are the structures called which all cranial nerves have in the brainstem from cranial nerve III onwards?
Cranial nerve nuclei
What is considered the brainstem?
Midbrain
Pons
Medulla
What is a nucleus in the brain?
A group of cell bodies of similar neurones
What 2 nuclei are located in the midbrain?
Occulomotor nuclei
Trochlear nuclei
What cranial nerve nucelus is located at the pontomedullary junction?
Abducens nuceli (VI)
What cranial nerve nuclei are located in the medulla?
IX
X
XI
XII
What part of the brain is there usually a lesion if theres disruption to swallowing?
Medulla
What is the name of type of vision where both eyes move in the same direction at the same time?
Conjugate gaze
What type of vision is conjugate gaze important for?
Binocular vision (needed for depth perception)
What are the 3 main cranial nerves/nuclei that need to communicate with each other for conjugate gaze to be achieved?
Occulomotor nuclei (III)
Trochlear nuceli (IV)
Abducens nuclei (VI)
What is the key structure by which the 3 cranial nuclei needed to achieve conjugate gaze communicate by?
Medial Longitudinal Fasciculus
think MiLF (i represents structure being moved)
What is the Medial Longitudinal Fasciculus? (MiLF)
Interneurones which connect the Occulomotor, Trochlear and Abducens nuclei so they can communicate eye movement to achieve conjugate gaze
Where do sensory neurones enter the spinal cord?
Where do lower motor neurones originate in the spinal cord?
Sensory = dorsal horn
LMN = ventral horn
What type of receptor is stimulated in the knee jerk reflex?
Spindle receptor (when patella tapped muscle detects it)
What is the myotome for knee Flexion?
L3
What muscles contract in the knee jerk reflex?
Which muscles must remain relaxed for the knee jerk reflex to occur?
Contract = Quads
Relaxed = Hamstrings
What prevents the hamstrings contracting along with the quadriceps in the knee jerk reflex?
(See Slide 2 if stuck)
The spindle fibres detecting the pressure on the tendon synapse to the Lower Motor Neurone Supplying the hamstrings but also give off a branch which travels and descends down to the L5 level and synapses to an inhibitory Interneurone which then synapses to a Lower Motor Neurone for the hamstrings preventing their contractions
What effect (Stimulatory or inhibitory) do most Upper Motor Neurones have on Lower Motor Neurones?
Most are stimulatory to LMN
What prevents unwanted contraction of skeletal muscle when the Upper Motor Neurones that directly synapse to the LMN are mainly Stimulatory?
Lots of inhibitory interneurones located in the ventral horn to help suppress the LMN
NET INHIBITION OF LMNs by the UMNs that synapse to inhibitory interneurones
How do Lower Motor Neurones end up being activated if there is an overall NET inhibition by inhibitory interneurones?
Very large stimulus sent down the Upper Motor Neurones which overcomes the inhibitory interneurones
What are the 2 main ways that Lower Motor Neurones can be damaged?
Cut axon
Damage cell body (in ventral horn)
What are lower motor neurone signs indicating theres being lower motor neurone damage?
Weakness
Hyporeflexia/aflexia
Hypotonia
Muscular atrophy
Fasciculation
Why do we get weakness with lower motor neurone damage?
You have disrupted the flow of electrical impulses/signals to the muscle
Why do you get hyporeflexia/aflexia with lower motor neurone injuries?
Lower Motor Neurone is needed for reflexes (disrupt the pathway)
Why do you get hypotonia with Lower Motor Neurone damage?
Unable to provide constant signals to muscle to provide muscle tone
Why do you get Muscular atrophy with Lower Motor Neurone damage?
Atrophy due to dennervation
The lower motor neurone normally r provides growth factor and ACh to the muscle, if damaged the muscle doesn’t get this
What is fasciculation?
Uncoordinated muscle contractions
Why do you get Fasciculations (uncoordinated muscle contraction) with lower motor neurone damage?
Muscle upregulates its ACh receptors which can lead to the muscle becoming over sensitive to circulating ACh leading to uncoordinated contractions
What is the corticospinal tract?
The pathway by which signals for skeletal muscle contractions are transmitted from the cerebral cortex to the spinal cord
What type of neurones are located in the cortical spinal tract?
Upper Motor Neurones
What is the name of the region of the cerebral hemisphere where the Upper Motor Neurones descend?
Corona radiata
What does the corona radiata go on to form as its axons get compressed?
Internal capsule
What 2 anatomical structures does the corona radiata get compressed between forming the internal capsule?
Thalamus and Lentiform nucleus
What is the cerebral peduncle?
What connect the Upper Motor Neurone from the internal capsule to the midbrain
What is the name of the structure where the upper motor neurone decussates following the cerebral peduncle?
Decussation of medullary pyramids
After the decussation of the medullary pyramids, what structure do th upper motor neurones go onto form before eventually synapsing to a lower motor neurone?
Lateral cortical spinal tract
What part of the body does the lateral cortico spinal tract go onto supply?
Limb musculature
Some upper motor neurones dont decussate at the decussation of medullary pyramids, what do they go onto form?
Anterior corticospinal tract
They descend on the Ipsilateral side until they eventually decussate and supply a LMN
What part of the body does the anterior corticospinal tract supply??
Trunk musculature
How does the lateral corticospinal tract and anterior spinal tract differ in terms of what parts of the body they supply?
Lateral corticospinal tract = limb musculature
Anterior corticospinal tract = trunk musculature
What is a peduncle?
Region where White matter connects to the brainstem
What does an Upper Motor Neurone (UMN) supplying the left lower limb travel?
Refer to slide 3 if stuck:
Upper Motor Neurone nucleus in medial aspect of primary motor cortex
Travels down the corona radiata to the internal capsule which is between the thalamus and lentiform nucleus
From the internal capsule the UMN travels to the cerebral peduncle
Then decussates at the medullary pyramid and then descends on the left side of the spinal cord in the LATERAL CORTICOSPINAL TRACT
Then synapses to LMN
What is the nerve responsible for control of the muscles of the face?
Facial nerve (VII)
How is the facial nuclei split?
Superior half
Inferior half
What part of the face does the superior half of the facial nuclei supply?
Upper half (above eyes, occipitofrontalis)
What part of the face does the inferior half of the facial nuclei supply?
Lower half of face (below eyes like Obicularis oris)
How does the lower half of the facial nuclei receive innervation from upper motor neurones?
Receives innervation from Upper Motor Neurone in contralateral hemisphere
Look at slide 3 if unsure
How does the upper half of the facial nuclei receive innervation from upper motor neurones?
Receives innervation from Upper Motor Neuornes bilaterally
So innervation from upper motor neurones in the right and left cortex
How does the upper motor neurone supply to the superior part of the facial nuclei differ to the inferior part of the facial nuclei?
Superior part receives innervation from left and right hemispheres
Inferior part receives innervation from the contralateral hemisphere
What is the name of a lesion that occurs in the Lower Motor Neurones following the facial nerve nuclei?
Bells Palsu
How does Bell’s palsy present?
Complete unilateral facial droop since affects LMN on that side
How does the facial droop of a stroke appear and why?
Facial droop of lower half of face on contra lateral side
UMN supplying the lower portion of the facial nuclei lost and th UMN on the side of the stroke supplying the superior portion is also lost however UMN from the other side of the brain unaffected by the stroke project to the superior portion so the Upper Half of face is spared
Upper spares upper (lesion)
What are the signs of an Upper Motor Neurone injury?
Spinal shock
Muscle weakness
Hypertonia/clasp knife rigidity
Hyper reflexia
Atrophy
What is spinal shock? (UMN damage))
During hours to days following UMN lesion, muscle becomes hypotonic (flaccid paralysis)
Unsure why
But eventually due to loss of inhibitory neurones on ventral Horn hypertonia occurs
Why does hypertonia occur with an UMN lesion?
ACh receptors upregulated so more sensitive to ACh
Less inhibitory interneurones acting on LMN
What is clasp knife rigidity?
When try to pull a flexed limb there’s resistance until suddenly there isn’t
What leads to clasp knife rigidity with an UMN lesion?
Golgi tendon organs get activated leading to sudden relaxation of the muscle to procect it from damage
What causes hyperreflexia in UMN lesions?
Skeletal muscels become very sensitive due to ACh up Regualtion
What causes the atrophy in UMN lesions?
Atrophy due to disuse (still being supplied with growth factor from LMN)
What is spasticity?
What is it a sign of?
Hypertonia + hyper-reflexia together is called spasticity
Sign of upper motor neurone lesion
What is the function of the medullary and pontine reticulospinal tracts?
Paralyse muscles in REM sleep
Muscle tone
What is the function of the lateral vestibule spinal tract?
Semicircular canals for balance connects to motor system via this tract
What is the vestibulo ocular reflex?
From medial longitudinal fasciculus
Allows you to shake head and still read(keep eyes still)
What is the function of the tectospinal tract?
Primitive vision
Primitive hearing (loud noise turn to look)
What does the internal capsule look like in a transverse section?
V shape
What is the genu of the internal capsule?
The apex/knee of the v of the internal capsule where Upper Motor Neuronesof face found
How is the lateral cortico spinal tract arranged in terms of body representation?
Medially = upper limb
Lateral = lower limb
Opposite to homunculus
Describe a lower motor neurone lesion in terms of:
-Power
-Tone
-Rigid/flaccid
-Reflexes
-Fasciculation
-Atrophy
Power = weak
Tone = Hypotonia
Rigid/flaccid = flaccid paralysis
Reflexes = hyporeflexia
Fasciculation = yes
Atrophy = dennervation
Describe a upper motor neurone lesion in terms of:
-Power
-Tone
-Rigid/flaccid
-Reflexes
-Fasciculation
-Atrophy
Power = weak
Tone = Hypertonia (clasp knife rigidity)
Rigid/flaccid = rigid paralysis
Reflexes = hyper-reflexia
Fasciculation = no fasciculations
Atrophy = disuse
