L28 Motor Control and Disease I (Imported from Quizlet)

Spinal motor, spinal sensory

Simple reflexes involve local circuit control of _________ ________ neurones by __________ _______ neurones

Lower motor neurons

All movements produced by the skeletal musculature are initiated by ...?

Central pattern generators

The spinal cord contains _________ ________ ____________ that generate complex behaviours without input from the brain

Muscle movement

What does stimulation of motor cortex elicit?

That electrical stimulation of part of the cortex elicits contraction of contralateral body muscles

When did Fritsch and Hitzig demonstrate (using dogs) in 1870s?

The motor cortex, or more specifically the primary motor cortex

What did the contralateral body muscle region become known as?

Upper motor neurons

What are the neurons found in the brain that control motor function called?

Somatotopically

Motor cortex is also ________________ mapped

Correlated the site of stimulation with the location of muscle contraction and demonstrated a topographic map similar to that of the somatosensory system

What did Sherrington and Penfield (early 1900s) do?

Medially, laterally

Lower body is represented __________, upper body __________

Density of innervation (and behavioural significance)

What do the proportions reflect?

Trunk movement

What do axial muscles control?

Shoulder, elbow, pelvis, knee movement

What do proximal muscles control?

Hands, feet, digits (fingers and toes) movement

What do distal muscles control?

Neuro Muscular Junction (NMJ)

Innervation is via a specialised synapse called the ...?

Alpha

Each muscle fibre receives input from a single lower motor neuron, which kind is it - alpha MNs or gamma MNs?

Alpha MNs

Muscles also contain muscle spindles that receive input from gamma motor neurons, so a single muscle will receive inputs from both alpha and gamma MNs - when we talk about lower motor neurons (LMNs) we are talking about ...?

Motor neuron and all the muscle fibres it innervates

What is a motor unit?

All the motor neurons that innervate a single muscle

What is a motor neuron pool?

Spinal cord

Motor pools are spatially organised in the __________ ______

Rod-shaped clusters, spinal cord, vertebral

All the motor neurons innervating a particular muscle - the motor pool for that muscle - are grouped in ____-___________ __________ within the _________ ______ extending over several ___________ segments

Tracers were injected into specific muscles, which then were transported back along the motor axons to the cell bodies in the spinal cord

- Injection into the gastroceneumius

- Labels a different set of motor neuron cell bodies to injection of the soleus

What were the experiments done in animals to help us understand motor pools?

Mediolateral, rostrocaudal, ventral horn

Even though the experiment labelled muscles in different legs, careful comparison makes it obvious the motor pools for each muscle occupy a distinct ______________ (and ______________) position within the __________ _______ of the spinal cord

Sections of spinal cord in which these tracers have been visualised

What does the middle diagram represent?

3D reconstruction of where the tracers went

What does the right hand diagram represent?

Somatotopically, medio-laterally, rostro-caudally

Motor pools are organised __________________ both _______-___________ and _______-__________ (A-P)

Whether its MNs innervate a proximal or distal muscle

What does the medic-lateral position of a motor pool reflect?

Its organisation reflects the organisation of the body (i.e. there is a 3D representation (map) of the body's musculature within the spinal cord)

What does somatotopic mean?

The location of the upper motor neurons that innervate lower motor neurons in the spinal cord

What does somatotopy in the motor cortex reflect?

Local sources, upper motor neurons

Lower motor neurons (LMNs) receive inputs from _________ ___________ in the spinal cord, but also directly from ________ ________ _________ (UMNs)

Descending tracts

Upper motor neurons project axons to lower motor neurons via the ______________ _________ of the spinal cord

Coritcospinal tract, lateral

Key among these for the control of voluntary movement is the __________________ _________ (CST) one of the __________ pathways of the spinal cord

Five (V)

The axons of the CST originate in which layer of the motor cortex?

Corticospinal tract

Pyramidal cells of the motor cortex project axons in the ...?

Six

90% of cortex, including the motor cortex, is a _____ layered structure

Stellate

Main inputs to the cortex are to __________ cells in layer IV (blue arrow)

III, V, VI

Main outputs are from layers ___ (brown arrow), _ (black arrow) and __ (yellow arrow)

Pyramidal, V

Axons of corticospinal tract derive from large _______________ cells (also known as Betz cells) in layer _

Lateral, medial

Similar to the somatosensory system, CST outputs to the upper body originate from ________ motor cortex, outputs to lower body from _________ motor cortex

Different sets of upper motor neurons control different functions

Posture

What do the ventromedial pathways control?

Ipsilaterally, medially

The ventromedial pathways project mainly ______________ and _________

Head balance and turning (inputs from vestibular system)

What is the vestobulospinal tract involved in?

Orienting response (inputs from visual system via superior colliculus)

What is the tectospinal tract involved in?

Antigravity reflexes

What do reticulospinal tracts control?

Complex voluntary movements

What do upper motor neurones of the motor cortex initiate?

Contralaterally, corticospinal, lateral

Upper motor neurons of the motor cortex project mainly ______________ via the _________________ tract primarily to muscles involved in precise limb movements, particularly those of the hands in humans - one of the _________ pathways of the spinal cord

Coritcobulbar

Upper motor neurons of the motor cortex also project via the __________________ tract to the hypoglossal nucleus in the brainstem, which controls the movements of the tongue - important for speech in humans

Maintenance of posture and balance

What are upper motor neurons of the brainstem more concerned with?

Reicular formation, vestibular nucleus (vestibular co-ordination) and superior colliculus (visual co-ordination)

Upper motor neurons of the brainstem are located in several nuclei including ...?

Ipsilaterally, axial, ventromedial

Upper motor neurons of the brainstem project mainly _____________ to lower motor neurons controlling ______ muscles concerned with maintaining posture - the ______________ pathways of the spinal cord

Lower motor neurons, muscle fibres

Upper motor neurons always synapse on __________ _________ __________ (or their interneuron circuitry) whereas lower motor neurons always synapse directly on _________ __________

Volunteer will lift lever in response to auditory stimulus (tone)

Recording from different muscles reveal that the first to contract are those in the leg

This anticipatory 'feedforward' mechanism pre-adjusts body posture to compensate for the forces that will be generated when the lever is lifted

Describe the experiment involving integration of postural control with voluntary movement

That upper MNs in the cortex influence spinal cord circuits by two routes

Feedforward mechanism makes sense when you realise what?

Precedes

Activity in the PMA ___________ activity in M1 and coincides with movement planning/anticipation

Move

Clearly motor neurons, both lower and upper are vital to our ability to ______ and hence to our behaviour and survival in complex environments

When they are dysfunctional the consequences are significant

A degenerative disease of motor neurons

What is MND/Amyotropic lateral sclerosis (ALS)?

Jean-Martin Charcot in 1869

When was MND/ALS first described and by whom?

Muscle atrophy (amyotrophic means 'loss of muscle nourishment') and sclerosis ('hardening' or 'scarring') of the lateral spinal cord, which is the mark of degeneration of axons in the CST (pink)

MND/ALS is characterised by what?

New York Yankees baseball star Lou Gehrig when he contracted it in 1938

Who made MND/ALS famous and when?

Muscle paresis (weakness) or paralysis

Loss of muscle tone due to loss of stretch reflexes

Ultimately, leads to severe muscle atrophy

Patients usually die from lung dysfunction (due to atrophy of intercostal muscles)

What is lower motor neuron disease characterised by?

Muscle weakness

Spasticity due to increased muscle tone (due to failure of modulation of stretch reflex)

Hyperactive reflexes

Loss of fine voluntary movement

Patients usually die from loss of input to the bulbar muscles (tongue and pharynx) via the corticobulbar tract

What is upper motor neuron disease characterised by?

Intellect

What is not compromised in neither version of motor neuron disease?

5

Most MNS patients die within _ years of diagnosis

Neurodegenerative

ALS is one of several ______________________ diseases

Where overstimulation, typically by glutamate, leads to neuronal cell death

Excitoxicity is a possibility of ALS, what is it?

Hypoxic

A 'vicious cycle' of glutamate release can occur particularly in _________ conditions e.g. after cardiac arrest, stroke or brain trauma

-> Lou Gehrig's ALS has been suggested to have been triggered by the blow of a baseball to his head

Blocker, glutamate

The only drug to have any effect on ALS is a __________ of ___________ release (Riluzole) but this only delays the disease by a couple of months

10

About __% of cases of ALS have a clear genetic (inherited) basis

Superoxide dismutase

One of these results from mutations in the gene encoding ____________ ___________ (SOD1), a key enzyme that 'maps up' the free radicals that accumulate in metabolically active cells

Descending pathways

The brain exerts control over spinal motor units via specific ______________ __________

Lower

Spinal motor neurons = ________ motor neurons

Upper

_________ motor neurons reside in brainstem and cortex, controlling postural and voluntary movements respectively

Voluntary

Postural control is integrated with ___________ movement and is part of movement planning/anticipation

Upper, lower

Motor neuron degeneration can affect either ________ or ________ motor neurons and is almost always fatal