129; Neurological Basis of Movement Flashcards
What is the Peripheral Nervous System?
All of the nerves outside of the brain and the spinal cord; Includes all Cranial Nerves except CN I and CN II
What is an Afferent Neuron?
Neuron conducting signals INTO the CNS
What is an Efferent Neuron?
Neuron conducting signals FROM the CNS
What is a Ganglion?
Collections of neurons (or nuclei of) usually collected outside of the brain
What are the 5 components of the reflex circuit?
- Sensory Receptor
- Afferent path to CNS
- Synapse with the CNS
- Efferent path from CNS
- Effector (muscle)
Describe the Myotatic reflex following a patellar tap
Patellar tap stretches the quadriceps muscle
- Muscle spindles are stretched
- Afferent neurone stimulated (1a afferent)
- Synapse with grey matter in spinal cord
- Direct synapse to excitatory à neuron
- Contraction of Quadriceps muscle (Homonymous muscle)
and
- Synapse with Inhibitory interneuron
- Inhibition of à motor neuron to the heterogymous muscle
What makes the reflex transient?
Recurrent inhibition
Renshaw cell is an inhibitory neuron
- It is excited by the à motor neuron
- Releases glycine back into à motor neuron
- Inhibits firing of à motor neuron
= Negative feedback
Glycine has the inhibitory effect here; the Tetanus toxin inhibits glycine release, which causes prolonged contraction of muscle.
Describe the inverse Myotatic reflex
It provides inhibitory feedback;
Golgi Tendon Organ has a higher threshold than Spindle
- It is activated by prolonged muscle tretch or contraction
- 1b afferent activation
Activation causes inhibition of homonymous muscle
Prevents damage to tendon
(eg, Drop heavy things)
What is the role of ŷ motor neurons?
Maintains tension on the muscle fiber, even following contraction of the muscle that may cause the spindle to become flacid
How do ŷ motor neurons maintain the tension over the spindle?
They stretch each end of the spindle causing contraction;
Set a reference range around which further muscle regulation is established.
Briefly describe à and ŷ motor neurones
à- cause muscle contraction
ŷ- cause spindle contraction
Where do motor neurones originate?
Pyramidal cells of the motor cortex
Describe the course of Motor Neurones through the Corticospinal tract
- Motor neurons originate in the pyramidal cells of the motor cortex
- They descend through the internal capsule
- Cross at ‘decussation of pyramids’ in the medulla
It is the largest descending ract
What are the major Cortical Motor Regions
- Primary Somatosensory Cortex- Parietal
- Pre-motor Area- Frontal
- Supplementalr Motor Area- Frontal
- Posterior Parietal Cortex- Parietal
What are the Main functions of the Primary somatosensory cortex?
- Recieve ascending sensory input from Thalamus
- (sensory homunculus)
- Sends descending fibers to sensory regions to filter irrelevant signals
What are the main functions of the Pre-motor area?
- Located in Frontal lobe
- Involved in planning of intended movements
- Particularly movements requiring visual guidance
What are the main functions of the Supplementary motor area?
- Coordination of voluntary movements
What are the main functions of the Posterior Parietal Cortex?
- Integration of other sensory information
What is Apraxia?
The inability to produce a specific motor event, even though sensory and motor pathways remain intact.
What is Apraxia and indication of?
- Damage to PMC, SMA or PPC
What is the difference between Ideomotor and Ideational Apraxia?
Ideomotor Apraxia
Cannot execute a specific movement upon request; alothough may understand concept, and able to do movement spontaneously
Ideational Apraxia
Unable to conceptualise the movement required
From where does tha Corticospinal tract arise?
Arises from the Cortex
What does the Reticulospinal tract modulate?
Spinal extensor reflexes
What does the Vestinulospinal tract modulate?
Posture & Balance
What does the Tectospinal modulate?
It directs head movements in response to stimuli.
What does the Rubrospinal tract modulate?
Flexor motor neurones.
What do the Ascending tracts convey to the brain?
Afferent neurons carrying sensory information
What information does the Spinothalamic tract convey?
- Pain
- Temperature
- Touch
- Pressure
They project this information to the thalamus
Thalamocortical projections convey info then to the cortex
What information do the Dorsal column neurons convey?
- Proprioception
- Soft touch
- Fine discriminatory touch
Conveyed to ventral, posterior, lateral nucleus of the thalamus
Thalamocortical projections then link to the cortex.
What information does the Spinocerebellar tract convey?
- Proprioception
Prijections travel directly to the cortex; do not synapse in thalamus first.
What is the difference between the type of movements the **cortex **and brainstem regulate?
Motor cortex
Planning, initiating and directing voluntary movements
** Brainstem Centres **
Basic movements and postural control
What is the relationship between UMN and LMN in Motor regulation?
What is a Lower Motor Neurone?
- They innervate skeletal muscle; release Ach
- There are 2 types; à and ŷ
- They arise in the brainstem and spinal cord
What is an Upper Motor Neurone?
- These innervate the LMNs
- Do not project directly to muscle
- They arise in the brain
- They are Glutamatergic neurons
List the signs and symptoms of LMN lesions
- Hyporeflexia
- Fasciculations
- Muscle atrophy
- Denervation
These signs are not present in UMN lesions
What are the causes of LMN lesions?
Trauma
Virus (ee. Polio)
What are the signs and symptoms of UMN damage?
- Paralysis or weakness of movement of affected muscles
- Hyper-reflexia
- Increased muscle tone; hyper-tonicity
- Spasticity
- Positive Babinski reflex
Immediately following damage may get hypo-tonia, loss of myotatic reflexes, and flaccid paralysis.
May also impede autonomic function if damage to descending autonomic fibres.
What is the consequence of UMN lesion at the Crevical level?
Quadriplegia
What is the consequence of UMN damage below the Cervical spine?
Paraplegia
What is decussation?
Crossing of nerve fibres
Where do most Corticospinal fibres decussate?
At the junction of the medulla and the spinal cord; Decussation of the pyramids
- Thise that do not decussate at this junction continue to the **anterior corticospinal tract, **to innervate the cervical and superior thoracic regions
What information does the spinothalamic tract convey?
Affrent fibres that convey info on:
- Temperature
- Pain
- Pressure
- Touch
Describe the route of the **spinothalamic **tract fibres.
- Fibres enter and synapse in the Dorsal horn
- Move forward and decussate in ventral white comissure
- Pain and Temp axons decussate within one segment
- Pressure and touch may decussate after several segments
- Ascend in contralateral side, in lateral white matter
- Synapse in the thalamus
Describe the route of fibres within the dorsal column.
Soft touch and Proprioception info is transmitted here
- Enter the dorsal horn
- Fibres from lower body ascend to gracile nucleus in Medulla
- Fibres from upper body ascend to cuneate nucleus
- Upper and lower body fibres synapse and decussate at the Medulla before ascending to the cortex
To summarise, what side of the spinal cord do the Spinothalamic thact and Dorsal column?
Spinothalamic
Contralateral
Dorsal Tract
Ipsilateral
What is Brown-Sequard Syndrome?
The signs associated with hemisection of the spinal cord.
What area of the spinal cord do th Motor, Spinothalamic and Dorsal Column neurones travel?
Motor pathway
Ventral horn
Spinothalamic
Lateral white matter (synapse in dorsal horn)
Dorsal Column
Gracile and Cuneate tracts in dorsal cord
