Descending Neural Pathways Flashcards
What are descending pathways ?
Pathways that are involved in us doing an action/ movement.
Also known as motor pathways
Describe some signs of upper motor neurone lesion
Increased muscle tome
Spasticity (painful)
Increased deep tendon reflexes
Clonus
Abnormal reflex (Babinski/ Hoffmann sign)
Describe some signs of lower motor neurone lesion
Reduced muscle tone
Flaccid paralysis
Decreased tendon reflexes
Fasciculation
Atrophy
Tests for motor neurone lesions
Babinski reflex
Hoffmann sign
Describe movement generation
- Goal/purpose
- Activation of relevant movement
- Feedback of movement
- Refinement/ correction of movement
- Cessation on completion
State the structures in the motor pathway
Idea
DLPFC and Parietal cortex
Thalamus
Basal nuclei
Supplementary motor area
Pre-motor cortex
Lateral cerebellum
Motor cortex
Brainstem
Spinal cord
Cerebellum function
Involved in spatial awareness
Where is the primary motor cortex (M1) located ?
Within the pre central gyrus
Anterior to the central sulcus
State input to the primary motor cortex
Somatosensory cortex
Premotor cortex
Supplementary motor cortex
Cerebellum
Function of the primary motor cortex
Gives rise to 60-80% of the corticospinal tract.
> 1/2 of the primary motor cortex controls hands and muscles of speech
Pre-motor cortex
One of secondary motor cortices
Function of the pre-motor cortex
Responds to external stimuli
Involved in bilateral postural fixation, planning and control of movement.
Coordinated muscle movements in more than 1 joint
Input to the pre-motor cortex
It receives cognitive inputs from the frontal lobe in the context of motor intentions and a rich sensory input form the parietal lobe incorporating tactile and visuospatial signals.
Function of the supplementary motor cortex
Responds to internal stimuli
Describe activation of supplementary motor cortex
Activated by the dorsi-lateral prefrontal cortex, when we intend to make a movement.
Difference between premotor and supplementary motor cortex
Premotor - responds to external stimuli
Supplementary motor - responds to internal stimuli
Supplementary motor cortex
Pre-programming movement sequences - built into motor memory
State other motor areas
Brocas area
Frontal eye field
Brocas area
Motor speech area
Dominant hemisphere location
Frontal eye field
Voluntary eye movement
State a structure involved in voluntary movement
Basal nuclei
Basal nuclei
A mass of grey matter / a mass of cell bodies found within the white matter of the brain/brainstem
State some features of basal nuclei
Has connections with the thalamus and cerebellum
Function of the basal nuclei
Involved in initiation, fine tuning of movement.
(Basal nuclei cannot initiate voluntary movement, it just helps)
Describe the circuit for motor, cognitive, limbic and oculomotor
Between cortex –> Basal Nuclei –> Cortex
Connections with thalamus and cerebellum
State the basal nuclei
Caudate nucleus
Putamen (lentiform nucleus)
Globus pallidus (lentiform nucleus)
Subthalamic nucleus
Substantia nigra
Where are the cell bodies of upper motor neurones found ?
Cell bodies found in the cortex and brainstem nuclei.
Restricted to the CNS and do not contact muscle.
Where are the cell bodies of lower motor neurones found ?
Cell bodies found in the brainstem and spinal cord.
Leave the CNS and contact muscle to stimulate.
State the function of the upper motor neurones
Executive function for lower motor neurones and circuits controlling LMNs
State the function of the lower motor neurones
Motor function to muscles
What can be found between upper and lower motor neurones ?
Sometimes :
Interneurones (which can have an inhibitory or excitatory effect)
Cortico-nuclear Tract
Axons of the UMN end up in the motor nuclei of cranial nerves.
Motor nuclei of cranial nerves are only found in the brainstem.
UMN synapse with LMNs found in the motor nuclei of some of the cranial nerves (usually bilateral).
What do LMNs in the cortico-nuclear tract supply ?
Extraocular muscles (CN III, IV and VI)
Muscles of mastication (CN V)
Muscles of Facial Expression (CN VII)
Pharynx and Larynx muscles (CN IX and X)
Tongue (CN XII)
Cotricospinal tract function
Concerned with voluntary, discrete, skilled movements, especially distal parts of the limbs.
Origins of the corticospinal tract
30% from the primary motor cortex
30% from the premotor and supplementary motor areas
40% from the somatosensory areas
Describe the corticospinal tract
Axons descend through corona radiate and posterior limb of the internal capsule to reach the brainstem
It continues through the crus of the midbrain and then pons to reach the medulla
In lower medulla, it forms the pyramid
About -85% of the fibres cross the midline in the pyramidal decussation.
Axons up to the decussation are referred to as the corticospinal tract.
State the structures of the corticospinal tract
Corona Radiata
Posterior limb of internal capsule
Cerebral peduncle of the midbrain
Pyramid (of medulla oblongata)
Pyramidal decussation
What is the lateral corticospinal tract ?
Axons that crossed the midline in the pyramidal decussation become lateral corticospinal tract and descend.
Synapse w LMNs vis interneurones.
Function of the lateral corticospinal tract
Voluntary movement of the limbs
What is the anterior corticospinal tract ?
Most of the axons that do not decussate in the pyramid descend ipsilaterally as the anterior corticospinal tract.
Function of the anterior cortciospinal tract
Controls voluntary movement of the axial and girdle muscles and proximal limb muscles.
Key function of anterolateral corticospinal tract
Helps control movements of axial muscles
What is the extra-pyramidal system ?
A system of nuclei and tracts that regulate involuntary motor functions to maintain posture and fine tune voluntary movements.
Difference between corticospinal tract and extra-pyramidal system
Corticospinal tract passes through the pyramid
Extra-pyramidal passes through the tegmentum rather than the pyramid
What happens if the corticospinal tract is severed ?
Discrete movements can still occur, except that the movements for fine control of the fingers and hands are considerably impaired.
(DONE WITH THE HELP OF EXTRA-PYRAMIDAL SYSTEM)
State the nuclei in the extrapyramidal system
Basal nuclei
Cerebellar nuclei
Reticular formation
Vestibular nuclei
Nuclear ruber
Substantia nigra
State the tracts in the extrapyramidal system
Reticulospinal
Vestibulospinal
Rubrospinal
Tectospial
Don’t originate form the cortex
Not voluntary, they are unconscious
Function of the extra-pyramidal system
Fine-tuning and adjustments of voluntary movements
Control of AN voluntary movements
Adjusting and Maintaining posture
Planning and preparation of involuntary movements
Control of reflex actions
Inhibition of involuntary movements
Vestibulospinal tract
Activate extensor muscles
Inhibit flexor muscles
Potine Reticulospinal tract
Activate extensor muscles
Inhibit flexor muscles
What is involved in posture ?
Ventromedial pathways of the extrapyramidal system are involved
Controlled and driven by the brainstem
Where is posture information integrated from ?
Muscle proprioceptors
Gravitational field
Visual Inputs
Sensory information predominantly integrated in the brainstem.
Decorticate posturing
Corticospinal tract interrupted
Extrapyramidal tracts beomce dominant distally
Flexion of upper limb, extension of lower limb
Lesion above red nucleus
Decerebrate posturing
Lesion inferior to red nucleus
Extension
Unopposed extension of vestibulospinal and pontine reticulo spinal tracts
