Motor function Flashcards
What are motor neurons involved in?
Pathways which carry efferent impulses from the CNS to the periphery of the head and body which ultimately activate effectors
What are motor neurons needed for?
- voluntary muscle contraction (somatic nervous system)
- involuntary muscle contraction (autonomic nervous system)
What else inputs to motor neurons as they pass through the CNS?
- eyes
- vestibular apparatus
- cerebellum
- basal ganglion loop system
What order is the hierarchy of motor pathways?
- primary motor cortex
- upper motor neurons
- lower motor neurons
Where is the primary motor cortex?
in the brain
What are upper motor neurons?
Axons from the primary motor cortex descending directly into the brainstem or spinal cord
What do the lower motor neurons do?
Receive an impulse from an upper motor neuron and then exit the CNS to cause the contraction of a muscle at the periphery
What lower motor neurons exit at the brainstem?
the cranial nerves, which innervate the muscles of the head and neck
Which motor neurons exit from the spinal cord?
Spinal nerves which innervate the muscles of the lower body
Which lower motor neurons synapse in the spinal cord?
Those which exit the spinal cord from the anterior horn of the grey matter
Each branch of the motor neuron will synapse with what?
A motor end plate - the region of the muscle that the neuron communicates with across the synapse
How is voluntary muscle contraction stimulated?
Motor neuron releases acetylcholine
Which areas of the frontal lobe are involved in motor movement?
- primary motor cortex (M1)
- premotor cortex (PM)
- supplemental motor area (SMA)
What does the premotor cortex do?
receives sensory input from parietal lobe and basal ganglia to help plan and prepare movement
What does the supplemental motor area do?
Coordinates complex fine movements and posture
Where is the primary motor cortex?
in the precentral gyrus of each hemisphere
How is the primary motor cortex arranged?
somatopically - body represented in the correct sequence but upside down
What are the main motor pathways divided into?
- the lateral pathways
- the medial pathways
What are the lateral motor pathways?
- corticospinal tract (from cerebral cortex)
- rubrospinal tract
What are the medial motor pathways?
- reticulospinal tracts
- tectospinal tracts
- vestibulospinal tract
- ventral corticospinal tract (from cerebral hemisphere)
Which are the pyramidal pathways?
- corticospinal tract
- ventral corticospinal tract
Which are the extrapyramidal pathways?
- rubrospinal tract
- reticulospinal tract
- tectospinal tract
- vestibulospinal tract
What is the function of the medial pathways?
To coordinate:
1. balance and posture
2. proximal limb muscles
3. guiding of limbs into positions for planned movement
Where does the vestibulospinal tract start?
in the vestibular spinal tract - spans pons and medulla
What do the vestibular nuclei do?
- receive info about balance from the semi circular canals in middle ear
- send info back from vesticulocerebrum to modulate and refine motor output
What doe the vestibulospinal tracts do?
Convey balance info to spinal cord where it remains ipsilateral, and controls balance and posture by:
1. innervating ‘anti-gravity’ muscle sin trunk and spine to maintain upright position
2. respond to changes in head position and movement - essential for reflexive adjustment to maintain balance and prevent falls
Where do the reticulospinal tracts arise from?
the reticular formation of the pons or medulla
What does the reticular system do?
receives sensory input from the spinoreticular tracts, red nuclei, and motor cortex
What do the reticulospinal tracts do?
Influence voluntary movement by controlling muscle tone and are involved in the synchronisation of complex movements
Where do the medial reticulospinal tracts arise from?
medullary reticular formation
What do the medial reticulospinal tracts do?
Facilitate voluntary movement and increases muscle tone
Where does the lateral reticulospinal tract arise?
pons
What does the lateral reticulospinal tract do?
Inhibits voluntary contraction and reduces muscle tone
Where does the venterolateral reticulospinal tract originate?
the medulla
What does the venterolateral reticulospinal tract do?
helps control muscle tone
What is the pathway of the tectospinal tracts?
- begin at superior colliculus in midbrain
- neurons then decussate and descend to enter the spinal cord
- terminate at cervical levels of spinal cord
What is the superior colliculus?
a structure which receives input from optic nerves from eyes
What do the tectospinal tracts do?
control reflex postural movements in response to visual stimuli
Where does the anterior corticospinal tract start?
in the cortex
Where does the anterior corticospinal tract decussate?
in the spinal cord at the level of its synapse with a lower motor neuron
What is the function of the anterior corticospinal tract?
to maintain balance, posture, and purposeful movements involving the axial musculature, esp in the trunk region
What is the function of the lateral motor pathways?
Mainly to coordinate voluntary movement?
1. fine voluntary movements (esp in hands and fingers)
2. flexor muscles of limbs, control, and coordination
Why are the lateral and anterior corticospinal tracts known as the pyramidal tracts?
Because they pass through the medullary pyramids
What the pathway of the lateral corticospinal tract?
- starts in cortex
- desucates in medulla
Which corticospinal tract is larger?
The lateral tract
What is the function of the lateral corticospinal tract?
Maintains posture, balance, and purposeful movements involving axial musculature, especially in the trunk if the region
What is the pathway of the corticobulbar tract?
- originate in primary motor cortex
- dessucate in medullary pyramids
- terminate on moter nuclei of cranial nerves, where they synapse with lower motor neurons
What is the function of the corticobulbar tract?
Controls voluntary facial expression, mastication, swallowing, vocalisation of speech. Uses bilateral control to coordinate movement on both sides
What are the inputs of the corticospinal and corticobulbar tracts?
- primary motor cortex
- premotor cortex
- supplementary motor cortex
- somatosensory area
What does the input from the somatosensory area do for the corticospinal and corticobulbar tracts?
Play a role in regulating the activity of the ascending tracts
What is the pathway shared by the corticospinal and corticobulbar tracts?
- pass through the internal capsule in somatotopic organisation
- enter the anterior part of the brainstem at the midbrain
What do the red nuclei receive output from?
The motor cortex and cerebellum - so info on state of contraction and stretch of muscles can be fed into motor pathways
What is the pathway of the rubrospinal tract?
- originates in red nuclei of midbrain
- nerve fibres desucate as they emerge and descend into spinal cord (contralateral innervation)
What is the function of the rubrospinal tract?
control voluntary flexor muscles of limbs (muscles that bend the limbs)
What does the anterior limb of the internal capsule contain?
- Axons projecting from the thalamus to the motor cortex
- corticopontine axons projecting from cortex to pontine nuclei
What does the posterior limb of the internal capsule contain?
the corticobulbar and corticospinal axons arranged somatopically
How does the internal capsule receive its blood supply?
through a series of small perforating arteries entering from the base of the brain - clinically imp as is susceptible to compression from haemorrhagic bleeds which can cause lesions of descending tracts
Where does the vestibulospinal tract desucate?
It doesn’t, it remains ipsilateral
Where does the reticulospinal tract desucate?
It doesn’t, it remains ipsilateral
Where does the tectospinal tract arise?
superior colliculus in midbrain
Where does the tectospinal tract dessucate?
As it leaves the midbrain
Where does the tectospinal tract terminate?
at the cervical levels of the spinal cord
Where does the lateral corticospinal tract arise?
in the cortex
Where does the lateral corticospinal tract decussate?
in the medulla
Where does the corticobulbar tract arise?
primary motor cortex
Where does the corticobulbar tract decussate?
in the medullary pyramids
What is the innervation of the corticobulbar tract?
bilateral to all except facial and hypoglossal
What is the corticobulbar innervation to the facial nerve?
bilateral to upper, contralateral to lower
What is the corticobulbar innervation to hypoglossal nerve?
contralateral
Where does the rubrospinal tract arise?
in the red nuclei of the midbrain
Where does the rubrospinal tract decussate?
as they emerge from the midbrain
What is the basal ganglia?
a system of nuclei located deep in the hemisphere and midbrain
What is the basal ganglia involved in?
regulating movement and reducing unwanted movement through complex loop systems between cortex, basal ganglia, and substantia niagra
What is the basal ganglia made up of?
- caudate nucleus
- lentiform nucleus
- substantia niagra
