Motor System Flashcards
What neurones innervate skeletal muscle
Alpha motor neurones
- cell bodies in Ventral root
- motor axons exit ventral root
What is a motor unit
Alpha motor neurone + all innervated muscle fibres
- each muscle fibre receives input from one motor neurone
- each motor neurone innervates several muscle fibres
What controls voluntary movement
- Descending motor controls
- Controlled by higher motor areas
- Upper&lower motor neurones
What controls involuntary movement
- Response evoked from peripheral stimulation
- Coupling sensory input to motor output
- Spinal reflexes
Describe Cutaneous reflexes
Flexion withdrawal reflex
- Cutaneous receptors detect noxious stimuli
- Primary afferent activated
- Synergistic activation and inhibition of muscles
Rapidly removes limb from harmful stimuli
Describe the Myotatic reflex
Prevents over-stretching the muscle
- One synapse
- Stimuli stretches attached muscle
- Subsequent contraction of same muscle restores muscle length
Describe how a muscle detects stretch
- Muscle spindles (proprioceptors)
- Sensory neurones in spindle encode information of muscle length
- Ia and II afferents monitor extent of stretch and synapse with motor neurones in the spinal cord
Describe the polysynaptic reflex
- Two or more synapses
- Stimulus is muscle stretch
- Inhibitory interneurones synapse alpha motor neurones
Role of Gamma motor neurones
- Innervates intrafusal fibres
- Adjusts sensitivity of muscle spindle
- Increased range of function
What are the three types of interneurones involved in motor system
A. Inhibitory interneurones
B. Excitatory interneurones
C. Renshaw cells
Role of inhibitory interneurones
- activated by PANs
- inhibits alpha motor neuron
- inhibits contraction of associated muscle
Role of excitatory interneurones
- activate Y motor neurone
- synapse onto intrafusal muscle fibre
- increased sensitivity of spindle
Role of Renshaw cells
- inhibitory interneurones
- activated by alpha motor neurone
- also inhibits alpha neurones (andromic inhibition)
- inhibits interneurones and y motor neurones
Describe the 3 types of spinal cord organisation
- Segmental
- basic circuits and connections at each level
- basic spinal reflexes mediate these - Prospinal system
- connecting different levels of SC
- enables coordination - Descending motor tracts
- controls muscle tone
Describe the crossed extensor reflex
Maintains balance
- flexion withdrawal removes ipsilateral limb
- simultaneous extension of contralateral limb
Law of reciprocal innervation
When contraction of a muscle is stimulated, there is a simultaneous inhibition of its antagonist
- essential for coordinated movement
What circuits are required to generate rhythmic movements
Only Spinal cord intrinsic circuits
- although modified and initiated by descending commands and sensory feedback
Define a Central pattern generator
Biological neural network that produces rhythmic patterned outputs without sensory feedback
Describe the half-centre hypothesis
Generation of alt activity involves two neuronal centres with mutual reciprocal inhibition
- two groups of spinal cord neurones
- mutually inhibiting each other
- capable of producing basic rhythm when coupled to each other
Describe half-centre oscillator theory
- Segmental pathways activated by high-threshold flexor reflex afferents (FRA)
- Excitation of flexors (by ipsilateral FRA) and of extensors (contralateral side)
- Reciprocally inhibitory interactions
TRANSMISSION IN ONE PREVENTS SIMULTANEOUS TRANSMISSION IN THE OTHER
Describe pacemaker neurones/ concept
Pacemaker neurone directing continuous rhythmic movement
What are the two types of motor system organisation
Parallel: each level issues commands that act directly on the lowest level
Okay hierarchical: motor system organised into a series of functional levels- higher command lower
What are the four major components of the motor system
- Pre-motor cortex
- Primary motor cortex
- Brainstem
- Spinal cord
Both parallel and hierarchical organisation
Describe the differences between higher and lower level damage
Lower: obvious specific deficit
Higher: higher commands lose ability to coordinate lower levels resulting in new patterns of activity
Difference between upper and lower motor neurones
Upper: from cerebrum or brainstem with connections to spinal cord
Lower: in cranial nerve nuclei in brainstem or spinal cord with connections to muscle/ periphery
Why is the Babinski sign (toes curl upwards) a sign of high motor neurone damage
Lesions to higher control frees lower centres from their normal functioning
Describe lesion at level of C1
- Spinal cord divided from CNS
- Lower motorneuones spared
- Flaccid paralysis (loss of voluntary muscle control and muscle tone)
Describe lesions at level of colliculi
- Dividing upper and lower brainstem
- Extensor muscles contract leading general stiffness
- Higher centres disconnected thus releasing lower levels of control
Name 3 organisational features of motor system
- Body maps
- distal branch of ventral horn controls distal muscles - Sensory feedback
- each level receives sensory feedback to correct movement - Descending motor control
- higher levels modulate levels of sensory input into motor system
Name two side loops of the motor system
- Basal ganglia
2. Cerebellum
What are the three types of stroke
Ischaemic- due to closure of blood vessel by blood clot
Haemorrhagic- blood vessel rupture and bleeding
Transient ischaemic attach (TIA)- temporary blockage of blood flow
What is an insufficient blood supply called
What is permanent brain damage called
Ischaemia
Infraction
Describe the corticospinal pathway
From motor area of cortex to spinal cord, synapsids in brainstem nuclei
With rubrispinal pathway Known as the lateral descending motor pathway
Describe the corticobulbar pathway
From brainstem nuclei to spinal cord
Medial white matter tract
What does the lateral descending motor pathway control
Distal musculature
Fine movement
