8+9) Motor System Flashcards
What is the corticospinal tract?
Descending motor tract controlling activity of lower motor neurones. Involved in voluntary (particularly precise) movements
Where are lower motor neurones located?
Axons start in CNS but are primarily in peripheral nervous system
Found in ventral horn of spinal cord and brainstem
Describe the pathway for a general spinal reflex:
Muscle spindle -> dorsal root ganglion -> LMNs -> contraction of muscle
Describe how the antagonistic muscles is controlled in a general spinal reflex:
Sensory neurone from muscle spindle sends collateral branch down spinal cord to antagonist muscle segment and synapses on inhibitory interneurone, inhibiting LMN and causing muscle relaxation
How do reflexes change as we develop?
Primitive survival reflexes disappear as they become modulated by descending pathways
Describe the plantar reflex:
Plantar flexion of toes when rubbing lateral side of foot
Describe the plantar reflex in babies and how it changes as they develop:
Dorsiflexion of foot and withdrawal of whole limb from stimulus (Babinski response)
Matures to adult reflex as baby is able to walk
What are some signs of LMN damage?
Weakness and wasting Areflexia/hyporeflexia Hypotonia Fasiculation Fibrillation
Where are upper motor neurones located?
Primary motor cortex
What is the net effect of UMNs on LMNs?
Inhibitory
What is the corona radiata?
Where axons of motor fibres run when they leave the motor cortex
Describe the path of UMNs from origin to synapse on LMNs:
Primary motor cortex -> corona radiata -> internal capsule -> cerebral peduncles -> pyramids of medulla -> decussation -> lateral cortciospinal tract
Where is the internal capsule located?
Between thalamus and lentiform nucleus
Describe the structure of the internal capsule and its topography:
V shaped with anterior limb, genu and posteiror limb
UMN of face found at genu and rest of body as you go down posterior limb
Where does the internal capsule connect to the midbrain?
Cerebral peduncles
Where are upper limb axons found in the lateral corticospinal tract?
More medial in the tract
Describe the ventral corticospinal tract:
Some UMNs remain ipsilateral at the medulla and decussate at the level of LMNs. Involved in trunk muscle control
What are the functions of the lateral and ventral corticospinal tracts?
LCT - precise control of limbs
VCT - trunk muscle control
What are some signs of UMN damage?
Weakness Hypertonia Spasticity Clasp knife reflex Hypereflexia Babinski sign
Why is there hypertonia and hyper-reflexia in UMN damage?
Mono-synaptic reflex arc becomes hyperactive as LMNs are no longer inhibited by UMNs
What is the function of golgi tendon organs?
Detect extreme stretch in tendons and send sensory neurones to inhibit LMNs (clasp knife reflex)
What is the initial paralysis in UMN damage?
Initially flaccid due to spinal shock
How are cranial nerve nuclei innervated by UMNs?
Receive bilateral innervation from UMNs
How is the facial nerve nucleus supplied by UMNs?
Has two halves, upper half receives bilateral innervation, lower half only has contralateral supply
When and why can there be forehead sparing?
If genu of internal capsule is damaged on one side then there will be forehead sparing due to the bilateral innervation to upper half of facial nerve nuclei e.g. stroke (capsular infarct)
What is the function of the tectospinal tract?
Unconscious reflex actions to visual and auditory stimuli
What does the rubrospinal tract run between?
Red nucleus to spinal cord
What is the function of the vestibulospinal tract?
Maintaining posture and balance, and head stabilisation when fixing gaze
What is the function of the reticulospinal tract?
Regulates muscle tone, involved in REM sleep
Why is there wasting of muscles in LMN damage?
LMN provides muscle with growth factors that maintain muscle bulk
