Zusammenfassung der Ressource
Local motor
control
- Motor neurones: many muscle
fibres. Smallest neurones
innervating the tonic and fatigable
muscle fibres, recruited first.
- Renshaw cell: lateral inhibition, discourage
synchronization.
- Somatotopic organisation: Medial neurones
innervate trunk. Lateral n innervate distal limbs.
Flexors and extensors governed by dorsal &
ventral groups.
- =Mechanism: withdrawal or flexion reflex: rapid
flexion when skin touched by hot object/ noxious
stimulus.
- Descending Pathways
- Reticular formation: extrapyramidal tract, direct
contact with MN. Located in Sc. Stretches from:
superior cervical SC intralaminar thalamic nuclei.
Dendritic fields perpendicular to axis of brainstem:
isodendritic core receive collaterals from sensory
fibres. 3 zones: raphe, medial & lateral. Level activity
& gen rhythm.
- Clinical aspects: reduced conscious states,
cushing reflex & abnormal respiratory
patterns.
- Project cerebellum & BG.
- Vestibular nuclei: movement head & gravity,
lateral vestibulospina- uncrossed, end
interneurons, excite monosynaptically.
- Medial tract exists: bilaterally from medial
VNcervical and upper thoracic regions.
- Maintain posture, control extensors.
- Red nucleus: rubrospinal. Flexion.
- Superior colliculus:
Tectospinal, vision &
hearing, spier reflex.
- Corticospinal: cerebral cortex, 80% cross in the medulla,
descend as lateral CST, uncrossed become anterior. 30% white
matter. Internal capsule- site of ischaemic stroke= paralysis.
Fine, skilled voluntary movements.
- SC isolated from brain=
- flaccid
paralysis: loss
voluntary
movements
and muscle
tone.
- below cerebral cortex: spasticity: resistance to
passive stretch.
- level of colliculi- rigidity:
hyperactive= rigid
- Sensory feedback from muscles
- Proprioception: sense of oneself in space
muscles & joints. Exteroception: sense of
external world. >Proprioceptive feedback:
Primary 1a from spindle (direct input onto
MN), Golgi 1b detect stretch & contraction.
- Sensory receptors in muscle
- Golgi tendon: Force transducer, clasp-knife
reflex- transduce loading of muscle. 1b
afferents. –ve feedback to reg tension.
- Muscle spindles: Muscle length, modified
y-efferent fibres to intrafusal fibres. parallel to
muscle fibres= regulation of muscle contraction
and matches F gen to motor task.
- Proprioceptive afferents (in joint capsules): protect &
respond extreme flexion & extension- 1 limb extended
other positioned similarly.= if disturbed= reposition to
inappropriate location.
- Sensory input: 1a sense stretch.
- Spindle reflex: 1a afferents monosynaptically excite MN= reflex
arc. Normal people response feeble, in patients the contraction
is ^.
- Muscle Tone: Spindles maintain the
attitude of the body against forces of
gravity. A innervate extrafusal and y
innervate intrafusal.
- Simple Servo hypothesis: Sensory endings: difference between amount of y
activity & shortness of muscle- spindle is comparator generator
- Load: Controlling manipulation: feedforward to predict
and regulate output. If load increases the cerebellum
would need to constantly monitor and review the
situation- instead decided position.
- Servoassistance: 1. Positon command- tells muscle via y & spindles
what the length is meant to be. 2. Force command: estimate of load.
Spindles= stretch reflex to correct the response & modify ballistic
programs for future.