Physiology of motor control (1)

Transcription

1 Physiology of motor control (1) Physiology of somatomotor system 1. Task: It controls the skeletal muscles 2. Content: Simple reflexes Muscle tone Posture Movement Sexual functions Motor component of emotions Motor components of intellectual functions 3. Organisation: Hierarchic Parallel organisation Somatotopy 1

2 The somatomotorsystem deals with the regulation of movement exerted by the cross-striated muscles The phases of movements 1. motivation 2. planning 3. programming 4. execution Sensori-motor system III Structure Task Sequence Time Limbic cortex Subcortical Motivational sub areas Frontal cortex Motivation Plan Ascending system Basal ganglia Cerebellum (vermis) Brainstem Interneuron g.v. Association cortex Thalamus Mot. nuclei Motor cortex Motoneuron (spinal) Cerebellum (hemispheres) Descending system Voluntary Posture Spinal motoric (Reflexes) Program 800 ms 50 ms Execution Receptor Muscle (effektor) Length, tension, position, joint relation (posture) Light, sound, temperature (environmental stimuli) 2

3 HUMANOID ROBOTS ASIMO (Honda) HRP 4C (Humanoid Research Group () FEDOR (Russia) ATLAS (Boston Dynamics) PETMAN (DARPA, US Military) T HR3 (Toyota) Hierarchic levels of organization 1. spinal cord 2. brainstem vestibular functions 3. cortex primary motor cortex premotor cortex supplementary cortex parietal cortex loops: cerebellar loop basal ganglialoop 3

4 Motor functions of the spinal cord Anatomy The spinal cord is 45 cm long in adults and is located in the vertebral canal. It consists of 31 segments (31 pairs of spinal nerves) 8 cervical segments 12 thoracicsegments 5 lumbal segments 5 sacral segments 1 (2) coccygeal segment Motor unit: an α-motor neuron and allmusclefibersit innervates Bell-Magendie rule: Afferents only in dorsal roots, Efferents only in ventral roots Reflex time: The time elapsed between the stimulation and the development of the first action potential(about ms; without the duration of the muscle contraction!!!) 4

5 Spinal reflexes: Reflexesarestereotyped reactionsof the organism to a stimulus, which aretriggeredunconditionally, whenever the stimulus is larger than the threshold. Mostreflexes occurwithoutconscious involvement. Function: fast response Components of reflex arch: receptor afferent nerve CNS (spinal cord or brain) efferent nerve effector (muscle or gland) 5

6 Reflex Types: Autonomic reflexes Somatic reflexes Proprioceptive reflexes: receptor and effector are in the same organ. Myotatic (stretch) reflex Inverse myotatic reflex Function: posture, voluntary movement, muscle tone Exteroceptive reflexes: receptor and effector are in different organs Flexor reflex Flexor- crossed extensor reflex Corneal reflex Palpebral reflex Function: protection (Axon reflex) Proprioceptive reflexes: Myotatic reflex (Stretch reflex) Regulates the length of the muscle; muscle spindle Inversemyotaticreflex Regulates the muscle force; Golgi tendon organ 6

7 Myotatic reflex (stretch reflex) Stimulus: stretching of muscle Receptor: muscle spindle Afferent fibers: Ia and II fibers Center: 1 synapsis: monosynaptic Reciprocal inhibition Efferent: Ia fiber Effector: extrafusal fibers Response: muscle contraction Segmental Areflexia, hyporeflexia, hyperreflexia Function: damping(prevent oscillation or jerkiness of body movements) Voluntary movements Stabilizes body position during action The muscle spindle 7

8 Anatomy of muscle spindle Location: in the muscle(paralel) Size: 5-10 mm Structure: 3-12 intrafusal muscle fiber 1 static nuclear bag fiber 1 dynamic nuclear bag fiber 1-10 static nuclear chain fiber Innervation: afferent, sensory(annulospiral): Ia fiber: innervates all fibers II: only static fibers are innervated efferent, motor: gamma efferent Innervation of the intrafusal fibers 8

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10 Extensor Stimuls: stretch Reciprocal innervation 10

11 Gamma-efferentation I a fiber II. fiber α-motor-neuron γ-motorneuron GAMMA-Efferentation 11

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13 Clinical application of the stretch reflexes (Tendon reflexes): Patella reflex: L4 Achilles reflex: S1 Biceps reflex: C5-6 Triceps reflex: C6-7 Masseter reflex: brainstem Role: assess the degree of facilitation of spinal cord centers. (e.g. lesions of motor cortex cause greatly exaggregated muscle jerks on the opposite side). 13

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15 Inverse myotatic reflex Golgi tendon organ, Ib fibers, interneuron (disynaptic) 15

16 Inverse myotatic reflex Stimulus: increased tension in the muscle Receptor: Tendon organ location, structure Function: sensation of tendon stretching Afferent nerve (Ib) Center: 2 synapsis Inhibition of efferent nerve Response: no further increase of muscle force, muscle relaxation Homonym reflex Reciprocal innervation Segmental Role of tendon organ/golgi tendon reflex Golgi tendon organ: detects muscle tension Reflex: It prevents the development of too much tension on the muscle (protective). It equalizes contractile forces of the separate muscle fibers 16

17 Golgi tendon organ inverse myotatic reflex 17

18 Exteroceptive reflexes (nociceptive reflexes) Exteroceptive reflexes/pain reflexes, nociceptive reflex/withdrawal reflex: a. Flexor reflex Stimulus: strong cutaneous stimulus Receptor: nociceptors(a delta or C fibers) Center: several synapses(polysynaptic) Reciprocal inhibition Efferent: Ia fiber Effector: flexor muscle Response: muscle contraction Heteronym Intersegmental Reflex irradiation b. Flexor-crossed extensor Flexor reflex + opposite limb extension 18

19 Flexor- crossed extensor reflexes Exteroceptive reflexes Skin reflexes - plantar (sole) reflexes (S1-2), Babinski reflex - abdominal reflexes (Th7-12) - cremaster reflex (L1) Brainstem reflexes (Corneal reflex: eye closure after mechanical stimulation of cornea (it can not be inhibited intentionally) Palpebral reflexes: eye closure after approach subjects to eye(it can be inhibited intentionally)) 19

20 Spinal injury Paraplegia Tetraplegia 20

21 Spinal injury Acute symptoms: spinal shock Encephalisation Duration: 2-4 weeks (human) Cause Signs/symptoms: areflexia, atony, paralysis anesthesia lack of thermoregulation vasodilation blood pressure lack of cardiovascular reflexes skin dry, red, warm urinary bladder atony => incontinency passive urinae incontinency passive alvi lack of sexual reflexes Recovery: Somatic reflexes: 1. flexor reflexes 2. proprioceptive reflexes 3. positive supporting reaction 4. mass reflex 5. reflex normalisation 6. scratching reflex 7. walking reflex (1 year) 21

22 Autonomic reflexes: 1. Incontinency active urinae and alvi 2. Blood pressure normalization 3. Sexual reflexes reoccur Permanent injury: Low muscle tone No antigravity reflexes No sensation No voluntary movement No thermoregulation No perfect cardiovascular regulation 22

23 Upper Motor Neuron: 1. lesion of neuron in the cortex or their axon fiber e.g. in the internal capsule 2. consequence a. If the lesion is small: loss of refined movement; e.g. unable to make independent finger movements. b.if the lesion is extensive. -initial > flaccid paralysis ( & loss of muscle tone) -later > because of increased motoneuron sensitivity to remaining inputs (e.g. spinal reflexes) spasticity is observed. Lower Motor Neuron: 1. lesion of alpha motoneurons or their axons e.g. poliomyelitis 2. consequence Symptoms include weakness or paralysis of isolated muscles which are flaccid. Upper Motor Neuron Lower Motor Neuron Symptoms include 1) hypertonia (antigravity muscles) 2) hyper-reflexia and clonus 3) Babinski sign 4) no fasciculations 5) no atrophy Symptoms include 1) hypotonia 2) hypo-reflexia 3) no Babinski (ie toe flexion) 4) fasciculations,fibrillations 5) atrophy (loss of mass) 23

24 Integrative function of spinal cord Spinal locomotion Scratching reflex 24

25 Locomotion Mechanisms of spinal inhibition 25

26 Renshaw-inhibition Renshawinterneurons release glicin. (Strichnin inhibits the glicin receptors) 26

27 Strichnos nux vomica Does contain approx.1% Strichnin. Lethal dose: 1-2 mg/kg Strichnin Brucin 27