Role of brainstem in somatomotor (postural) functions

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Buddy Carroll
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Role of brainstem in somatomotor (postural) functions (vestibular apparatus) The muscle tone and its regulation VESTIBULAR SYSTEM (Equilibrium) Receptors: Otolith organs Semicircular canals Sensation

1 Role of brainstem in somatomotor (postural) functions (vestibular apparatus) The muscle tone and its regulation VESTIBULAR SYSTEM (Equilibrium) Receptors: Otolith organs Semicircular canals Sensation (information): Position of the head, Linear acceleration, Angular acceleration Function: Equilibrium Muscle tone regulation mainly in the antigravity muscles. Coordination of eye movements Coordination of head movements 1

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3 utriculus 3

4 The structure of the hair cells 4

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perilymph (high Na + and low K + extracellular fluid)

6 Function of hair cells Mechanosensitive cells Mechanoelectric transduction Basal surface: attach with perilymph (high Na + and low K + extracellular fluid) Apical surface: attach with endolymph (high K + and low Na + secretion IC) 6

7 Apical surface: stereocilia + 1 kinocilium tip-link Mechanosensitive Kation (K + ) channels Resting situation: 10-15% opened K + channels partial depolarisation opening of some voltage gated Ca 2+ channels IC Ca 2+ (from perilymph) transmitter release - glutamate action potential on the afferent nerve 7

8 Activation (µs): Stereocilia move to the kinocilium opening of the mechanosensitive channels increased depolarisation opening of more voltage gated Ca 2+ channels IC Ca 2+ (from perilymph) Increased transmitter release - glutamate Increased action potential frequency in the afferent neurons Inhibition Stereocilia move away from the kinocilium closing of the mechanosensitive channels decreased depolarisation closing of voltage gated Ca 2+ channels IC Ca 2+ Decreased transmitter release Decreased action potential frequency in the afferent neurons 8

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10 Cerebral cortex eyes Cerebellum Proprioceptors vestibular nuclei 10

11 NYSTAGMUS Nystagmus is a form of involuntary eye movement. It is characterized by alternating smooth pursuit in one direction and saccadic movement in the other direction. Vestibulo-ocular reflexes: Rotatory nystagmus Postrotatory nystagmus Caloric nystagmus Optokinetic nystagmus Optokinetic Nystagmus 11

Caloric nystagmus Sensori-motor system Limbic cortex Structure Subcortical Motivational sub areas Frontal cortex Task Motivation Sequence Plan Tim e Ascending system Basal ganglia Cerebellum (vermis)

12 Caloric nystagmus Sensori-motor system Limbic cortex Structure Subcortical Motivational sub areas Frontal cortex Task Motivation Sequence Plan Tim e 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) 12

13 Brainstem structures in muscle tone regulation: (tonic control) 1. Red nucleus, nucleus ruber, rubrospinal pathway (extensor inhibition) 2. Deiters nucleus, vestibulospinal pathway (extensor facilitation) 3. Pontine reticular formation (extensor facilitation) 4. Medullary reticular formation (extensor inhibition) Midbrain: Tectum Red Nucleus Pons: Lateral (pontine) reticular formation Medulla: Medial (medullary) reticular formation Vestibular nuclei Centers 13

Pontine reticulospinal tract: activation of extensor muscle for postural control Medullary

14 Descending pathways Vestibulospinal tracts: information from vestibular system for reflex-control and balance. Pontine reticulospinal tract: activation of extensor muscle for postural control Medullary reticulospinal tract: inhibition of extensor muscles Rubrospinal tract: activation of medullary reticular center; activation of motoneurons of distal muscles Tectospinal tract: control of eye and head movements 14

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16 Decerebrated animal at low level Section below the midlevel of mesencephalon => the pontine and medullary reticular nuclei and the vestibulary system are intact. Increased tone in the antigravitiy muscles => decerebrate rigidity Tonic neck and labyrinthine reflexes 16

17 Causes: 1. Lack of inhibition of higher centers 2. Lack of activation of medullary reticular formation by higher centers 3. Pathways: Lateral vestibulospinal tract Medial (pontine) reticulospinalis tract Decerebrated animal at high level Section at the high level of mesencephalon, the pontine and medullary reticular nuclei and the vestibulary system and red nucleus are intact. Signs (in lower animals: cat, dog etc.): - Spontaneous righting - No rigidity - Righting reflexes: Receptors: vestibular app, neck muscle, neck joints, mechanical stimulus on the skin Labyrinthine righting reaction Neck righting reaction Body on head righting reflexes Body on body righting reflexes Vestibular placing reaction: extension of limbs and toes. 17

18 Causes: Inhibiton by red nucleus, Inhibition by cerebellum Inhibition by medullary reticular formation Signs in primates (monkey, human): Rigidity in the extensors in the lower limbs Increased tone in the flexors in the upper limbs Paralysis, no righting reflex Grasping reflex Pupil reflex, nystagmus Lift reaction: down: extension, up: flexion Decortication: Section in front of the subthalamic region Signs in lower animals (cat, dog): Spontaneous righting, walking, Normal behavior No learning Sings in primates: Rigidity in the extensors in the lower limbs Increased tone in the flexors in the upper limbs Paralysis, no righting reflex Grasping reflex 18

19 Decortication rigidity Decerebration rigidity extensor spasm in all four extremities 19

20 Brainstem postural reflexes (dynamic control) Principles 1. vestibular and neck reflexes stabilize the head and eyes 2. vestibular and neck afferents are synergetic on the neck but antagonistic on the limbs 3. vestibular and neck afferents are converging on vestibular nuclei and propriospinal neurons Brainstem control of motor function Postural reflexes Control of many stereotype movements of the body Control of equilibrium Control of eye, neck and axial (antigravity) muscle movements 20

Postural reflexes integrated in the brainstem: Tonic labirynthine reflexes Stimulus:

muscles (rigidity) Placed on its back: maximal extension in the four limbs Turned to left

Prone position: rigidity is minimal Head turned up: extension in the limbs Head turned

reflexes Stimulus: head turned Receptor: neck proprioceptors Center: medulla Responses:

21 Postural reflexes integrated in the brainstem: Tonic labirynthine reflexes Stimulus: gravity Receptor: otolithic organs Center: medulla Responses: contraction of limb extensor muscles (rigidity) Placed on its back: maximal extension in the four limbs Turned to left side: the rigidity level is higher at left side. Prone position: rigidity is minimal Head turned up: extension in the limbs Head turned down: flexion in the limbs Postural reflexes integrated in the brainstem: Tonic neck reflexes Stimulus: head turned Receptor: neck proprioceptors Center: medulla Responses: change in pattern of extensor contraction 1. to side: extension of limbs on side to which head is turned 2. up: hind legs flex 3. down: forelegs flex 21

Postural reflexes integrated in the brainstem Labyrinthine righting reflexes Stimulus: gravity Receptor: otolithic organs Center: midbrain Responses: head kept level Postural reflexes

22 Postural reflexes integrated in the brainstem Labyrinthine righting reflexes Stimulus: gravity Receptor: otolithic organs Center: midbrain Responses: head kept level Postural reflexes integrated in the brainstem: Neck righting reflexes Stimulus: stretch of neck muscles Receptor: muscle spindles Center: midbrain Responses: righting of thorax and shoulder, then pelvis 22

23 Postural reflexes integrated in the brainstem: Body on head righting reflexes Stimulus: pressure on side of body Receptor: exteroceptors Center: midbrain Responses: righting of head Postural reflexes integrated in the brainstem: Body on body righting reflexes Stimulus: pressure on side of body Receptor: exteroceptors Center: midbrain Responses: righting of body even when head held sideways 23

24 Postural reflexes integrated in the cortex: 1. Visual righting reflex 2. Visual placing reaction 3. Tactile placing reaction 4. Tactile grasping and avoiding reactions 5. Visual grasping and avoiding reactions 6. Babinsky test positive 7. Grasping reflex: flexion or clenching of the fingers or toes on stimulation of the palm or sole, normal only in infancy. Cerebral motor cortex Most "voluntary" movements initiated by the cerebral cortex are achieved when the cortex activates "patterns" of function stored in lower brain areas (spinal cord, brainstem). These lower centers, in turn, send specific control signals to the muscles. For a few types of movements, however, the cortex has almost a direct pathway to the anterior motor neurons of the cord, bypassing some motor centers on the way. This is especially true for control of the fine dexterous movements of the fingers and hands. Characteristics: complexity, flexibility, somototopy, contralateral, homunculus, feed-back 24

control of eye movements Phases: Identification, localization, motivation:

25 (1) the primary motor cortex, (2) the premotor area, (3) the supplementary motor area. Br8. control of eye movements Phases: Identification, localization, motivation: Cingular and dorsal part of parietal cortex Planning: premotor and supplementary areas Execution: primary motor cortex Homunculus, somatotopy 25

26 Execution: Primary motor cortex Precentral gyrus (Br 4): Contralateral Somatotopy Nerve signals generated the discrete patterns of muscle contractions Efferentation: corticospinal pathway Neurons are active before the muscle contraction The activity of neurons increases with the strength of the contraction Lesion: muscle weakness Supplementary and Premotor cortex (Br. 6): Nerve signals generated in the premotor area cause complex "patterns" of movement. Bilateral Planning, Motor image of the total muscle movement, Connection of the visual and auditory informations Regulation of posture for the correct movements Efferentation: Br4, basal ggl., spinal cord Lesion: apraxia (loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements) especially for bilateral tasks, uncoordinated finger movements 26

27 Pyramid tract (Corticospinal pathway) 10 6 neuron Origin: 50% primary motor cortex Premotor area Somatosensory cortex Pathway: crossed, uncrossed End: alfa-, gamma-motoneurons, interneurons Lesion: decreased muscle tone, paralysis Collaterals: other pyramid cells, red nucl. thalamus, brainstem, striatum, cerebellum 27

28 Lateral cortico-spinal tract Ventral cortico-spinal tract % crossed to lateral ventral horn - monosynaptic to motoneurons of distal muscles -this enables fine independent finger movements - not fully developed at birth - most highly developed in primates - uncrossed - bilateral & polysynaptic to medial motoneurons of proximal/axial muscles - for posture 28

29 Corticomotoneuronal system 29

I: To describe the pyramidal and extrapyramidal tracts. II: To discuss the functions of the descending tracts.

Descending Tracts I: To describe the pyramidal and extrapyramidal tracts. II: To discuss the functions of the descending tracts. III: To define the upper and the lower motor neurons. 1. The corticonuclear