Muscular Tone, Reflexes

Dr. Věra Valoušková, PhD The 2nd Medical Faculty, Charles University, Prague

Reflexive and non-reflexive activity Function of proprioreceptors

•tendon organ

•muscle spindle

Muscular tone

Attributes of neuronal nets Reflexes

•Unconditioned

•Conditioned

Muscular Tone, Reflexes

Non reflexive activity

1. Pacemakers – nuclei of medulla oblongata (breathing centers ) , AV, VA - nodes fibres of Purkynye, RF…

2. Spontaneous neuronal activity - basal neuronal activity - „inborn“ activity of neurons - nuclei (ANS), diffuse N-ns – connected to a net (RF, c-x,

thalamus….)

Automatic basic life functions – default setting of basic mechanism, homeostasis

Reflexive activity

- Disbalance of homeostasis (blood pressure, pH, osmoses, O₂, CO₂…) - automatically return to „default“ settings

- Reflexive food processing (GIT reflexes)

- Reflexes connected with reproduction - birth, breast feeding, sucking reflex…

- danger of a body from outer environment (movement - defensive, protective R-xes) - nociceptors, muscle spindle, Golgi tendon organ) spontaneous neuronal activity

Reflexive and non reflexive activity of the CNS

Synaptic potential = sum of „channel“ potentials

Integrating centre

generator potential

action potential

action potential action

potential

plate potential

Reflex - reflex arc

Reflex = automatic answer to biological significant stimuli (inborn, learned)

Reflex arc

Brain, spinal cord, ganglions (enteric…)

receptor ^neuro-

muscular plate

muscle

Reflex arc

Anatomic base

• Receptor

• Afferent path

• Integrative centre

• Efferent path

• Effector (muscle, gland)

Generator (receptor) potential

- coding of stimulus

Sensory neuron:

stimulus intensity - frequency of AP

stimulus duration - duration of a series of AP

neurotransmitter release varies with the pattern of action potentials

receptor

potential trigger zone axon

- strenght and duration vary with the stimulus

Motor control (sensory feedback)

(Houk, JC and Rymer, WZ 1981. Neural control of muscle length and tension. Handbook of Physiology.

Section 1. The Nervous System, Vol. II, Motor Control, Part 1. Am Physiol Soc, Bethesda, pp 257−323)

Primary motor cortex (voluntary movement)

Golgi tendon organ Muscle spindles

Skin tactile receptors Upper centers

Classification of sensory nerves

Muscle spindle

IA 70- 120 ms^-1 (primary ending) II 25 - 65 ms^-1 (secondary ending) Golgi tendon organ

IB 65-110 ms^-1

(speed of stimuli conductance)

Golgi tendon organ - signals

Berne R.M. at al. (Eds.), Physiology, Elsevier, 2004

IB fibers

Tonic contraction

Golgi tendon organ - ^GTO

Function – GTO signals tension generated by muscle fibers (muscle and its insertion)

Muscle contraction –> stretch capsula of GTO –> Ib afferents –> interN-on –> inhibition of

a-

Guyton and Hall, Textbook of Medical Physiology,Elsevier Inc., 2006

Controls tension of contraction

Reflexive protection - passive relaxation

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004

Reflexive (passive) muscle relaxation

Protection of the muscle ligament

Innervations of muscle spindle

Gamma loop

Motor centers

strech sensitive channels

tension

Guyton and Hall, Textbook of Medical Physiology,Elsevier Inc., 2006

Primary afferentation-Ia - quick adaptation (both types of fibres), body balance

Secondary afferentation -II - slow adaptation (tonic activity) - degree of streching, static lenght

IA 70 - 120 ms^-1 II 25 - 65 ms^-1

Afferents from muscle spindle to a motoneurons

Muscle spindle

response of primary and secondary endings

Primary endings –lenght and the rate of change in length of the muscle

Secondary endings –only static length of the muscle

Berne R.M. at al. (Eds.), Physiology, Elsevier, 2004

Dynamic (phasic) Static (tonic)

monitores speed of contraction and stretch

Functions of gamma loop (muscle spindle)

• maintains sensitivity of muscle spindle

• responsible for smooth contraction of the muscle

• correction of muscle contraction (cortex)

• protection of muscle against damage (stretch)

only a motoneuron is activated transection of g innervation

g - motoneuron - efferent innervation -

maintains sensitivity of muscle spindle

desensitivní sensitive

contemporary activation of a-, g- motoneurons

sensitive

Intrafusal extrafusal

relaxation

contraction

Transection of g innervation

intrafusal extrafusal

slacked Wavy line - elastice element (receptor part) rectangle - contractile element

Muscle spindle

Guyton and Hall, Textbook of Medical Physiology,Elsevier Inc., 2006

contributes to smooth contraction of the muscle

Muscle contraction 82 days after dennervation (afferent transection of muscle spindle Axons - dorsal horns)

1. Muscle spindle protects muscle against oscilation, it is responsible for smooth contraction

sensitivní relaxation

„normal“ contraction intrafusal extrafuzal

a motoneuron

mild-relaxation

contraction

efferent a MN-ns

efferent g MN-ns

Sine curve - elastic component (receptor part) rectangle - contractile component

Intrafusal extrafusal

Guyton and Hall, Textbook of Medical Physiology,Elsevier Inc., 2006 AP of spindel sensory N-on

= stimulation of a motoN-on

AP of a motoN-on

reverberation

- fusimotor (intrafusal) fibres contract more than sceletal (extrafusal)

2. Correction of muscle contraction (cortex)

sensitivní

relaxation

tonic contraction intrafusal

extrafusal

a motoneuron and sensory

information to higher brain centres

phasic contraction

Sine curve - elastic component (receptor part) rectangle - contractil componen

Intrafusal extrafusal

Command to a and g motoN-ons heavy load- muscle tone increases but no change in the lenght of extrafusal muscle fibres

3. Protection muscle against damage (stretch) (Rx protection)

sensitivní relaxation

intrafusal extrafusal

a motoneuron

reverse Rx contraction Pasive prolongation

Sine curve - elastic component (receptor part) rectangle - contractil componen

Intrafusal extrafusal

Muscle tone

= consequence of continuous (tonic) activity of lower a - motoneurons

= power (tension) working against muscle stretching

Tone reduction – hypotonic

Tone elevation - hypertonic (spasticity)

a– motoneurons upper Cx a- motoneurons lower - SC

Influenced by ascendent

descendent paths

- influences reflexes

muscle spindles

g

muscle fibers a

lower moto N-ns

+

medullary reticulospinal - tecto spinal

ventral corticospinal

vestibulospinal (medial,lateral)

- flexors,+ extensors

corticospinal, rubrospinal

+ flexors, - extensors

pontine reticulo spinal +

g mN-n

+

Ia, Ib afferent from distal muscle

Ia from its antagonist

nococeptive from a limb

a mN-n

Driving forces to lower a - and g -motor

Reticular formation

RF – influences muscle tone (axial extensors, antigravity muscles) , modulation of tr. corticospinalis laterale

Pontine reticulospinal tr – ipsilateral -excitation

Medullary reticulospinal tr. – contralateral (muscle tonus) – inhibition (activated by cortex, n. ruber, BG….)

n. vestibularis - excitation and control of

antigravity muscles (important for a balance) - signal from vestibular apparatus, automatic control of balance

Decerebral rigidity - interruption of excitatory influences of Cx, BG, n. ruber to inhibitory N-ns of RF - excitation of antigravitory muscles predominates

pontine reticular nuclei

+

lower moto N-ns

+

upper moto N-ns

tr.cortico spinalis

+

-

medullary reticular nuclei

cortex +

RF –influences muscle tone (axial extensor - antigravitational muscles), modulates tr. corticospinalis laterale

vestibular nuclei +

axial extensor muscles

BG, n. ruber….

desreases tonic level of antigravitational muscles determines muscle tone of

antigravitational muscles

controls antigravitational muscles (important for balance) - signals from vestibular apparatus - automatic control of balance

L Muscle tone - RF P

muscle spindle Appeared by disconnection of excitatory influence of Cx to inhibitory neurones of RF => excitation of antigravitational muscles became predominant

pontine reticular nuclei

+

lower moto N-ns

+

upper moto N-ns

tr.cortico spinalis

+

-

medullary reticular nuclei

cortex +

vestibular nuclei

+

axial extensor muscles cortex

+ +

LATERALITY

Decerebral

rigidity

Integrating centers:

brain vs. SC

Brain „solves“ biologically significant stimuli

SC reduces „ load“ on the brain, responses automatically -

reflexes

Integrating centre of SC

(gray matter)

1 segment - several millions of N-ns Sensory neurons

•Propriocepction, nociocepction, sensory

•Integrated in SC

•Upper activity a motoneurons

• extrafuzal muscle fibres

•3 to several hundred muscle fibres (motor unit) g motoneurons

• intrafuzal muscle fibres of muscle spindle

• 2x smaller than a-mN

Interneurons – integration (ventral root a intermedial gray matter)

• numerous than motoneurons

• frequency up to1 500/sec

• synapses from the most of sensory N-s

• reciprocal connections between motor units of antagonists (-) and synergists (+)

• funiculi anterolateralis (ascendent, descendent) – propriospinal fibres(more than half of nerve fibers)

• ccommissural connections - contralateral

Renshaw cells- inhibitory, small, near to motoneurons - lateral inhibition

Properties of ^neuron al network I

Divergency

1 2 3 4 5

interneuron

Anterior MN-on Control of muscle function

Convergency

1 - corticospinal fibers 2 - reticulospinal

3- rubrospinal

4 - receptors from periphery 5 -propriospinal fibers

(from other segments)

Summation + convergency

3 sensory fields

Primární sensorické N-ny

Transfer of signal from cortex to muscle cells (divergency)

upper motoN-n (CX)

lower motoN-ns (SC)

motor units

muscle fibers

Motor unit (MU)

Antigravity muscles – large MU– more than 1 000 fibers Fine motor activity – fingers – 2-3 fibres

Motoneuron „pool“

= group of motoneurons innervating critical unit of muscle fibres of 1 muscle

Tendon organ - 10-15 fiberses, muscle spindle - 3-1200 fibres

= sum of muscle fibres innervated by one motoneuron

Principle of size of LMN - treshold

important for finer muscle contraction

Properties of neuronal network ^II

Lateral inhibition

(i.e.enhance perception of pain, visual sharpness)

Reverberation circuits (recurrent excitation)

Interneurons - Renshaw cells

Reverberation circuits

subsequent discharges of N-ons - prolonged stimulation of m. fibre - allow to finish contraction - recurrent path

Reverberation is mute by fatigue of synapses = automatic down-up regulation of excitability

Excessive used parts of the net -> lower sensitivity (low amount of transmitters, occupied receptors, degradation)

Seldom used parts of the net - increased sensitivity - more receptors (EPR-Golgi apparatus - continuous geneses of new receptors)

It allowes equal use of motor units

We feel pain when certain pressure by sharp subject (a pin) is applied but we do not when the

same pressure by rounded one is used.

Why?

tonic activity

Lateral inhibition

(modulation of perception of the pain)

Sharp vs. blunt subject - pressure (dominanta)

pin

no stimulus

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004

Receptive field

blunt stick

Functions of spinal cord

Communication between CNS and periphery (white matter):

a) motor tracts – vestibulospinal ( inhib N-ns to the neck, back); tectospinal from colliculus sup. – visual and auditory orientation – eye movement

these tracts cooperate => orientation response

b) pontine reticulospinal tr. – ipsilat – innervation of gamma and alpha motoN-ons (limbs) - increases muscle tone

c) medullary reticulospinal tr.– balance the excitatory drive from pontine

reticulospinal tr. (inhib. motoN-ons, decreases axial and extensor muscle tone)

Integration control between spinal segments Integration center (gray matter)

Basic reflexes (monosynaptic, polysynaptic, nociceptive,

extensor/flexor, crossed extensor reflex)

Reflexes

Pavlov Ivan Petrovič - (1849 - 1936) conditioned Rx

russian physiologist, describe „conditioned reflex“1904 - Nobel´s award

Operant conditioning

John Broadus Watson (1878 -1958)

american psychologist, founder of behaviorism (+ - reward)

Burrhus Frederic Skinner -(1904 - 1990) american psychologist, neobehaviorist.

Procházka Jiří - (1749 - 1820)

czech physiologist and anatomist, established the term „reflex“

Types of reflexes

Unconditioned -

Conditioned - simple associative learning

• classic

• operant (instrumental)

Classification of reflexes

Spinal reflexes

unconditioned, inborn

Spinal reflexes – involuntary muscle reactions

segmental (stretch RX) intersegmental (flexor Rx) suprasegmental (+ brain)

Proprioceptive Exteroceptive

Defence Rx- extensors - to push smth off Protective Rx - flexors - to move body away

Basic spinal reflexes

Golgi tendon organ - protective Rx

Protection of the muscle ligament

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004

Stretch reflex (myotatic) - protective

A stretch reflex (myotatic) - a muscle contraction in response to stretching within the muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal muscle length.

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004

Extensor (stretch) patellar (knee) reflex

(defense)

Activation of muscle spindle =>

activation of sensory neuron =>

1) activation of extensor motor neuron (contraction of extensor)

2) simultaneous activation of

interneuron => inhibition of activity of flexor motor neuron (relaxation of flexor)

+ -

activation of Ia and II afferents a motoneurons

reciprocal inhibition short and descrete

Parallel activation of flexor and inhibition of extensor after painful stimulus

Polysynaptic flexor and extensor reflexes (pain)

Strong nociceptive stimulus

Guyton and Hall, Textbook of Medical Physiology,Elsevier Inc., 2006 Fatigue of flexor R-x

Inverse myotatic and flexion reflexes

Afferent (sensory) axons send collaterals also into contralateral motor nucleus of spinal cord

Coordination of 4 limb movement - analogous – principle - ipsi- and contralateral excitation and inhibition of flexors and extensors (ipsi- and contralateral

connections between spinal segments, e.g. a walk)

+ -

- +

Guyton and Hall, Textbook of Medical Physiology,Elsevier Inc., 2006

„Mark Time“ Rx , excitation of reflexes

Excitation of R-xes after midbrain transection, newborns…, (Activation of inhibitory RF by CX, BG, cerebellum is lower)

Berne R.M. at al. (Eds.), Physiology, Elsevier, 2004

„Mark Time“ Rx

Stretch on the limb elicits stepping R-xes (involve all 4 limbs)

Spinal transection above the forelimb area

Stretch RX

stretch created by a blow upon a muscle tendon:

Biceps reflex C5/C6

Brachioradialis reflex C6 Extensor digitorum reflex C6/C7

Triceps reflex C7/C8

Patellar reflex L2-L4 (knee-jerk)

Ankle jerk reflex S1/S2

Plantar reflex L5-S2

Another example is the group of fibres in the calf muscle, which synapse with motor neurons supplying muscle fibres in the same muscle. A sudden stretch, such as tapping the Achilles' tendon, causes a reflex contraction in the muscle as the spindles sense the stretch and send an action potential to the motor neurons which then cause the muscle to contract; this particular reflex causes a contraction in the soleus-gastrocnemius group of muscles

Plantar Rx

(L5 – S2)

Babinski's Sign in a healthy newborn

Three possible types of responses :

- Flexor: the toes curve inward and the foot averts; this is the response seen in healthy adults (and known as a "negative Babinski")

- Indifferent: there is no response.

- Extensor: the hallux dorsiflexes, and the other toes fan out; this is the

"positive Babinski's sign" which indicates damage to the central nervous system.

The Babinski response is normal while asleep and after a long period of walking.

Adults - pathology

Tonic neck reflexes

- limb position(postural)

Berne R.M. at al. (Eds.), Physiology, Elsevier, 2004

Dorsiflection of the neck - extension of forelimbs and flextion of the hindlimbs.

Ventriflection - in reverse

Neurohumoral and autonomic

reflexes

Vegetative (autonomic) reflexes

polysynaptic

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004

Enteric (cephalic) Rx

Short reflexes - local, originate and integrated within enteric NS

Long reflexes - cephalic sensory N-ns in submucosal nerve plexus

- integrating centre (mesenteric motoN-ons)

- coordination with autonomic neurons (signals from CNS) - parasympaticus (vagus) - excitatory;

sympaticus - inhibitory

Feedforward reflexes - digestive system reflexes (response motolity, secretion, ..)

(stimuli - smell, sight, pH, productions of digestion)

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004

Urination

(motor-vegetative spinal reflex)

Simple spinal Rx

Filled up bladder- strech receptors – spinal cord - excitation of parasympaticus – smooth muscles of the bladder contracts

parallel

Inhibition of motoneurons of sphincter and

Passive relax of internal sphincter (weight of urine)

Learned – conditioned Rx

Unconditional Rx supressed (unsuitable enviroment) bladder – additional sensory (stretch) N-ns –

brain stem and cortex - inhibition of parasympaticus (strengthen of sphincter contraction)

Suitable place – conscious release of sphincter - identical path

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004 contraction

Parasympathic N-n

relaxation

Neurohumoral Rx

(milk ejection R-x)

Unconditioned:

Suckling reflex

Reflexive secretion - release of milk

Prolaktin (anter. Pituitary gland) - milk secretion -spec. epithelial cells

Inhibition of lactation -prolaktin ihibitory hormon (PIH) (hypothalamus) hypothalamus - oxytocin (poster. pituitary gland) - myoepitelial cells contraction

n. supraopticus n. paraventricularis

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004

Conditioned Rx: milk ejection (emotions)

Conditioned RX

Simple form of learning

(needs positive or negative feetback ; role of emotions) Extinction of reflexes - biologically insignificant stimuli

Associative learning

Classical (associative) conditioning

Unconditioned stimuli (US) – „body“ answer (inborn reflex) conditioned stimuli (CS) – no „body“ answer

US + CS - „body“ answer (inborn reflex)

CS - „body“ answer (retrieved reflex, acquisition)

extinction of Rx -CS not followed by biologically significant stimuli (US, positive or negative emotions)

Taste aversion -

Instrumental (operant)

conditioning

Conditioned stimuli (i.e. voice, light, arm movement, …) -no action of a subject – no feedback

-required action of a subject (coincidental) – positive feedback (food, emotions) -undesirable action - punishment for (negative feedback)

Multiple repeat => required movement has to be followed by a positive feedback (i.e. dressur, upbringing of a child)

+ - emotions

Assumption - activity of a subject

Summary

• Muscular tone - RF, upper structure -> a-LMN

• Sensory feedback (tendon organ, muscle spindle)

• Properties of neuronal networks (divergence, convergence, lateral inhibition, reverberration)

• Reflex arc, (un)conditioned reflexes…..

…………..

Guyton and Hall, Textbook of Medical Physiology, Elsevier Inc.

Silverthorn, D.U., Human Physiology, Pearson Educ. 2004 Recomended textbooks:

Electric impulses in the NS

1. LOCAL POTENTIALS OR CURRENTS - graded, spreading with decrement

generator or receptor potentials - sensory terminals – transduction of energy i.e. mechanic or thermal to electric (graded according to the number of activated receptor cells and intensity of activation);

(post)synaptic potential (current), graded according to - number of excreted quanta of neuromediators:

inhibitory (hyperpolarization of postsynaptic membrane several ms - Cl channels)

excitatory (depolarization – Na and/or Ca channels)

- number of active receptors (postsynaptic membrane)

2. ACTION POTENTIALS (spikes)