﴿و ما أوتيتم من العلم إلا قليلا﴾

Name: ﴿و ما أوتيتم من العلم إلا قليلا﴾
Uploaded: 2017-06-28T02:04:47+00:00
Duration: PTM32S30
Channel: Gregory Barker
Description: ﴿و ما أوتيتم من العلم إلا قليلا﴾

﴿و ما أوتيتم من العلم إلا قليلا﴾
بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

Assist Prof of Medical Physiology
Physiology of CNS Somatic Motor System By Dr. Abdel Aziz M. Hussein Assist Prof of Medical Physiology

Inverse Stretch Reflex

It is a reflex relaxation (or lengthening) of a ms in response to excessive stretch or contraction of that ms.

Neural pathway: Stimulus: ↑ed ms tension by; Overstretch or Severe contraction Receptors: Golgi tendon organs 1) Site: tendons of skeletal ms in series with ms fibers 2) Structure: Are encapsulated sensory receptor 6-20 elastic fibers 3) Innervations: Type Ib or A alpha afferent fibres

Golgi Tendon Organs (GTOs)
Receptors: GTOs Stimulated by ↑ed ms tension caused by passive overstretch or active contraction of the ms Afferents: A alpha or Ib Center : a)inhibitory interneurons→ inhibit the α-MNs supplying the same ms b)excitatory interneurons→ excite the α-MNs supplying the antagonistic ms Response: Relaxation of the same ms Contraction of antagonistic group of ms.

Significance GTR: a)Physiological significance: Protective reaction which prevent tearing of the ms or avulsion of its tendon from its bony attachment when the ms is overstretched.

Significance GTR: b)Clinical significance: (clasp knife effect) Demonstrated clinically by passive flexion of a spastic limb (e.g. in upper motor neuron lesions) at its main joint. As the limb is flexed, an initial resistance occurs due to contraction of this ms a result of the stretch reflex. With persistent flexion, at a certain point, GTR is excited→ sudden disappearance of the initial resistance → the limb flexes easily, as occurs during closing-of a pocket knife→ clasp knife effect. E.g. Flexion of knee and ankle

Tendon Jerk

Tendon Jerks Def., Rapid contraction followed by relaxation of a ms due to sudden stretching of that ms by tapping on its tendon using a medical hammer Mechanism: It is a dynamic type of the stretch reflex

The Tendon Reflex Alpha MNs 1ry endings Ms contraction Sudden stretch
6 Primary afferent neuron stimulates inhibitory interneuron To brain 4 Primary afferent neuron stimulates alpha motor neuron to extensor muscle 7 Interneuron inhibits alpha motor neuron to flexor muscle Alpha MNs 1ry endings 5 Alpha motor neuron stimulates extensor muscle to contract 3 Primary afferent neuron excited Ms contraction Sudden stretch Nuclear bag 2 Muscle spindle stimulated Flexor muscle (antagonist) relaxes 1 Extensor muscle stretched 8

Tendon Jerks

Tendon Jerks Cause of relaxation after contraction in the tendon jerk:
Stoppage of discharge from the ms spindles. Stimulation of the Golgi tendon organs. Stimulation of the Renshaw’s Cells.

Examples of Tendon Jerks
Center Limb position Tendon Response Biceps jerk C5,6 The elbow is 120° Tapping on biceps tendon Flexion of the forearm Triceps jerk C6,7 The elbow is 90° Tapping on triceps tendon directly Extension of the forearm Knee jerk L2, 3 & 4 knee is semi flexed by seating with the leg to be tested crossing over other Tapping on patellar tendon Extension of the knee Ankle jerk S1,2 feet slightly dorsiflexed Tapping on tendoachilles Plantar flexion. Jaw jerk Trigeminal nerve Mouth slightly opened Tapping on chin Closure of mouth

Biceps Jerk

Triceps Jerk

Knee Jerk

Ankle Jerk

Tendon Jerk Reinforcement of the tendon jerks
Response of the tendon jerks can be reinforced by facilitating the spinal centers. Can be done by either; a) Jendrassik's maneuver → ask the patient to hook his fingers or to clench his teeth→ send signals from the contracted ms which stimulating γ-MNs. b) Distracting patient’s attention→ prevents any voluntary inhibition of the reflex.

Clinical Significance of TJ
1. Localization of spinal cord lesions: Loss of TJ means the lesion in its center e.g. ankle jerk is lost in sacral region lesion. 2. Assessment of the ms tone : In hyperreflexia (exaggerated tendon jerks) → hypertonia (↑ms tone). In hyporeflexia (↓ed tendon jerks) → hypotonia (↓ms tone). In areflexia (lost tendon jerks) → atonia (lost ms tone).

Clinical Significance of TJ
3. Assessment of the integrity of pathway of stretch reflex: so areflexia or absent tendon jerk may be due to; 4. Assessment of the state of Supraspinal centers: Site of lesion Condition Afferent lesion Tabes dorsalis Center (AHC) lesion Poliomyelitis Efferent lesion Trauma or neuritis Hyperactive(exaggerated) TJ Hypoactive (decreased) TJ Physiological causes Anxiety and nervousness Sleep and anaesthesia Pathological causes UMNL Lesion in area 6 Tetany and hyperthyroidism Paleocerebellum lesion LMNL Lesion in area 4 Hypothyroidism Neocerebellar syndrome

Pendular Knee Jerk Occurs in the neocerebellar syndrome and chorea.
Characterized by hyporeflexia & hypotonia Knee jerk is weak than normal and during relaxation of the quadriceps ms, the leg falls like a dead weight(due to hypotonia) & swings for sometime like a pendulum before resting.

Clonus Def. Alternating regular rhythmic contractions with incomplete relaxations of a ms (its MNs is in a state of facilitation) in response to sudden maintained stretch. Cause: UMNL

Clonus Types 1) Ankle Clonus:
Produced by sudden maintained dorsiflexion of the foot  leads to regular rhythmic planter flexions due to rhythmic contractions of soleus and gastrocnemius muscles. 2) Knee Clonus: Produced by the sudden downward displacement of the patella  rhythmic oscillations of the patella.

Clonus Mechanism of clonus:
Clonus is the result of a stretch reflex - inverse stretch reflex sequence, which occurs as follows : Sudden stretch of the ms results in its contraction through the stretch reflex. This is followed by relaxation due to; a) Stoppage of impulse discharge from the ms spindles. b) Initiation of an inverse stretch reflex due to stimulation of the GTOs. As stretch is maintained, a new stretch reflex occurs (helped by the state of excessive spinal facilitation), and the cycle is repeated.

Somatic Motor System

Higher Motor Centers in CC Descending Motor Tracts
Somatic Motor System Higher Motor Centers in CC Midbrain Descending Motor Tracts L Pons A Lower MNs In Brain Stem Medulla Motor centers in brain stem e.g. RF Lower MNs in AHCS Spinal Cord

Somatic Motor System Consists of 2 sets of motor neurons;
1. Upper Motor neurons: Cell bodies are present in motor areas of cerebral cortex and other motor centers in brain stem Axons form descending motor tracts 2. Lower motor neurons: Cell bodies are present in AHCs of spinal cord or motor nuclei of cranial nerves Axons form peripheral nerves that supply skeletal ms

Higher Motor Centers in CC
Upper Motor Neuron Higher Motor Centers in CC Midbrain Upper Motor Neuron L Pons A Brain Stem Nuclei Medulla Motor centers in brain stem e.g. RF AHCS Spinal Cord

Somatic Motor nuclei of cranial nerves
Lower Motor neurons Somatic Motor nuclei of cranial nerves Midbrain Left Internal Capsule L Pons A Medulla AHCs Spinal Cord

Cortical Motor Areas (Motor Cortex)

Motor Cortex 1. Primary motor area (area 4) 3. Supplemental motor area
Initiation and performance of voluntary movements are the result of motor commands signals from the motor cortex to the lower motor centers via the descending motor tracts Motor cortex is located in the frontal lobe, and comprises; 1. Primary motor area (area 4) 2. Premotor area (area 6) 3. Supplemental motor area

Area 4 Premotor area Supplemental area 4 6

Primary Motor Area Area (4)

Primary Motor Area (MI)
Site: Precentral gyrus in frontal lobe Central sulcus Precentral gyrus

Body representation: 1. Contralateral: i.e. Body ms from the Rt side of the body is represented in the left hemisphere and Lt half of body is represented in Rt hemisphere N.B. some facial muscles are represented bilaterally

Primary Motor Area Body representation:
2. Inverted: i.e. the ms of the face are controlled by the lowermost part of area 4 & muscles of the lower limbs controlled by the upper most part of area 4

Primary Motor Area Body representation:
Homunculus 3. Ms involved in fine voluntary movements are represented by relatively large areas than those involved in gross movements

Premotor and supplemental motor areas. Connections: Area 4 a) Afferents: Visual and auditory areas Basal ganglia and cerebellum. Prefrontal area Proprioceptors (Sensory Feedback)

Primary Motor Area Connections: b) Efferents: Corticobulbospinal tract
4 b) Efferents: Area 4 on opposite side Basal ganglia and cerebellum (Large No. of fibers. Red nucleus and RF (moderate No. of fibers) Corticobulbospinal tract (30%)

Primary Motor Area Functions:
1. Initiation of voluntary movements done by the distal limb muscles 2. Facilitatory to the tone of the distal muscles

Primary Motor Area Lesion:
1. loss of voluntary movements (paralysis) of the distal limb muscles on opposite side 2. Hypotonia and inhibition of tendon jerks 3. Babinski’s sign with dorsiflexion of the big toe only

Premotor Area Area (6)

Premotor Area (6) Site: Frontal lobe in front of area 4 Premotor area

Premotor Area (6) Body representation: Contralateral and inverted

Basal ganglia and cerebellum. Corticobulbospinal tract
Premotor Area (6) Connections: Area 4 Supplemental area Area 6 Basal ganglia and cerebellum. Corticobulbospinal tract (30%)

Premotor Area Functions:
1. shares in planning of complex movements together with area supplemental motor area 2. initiates the gross movements as those done by the trunk 3. with B.G. involved in postural adjustment during voluntary distal movements 4. inhibitory effect on muscle tone 5. with basal ganglia, initiate & control the automatic associative movements

Premotor Area Functions: contains special areas in area 6

Premotor Area Broca’s area

Premotor Area Hand skills Head rotation Eye movements area

Primary Motor Area Lesion:
1. impairment of complex movements or paresis 2. Hypertonia and exaggeration of tendon jerks 3. Loss of automatic associative movements 4. Babinski’s sign with fanning of the lateral four toes only 5. Motor aphasia 6. Motor apraxia

Supplemental Motor Area

Site: Upper medial side of frontal lobe above area 6 supplemental area

Supplemental motor Area Basal ganglia and cerebellum.
Connections: Supp. Area Area 4 Premotor area Basal ganglia and cerebellum. Corticobulbospinal tract

Functions: 1)Evokes complex movements which often involve both sides of the body e.g.: causing both hands to perform a motor act together. 2) With the premotor area (6) in providing suitable background for the performance of the fine skilled movements by hands and fingers that are mediated by the C.B.S tract. 3)Shares in the planning and programming of the complex movements with area 6.

Descending Motor Tracts

Classified by 2 ways ; a) Pyramidal and extrapyramidal tracts: If the tract passes through the pyramids of the medulla→ pyramidal tract. If the tract does not pass through the medullary pyramids→ extrapyramidal tract .

Pyramidal Tract

Extrapyramidal Tracts

Medial and Lateral Motor System
Medial motor system

b) Medial and lateral motor system: i) Medial motor system→ composed of tracts that terminate primarily on the ventromedial neurons → innervate axial and girdle ms → concerned with postural control. ii) Lateral motor system→ composed of tracts that terminate primarily on the lateral neurons → innervate distal ms of the limbs → concerned with control of fine voluntary movements.

5 important sets of descending motor tracts, named according to the origin of their cell bodies and their final destination: Corticobulbospinal tract (= Pyramidal tract) Rubrospinal tract, Reticulospinal tracts, Vestibulospinal tracts Tectospinal tract Extrapyramidal tracts

Corticobulbospinal Tract
Pyramidal Tract or Corticobulbospinal Tract

Motor areas, somatic sensory areas
Pyramidal Tract Motor areas, somatic sensory areas Corticonuclear tract Midbrain Left Internal Capsule L Pons A Corticobulbar tract Medulla Corticospinal tract Spinal Cord

Pyramidal Tract Origin: 2. Premotor and supplemental areas → 30%
1. Primary motor area (area 4) → 30% 2. Premotor and supplemental areas → 30% 3. Somatic Sensory areas → 40%

Premotor area and supplemental motor area
Pyramidal Tract Origin: Area 4 Premotor area and supplemental motor area Area 3,1,2 and Area 5,7, 30 % 40 % 30 %

Pyramidal Tract Divisions:
1) Corticospinal tract : from cortex to spinal cord 2) Corticonuclear tract: from cortex to cranial nerves nuclei (3,4,6) that supply extraocular muscles 3) Corticobulbular tract: from cortex to other cranial nerves (5,7,9,10,11,12) of brain stem

Pyramidal Tract Corticospinal Tract 4 M1 Left Internal Capsule
Genu Corticospinal Tract Anterior Limb Posterior Limb Left Internal Capsule Midbrain Pons Pyramidal Decussation Mid Medulla Caudal Medulla Spinal Cord

Corticospinal Tract (a) 90% cross to the opposite side and descend in the lateral column of the spinal cord as lateral corticospinal tract→ terminate on lateral AHCs →innervate the distal ms (b) 10% not cross → descend ipsilaterally as ventral corticospinal tract. About 9% of these fibers cross and terminate on medial AHCs → innervate the axial muscles of the opposite side. Only 1% of the fibers terminate on the A.H.Cs of the same side (bilateral innervations as respiratory muscles).

CC Pathway: Internal capsule Medulla Spinal cord Lateral CST
Ventral or medial CST Spinal cord

Pyramidal Tract Corticobulbar Tract LOWER MOTOR NEURON NUCLEI
F A L Left Internal Capsule Corticobulbar Tract is crossed and uncrossed EXCEPT to lower motor neurons which control lower half of the face and tongue are crossed only. V V LOWER MOTOR NEURON NUCLEI Midbrain PONS F Upper Face Lower Face VII VII Pons IX IX Mid Medulla MEDULLA X X Caudal Medulla Spinal Cord XII XII Ipsilateral Side Contralateral Side

Pyramidal Tract Corticonuclear Tract LMN Supplying eye muscles III III
Area 8 Pyramidal Tract Corticonuclear Tract F A L Left Internal Capsule LMN Supplying eye muscles III III Midbrain Midbrain F IV IV Pons PONS VI VI Mid Medulla Caudal Medulla Spinal Cord Ipsilateral Side Contralateral Side

Pyramidal Tract Functions:
The C.B.S tract is primarily concerned with the mediation of voluntary motor commands from the cerebral cortex to lower motor centers: a- Corticonuclear tract controls the extraoccular ms. b- Corticobullar tract controls the ms of lower part of the face and tongue which are involved in articulate speech. c-Lateral corticospinal tract controls distal ms that subserve skilled movements as those used in manipulation by hands and fingers.

2) Medial C.B.S tract controls axial ms concerned mainly with regulation of posture. 3) C.B.S tract is also facilitatory to the tone of the distal limb muscles.

They are classified by 2 ways ; a)Pyramidal and extrapyramidal tracts: If the descending motor tract passes through the pyramids of the medulla→ pyramidal tract. If the descending motor tract does not pass through the medullary pyramids→ extrapyramidal tract .

Pyramidal Tract

Extrapyramidal Tracts

AHCs Medial motor system Lateral motor system

b) Medial and lateral motor system: i) Medial motor system→ composed of tracts that terminate primarily on the ventromedial neurons → innervate axial and girdle ms → concerned with postural control. ii) Lateral motor system→ composed of tracts that terminate primarily on the lateral neurons → innervate distal ms of the limbs → concerned with control of fine voluntary movements.

Extrapyramidal tracts
There are 5 important sets of descending motor tracts, named according to the origin of their cell bodies and their final destination: Corticobulbospinal tract (= Pyramidal tract) Rubrospinal tract, Reticulospinal tracts, Vestibulospinal tracts Tectospinal tract Extrapyramidal tracts