Difference between UMN and LMN lesion: Physiology

Difference between Upper motor neuron lesion vs lower motor neuron lesion

	UMN	LMN
Bulk	Normal till disuse atrophy	Prominent weakness and atrophy occurs early
Tone	Increased Except in spinal shock where tone will be flaccid and recovers in around 2 weeks	Always HYPOTONIA
Power	Reduced, tends towards normal over period of time if adequate stimulation maintained	Severely decreased
Abnormal movement	Fasciculation are not usually seen	Fasciculation is due to degenerative process in anterior horn cell
Reflexes	Brisk	Decreased to absent
Plantar/ Babiknsi	Up going	Downgoing

>>Learn about the plantar reflexes and its variants with video demonstration

The most important thing to know is the intactness of the muscle stretch reflex. The tone is maintained under the influence of gamma motor neuron by the alpha motor neuron and the bulk and power is the pure function alpha motor neuron. The reflex is complete if its loop is complete.

Muscle Reflex arc

Learn the analogy of muscle and bladder on UMN and LMN lesions.

Upper Motor Neuron lesions are the lesion occurring anywhere in the central nervous system from the brain upto the spinal cord before the alpha motor neurons arise from the spinal cord. The lesion could arise from the cerebral cortex, internal capsule, midbrain, pons, medulla and the cortico spinal tract in the spinal cord. The lesions can be anything from vascular, traumatic, degenerative, and inflammatory to infective.

The lesions occurring after the alpha motor neuron accounts for the lower motor neuron lesions. The lesions could arise in the nucleus of alpha motor neuron (Polio myelitis, Amylotrophic lateral Sclerosis, brown sequard syndrome), Lesions in the nerve (Traumatic resection, entrapement, neuritis), Lesion in the NMJ (Myasthenia gravis, Lambert Eaton Syndrome) and the muscle (Duchenne Muscular Dystrophy, Beckers Muscular Dystrophy )itself.

The two principle that determine the features of upper motor and lower motor neuron include the completeness of muscle reflex arc and the higher motor control over it.

The motor reflex arc consists of the Ia fibres carrying the signal from muscle spindle which prevents the excessive stretch of muscle by contracting it. The afferent fibres mono synaptically fires the alpha motor neurons at the anterior horn and causes the muscle contraction. This reflexes is controlled further by higher centre and is thus there is an inhibitory mediatory released via an intermediate neuron coming from the corticospinal tract. If this closed loop of nerve are intact the muscle tendon reflex is intact and so is the deep tendon reflex which is elicited using reflex hammer.

Learn about the effect of UMN and LMN lesion on bladder.

The tone is the inherent state of contraction of muscles to maintain the posture of the body. It is in medicated by the Gamma motor neuron coming together wit alpha motor neuron and innervates the intrafusal fibres of muscle spindle and thus increases the sensitivity of change in length of the muscle. It is also directly innervated from the corticospinal tract and thus is affected in response to UMN lesion.  Along with that the gamma motor neurons are spontaneously firing and thus influence the sensitivity of alpha motor neurons and thus affect the tone.

In lower motor neuron lesion, the alpha motor neuron and distal is injured. So the loop can not be complete and hence no reflex contraction of muscle in response to stretch of muscle spindle receptor. In upper motor neuron lesion, the higher inhibition over the reflex arc is lost. This causes the excessive firing from alpha motor neuron and hence exaggerated deep tendon reflex.

The lower motor neurone lesion will develop flaccid paralysis because there is no innervation to muscle fibre to cause its contraction and hence they easily go into disuse atrophy early and the bulk is reduced. Contrary to the Upper motor neuron lesion where the higher control of the muscle is lost but still the muscle can be contracted locally. So, constant use of muscle via passive movement can preserve the bulk of the muscle.

The tone in upper motor neuron lesion is exaggerated because the supraspinous modulation over the gamma motor neuron is lost and they are firing spontaneously.  This increases the tone of the muscle with increases sensitivity of muscle spindle to passive stretch and increased firing in the Ia fibres. This increased firing induces increased firing in alpha motor neuron and increased contraction.The tone is higher in the antigravity muscle and hence clasp knife rigidity is due to the greater bulk of the antigravity muscles and hence the paralysis is spastic type in upper motor neuron lesion.

However, in the lower motor neuron lesion , again the same nerve that complete the muscle reflex is incomplete and hence the normal tone is present due to absence of innervation in the muscle to bring about the contraction and hence the tone is flaccid and hence the paralysis flaccid paralysis.

In LMN lesion, the muscle become hypersensitive to neurotransmitter as it is denervated. Similarly the damaged lower motor erratically discharges the neurotransmitter stored within itself as the neuron degrades. So, both increased hypersensitivity and erratic release of neurotransmitter causes fasciculations. However, in UMN lesion, there is regular firing to prevent the atrophy of muscles.

Learn about Cranial nerve examinations 

Difference between UMN and  LMN lesion in tabulated form.

Examination of Ulcer: How to describe.

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Abdominal | Respiratory | Cardiovascular | Nose and PNS | Oral Cavity | Ear | Digital Rectal Examination | Ulcer | 

Examination of an Ulcer

(The description below does not match with the images given beside the text. The images are only for illustrative purposes.)

Inspection

Ulcer over the sole.

On inspection of the right leg, the leg is slightly elevated on the pillow and slightly flexed over the knee joint. (Attitude of the limb).

A single (number), irregularly shaped (shape) ulcer of size around 10 cm x 5cm (size) is present over the dorsum of the foot (site), extending from the lateral malleolus up to the base of the toes (extension).

The floor of the ulcer is pinkish to red (color) with minimal (amount) serous (type of discharge) discharge. No slough, foreign bodies or any other debris (Content on the floor). Multiple tendons are visible towards the distal end (base).

The edge of the ulcer is sloping type (character), with healthy pink granulation tissue (content) and the margin is sharp and regular.

The surrounding skin is exfoliated upto the level of ankle joint. The skin around the ulcer is non-erythematous, and non-edematous. No scars, abnormal pigmentation, or excoriation marks present.

The joint mobility of the proximal and distal joint along with that of the entire limb is not impaired. (Gross motor status and Range of motion of the affected joints)

Palpation

Ulcer over the dorsum of foot

On palpation, there is local rise in temperature and mid tenderness over the ulcer.

The edges are not indurated and the base of the wound are also not indurated. The ulcer is 3-4mm deep, does not bleed on touch, and mobile over the underlying base.

The skin around the ulcer has mild rise in temperature locally with tenderness present. The skin is freely mobile on the underlying structure.

Dorsalis pedis artery, anterior tibial and posterior tibial artery are palpable and bilaterally symmetrical. Capillary refill time over the distal phalanges is more than 2 s.(Gross vascular status)

Active and passive range of motion over the limb is not restricted. Sensation is grossly intact over the area distal to the ulcer. (Gross Neurological status and range of motion)

The draining lymph nodes over the left inguinal region are not palpable significantly.

Ulcer examination is incomplete without draining lymph nodes palpation. 

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Complete Chest Examination (Respiratory System): How to describe.

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>>May be first you want to see how to write a history of COPD.

Elderly  gentleman, ill looking, thin built (with Temporal hollowing, Buccal Hollowing, Supraclavicular, suprasternal hollowing, Subclavicular hollowing, with thin limbs, thin skin and prominently visible vessels) lying in semirecumbent position with IV canula of 20G and nasal prongs delivering 3l of O2/min is conscious, cooperative and well oriented to time, place and person.

On general physical examination, there is central cyanosis with peripheral cyanosis.

Bilateral pitting edema extending upto the mid thigh is present which is non tender with normal overlying skin. Sacral edema is present.

But no clubbing, no pallor, no icterus seen. Hydration status of the patient is normal. Accessible Lymph nodes are not palpable.

On examination of the vital signs,

Pulse is 70 beats/min taken on right radial artery, regular, catacrotic, euvolemic, no radio radial and radio femoral delay. All the peripheral pulses are palpable, and no carotid bruit heard. Condition of the arterial wall is normal.

Blood pressure measured on the right arm in sitting position was 130/80 mm of mercury.
Temperature taken on right axilla was 37.2^oC.

Respiratory rate is 22/min, thoracoabdominal type with nasal flaring, pursed lip breathing and use of accessory muscles of respiration.

JVP was elevated and was 5 cm from the manubriosternal angle in the semirecumbent position.

On examination of the respiratory system

On Inspection of the upper respiratory tract , no DNS, Polyp, discharge or congestion present on the nose. Nasal flaring and Pursed lip breathing present. Use of accessory muscles of respirations seen (with prominent SCM, Scalene, trapezius. Rectus abdominis, pectoralis). The oral cavity looks grossly normal with no congestion, ulcerations on posterior pharynx and bilateral tonsils looks grossly normal.

On inspection of Lower respiratory system, shape of the chest is tending to barrel. 
Trachea is present in the midline.

Bilateral symmetry of chest wall is seen. Bilateral equal movement with respiration present.

Apical Impulse is not visible.

No other visible pulsation, scar marks and dilated vessels seen.

Presence of Supra and Infrascapular hollow is present and equal in both side. 

Prominent and Horizontal ribs with widened and hollow intercostal space seen but no intercostal indrawing, no subcostal indrawing and no intercostal fullness.

Spine is centrally placed and no skeletal deformity present. No drooping of Shoulder. 

No Respiratory examination is complete without Cardiac examination. Click here to know how to describe the precordium.

On palpation, Trachea is centrally placed. Apical impulse is not palpable.

Chest movement is bilaterally equal.

On measurement of the chest, chest expansion on inspiration was 84.5cm and expiration was  82cm with inspiratory expiratory difference of 2.5cm. The Anteropostero Diameter was 35 cm and Transverse diameter is 40cm and AP to Transverse ratio being 7:8(tending  to barrel). 
The Right hemithorax is 41 cm and left hemithorax is 41 cm.

Increased vocal fremitus palpable in the right subcostal  area.

On percussion, dull note was present over the right sub mammary region.  Resonant sound heard on the other area all over the  chest.

Liver dullness started from 6^th right Intercostal area in the midclavicular line.

Cardiac Dullness was not obliterated.

On Auscultation,  Bilaterally decreased air entry with prolonged expiration is present. Bronchial breath sound heard over the right sub mammary region along with Crackles present. Increased vocal fremitus present with aegophony on right sub mammary region.

Provisional diagnosis: COPD with right inframammary consolidation.

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Rule of 3: Cerebellum

Rule of three 

Cerebellum

 Rule of three applies in cerebellum where it can be divided in 3 zones based upon its fucntion and phylogey. Similarly, three lobes are formed by primary and posterior fissures. The cerebellum is suppied by three arteries viz Superior cerebellar artery (SCA) and Anterior inferior cerebellar artery (AICA) both branches of basilar artery while posterior inferior cerebellar artery (PICA) is a branch of pair of ascending vertebral arteries.  On cellular level  the superficial layers are formed by basket cells and stellate cells forming the molrcular layer. These cells project into Purkinjee fibers which are the inhibitory cells releasing GABA and project into the deep nucleus. Deep Nucleus includes Globose, Emboliform , Dentate and Fascitigeal nuclei. 

There are three surfaces anatomically the superior or the tentorial surface beneath the tentorium cerebri. Lateral Surface covered by the petrosal bone and posterior by the occipital bones.