motor system2 pathways
TRANSCRIPT
![Page 1: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/1.jpg)
Motor System
• Starts at the motor cortex
• Motor cortex is located at the frontal lobe– precentral cortex
![Page 2: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/2.jpg)
![Page 3: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/3.jpg)
![Page 4: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/4.jpg)
![Page 5: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/5.jpg)
![Page 6: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/6.jpg)
Motor homunculus
First discoveredbyPenfield
![Page 7: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/7.jpg)
Brodmann areas
![Page 8: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/8.jpg)
Motor cortex
• different areas of the body are represented in different cortical areas in the motor cortex
• Motor homunculus– somatotopic representation – not proportionate – distorted map– upside down map
![Page 9: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/9.jpg)
Motor cortical areas
• primary motor cortex (MI)– precentral gyrus
• secondary motor cortex (MII)– premotor cortex– supplementary motor area
![Page 10: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/10.jpg)
primary motor cortex
Functions• Corticospinal tracts (pyramidal tracts)
starts here• Cell bodies are located in the cortical area
(large cell bodies are known as Betz cells)• Corticospinal tract descends down
![Page 11: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/11.jpg)
Course of the corticospinal tract
• Descends through– internal capsule– at the medulla
• cross over to the other side
– descends down as the corticospinal tract– ends in each anterior horn cell– synapse at the anterior horn cell
![Page 12: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/12.jpg)
Medulla
motor cortex
internal capsule
Uppermotorneuron
Lowermotorneuron
anterior horn cell
![Page 13: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/13.jpg)
Functional role of primary and secondary motor areas
• SMA (Supplementary Motor Area) assembles global instructions for movements
• It issues these instructions to the PreMotor Area.
• PreMotor Cortex (PMC) works out the details of smaller components
• And then activates specific Primary Motor Cortex (MI)
• Primary Motor Cortex through corticospinal tracts (CST) activate specific motor units
SMA
PMC MI
CST
Motor units
![Page 14: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/14.jpg)
Motor system
• Consists of – Upper motor neuron– Lower motor neuron
![Page 15: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/15.jpg)
Lower motor neuron
• consists of mainly
• alpha motor neuron– and also gamma motor neuron
alpha motor neuron
gamma motor neuron
![Page 16: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/16.jpg)
alpha motor neuron
gamma motor neuron
corticospinal tract
Arrangement at the anterior horn cell
![Page 17: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/17.jpg)
alpha motor neuron
• this is also called the final common pathway
• Contraction of the muscle occurs through this whether – voluntary contraction through corticospinal tract
or– involuntary contraction through gamma motor
neuron - stretch reflex - Ia afferent
![Page 18: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/18.jpg)
motor unit
• muscle contraction occurs in terms of motor units rather than by single muscle fibres
• a motor unit is defined as– anterior horn cell– motor neurone– muscle fibres supplied by the neuron
![Page 19: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/19.jpg)
motor unit
• Innervation ratio– motor neuron:number of muscle fibres
• in eye muscles– 1:23 offers a fine degree of control
• in calf muscles– 1:1000 more strength
![Page 20: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/20.jpg)
Upper motor neuron
• Consists of – Corticospinal tract (pyramidal tract) – Extrapyramidal tracts
![Page 21: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/21.jpg)
Extrapyramidal tracts
• starts at the brain stem
• descends down either ipsilaterally or contralaterally
• ends at the anterior horn cell
• modifies the motor functions
![Page 22: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/22.jpg)
Extrapyramidal tracts
• there are 4 tracts– reticulospinal tracts– vestibulospinal tracts– rubrospinal tracts– tectospinal tracts
![Page 23: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/23.jpg)
reticulospinal tract
• relay station for descending motor impulses except pyramidal tracts
• receives & modifies motor commands to the proximal & axial muscles
• maintain normal postural tone• excitatory to alpha & gamma motorneurons• end on interneurons too • this effect is inhibited by cerebral influence• mainly ipsilateral
![Page 24: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/24.jpg)
midbrain
pons
medulla
spinal cord
reticulospinal tract
![Page 25: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/25.jpg)
• pontine reticular formation – medial reticulospinal tracts
• controls proximal muscles (axial), excitatory to flexor
• medullary reticular formation – lateral reticulospinal tracts (also medial)
• excitatory or inhibitory to axial muscles
![Page 26: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/26.jpg)
vestibular nuclei & tracts
• responsible for maintaining tone in antigravity muscles & for coordinating the postural adjustments in limbs & eyes
• connections with vestibular receptors (otolith organs) & cerebellum
• mainly ipsilateral
• supplies extensors
![Page 27: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/27.jpg)
midbrain
pons
medulla
spinal cord
vestibulospinal tract
mainly extensors
![Page 28: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/28.jpg)
• vestibulospinal tracts– lateral vestibulospinal tract– medial vestibulospinal tract
– excitatory to antigravity alpha motor neurons & supplies interneurons too
– lateral tract• excitation of extensor muscles & relaxation of flexor muscles
– medial tract• inhibition of neck & axial muscles
![Page 29: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/29.jpg)
red nucleus
• present in the midbrain• rubrospinal tract originates from the red nucleus• ends on interneurons• control the distal muscles of limbs• excite limb flexors & inhibit extensors• higher centre influence (cerebral cortex)• mainly contralateral• supplies flexors
![Page 30: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/30.jpg)
midbrain
pons
medulla
spinal cord
rubrospinal tract
mainly flexors
![Page 31: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/31.jpg)
tectospinal tract
• tectospinal tract originates from the tectum of the midbrain
• ends on interneurons
• mainly contralateral
• supplies cervical segments only
![Page 32: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/32.jpg)
midbrain
pons
medulla
spinal cord
tectospinal tract
cervical segments
![Page 33: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/33.jpg)
inferior olivary nucleus
• present in the medulla
• function: – motor coordination
• via projections to the cerebellum• sole source of climbing fibres to the cerebellum
– motor learning
![Page 34: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/34.jpg)
Renshaw cells• Renshaw cells are inhibitory interneurons
found in the spinal cord
• They receive excitatory collateral from the alpha motor neuron’s axon as they emerge from the motor root– (they are "kept informed" of how vigorously
that neuron is firing)
• They send their own inhibitory axon to synapse with the cell body of the initial alpha neuron
• In this way, Renshaw cell inhibition represents a negative feedback mechanism
• A Renshaw cell may be supplied by more than one alpha motor neuron collaterals and it may synapse on multiple motor neurons
![Page 35: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/35.jpg)
Uppermotorneuron
Lowermotorneuron
extrapyramidal tracts
pyramidal tracts
alpha motor neurone
gamma motor neurone
![Page 36: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/36.jpg)
Clinical Importance of the motor system examination
• Tests of motor function:– Muscle power
• Ability to contract a group of muscles in order to make an active movement
– Muscle tone• Resistance against passive movement
![Page 37: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/37.jpg)
Basis of tests
• Muscle power– Test the integrity of motor cortex, corticospinal
tract and lower motor neuron
• Muscle tone – Test the integrity of stretch reflex, gamma motor
neuron and the descending control of the stretch reflex
![Page 38: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/38.jpg)
Muscle tone
• Resistance against passive movement
– Gamma motor neuron activate the spindles – Stretching the muscle will activate the stretch
reflex – Muscle will contract involuntarily
– Gamma activity is under higher centre inhibition
![Page 39: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/39.jpg)
• There is a complex effect of corticospinal and extrapyramidal tracts on the alpha and gamma motor neurons (in addition to the effect by muscle spindle)
• There are both excitatory and inhibitory effects
• Sum effect – excitatory on alpha motor neuron– Inhibitory on gamma motor neuron
Corticospinal tract
Extrapyramidal tracts
Alpha motor neuron
Gamma motor
neuron•Voluntary movement•Muscle tone
Muscle spindle
![Page 40: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/40.jpg)
Clinical situations
• Muscle power– Normal– Reduced (muscle weakness)
• muscle paralysis• muscle paresis
• Muscle tone – Normal– Reduced
• Hypotonia (Flaccidity)
– Increased • Hypertonia (Spasticity)
![Page 41: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/41.jpg)
Main abnormalities
• Muscle Weakness / paralysis– Reduced muscle power
• Flaccidity– Reduced muscle tone
• Spasticity– Increased muscle tone
![Page 42: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/42.jpg)
• Lower motor neuron lesion causes– flaccid paralysis
• Upper motor neuron lesion causes– spastic paralysis
![Page 43: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/43.jpg)
Lower motor neuron lesion
• muscle weakness• flaccid paralysis• muscle wasting (disuse atrophy)• reduced muscle tone (hypotonia)• reflexes: reduced or absent• spontaneous muscle contractions (fasciculations)• plantar reflex: flexor• superficial abdominal reflexes: present
![Page 44: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/44.jpg)
Upper motor neuron lesion
• muscle weakness• spastic paralysis• increased muscle tone (hypertonia)• reflexes: exaggerated• Babinski sign: positive• superficial abdominal reflexes: absent• muscle wasting is very rare• clonus can be seen:
– rhythmical series of contractions in response to sudden stretch
• Clasp knife effect can bee seen– Passive stretch causing initial incerased resistance
which is released later
![Page 45: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/45.jpg)
tendon jerks (reflexes)
• reflex level
• biceps jerk C 5 6
• triceps jerk C 7 8
• knee jerk L 3 4
• ankle jerk S 1 2
![Page 46: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/46.jpg)
Babinski sign• when outer border of the sole of the foot is scratched
• upward movement of big toe
• fanning out of other toes
• feature of upper motor neuron lesion
• extensor plantar reflex
• seen in infants during 1st year of life (becuase of immature corticospinal tract)
![Page 47: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/47.jpg)
positive Babinski sign
![Page 48: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/48.jpg)
Site of lesions
Cortex
Internal capsule
Brain stem
Spinal cord
Anterior horn cell
Motor nerve
Neuromuscular junctionMuscle
![Page 49: Motor system2 pathways](https://reader035.vdocuments.us/reader035/viewer/2022081508/557d14f1d8b42a3d3d8b4961/html5/thumbnails/49.jpg)
Site of lesions
monoplegiaonly 1 limb is affected either UL or LL,lower motor neuron lesion
hemiplegiaon half of the body includingUL and LLlesion in the Internal capsule
paraplegiaboth lower limbsthoracic cord lesion
quadriplegia (tetraplegia)all 4 limbs are affected
cervical cord or brain stem lesion