Motor system Flashcards
List the 4 main parts of the motor system
- upper motor neurons
- lower motor neurons
- extrapyramidal motor system
- cerebellar system
What are upper motor neurons
- belong to the pyramidal system
It refers to the giant pyramidal (Betz) cells, found in the 5th cortical layer of the precentral gyrus, along with their descending fibres called the pyramidal tract; including the corticospinal tract (spinal cord) and corticobulbar tract (brainstem) - the upper motor neurons control the lower motor neurons
What are the lower motor neurons
- acts as the final common pathway for impulses from the upper motor neurons, cerebellar system and extrapyramidal system
- refers to the anterior horn cells of the spinal cord and the motor nuclei of the brainstem; as well as their axons forming peripheral nerves and cranial nerves
Describe the different motor pathways
Precentral gyrus (Betz cells) –>pyramidal tract (corticobulbar/spinal) –> internal capsule
- corticobulbar tract –> cross to other side at different brainstem level –> cranial motor nuclei –> cranial n
- corticospinal tract –> middle basis of cerebral peduncle –> basis of pons –> most fibres cross at pyramidal decussation –> lateral corticospinal tract –> motor neurons of anterior grey horn –> anterior root –> spinal n –> skeletal m
Based on clinical types, what are the 5 classifications of paralysis
- monoplegia: paralysis of one extremity only
- paraplegia: symmetric paralysis of 2 extremities
- quadriplegia: paralysis of all 4 extremities
- hemipleglia: paralysis of one side of the body, limited by the median line
- crossed paralysis: paralysis of one or more ipsilateral cranial nerves and contralateral hemiplegia
Based on the location of a lesion, what can paralysis be classified into
- Neurogenic paralysis: lesion on motor neuron or peripheral nerve
- Myogenic paralysis: caused by muscular diseases
Based on clinical characteristics, how can paralysis be classified
- UMN paralysis: spastic paralysis or central paralysis or hard paralysis
- LMN paralysis: flaccid, peripheral or soft paralysis
What is the difference between UMN and LMN paralysis?
First UMN paralysis, 2nd LMN paralysis
Distribution of paralysis: General (mono, hemi, para) Local, often involving some muscle group
Muscle tone: Hyper myotonia Hypo myotonia
Tendon reflex: Hyperactive Hyporeflexia
Pathologic reflex: Yes No
Muscular atrophy: No (or diffuse) Yes, early
Reaction of degeneration: No Yes
How would one diagnose paralysis of precentral gyrus
The precentral gyrus is a long stripe
- local destructive lesion usually damages part of it causing contralateral monoplegia with or without contralateral facial palsy
large lesion may cause contralateral hemiplegia
- irritative lesion often causes epilepsy of contralateral extremity
How would one diagnose paralysis of the internal capsule
The internal capsule is the most concentrated part of the pyramidal tract; lesions will cause:
- contralateral hemiplegia, central facial palsy and central hypoglossal palsy
- contralateral hemianaesthsia
- hemianopsia is sometimes present
How would one diagnose paralysis of the brainstem
- indication of brainstem lesion in crossed paralysis (because involvement of ipsilateral motor nucleus of cranial neve and uncrossed pyramidal tract
i.e., midbrain lesion: weber syndrome
Pons lesion: Millard-Gubler syndrome
How would one diagnose paralysis of the spinal cord?
- Spinal hemisection syndrome
- ipsilateral deep sensation disturbance
- ipsilateral UMN paralysis belowe level of lesion
- contralateral superficial sensation disturbance below level of lesion - Spinal transection lesion
- loss of all sensation below level of lesion
- paraplegia or quadriplegia below level of lesion
- disturbance of bladder and rectum function
What is the location diagnosis paralysis for the anterior horn cells
- ipsilateral segmental lower motor neuron paralysis of the muscles that these cells supply, usually with fasciculation but no sensory disturbance
(polymyelitis)
What is the location diagnosis paralysis for anterior root lesions
- ipsilateral segmental lower motor neuron paralysis of muscles that the anterior root supplies, radicular pain may be presented if posterior root is involved as well
What is the location diagnosis paralysis for the peripheral nerve
The peripheral nerve is a mixed nerve, so lesion involving a peripheral nerve will cause motor and sensation disturbance of muscles and skin that the nerve supplies
Describe the anatomy of the extrapyramidal system
- corpus striatum
- neostriatum (caudate nucleus, putamen)
- paleostriatum/globus pallidu (red nucleus, substantia nigra, subthalamic nucleus)
*lenticular nucleus = globus pallidua + putamen
What is the extrapyramidal system mainly related to and what is the main structure relating to its function
- main function is movement adjustment
- corpus striatum is the main structure
Why is the corpus striatum the main structure regarding movement adjustment?
The structures within the the corpus striatum have extensive connections to each other and to the cerebral cortex and many other subcortex structures (red nucleus, substantia nigra and brain stem reticular formations)
What is the
1. anatomic basis
2. biochemical basis
of movement adjustment
- fibre connection circles
- neurotransmitters (Glu, GABA, DA)
Generally speaking, lesions to the extrapyramidal system will result in______
changes in muscle tone (hypertonia, hypotonia) and involuntary movements
What are two main clinical syndromes relating to the extrapyramidal system
- hypertonia hypokinesia syndrome: caused by lesion of globus pallidus and substantia nigra –> present with static tremor (parkinson’s disease)
- hypotonia hyperkinesia syndrome: lesion of caudate nucleus and putamen –> Gilles de la tourette syndrome
Provide the general anatomy of the cerebellum
- posterior fossa of the skull, behind the pons and medulla
- separated from the overlying cerebrum by the cerebellar tentorium
- connected to the midbrain, pons and medulla by way of its 3 pairs of cerebellar peduncles
- cerebellum is composed of small unpaired medial port, the vermis and 2 large lateral masses (cerebellar hemispheres)
List the 3 main functions of the cerebellum
- keeping the balance of the body in space
- adjusting the muscle tonus
- coordinating movements of the extremities
What is meant by “ataxia”
decompostion and inco-ordination of movements caused by a lesion in the cerebellum, cerebrum, deep sensation pathway or vestibular structures
List the 4 types of ataxia
- cerebellar ataxia
- cerebral ataxia
- sensory ataxia
- vestibular ataxia
Describe cerebellum ataxia
- how is it caused
- symptoms
**most important symptom of cerebellar disease is ataxia
caused by:
1. lesion of vermis:
*cause disturbance of equilibrium and truncal gait: gait is unsteady, wide-based, irregular and drunken
2. lesion of the cerebellar hemispheres
*causes ataxia of the ipsilateral extremities: finger-to-nose and heel-knee-shin test is inaccurate, dysmetria, adiadokokinesia, intention tremor, nystagmus, hypotonia, explosive and slurred speech, tendency to lean and fall to the side of the lesion
Describe cerebral ataxia
there are fibre connections between the cerebellum and cerebrum (frontal, temporal, parietal lobe), so lesions of cerebrum may cause ataxia
*symptoms are relatively mild
Describe sensory ataxia
Lesion of posterior column of spinal cord may cause disturbance of deep sensation and sensory ataxia
- difficulty standing steady (especially in the dark or when patient closes eyes - Romberg’s sign)
often seen in neurosyphilis and spinal combined degeneration
Describe vestibular ataxia
Vestibulocochlear tract carries impulses from vestibular nuclei to the flocculonodular lobe (participate in keeping bodies balance in space and movement of eyes
Lesion on the vestibular system may cause vestibular ataxia
- vertigo
- vomitting
- nystagmus
