The Motor Systems of the Brain L4 Flashcards
What is a homunculus?
representation of the body on cortices
Cant be either a Motor Homonculus or Sensory Homunculus
What is the Motor homunculus?
Motor map of the body
Representation is proportional to the Complexity of control over those muscles, Dexterity of those muscles, or Degree of Activity.
Somatotopical map in the Motor Cortex
Different muscles are represented unequally in the 1 Primary Motor area
Large representation= thumb, fingers, lips and tongue
Small representation = toes, trunk/abdomen
More cortical area is devoted muscles involved in Movement which is Skilled, Complex and or Delicate
What areas of the body have a large representation on the Motor homunculus?
Thumb Fingers Face tongue Lips
What ares of the body have a small representation on the Motor Homunculus?
Toes
Trunk
Abdomen
What is the reason behind more cortical motor area devoted to particular parts of the body over others?
More cortical area is devoted to muscles involved in Movement which is Skilled, Complex and Delicate
What is the representation on the motor homunculus proportional to?
Complexity of control
Dexterity of the muscles
Degree of activity
What is the sensory homunculus?
Sensory map of the body
Representation is proportional to the number of specialised sensory receptors within the corresponding body part
A larger representation means the body part has a more highly specialised sensory function (has more cortical area devoted to it)
Large representation= Lips(bigger than motor) and Fingertips
Smaller representation = trunk and abdomen
More sensitive, able to Localise specifically (discriminative)
Large number of receptors = larger representation on homunculus =/= does not equal larger size of the body part (lips and finger tips are small yet they are largely represented on the primary somatosensory cortex)
What areas of the body have a large representation on the Sensory homunculus?
Lips (bigger than on motor homunculus)
Finger tips
What areas of the body have a small representation on the Sensory homunculus?
Trunk
Abdomen
What is the reason behind more cortical sensory area devoted to particular parts of the body over others?
Representation is proportional to the number of specialised sensory receptors within the corresponding body part
Large number of receptors = larger representation on homunculus =/= does not equal larger size of the body part (lips and finger tips are small yet they are largely represented on the primary somatosensory cortex)
What is the reason behind more cortical sensory area devoted to particular parts of the body over others?
A larger representation on the sensory cortex means the body part has a More Highly Specialised Sensory Function (more cortical area devoted to it)
-More Sensitive
-More able to localise sensation specifically (Discriminative)
-Greater discrimination and precision
-More receptors
Large number of receptors = larger representation on homunculus =/= does not equal larger size of the body part (lips and finger tips are small yet they are largely represented on the primary somatosensory cortex)
How many neurons do the Sensory neuron pathways consist of?
3
1st order neuron
2nd order neuron
3rd order neuron
How many neurons do the Motor neuron pathways consist of?
2 mainly - UMN + LMN
3 sometimes - UMN + interneuron + LMN
What does the Primary Motor Cortex do?
Primary motor cortex controls the movement of muscles CONTRALATERALLY (on the opposite side of the body to the brain) Highly Organised and Intricate system Organised via homunculus Controls VOLUNTARY movements Contains Upper Motor Neurons (UMNs)
What does the Cerebellum do?
Cerebellum controls the Co-ordination of movements, as you do them, at every point in time, IPSILATERALLY (on the same side of the body to the brain(cerebellum))
What does Contralaterally mean?
Control on the OPPOSITE side of the body to certain area
-Majority of brain control is contralateral
Esp:
- 1 motor cortex
- 1 somatosensory cortex
NOT cerebellum
What does Ipsilaterally mean?
Control on the SAME side of the body to the certain area
- ONLY ONE region in the brain has Ipsilateral control (all the rest contralateral control)
- is the CEREBELLUM
What are Upper Motor Neurons (UMNs)?
UMN’s cell Bodies are located in the 1 Primary motor area and Premotor area
Axons extend down through brain (pyramidal/corticospinal tract) and spinal cord(lateral or ventral corticospinal tract)
UMNs extending down through Lateral Corticospinal Tract =70-90%
UMNs extending down through Ventral Corticospinal Tract =10-30%
Extend to the specific area of the body which is required to move
Terminate in Ventral gray horn, either directly onto LMN or onto Inter Neuron
Are LARGE PYRAMIDAL cells
LArge cell bodies
Long and Myelinated axons
Oligodendrocytes - as in CNS Central NS - increased Insulation and Conduction
50ms-1 –> 100ms-1
Organised in the Primary Motor Cortex via the Motor Homunculus
Controls voluntary Movements
Tells LMN when to Fire, to give Smooth movements
CNS –> effector muscles
Pathway: 1 Primary Motor cortex –> Internal capsule (big fat fibre tract) –> Crus Cerebri of Midbrain (big fat fibre tract still) –>(Pyramidal/Corticospinal Tract)–> Pons (in separate fasicles) –> Pyramid of Medulla (in ventral bulges called pyramids) –> Spinal Cord –> a. pyramidal decussation and then Lateral Corticospinal Tract (70-90%) b. no decussation and instead down Ventral Corticospinal tract (10-30%)
What does the internal capsule directly translate to?
Capsule = Fibre bundle
is a Big Fat fibre bundle Tract
What does Capsule mean?
Fibres bundle
What is another name for pyramidal cells?
Upper Motor Neurons (UMNs)
What is another name for the Pyramidal Tract?
Corticospinal Tract
What is another name for the Corticospinal Tract
Pyramidal Tract
What is the Pyramidal/Corticospinal Tract?
1000 or so fibres
Highly organised
Compact motorway
AXONS of UPPER MOTOR neurons (UMNs) come together to form a Nerve Bundle
In the Brain and brainstem (following is ventral and lateral corticospinal tract in spinal cord)
What is the Upper Motor UMN Axon pathway like in the Crus if Cerebri of Midbrain?
Within the Internal Capsule
So Big and Fat Thick pathway
In the Crus of Cerebri of the Midbrain
What is the Upper Motor UMN Axon pathway like in the Pons?
broken up into fasicles
What is the Upper Motor UMN Axon pathway like in the Medulla?
Recollected after Pons
Begins its pyramidal shape formation
Form VENTRAL BULDGES called Pyramids
Pyramid of Medulla Oblongata
What is the uppermost decussation of UMN’s called?
Pyramidal decussation
What do neurons C5-C7 control?
arms
forearms
fingers
What is the Lateral Corticospinal Tract?
70-90% of all UMNs undergo pyramidal decussation and go down the Lateral Corticospinal tract
Decussation at the Medulla, to the Opposite side of the body
- at the pyramids
-Massive decussation, involved Millions of fibres
Towards Spinal cord
Pathway is the biggest at the top, as neurons peel to terminate off to their respective effector muscle under dermatomes as the spinal cord goes down
Precise, Agile and highly skilled movements - (hands and finger tip’s movements)
Towards muscle in the Distal parts of limbs
Where is the Lateral Corticospinal Tract the thickest?
Pathway is the biggest/(containing the most UMN axons) at the top, as neurons peel to terminate off to their respective effector muscle under dermatomes as the spinal cord goes down
What is the trend of termination for UMNs?
Terminate in Ventral gray horn
Either directly onto LMN or onto Inter Neuron
The majority of UMNs terminate directly on LMNs, but also a significant number terminate onto interneurons
UMNs extending down through Lateral Corticospinal Tract =70-90%
UMNs extending down through Ventral Corticospinal Tract =10-30%
Where does every UMN terminate?
Ventral gray horn of the spinal cord
What is the pathway of muscle innervation beginning at cortex?
1 Primary Motor Cortex –> UMN –> (interneuron) –> LMN –> Synaptic Junction –> Motor End Plate –> Effector Muscle/Organ/Cell
What is a Lower Motor Neuron LMN?
PNS
Large
Cell bodies in Ventral Gray horn
Myelinated -conduction and insulation
Schwann Cells
50ms-1
Grouped according to the muscles groups they supply
undergo a Synapse with UMN at the Ventral gray horn
Lower Motor LMNs are critical for PROVIDING the OUTput from the CNS –> skeletal muscle fibres
What nervous system is the UMN part of?
Central CNS
-therefore myelinated by Oligodendrocytes
What nervous system is the LMN part of?
Peripheral PNS
-therefore myelinated by Scwhann cells
Are Lower Motor Neurons LMNs grouped?
Yes
Lower Motor Neurons LMNs are grouped according to the muscle groups that they supply
What are Upper Motor Neurons critical for?
Highly specialised movments
Where to UMNs axons extend to?
specific area of the body which is required to move
via Co-ordinated Specific muscle contractions
What must Upper Motor Neurons UMNs receive in order to produce smooth, co-ordinated muscle movements?
From the THALAMUS, must receive very Refined, Complex information about When, How Many, How Often to send impulses out, in order to produce, Smooth, Co-ordinated muscle movements
What forms the Pyramidal/corticospinal tract?
UMNS
they for the corticospinal/pyramidal tracts via the Pyramidal pathway, via the Internal Capsule (DEEP) of the cerebrum
Where is the Internal capsule located?
cerebrum
What is the pathway of Upper Motor N?
1 Primary motor cortex –> Internal capsule (big fat fibre tract) –> Crus cerebri of Midbrain (big fat fibre tract still) –>(Pyramidal/Corticospinal Tract)–> Pons (in separate fasicles)–> Pyramid of Medulla (in ventral bulges called pyramids) –> Spinal Cord –> a. pyramidal decussation and Lateral Corticospinal tract.(70-90%) b. no decussation and then down Ventral corticospinal tract (10-30%)
What is the Ventral Corticospinal Tract?
10-30% of all UMNs DONT pyramidal decussate and Instead go Straight down the Lateral Corticospinal tract
Decussation is at the Level of the Spinal Cord, via the AWC Anterior White Commissure
Fibres REMAIN Ipsilateral (same side of the body) Until muscle
responsible for Co-ordinating movements of the Axial skeleton
Goes to the muscles in the Trunk and Proximal parts of the limbs
What is thicker: Ventral or Lateral Spinothalamic Tract?
Lateral
What is the role of the Lateral Spinothalamic Tract?
Responsible for movements which are:
Precise, Agile and Highly skilled
e.g. hand or fingertip movemnts
What is the role of the Ventral Spinothalamic Tract?
Responsible for Co-ordinating movements in the Axial skeleton
goes to the muscles in the Trunk and the Proximal parts of limbs
What co-ordinates the movements of the Axial skeleton?
Ventral Spinothalamic Tract UMN neurons (10-30% which don’t decussate at the medullary pyramidal decussation)
Does the Trunk or Leg have a larger representation on the Motor homunculus?
LEG has a greater representation
Leg>trunk (tiny)
Why are Upper Motor Neurons UMNs critical?
UMNs are critical at transferring the highly important and specific information from the cortex to the LMN
Why are Lower Motor Neurons LMNs critical?
LMNs are critical for PROVIDING the OUTput from the CNS –> to skeletal muscle fibres
What does the Thalamus talk to?
1 cortexes
What is the VP nuclei of the Thalamus involved in?
Sensory INput information
2nd order Sensory neuron termination
Ventro Posterior Nucleus of the Thalamus
On the inner part of the thalamus (closer to midline)
What is the VAVL nuclei of the Thalamus involved in?
its neuron Controls/Tells that UMN the Motor OUTput information for effector muscles/co-ordinated movement
VAVL itself (before UMN) is affected by Basal Ganglia and Cerebellum
Ventro Anterior Ventro Lateral Nucleus of the Thalamus
Outer part of the thalamus
What input does the VAVL get?
2x Thalamic inputs
from the Basal Ganglia (GPi)
from the Cerebellum (cerebellar cortex) N
What is the Cerebellar cortex?
Cerebellum’s (little brain’s) cortex
What is the Cerebral cortex?
5-7mm thick gray matter covering the brain (cerebrum)
What is a Spastic Paralysis?
Pyramidal Tract
lesion in the UPPER Motor UMN
-still hasn’t decussated by the brain stem
Results in:
1. Increased Reflexes (heightened involuntary movements)
2. Decreased Precision of Voluntary movements (more crude)
3. Increased Tone and Increased Rigidity (muscles are continually contacting causing increased stiffness and tightness)
-patients may or may not know or feel the continuous contractions
Becomes HypERsensitive and Spasms occur
Lost input into the Lower Motor Neurons, so the LMN is very sensitive to input from other areas such as the brainstem and other reflexes (no interference from other motor pathways (non-voluntary inputs))
Lesions occur in association with spinal cord injuries (brain trauma)
What is Flaccid Paralysis?
can be caused by the Polio Virus (disease of LMN)
Lesion in the LOWER motor Neuron LMN
There are NO Neural Pathways to the Effector Muscle!! therefore:
Results in:
1. No reflexes (voluntary or involuntary)
2. No Movement (muscles flop)
3. Decreased Tone of muscles (wasted away) (characterised by wasted muscles, weakness, paralysis) (DISUSE ATROPHY)
disuse atrophy is the waste/degeneration of muscles/cells/organs, and therefore these muscles are no longer used (NO TONE and NO NEURAL INPUT)
Overall there is NO NERVE IMPULSES (neural input) AT ALL as the path to the LOWER MN (LMN) is now Impaired
What is the Polio Virus?
Disease of the Lower Motor Neuron LMN
Leads to Flaccid paralysis
causes Disuse Atrophy
What is Atrophy?
Waste/Degeneration of body tissue/cells/organ
DISUSE atrophy occurs in Flaccid Paralysis
characterised by:
1. waster muscles
2. weakness
3. paralysis (flaccid)
What 3 things does Flaccid paralysis result in?
- No reflexes
- No movement
- Decreased Tone -Wasting away of muscles – Disuse Atrophy
What 3 things does Spastic paralysis result in?
- Increased reflexes (hypersensitive an spasms)
- Decreased Precision (more crude) of Voluntary movements (More Crude movements)
- Increased Tone, + increased rigidity (more stiff and tight as the muscles are continually contracting/in a more partially contracted state)
What is an Ataxia?
damage to the Cerebellum, Spinal Cord and Peripheral Nerves
Results in:
1. Un-co-ordinated movements
2. Loss of balance
Disorder in Muscle co-ordination due to Damage to the cerebellum such as Trauma or Disease
What is spastic paralysis caused by?
Lesion in Upper Motor Neurons
What is flaccid paralysis caused by?
Lesion in the Lower Motor Neuron
could be Polio Virus
What is Ataxia caused by?
Damage to either 3 things
Damage to the Cerebellum, or Spinal cord or Peripheral Nerves
What is Paraplegia caused by?
Spinal cord injury
What does ataxia result in?
2x:
- Unco-ordinated movements
- Loss of Balance
What sort of Ataxia does the cerebellum result in?
IPSIlateral ataxia
Affects the same side of the body as the brain
- as the Cerebellum is the only part of the brain which controls activity on the same side of the body
What sort of Ataxia does the Spinal cord or Peripheral nerve result in?
CONTRAlateral ataxia
loss of movement co-ordination and balance on the opposite side of the body to side of damage
What is Paraplegia?
Damage to the spinal cord Results in: 1. Paralysis 2. Loss of sensation Causes an impairment of BOTH Sensory AND Motor function In the LOWER extremities
What causes Paraplegia?
Damage to the spinal cord
What does Paraplegia result in?
Results in: 1. Paralysis 2. Loss of sensation Causes an impairment of BOTH Sensory AND Motor function In the LOWER extremities
What can you deduce the paralysis to be if the lesion is in the Same side?
Spastic Paralysis: UMN
- 1 motor cortex
- brainstem = brain
- still hasn’t decussated therefore still opposite
What can you deduce the paralysis to be if the lesion in on the Opposite side?
EITHER
- Spastic Paralysis : UMN
- Spinal Cord - some UMN some LMN - Flaccid Paralysis - LMN
- Spinal Nerve - EFFECTOR
Is a Spastic Paralysis always on the opposite side?
No
Same side if the lesion is in the Brain stem/brain, as hasn’t decussated to opposite side
OR
Opposite side if lesion is in the Spinal Cord - Some UMN some LMN
Is a Flaccid Paralysis always on the opposite side?
Yes
Flaccid Paralysis: LMN
spinal NERVE lesion
affects the Effector
What are the 3x motor-neuron systems of the brain?
- Pyramidal System
- Basal Ganglia System
- Cerebellar System
What is the role of the 3x Motorneuron systems of the brain
The INput the a LOWER Motor LMN RECEIVES involves the 3x motorneuron systems
to CO-ORDINATE and CONTROL movements
-when and how to fire
-when and how to do movements
What does the Basal Ganglia Motor Neuron System consist of?
4x groups of Nuclei 1. Striatum (caudate nucleus + putamen) \+ 2. Globus Pallidus (GPinterna + GPexterna) \+ 3. Subthalamic Nucleus (SUT) \+ 4. Substantia Nigra (Snc + Snr)
What does the Striatum consist of?
Caudate Nucleus
Putamen
is divided into two parts bt the internal capsule
-is one of the two main nuclei of the Basal Ganglia
What does the Globus Pallidus consist of?
GPi
GPe
-is one of the two main nuclei of the Basal Ganglia
What does the Sub-thalamic nucleus consist of?
SUT
What does the Substantia Nigra consist of?
Snc = pars compacta Snr = pars reticulata
Where is the Substantia Nigra located?
in the Midbrian
What isn’t seen on the cross section/is in the Midbrain?
Substantia nigra
What are some features of the Snc?
Substantia Nigra pars Compacta In the Midbrain Contains all the pigmented cells More Compact cells Makes the Substantia Nigra Black
What are some features of the Snr?
Substantia Nigra pars Reticulata
In the Mid brain
No pigmented cells (doesn’t contribute to colour)
More Dispersed cells
What is the Pyramidal system?
Directly gives information from the UMN –> to the LMNs
responsible for Precise Voluntary movements
Lesion in the UMN would result in Spastic Paralysis
What is the Pyramidal system responsible for?
Voluntary movements that are Precise
What is the Basal Ganglia System?
2 main nuclei are the Striatum and the Globus Pallidus
Controls how the UMN works and functions
Receives input from the cerebral cortex
Output is to –> Prefrontal premotor and motor cortices, VIA the Thalamus
Involuntary movements –> Huntington’s disease
Releases Inhibitory Neurotransmitter GABA (-) via the Thalamus
What are some features of the Substantia Nigra?
Located in the Midbrain Black More distinct "black Substance" Is affected in Parkinson's disease
What is the Cerebellar system?
Controlled by the Cerebellum (little brain) at the Base of the brain
contains Billions of Neurons
Cerebellum controls the Same side of the body (exclusively the only part of the body which has ipsilateral control)
Releases Excitatory neurotransmitter Glutamate
What is the combination which produces perfect co-ordinated smooth movements?
combination of the relase of Basal Ganglia’s/Gpi’s GABA inhibitory neurotransmitter and Cerebellum’s/Cerebellar systems Glutamate excitatory neurotransmitter release
What are some features of the striatum?
divided into 2 x parts by the Internal capsule(the big white matter tract which allows the passage of axons from the cortex to the thalamus)
Gets input from the substantia nigra
No direct input/output between the spinal cord and basal ganglia
-Striatum is largely controlled by motor areas of the frontal cortex
What is the striatum largely controlled by?
Motor areas of the frontal cortex
What is the pathway of the corticospinal tract?
UMN from the cerebral cortex –> via the LMN to/down the spine
What are some features of the Thalamus?
Divided into the VP(for sensory Input) and VAVL(for motor Output)
Complex Relay system
an Intermediate between the brain’s target organ’s/ structures
Processes information
Relays information on sensory information form the periphery of the brain
What 4x things does the Basal Ganglia system do?
- Initiate and Terminate Movements (GABA release)
- Muscle Tone (readiness of movement so not flying everywhere)
- Memory and Planning of movement (initiation of impulses)
- Mood and Movements (muscle emotional expression -espec. Face, and some hands)(integrates with projections from other areas
What is the characteristic symptom of Huntington’s disease?
INvoluntary movements
Basal Ganglia is affected
What are the 3x characteristic symptoms of a lesion in the Basal Ganglia?
- Rigidity
- Tremor at rest
- HypOkinesia (decreased movement)
What neurotransmitter does the Basal Ganglia release?
GABA
inhibitory
from the GPi
What 3x things does the Cerebellar system do?
Cerebellum (little brain) contributes to:
- Posture
- Balance
- Co-ordinates movement (as you do them - at every point in time) (avoids over or undershooting)
What are some features of the cerebellum(little brain)/Cerebellar system?
90% of the cells in the brain are located in the cerebellum, as the are packed Very tightly and are Very small
contain Purkinje fibres
If an athlete is working, she is training her cerebellum in particular , as well as basal ganglia, to retain movement which is co-ordinated
What does an athlete do in training?
If an athlete is working, she is training her cerebellum in particular , as well as basal ganglia, to retain movement which is co-ordinated
Where is the major of the brain’s’ cells?
90% of brain cells are in the Cerebellum (little brain)
as the cells are SMALL and VERY TIGHTLY PACKED
What are the 3x characteristic symptoms of a lesion in the Cerebellum?
- Ataxia (loss of co-ordinated muscle movement)
- Loss of Balance
- Intention tremor (loss of co-ordinated muscle movement)
- Looks to be drunk
What neurotransmitter does the Cerebellum release?
Glutamate
Excitatory
(Cerebellar system)
What could someone have if they were characteristically acting as if they were drunk?
Lesion in the Cerebellum which controls balance and coordination of movement (avoids ataxia and intention tremor)
Involving the motor neuron systems, where do the excitatory and inhibitory neurons get released?
VAVL nucleus of the Thalamus
which then effects the Cerebral cortex with the UMN
