Lecture 4 - The Motor Systems of the Brain Flashcards
What are some features of the Motor Cortex?
Motor Homunculus
representation is proportional to the complexity of control over those muscles (dexterity of the muscles)
millions of large neurons
Upper Body Neurons
lie right o top of the brain
spread throughout the central/primary motor cortex
Somatopical map in the cortex
Relative proportions
More cortical areas is devoted to muscles involved in Skilled, Complex or Delicate Movements
What does the order of representation represent?
Complexity of control or The degree of dexterity that you have over these muscles
Degree of precision
over 1/3 face
large area (1/3.5) hand
More CORTICAL area is devoted to muscles involved in SKILLED,COMPLEX or DELICATE movements
Where do you think/generate the idea of a movement?
Pre Frontal Area
What is the UMN?
Upper Motor Neuron
large number of neurons
large cell bodies
long and Myelinated Axons
Cell bodies are in Primary Motor Area AND Pre-Motor Area
goes through the Pyramidal/Corticospinal Tract
Excites the Lower Motor Neurons
What is the Corticospinal Tract?
Pyramidal Tract (southern motorway)
Axons=continuation of cell bodies which are in the cortex
Axons of UMN come together to form nerve bundle
atleast 1 million fibres
cortex–> midbrain–> pons–> medulla–> spinal cord
dorsal decussation at medulla=Pyramidal decussation
ventral decussation at spinal cord
Where is the Dorsal decussation and what is the tract the impulse proceeds through?
at the medulla
then after Anterior White Commissure proceeds down the Lateral Corticospinal Tract
(70-90%)
Where is the Ventral decussation and what is the tract the impulse proceeds through?
at the spinal cord
same level as the input
then after decussation proceeds down Ventral Corticospinal Tract
(10-30%)
How many fibres are needed to contract a muscle?
millions
therefore one is insufficient
What are some features of the sensory cortex?
Sensory Homunculus
representation is proportional to the number of specialised sensory receptors within the corresponding body part
larger representation in the 1 somatosensory cortex means that a body part has a more Highly SPECIALISED Sensory Function, so more of the cortical area is devoted to it
e.g. lips > trunk
more sensitive = larger # receptors
Why is the Corticospinal Tract essential?
pathway of control of Voluntary movements
millions of impulses going down
different groups of fibres going down at different rates
Motor information coming out of the brain is critical to everyday movements
Made up of Longitudinal bundles
What happens as the UMN exits the motor cortex?
The have to pass through the singular exit
INTERNAL CAPSULE of the cerebrum (IC->midbrain->pons)
bundles in the midbrain (corticospinal tract)
break up into a number of fibre bundles at pons
become solid bundle is the medulla and looks like a pyramid
ventral bulges = pyramids
When at spinal cord decussation occurs of the Dorsal root, crossing to other side of spinal cord
What is the Lateral Corticospinal Tract?
70-90% of UMNs take this pathway
Decussate at Medulla Pyramids=
PYRAMIDAL Decussation=
-massive decussation of millions of fibres
-to Contralateral (opposite) side of the medulla
Towards spinal cord
Precise, Agile and Highly skilled movements
-hand movements,fingertips
to muscles in the DISTAL parts of limbs
What is the Ventral Corticospinal Tract?
10-30% (fewer) of UMNs take this pathway
Decussate at the Spinal Cord Level= via the Anterior White Commissure = fibres REMAIN on the Ipsilateral (same side) and continue down until reach spinal cord “late crosses”
Termination=
a. directly at the LMN
b.indirectly via little InterNeurons which then project onto LMN
responsible for co-ordinating movements of the AXIAL skeleton
LONG pathway=to muscles in the TRUNK and PROXIMAL part of limbs
What do lesions result in in a general sense?
loss of movement
What would you decide if there was a lesion in the opposite side of the body which has a loss of movement?
SPASTIC paralysis No voluntary/precise movements UpperMN=spastic 1 motor cortex opposite=Brainstem/brain lesion
= because still hasn’t decussated
What would you decide if there was a lesion in the same side of the body?
could be 2 options a. SPASTIC Paralysis No voluntary/precise movements UMN spinal cord = some LMN + all UMN
b. FLACCID Paralysis
LMN
Spinal nNerve=effector
What happens to the Pyramidal/Corticospinal Tract at the Pons?
Tract breaks up into fasicles
Longitudinal bundles
What is the importance of the Ventral Gray Horn?
Upper Motor Neurons Terminate at the level of the spinal cord at the Interneuron
Synapse with LMN’s are at the Ventral Gray Horn
Inner Fibres = upper part of body
Outer Fibres = lower part of body
=HIGHLY ORGANISED
What is the function of Lower Motor Neurons?
UMNs terminate at the level of the spinal cord at the interneuron or at the LMN
synapse with the LOWER.M.N. is at the Ventral Gray horn
LMN provide OUTPUT from CNS –> out too skeletal muscle fibres
(terminate on MOTOR-End-Plate)(ACh)
What is the trend regarding extensions off the Lateral Corticospinal Tract?
further down spinal cord =more fibres come off = smaller corticospinal tract
(upper-most region = contains all fibres)
What would happen if the Lateral Corticospinal Tract was compressed (e.g. by a blood-pressure blockage/tumour)?
lower motor neurons = no info from motor cortex= paralysis
caused by stroke
What does Spastic Paralysis result in and where does the Lesion occur?
INability to do Voluntary or Precise movements
Increased Reflexes
Lesion in UpperMN (UMN Lesion)
LMN no longer gets input from UMN/motor cortex, therefore doesn’t know which muscle to activate -when and what to use
Lots of motor neurons terminate on the LMN, lots from Dorsal Root which have to do with REFLEXES=
OTHER INPUT = has a big impact on LMN
Hypersensitive=exaggerated movements=reflexes heightened=LOCAL Reflexes= difficulty doing precise movements ONLY CRUDE movements
What does Flaccid Paralysis result in and where does the Lesion occur?
Trauma or characteristic infection which results in lesion of LOWER Motor Neuron
POLIO Virus literally kills LMN= output to muscles are inhibited= loss of innervation to muscles = no impulses to move
Loss of impulses to muscle=Floppy muscle=no movements/just lies there
No impulses= No reflexes= No Movement= Decrease in size (gets thinner/wastes away) = cannot move limb
What are 2x critical pathways?
Lateral Corticospinal Tract
LMN
What is the Pyramidal System?
=Corticospinal System
Directly gives info via UMN to the LMN
responsible for VOLUNTARY movements which are PRECISE
Disfunction of Pyramidal System= inability to complete precise movements = Lesion in UMN = Spastic Paralysis = crude movements only
LMN lesion=Flaccid paralysis
Why system controls how UMNs work and function?
Basal Ganglia System
What are the Motor Systems of the brain?
Pyramidal system
Basal Ganglia system
Cerebellar system
3x motor neuron systems which provide LMN input, that coordinates and controls movement
What are the main parts of the Basal Ganglia?
4x main groups
(large) Caudate Nucleus Putamen =STRIATUM (can touch and feel)
GLOBUS PALLIDUS
=pale
1x External part + 1x Internal part
=GPe + GPi
underneath Thalamus= SUT=
SUB-THALAMIC NUCLEUS
lies upon midline(midline)
SUBSTANTIA NIGRA
“substance black”
What is the Basal Ganglia System?
Striatum (caudate-nucleus&putamen) + Globus Pallidus (GPe&GPi) + Sub-Thalamic Nucleus + Substantia Nigra
are all connected to one another
major OUTput of the B.G.M.S=Thalamus
Control of movement is at VA-VL = Ventral Anterior and Ventral Lateral = large area involved in bringing information in about movement control
controls how the UMN works and functions INITIATION of movements
controls TONE of muscles (certain degree or contraction or relaxation)
controls MEMORY and PLANNING
controls mood and movement (converting how you FEEL, to CONVEY MOOD through your muscles)
receives input form cerebral cortex
output is to prefrontal premotor &motor cortices (via the thalamus)
releases INHIBITORY neutoransmitters (GABA) to the Thalamus
Diseases which effect the Basal Ganglia: Parkinson’s disease + Huntington’s Disease = INVOLUNTARY MOVEMENTS
What is the VA-VL?
Ventral Anterior and Ventral Lateral = large nucleus where you can map all area of muscle
the part of the Thalamus which is a LARGE area which is involved in bringing in information about MOVEMENT CONTROL
tells when to fire
“motor-analysis centre”
Then talks to motor cortex
What is the major Input which tells when to fire?
VA-VL part of the Thalamus –> MOTOR CORTEX
gets info from Basal Ganglia
What are diseases which effect the Basal Ganglia?
Huntingtons Disease
Parkinsons Disease
What is the Cerebellar system?
Involved with movement
at the Base of the Brain
Billions of neurons
Feeds into same area of the Thalamus as does the Basal Ganglia (VA-VL), but provides POSTURE(co-ordinates muscle in your back) and BALANCE information which CO_ORDINATES movements of muscles so that they are PRECISE and CORRECT
side of cerebellum controls SAME SIDE of the body, and is the ONLY PART of the brain which controls activity on the same side
Communicates with Thalamus and UMN
COMPLEMENTS basal ganglia
releases Excitatory neurotransmitters : e.g. GLUTAMATE
What is the Thalamus controlled by?
How to fire and WHEN to fire Basal Ganglia (for initiation and tone) and Cerebellar (for co-ordination and precision)
What is Ataxia?
Damage to the Cerebellum, Spinal Cord and Peripheral Nerves.
e.g. Trauma or Disease
Results in UN-COORDinated muscle movements and LOSS of BALANCE
(like when drunk and alcohol effects your cerebellum)
Ipsilateral ataxia: same side of body
What side of the body does the CEREBELLUM co-ordinate?
CEREBELLUM is the only part of the brain which controls activity on the SAME SIDE of the body
What is Ipsilateral Ataxia?
Ataxia which is on the same side of the body as the effected side of the cerebellum
Fibres to lower motor neuron go STRAIGHT DOWN
What are some differences between the motor systems of the brain?
different functions
different effects when they’re effected by pathology
What is Paraplegia?
Spinal cord injury
Results in paralysis and loss of sensation
Impairment in motor and/or sensory function in the LOWER EXTERMITIES
What balance is present in your VA-VL?
Mixture of inhibitory neurotransmitters released by the basal ganglia and excitatory neurotransmitters released by the cerebellum
balance so info passing through UMN is precise –> precise muscle movement
-fine tuning
Which sides of the body do the Basal Ganglia and Cerebellum control?
Basal Ganglia controls opposite sides(contra)
Cerebellum controls the same side (ipi)
-up DO cross
-down to LMN DONT cross
