Basal Ganglia Flashcards
What is basal ganglia made up of
Caudate nucleus Putamen Globus pallidus (external/internal) Substantia nigra (SNc/SNr--> compact/recticular) Subthalamic Nucleus
What makes up the corpus striatum
Caudate nucleus and globus pallidus
what makes up the straitum
caudate nucleus and putamen
what makes up the lentiform nucleus
Putamen and globus pallidus
what are the segments of the globus pallidus
internal and external/medial and lateral segment
What are the parts of substantia nigra
Pars compacta–> contains dopaminergic neurons that contain melanin
Pars reticularis: contains gamma-aminobutyric acid (GABA)-ergic neurons
Where is the substantia nigra located
midbrain
Why is substantia nigra black
It releases dopamine, and a by product of dopamine in a healthy brain is melanin
What kind of dendrites do cells in the striatum have
Cells have ‘shiny dendrites’
What info does striatum recieve
recieves cortical afferents
mainly from M1 and S1 and projects efferents to GPi/SNr
Where does the globus pallidus lie
between putament and internal capsule (medial)
What are the 2 nuclei of globus pallidus
- Lateral/external–> GPl/GPe
- Medial/Internal–> GPm/GPi
What does the GPi do
gathers many bits of information including movement-related activity from the striatum
What does the GPe do
Integrates info from GPi
GPm/GPi are functionally identical to what
SNR
what are most neurons in GP immunoreactive to
GABA–> therefore probably not NT
Where is the substantia nigra located
midbrain
What are the 2 sub-nuclei of SN
- Substantia nigra reticular part–> SNr
- Substantia nigra compact part–> SNc
What do neurons in SNc produce
Dopamine
-carried to striatum and used there as a NT
Where do neurons in GPi/SNr project to
thalamus
superior colliculus
reticular formation of brainstem
Where is the subthalamic nucleus located
lies just medial to internal capsule and ventral lateral to thalamus
what are cells in subthalamic nucleus immunoreactive to
glutamate and may use it as a transmitter
What side does the basal ganglia circuitry occur
ipsilateral side of the brain–> hence basal ganglia affects function mediated by the ipsilateral motor cortex
what side does movement from circuitry occur on
Output/movements affected on contralateral side
Corticospinal tract crosses at medualla oblongata
Describe the connections of the basal ganglia
Fibres from cerebral cortex to striatum
- striatum sends fibres to GP or to STN then to GP
- GP sends fibres to ventral thalamus
- thalamus sends fibres back to the principle motor areas of cerebral cortex
what is disinhibition
a decrease in inhibition
decreasing inhibition–> possibility of more excitation
What is the main purpose of direct pathway
increases motor activity
What is the main purpose of indirect pathway
decreases motor activity
What affect does the GPi normally have on thalamus
thalamus is normally under inhibition from the GPi
Explain Direct pathway
Read notes
Explain dopamine modulation of direct pathway
Read Notes
Explain Indirect Pathway
Read notes
Explain dopamine modulation of indirect pathway
Read notes
what projection neurons use glutamate
projection neurons in cortex, subthalamic nucleus and VA/VL of thalamus
What is the effect of glutamate
excitatory
What projection fibres use GABA
projection fibres in striatum and both segments of GP
what is the effect of GABA
inhibitory
what is the overall effect of the dopaminergic modulation on the pathways
increase in motor activity
what is the result of the cholinergic modulation on the pathways
decrease in motor activity
What is the blood supply to the caudate nucleus
ACAp
MCAp
Look at pics!!!!!!!!!
What is the blood supply to the putamen
ACAp
MCAp
Look at pics!!!!!!!!!
What is the blood supply to the GP
AChA (anterior choroidal artery–> branch on internal carotid artery)
MCAp
Look at pics!!!!!!!!!
What is the blood supply to the SN
PCAp
PcoAp
Look at pics!!!!!!!!!
What is the blood supply to the STN
PCAp
PcoAp
Look at pics!!!!!!!!!
define akinesia
loss or impairment of the power of voluntary movement; loss of ability to move muscles voluntarily
Define dyskinesia
abnormality or impairment of voluntary movement; unwanted involuntary movement
define bradykinesia
slowness of movement and is the cardinal manifestation of Parkinson’s disease; slow movement and an impaired ability to move body shiftly on command
define rigidity
the quality or state of stiffness or inflexibility, abnormal stiffness of muscle not allowing it to bend or be bent
What do lesions of the basal ganglia cause/affect
Don’t cause paralysis
-Affect the quality of movement–> disturbance in the initiation or cessation of motor activity
Result of a lesion is dyskinesia–> hypokinetic/hyperkinetic
What are motor disturbances characterised by
involuntary movement
alterations in muscle tone
disturbances in body posture
What are hypokinetic disorders
- bradykinesia/hypokinesia–> slowness in beginning of movt, reduced ROM and force of movement
- Reduced or absent emotional response
- loss of balance
- loss of postures associated with skilled motion
- usually accompanied by muscular rigidity and tremor
What are hyperkinetic disorders
hyperkinesia–> excessive motor activity, release of motor patterns at inappropriate times/continuously
What do involuntary movements consist of
choreiform movement athetoid movement ballismus disorders dystonias dyskinesias
What does a lesion to subthalamic nucleus result in
- Loss of excitatory STN projections= disinhibit thalamus
- failure to surpress some cortical outputs
- hyperkinetic disorder
What does a lesion to SN result in
Loss of dopamine neurons–> can excite direct and inhibit indirect pathway
-hence decreased activity of direct and increased activity of indirect
-enhances output of GPi/SNr
inhibition of thalamus
decreased out–> bradykinesia/hypokinesia
-hypokinetic disorder
Define Chorea
continuous series of rapid, idependent, jerky involuntary movements that are fragments of purposeful movement; associated with atrophy of striatum
Define Dystonia
another type of involuntary movement where, in extreme form, joints are forced into a locked position for a long period by extreme contraction of antagonistic muscle groups
define athetosis
- uncontrolled writhing
- One spontaneous movement blends into the next creating constant sinuous and purposeless motion
- Usually involve hands and face
- Movements are frequently combinations of alternating antagonistic motions such as supination/pronation
define tics
- type of uncontrollable compulsive behaviour
- Like the movements of chorea, tics are quick fragments of a purposeful movement.
- They differ from chorea in that they are endlessly repeated in a stereotyped manner
What are S&S huntington’s disease
hereditory (autosomal dominant)–> chromosome 4
chronic progressive -chorea (jerking uncontrolled movt)
dystonic posturing
dementia
memory loss
psychological changes–> impulsiveness, moodiness, antisocial behaviour
-gradual physical, mental and emotional changes
What are S&S of parkinsons disease
resting tremor rigidity bradykinesia mask-like face (expressionless) slow festinating gait systemic symptoms--> depression, dementia, autonomic symptoms (sweating, dysphagia, orthostatic hypotension)
Is parkinsons disease a hypo/hyperkinetic disorder
- hypokinetic
- insufficient direct pathway output
- excess indirect pathway output
is huntington’s disease a hypo/hyperkinetic disorder
- hyperkinetic
- excess direct pathway output
- insufficient indirect pathway output
what is the pathology of parkinson’s disease
- Decrease in the number of nerve cells in the substantia nigra pars compacta and pedunculopontine nucleus
- Subsequent decrease in available dopamine
- Loss of dopamine to the putame, reduces activity in motor areas of the cerebral cortex, decreasing voluntary movements.
- Loss of pedunculopontine cells, combined with increased inhibition of the PPN, disinhibits the reticulospinal tracts, producing excessive contraction of postural muscles
what is the pathology of huntingtons disease
• A hereditary disorder that causes degeneration in many areas of the brain
what are the effects of huntington’s disease on the striatum and cerebral cortex
oAtrophy of the striatum
oCaused by faulty gene on chromosome 4
oAffects areas of the brain involved in emotions, intellect, and movement
what are the effects of huntington’s disease on GABA neurons
• Loss of striatal GABAergic neurons
o GABAergic = inhibitory NT
o This overall reduction of inhibitory structures results in an overall increase in excitatory stimulus being passed through to the CST via the motor cortex.
o Therefore, causes an increase in motor activity (Hyperkinetic disorder)
what is the effect of lesions of basal ganglia
- do not cause paralysis, but affect the quality of movement: in that there is disturbance in the initiation or cessation of motor activity
- The result of a lesion to the basal ganglia is unwanted involuntary movement - dyskinesia: hypokinetic or hyperkinetic.
- Motor disturbances are characterised by involuntary movements, alterations in muscle tone, and disturbances in body posture
what are different types of hypokinetic basal ganglia movement disorders
o Parkinson’s Disease Akinetic/Rigid Parkinson’s Disease Tremor-Dominant Parkinson’s Disease o Parkinson-Plus Syndromes o Parkinsonism
what are different types of hyperkinetic basal ganglia movement disorders
what are different types of hypokinetic basal ganglia movement disorders