Where do the anterior limb of the internal capsule and genu of the internal capsule carry fibres from?
From the DM nucleus of the thalamus to the frontal lobe.
What does the posterior limb of the internal capsule carry?
Sensory and motor fibres to/and from the sensory and motor cortex in the parietal and frontal lobes to their contacts in the thalamus, brainstem, and spinal cord.
How is the homunculus of the internal capsule organized?
The fibres from the upper limbs and head are closer to the genu while those in the lower limbs are further from the genu.
How do the fibres from the medial geniculate body to the auditory cortex travel to reach the auditory cortex?
The fibres going from the medial geniculate body to the auditory cortex dive under the lentiform nucleus in the sublenticular limb of the internal capsule to reach the auditory cortex.
Where do the visual fibres turn backward?
Backward in the retrolenticular limb of the internal capsule
What structures do the anterior limb of the internal capsule separate?
The lentiform nuclei (globus pallidus and putamen) from the head of the caudate nucleus
What structures does the posterior limb of the internal capsule separate?
Separates the lentiform nuclei from the thalamus
Where do the anatomical basal ganglia develop from?
What structures does it include?
Telencephalon
- Globus pallidus
- Putamen
- Caudate nucleus
- Subthalamus
- Substantia nigra
What does the basal ganglia do for the motor cortex?
Imposes constant inhibitory control over the motor cortex. It maintains that inhibition which it selectively removes to permit patterned and learned motor activity
All the programs are ready and in the computer, but they are held back until released to go.
Inhibiting (usual state) or disinhibiting (selectively allowing) motor patterns.
What happens if basal ganglia influence is lost? (If a lesion occurs)
Motor program is affected Lost: through disease or injury - unwanted motor patterns emerge
What do the basal ganglia influence?
Influence muscle tone, modify automated movement patterns, and suppress unwanted movement patterns, all through programming. This applies to muscles involved in articulation as well
What structures are involved with the basal ganglia?
Intralaminar, VA and VL nucleus of the thalamus (sensory-motor integration centre) Red nucleus (output to the extrapyramidal tracts) Reticular formation (output to the extrapyramidal tracts), Motor cortex Supplementary motor area (SMA)
How does the motor control centre influence the motor cortex?
Through the VA and VL of the thalamus. Also influences the extrapyramidal pathways through the reticular system and red nucleus
How does Parkinson’s arise?
Failure of production of dopamine (NT) in the cells (actually the cells die) in the substantia nigra BUT the problem is lack of the release of sufficient dopamine at their destination in the globus pallidus.
How can Parkinson’s be treated?
What happens if a person is over-treated?
Treatment by adding dopamine (L-dopa) through medication can improve the balance and reduce symptoms
Receive implantation of dopamine producing stem cells in the lentiform nucleus (where the NT is needed) or implanted stimulators.
- Over treated patient begins to look like the opposite problem, Huntington’s Chorea
What are the signs of Parkinson’s? (9)
Resting tremor (face or jaw; pill-rolling like movement
Shuffling gait
Dysphagia
Cogwheel muscular rigidity Expressionless ‘masked’ face
Bradykinesia
Stooped posture
Dyskinesia or akinesia Hypokinetic dysarthria
What is Huntington’s Chorea? How does it arise?
- Chorea means “dance”. Is a hereditary disorder associated with damage to the caudate nucleus and some changes in associated motor cortex.
- Imbalance of the neurotransmitters, particularly insufficient production of GABA which results in excess influence of dopamine
What are the signs of Huntington’s? (7)
Choreoform limb movements (face, tongue, pharynx)
Athetosis
Choreoform trunk movements, falling Dementia
Hyperkinetic dysarthria Dysphagia
Personality changes
Speech - appear intoxicated
What is Ballism?
How does it arise?
- Damage to the subthalamus and its bidirectional circuit with the lentiform nuclei. Often occurs on one side and is therefore often called Hemiballism
- Result from a loss of the facilitatory output from the subthalamic nucleus to the globus pallidus - sends more net inhibitory projections to the thalamus and to the motor cortex
What are the signs of Ballism?
Ballistic movements of arms
Ballistic movements of legs
Ballistic speech patterns
Speech is similarly affected
What is essential tremor?
What does it result from?
What are symptoms?
Presents as mild to intense resting tremor.
- Results from a low-threshold discharging system.
- Symptoms for resting – masked face, infrequent blinking, slow movement, disturbed equilibrium, impaired speech and swallowing
What is dystonia?
Where can it occur in the body?
- This can be considered a “fusing” of motor instructions. - Can occur to any muscles or muscle groups in the body. When it occurs in laryngeal muscles, this causes spasmodic dysphonia (a voice disorder),
What is athetosis?
What are signs?
- Lesions in the globus pallidus that produce slow twisting movements of limbs and trunk and muscle of speech, often associated with cerebral palsy
- Causes speech to become dysarthric
- Movements occur in a sequence so that they blend together to form a continuous action
What is the name for the lesion above/below the red nucleus?
Lesion above the red nucleus results in decorticate rigidity
Lesion below the red nucleus results in decerebrate rigidity.
What are some signs of decorticate rigidity?
What is the role of the red nucleus?
- Lesions above the red nucleus typical of stroke patients – in this case there is a flexion pattern of the arm and extension pattern of the leg. Increase in tone is moderate to heavy.
- Red nucleus is in the midbrain at the level of the superior colliculus and is responsible for constant reflex pattern of flexion of the upper limbs and extension of the lower limbs
Where is the lesion located in decerebrate rigidity? Signs?
- Lesion below the midbrain and above the vestibular system (between the midbrain and the pons) with the very strong spastic extensor pattern of arm and leg
How does motor learning work?
Is it part of memory for facts?
Motor learning is not part of memory for facts. When an individual is learning a motor task, they rely heavily on their sensory input, particularly proprioception. They must try the task to bring this element into the learning of the task
What is athetosis?
Slow, continuous, involuntary movements; repeating pattern; seen in some forms of cerebral palsy
What is dystonia?
Repeated of maintained co-contraction of hypertonic muscles
What is hypertonia?
Increased muscle tone due to increased activity in the tendon or stretch reflexes (spinal cord lesions) and from disinhibition of input from higher centres – can be present in both upper motor neuron lesions and motor control disorders
What is hypotonia?
Reduced muscle tone due to diminished influence on the gamma motor neurons
What is a spasm?
Sudden involuntary movements of large groups of muscles
What is spasticity?
Velocity-dependent increased resistance to passive movement
What is rigidity?
Velocity-independent increased resistance to passive movement
What is a tremor?
Rhythmic involuntary movements
- resting tremor – occurs at rest (Parkinson’s Disease)
- Intention tremor – occurs during movement due to impairment of the dampening of antagonist activity (cerebellar disease)