-
1
Dental Neuroanatomy Suzanne S. Stensaas, Ph.D.
Marcjh 8, 2011 Reading: Waxman pp. 141-146 are not very helpful!
Computer Resources: HyperBrain, Chapter 12
THE BASAL GANGLIA
Objectives: 1. What are the main manifestations of Basal Ganglia
disease? 2. Be able to contrast signs and symptoms of:
• Basal Ganglia Disease • Cerebellar Disease • Corticospinal
Tract Disease = Upper motor neuron • Motor Neuron Disease = Lower
Motor neuron
3. Identify the structures involved in: • Huntington's Disease •
Parkinson's Disease
I. Introduction
A. General features of the basal ganglia, one of our 3 major
motor control centers:
1. Involved in motor, cognitive and affective tasks 2. Do not
project directly to targets below the midbrain 3. Act mainly on the
premotor cortex via the thalamus, similar to cerebellum.
B. What Do the Basal Ganglia Do?
1. We are beginning to understand that there are more than 3
different loops or parallel circuits and functions (motor,
cognitive and affective) all influenced by a dopaminergic
mesencephalic system.
2. The only one we will focus on is the motor loop. Motor
pattern generators permit voluntary movements to take place in what
seems like an automatic manor.
3. Normally the BG are the “brakes” on the voluntary motor
system. 4. Selectively facilitate some movements and inhibit
others, and/or
compare commands for movement from the precentral motor cortex
with proprioceptive feedback from the movement in progress.
5. Play a role in initiating internally generated movements C.
Definitions 1. Basal ganglia a. Corpus striatum 1. Caudate \ = the
striatum 2. Putamen / 3. Globus pallidus = the pallidum
b. Though technically not part of the basal ganglia, the
subthalamic nucleus and substantia nigra are presented with the
basal ganglia because of their connections and involvement in
disease.
-
2
2. Lenticular nucleus is an old descriptive term for the
lens-shaped gray matter
just lateral to the internal capsule; it includes both the
globus pallidus and putamen. Another term is lentiform, even more
confusing. Avoid using either term.
-
3
From The Digital Anatomist Interactive Brain Syllabus. John
Sundsten and Kate Mulligan, Univ. Washington School of Medicine.
1998 ©
Source: Kandel?
-
4
II. Connections of Basal Ganglia A. The caudate and putamen are
a single entity that is divided by the anterior limb of the
internal capsule. Both have similar connections, cell types and
neurotransmitters. There is evidence that the caudate is more
involved in cognitive functions and the putamen more with motor
functions
B. Striatal Afferents 1. From the Cerebral CORTEX:
Corticostriate afferents
Nearly every region of the cerebral cortex sends axons to the
ipsilateral caudate and putamen. See diagram by Dr. Voron next
page
(a. Visual cortex projects to the tail of the caudate and cells
there respond to complex patterned visual stimuli.) b. Frontal
cortex projects to the head of the caudate; therefore, this part of
the caudate responds to environmental stimuli that are important in
preparing for movement.
2. From the SUBSTANTIA NIGRA: Nigrostriatal afferents. These
neurons use dopamine as their neurotransmitter. See diagram by Dr.
Voron next page
C. Striatal Efferents – Globus Pallidus. See diagram by Dr.
Voron next page
D. Efferents to Thalamus: The Globus Pallidus –
1. Pallidothalamic axons terminate in thalamic nuclei. In
different region
from the axons coming from the cerebellum. Myelin stained
section through thalamus and BG, Stensaas
E. The Thalamic nuclei project to the premotor and supplementary
cortex in front of the precentral gyrus.
-
5
F. The premotor and supplementary motor cortex is a region
important in planning movements.
1. Premotor cortex is the part of area 6 on the lateral surface
of the
hemisphere in front of the precentral gyrus. 2. Supplementary
motor cortex is the part of area 6 on the medial surface
of the hemisphere. . 3. These areas then project to area 4 (the
precentral gyrus), primary motor
cortex and hence to the corticospinal tract.
III. Striatal Motor Functions The striatum is thought to link
sensory cues to motor behavior integrating nearly all the activity
occurring in the cortex.
1. Many reciprocal connections (subthalamus and globus pallidus,
substantia nigra and striatum).
2. A role in initiating internally generated movements like
associated
movement when walking.
3. Interplay of inhibition and excitation results in normal
motor behavior. Interruption of either the Direct or Indirect
pathways results in decrease or increase in movement. We call these
diseases: Movement disorders which usually occur at rest.
© Stephen C. Voron, M.D., 2004
Excitatory (Glu):
Cortex, Subth Nuc, VL ThalInhibitory (GABA):
Striatum, GPe, Gpi/(SNr)Both inhibitory and excitatory:
SNc: dopamineStriatum interneurons: ACh
Indirect pathway - Inhibits extraneous movementDirect pathway -
Facilitates intentionalmovement
-
6
IV. Basal Ganglia Diseases-Often called Involuntary Movement
Disorders. There may be an increase or a decrease in movements
depending on the disease and structures involved.
A. Involuntary movements during wakefulness. In general there
are POSITIVE (hyperkinetic) signs such as rigidity, chorea,
athetosis, resting tremor, etc.
In addition there are NEGATIVE (hypokinetic) sympto ms such as
akinesia, bradykinesia, masked face, decreased blinking, loss of
associated movements, difficulty planning movements.
B. Basal ganglia disease is relatively common and results from
release (or
disinhibition),
Suzanne Stensaas©
C. Parkinson's disease was the first example of a neurological
disorder with a molecular basis. It is a slowly progressive
disorder characterized by bradykinesia (trouble initiating
movement), festinating gait, resting tremor, lead pipe or cogwheel
rigidity, and masked facies. .
1. Substantia nigra (pars compacta) contains pigmented
dopaminergic neurons that project to the striatum; the dopamine has
the general effect of facilitating movement.
2. In Parkinson's disease, >70% of dopaminergic neurons in
the substantia nigra die. There is also neuronal loss in other
monoamine-containing nuclei, but the nigrostriatal dopamine loss is
considered most important for the movement disorder. This loss in
turn affects the direct pathway
3. L-DOPA therapy increases dopamine and provides significant
improvement in movement in many patients.
-
7
D. Huntington's disease is an autosomal dominant disorder (CAG
repeat)
resulting in degeneration of cholinergic and inhibitory
GABAergic neurons in the striatum and cerebral cortex, probably via
glutamate-mediated excitotoxic mechanisms. Huntington's Disease
usually includes choreoathetosis, dementia, and death within 10-20
years of the onset of symptoms. No specific treatment is available.
Disease is often diagnosed after reproductive years reached and
offspring produced.