Quiz 4: Lecture: Basal Nuclei- Motor Circuitry Flashcards
What is the basal nuclei also called?
Cerebral nuclei
What is the basal nuclei?
Masses of gray matter; embedded in white matter of cerebrum
What does the basal nuclei do?
Direct subconscious activities
The basal ganglia are the principal component of a family of subcortical circuits linking the _____ with the _____ _____.
thalamus; cerebral cortex
The 4 functions of the basal nuclei are:
▪ The initiation of voluntary movement
▪ The coordination of learned movement patterns (walking, lifting)
▪ The subconscious control of skeletal muscle tone
▪ Participation in cognitive functions, mood, non-motor behavior
The main 5 subdivisions of the basal ganglia are:
- Caudate
- Putamen
- Globus pallidus (with two functionally distinct parts:
external and internal pallidal segment) - Substantia nigra
- Subthalamic nucleus
What are the two functionally distinct parts of the globus pallidus called?
external (GPE) and internal (GPI) pallidal segment
Which two parts are collectively called the striatum?
Caudate (-nucleus; head) and Putamen
What is the caudate involved in?
Non-hippocampul memory
What are the two components of Substantia nigra?
Pars compacta and Pars reticulara
What is the Substantia nigra pars compacta?
Melanin made in synthesis of dopamine
What is the Substantia nigra pars reticulara?
GABAminergic neurons
What makes up the basal ganglia (5 parts)?
Caudate nucleus, putamen, globus palladus (GPe, GPi), subthalamic nucleus (STN), and substantia nigra (SN)
What is the thin membrane located at the midline of the brain between the two cerebral hemispheres, or halves of the brain called?
Septum pellucidum
Lateral view of the basal ganglia
Top left: Head of caudate nucleus
Bottom left: Amygdaloid body
Top right: Lentiform nucleus
Bottom right: Tail of caudate nucleus and thalamus
What two parts make up the Lentiform nucleus?
Putamen, globus pallidus
What is the dural fold in the middle called?
Falx cerebri
What means “sickle” in Latin?
Falx
Where is the superior saggital sinus and inferior saggital sinus located?
The superior saggital sinus is above the Falx cerebri and inferior saggital sinus is more inner.
The internal capsule sends which information up and which information down?
Sensory info up, Motor info down
What is in the space between the thalamus?
Third ventricle
What is the major input nucleus to the basal ganglia?
Striatum
The striatum is composed of:
• Caudate nucleus
• Putamen
• Ventral striatum (including Nucleus accumbens)
What are the structures of the basal nuclei?
▪ Caudate nucleus (Curving, slender tail)
▪ Lentiform nucleus (Globus pallidus, Putamen)
How is the tail of the caudate nucleus located?
Laterally to avoid running into the thalamus
The C-shaped _____ _____ is located _____ and forms part of the wall of the _____ _____.
Caudate nucleus; medially; lateral ventricle
The head of the caudate nucleus is located _____ the _____ _____ _____ and it is separated from the _____ by the _____ limb of the _____ _____.
above; anterior; Substantia perforata
Putamen; anterior; internal capsule
The Putamen lies _____ to the _____ _____ and _____ to the _____.
laterally; Caudate nucleus; medially; Insula
Left basal ganglia dorsal view:
Left to right: Body of caudate nucleus, Head of caudate nucleus, Tail of caudate nucleus, Putamen, Internal capsule
The Pallidum (Globus pallidus) consists of two functionally distinct subdivisions:
the external (GPe) and internal (GPi) pallidal segment
The GP has a _____ _____ onto the _____ to _____ it.
resting discharge; thalamus; inhibit
The _____ _____ _____ represents one of the _____ _____ _____ of the basal ganglia.
internal pallidal segment (GPi); major output nuclei
Both GPE and GPi are:
inhibitory
What are the parts of the basal ganglia (5 parts)?
Head of caudate nucleus, body of caudate nucleus, Putamen, Globus pallidus, Tail of caudate nucleus
The _____ _____ is located between the _____ (cranially) and the _____ part of the _____ _____(caudally)
Subthalamic nucleus (STN); thalamus; anterior; Substantia nigra
The _____ is the only component of the basal ganglia sending _____ _____.
STN; excitatory output
How is the STN located?
Posteriorly
Where is the Substantia nigra (SN) located?
in the rostral midbrain
SN has two histologically and functionally distinct components:
Pars compacta, Pars reticularis
Pars compacta (dorsally) - contains what?
• Pars reticularis (ventrally) - contains what?
Pars compacta: contains dopaminergic neurons
• Pars reticularis: contains GABA-ergic neurons
Superior colliculus function:
Visual movement
Hyperdirect pathway contains what?
Myelinated fibers
Direct pathway function:
directs;facilitates movement
Indirect pathway function:
Inhibits movements
What happens when the direct and indirect pathway work together?
They facilitate some cortical areas while inhibiting others.
Direct pathway
Cortex [excitatory]> CPu (SNc [excitatory] to CPu) [inhibitory]> GPe [inhibitory]> GPi [thin inhibitory]> Thalamus [excitatory]> Cortex [excitatory]> Cortical output
Indirect pathway
Cortex [excitatory]> CPu (SNc [inhibitory] to CPu) [inhibitory]> GPe [inhibitory]> STN [excitatory] to > GPi and SNr [both inhibitory] > Thalamus [thin excitatory] > Cortex [thin excitatory] cortical output
CPu stands for
Striatum (caudate and Putamen)
D1R is a
receptor
Direct pathway has unmileanated meaning
slow
What does inhibit GPi mean?
basal inhibition of the thalamus
What parts are used in respiration?
Pons and medulla
Disinhibit would
increase
Making movement leads to:
disinhibition of the thalamus
Indirect pathway is
Center surround (facilitate movement in one and inhibit other areas)
Huntingtons disease is from
Indirect pathway
SNc is
GABA-ergic
In indirect pathway,
disinhibition of GPe would mean more inhibition of STN so less output (less excitation, less output)
Indirect pathway would
increase output so undesired movements
Parkinson’s disease
Degeneration of Substantia nigra so D1R (Direct pathway)
Huntingtons disease
Striatum (D2 receptors so Indirect pathway)
Tardive dyskinesia results in:
Involuntary and repetitive movements
Tardive dyskinesia medication:
Dopamine receptor blocking medications lead to receptor supersensitivity
Tardive dyskinesia is
Rare (less than 200k per year)
Tardive dyskinesia (treatment and diagnosis)
May lead to punding
Treatable
Differential disgnoses : HD, CP, Tourette’s, dystonia
Tardive dyskinesia is a neurological disorder that results in
Involuntary and repetitive movements
Cocaine acts in the striatum
For both cocaine and meth, the uptake into the striatum paralleled the subjective effects reported. Cocaine primarily bound in the striatum. Meth also extended to many other areas and had a longer duration.
Cocaine acts on the striatum can be seen through
PET scans (radioactive sugar added)
(Entire brain is always metabolically active)
Increased D2R following abstinence
D2R availability increases with abstinence suggesting adaptation rather than cell death. Behavior did not parallel D2R recovery.
Looking at meth users’ recovery with abstinence
Looking at D2 receptor; have to increase dosage (effective dose/lethal dose)
Will crash if cut cold-turkey
D2R binding as a biomarker for addiction
Successful responders to treatment were found to have higher D2 levels than those who had relapsed.
Low D2R associated with high impulsivity
D2R correlates with trait impulsivity. Lower D2R = most impulsive.
(Problem: Did drug use cause a decrease in D2R or did low D2R/high impulsivity make them more likely to use drugs?)
Genetic variation may affect smoking cessation
Individuals with one genotype (left) released more dopamine during the smoke break than those with another genotype (right). Suggests genetics makes smoking more rewarding for some than others.
Which of the following is NOT one of the basal nuclei?
• Caudate nucleus
• Globus pallidus
• Putamen
• Hippocampus
• Amygdaloid body
Hippocampus and Amygdaloid body (limbic system)
The cerebrum
Motor and Sensory Areas of the Cortex
What separates the motor and sensory areas?
Central sulcus
Motor areas (3):
Precentral gyrus of frontal lobe, Primary motor cortex, Pyramidal cells
Precentral gyrus of frontal lobe function
Directs voluntary movements
Primary motor cortex:
– is the surface of
Precentral gyrus
Pyramidal cells:
– are
neurons of primary motor cortex
Primary motor cortex location
precentral gyrus of the frontal lobe
primary motor cortex posterior limit:
central sulcus, which separates the precentral gyrus from the postcentral gyrus (primary somatosensory cortex)
Primary motor cortex anterior limit:
Precentral gyrus
Primary motor cortex inferior limit:
lateral sulcus (Sylvius)
The primary motor cortex is contiguous with:
paracentral lobule on the medial aspect of the cerebral hemisphere
The cerebrum lateral view:
Left to right: Precentral gyrus, Frontal lobe (left cerebral hemisphere), Lateral sulcus, Branches of middle cerebral artery, Temporal lobe, Pons, Medulla oblongata
Central sulcus, Postcentral gyrus, Parietal lobe, Occipital lobe, Cerebellum
Components of the Primary Motor Cortex
Paracentral lobule, Central sulcus, Precentral gyrus
There is a precise somatotopic representation of the different body parts in the primary motor cortex:
foot and leg areas located close to the midline; head and face areas located laterally on the convexity of the cerebral hemisphere (motor homunculus)
The size of the cortical representation for a specific body part is proportional to
the complexity of the movements performed by that particular body part
(ex: surface of hand area is significantly larger than foot area)
Primary motor cortex:
Leg area
Face Area; Hand Area
Leg area: Paracentral lobule
Face area: central sulcus (?)/ Precentral gyrus
Hand area: Precentral gyrus
The motor system is organized _____:
hierarchically
spinal cord, brainstem and forebrain contain successively more complex motor circuits
The primary motor cortex controls:
voluntary movement; projects to the brainstem and spinal cord motor neurons (lower motor neurons) via the corticobulbar and corticospinal tract respectively
The activity of the motor cortex and brainstem is influenced by which two parts?
Basal ganglia and cerebellum
Eye movements (subdivisions of the frontal lobes)
Top to left: Motor, Premotor, Frontal eye fields, Dorsolateral; Broca’s area; Orbital
The components of the corticospinal tract:
Corticospinal tract, Precentral gyrus (primary motor cortex), Internal capsule
The corticospinal tract (CST) is:
a massive collection of axons originating in the giant pyramidal cells (Betz), in the layer V of the primary motor cortex
The axons of the CST converge in the
posterior limb of the internal capsule
At the level of the midbrain, the CST occupies
the ventral aspect of the cerebral peduncle; the fibers continue their descent through the ventral pons and ventral medulla oblongata
What forms the corticobulbar tract?
The axons that synapse with motor neurons in the (mostly) contralateral cranial nerve nuclei (III, IV, VII, IX, X, XI, XII)
At the level of the lower medulla oblongata, most (ca. 80%) of the corticospinal axons cross over to the contralateral side (pyramidal decussation), and then continue their descent through the brainstem and spinal cord as the
lateral corticospinal tract
The CST axons that do not cross at the medulla level continue their travel down the
spinal cord as the ventral corticospinal tract; most of these fibers cross over to the contralateral side shortly before reaching their target, the lower motor neurons, located in the anterior horn of the spinal cord
Motor system diagrams
1- top to bottom: motor cortex, cerebral peduncle, corticospinal tract, pyramids, lateral c.s. tract, anterior c.s. tract
2- left to right: postcentral gyrus, central sulcus, precentral gyrus
Motor systems diagrams 2
1- top to bottom: cortex (internal capsule, corticospinal tract), midbrain (cerebral peduncle), middle pons (collaterals to reticular formation, pyramid), caudal medulla (pyramidal decussation, spinal cord)
[Lateral corticospinal tract, alpha motor neuron)
2- top to bottom: Dendrites, Cell body, Axon, Direction of message, Axon terminals synapse with dendrites on target cell, Axon
What are the 2 sensory areas of the Motor System?
Postcentral gyrus of parietal lobe, primary sensory cortex
Postcentral gyrus of parietal lobe function
receives somatic sensory information (touch, pressure, pain, vibration, taste, and temperature)
Location of Primary sensory cortex:
surface of postcentral gyrus
Somatisensory function (Somatosensory Tracts)
top to bottom: Primary somatosensory cortex, Ventral posterior nucleus of thalamus, Medial lemniscus, Midbrain (bold), Nuclei of the dorsal columns, Medulla (bold), Spinothalamic tract (pain, temperature), Dorsal columns (precise touch, kinesthesia), Dorsal root ganglion, Spinal cord (bold)
