BG
Role of BG
activates a set of particular movements while suppressing others
Caudate + Putanum
Striatum
-
Receives input from:
Motor cortices (M1, premotor)
Thalamus
- Inputs are generally excitatory
Substantia Nigra
Located within the midbrain of the brainstem
Black pigment gives it it’s name
2 parts:
◦ Pars Compacta (SNpc) ◦ Pars Reticulata (SNpr)
FUNCTION
Involved in background communication with subthalamic nucleus
Produces dopamine to send signals to the striatum
REWARD
Behavioral flexibility
recognition of social disapproval, self-regulation, maintaining attention
Behind scenes of DP
Substantia nigra compacta sends dopamine to the striatum→further increases the inhibitorymessages sent to the GPi→further increases excitation of the thalamus
Subthalamic nucleus excites the substantia nigra, increasing this process
When desired movement has been achieved, substatia nigra communicates back to the subthalmaic nucleus to stop the process
BG Overview
Large collections of nuclei (4) in both hemispheres Help plan and control complex movement patterns Feedback loops within the motor cortex
Caudate Nucleus
Anatomy - Large C-shaped structure that begins just behind the frontal lobe
Has head, body, and tail
Almost completely encircles the remaining nuclei
Function - involved in planning and execution of movement
feedback processor
plays a role in repetitive movement
Nucleus Accumbens
Receives input from prefrontal cortex via VTA Sends input back via the globus pallidus
Involved in reward circuitry, pleasure, motivation, decision-making
Limbic
reward-guided behaviors, identifying the value of stimuli
Indirect pathway overview
Goal = increased inhibition of thalamus so it can’t send excitatory input to motor cortex
turn down motor system
BG function
Regulation of movement
-initiating and planning
-suppression of unwanted movement
* output generally inhibitory
Putamen
Anatomy
"shell"
lies under and behind the front of caudate
Function
Involved in coordinating automatic behaviors:
Riding a bike
Driving a car
Working an assembly line
Motor
regulating muscle contraction/force, organizing multi-joint movements, sequencing of movements
What roles do the following play for movement?
Motor cortex (B4)
Premotor cortex (B6)
Thalamus
initiate movement
planning movement
relay center to send msg
IP sequence
Motor cortex projects to striatum (excitatory)
Striatum sends inhibitory message to globus pallidus external, turning it down
*GPe is now unable to inhibit the subthalamic nucleus→STN gets excited and firing increases
STN sends more excitatory messages to GPi→GPi gets excited and firing increases
GPi sends more inhibitory messages to the thalamus
Thalamus sends less messages to the motor cortex
Less messages = less movement
How does Bg influence movement
BG has no direct pathways to LMNs, therefore it can NOT initiate movement
-it influences movement by communicating with UMN in cortex
Globus Pallidus
Anatomy-
"Pale globe"
located just inside the putamen
2 parts- internal and external (direct & indirect)
Function
Receives input from striatum
Provides outputs to the substantia nigra & thalamus
Also has communications with subthalamic nucleus
Suppresses thalamus to prevent unwanted movements!
Oculomotor
regulating eye movements, initiating fast eye movements
Overview of Direct Pathway
With BG control, the thalamus inhibits movement
Goal: stop inhibition of the thalamus (VA & VL nuclei) on the motor cortex
ID pathway behind the scenes
When desired movement has been achieved, substatia nigra communicates back to stop the process
Subthalamic nucleus excites the substantia nigra compacta
BG nuclei
1. Caudate Nucleus
2. Putamen
3. Globus Pallidus
4. Subthalamic Nucleus
Sometimes included/ closely associated:
Substantia Nigra
Nucleus Accumbens
Subthalamic nucleus
Anatomy
Lens Shaped Nucleus
Sits under the thalamus in diencephalon
Function
Receives main input from the globus pallidus
Communicates with substantia nigra (background)
Exec Function.
decision making for goal directed behavior (in context)
DP Sequence
Motor cortex projects to striatum (excitatory)
Striatum sends inhibitory message to globus pallidus internal, turning it down
*GPi is now unable to inhibit the thalamus→thalamus gets excited & firing increases
Thalamus sends excitatory messages to the motor cortex
Motor cortex sends excitatory messages to skeletal muscles
Muscles contract→movement occurs
GABA and Glutamate ?
- and +