BASAL GANGLIA 1: INTRODUCTION
TO THE MOTOR SYSTEMS
Readings for the Basal Ganglia section:
Carlson: Chapter 8: 272-278, 264-269, 285-
289, 277-282 (motor systems), Chapter 15:
537-543, 533-540 (BG disorders); Olanow
(therapy); Dunnett et al. (early transplant
article); Bergman et al. (early DBS/surgery
Functions of the Motor System
Cortical Motor Areas
Descending Motor Pathways
Further Terms / Definitions
Progress of the Course 1. DEFINITIONS
Motor system – produces movement
• We’re going to focus on voluntary movementthrough striate muscles.
i) neuron in ventral horn of spinal
grey that attaches to the muscles
(“primary” motor neuron)
• Motor neurons are down in ventral horn of spinal cord. Motor neurons can be
defined in two ways. Strictest definition is a neuron in the ventral horn of spinal
grey that attaches to the muscles. So runs from cell body in ventral horn of spinal
the muscle. This would also be called the primary motor neuron: the end of motoron
ii) neuron within three synapses of
the ventral horn neuron – that
yields motor evoked potentials
• Used in a freer sense, it’s a neuron within 3 synapses or so of this primary motor
neuron in the ventral horn.
• If you want to define it he says 3 synapses. But perhaps a better definition is that
had evoked potentials used to measure velocity of the nerves, the peripheral, we
nerves, so called compound potential. And we talked about evoked potentials
registered in primary centres of the brain (visual, auditory etc). Those are ways
you can watch the receptors in periphery of body recording into brain of sensory
systems. And when they’re looking for brain damage would use somatosensory
evoked potentials to see whether if they stimulate your legs would find evoked
potential in areas 3 1 or 2.
• We have sensory evoked potentials, also intracranial evoked potentials (left cortex
stimulationevoked potential in right cortex). Motor evoked potential – moving
the body by stimulating the brain
• Finally term evoked potential is applied in stimulating motor centre in brain and
observe body movement. Moving body by stimulating the brain. And a number of
places in the brains that can do this.
o mganglia (thought to be wired in a circuit with neocortex), red nucleus in
brain stem, and throughout reticular core of brain stem. When talked about
reticular core in arousal, talked about its ascending effects, but also has
descending which can move the body
2. FUNCTIONS OF THE MOTOR
• Talked about nature of life as being self producing molecule, and behaviour exists
because it interacts with environment to reverse entropy and maintain structure.
So teleological point of view is to act on…
Teleological – to act on the
environment to maintain life (to
Engineering – to adjust muscle
tension in relation to sensory input – to
adjust sensory input
• muscle tension to change sensory input. Now if you listen to neuroscientists
argue, ones that do sensory systems argue that whole brain is extended sensory
systems. And others argue the opposite. Probably the proper formation is including both. Essentially what motor systems do is to change sensory input
(hunger etc). Let’s work on that thought more.
- reflex – preset change
- with a reflex it’s a fixed change. If you you’re your arm out,
sensory input is saying gravity is trying to pull it down, and
monosynaptic response is to keep it in place: a simple reflex.
Essentially it’s a preset change; if you stick a needle in your
hand, it will move away. Once again, a preset change. In each
case, changing sensory input. We’ve given you defensive
reflexes that move you from harm, but what your muscles will
do is take you away from a bad stimulus. If you look at
swallowing, this would be a good thing, will swallow
involuntarily, once again an approach behaviour, a preset,
changing sensation in your mouth to your stomach. So reflexes
are simple preset changes and their job is to change sensory
- Instinctinve patterns are approach/avoidance behaviours
designed to maximize…
- instinctive pattern – maximize
(minimize) a sensation or
- in out of the cold. Behaviour will change sensory input. Andl come
when dealing with instinctive patterns change it in a way that is
predictable in other members of your species.
- purposive pattern – adjust
input to match an image of a
- Finally purposive pattern, in terms of discussion in this course
as thinking of imaging non-present objects. Imaging it and then
you will approach or avoid those non-present objects. If you’re
hungry, visualize what you’ll have for lunch and walk over there and get it. Change sensory input to what will be good for
you in the long run.
- So simple idea of engineering approach is we make
movements to change sensory input and the meaning of
that is to get things in environment that keep us alive!
3. CORTICAL MOTOR AREAS
(Figs. 8.8 and 8.13 in Carlson) - all “pre-
- motor cortex (M 1, Brodmann’s 4,
precentral gyrus, motor homunculus):
- “movements not muscles”
• Diagram of human brain: have central culcus, and precentrally have motor strip.
That’s brodmann’s 4, and then you’ll have supplementary motor area, and then
• B4 is motor strip specifically, also called M1 or precentral gyrus or motor
homunculus. Stimulating towards the top moves the toes or legs, lowerarms etc.
• It produces movements not muscles, meaning several muscles will move together.
If you want to move a muscle individually, go down to spinal cord, but in the
brain, will move as a group.
• The premotor areas and SMA are playing down on the M1. Some books will call
these areas Broadmann’s area 6. If m1 is a keyboard, B6 is playing the keyboard.
- supplementary motor cortex
(medial) (“motor association
• Moving on here which is more medial. It will be called motor
association cortex. Supplementary and premotor are called
motor association cortex, area in front of them is frontal association cortex. Part of frontal lobe specifically occupied with
movement but not the motor strip is motor association cortex.
• Looked this up on Wikipedia because prof was confusing: The
premotor cortex occupies the part of Brodmann area 6 that lies on
the lateral surface of the cerebral hemisphere. The medial extension
of area 6, onto the midline surface of the hemisphere, is the site of
the supplementary motor area, or SMA.
- ouputs to M 1
- behavioural sequences
• What does this do? Produce a series of movements, sequence is important.
Incidentally the stimulus for the next movement is the last movement.
- premotor cortex (lateral) (“motor
– inputs to M 1
• something that’s probably fairly specific to human beings. Its is
means that if he says would you look up, everyone would look
up. That’s arbitrary stimulus because it will depend on language
you use. Words are arbitrary stimuli and