Transcript Evolution of brain and behaviour

Movements and actions
Chapter 11
Movements vs actions
•Movements are brief unitary activities of muscle
•Reflexes
•Postural adjustments
•Sensory orientation
•Actions are complex, goal-oriented sets of movements
•Walking
•Gestures
•Acquired skills (speech, tool use, etc.)
There is a complex relationship
between movements and actions
Old idea was that actions are collections of
reflexes chained together
Counterexamples abound:
Spooner’s ‘Queer old dean’
Control systems theory and
movement
1. Closed-loop movements: Information flows
from whatever is being controlled back to the
device that controls it
2. Open-loop movements: Ballistic movements
where once movement is initiated, there is no
opportunity for feedback – accuracy is
controlled through anticipation of error.
Overview of neural control of
movement
Movements are constrained by
the skeletal system
Muscles control the actions of the
skeletal system
-antagonists
-synergists
The composition of muscles
The neuromuscular junction
Innervation ratios and neural
integration
Motor unit=a single motor axon and all muscle
fibres it innervates
Innervation ratio = # motorneurons/#muscle fibres
High innervation ratio means each motorneuron
innervates only a few muscle fibres (oculomotor or
finger muscle)
Low innervation ratio means each motorneuron
innervates many muscle fibres (leg)
The importance of sensory
feedback
Proprioception=information about body movements
and positions
“Pride and a Daily Marathon”
-patient with viral infection that attacked parts of dorsal
roots that gave kinesthetic information
-had to completely relearn to move in a new way that
depended on visual feedback (turn off lights – falls
down)
Receptors for movement
Muscle spindles signal muscle
length
Golgi tendon organs signal
muscle tension
John Hughlings-Jackson and the
motor system as the Royal Navy
The royal navy is organized as a hierarchy, but each
level has some autonomy
-if the admiral dies, all the ships on the sea don’t
suddenly stop
The motor system is organized as a hierarchy, but
each level in the hierarchy has some autonomy
-if the hierarchy is beheaded, we don’t stop all
movement
Spinal reflexes mediate automatic
responses
-withdrawal, stretch, scratch are movements
organized at the spinal level
-animals with spinal cord transections can support
weight and even generate some of the patterned
muscular contractions required for walking
Brainstem organization for
movement: The extrapyramidal
system
Decorticate animals can still move:
Walking, feeding, grooming, sexual behaviour are
all, in some ways, intact
Circuitry involved is mostly in the reticular
formation of the brainstem
Overview of neural control of
movement
Cortical organization for
movement
-Frau
Hitzig’s dressing table
-the Jacksonian march of spasm
Orderly representation in motor
cortex
Outputs from cortex: The
pyramidal system
Beyond MI: Supplementary and
premotor cortex
Apraxia
Ideomotor apraxia – inability to carry out a simple motor
activity in response to a verbal command
Ideational apraxia – inability to carry out a sequence of
actions that are components of a behavioural script
-anatomy is very complex (most
strokes cause some degree of
apraxia
-may involve disconnection of
motor cortical areas from the
rest of cortex
Basal ganglia and movement
The basal ganglia are best thought of as a massive
feedback loop
-receive huge input from cortex, process this input
and then send output to motor cortex
-thought to control amplitude and direction of
movments
-especially important in producing remembered
movements
-most known because of involvement in
Parkinson’s disease
Cerebellar contributions to
movement
1. The cerebellum is a modular structure
2. One part of the cerebellum is involved in
posture and balance (ataxia)
3. Another part of the cerebellum is involved
in producing precise timing in neural
“programs” for the control of skilled
movement
Overview of neural control of
movement