Download Movement

Movement
Movement
• Basic Muscle Physiology
• Control and Coordination of
Movement
• Movement as a behavioural measure
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
Basic Muscle Physiology
The following steps are involved in muscle contraction:
(1) The sequence of events leading to contraction is initiated
somewhere in the central nervous system, either as
voluntary activity from the brain or as reflex activity from
the spinal cord.
(2) A motor neuron in the ventral horn of the spinal cord is
activated, and an action potential passes outward in a ventral
root of the spinal cord.
(3) The axon branches to supply a number of muscle fibres
called a motor unit, and the action potential is conveyed to a
motor end plate on each muscle fibre.
(4) At the motor end plate, the action potential causes the
release of packets or quanta of acetylcholine into the
synaptic clefts on the surface of the muscle fiber.
Basic Muscle Physiology
• Acetylcholine causes the electrical resting potential under
the motor end plate to change, and this then initiates an
action potential which passes in both directions along the
surface of the muscle fiber.
(6) At the opening of each transverse tubule onto the muscle
fiber surface, the action potential spreads inside the muscle
fiber.
(7) At each point where a transverse tubule touches part of
the sarcoplasmic reticulum, it causes the sarcoplasmic
reticulum to release Ca++ ions.
(8) The calcium ions result in movement of troponin and
tropomyosin on their thin filaments, and this enables the
myosin molecule heads to "grab and swivel" their way along
the thin filament. This is the driving force of muscle
contraction.
Basic Muscle Physiology
• Contraction is turned off by the following sequence of
events:
(9) Acetylcholine at the neuromuscular junction is broken
down by acetylcholinesterase, and this terminates the
stream of action potentials along the muscle fiber surface.
(10) The sarcoplasmic reticulum ceases to release calcium
ions, and immediately starts to resequester all the calcium
ions that have been released.
(11) In the absence of calcium ions, a change in the
configuration of troponin and tropomyosin then blocks the
action of the myosin molecule heads, and contraction ceases.
(12) In the living animal, an external stretching force, such
as gravity or an antagonistic muscle, pulls the muscle back to
its original length.
Basic Muscle Physiology
Control and Coordination
• Spinal Cord Circuits – These are the neuronal circuits
that make up the final common pathway for the
regulation of skeletal muscle contraction and relaxation.
All central, or higher order, regulation of movement must
be mediated through these neurons.
• Descending Systems – These are neural systems whose
output neurons have direct synaptic contact with the
motor neurons of the spinal cord. They can be broadly
subdivided into two categories: primary and pre motor
cortex.
• Brainstem – There are multiple nuclei located in the
brainstem that are responsible for integrating sensory
information (vestibular, somatosensory, visual) with
descending motor commands to control balance and
posture.
Control and Coordination
Pyramidal System
• Motor Cortex – As with the
sensory cortical areas, the
motor cortex is subdivided
into primary and secondary
motor areas. These areas,
particularly the primary motor
cortex, project directly to
the motor neurons in the
spinal to control muscle
contractions directly. The
motor cortical areas are
somatotopically organized and
lie anterior to the central
sulcus.
Control and Coordination
Extrapyramidal system
Regulatory Systems – These
are neural systems that do
not have direct access to the
spinal motor neuron pools.
They can exert control over
movement by affecting the
systems that do. They also
fall into two general
categories: basal ganglia and
cerebellem
Control and Coordination
• Basal Ganglia – This is collection of brain regions located
behind the thalamus. They function to provide regulatory
input to the motor cortex via the thalamus. They are
thought to regulate some of the higher order aspects of
motor planning and timing.
• Cerebellum – This is a large structure that provides input
to multiple levels of the motor system including the spinal
cord, brainstem, thalamus and motor cortex. This system
is involved in multiple aspects of motor coordination and
control (explosive movements and automated aspects of
walking).
Movement as a behavioural
measure
Movement is often the only measure that experimental psychologists
have to independently observe or verify behaviour.
For example:
– Child behaviour can often only be studied by observing their movement.
– Stress, joy, sadness, play and work are often more accurately displayed
by one movement than by answering a questionnaire that may
“artificially” ascertain a psychological behaviour.
– Also animal studies rely entirely on watching quantifying and
interpreting movement
Consider the following examples:
One would consider this
posture to convey sadness
of some sort…..
And no matter what this
person said to us we would
be more convinced by the
person’s movement than
their words
Whereas these movements are meant
to convey fear
And even animals convey their love or happiness
through certain kinds of movement
Spatial Memory tests
• Movement is required to act out a test of
memorizing where a place (or location is).
• A favourite test of this is a Morris water
maze.
• So lets imagine the following experiment
….
Our experiment
• You want to know if stress effects the
acquisition of memory
• Your hypothesis is
• “Acute stress will prevent the acquisition of
a learned task that requires spatial memory.”
Our experiment
• The stress : predator smell will be presented
to rats in a cage where they cannot escape.
• The test: they will be tested to see how they
perform in a Morris Water maze.
• What is a morris water maze?
Our Experiment
Platform
Rat
Our experiment
First Trial
After Learning
Our experiment
• Control
Trials to learn : 8
Time to find platform: 32.3 s
Stress
15
62.2 s
Our conclusions
•
•
•
•
•
Stress increased time to learn
But the task took longer too
SO WHAT DID OUR EXPERIMENT MEASURE?
Is there a confound because there were movement deficits
Thus a separate set experiments to assess movement would
be required.
– Inclined ladder
– Roto rod