Movement

Basic Muscle Physiology Control and Coordination of Movement Movement as a behavioural measure Movement

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 Rat Platform

Our experiment First TrialAfter Learning

Our experiment Control Stress Trials to learn : 8 15 Time to find platform: 32.3 s 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