Motor System Flashcards
How are flexors and extensors arranged around the joint?
in an agonist/antagonist fashion
What are the 3 types of movement?
- voluntary (goal-directed)
- rhythmic motor patterns that require voluntary initiation and termination
- involuntary reflexes
What is the corticospinal tract?
the main tract for nearly all voluntary muscle activity
Where are neurons that supply the leg and foot muscles?
on the medial aspect of the hemisphere
Where are neurons that supply the hand and face?
on the lateral aspect of the hemisphere
What is the pathway of axons in the corticospinal tract?
- pass down through the internal capsule into the cerebral peduncles in the midbrain
- continue down the brainstem to reach the pyramids in the medulla oblongata
- cross to the opposite side and continue as the lateral corticospinal tract in the spinal cord
- at each level of the spinal cord, axons peel off and enter the ventral horn
- terminate by synapsing with lower motor neurons
What is the ventral corticospinal tract?
the axons that do not cross over at the medulla and continue down the spinal cord and peel off at each level to enter the ventral horn and terminate on the lower motor neurons
How do lower motor neurons send out their axons?
via the ventral roots
What are the corticospinal and rubrospinal tracts?
lateral systems that influence distal muscles
What are the vestibulospinal and reticulospinal tracts?
medial systems that influence axial and proximal muscles to maintain balance and posture
How do efferent fibres control different skeletal muscles and their movements?
on excitation, the efferent will release ACh at the synapse with the skeletal muscles which will act on nicotinic receptors leading to calcium influx and subsequent muscle contraction
What is the dorsal horn related to?
sensory activity (site of second order sensory neuron)
What is the ventral horn related to?
motor activity
What are the basal ganglia crucial for?
regulating and modulating motor functions, including movement initiation, coordination, and control
What are the 5 nuclei of the basal ganglia?
- caudate nucleus
- putamen
- globus pallidus
- subthalamic nucleus
- substantia nigra
What is the caudate nucleus involved in?
the regulation of voluntary movement and the integration of spatial information
What is the striatum?
caudate and putamen nuclei together
What is the putamen involved in?
regulation of autonomic and repetitive movements; also helps initiate and control gross motor activities
What is the globus pallidus involved in?
the regulation of voluntary movement, acting as a major output nucleus of the basal ganglia; influences the thalamus, which in turn modulates motor activity
What does the subthalamic nucleus do?
inhibit unwanted movements; important in the regulation of motor activity, particularly in modulating the activity of the globus pallidus and substantia nigra
What is the substantia nigra crucial for?
motor control, especially in the production of dopamine, which modulates the activity of the striatum
What is the order of motor hierarchy?
- cortex - voluntary movement
- brain stem - postural reflex and rhythmic motor patterns
- spinal cord - site of motor neurons that control muscle activity
What is the result of disrupting activity of the premotor cortex in humans?
the individual not knowing which series of actions to perform
What does increased activity of corticospinal neurons on flexor muscles do?
cause muscle contraction
Why will balance not be overly affected in a motor cortex lesion?
the brainstem is more involved with this, specifically the cerebellum
What can lesion of the vestibular nuclei result in?
inability to stand
What are the 2 disorders caused by damage to the basal ganglia?
- disorder of movement
- disorder of posture
Give examples of disorders of movement
- tremor at rest
- rapid flicking movements
- violent flailing movements
- athetosis/dystonia
- bradykinesia
How can PD arise?
loss of signalling in dopamine neurons in the basal ganglia
What does one motor neuron control?
multiple muscle fibres to form a motor unit
What is the relationship between number of motor units activated and force of movement?
the more motor units activated, the greater the fore of the movement
What do alpha motor neurons do?
provide motor control to the skeletal muscle
What is a reflex arc?
the neuronal circuit that directs the motor response and serves to protect muscles from overextending and to prevent damage to the body
What do reflex arcs consist of?
- sensory receptors
- sensory afferents (group 1a and II afferents)
- interneurons in the spinal cord
- motor efferents (alpha motoneurons)
What is the simplest type of reflex?
stretch reflex since it only contains one synapse on the alpha neuron on the spinal cord
What are the 6 steps of the stretch reflex?
- patella tendon is hit with a hammer
- extrafusal fibres in the quadriceps muscle stretch momentarily
- muscle spindles detect the stretch and send afferent signals up to the spinal cord where they synapse on the alpha motor neuron of the quadriceps muscle
- once the sensory afferent has synapsed, the alpha motor neuron is inhibited and contraction increases
- simulatenously, the sensory afferent also synapses on an inhibitory interneuron which inhibits the alpha motor neuron and therefore the activity of the flexor muscle
- the flexor muscle relaxes, and the knee jerk response takes place
