Reflex & Posture Flashcards
What is the motor control system responsible for?
Planning, initiating, coordinating, and executing voluntary and involuntary movements.
What does it mean that the motor control system is hierarchical?
It has multiple levels of control from spinal cord reflexes to complex voluntary movement in the brain.
What are the three main hierarchical levels of motor control?
- Spinal cord – reflexes
- Brainstem – posture and balance
- Cerebral cortex – voluntary movement
What is a reflex action?
An involuntary, unplanned, and nearly instantaneous response to a stimulus.
What is a reflex arc?
The neural pathway that mediates a reflex.
What are the components of a reflex arc?
Stimulus → sensory receptor → sensory neuron → integration center → motor neuron → effector.
What are the two types of reflex arcs?
- Visceral (autonomic) – controls smooth muscle and glands
- Somatic – controls skeletal muscle
What is a monosynaptic reflex?
A reflex involving one synapse between a sensory and motor neuron.
What is a polysynaptic reflex?
A reflex involving one or more interneurons between sensory and motor neurons.
Give an example of a monosynaptic reflex.
The knee-jerk (patellar) reflex.
Give an example of a polysynaptic reflex.
Withdrawal reflex (e.g. touching something hot).
Which is faster: monosynaptic or polysynaptic reflexes?
Monosynaptic, due to fewer synapses.
What is a muscle spindle?
A specialized stretch receptor in skeletal muscle that detects changes in muscle length.
Where are muscle spindles located?
Inside the muscle belly, composed of intrafusal fibres.
What do muscle spindles detect?
Rate and extent of stretch in muscle fibres.
Which afferent fibres are associated with muscle spindles?
Ia and II afferent fibres.
What is the function of gamma motor neurons in the muscle spindle?
They regulate spindle sensitivity by adjusting intrafusal fibre contraction.
What is the role of muscle spindles in motor control?
Provide sensory feedback to the CNS for adjusting movement and posture.
Where is the motor cortex located?
Frontal lobe, in the precentral gyrus.
What are the three areas of the motor cortex?
- Primary motor cortex – sends commands to muscles
- Premotor cortex – plans complex movements
3.Supplementary motor area – involved in movement initiation
What does the motor homunculus represent?
The cortical area dedicated to control of body parts—larger for parts needing fine motor control.
What is the role of the cerebellum in movement?
Fine-tunes movement, balance, and proprioception.
What is the function of red nuclei?
Modulate and regulate motor output.
What does the basal ganglia do?
Regulates initiation and coordination of voluntary movement.
What is postural control?
CNS regulation of sensory input to maintain upright, stable positions.
What are the three main systems involved in postural control?
- Visual system
- Vestibular system
- Proprioceptive (somatosensory) system
What are the two functional classes of eye movement for posture?
- Gaze stabilization – keeps eyes stable during head movement
- Gaze shifting – tracks moving visual targets
What does the vestibular system detect?
Head position and movement; contributes to balance and postural orientation.
How does the vestibular system help posture with eyes closed?
Maintains trunk verticality using internal sensory cues.
What is the function of the proprioceptive system?
Senses limb and joint position to adjust motor output for balance.
What receptors contribute to proprioception?
Muscle spindles, joint receptors, and Golgi tendon organs.
