Algonquin College
8.2 - Reflexes
Reflexes are involuntary reactions to stimuli (internal or external) that are processed in the brain or spinal cord reflex centers.

Functional types

Somatic reflexes stimulate responses in the voluntary skeletal muscles, producing movement. They are typically very quick to respond (within milliseconds), since skeletal muscles have very fast contractions.

Somatic reflexes can be simple or conditioned.

Simple (basic) reflexes are unlearned responses to stimuli.
  • Ex. Knee-jerk (patellar) reflex; withdrawing your hand from a hot object
Acquired (conditioned) reflexes are a result of practice and learning or training.
  • Ex. Spiking a volleyball
Autonomic reflexes stimulate effectors of the autonomic nervous system to respond. These effectors are smooth muscles or glands, and their response is much slower than that of somatic reflexes (seconds).
  • Ex. Salivation at the smell of food
Structural types

Reflexes are classified structurally according to the location of cell bodies that integrate the response and the number of neurons involved in the reflex pathway.

Location:
Number:
Monosynaptic reflex arc
Figure 8.2.1 - A monosynaptic reflex arc. The sensory neuron detects the hammer hitting the knee and directly activates the leg muscle effectors to contract.
 Polysynaptic reflex arc

Figure 8.2.2 - A polysynaptic reflex arc. The sensory neuron detects the ball on the foot. Interneurons in the cerebellum integrate the sensory input and determine the appropriate muscle response to be able to kick the ball.