Reflex Arcs - Anatomy & Physiology

Introduction

A reflex arc represents a mechanism by which a physiological function is automatically managed or regulated. Reflex arcs can be found throughout the body, ranging from skeletal muscles to glands. Reflex arcs are initiated via the excitation or stimulation of specific sensory cells that are directly connected to motor neurons thus enabling motor nerve impulses to be automatically passed on to that particular muscle or gland. Therefore a basic reflex arc consists of sensory cells and their associated nerve fibers, motor nerve fibres and the ultimate muscle or gland. Some reflex arcs can include a coordination centre within the spinal cord or brain prior to stimulation of the motor nerve.

• The reflex arc is the basic functional unit of the nervous system and consists of 2 linked components: the sensory input and the output response.

Detection via sensory receptors e.g:	Response via effectors e.g:
Skin receptors	Skeletal Muscle
Muscle Spindles	Smooth Muscle
Retina	.
Organ of Corti	.
Olfactory Mucosa	.

• Animals are divided into body segments, according to the segmental nature of the spinal cord.
  • Reflex arcs may involve a single segment, or mutliple segments up and down the body.
  • However, reflex arcs do not require brain input in order to function.
• The brain can act to modulate reflex; for example, some reflex pathways may be inhibited by the brain.
  • The brain obtains its afferent information via the ascending sensory tracts of the spinal cord.
  • The descending tracts originate from the brain to allow responses to be modulated.
  • These tracts constitute the white matter of the spinal cord.