Inside the heart of crayfish
hearts are known to be neurogenic. The cardiac rhythm is originated in
The cardiac ganglion is composed of the pacemaker
(small) and follower (large) neurons. The pacemaker
neurons exhibit spontaneous bursting activity, and induce firing of follower
neurons through excitatory synapses. The follower neurons make excitatory
neuromuscular junctions onto the cardiac muscle and cause muscle
contraction, the heartbeat.
The cardiac muscles are simply driven by the motor
neurons (followers) in the cardiac ganglion just like other skeltal muscles
that are driven by their own motor neurons in the CNS.
In crayfish, the cardiac ganglion is often buried
under the cardiac muscle fibers.