Corpus: Plantaris muscle
from Latin: planta - sole of the foot
1. Definition
The plantaris muscle is a small, two-jointed muscle that is part of the lower leg muscles. Some authors regard it as a separate entity, others classify it as part of the triceps surae muscle.
2. Anatomy
The plantaris muscle has a relatively short, weakly developed muscle belly, which extends into a long, thin tendon (30-40 cm). The muscle may be rudimentary or completely absent.
2.1. Origin
The plantaris muscle originates from the lateral supracondylar line of the femur, slightly superior to the origin of the lateral head of the gastrocnemius muscle. Additional fibers originate from the joint capsule of the knee.
2.2. Attachment
The long tendon of the plantaris muscle radiates into the fascia of the soleus muscle and the Achilles tendon. Occasionally, it can also insert on the medial side of the calcaneal tuberosity or on the plantar aponeurosis.
3. Innervation
The plantaris muscle is innervated by the tibial nerve from the sacral plexus. The motor neurons are located in the spinal cord segments L5 and S1.
4. Function
The plantaris muscle has little functional significance in humans. It originally supported the climbing process, which is why it is much more developed in lower apes and prosimians, extending over the calcaneal tuberosity into the plantar aponeurosis. In humans, it weakly supports plantar flexion in the ankle joint and flexion in the knee joint.
Due to the high receptor density of the muscle, it is assumed that its actual significance in humans lies in proprioception.