Communication between Nervous and Muscular System

Birds are arguably the most acrobatic vertebrates on the planet, capable of incredible speed and agility in the water, on the land, or in the sky. Diving into the water to snatch a fish or catching a bug out of mid-air at 60 miles an hour requires a level of coordination and muscular precision that we can only dream of!

Each incredible avian feat relies on integrated sensory, muscular, and nervous systems, and each action results from combined chemical and electrical signals communicated by the brain or spinal cord. The field of neuromuscular biology explores these relationships and teaches us more about how birds’ bodies work and interact with the world around them.

This article is all about how birds use their brains to move their muscles. Read along as we explore the interface between the avian muscular and nervous systems.

Basics of Neuromuscular Communication

Neural Control of Muscles

Apart from reflexive movements (discussed later in this article), skeletal muscles are coordinated by the cerebellum of the avian brain. This component of the brain consists of various lobes, each corresponding to a different muscle group. Information from the brain is sent to muscles via the spinal cord and motor neurons in the form of electrical impulses.

But, how do signals traveling through neurons communicate with muscles?

Synaptic Transmission

Motor nerves carry the electrical impulses along their axons, which meet the bird’s muscle at synapses called neuromuscular junctions. Electrical impulses traveling through the nerve cause the release of a neurotransmitting chemical called acetylcholine (ACh) at these junctions. When ACh reaches the muscle, it causes yet another electrical impulse, which results in a muscle contraction.

Birds are arguably the most acrobatic vertebrates on the planet, capable of incredible speed and agility in the water, on the land, or in the sky. Barn Owl

The Avian Motor System and Flight

Flight Muscles

Sustained flapping flight requires powerful muscles and perfectly timed impulses from the avian nervous system.

The downstroke is the most physically demanding action, powered by the pectoralis major muscles in the chest. The wing must then be lifted before the bird can flap again, and this ‘return stroke’ is powered by another muscle in the chest called the supracoracoideus.

Of course, there’s more to flight than simply flapping up and down, so birds have nearly twenty other smaller muscles in the shoulder and wing that control important movements like feather position and the flex of the forearm.

Wing Movement Coordination

Powering wing strokes requires precise input from the cerebellum to stimulate many muscles acting both in sequence and in opposition to each other.

For example, electrical impulses already begin to stimulate the pectoralis major halfway through the bird’s upstroke. Therefore, the pectoralis muscles function both to generate lift and thrust on the downstroke and to control the return stroke.

Flapping, gliding, and soaring flight rely on very different muscular coordination, but each technique requires sensory input. Birds rely primarily on sharp eyes and excellent vision to guide their path, but senses like sound, smell, and even magnetoreception are also important in flight.

Neuromuscular Adaptations for Avian Locomotion

Walking and Running

Flight isn’t the only mode of locomotion that birds use when foraging or getting from A to B. Many species are incredibly agile on their feet, and some are impressive sprinters.

Even while moving on terra firma, birds rely on precise neuromuscular coordination to put one foot in front of the other. Such coordination requires a high capacity for neuromuscular communication, so birds have an enlarged area on the lower spinal cord called the lumbar enlargement.

Swimming

Swimming is the most important means of locomotion for many birds, including aquatic species like Grebes and seabirds like Penguins. However, there are some important differences in the neuromuscular pathways between these examples.

Penguins propel themselves primarily with their wings, which involves pathways through the brain, spinal cord, and cervical enlargement before reaching the target muscles via the peripheral nervous system.

Grebes, Waterfowl, and most freshwater birds use coordinated contractions of hindlimb muscles to drive their webbed feet and create thrust in the water, relying instead on pathways through the lumbar enlargement of the spinal cord.

Flight isn’t the only mode of locomotion that birds use when foraging or getting from A to B. Many species are incredibly agile on their feet, and some are impressive sprinters. African Ostrich

Swimming is the most important means of locomotion for many birds, including aquatic species like Grebes and seabirds like Penguins. Humboldt Penguin

Sensory Feedback and Movement Adjustment

Proprioception

So far, we’ve discussed how birds send commands from their brain to their muscles to perform voluntary actions, but there is another important aspect of motion control that must take place before and during motor actions.

Birds use proprioception to monitor the state of their muscles, the position of their joints and limbs, and their posture and movements. They do this with proprioceptors located in the muscles, joints, and tendons that communicate with a region of the brain called the cerebellum.

Reflex Actions

Just as you might instantly pull your hand away from a hot stove top, birds rely on reflexes for rapid evasive actions. Reflexes result from communications between the peripheral nervous system and the spinal cord and do not require input from the brain.

Reflexive actions occur when a stimulus, such as pain, activates receptors that send signals to the spinal cord via sensory neurons. Impulses are then sent along motor neurons to target muscles that contract in response. This shortened pathway decreases response time in potentially dangerous situations.

Neuromuscular Health and Disease in Birds

Common Disorders

Disease or trauma of the nervous and muscular system has serious consequences for birds, causing symptoms like muscle paralysis, seizures, and loss of coordination. Birds can suffer damage to the nervous and muscular system through various causes, including the following examples:

Physical trauma

Birds may suffer neuromuscular damage after physical trauma like window collisions. Common symptoms include a tilted head, depression, or partial paralysis.

Nutritional deficiencies

Deficiencies of vitamin B, E, and selenium may cause a variety of neurological or muscular symptoms, including muscle weakness, head tilting, curled toes, and coordination problems.

Toxin exposure

Exposure to heavy metals like zinc and lead, and various pesticides can result in devastating damage to birds. Some common symptoms include depression, tremors, paralysis, and seizures.

Injury and Recovery

Depending on the cause and severity of the injury, a bird may or may not recover from nervous system damage. Avians may display a remarkable ability to heal, although it can take weeks or even months of progress, during which time they may need supportive care.

Unfortunately, wild birds cannot survive for long with severely limited mobility and the resulting inability to feed, shelter, and protect themselves. Therefore, captive birds are far more likely to survive severe injuries.

Just as you might instantly pull your hand away from a hot stove top, birds rely on reflexes for rapid evasive actions. Flock of Mallard Ducks

Research and Discoveries in Avian Neuromuscular Biology

Current Studies and Technological Advances

Researchers continue to make exciting new discoveries regarding the avian brain and nervous system. Modern technologies like 3D polarized (3dPLI) lighting imagery have recently confirmed that the avian brain is surprisingly similar to our own, even if our feathered friends don’t have a typical neocortex.

Summary

Whether flying across an ocean or pecking at the dirt, every move a bird makes is the product of a complex and coordinated sequence of actions involving the skeletal muscles and nervous system.

Communication between these two systems relies on electrical impulses fired at incredible speeds between the brain and peripheral nervous system. These messages transform into a chemical signal and then back into an electrical to produce a muscular contraction, all in the blink of an eye!

Science has made important headway into understanding these vital physiological processes, but continued research can only strengthen our understanding and help us develop new ways to treat and protect birds.