Rotator Cuff

The four muscles that make up the rotator cuff are supraspinatus, infraspinatus, teres minor, and subscapularis. Subscapularis inserts on the lesser tubercle of the humerus while the other three muscles insert onto the greater tubercle.

It is believed that swimmer's shoulder is caused by the impingement of the tendon of the supraspinatus muscle as it passes through the subacromial space. This also makes the supraspinatus more suspectible to tear.

Thanks to Honglin!

Acetylcholine

Unlike dopamine, there is an increase in acetylcholine in Parkinson's disease. This neurotransmitter is synthesized in the basal nucleus of Meynert (basal forebrain). In the autonomic nervous system, it serves as the neurotransmitter for sweat glands and adrenal medulla. In the peripheral nervous system, acetylcholine plays a role in skeletal muscle activation, specifically between the motor nerve and skeletal muscle. In the central nervous system it is involved in alertness, attention, and learning. Acetylcholine receptors are classified as either nicotinic or muscarinic.

Other disorders involving acetylcholine include Myasthenia gravis and Alzheimer's disease.

1. Myasthenia gravis
In Myasthenia gravis, the body produces antibodies against acetylcholine nicotinic receptors, inhibiting proper acetylcholine signal transduction. As a result, the patient suffers from weakness and fatigue.

2. Alzheimer's disease
In Alzheimer's disease, plaques are formed in the brain. The plaque lead to cell death and decreased levels of the acetylcholine in the cerebral cortex and caudate nucleus. Treatment of Alzheimer's include acetylcholinesterase inhibitors, which prevent the breakdown of acetylcholine to make up for the lack of neurotransmitter.

Dopamine

Parkinson's Disease is a neurological disorder marked by tremors, stiffness and decreased movement. The main pathological characteristic is cell death in the substantia nigra (specficially the pars compacta), where dopamine is produced. Dopamine is a neurotransmitter that is responsible for movement and emotional responses. It also acts in regulating the rewards and pleasure centers of the brain. Therefore decrease in dopamine would result in less movement. A lack of dopamine also affects the basal ganglia, a group of nuclei at the base of the forebrain. The basal ganglia are involved in voluntary motor control, habit learning, eye movements, and cognitive and emotional functions.

Decreased levels of dopamine are also seen in depression, while increased levels are seen in schizophrenia (difficulty distinguishing reality from imagination) and Huntington Disease (chorea and dystonia).