Definition of Afferent nerve

Afferent nerve: A nerve that carries impulses toward the central nervous system (CNS). The opposite of an afferent nerve is an efferent nerve that carries impulses away from the CNS.

Definition of Acetylcholinesterase

Acetylcholinesterase: An enzyme that breaks down the neurotransmitter acetylcholine at the synaptic cleft (the space between two nerve cells) so the next nerve impulse can be transmitted across the synaptic gap. Pesticides of the organophosphate and carbamate types act to paralyze and kill insects by inhibiting their acetylcholinesterase. Abbreviated AChE.

Definition of Acetylcholine

Acetylcholine: A key chemical in neurons (nerve cells) that acts as a neurotransmitter and carries information across the synaptic cleft, the space between two nerve cells. Abbreviated ACh.

Definition of Accessory neuropathy

Accessory neuropathy: Disease of the accessory nerve which is the eleventh cranial nerve. The accessory nerve supplies the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is in the front of the neck and turns the head. The trapezius muscle moves the scapula (the wingbone), turns the face to the opposite side, and helps pull the head back.
Damage to the accessory nerve can be confined to the accessory nerve or it may also involve the ninth and tenth cranial nerves which exit through the same opening (foramen) from the skull . Accessory neuropathy can sometimes occur and recur for unknown reasons. Most patients recover.
Paralysis of the accessory nerve prevents rotation of the head away from that side and causes drooping of the shoulder.

Definition of Accessory nerve

Accessory nerve: The eleventh cranial nerve, which emerges from the skull and receives an additional (accessory) root from the upper part of the spinal cord. It supplies the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is in the front of the neck and turns the head. The trapezius muscle moves the scapula (the wingbone), turns the face to the opposite side, and helps pull the head back. The accessory nerve is so-called because, although it arises in the brain, it receives an additional (accessory) root from the upper part of the spinal cord.
Damage to the accessory nerve can be isolated (confined to the accessory nerve) or it may also involve the ninth and tenth cranial nerves which exit through the same opening (foramen) from the skull . Accessory neuropathy (nerve disease) can sometimes occur and recur for unknown reasons. Most patients recover.
Paralysis of the accessory nerve prevents rotation of the head away from that side and causes drooping of the shoulder.

Definition of ABR test

ABR test: Auditory brainstem response test. A test for hearing and brain (neurological) functioning. ABR may be used in the evaluation of:

Hearing integrity (and neurologic normalcy) in infants and young children.
Neurologic integrity (and hearing) in patients who are comatose, unresponsive, or impaired due to a stroke, an acoustic neuroma (tumor on the hearing nerve), Meniere's disease, etc.


The ABR test involves attaching electrodes to the head to record electrical activity from the auditory nerve (the hearing nerve) and other parts of the brain. Also known as brainstem auditory evoked potentials (BAEP).