What Is the Difference Between Afferent and Efferent?

Efferent nerve: Also called motor nerve, the nerve that transmits the excitement of the central nervous system to various organs or peripheral parts. Nerves composed of efferent nerve fibers. Can transmit the excitement of the central nervous system to various organs or peripheral parts. Refers to the nerves that transmit information from the central nervous system to the periphery (effect organs) in the form of nerve impulses. It is the outgoing part of the reflection arc. For example, motor nerves that are distributed in muscle tissue and contract are classified as efferent nerves. Fibers of neurons that conduct impulses from the nerve center. For example, motor nerves and efferent nerves that conduct impulses from the brain and spinal cord to muscles are the fourth component of the reflex arc.

Efferent nerve: Also called motor nerve, the nerve that transmits the excitement of the central nervous system to various organs or peripheral parts. Nerves composed of efferent nerve fibers. Can transmit the excitement of the central nervous system to various organs or peripheral parts. Refers to the nerves that transmit information from the central nervous system to the periphery (effect organs) in the form of nerve impulses. It is the outgoing part of the reflection arc. For example, motor nerves that are distributed in muscle tissue and contract are classified as efferent nerves. Fibers of neurons that conduct impulses from the nerve center. For example, motor nerves and efferent nerves that conduct impulses from the brain and spinal cord to muscles are the fourth component of the reflex arc.

Chinese name

Efferent nerve

Species

Cholinergic nerve

Effect

Choline receptor

Application

Selection of experimental methods and animals

Transmitters and classification of efferent nerves

According to the different neurotransmitters secreted from the nerve endings, the efferent nerves are mainly divided into two categories:

I. Cholinergic nerves include all sympathetic and parasympathetic preganglionic fibers; all postsympathetic ganglion fibers; motor nerves; very few postsympathetic ganglion fibers, which release acetylcholine at the periphery when excited (dominates sweat gland secretion and bone and vasodilation) The nerves).

Second, noradrenergic nerves include most of the postganglionic sympathetic nerves (excluding the fibers that govern the sweat glands and skeletal muscles). And certain peptide energy fibers. When excited, noradrenaline is released from its periphery.

In addition, dopamine nerves are still present in some effectors.

Receptors and effects of efferent nerve

The efferent nerve endings mainly release two kinds of transmitters, so the receptors receiving these transmitters are also divided into two major categories:

I. Choline receptors and effects

Receptors that can selectively bind to acetylcholine are called choline receptors. They can be divided into:

(1) Muscarinic Choline Receptor (M Receptor for short) A receptor that selectively binds to muscarinic. It is mainly distributed on the effector organs dominated by the fibers of the parasympathetic ganglia.

(2) Nicotinic choline receptors (referred to as N receptors) Receptors that can selectively bind to nicotine can be divided into two subtypes of N1 receptor and N2 receptor. N1 receptors are mainly distributed on the cell membrane of vegetative ganglion neurons. When they are excited, they can cause ganglion excitement and impulse transmission along the postganglionic fibers, which can release noradrenaline and parasympathetic nerves after the fiber ends of the sympathetic ganglia The acetylcholine is released from the fiber end of the post-ganglion, and the corresponding effect appears; N2 receptors are mainly distributed in skeletal muscle, which manifests as skeletal muscle contraction when excited.

Adrenaline receptors and effects

A receptor that can selectively bind to norepinephrine or epinephrine is called an adrenaline receptor.

(A) a-adrenoceptor (a-receptor for short) can generally be divided into two subtypes a1 and a2.

(B) adrenergic receptors (referred to as receptors) can be divided into three subtypes 1, 2 and 3. receptors are mainly distributed on the effector cell membranes dominated by sympathetic nerve fibers.

(3) Dopamine receptor (DA receptor for short) can select the receptor that binds to DA.

Selection and application of efferent nerve and efferent neuropharmacology experiments

(A) general experimental methods and selection of animals

In the determination of the new drug's acute toxicity test (LD50), animals with vertical hairs, increased activity, excitement, and development of tonic-clonic convulsions can be considered as sympathomimetics. Furthermore, the animal (or cat) blood pressure response can be observed. For example, if the -receptor is excited, it will have a greater effect on the blood pressure and slow down the heart rate reflexively. If the -receptor is excited, the blood pressure will decrease and the heart rate will increase significantly. In order to distinguish the effects on and receptors more accurately, phentolamine, an alpha blocker, and propranolol, a beta blocker, can be used as tools. In addition to blood pressure experiments, experimental methods such as cat transient membranes and cat (or dog) intestinal activity can also be used. Some in vitro experiments can be used to analyze the site of action of sympathomimetics. One of the most sensitive experiments is the rat stomach bottom strips. In addition, rabbit head muscles, isolated rabbit ears, guinea pig tracheal chains, guinea pig ileum, and chicken caecum were prepared. Known or -receptor stimulants can be used as standards, and their interaction with or -receptor blockers can be observed to determine their site of action.

Acetylcholine has muscarinic and nicotinic effects, the former can be blocked by atropine, and the latter can be blocked by ganglion blockers and rhabdomyoplasty relaxants. Tears, salivation, urination, and defecation syndrome can occur with drugs that excite parasympathetic effect points directly or indirectly. Therefore, a preliminary impression can be obtained in the mouse LD50 experiment, and then its response to blood pressure, saliva, pupil, and gastrointestinal tract can be observed separately. In cat blood pressure test, frog heart, frog abdominal rectus muscle, leeches back muscle and other specimens can be tested and the role of anticholinergic drugs can be tested, can also be used in overall experiments such as inhibiting gastric ulcer in rats, inhibiting the intestinal activated carbon in rats Observe it by other methods.

(Two) cardiovascular experiments

The blood pressure test is a very sensitive method for testing efferent nerve drugs. Generally, an acute blood pressure test is used, and dogs, cats, rabbits and rats are commonly used in animals. Rabbits are not suitable for hypotensive experiments because they are prone to death. The experiment can be anesthetized or brain-destructed animals, because the blood pressure of anesthetized animals often has three levels of fluctuations (the first level of fluctuations, also known as pulse fluctuations, is caused by each heartbeat affecting blood pressure, the second level of fluctuations, also known as respiratory fluctuations That is, the blood pressure slightly rises during inhalation, and decreases slightly during exhalation; the third level fluctuation, the vascular movement center at a slightly longer interval, the excitability periodically changes), making the blood pressure rise and fall unstable. For example, after an animal's brain is destroyed, the influence of the central nervous system above the spinal cord on blood pressure can be ruled out. Only first-order fluctuations occur, and the blood pressure curve is extremely unbalanced.

Isolated rabbit aortic strip experiment: Rabbit aorta contains -receptor, which is a good specimen for determining the effect of -receptor drugs. It has been widely used to identify and analyze sympathomimetics and their antagonists. effect. Rabbit aorta preparation has been trial-produced in a variety of forms, such as aortic rings, slices, and strips, etc., but rabbit aortic spiral strips are one of the most suitable methods. This specimen has many advantages. For example, 3 to 4 specimens can be made from one aorta, which can be used for pairing experiments. It is sensitive to low-level sympathomimetic drugs, has good tissue stability, and can be maintained for a long time.

(Three) digestive tract smooth muscle experiment

The isolated intestine of a variety of animals can be used to test efferent nerve drugs. Generally, the intestines of guinea pigs and rabbits are mostly used. Guinea pig ileum has less spontaneous activity and has a stable baseline during tracing, which is suitable for drug identification. The rabbit intestine (especially the jejunum) has a regular swinging motion, which is suitable for observing the effects of drugs on this animal. Guinea pig ileum specimens have completely relaxed after loading, so adding sympathomimetics will not make them more relaxed.

Isolated guinea pig ileum can be used to observe the dose-response relationship between acetylcholine (Ach) and choline-like drugs; the content of Ach and choline-like drugs can be determined. Isolated rabbit jejunum has rhythmic contractile activity, and the effects of drugs such as epinephrine (4 g) and detoxidine (2 g) on the jejunal swing motion can be observed. The rat stomach bottom strip is the most sensitive specimen for testing catecholamines and serotonin (5-HT). Mainly observe the effect of drugs on longitudinal gastric muscles, because the circular muscles in the specimen have been cut off. It has been verified that catecholamines are 10 to 100 times more sensitive than uterine specimens from rats. The chicken esophagus is innervated by parasympathetic nerves, so isolated chicken esophagus specimens are suitable for testing parasympathetic drugs. Because its effect cannot be completely blocked by ganglion blocking drugs, it is not suitable for testing drugs that act on ganglion.