Adrenergic and Cholinergic Synaptic Transmission

Acetylcholine (ACh) is the neurotransmitter of all preganglionic fibers (both sympathetic and parasympathetic). Acetylcholine is also the transmitter released by most parasympathetic post-

ganglionic fibers at their synapses with effector cells (fig. 9.7). Transmission at these synapses is thus said to be cholinergic.

The neurotransmitter released by most postganglionic sympathetic nerve fibers is norepinephrine (noradrenaline). Transmission at these synapses is thus said to be adrenergic. There are a few exceptions, however. Some sympathetic fibers that innervate blood vessels in skeletal muscles, as well as sympathetic fibers to sweat glands, release ACh (are cholinergic).

In view of the fact that the cells of the adrenal medulla are embryologically related to postganglionic sympathetic neurons, it is not surprising that the hormones they secrete should consist of epinephrine (about 85%) and norepinephrine (about 15%). Epinephrine differs from norepinephrine only in that the former has an additional methyl (CH3) group, as shown in figure 9.8. Epinephrine, norepinephrine, and dopamine (a transmitter within the CNS) are all derived from

Epinephrine Norepinephrine

Figure 9.7 Neurotransmitters of the autonomic motor system. ACh = acetylcholine; NE = norepinephrine; E = epinephrine. Those nerves that release ACh are called cholinergic; those nerves that release NE are called adrenergic. The adrenal medulla secretes both epinephrine (85%) and norepinephrine (15%) as hormones into the blood.

Figure 9.7 Neurotransmitters of the autonomic motor system. ACh = acetylcholine; NE = norepinephrine; E = epinephrine. Those nerves that release ACh are called cholinergic; those nerves that release NE are called adrenergic. The adrenal medulla secretes both epinephrine (85%) and norepinephrine (15%) as hormones into the blood.

The Autonomic Nervous System the amino acid tyrosine and are collectively termed catecholamines (fig. 9.8).

Where the axons of postganglionic autonomic neurons enter into their target organs, they have numerous swellings, called varicosities, that contain the neurotransmitter molecules. Neurotransmitters can thereby be released along a length of axon, rather than just at the axon terminal. Thus, autonomic neurons are said to form synapses en passant ("synapses in passing") with their target cells (fig. 9.9). Sympathetic and parasympathetic axons often innervate the same target cells, where they release different neurotransmitters that promote different (and usually antagonistic effects).

Varicosity

Tyrosine

(an amino acid)

DOPA

(dihydroxyphenylalanine)

Dopamine

(a neurotransmitter)

Norepinephrine

(a neurotransmitter and hormone)

Epinephrine

(major hormone of adrenal medulla)

H cOOH

OH H

OH H

H cOOH

OH H

OH H

■ Figure 9.8 The catecholamine family of molecules.

Catecholamines are derived from the amino acid tyrosine, and include both neurotransmitters (dopamine and norepinephrine) and a hormone (epinephrine). Notice that epinephrine has an additional methyl (CH3) group compared to norepinephrine.

Smooth muscle cell

Varicosity

Smooth muscle cell

Synaptic Terminals Smooth Muscle Cells

Synapses en passant

Parasympathetic neuron neuron

-Sympathetic

Synapses en passant

Parasympathetic neuron

Axon of Sympathetic Neuron

Synaptic vesicle with norepinephrine (NE)

Axon of Sympathetic Neuron

Synaptic vesicle with norepinephrine (NE)

Cholinergic Synaptic Vesicle

Axon of Parasympathetic Neuron

Synaptic vesicle with acetylcholine (ACh)

Axon of Parasympathetic Neuron

Synaptic vesicle with acetylcholine (ACh)

■ Figure 9.9 Sympathetic and parasympathetic axons release different neurotransmitters. (a) The axons of autonomic neurons have varicosities that form synapses en passant with the target cells. (b) In general, sympathetic axons release norepinephrine, which binds to its adrenergic receptors, while parasympathetic neurons release acetylcholine, which binds to its cholinergic receptors (discussed in chapter 7). In most cases, these two neurotransmitters elicit antagonistic responses from smooth muscles.

neuron

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Responses

  • emma
    Are there antagonistic hormones for epinephrine and norepinephrine?
    7 years ago
  • wolfgang
    Which synapse release norepinephrine?
    7 years ago
  • taija
    Which autonomic neurons release norepinephrine as a neurotransmitter?
    7 years ago
  • piper
    Why is epinephrine both a neurotransmitter and hormone?
    7 years ago
  • feaven asmara
    Where epinephrine is located in the human body?
    7 years ago
  • Eemil
    What neurotransmitter released from the postganglionic parasympathetic axon terminal is:?
    7 years ago
  • RITA
    Why is smooth muscle response to both ach and noradrenaline neurotransmitters?
    7 years ago
  • Marina Schmidt
    Do varicosities secret neurotransmitters?
    7 years ago
  • SANTO BARESE
    Where is parasympathetic or other cholinergic nerve fibers?
    7 years ago
  • ARNOR
    What are NE, epinephrine, dopamine adrenergic?
    7 years ago
  • tanja
    How is epinephrine released?
    7 years ago
  • terzo
    What are cholinergic and adrenergic fibers?
    6 years ago
  • Aatifa
    Is epinephrine a cholinergic?
    6 years ago
  • Uwe
    What is synaptics in the human body?
    6 years ago
  • rose
    What neurotransmitter secret from adrenergic fibers?
    6 years ago
  • fatima
    Which neurotransmitter is released at the sympathetic terminal receptors?
    6 years ago
  • gilly
    Is norepinephrine part of te cholinergic system?
    6 years ago
  • aira
    What do adrenergic fibers release?
    4 years ago
  • jessika
    What is cholinergic synapse and adrenergic synapses?
    3 years ago
  • phillip
    What is defrence betewen adrenergic and cholinergic synaptic transmision?
    3 years ago
  • Vihtori
    What difference between cholenergic and adrenergic synaptic transmission?
    3 years ago
  • marco
    What is ach and norepinephrine neuro transmitter in human?
    3 years ago
  • helmi koivisto
    Do Cholinergic fibers release epinephrine.?
    2 years ago
  • NASIH IDRIS
    How do adrenergenic and colinergenic synaptic transmission system differ?
    2 years ago
  • sara
    Which neurotransmitters is released by the cholinergic nerve in synapse?
    2 years ago
  • Uwe Gottlieb
    Do cholinergix fibers release epinephrine?
    1 year ago
  • togo
    How are cholinergic transmission released?
    6 months ago
  • Briffo
    Which of these neurotransmitters is released at CNS adrenergic synapses?
    4 months ago
  • Lana
    What happens first in an adrenergic sybaptic transmission?
    4 months ago
  • Caoimhe
    WHAT NEUROTRANSMITTERS AR SECRETED FROM THEC HOLINERGIC AND ADRENERGIC FIBERS?
    3 months ago
  • esther
    Which of these happens first in an cholinergic synaptic transmission?
    1 month ago

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