KINE 301 Chapter 11

Efferent nervous system

The outgoing portion of the nervous system, divided into autonomic and somatic motor subdivisions

Autonomic neuron targets

Smooth muscle, cardiac muscle, glands, and some adipose tissue

Somatic motor neuron targets

Voluntary skeletal muscle

Sympathetic subdivision

Known as fight or flight, activated when something is perceived as life threatening

Parasympathetic subdivision

Known as rest and digest, associated with relaxation and digestion

Antagonistic control

The predominant control of the autonomic nervous system where one branch is excitatory and the other inhibitory on the same tissue

Tonic control

Control seen in tissues with only sympathetic innervation, such as sweat glands and blood vessel smooth muscle, where responses are turned up or down like a volume knob rather than opposed by another branch

Ganglion

A group of nerve cell bodies located in the peripheral nervous system

Preganglionic neuron

Neuron that runs from the central nervous system to the ganglion

Postganglionic neuron

Neuron that runs from the ganglion to the target tissue

Sympathetic origin

Thoracic and lumbar regions of the spinal cord

Parasympathetic origin

Brainstem cranial nerves, especially the vagus nerve (cranial nerve ten), and the sacral region of the spinal cord

Sympathetic ganglia location

Located in ganglionic chains that run bilaterally alongside the vertebral column

Parasympathetic ganglia location

Located on or near the target organ

Sympathetic preganglionic neuron length

Relatively short, since the ganglia are close to the spinal cord

Parasympathetic preganglionic neuron length

Relatively long, since the ganglia are located near the target organ far from the spinal cord

Sympathetic postganglionic neuron length

Relatively long, since the ganglia are near the spinal cord and must reach a distant target organ

Parasympathetic postganglionic neuron length

Relatively short, since the ganglia are already near the target organ

Preganglionic neurotransmitter (both divisions)

Acetylcholine released onto nicotinic cholinergic receptors on the postganglionic cell

Sympathetic postganglionic neurotransmitter

Norepinephrine, received by adrenergic receptors on the target cell

Parasympathetic postganglionic neurotransmitter

Acetylcholine, received by muscarinic cholinergic receptors on the target cell

Sweat gland exception

Sweat glands have sympathetic cholinergic neurons that release acetylcholine rather than norepinephrine, and are under tonic rather than antagonistic control

Non-adrenergic non-cholinergic neurons

Autonomic neurons that use other neurotransmitters such as substance P, nitric oxide, or ATP

Adrenal medulla

Neuroendocrine tissue that acts as a modified sympathetic ganglion and secretes norepinephrine directly into the blood

Neuroeffector junction

The synapse between a postganglionic autonomic neuron and its target cell

Varicosity

A swelling along the end of an autonomic neuron that diffusely releases neurotransmitter rather than targeting one cell

Monoamine oxidase (MAO)

Enzyme that degrades catecholamines such as epinephrine and norepinephrine, ending their effect

Acetylcholinesterase

Enzyme that degrades acetylcholine, ending its action at the synapse

Adrenergic receptor

Receptor type used by the sympathetic nervous system, responds to norepinephrine and epinephrine, a G protein coupled receptor

Alpha type one receptor

Sympathetic receptor that leads to muscle contraction or gland secretion when activated

Alpha type two receptor

Sympathetic receptor that decreases cyclic AMP when activated, leading to smooth muscle relaxation or decreased secretion

Beta type one receptor

Sympathetic receptor found in cardiac muscle and kidneys, responds equally to epinephrine and norepinephrine

Beta type two receptor

Sympathetic receptor found in blood vessels and smooth muscle, prefers epinephrine

Beta type three receptor

Sympathetic receptor found in some adipose tissue, prefers norepinephrine

Muscarinic receptor

Receptor type used by the parasympathetic nervous system, receives acetylcholine on the target cell

Somatic motor neuron

A single long myelinated neuron originating in the anterior or ventral horn of the spinal cord that directly targets skeletal muscle

Neuromuscular junction

The specific synapse where a somatic motor neuron meets a skeletal muscle fiber

Bouton

The swelling at the end of a somatic motor neuron axon

Motor end plate

The specialized region of folded skeletal muscle membrane where the bouton synapses with the muscle fiber

Somatic motor receptor and neurotransmitter

Nicotinic cholinergic receptor that receives acetylcholine released by the somatic motor neuron

Somatic motor contraction steps

Action potential reaches the axon terminal, voltage gated calcium channels open, calcium influx triggers acetylcholine release, acetylcholine crosses the synapse and binds nicotinic receptors, monovalent cation channels open, sodium influx causes depolarization, leading to muscle contraction

Curare

A neurotoxin that blocks somatic nicotinic receptors, preventing muscle contraction and causing death by respiratory paralysis, though its effect is reversible

Nicotine poisoning

Nicotine acts as an agonist at nicotinic cholinergic receptors, depolarizing the cell without allowing repolarization, which can cause death by respiratory paralysis and is especially dangerous for children