The Peripheral Nervous System: Efferent Division

Human Physiology - From Cells to Systems Lauralee Sherwood Chapter 7

Efferent division

communication link

• CNS controls muscles and glands

Autonomic nervous system

involuntary branch of peripheral efferent division

Somatic nervous system

branch of the efferent division subject to voluntary control

Preganglionic neuron

synapses with the cell body of the postganglionic fiber in a ganglion outside the CNS

Postganglionic neuron

sends axons that end on the effector organ

norepinephrine

Sympathetic postganglionic fibers release:

acetylcholine

Parasympathetic postganglionic fibers release:

acetylcholine

What neurotransmitter is released from the parasympathetic preganglionic fiber?

a.) sodium

b.) dopamine

c.) acetylcholine

d.) norepinephrine

Parasympathetic

• maintains homeostasis

• “rest and digest”

Sympathetic

"fight or flight” response

Dual innervation

innervation of a single organ by both branches of the autonomic nervous system

autonomic nervous system

Cardiac muscle, smooth muscle, most exocrine glands, some exocrine glands, and adipose tissue are innervated by the ________.

a.) somatic nervous system

b.) sensory-somatic nervous system

c.) autonomic nervous system

d.) cranial nerves

Adrenal medulla

modified part of the sympathetic nervous system

• secretes catecholamine hormones on stimulation

• the glands are endocrine glands

Cholinergic receptors

nicotinic and muscarinic receptors

Adrenergic receptors

alpha and beta receptors

Agonist

binds to a receptor and ACTIVATES it

• mimics the natural ligand (e.g., hormones or neurotransmitter) that normally activates the receptor

• produces biological response similar to natural ligand

Antagonist

binds with the receptor, but does NOT activate it

• blocks the natural ligand from binding to the receptor

• prevents or reduces the biological response caused by the natural ligand

Nicotinic receptor

ACh from autonomic preganglionic fibers / Ach from motor neurons

• opens nonspecific cation receptor-channels

• excitatory

Mucarinic receptor

ACh from parasympathetic postganglionic fibers

• activates various G-protein-coupled receptor pathways, depending on the effector

• excitatory or inhibitory, depending on effector

dual innervation

Innervation of a single organ by both branches of the autonomic nervous system is known as:
a.) binocular innervation

b.) biphasic innervation

c.) dual innervation

d.) bipolar innervation

Medulla

the region most directly responsible for autonomic output

• within the brain stem

Hypothalamus

plays a role in integrating autonomic, somatic, and endocrine responses

autonomic activity

can be influenced by the prefrontal association cortex

Somatic nervous system

motor neurons supply skeletal muscle

• bring about movement

• motor neurons are final common pathway

• motor neurons axon terminals release ACh to stimulate muscle contraction

• Axons of motor neurons originate in the CNS & end on skeletal muscle

voluntary

What type of control exists in the somatic nervous system?

a.) involuntary

b.) voluntary

c.) automatic

d.) partial

Neuromuscular junction

sites where the motor neurons and skeletal muscle fibers are chemically linked

Muscle fiber

single, long, and cylindrical muscle cell

Terminal button

enlarged knoblike structure at the end of axon terminal branches

Motor end plate

shallow depression where axon terminals end

action potential propagation in motor neuron

1. action potential in a motor neuron is propagated

2. local action potential triggers the opening of voltage-gated Ca2+ channels

3. Ca2+ releases into the system & causes the vesicles to move out through exocytosis

4. Contents of vesicle release into the synaptic junction & attaches to the motor end plate receptors

5. Na+ and K+ movement toward the end plate, which causes the contraction of the muscle fiber

Acetylcholine

neuromuscular junction neurotransmitter

• released at the neuromuscular junction

• collective potential change resulting from ion movements across all of the terminal buttons within neuromuscular junction

Acetylcholinesterase

ends ACh activity at the neuromuscular junction

• enzyme in the motor end-plate membrane that turns off muscle cell’s electrical response

agents/disease

Impacts of ______/_____ on the neuromuscular junction:

• black widow spider venom causes explosive release of Ach

• Botulinum toxin blonds release of ACh

• Curare blocks action of ACh at receptor-channels

• Organophosphates prevents inactivation of ACh

• Myasthenia gravis inactivates ACh receptor-channels

2 essential outcomes:

too much ACh or NO ACh