UCI BioSci D170, Williams Autonomic Nervous System (ANS)
Reading: Chapter 15
What are the main functions of the autonomic nervous system? What types of neurons are
prevalent in the ANS? What effectors do they act on?
The ANS consists of motor neurons that innervate the smooth muscle, cardiac muscle,
and glands. Thus the ANS regulates heart rate, blood pressure, digestion, and urination.
Motor neurons+visceral functions= general visceral motor division of PNS.
Define the following terms:
Synapse – junction b/w 2 neurons.
Presynaptic neuron – neuron carrying the message.
Post synaptic neuron – neuron receiving the message.
Ganglia – cluster of neuronal cell bodies in the PNS.
Describe how the somatic motor nervous system works by answering these
questions.
A long myelinated axon extends out from the ventral root to innervate
skeletal muscle cells.
Where is the cell body of a somatic motor neuron? Ventral horn of gray
matter in a spinal cord segment.
How many neurons are in a pathway? One-neuron pathway.
What is a motor unit? A single neuron plus the skeletal muscle cell it
innervates.
What neurotransmitter is used in this system? Acetylcholine.
Describe how the autonomic nervous system works, including an overview of the following
structures:
The preganglionic neuron slowly sends signals to the postganglionic neuron, which
stimulates muscle contraction or gland secretion in the effector.
Preganglionic neuron – one of the 2 motor neurons in the ANS pathway. Cell body lies in
the CNS.
Preganglionic axon (fiber) – axon of the preganglionic neuron. Thin, myelinated.
Postganglionic neuron – the second motor neuron in the ANS pathway; it synapses w/ the
preganglionic axon. It innervates effector organs in the periphery.
Autonomic ganglion – area in which pre- and post- ganglionic neurons form a
synapse. Motor ganglia that can be found in the head, along the vertebral column, and
cervical region.
Postganglionic axon (fiber) – axon of the postganglionic neuron. Thinner,
unmyelinated.
, UCI BioSci D170, Williams Autonomic Nervous System (ANS)
What are the main functional differences between the sympathetic and parasympathetic
divisions?
The parasympathetic division controls routine maintenance functions/active when the
body is at rest, while the sympathetic division becomes active when extra metabolic
effort is needed (fight-or-flight).
What are the main structural differences between the sympathetic and parasympathetic
divisions?
1. Origin of fibers. Fibers of sympathetic division emerge from the thoracic and superior
lumbar regions of the spinal cord (thoracolumbar division). Fibers of the parasympathetic
division emerge from the brain and sacral region (craniosacral division).
2. Length of axons and origin of ganglia. Sympathetic pathways have long
postganglionic axons and ganglia that lie near the spinal cord. Parasympathetic
pathways have shorter postganglionic axons and ganglia that lie in or near the organs
innervated.
3. Branching of fibers. Sympathetic fibers branch profusely, allowing many organs to be
mobilized simultaneously during a flight-or-fight response. Parasympathetic fibers do not
branch as much, allowing for a more localized effect on an organ.
Reading: Chapter 15
What are the main functions of the autonomic nervous system? What types of neurons are
prevalent in the ANS? What effectors do they act on?
The ANS consists of motor neurons that innervate the smooth muscle, cardiac muscle,
and glands. Thus the ANS regulates heart rate, blood pressure, digestion, and urination.
Motor neurons+visceral functions= general visceral motor division of PNS.
Define the following terms:
Synapse – junction b/w 2 neurons.
Presynaptic neuron – neuron carrying the message.
Post synaptic neuron – neuron receiving the message.
Ganglia – cluster of neuronal cell bodies in the PNS.
Describe how the somatic motor nervous system works by answering these
questions.
A long myelinated axon extends out from the ventral root to innervate
skeletal muscle cells.
Where is the cell body of a somatic motor neuron? Ventral horn of gray
matter in a spinal cord segment.
How many neurons are in a pathway? One-neuron pathway.
What is a motor unit? A single neuron plus the skeletal muscle cell it
innervates.
What neurotransmitter is used in this system? Acetylcholine.
Describe how the autonomic nervous system works, including an overview of the following
structures:
The preganglionic neuron slowly sends signals to the postganglionic neuron, which
stimulates muscle contraction or gland secretion in the effector.
Preganglionic neuron – one of the 2 motor neurons in the ANS pathway. Cell body lies in
the CNS.
Preganglionic axon (fiber) – axon of the preganglionic neuron. Thin, myelinated.
Postganglionic neuron – the second motor neuron in the ANS pathway; it synapses w/ the
preganglionic axon. It innervates effector organs in the periphery.
Autonomic ganglion – area in which pre- and post- ganglionic neurons form a
synapse. Motor ganglia that can be found in the head, along the vertebral column, and
cervical region.
Postganglionic axon (fiber) – axon of the postganglionic neuron. Thinner,
unmyelinated.
, UCI BioSci D170, Williams Autonomic Nervous System (ANS)
What are the main functional differences between the sympathetic and parasympathetic
divisions?
The parasympathetic division controls routine maintenance functions/active when the
body is at rest, while the sympathetic division becomes active when extra metabolic
effort is needed (fight-or-flight).
What are the main structural differences between the sympathetic and parasympathetic
divisions?
1. Origin of fibers. Fibers of sympathetic division emerge from the thoracic and superior
lumbar regions of the spinal cord (thoracolumbar division). Fibers of the parasympathetic
division emerge from the brain and sacral region (craniosacral division).
2. Length of axons and origin of ganglia. Sympathetic pathways have long
postganglionic axons and ganglia that lie near the spinal cord. Parasympathetic
pathways have shorter postganglionic axons and ganglia that lie in or near the organs
innervated.
3. Branching of fibers. Sympathetic fibers branch profusely, allowing many organs to be
mobilized simultaneously during a flight-or-fight response. Parasympathetic fibers do not
branch as much, allowing for a more localized effect on an organ.
