Biology 322 Human Anatomy I Autonomic Nervous System

Autonomic Nervous System

The efferent (motor) component of the peripheral nervous system includes two types of neurons: Somatic Neurons regulate voluntary movement (contraction of skeletal myocytes) Autonomic Neurons regulate involuntary functions (rate & force of cardiac myocyte contraction) (contraction of smooth myocytes) (secretion of glands) Both types of efferent neurons run through the same cranial or spinal nerves

Comparison: Somatic vs Autonomic efferent neurons Voluntary Involuntary Effectors: Skeletal M. Effectors: Cardiac M. Smooth M Glands Neurons extend from CNS to effectors without synapsing. Two neurons to get from CNS to effectors; Therefore one synapse. "Two neuron chain"

Autonomic Nervous System has two divisions based on two criteria: a) Where the cell body of the first neuron is located (Brain, or specific region of spinal cord) b) Where the axon of the first neuron synapses with the dendrites of the second neuron (Far away from effector cells; or near effector cells)

They do so in a ganglion located somewhere in the body Since there are always two neurons between the central nervous system and the effector cells in an autonomic pathway, they must synapse somewhere. They do so in a ganglion located somewhere in the body (more about this in a moment) First cell = Preganglionic neuron Second cell = Postganglionic neuron Postganglionic Neuron Preganglionic Neuron

Sympathetic Division of Autonomic Nervous System Preganglionic neuron starts in thoracic or lumbar levels of spinal cord. Preganglionic neuron synapses with postganglionic neuron relatively far from the effector cells Parasympathetic Division of Autonomic Nervous System Preganglionic neuron starts in brain or sacral level of spinal cord. Preganglionic neuron synapses with postganglionic neuron very near the effector cells

Let’s Start Out With The Sympathetic Division of the autonomic nervous system Preganglionic neurons start in the thoracic or lumbar levels of the spinal cord and They synapse with postganglionic neurons in ganglia which are located relatively far from the effector cells (smooth myocytes, cardiac myocytes, gland cells)

Sympathetic Division of the autonomic nervous system That synapse between preganglionic neurons and postganglionic neurons can occur in either of two sets of ganglia: Paravertebral Ganglia Prevertebral Ganglia Note: Since there are only two neurons which reach from the central nervous system to the effector cells, a sympathetic synapse can occur in either set of ganglia, but not both

Sympathetic Division of the autonomic nervous system Some preganglionic sympathetic neurons synapse with their postganglionic neurons in paravertebral ganglia which form a “chain” next to the vertebrae

(Sympathetic Division) Note that this chain of paravertebral ganglia extends up into the neck to supply sympathetic innervation to structures in the head, neck, and upper thorax

Three things can happen in a paravertebral ganglia of the sympathetic division: A. The preganglionic and postganglionic neurons synapse in the ganglion at the same level and The axon of the postganglionic neuron goes back into the spinal nerve at the same level to reach its effector cells.

Three things can happen in a paravertebral ganglia of the sympathetic division: B. The preganglionic neuron enters the ganglion but goes up or down one or more levels before it synapses with the postganglionic neuron and The axon of the postganglionic neuron then goes back into the spinal nerve at this new level to reach its effector cells.

Three things can happen in a paravertebral ganglia of the sympathetic division: C. The preganglionic neuron just passes through the ganglion and continues to a prevertebral ganglion, where it synapses with the postganglionic neuron. The axon of the postganglionic neuron then goes directly to its effector cells in the abdomen.

(Sympathetic Division of the autonomic nervous system) 2) Preganglionic sympathetic neurons in pathways to abdominal organs pass through the paravertebral ganglia (see previous slide) to synapse with their postganglionic neurons in prevertebral ganglia which are located near major arteries of the abdomen. There are three of these prevertebral ganglia: Celiac ganglion Superior mesenteric ganglion Inferior mesenteric ganglion

The second half of the autonomic nervous system is its Parasympathetic Division Preganglionic parasympathetic neurons start in the brainstem or in sacral levels of the spinal cord and They synapse with postganglionic parasympathetic neurons in ganglia which are located relatively near the effector cells: (smooth myocytes, cardiac myocytes, gland cells)

The second half of the autonomic nervous system is its Parasympathetic Division In the head, there are four larger parasympathetic ganglia located near the effector cells Ciliary ganglion (posterior to eye in orbit) Pterygopalatine ganglion (posterior to maxilla) Submandibular ganglion (near angle of mandible) Otic ganglion (inferior to foramen ovale)

The other part of the autonomic nervous system is its Parasympathetic Division 2. Below the head: small parasympathetic ganglia are located within the walls of target organs such as intestines, heart, uterus, etc.

Parasympathetic Autonomic Ganglia Usually very small, often only a few dozen neuron cell bodies

Most organs have both sympathetic and parasympathetic innervation, each of which acts in opposition to the other to balance the functions of the effector cells.

Most organs have both sympathetic and parasympathetic innervation, each of which acts in opposition to the other to balance the functions of the effector cells. Sympathetic: Fear Fight Flight Sexual intercourse, orgasm, ejaculation Parasympathetic: "Rest, Digest, and Sexual Foreplay"

For example: Heart: Sympathetic increases heart rate & force of contraction Parasympathetic decreases heart rate & force of contraction

For example: (Heart: Sympathetic increases rate & force Parasympathetic decreases rate & force ) Lungs: Sympathetic dilates air passages Parasynpathetic constricts air passages

For example: (Heart: Sympathetic increases rate & force Parasympathetic decreases rate & force ) (Lungs: Sympathetic dilates air passages Parasynpathetic constricts air passages) Digestive System: Sympathetic decreases activity; constricts anal sphincter Parasympathetic increases activity; relaxes anal sphincter

For example: (Heart: Sympathetic increases rate & force Parasympathetic decreases rate & force ) (Lungs: Sympathetic dilates air passages Parasynpathetic constricts air passages) (Digestive System: Sympathetic decreases activity Parasympathetic increases activity) Urinary System: Sympathetic inhibits urination Parasympathetic promotes urination