Nervous System 2b

Chapter 11

Autonomic Nervous System

• A division of the peripheral nervous system

• Remember: the sympathetic nervous system is associated with the “bear”

• The parasympathetic nervous system is associated with the “book”

Sympathetic NS

Originates in the thoracolumbar egments of the spinal cord (Thoracolumbar system)

Synapses in ganglia near the spinal cord

Synapses with neurons to several organs

Effect is widespread

Parasympathetic NS

Originates in the cranial nerves and sacral segments of the cord (craniosacral system)

Synapses in ganglia near the visceral effector

Synapses with neurons to a single organ

Effect is local

Sympathetic NS

Fight or flight

Preganglionic fibers release ACh (cholinergic)

Postganglionic fibers release norepinephrine (adrenergic)

Receptors are 1,2, β1, β2

Parasympathetic NS

Maintenance functions: feed and breed

Preganglionic fibers release ACh

Postganglionic fibers release Acetylcholine

Receptors are nicotinic and muscarinic

• Notice: even though it is small in the previous slide – the adrenal gland is innervated by the sympathetic nervous system. When the sympathetic nervous system is activated, it causes norepinephrine and epinephrine to be released from the adrenal medulla into the blood stream. It takes about 20 minutes for these hormones, which mimic the effects of the sympathetic nervous system, to be inactivated.

Cranial Nerves• Part of the peripheral N.S.• Twelve pairs• Designated by Roman NumeralsI – Olfactory – sensory nerve that functions in

the sense of smellII – Optic nerve – arises from the retina of the

eye and functions in visionIII – Oculomotor – mostly motor function –

most of the muscles of the eye, eyelid, and pupillary constriction

• IV – Trochlear – moves the superior oblique muscle of the eye that passes through a ring of tissue called the trochlea

• V – Trigeminal – three branches – motor- chewing; sensory – skin of the face

• VI – Abducens – lateral rectus eye muscle – abducts the eye

• VII – Facial nerve – motor to muscles of facial expression and secretion of saliva and tears; sensory – taste and proprioception

• VIII –vestibulococholear – sensory –hearing and equilibrium (balance)

• IX – Glossopharyngeal – motor- secretion of saliva; sensory – taste, regulation of blood pressure, and proprioception of muscles involved in swallowing

• X – Vagus – “the wanderer” - motor- smooth muscle contraction and relaxation, secretion of digestive fluids; heart, lungs – parasympathetic innervation; sensory from visceral organs it supplies and proprioception.

• XI – Accessory nerve – motor: swallowing and movements of the head

Sensory - proprioception

• XII – Hypoglossal – motor- movement of tongue during speech and swallowing

sensory- proprioception

One more thing…..

• The blood supply to the brain has many alternate pathways, or anastomoses. The blood vessels that supply the brain, the vertebral arteries and the internal carotid arteries, form branches and link at the base of the brain in a structure called the Circle of Willis. This means that if a blood clot blocks the flow of blood through one pathway, that area of the brain can still be supplied through an alternate vessel.