THE AUTONOMIC NERVOUS SYSTEM

Honors Anatomy & Physiology

ANS in PNS operates via reflex arcs includes:

autonomic sensory neurons integrating centers in CNS autonomic motor neurons

AUTONOMIC REFLEX ARC

AUTONOMIC MOTOR NEURONS when somatic motor neurons sends impulse

to a muscle the effect always excitatory…if they stop sending impulses that muscle atrophies

autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues (cardiac or smooth muscle, glands)

COMPARISONS OF ANS & SOMATIC NS

AUTONOMIC SENSORY NEURONS

source of most input to ANS via sensory receptors called interoceptors

not consciously perceived most of time located in:

blood vessels visceral organs muscles in nervous system

AUTONOMIC RESPONSES

most cannot be altered to any great degree making some responses ideally suited for lie detector tests

AUTONOMIC MOTOR PATHWAYS

most consist of 3 motor neurons in series

1st neuron has cell body in CNS myelinated axon synapses in autonomic ganglion with 2nd motor neuron cell body: its unmyelinated axon effector

except

AUTONOMIC MOTOR PATHWAY

2 BRANCHES OF MOTOR PART OF ANS

SYMPATHETIC DIVISION PARASYMPATHETIC DIVISION

preganglionic axons from thoracolumbar nerves

ganglia far from visceral effector in: sympathetic chain or

collateral ganglia neurotransmitter used:

ACh in ganglia NE in effector organ

preganglionic axons from craniosacral nerves

ganglia near or w/in visceral effector organs

neurotransmitter used: ACh in ganglia ACh in effector organ

MOTOR PART OF ANS

most organs have dual innervation nerve impulses from 1 will increase

activity (excitation) & impulses from other decrease activity (inhibition)

SYMPATHETIC GANGLIA

2 groups:1. sympathetic trunk ganglia

1. lie in vertical row, either side of vertebrae

2. prevertebral ganglia1. lie anterior to vertebral column close

to large abdominal arteries

SYMPATHETIC DIVISION OF ANS

PARASYMPATHETIC GANGLIA

most close to or w/in effector organ

EFFECTS OF SYMPATHETIC & PARASYMPATHETIC DIVISIONS OF THE ANS

HOMEOSTATIC IMBALANCES OF THE ANS

Raynaud’s phenomenon: due to excessive sympathetic stimulation

of smooth muscles in arterioles of digits digits become ischemic (lack of blood)

after exposure to cold or with emotional stress

MEDICAL TERMINOLOGY

autonomic nerve neuropathy: often caused by long-standing diabetes, neuropathy affects 1 or more autonomic nerves, can interfere with reflexes

hyperhydrosis: profuse sweating due to intense stimulation of sweat glands

vagotomy: cutting vagus nerve; often done to decrease production of HCl in patients with severe ulcers