Autonomic and Somatic Nervous Systems

what does the autonomic nervous system consist of

motor neurons that innervate visceral effectors

• ex: smooth muscles, cardiac muscle, glands

what is the autonomic nervous system responsible for

routine homeostatic activities

examples of routine homeostatic activities

shunting blood to areas that need it

adjusts heart rate, blood pressure, digestion, etc

the autonomic nervous system operates via what type of control?

subconscious (involuntary) control

What are the two major divisions of the autonomic nervous system

sympathetic nervous system - fight, flight, or freeze

parasympathetic nervous system - rest and digest

The somatic nervous system has what types of neurons

both sensory and motor neurons

motor neurons

innervate skeletal muscles

sensory neurons

touch, pain, temperature, proprioception (sense of self position), sight, hearing, taste, smell, and equilibrium

Both the ANS and Somatic nervous system have

motor fibers

what do the ANS and Somatic nervous system differ in

efferent pathways and ganglia

target organ responses to neurotransmitters

Both the ANS and the somatic nervous system are regulated and coordinated by

higher brain centers

Most spinal and many cranial nerves contain

both somatic and autonomic fibers

Adaptions usually involve

both skeletal muscles and visceral organs

somatic nervous system

one-neuron motor pathway

the somatic nervous system directly synapses with the

effector

which two motor neurons does the autonomic nervous system use in series

preganglionic neuron

postganglionic neuron

preganglionic neuron

cell body in CNS

axon extends to an autonomic ganglion

postganglionic neuron

cell body and dendrites located in an autonomic ganglion

unmyelinated axon extends from ganglion to effector

Where does the postganglionic neuron synapse with preganglionic axons

in an autonomic ganglion

pathway of an autonomic motor neuron in the ANS

preganglionic cell body (CNS) → preganglionic axon → autonomic ganglion (postganglionic dendrites and cell body) → postganglionic axon → effector

effectors in SNS

skeletal muscle

efferent pathways in SNS

one nerve fiber from CNS to effector

no ganglia

neurotransmitters in SNS

acetylcholine

effect on target cells in SNS

always excitatory

effect of denervation in SNS

flaccid paralysis

control of SNS

usually voluntary

effectors in ANS

glands, smooth muscle, cardiac muscle

efferent pathways in ANS

two nerve fibers from CNS to effector

synapse at a ganglion

Neurotransmitters of ANS

ACh and Norepinephrine

ANS’ effect on target cells

excitatory or inhibitory

ANS’ effect of denervation

denervation hypersensitivity

ANS control

usually involuntary

SNS sensory input

from somatic senses and special senses

SNS control of motor output

voluntary control from cerebral cortes

SNS motor neuron pathway

one-neuron pathways

somatic motor neuron extending from CNS synapse directly with effector

SNS response

contraction of skeletal muscle

ANS sensory input

mainly from interoceptors

some from somatic and special senses

ANS control of motor output

involuntary control from hypothalamus, limbic system, brainstem, and spinal cord; limited control from cerebral cortex

ANS motor neuron pathway

usually two-neuron pathway

ANS responses

contraction or relaxation of smooth muscle

increased or decreased rate and force of contraction of cardiac muscle

increased or decreased secretions of glands

divisions of ANS

parasympathetic division

sympathetic division

parasympathetic division

promotes maintenance functions

conserves energy

sympathetic division

mobilizes body during activity

dual innervation

all visceral organs are served by both divisions, but these divisions cause opposite effects

what is the purpose of dynamic antagonism between the two divisions of the ANS

maintains homeostasis

the sympathetic division is referred to as

fight or flight system/ E division

What activates the sympathetic divison

exercise, excitement, emergency, embarrassment

bodily reaction to sympathetic division activation

increased heart rate and blood pressure

dry mouth

cold, sweaty skin

dilated pupils

during vigorous physical activity, the sympathetic division

shunts blood to skeletal muscles and heart

dilates airways

causes liver to release glucose

The parasympathetic division aims to

keep body energy use as low as possible, even while carrying out maintenance activities

what is the parasympathetic division referred to as

rest and digest system

D division

what does the parasympathetic division direct

directs digestion, diuresis, defecation

example of the parasympathetic division - person relaxing and reading after a meal

• blood pressure, heart rate, and respiratory rates are low

• GT activity is high - increased salivation, increased secretions and motility

• pupils constricted; lenses accommodated for close vision

ganglia

sites of synapses between preganglionic and postganglionic neurons in the PNS

parasympathetic ganglia

terminal ganglia

sympathetic ganglia

sympathetic trunk (paravertebral) ganglia

prevertebral ganglia

sympathetic trunk (paravertebral) ganglia

lie in a vertical row on either side of the vertebral column

prevertebral ganglia

lie anterior to the vertebral column and close to the large abdominal arteries

Sympathetic division site of origin

thoracolumbar (T1 - L2/3)

Sympathetic division preganglionic fiber length

short

sympathetic division postganglionic fiber length

long

sympathetic division ganglia location

close to spinal cord

sympathetic division neurotransmitters released

preganglionic - ACh

postganglionic - mostly NE, some ACh

parasympathetic sites of origin

craniosacral (CN III, VII, IX, X, and S2-S4)

Parasympathetic preganglionic fiber length

long

parasympathetic postganglionic fiber length

short

Parasympathetic ganglia location

in or near their visceral effector organ

parasympathetic neurotransmitters released

preganglionic - ACh

postganglionic - ACh

What is the complexity and innervation of the sympathetic division like in comparison to the parasympathetic division

the sympathetic division is more complex and innervates more organs than the parasympathetic division

what structures are innervated only by the sympathetic division

sweat glands

arrector pili muscle

smooth muscles of all blood vessels

The sympathetic division includes which ganglia

sympathetic trunk ganglia and prevertebral ganglia

the sympathetic division innervates which gland

adrenal glands

organization of sympathetic division diagram

what are the two areas of the parasympathetic division

cranial and sacral

In the parasympathetic division, where do the long preganglionic fibers extend from and to

extend from the CNS almost to target organs

in the parasympathetic division, what do the long preganglionic fibers synpase with

synapse with postganglionic neurons in ganglia that are close to (terminal ganglia) or within (intramural ganglia) target organs

in the parasympathetic division, what do short postganglionic fibers synapse with

synapse with effectors

Terminal ganglia of the parasympathetic division

ciliary ganglion

pterygopalatine ganglion

submandibular ganglion

otic ganglion

Where do preganglionic axons branch off of, and what do they form

sacral nerves

form pelvic splanchnic nerves

where are the cell bodies of the parasympathetic division located

the brain stem

Cranial nerves that carry parasympathetic fibers

Oculomotor (III)

Facial (VII)

Glossopharyngeal (IX)

Vagus (X)

oculomotor in Parasympathetic division

constrict pupils, adjust lens for focus

Facial nerve in parasympathetic division

stimulate nasal and lacrimal glands

stimulate submandibular and sublingual salivary glands

glossopharyngeal nerve in parasympathetic division

stimulate parotoid salivary glands

vagus nerve in parasympathetic division

90% of all preganglionic parasympathetic fibers

Preganglionic fibers for vagus nerve arise from

the medulla

where do the preganglionic fibers for the vagus nerve synapse in

ganglia in walls of all thoracic and abdominal viscera

functional effects of the vagus nerve in the parasympathetic division

slows heart rate

serves lungs and bronchi

sends branches to stomach, liver, gallbladder, pancreas, small intestine, and part of large intestine

Where does the sacral part of the parasympathetic division originate from

neurons in S2-S4

what does the sacral part of the parasympathetic division serve

pelvic organs and distal half of large intestine

where do axons in the sacral part of the parasympathetic division travel

in the ventral root of spinal nerves

they then branch off to form pelvic splanchnic nerves

preganglionic parasympathetic neurons in the sacral part of the parasympathetic division synapse with

ganglia in the pelvic floor

intramural ganglia in walls of distal half of large intestine, urinary bladder, ureters, and reproductive organs