ANS Lecture 1 - Sympathetic Nervous System

What is the autonomic nervous system

Carries out functions involuntarily (below level of consciousness)

Functions of the ANS

1. Maintains homeostasis or the constancy of the internal environment
2. Fight or flight system - involved in the activation of emergency mechanisms or response to stress
3. Rest or digest (housekeeping functions)

2 anatomical divisions of the nervous system

Central nervous system and the peripheral nervous system

CNS

Consists of brain and spinal cord. Neural control center. Revceivings incoming information, analyzes/organizes, and initiates appropriate action

PNS

Found outside the CNS - made of cranial + spinal nerves and the sensory receptors

2 divisions of the PNS

Afferent/sensory division and efferent/motor division

Afferent/Sensory division

Carries information detected by receptors to the CNS. Comprises afferent nerves - carries info from sensory receptors to CNS

Somatic sensory information

Sensory info on touch, pain, temperture

Visceral sensory information

Information from internal organs

Special sensory information

Information from special sense organ - visual, olfactory, and auditory sensation

Efferent/motor division

Carries information from the CNS to the effectors, such as glands or muscles that carry out actions directed by CNS

Divisions of the motor system

Somatic nervous system - controls voluntary movements of skeletal muscle and mediation of involuntary reflex arc

Autonomic nervous system - Autonomic motor nerves control smooth muscle, cardiac muscle, and glands

Is the autonomic system voluntary

No - it is involuntary

Sections of the autonomic nervous system

Sympathetic division, parasympathetic division, and the enteric nervous system

Smooth muscle

Muscle tissue that the contractile fibers are not highly ordered. Found in hollow organs (GI tract, bladder, uterus, blood vessels)

Cardiac muscle

Involuntary muscle tissue found only in the heart.

Cranial nerves

12 nerves that emerge directly from the brain, including the brain stem

Vagus nerve

Central nerve 10 -important for parasympathetic division of ANS

Spinal nerves

31 pairs of nerves (afferent + efferent fibers) from the spinal cord

Organization of spinal cord nerves

Cervical (neck), thoracic (chest), lumbar + sacral + coccygeal (lower abdominal and pelvic regions)

Somatic nervous system motor neuron structure

Cell body of neuron found in the CNS. Single axon extends to target organ - the skeletal muscle (1 single synapse between nerve and muscle)

Activation of somatic neuron results in...

Muscle contraction via acetylcholine release

Where does inhibition of muscle contraction occur

In the CNS - efferent neuron is not activated

Somatic nervous system speed of conduction

Faster than autonomic - neurons are large and myelinated

Autonomic nervous system structure

Organized into a chain of 2 neurons - connect the CNS and target tissue organ via a ganglion

Ganglion

Where the preganglionic neuron synapes with the postganglionic neuron. It is a cluster of cell bodies outside the CNS

Preganglionic neuron

First neuron of the chain - cell body is isnide of the CNS - extends from CNS to ganglia

Postganglionic neuron

Second neuron of the chain - cell bodies are inside the ganglia, outside the CNS. Axon leaves ganglia and travels to tissue

Speed of autonomic nervous system

Slower than somatic nervous system - preganglionic neurons are lightly myelinated and postganglionic neurons are unmyelinated

Comparison of somatic and autonomic control

Somatic = voluntary
Autonomic = involuntary

Comparison of somatic and autonomic response

Somatic = skeletal muscle
Autonomic = smooth muscle, cardiac muscle, glands

Comparison of somatic and autonomic efferent (motor) pathway

Somatic - one neuron
Autonomic - 2 neuron chain connected by ganglion

Comparison of somatic and autonomic neurotransmitter

Somatic = Acetylcholine
Autonomic = ACh, norepinephrine, epinephrine, many others

Comparison of somatic and autonomic myelination

Somatic = myelinated
Autonomic = myelinated preganglionic fiber, unmyelinated postganglionic fiber

Subdivision of the autonomic nervous sytem

Sympathetic (SNS) and parasympathetic nervous system (PSNS)

Ganglion location in PSNS

Ganglion is very closer to or even within the walls of target organ. Preganglionic neuron is long, post is short (more isolated signal)

Ganglion location in SNS

Ganglion is located close to spinal cord. Preganglionic neuron is short, post is long (allows for branching and mass discharge)

Mass discharge of SNS

Many organs and tissues are activated following SNS activation

Where the cell bodies of the SNS located

Thoracic (T1-T12) and lumbar (L1-L2) regions of spinal cord

Where are the cell bodies of the PSNS located

In the brainstem and sacral region of the spinal cord

Why is the sympathetic nervous system also called the thoracolumbar division

Cell bodies of preganglionic neurons are found in thoracic or lumbar region of spinal cord

Sympathetic ganglia

Paravertebral ganglia - run parallel to spinal cord on each side

Dorsal root of spinal crod

Pathway into spinal cord - carries sensory information. Contains axons of afferent/sensory pathway

Ventral root of spinal cord

Pathway leaving spinal cord - carries motor information. Contains axons of motor/efferent pathway

Sympathetic trunk/chain

Paired chains of interconnected sympathetic ganglion that lie on either side of vertebral colum. Signals can leave the ventral root into the sympathetic trunk, and can enter the nearest ganglion or travel up and down the trunk

SNS Collateral ganglia (pre-vertebral ganglia)

Ganglia located in front of the vertebral column. Sympathetic pre-ganglionic axon leaves the spinal cord via the ventral root and passes through the sympathetic trunk. The axon travels into collateral ganglion to synapse

The 3 collateral ganglia

Celica ganglion, superior mesenteric ganglion, inferior mesenteric ganglion

Location of collateral ganglia

Lie close to the viscera (internal abdominal organs)

Collateral ganglia function

Innervate abdominal and pelvic viscera

3 pathways a sympathetic preganglionic fiber can take when it leaves the spinal cord

1. Synapse immediately with postganglionic neruon in sympathetic ganglion the same level

2. Travel up or down the sympathetic chain and synapse and ganglia at other levels of the vertebral column

3. Travel through the chain without synapsing, and continute to collateral ganglion as a splanchnic nerve

Communicating rami

Branches or connections between the spinal nerv and the ganglia

White ramus communicans

Branch that leads into the ganglion from the spinal nerve

Why is the white ramus white

Carries myelinated pre-ganglionic fiber (white in color)

Grey ramus comunicans

Branch that goes back into the spinal cord

Why is the gray ramus grey

Carries unmyelinated post-ganglionic fiber (gray in color)

Though the pathways in the SNS are different, what is one similar feature

The pre-ganglionic neuron is short, and the post-ganglionic neuron is long

Function of the sympathetic nervous system

Fight or flight response - how the body reacts in a stressful/fearful situation

Sympathetic nervous system effect on eyes

Dilation of pupils, adjustment for far vision (can see danger better)

Sympathetic nervous system effect on Cardiovascular orgns

Increases heartrate and force of contraction (provide oxygen to muscles)

Sympathetic nervous system effect on arterioles and veins

Constriction - push blood to musles

Sympathetic nervous system effect on skeletal muscle blood vessels

Dilation - allow more oxygen into muscles to run away or fight

Sympathetic nervous system effect on lungs

Dilation of bronchioles and inhibition of mucous secretion - grab more O2 from environment and give to blood

Sympathetic nervous system effect on digestive tract

Decreased motility, inhibition of digestive secretions - body focuses on running/fighting instead of eating

Sympathetic nervous system effect on endocrine glands (adrenal medulla)

Stimulation of epinephrine and norepinephrine secretion

Sympathetic nervous system effect on sweat glands (exocrine)

stimulation of secretion

Sympathetic nervous system effect on salivary glands (exocrine)

stimulate small volume of thick saliva (rich in mucous)

Sympathetic nervous system effect on bladder

Prevent urination

Sympathetic nervous system effect on genitals

Males - emission
Females - uterus contraction

Adrenal medulla

Part of the adrenal gland - acts like a modfied sympathetic postganglionic neuron (with no axon or cell body)

Function of adrenal medulla

Preganglionic neurotransmitters activate, cause secretion of epinephrine and norepinephrine into the blood stream

Use of epinephrine and norepinephrine in bloodstream

Travel to different targe tissues/organs to produce a response, allowing hormones to reach places that do not receive nervous innervation

Use of adrenal medulla hormones being broken down in the liver

Allows for prolonged effect on the body