ch 16

Preganglionic neurons​

Cell bodies in brainstem and spinal cord

Preganglionic fibers

axons of preganglionic neurons

postganglionic neurons (ganglionic neurons)

Project to autonomic ganglia and synapse with

Postganglionic neurons​

Cell bodies in autonomic ganglia

Postganglionic fibers

axons of postganglionic neurons​

Synapse with peripheral target organs

Sympathetic division

– “fight or flight”​

Prepares the body to deal with stress or emergency​

Increases alertness, respiratory rate, metabolic rate, and muscular abilities

Parasympathetic division

– “rest and digest”​

Conserves energy and maintains the resting metabolic rate

Sympathetic and parasympathetic divisions​

Usually have opposing effects​

If one causes excitation, the other causes inhibition​

May also work independently​

Only one division innervates some structures​

May work together, with each controlling one stage of a complex process

Effects of sympathetic activation

Heightened mental alertness​

Increased metabolic rate​

Reduced digestive and urinary functions​

Activation of energy reserves​

Increased respiratory rate and dilation of respiratory passageways​

Increased heart rate and blood pressure​

Activation of sweat glands

Effects of parasympathetic activation

Decreased metabolic rate​

Decreased heart rate and blood pressure​

Increased secretion by salivary and digestive glands​

Increased motility and blood flow in digestive tract​

Stimulation of urination and defecation

Organization of the sympathetic division​

Sympathetic preganglionic fibers are myelinated and are located between T1 and L2 of the spinal cord.​

They pass through spinal ventral roots and then through white rami communicantes to reach the sympathetic ganglia

Sympathetic ganglia

- clusters of cell bodies of postganglionic neurons

ganglion

Each _____innervates a particular body organ or group of organs

Sympathetic chain ganglia (paravertebral ganglia)​

On either side of the vertebral column​

3 cervical, 10–12 thoracic, 4–5 lumbar, 4–5 sacral, 1 coccygeal chain ganglion​

One preganglionic fiber synapses on many postganglionic neurons​

Postganglionic fibers are unmyelinated and pass through gray rami communicantes ​

Postganglionic neurons innervate effectors in the body wall, thoracic cavity, head, neck, and limbs

Collateral ganglia (prevertebral ganglia) ​

Anterior to the vertebral column​

Originate as paired ganglia (left and right), but typically unpaired in adults due to fusion​

Preganglionic fibers from the seven inferior thoracic spinal segments synapse at the celiac ganglion or the superior mesenteric ganglion ​

splanchnic nerves

Preganglionic fibers from the lumbar segments form____ in the posterior wall of the abdominal cavity and synapse at the inferior mesenteric ganglion

Celiac ganglia

Collateral ganglia

– pair of interconnected masses of gray matter located at the base of the celiac trunk​

Postganglionic fibers innervate the stomach, liver, gallbladder, pancreas, and spleen

Superior mesenteric ganglion

Collateral ganglia

– near the base of the superior mesenteric artery​

Postganglionic fibers innervate the small intestine and proximal two-thirds of the large intestine

Inferior mesenteric ganglion

Collateral ganglia

– near the base of the inferior mesenteric artery​

Postganglionic fibers innervate the kidneys, urinary bladder, last segment of large intestine and sex organs

Adrenal medulla

– modified sympathetic ganglion at the center of each adrenal gland​

Postganglionic neurons have very short axons​

Preganglionic neurons synapse on secretory cells.​

When stimulated, they release epinephrine (adrenaline) and norepinephrine (noradrenaline) into the bloodstream​

The neurotransmitters function as hormones to cause changes in the metabolic activities of different target cells, including cells not innervated by sympathetic postganglionic fibers​

The effects last much longer than those produced by direct sympathetic innervation

Sympathetic activation

– the entire sympathetic division responds during a crisis

Effects of sympathetic activation

​

Increased alertness​

Feelings of energy and euphoria​

Increased blood pressure, heart rate, breathing rate, and depth of respiration​

Elevation of muscle tone ​

Mobilization of energy reserves

varicosities

Neurotransmitters​

Postganglionic neurons branch into telodendria with many swollen segments that store neurotransmitter called _____​

norepinephrine

Most postganglionic neurons release _____ (N E) at target organs ​

Synapses that use N E are called adrenergic​

N E from the synaptic cleft can be reabsorbed into varicosities and reused or is broken down by the enzymes monoamine oxidase (M A O) or catechol-O-metyltransferase (C O M T)

cholinergic

When stimulated, preganglionic neurons release ACh at synapses with ganglionic neurons. Such synapses are called

adrenergic

Most ganglionic neurons release NE at the varicosities. Such neurons are called

A C h​

A few postganglionic neurons release ____Varicosities releasing _____ are in the body wall, the skin, the brain and skeletal muscle​

epinephrine and norepinephrine

The adrenal medulla releases_____ as hormones with long lasting effects.

Adrenergic receptors

– membrane G-protein-coupled receptors that bind to norepinephrine and epinephrine

Alpha-1 receptors

More common​

Found primarily in smooth muscle cells​

Stimulation has excitatory effect (release of intracellular calcium ions)

alpha and beta receptors

Alpha-2 receptors

Found on both pre- and postsynaptic sympathetic and parasympathetic neurons​

Stimulation lowers c A M P levels in cytoplasm and has inhibitory effect ​

Coordinates activities of the A N S

Beta receptors​

Located in skeletal muscles, lungs, heart, liver, etc.​

Stimulation increases intracellular c A M P levels and triggers changes in metabolic activity

Beta-1 receptors

cause increase in metabolic activity in muscles and the heart

Beta-2 receptors

stimulation triggers relaxation of smooth muscles along respiratory tract (dilation of respiratory passageways)

Beta-3 receptors

stimulation leads to lipolysis, the breakdown of triglycerides in adipocytes

Parasympathetic preganglionic fibers

Fibers that leave the brain are in cranial nerves III, VII, IX, X

Synapse in the ciliary, pterygopalatine, submandibular and otic ganglia​

The vagus nerve provides 75% of all parasympathetic output

pelvic nerves​

Parasympathetic preganglionic fibers

Fibers that leave the sacral segments of the spinal cord form____

Synapse at intramural ganglia in the walls of the kidneys, urinary bladder, terminal portion of large intestine and sex organs

Major effects of parasympathetic activation:

Constriction of pupils and focusing the lenses on near objects​

Secretion by digestive glands, such as salivary, gastric, intestinal, duodenal glands, the pancreas and the liver​

Secretion of hormones that promote the absorption and use of nutrients by peripheral cells​

Changes in blood flow and glandular activity are associated with increased energy​

Increased smooth muscle activity along the digestive tract​

Stimulation and coordination of defecation​

Contraction of the urinary bladder during urination​

Constriction of the respiratory passageways​

Reduction in heart rate and the force of contraction

Organization of the parasympathetic division

Long preganglionic fibers​

A typical preganglionic fiber synapses on 6-8 ganglionic neurons all in the same ganglion

Terminal ganglion

– near the target organ​

Usually paired

Intramural ganglion

– embedded in the tissues of the target organ​

Consists of interconnected masses and clusters of ganglion cells

Postganglionic fibers

_______innervate visceral structures of the head and neck and organs in the thoracic and abdominopelvic cavities.

Cholinergic receptors

– receptors for A C h

Nicotinic receptors

– on postganglionic neurons of both the sympathetic and parasympathetic divisions​

Also occur at the neuromuscular junctions in the S N S​

The receptors is a chemically gated Na+ channel​

Activation by A C h causes excitation of postganglionic neuron

Muscarinic receptors

– at target organs and tissues of the parasympathetic division and at cholinergic synapses at target organs in the sympathetic division​

G protein-coupled receptors​

Response can be excitatory or inhibitory depending on the activation or inactivation of specific enzymes

Environmental toxins that bind to adrenergic receptors

Nicotine

Environmental toxins that bind to adrenergic receptors

– binds to ____ receptors​

Targets autonomic ganglia and skeletal neuromuscular junctions ​

_____ poisoning results from widespread exaggerated autonomic activation and may result in coma or death

Muscarine

Environmental toxins that bind to adrenergic receptors

– binds to _______ receptors​

Produced by some poisonous mushrooms​

Results in exaggerated parasympathetic effects at target organs and sweating because of activation of ______ receptors

The sympathetic division has widespread effects

Two sets of sympathetic chain ganglia, three collateral ganglia, and two adrenal medullae​

Short preganglionic fibers, long postganglionic fibers​

Extensive divergence​

Preganglionic neurons release A C h; most postganglionic fibers release N E and some release A C h or N O​

Receptors on postganglionic neurons are nicotinic cholinergic and receptors on target cells are adrenergic and some muscarinic cholinergic​

Effector response depends on second messengers

Parasympathetic division has more specific effects

Ganglionic neurons are located in ganglia within or next to target organs​

Innervates regions serviced by cranial nerves and organs in thoracic and abdominopelvic cavities​

Much less divergence ​

All neurons are cholinergic​

Receptors on postganglionic neurons are nicotinic cholinergic and receptors on target cells are muscarinic cholinergic​

Effects are generally brief and restricted to specific sites

Visceral motor nuclei are associated with cranial nerves III, VII, IX, and X and spinal segments S2 to S4

Dual innervation

– most vital organs are innervated by both the sympathetic and the parasympathetic divisions​

The two divisions commonly have opposing effects

Autonomic tone

– resting level of activity of autonomic motor neurons have ​

Important aspect of A N S function​

Nerves maintain background level of activity, and they can increase or decrease activity to provides greater range of control​

Significant where dual innervation occurs, but more important where it does not occur

The heart receives dual innervation

A C h released by parasympathetic postganglionic fibers slows the heart rate​

N E released by varicosities of sympathetic postganglionic fibers accelerates the heart rate​

Small amounts of both are released continuously, producing autonomic tone​

The parasympathetic division dominates at rest​

Crisis speeds the heart rate by stimulating sympathetic and inhibiting parasympathetic nerves

Visceral reflexes

– autonomic polysynaptic reflexes that provide automatic motor responses in glands and nonskeletal muscle organs​

Can be modified, facilitated, or inhibited by higher centers, especially hypothalamus

Receptor​

Sensory neuron​

Processing center (one or more interneurons)​

Two visceral motor neurons (preganglionic and postganglionic)​

Peripheral effector

Visceral reflex arc consists of​

Long reflexes

– coordinate the activities of an entire organ​

Visceral sensory neurons deliver information to C N S​

Processing by interneurons in C N S​

A N S carries motor commands to visceral effectors​

Most important in regulating visceral activities in internal organs

Short reflexes

– bypass the C N S and control the activity in one part of an organ​

Involve sensory neurons and interneurons whose cell bodies lie in autonomic ganglia​

Interneurons synapse on postganglionic neurons, which carry the motor commands to effectors​

Control simple motor responses with localized effects​

Important for functions of the digestive tract

Enteric nervous system

​

Capable of controlling digestive functions independent of C N S​

Ganglia in the walls of the digestive tract contain cell bodies of visceral sensory neurons, interneurons and visceral motor neurons​

Their axons form extensive nerve nets

Short-term memories

– do not last long, but the information can be recalled immediately​

Contain small bits of information

Memory consolidation

– converting a short-term memory into along-term memory​

Involves repeating the information

Long-term memories

– long-lasting memories​

Secondary memories

– fade with time and require effort to recall​

Tertiary memories

– last for a lifetime and do not fade

Conscious state

– implies an awareness of and attention to external events and stimuli​

Varying degrees of the conscious state exist

Unconscious state

– unresponsive state which can be light or deep

C N S

Degree of wakefulness indicates the level of ongoing ____ activity​

When the _____ function is abnormal or depressed, the state of wakefulness is affected

Deep sleep

– slow-wave or non-R E M (N R E M) sleep​

The entire body relaxes​

The cerebral cortex activity is at a minimum​

The heart rate, blood pressure, respiratory rate, and energy use decline up to 30%

Rapid eye movement (R E M) sleep​

Active dreaming occurs and eyes move rapidly​

The blood pressure and respiratory rate fluctuate​

Muscle tone decreases markedly, and the person is less receptive to outside stimuli than in deep sleep​

Intense inhibition of somatic motor neurons​

E E G resembles awake state

REM, deep sleep

We alternate between ___ and ____

____ periods initially average 5 minutes and increase to 20 minutes during an 8-hour period​

____ periods last about 90 minutes

Sleep produces:

Minor changes in the physiological activities of organs and systems, not essential for normal function​

Increased protein synthesis in neurons

Insomnia

Extended periods without sleep lead to disturbances in mental function​

- trouble falling asleep and poor sleep quality

Serotonin​

Affects sensory interpretation and emotional states​

Compounds that enhance its effects also produce hallucinations ​

Example: lysergic acid diethylamide (L S D)

Compounds that inhibit its production or block its action cause severe depression and anxiety

Selective serotonin reuptake inhibitors (S S R I s)

antidepressants that slow the removal of serotonin at synapses and make it available for longer​

Fluoxetine (Prozac), Celexa, Luvox, Zoloft, Paxil

Norepinephrine

​

Used throughout the brain​

Compounds that stimulate _____ release cause exhilaration​

Compounds that inhibit _____ cause depression

Dopamine

​

Important in nuclei that control intentional movements and in other centers of the diencephalon and the cerebrum​

Inadequate levels cause motor problems of Parkinson’s disease​

Excessive production may be associated with schizophrenia​

Amphetamines (“speed”) stimulate ______ secretion

Reduction in brain size and weight ​

Common age-related anatomical changes ​

Decrease in volume of the cerebral cortex​

Elderly people have narrower gyri, wider sulci, and larger subarachnoid space

Decrease in blood flow to the brain ​

Common age-related anatomical changes ​

Fatty deposits build up in the walls of blood vessels and reduces blood flow through arteries (arteriosclerosis)​

Increased chances of cerebrovascular accident (C V A), or stroke​

Changes in the synaptic organization of the brain ​

Common age-related anatomical changes ​

Synaptic connections are lost​

The rate of neurotransmitter production declines

Reduction in the number of neurons​

Common age-related anatomical changes ​Brain shrinkage linked to loss of cortical neurons​

No neuronal loss in brainstem nuclei

Decrease in blood flow to the brain ​

Common age-related anatomical changes

Fatty deposits build up in the walls of blood vessels and reduces blood flow through arteries (arteriosclerosis)​

Increased chances of cerebrovascular accident (C V A), or stroke

Changes in the synaptic organization of the brain ​

Common age-related anatomical changes

Synaptic connections are lost​

The rate of neurotransmitter production declines

Anatomical changes lead to functional changes​

Memory consolidation becomes more difficult​

Secondary memories become harder to access​

Hearing, balance, vision, smell, and taste become less acute​

Reaction times are slowed​

Reflexes weaken or disappear​

Precision of motor control decreases​

Motor patterns take longer to perform