Nervous System VII

Postganglionic axons of parasympathetic neurons release what?

Acetylcholine (ACH).

Preganglionic axons of both parasympathetic and sympathetic divisions release what?

Acetylcholine (ACH).

Ventral rami

All ventral rami except T2-T12 form interlacing nerve networks called nerve plexuses (cervical, brachial, lumbar, and sacral). Dorsal rami do not form nerve plexuses.

Drugs to influence sympathetic tone

Alpha-blocker drugs interfere with vasomotor fibers. Used to treat hypertension by blocking NE signaling via b1 andrenergic receptors.

Atropine

Anticholinergic; blocks muscarinic ACh receptors. Used to prevent salivation during surgery, and to dilate pupils for examination.

Parasympathetic pre-ganglionic neurons

Are long, traveling to distant ganglion close to tissue affected.

Sympathethic pre-ganglionic neurons

Are shorter traveling primarily to ganglia in the sympathetic trunk via white rami communicans.

Where do spinal nerves exit?

At the interverbral foramen.

Parasympathetic motor nerves originate from cranial nerves and sacral spinal nerves. It is also called the?

Craniosacral division.

Franklin D. Roosevelt was paralayzed from the waist down by a polio infection. He was?

Paraplegic.

A horseback riding accident left Christopher Reeve paralyzed from the neck down. This paralysis is called?

Quadraplegia.

What does RRNR stand for?

Rootlet - Root - Nerve - Ramus

Spinal nerves - rami

Spinal nerves are quite short (1-2 cm). Each branches into mixed rami: 1) Dorsal ramus 2) Ventral ramus - larger than the dorsal ramus.

What do over-the-counter drugs for colds, allergies, and nasal congestion do?

Stimulate alpha-adrenergic receptors to cause vasoconstriction.

What do spinal nerves do?

Supply all body parts but head and part of neck (cranial nerves). 8 cervical - (C1-C8) 12 thoracic - (T1-T12) 5 Lumbar - (L1-L5) 5 Sacral - (S1-S5) 1 Coccygeal - (C0)

Sympathetic division controls

Sympathetic division controls: 1) Thermoregulatory responses to heat 2) Release of renin from kidneys (blood pressure) 3) Metabolic effects: Increases metabolic rates of cells Raises blood glucose levels Mobilizes fats for use as fuels

What do the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels have in common?

They receive only sympathetic fibers.

Sympathetic motor nerves originates from thoracic and lumbar spinal nerves. It is also called the _____________ division.

Thoracolumbar.

Adrenergic receptors

Two major classes: Alpha (subtypes a1, a2) Beta (subtypes b1, b2 , b3)

Cholinergic receptors

Two types of receptors bind ACh: 1) Nicotinic 2) Muscarinic Named after drugs that bind to them and mimic ACh effects.

Effects of NE depend on?

Which subclass of receptor predominates on target organ. B2 is expressed on the blood vessels of the heart, lungs and skeletal tissues. NE binding causes vasodilation and opens bronchioles. A1 is expressed on the blood vessels of the skin. NE binding causes vasoconstriction.

Neurotransmitters

1) Cholinergic fibers release neurotransmitter acetylcholine (Ach) 2) Parasympathetic and sympathetic preganglionic axons 3) All parasympathetic postganglionic axons release Ach 4) Adrenergic fibers release neurotransmitter norepinepherine (NE)

Receptors for neurotransmitters

1) Cholinergic receptors for ACh 2) Adrenergic receptors for NE

Cortical controls

1) Connections of hypothalamus to limbic lobe allow cortical influence on ANS 2) Voluntary cortical control of visceral activities is possible 3) Biofeedback: a) Awareness of physiological conditions with goal of consciously influencing them b) Biofeedback training allows some to control migraines and manage stress

Effects of age on ANS

1) Constipation 2) Dry eyes 3) Frequent eye infections Orthostatic hypotension: Low blood pressure after position change Pressure receptors less responsive to blood pressure changes Cardiovascular centers fail to maintain healthy blood pressure

Hypothalamic controls

1) Control may be direct or indirect (through reticular system) 2) Centers of hypothalamus control: a) Heart activity and blood pressure b) Body temperature, water balance, and endocrine activity c) Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex) d) Reactions to fear and "fight-or-flight" system

Developmental aspects of the ANS

1) During youth, ANS impairments are usually due to injury 2) ANS efficiency declines in old age, partially due to structural changes at preganglionic axon terminals

Homeostatic imbalances of the ANS

1) Hypertension (high blood pressure) Overactive sympathetic vasoconstrictor response to stress Treated with adrenergic receptor - blocking drugs 2) Raynaud's disease Exaggerated vasoconstriction in fingers and toes Pale, then cyanotic and painful Treated with vasodilators

Control of ANS function

1) Hypothalamus—main integrative center of ANS activity 2) Subconscious cerebral input via limbic system structures on hypothalamic centers 3) Other controls come from cerebral cortex, reticular formation, and spinal cord

Regeneration of nerve fibers

1) Mature neurons are amitotic (they don't divide) 2) If cell body is damaged nerve cannot regenerate 3) If peripheral axon damaged, regeneration of the axon can occur 4) Greater distance between severed ends decreases the chance of regeneration

Interactions of the autonomic divisions

1) Most visceral organs have dual innervation 2) Dynamic antagonism allows for precise control of visceral activity 3) Sympathetic division increases heart and respiratory rates, and inhibits digestion and elimination 4) Parasympathetic division decreases heart and respiratory rates, and allows for digestion and discarding of wastes.

Parasympathetic tone

1) Parasympathetic division normally dominates heart, smooth muscle of digestive and urinary tract organs, activate most glands except for adrenal and sweat glands. Slows the heart. Dictates normal activity levels of digestive and urinary tracts. 2) The sympathetic division can override these effects during times of stress 3) Drugs that block parasympathetic responses increase heart rate and cause fecal and urinary retention

Localized versus diffuse effects

1) Parasympathetic division: short-lived, highly localized control over effectors ACh quickly destroyed by acetylcholinesterase 2) Sympathetic division: longer-lasting, bodywide effects NE inactivated more slowly than ACh NE and epinephrine hormones from adrenal medulla prolong effects

Efferent motor neurons of the autonomic nervous system involve a two-neuron circuit. What are these called?

1) Pre-ganglionic neuron 2) Post-ganglionic neuron

Two arms of the autonomic nervous system

1) Sympathetic "Fight or Flight" 2) Parasympathetic "Rest and Digest" Most tissues are innervated by both parasympathetic and sympathetic motor neurons which act in opposition to one another.

Sympathetic tone

1) Sympathetic division controls blood pressure, even at rest 2) Vascular system ~ entirely innervated by sympathetic fibers 3) Sympathetic tone (vasomotor tone): Keeps blood vessels in continual state of partial constriction Sympathetic fibers fire more rapidly to constrict blood vessels and cause blood pressure to rise 4) Sympathetic fibers fire less rapidly to prompt vessels to dilate to decrease blood pressure

Neuronal connection to the spinal cord occurs via two roots. What are they called?

1) Ventral roots 2) Dorsal roots

Spinal Nerves - plexuses

1) Within nerve plexus fibers criss-cross - each branch contains fibers from several different spinal nerves. 2) Redundancy: Each limb muscle is innervated by more than one spinal nerve 3) Damage to one does not lead to paralysis

What are spinal nerves?

31 pairs of mixed nerves named for point of issue from spinal cord.

What is a mixed nerve?

A mixed nerve contains both sensory and motor neurons.

Herniated disc

Damage to obturator nerve due to herniated disk - causes gait problems.

Spinal nerves - roots

Dorsal and ventral roots unite to form spinal nerves, which emerge from vertebral column via intervertebral foramen.

Beta-blockers

Drugs that attach to B2 andrenergic receptors to dilate lung bronchioles in asthmatics; other uses. NE mimetic.

Postganglionic axons of sympathetic neurons release what?

Epinepherine and norepinepherine (also known as adrenalin and noradrenaline).

Muscarinic receptors

Found on: 1) All effector cells stimulated by postganglionic cholinergic fibers (parasympathetic) 2) Effect of ACh at muscarinic receptors: Can be either inhibitory or excitatory Depends on receptor type of target organ

Nicotinic receptors

Found on: 1) Sarcolemma of skeletal muscle cells 2) All postganglionic neurons (sympathetic and parasympathetic) 3) Hormone-producing cells of adrenal medulla Effect of ACh at nicotinic receptors is always stimulatory - opens ion channels, depolarizing postsynaptic cell

Neostigmine

Inhibits acetylcholinesterase that breaks down ACh. Used to treat myasthenia gravis.

Autonomic nervous system

Is the motor division of the peripheral nervous system that controls body activities involuntarily.