Ch. 14

CNS & PNS

Brain & spinal cord

Nerves & ganglia (collections of cell bodies)

carry sensory info into brain/spinal cord

signals from skin, muscles, joints, special senses

signals from body organs

carry motor info from CNS to effectors

signals to skeletal muscles, voluntary

signals to smooth muscle, cardiac muscle, glands, involuntary

“fight or flight”

“rest and digest”

self-governed & fully independent

Fundamental states & life processes (heart rate, BP, & body temp)

Walter Cannon

a motor nervous system that controls glands, cardiac muscle, & smooth muscle; involuntary

• Viscera of thoracic & abdominal cavities • Some structures of body wall (cutaneous blood vessels vasodilation/constriction, sweat glands, arrector pili muscles)

Involuntarily

do not depend

1. High blood pressure detected by arterial stretch receptors 2. afferent neruon carries signal to CNS 3. efferent neruon signals travel to the heart 4. heart slows reducing blood pressure

1. Baroreceptors sense increased blood pressure 2. Glossopharyngeal nerve transmits signals to medulla oblongata 3. Vagus nerve transmits inhibitory signals to cardiac pacemaker 4. Heart rate decreases

central & peripheral

Control nucleus in the hypothalamus & other brainstem regions

message

A motor neuron from the Brainstem or spinal cord has a myelinated axon that reaches all the way to the skeletal muscle

- Signal must travel across two neurons to get to the target organ - Must cross a synapse where these two neurons meet in an autonomic ganglion

- Presynaptic (preganglionic) neuron - Synapses with a postganglionic neuron

The first neuron has a soma in the Brainstem or spinal cord

Their axon extends the rest of the way to the target cell

Two neurons from CNS to effectors

CNS

peripheral ganglion

Sympathetic & parasympathetic nervous system

Action: exercise, trauma, arousal, competition, anger, or fear (fight or flight)

• Increases heart rate, BP, airflow (bronchiole dilation), blood glucose levels, etc (whole body to cells) • Reduces blood flow to the skin & digestive tract

Calms many body functions reducing energy expenditure & assists in bodily maintenance (rest & digest) - Digestion & waste elimination - “Resting & digesting” state

Most viscera receive nerve fibers from both parasympathetic & sympathetic divisions

Antagonistic & cooperative

oppose each other

Two divisions act on different effectors to produce a unified overall effect

• Digestive tract: parasympathetic innervation high, sympathetic low • Heart: opposite

Sympathetic division

Parasympathetic division

oppose each other two ways

Through dual innervation of same effector cells

• Heart rate decreases (parasympathetic) • Heart rate increases (sympathetic)

Exerted because each division innervated different cells

• Pupillary dilator muscle (sympathetic) dilated pupil • Constrictor pupillae (parasympathetic) constricts pupil

when two divisions act on different effectors to produce a unified effect

• Parasympathetics increase salivary serous cell secretion • Sympathetics increase salivary mucous cell secretion

Autonomic tone, parasympathetic tone, & sympathetic tone

normal background rate of activity that represents the balance of the two systems according to the body’s changing needs

Parasympathetic & sympathetic

• Maintains smooth muscle tone in intestines • Holds resting heart rate down to about 70 to 80 beats per minute

• Keeps most blood vessels partially constricted and maintains blood pressure

• Vasoconstriction - increase in firing frequency • Vasodilation - decrease in firing frequency • Can shift blood flow from one organ to another as needed

blocks action of sympathetic fibers to treat high blood pressure

• prioritizes blood vessels to skeletal muscles and heart in times of emergency • blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise

1. Strong sympathetic tone 2. Smooth muscle contraction 3. Vasoconstriction

1. Weaker sympathetic tone 2. Smooth muscle relaxation 3. Vasodilation

glandular secretion

increased blood flow; increased secretion

decreased blood flow; decreased secretion

employs acetylcholine (ACh) as its neurotransmitter • ACh excites some postsynaptic cells (skeletal muscles) • Inhibits others (cardiac)

direct

Effects determined by types of neurotransmitters released and types of receptors found on target cells

different

• All autonomic fibers secrete either acetylcholine or norepinephrine • There are two classes of receptors for each of these neurotransmitters

two neurons from CNS to effectors

CNS

peripheral ganglion

preganglionic neurons; postganglionic parasympathetic neurons

• Called cholinergic fibers • Any receptor that binds it is called cholinergic receptor

1. Muscarinic receptors 2. Nicotinic receptors

all cardiac muscle, smooth muscle, and gland cells have muscarinic receptors; excitatory or inhibitory due to subclasses of muscarinic responses

• On all ANS postganglionic neurons, in the adrenal medulla, and at neuromuscular junctions of skeletal muscle • Always excitatory when ACh binding occurs

sympathetic postganglionic neurons (called adrenergic fibers)

1. Alpha-adrenergic receptors 2. Beta-adrenergic receptors

•Usually excitatory • Two subclasses use different second messengers (a1 and a2) • Involved in vasoconstriction •Alpha blockers lead to vasodilation

• Usually inhibitory • Two subclasses with different effects, but both act through cAMP as a second messenger (B1 and B2) • Involved in increasing heart rate • Beta blockers decrease heart rate Post HA

Short-lived, highly localized control over effectors (ACh quickly destroyed by acetylcholinesterase)

Longer-lasting, bodywide effects (sym pathos)

reabsorbed • Effects may last several minutes before the circulating NE is broken down by the liver

prolongs effects (increase BP, increased release of NT from glands)

receive only sympathetic fibers

• Thermoregulatory responses to heat • Release of renin from kidneys (regulates blood pressure hormonally) • Metabolic effects (increases metabolic rates of cells, raises blood glucose levels, mobilizes fats for use as fuels) • Prepares muscles to work on a hair trigger (recruitment synchronicity)

frontal lobe

emotional input

The boss”: overall integration of ANS

Regulates pupil size, heart, blood pressure, airflow, salivation, etc.

Reflexes for urination, defecation, erection, and ejaculation

• Hypothalamus - main integration center of ANS activity • Subconscious cerebral input via limbic system structures on hypothalamic centers • Other controls come from cerebral cortex, reticular formation, and spinal cord

• Controls may be direct or indirect (through reticular system) • Centers of hypothalamus control - Heart activity / BP - Body temp, water balance, and endocrine activity - Emotional stages (rage, pleasure) and biological drives (hunger, thirst, sex) - primitive functions - Reactions to fear and activation of “fight-or-flight” system

connections of hypothalamus to limbic system allow cortical influence on ANS

• Connects sensory and mental experiences with the ANS • Powerful emotions influence the ANS because of the connections between our limbic system and the hypothalamus

• Awareness of physiological conditions with goal of consciously influencing them • Biofeedback training allows some to control migraines and manage stress (BP)

• Hypertension • Raynaud’s disease • Autonomic dysreflexia

• Overactive sympathetic vasoconstrictor response to stress • Treated with adrenergic receptor - blocking drugs (alpha blockers)

• Exaggerated vasoconstriction in fingers and toes - Pale, then cyanotic and painful - Treated with vasodilators - Sympathectomy