Chapter 7: PNS- Efferent Division

What is the sequence of events at a neuromuscular junction? (7)

(1) Axon terminal of motor neuron forms neuromuscular junction with a single muscle cell (2) Signals are passed between nerve terminal and muscle fiber by means of neurotransmitter Ach (3) Released ACh binds to receptor sites on motor end plate of muscle cell membrane (4) Binding triggers opening of specific channels in motor end plate (leads to more Na+ in the cell and less K+ out of cell) (5) Ion movements depolarize motor end plate, producing end-plate potential (6) Local current flow between depolarized end plate and adjacent muscle cell membrane brings adjacent areas to threshold (7) Action potential is initiated and propagated throughout muscle fiber

What is the 2 neuron chain in the ANS?

(1) Preganglionic fiber (synapses with cell body of second neuron) (2) Postganglionic fiber (innervates effector organ)

What are the two division of the peripheral nervous system?

1. Autonomic NS 2. Somatic NS

What is the effect of parasympathetic stimulation on our bodies? (9)

1. Constricts pupil and adjusts for near vision (let less light in and decrease visual acuity - rest) 2. Stimulates flow of saliva (large volume) 3. Slows heartbeat 4. Constricts bronchi 5. Stimulates peristalsis and secretion (rest and digest) 6. Stimulates release of bile 7. Contracts bladder contraction 8. Dilation of vessels supplying the penis and clitoris only 9. Restoring energy supplies (glycogen synthesis_

What is the effect of sympathetic stimulation on our bodies? (10)

1. Dilates pupil and adjusts for far vision (let more light in and increase visual acuity) 2. Inhibits flow of saliva (only small volume) 3. Accelerates heartbeat 4. Dilates bronchi 5. Inhibits peristalsis and secretion (don't need the GI tract now) 6. Conversion of glycogen to glucose/activates liver enzymes (quick energy) 7. Secretion of adrenaline and noradrenaline - adrenal medulla (endocrine) 8. Increases alertness in brain 9. Constricts blood flow (only goes to organs that are use to fight or run away (skeletal mm., lungs, brain)) 10. Stimulation of secretion by most seat glands

What are the two subtypes of cholinergic receptors?

1. Nicotine receptors 2. Muscarinic receptors ***both are activated by ACh

What are the two subdivisions of the autonomic nervous system?

1. Sympathetic 2. Parasympathetic

What is the percentage of norepinephrine that's released from the adrenal medulla?

20%

What is the percentage of epinephrine (adrenaline) that's released from the adrenal medulla?

80%

What do postganglionic fibers release in the parasympathetic NS?

ACh

What NT does the somatic nervous system release? What effect does it have?

ACh, stimulates muscle contraction (nicotinic receptor)

Which enzyme breaks down ACh in the synapse and helps stop muscle contraction?

Acetylcholinesterase (AChE)

What are betablockers?

Block beta receptors, but NOT alpha in heart to help decrease HR & BP - vasodilator

What are adrenergic receptors bounded by?

Bound by norepinephrine and epinephrine

How is the sympathetic nervous system able to constrict and dilate blood vessels?

By their RECEPTORS (alpha and beta

Muscarinic receptors

Cholinergic receptors that are activated by mushroom poison muscarine and ACh Found on the effector tissue of the PNS

Nicotine receptors

Cholinergic receptors that are activated by nicotine and ACh -Found on the post ganglionic neuron of autonomic NS and muscle fibers

Epinephrine =

Endocrine = must be released in the blood

What effect do inhalers have on sympathetic NS?

Inhalers ==> dilates bronchi ==> stimulates beta receptors and sympathetic NS

Autonomic Nervous System

Involuntary branch of PNS; subconscious Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue

What is the length of the postganglionic fiber in sympathetic NS?

LONG postganglionic fiber

Where are adrenergic receptors located?

Located on the target tissue of the sympathetic nervous system pathways -Mediates the sympathetic NS response

What are the differences between the neuron synapse and NMJ?

NMJ only uses ACh The post synaptic membrane action potential generated depolarizes muscle not neural tissue NMJ is always excitatory EPP, while synapse can either be EPSP or IPSP NMJ exists between a motor neuron and skeletal muscle fiber, while synapse is junction between 2 neurons NMJ has a one-to-one transmission of APs, whereas one AP in a presynaptic neuron can NOT bring it to the AP in postsynaptic neuron (AP in the post. neuron only occurs during summation of EPSPS brings it to threshold)

Norepinephrine =

Neurotransmitter = must be released into the synaptic cleft

Where do the motor neurons originate in the somatic NS? Where do they end?

Originate in the ventral horn of the spinal cord or brain stem Ends on the skeletal muscle

Where do the fibers originate in the sympathetic NS?

Originate in thoracic and lumbar regions of the spinal cord

Where do the fibers originate in the parasympathetic NS?

Originates from cranial and sacral areas of the CNS

What is the length of the preganglionic fiber in parasympathetic NS?

Preganglionic fiber is LONGER (almost at target organ)

What is the length of the preganglionic fiber in sympathetic NS?

Preganglionic fiber is SHORT (close to spinal cord)

__________________- are the final common pathway by which various regions of CNS exert control over skeletal muscle activity.

Somatic motor neurons -These areas of CNS include spinal cord, motor regions of cortex, basal nuclei, cerebellum, and brain stem

(T/F) Most of the time, sympathetic and parasympathetic nervous systems innervated the same tissue, but they have opposite effects.

TRUE Ex: Iris/pupil

What is the length of the postganglionic fiber in parasympathetic NS?

VERY SHORT postganglionic fiber

Somatic Nervous System

Voluntary control of PNS; conscious Innervates skeletal muscle Extends from CNS to viscera/involuntary organs

What do preganglionic fibers release in BOTH the parasympathetic and sympathetic NS?

acetylcholine (ACh)

What are the two neurotransmitters involved in the ANS?

acetylcholine (ACh) and norepinephrine

What are the types of adrenergic receptors?

alpha: -alpha 1 receptors -alpha 2 receptors beta: high conc. on heart -beta 1 receptors -beta 2 receptors -beta 3 receptors (on lipid and bladder tissue [breaks down lipids for energy]) ***both bind to norepinephrine and epinephrine

epinephrine + alpha receptor =

blood vessel constricts The sympathetic NS vasoconstricts blood vessels that don't need it (GI tract, skin [scared=we're pale]) -limits blood available so it can go elsewhere

What is the neuromuscular junction?

connection/synapse between the motor neuron and the muscle fiber -found ONLY in skeletal muscles

What are cholinergic fibers?

fibers that release ACh

What are adrenergic fibers?

fibers that release norepinephrine (adrenaline)

Sympathetic NS

fight or flight response; dominates in emergency/stressful situations -Promotes responses that prepare body for strenuous physical activity

Ganglion =

group of cell bodies in PNS (OUTSIDE the CNS)

What is the electromechanical coupling?

linking electricity in the neuron to mechanical movement in the muscle

What is the adrenal medulla?

modified part of the sympathetic ganglion ("glorified SNS ganglion") -Does NOT give rise to postganglionic fibers -Stimulation of preganglionic fibers ==> secretion of hormone into blood

What do postganglionic fibers release in the sympathetic NS?

norepinephrine

epinephrine + beta receptor =

vessel dilates The sympathetic NS vasodilates blood vessels that need it - skeletal, heart and brain