Chapter 11: Efferent Division - Autonomic & Somatic Motor Control Flashcards
how is the peripheral nervous system divided?
- sensory division
-visceral sensory division
-somatic sensory division - motor division
-visceral motor division (ANS)
~sympathetic division
~parasympathetic
-somatic motor division
- Control skeletal muscles
- Mostly voluntary (except for reflexes such as swallowing and the knee jerk reaction)
somatic motor neurons
regulate organs to maintain homeostasis
autonomic neurons (visceral)
innervate most effector organs
Both divisions of the autonomic nervous system
tend to be antagonistic
Parasympathetic and sympathetic activities
rest and digest
parasympathetic nervous system
fight or flight reponse
sympathetic nervous system
what are the effector organs of the autonomic nervous system?
- cardiac muscle
- smooth muscle
- glands
- adipose tissue
initiate autonomic, endocrine and behavioral responses
hypothalamus, pons and medulla
initiate behavioral response
- limbic system
- cerebral cortex
under antagonistic control
most internal organs
what are the branches of antagonistic control?
one autonomic branch is excitatory and the other is inhibitory
what are the exceptions to dual antagonistic innervation?
sweat glands, smooth muscle (sympathetic only)
what are the two efferent neurons of the autonomic pathways?
- 1st neuron is preganglionic (arises within CNS)
- 2nd neuron is post ganglionic (outside CNS)
where do the sympathetic neurons originate in the CNS?
thoracic and lumbar regions of the spinal cord
where do parasympathetic neurons originate in the CNS?
brain stem (cranial nerves) and sacral region
Sympathetic ganglia in two ganglion chains along either side of the vertebral column
chain ganglion
are mainly found along to chains that run parallel to the spinal cord and along the aorta (short pre>long post)
sympathetic ganglia
are on or near target (long pre>short post)
-vagus nerve
parasympathetic ganglia
- Contains about 75% of all parasympathetic fibers
- Sensory information from internal organs to brain
- Output from brain to organs
vagus nerve (X)
release acetylcholine (ACh) onto nicotinic cholinergic receptors (nAChR) on the postganglionic cell
Sympathetic and parasympathetic preganglionic neurons
secrete norepinephrine (NE) onto adrenergic receptors on the target cell.
Most postganglionic sympathetic neurons
secrete ACh onto muscarinic cholinergic receptors (mAChR) on the target cell.
Most postganglionic parasympathetic neurons
use acetylcholine and
norepinephrine.
sympathetic pathways
use acetylcholine
parasympathetic pathways
receptors in the sympathetic division
adrenergic receptors
located in the plasma membrane of target cells
adrenergic receptors
what are the two types of adrenergic receptors?
- alpha receptors
- beta receptors
- Generally stimulated by NE and E
- Stimulation activates associated G proteins on cytoplasmic side of plasma membrane
- Activation triggers different activities in the cell
alpha receptors
generally excitatory
alpha 1 receptors
generally inhibitory
alpha 2 receptors
- Generally stimulated by E
- Stimulation of beta receptors and G protein activation triggers changes in metabolic activity of the target cell
beta receptors
what are the 3 types of beta receptors?
beta-1 (β1), beta-2 (β2), beta-3 (β3)
Cardiac muscle
stimulation and
increased tissue
metabolism
beta-1 (β1) receptor
Relaxation of smooth muscle in respiratory passages and in the blood vessels of skeletal muscle
beta-2 (β2) receptor
Release of fatty acids
by adipose tissue for
metabolic use in
other tissues
b3 receptor
Neurotransmitter for all parasympathetic activity is …?
acetylcholine (ACh)
cholinergic receptors
parasympathetic receptors
what are the two types of cholinergic receptors?
- nicotine receptors
- muscarinic receptors
- On all postganglionic neurons
- At the neuromuscular junctions of skeletal muscle fibers
- always excitatory
nicotinic receptors
- G protein-coupled receptors
- Activation produces longer-lasting effects than at nicotinic receptors
- Response can be excitatory or inhibitory
muscarinic receptors
the synapse between a postganglionic autonomic neuron and its target cells (effector).
neuroeffector junction
are series of swollen areas (like beads on a string) at their distal ends containing neurotransmitters
Varicosities of neuroeffector junction
diffuse into the synapse and bind to receptor
neurotransmitters at neuroeffectors junction
release neurotransmitter over the surface of target cells.
Autonomic varicosities
modulated by adjusting the concentration of neurotransmitter in the synapse (more neurotransmitter=longer or stronger response)
Autonomic control over target cells
- diffuses away
- metabolized by enzymes in the extracellular fluid
- actively transported into cells
- monoamine oxidase (MAO) degrades norepinephrine
Autonomic control over target cells is modulated by adjusting the concentration of neurotransmitter in the synapse
is endocrine tissue (of epidermal origin, secretes corticoid hormones)
adrenal cortex
- neuroendocrine tissue
- associated with sympathetic branch
adrenal medulla
what is the primary neurohormone of the adrenal medulla?
epinephrine (fight or flight response)
-secreted into the blood
secretes epinephrine into the blood
adrenal medulla
-a true endocrine gland
adrenal cortex
a modified sympathetic ganglion
adrenal medulla
neurohormone that enters the blood
epinephrine
is a modified
postganglionic
sympathetic
neuron.
chromaffin
- projects axon to skeletal muscle
- CNS origin
- myelinated
- always excitatory
- can be up to a meter long
single neuron of somatic motor division
what is the terminus of the single neuron of the somatic motor division?
branches that innervate many muscle fibers
- Presynaptic axon terminal filled with synaptic vesicles and mitochondria
- Synaptic cleft
- Postsynaptic membrane of the skeletal muscle fiber
neuromuscular junction (NMJ) of somatic motor division
-series of folds on muscle fibers
-has Nicotinic ACh receptors
and Acetylcholinesterase that degrades neurotransmitter
motor end plates
what are the autonomic targets?
- Smooth and cardiac muscles
- Some endocrine and
exocrine glands - Some adipose tissue
consists of axon terminals, motor
end plates on the muscle
membrane, and Schwann cell
sheaths.
The neuromuscular junction
a regionof muscle membrane thatcontains high concentrations ofACh receptors.
motor end plate
is modified into a
motor end plate.
Postsynaptic membrane
arrives at the axon terminal, causing
voltage-gated Ca2+ channels to open
action potential (at NMJ)
causes synaptic vesicles to fuse with the presynaptic membrane and release ACh into the synaptic cleft.
calcium entry (at NMJ)
binds two ACh
molecules, opening a nonspecific monovalent cation channel
-open channel allows Na+ and K+ to pass.
-Net Na+ influx depolarizes the muscle fiber
nicotinic cholinergic receptor (of MNJ)
Which of the following physiological responses results from sympathetic action?
- increase in heart rate
- dilation of blood vessels
- stimulation of glycogenolysis
The parasympathetic nervous system is characterized by….?
long preganglionic and short postganglionic nerve fibers.
The neurotransmitter in the synapse between pre- and postganglionic autonomic neurons is…..?
acetylcholine.
The neurotransmitter norepinephrine is synthesized from
tyrosine
