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Topic 8: Peripheral Nervous System: Efferent Division


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Describe the organization of the efferent division (the two branches).
~Autonomic: 1. involuntary branch 2. two parts: -sympathetic -parasmpathetic ~Somatic 1. voluntary branch 2. affects skeletal muscle
How is the Autonomic Nervous system structure common in both Sympathetic and Parasympathetic systems?
*Every pathway in each autonomic pathway consists of a two neuron chain *cell body of first neuron lies in the CNS *Its axon synapses with cell body of 2nd neuron in chain in a ganglion *axon of 2nd neuron innervates the effector organ
What is a ganglion?
A cluster of neuron cell bodies in the peripheral nervous system.
What is the autonomic structure of the Sympathetic system?
*Originate in the thoracic (chest) and lumbar (abdominal) regions of the spinal cord *Adrenal Medulla (inner part of the adrenal) is modified sympathetic ganglion -it secretes hormones into the blood when stimulated
What is the autonomic structure of the Parasympathetic system?
*Originates in the cranial (brain) and sacral (pelvic) areas of the CNS *Ganglia close to effector organs
Describe what the Sympathetic neurotransmitter chain releases.
*1st neuron in chain releases acetylcholine *2nd neuron in chain relaeases norepinephrine *adrenal medulla releases mostly epinephrine into the blood
Describe the Parasympathetic neurotransmitter chain releases.
*1st neuron in chain releases acetylcholine *2nd neuron in chain releases acetylcholine
How do the neurotranmitters work on the effector organs (para/sympathetic).
*Sympathetic releases norepinephrine and epinephrine while *parasympathetic releases acetylcholine
How do effector organs responsd to para/sympathetic?
Depends on: -effector organ -its receptors -neurotransmitter
Describe acetycholine receptors.
*located on 2nd neuron in all autonomic neuron chains *on membrane in effector organs
Describe norepinephrine and epinephrine receptors that are distributed on effector organs. (alpha, beta-1, beta-2)
*alpha: binds NE preferentially, usually causes contriction/contraction *beta-1: binds NE and epi equally, found primarily in the heart, causes stimulation of heart *beta-2: binds mostly epi, usally causes local dialation/relaxation
How are sympathetic and parasympathetic working on organs the same as a shower?
They work in exact opposition to get it just right.
How is the sympathetic and parasympathetic working in opposition have exceptions?
-blood vessels get only sympathetic (except genital) -sweat glands supplied by sympathetic only -salivary glands supplied by both but different kinds of saliva produced by each
What is Sympathetic/Parasympathetic Tonic Activity?
When both sysmtems active at low levels.
Use example of Flight or Fight situation to explain how the Sympathetic system dominates, what is going on?
1. Blood vessels to most organs contricted = reduced blood flow to degestive organ (caused by alpha receptors binding NE) 2. blood vessels to heart dilated (caused by beta-2 receptors binding epi) 3. Increased heart rate and increased force of contraction of whole heart (caused by beta-1 receptors binding epi and NE) 4. Blood vessels to skeletal muscle dilated (caused by beta-2 receptors binding epi) 5. Airways in lung dilated (caused by beta-2 receptors binding epi) 6. Glucose released (caused by beta-2 receptors in liver binding epi)
When is parasympathetic system dominant?
In quiet situations, involved in regulating normal housekeeping functions ie: digestion etc.
Male Sex Cycle: Erection.
1. penis spongy tissue of veins and capillaries during arousal fills with blood, increased pressure closes off veins = vasocongestion = erection 2. Erection controlled by spinal reflex btwn mechanoreceptors and the erection generating center in spinal cord 3. efferent response: parasympathetic -> vasodilation of blood ->vasocongestion = erection 4. regions in brain can enhance or retard erection
Male Sex Cycle: Emission of sperm from testis.
Stimulation becomes intense, penis spinal reflex switches to sympathetic efferent causing smooth muscle in penis and testes to contract to emit sperm and seminal fluids into urethra
Male Sex Cycle: Expulsion of Sperm from Penis.
1. urethra fills with semen triggers sympathetic response that activates skeletal muscle at base of penis and smooth muscle in penis 2. rythmic contraction at .8 second intervals increases pressure inside penis forcibly expelling semen = orgasm 3. Refractory - caused by hormone prolactin from pituitary gland
Female Sex Cycle.
1. stimuli triggers spinal reflex causes parasympathetic induced vasodilation of blood vessels in vagina 2. clit composed of spongy vascular tissue becomes erect 3. vasocongestion of vagina causes release of lube, allows entry 4. vasocongestion also occurs in breasts and face becomes flushed from blood flow 5. vasocongestion = reduces inner circumfrence 6. uteris raises lifting cervix, creating space for ejaculation 7. stimulation continues, sympathetic induced rythmic contractions of pelvis muscles, especially lower 1/3 of vaginal canal at .8 second intervals = orgasm 8. no refractory period
Somatic Nervous System: Structure of Motor Neurons.
~Cell bodies are in ventral horn of the spinal cord ~axon of motor neuron is continuous from spinal cord to termination in skeletal muscle 3. Axon terminals relase acetylcholine
Somatic Nervous System: Control of Motor Neuron Function.
~ Ach (acetylcholine) relase causes excitation and contraction of the muscle ~can only stimulate skeletal muscle ~control and level of activity exerted by relative balance of EPSP and IPSP from excitatory and inhibitory presynaptic inputs; thus on-off system unlike autonomic ~some inputs are part of spinal-reflex pathways; others are part of descending pathways from parts of the brain (especially motor regions of brain) ~somatic nervous system considered voluntary, but much of skeletal activity is subconscious (walk, balance, posture)
Somatic Nervous System: Neuromuscular Junctions: Structure.
-motor neuron has long myelinated axon -part of axon near muscle divides into many axon terminals which are unmylinated -each axon terminal forms a neuromuscular junction with one of many muscle cells (aka muscle fiber) -muscle fiber is long and cylindrical -axon terminal has a knob at end called terminal button - part of muscle fiber under terminal button is called motor end plate
Somatic Nervous System: Neuromuscular Juncitons: Function.
-motor neuron AP reaches terminal button -triggers of Ca channels; Ca enters terminal button -Ca triggers release of acetylcholine from terminal buttom -Ach diffuses across gap and binds receptors on membrane of motor end plate -binding of Ach results in opening of cation channels; result: lots of Na enters muscle cell, a little K+ leaves cell, membrane depolarizes -entry of Na+ results in end plate potential, which is a graded potential, and is called an end plate potential. Local current flow leads to AP in membrane of muscle fiber next to motor end plate; AP goes in both directions -Ach is destroyed by acetylcholinesterase, terminating the muscle cell response

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