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What is the PNS?
- - all neural structures outside the brain and spinal cord
- - includes sensory receptors, peripheral nerves, associated ganglia, and motor endings
- - provides links to and from the external environment
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Sensory Receptors
- - Structures specialized to respond to stimuli
- - three ways to classify
- - by stimulus
- - by location
- - by structural complexity
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Receptor Classification By Stimulus Type
- 1. Mechanoreceptors - respond to touch, pressure, vibration, stretch, and itch
- 2. thermoreceptors - sensitive to changes in temperature
- 3. Photoreceptors - respond to light energy (e.g. retina)
- 4. Chemoreceptors - respond to chemical (e.g. smell, taste, changes in blood chemistry)
- 5. Norciceptors - sensitive to pain-causing stimuli
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Receptor Classification by Location
- 1. Exteroceptors
- - respond to stimuli arising outside the body
- - found near the body surface
- - sensitive to touch, pressure, pain, and temperature
- - include the special sense organs
- 2. Interoceptors
- - respond to stimuli arising within the body
- - found in internal viscera and blood vessels
- - sensitive to chemical changes, stretch, and temperature changes
- 3. Proprioceptors
- - respond to degree of stretch of the organs they occupy
- - found in skeletal muscles, tendons, joints, ligaments, and connective tissue
- coverings of bone and muscles
- - constantly “advise” the brain of one’s movements
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Receptor Classification by Structural Complexity
- - receptors are structurally classified as either simple or complex
- - most receptors are simple and include encapsulated and unencapsulated varieties
- - complex receptors are special sense organs
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Simple Receptors
- 1. Encapsulated
- - free dendritic nerve endings with knob-like swellings
- - respond chiefly to temperature and pain
- - merkel (tactile) discs
- - hair follicle receptors
- 2. Unencapsulated - enclosed within connective tissue
- - meissner’s corpuscles
- - abundant in hairless skin
- - detect light pressure and discriminative touch
- - pacinian corpuscles
- - located deep in skin
- - deteck deep pressure and high frequency vibration
- - muscle spindles
- - located within skeletal muscle and detect stretching
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What is Sensation?
the awareness of changes in the internal and external environment
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What is Perception?
the conscious interpretation of those stimuli
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what is a nerve?
a cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue
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Endoneurium
loose connective tissue that surrounds axons
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Peroneurium
coarse connective tissue that bundles fibers into faciscles
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Epineurium
touch fibrous sheath around a nerve
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Classification of Nerves
- - sensory and motor divisions
- - sensory (afferent) - carry impulses to the CNS
- - motor (efferent) - carry impulses from CNS
- - mixed - sensory and motor fibers carry impulses to and from CNS; most common type of nerve
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What are the four types of mixed nerves?
- - somatic afferent and somatic efferent
- - visceral afferent and visceral efferent
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What are mixed nerves?
carry somatic and autonomic (visceral) impulses
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Where do peripheral nerves originate?
From the brain (cranial nerves) and spinal cord (spinal nerves)
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Facts about cranial nerves
- - twelve pairs of cranial nerves arise from the brain
- - they have sensory, motor, or both sensory and motor functions
- - each nerve is identified by a number (1 - 12) and a name
- - first two originate from the forebrain
- - last ten originate from the brain stem
- - generally, cranial nerves innervate the head and neck
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Cranial Nerve 1
- Olfactory Nerve
- - arises from the olfactory epithelium
- - carries smell to the primary olfactory cortex
- - afferent only nerve
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Cranial Nerve 2
- Optic Nerve
- - arises from the retina of the eye
- - carries visual information to the primary visual cortex
- - afferent only nerve
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Cranial Nerve 3
- Ocularmotor Nerve
- - serves the muscles that moves the eye
- - functions include directing the eyeball, raising the eyelid, controlling lens shape, and constricting the iris.
- - motor only
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Cranial Nerve 4
- Trochlear Nerve
- - primarly motor nerve that directs the eyeball
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Cranial Nerve 5
- Trigemial
- - largest cranial nerve
- - primary sensory nerve of the face with some motor function
- - three division: ophthalmic (V1), maxillary (V2), and mandibular (V3)
- - conveys sensory impulses from various areas of the face (V1 & V2) and supplies motor fibers (V3) for mastation
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Cranial Nerve 6
- Abducens
- - primary motor nerve innervating the lateral rectus mucles
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Cranial Nerve 7
- - main motor nerve of the face
- - mixed nerve with five branches: temporal, zygomatic, buccal, mandibular, and cervical
- - motor functions include
- facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands
- - sensory functions is taste from the anterior two-thirds of the tongue
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Cranial Nerve 8
- Vestibulocochlear
- - fibers arise from the hearing and equilibrium apparatus of the inner ear
- - two divisions - cochlear (hearing) and vestibular (balance)
- - mixed nerve with very little motor functions
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Cranial Nerve 9
- Glossopharyngeal
- - nerve 9 is a mixed nerve with motor and sensory functions
- - motor - innervates part of the tongue and pharynx
- - sensory - fibers conduct taste and general sensory impulses from the tongue and
- Pharynx
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Cranial Nerve 10
- Vagus
- - the only cranial nerve that extends beyond the head and neck
- - the vagus is a mixed nerve
- - most motor fibers are parasympathetic fibers to the heart, longs, and visceral organs
- - its sensory function is in taste
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Cranial Nerve 11
- Accessory
- - travels with the vagus to innervate muscles of the neck, larynx, and pharynx
- - motor only nerve
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Cranial Nerve 12
- Hypoglossal
- - innervates both extrinsic and intrinsic muscles of the tongue, which contribute to
- swallowing and speech
- - motor only nerve
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Spinal Nerves
- - thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the
- body except the head
- - they are named according to their point of issue
- - 8 cervical (C1 - C8)
- - 12 thoracic (T1 - T12)
- - 5 lumbar (L1 - L5)
- - sacral (S1 - S5)
- - 1 cockerel (Cnot)
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Spinal Nerves: Rami
- - the short spinal nerves (about an inch) branch into two major rami
- - dorsal ramus
- - short and extends dorsally
- - carries both sensory and motor
- - serves body tissue posterior to spinal cord
- - ventral ramus
- - large and extends ventrally
- - carries both sensory and motor
- - serves the body tissue anterior to spinal cord
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Nerves Plexuses
- - all ventral rami except T2 - T12 form interlacing nerve networks called plexuses
- - T1 - T12 form intercostal nerves
- - plexuses are found in the cervical, brachial, lumbar, and sacral regions
- - each resulting branch of a plexus contains fibers from several spinal nerves
- - fibers travel to the periphery via several different routes
- - each muscles receives a nerve supply from more than one spinal nerve
- - damage to one spinal segment cannot completely paralyze a muscle
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Cervical Plexus
- - the cervical plexus is formed by ventral rami of C1 - C4
- - most branches are Cutaneous nerves of the neck, ear, back of head, and shoulders
- - deep to sternocleidomstoid muscle
- - the most important nerve of this plexus is the phrenic nerve
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Brachial Plexus
- - formed by C5 - C8 and T1 (C4 and T2 may also contribute to this plexus)
- - located near the meeting of the shoulder and neck
- - it gives rise to the nerves that innervate the upper limb
- - easily damaged by either an inferior jerking force to the arm or a bow to the
- shoulder that forces the humerus inferiorly
- - nerves = axillary, musculocutatneous, radial, median, and ulnar
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Lumbar Plexus
- - arises from L1 - L4 and innervates the thigh, abdominal wall, and psoas muscle
- - anterior to the pelvis
- - the major nerves are the femoral and the obturator
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Sacral Plexus
- - Arises from L4 - S4 and serves the buttock, lower limb, pelvic structures, and the
- Perineum
- - lies posterior to the pelvis
- - the major nerve is the sciatic, the longest and thickest nerve of the body
- - the sciatic is actually composed of two nerves: the tibial and the common fibular (peroneal) nerves
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Dermatomes
- - a dermatome is the area of skin innervated by the cutaneous branches of a single
- spinal nerve
- - all spinal nerves except C1 participate in dermatomes
- - illustrated in a striped map of sensory innervation
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Regeneration of Nerve Fibers
- - damage to nerve tissue is serious because mature neurons are amitotic
- - if the soma of a damaged nerve remains intact, damage can be repaired
- - regeneration involves coordinated activity among
- - macrophages - remove debris
- - Schwann cells - form regeneration tube and secrete growth factors
- - axons - regenerate damaged part
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The ANS consists of motor neurons that...
- - innervate smooth muscle and cardiac muscle and glands
- - make adjustments to ensure optimal support for body activities
- - operate via subconscious control
- - control centers are the brain stem and hypothalamus
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Efferent Pathways
- - Axons of the ANS are a two-neuron chain
- - the presynaptic (first) neuron has a lightly myelinated axon
- - the postsynaptic (second) neuron extends to an effector organ
- - the cell body is within ganglion (outside CNS)
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What are the ANS divisions? What do they do?
- - ANS Divisions: sympathetic and parasympathetic
- - the sympathetic mobilizes the body during extreme situations
- - the parasympathetic performs maintenance activities and conserves body energy
- - the two divisions counterbalance each other
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Structure of Parasympathetic System
- - long presynaptic neuron
- - short postsynaptic neuron, very near target tissue
- - neurons emerge from brain stem and sacral region of the spinal cord
- - neurons may run within cranial nerves, but never run within spinal nerves
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Oculomotor Nerve causes...
- - causes pupils to constrict and lenses to bulges
- - modifies vision to focus on near objects
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Facial Nerves stimulates...
- - stimulates glands of the face
- - nasal, lacrimal, salivary
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Glossopharyngeal Nerves stimulates...
- stimulates the large parotid salivary gland
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Vagus Nerve
- - accounts for about 90% of parasympathetic activity
- - innervates the abdominal cavity
- - stomach, liver, kidneys, gallbladder, esophagus, pancreas, small intestine, and
- proximal half of the large intestine
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Splanchnic Nerve
- - splanchnic nerves run deep to serve organs
- - innervate distal large intestine, urinary bladder and reproductive organs
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Functions of Parasympathetic Divisions
- - concerned with keeping the body energy use low
- - involves the D activities - digestion, defecation, and diuresis
- - resting and digesting
- - waiting and mating
- - its activity is illustrated in a person who relaxes after a meal
- - blood pressure, heart rate, and respiratory rates are low
- - gastrointestinal tract activity is high
- - the skin is warm and the pupils are constricted
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Neurotransmitters
- - Ach is released by both presynaptic and postsynaptic neurons
- - one neurotransmitter, but two different types of receptors
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Neurotransmitter Receptors
- 1. Muscarinic receptors
- - activated by muscarine
- - found on target such as smooth muscle, cardiac muscle, and glands
- - receptor activation can be excitatory or inhibitory
- 2. Nicotinic receptors
- - activated by nicotine
- - found on skeletal muscles, all postsynaptic neurons, and the adrenal medulla
- - always stimulatory
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What is an agonists?
bind to receptors and stimulate a response
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what is an antagonist?
- - bind to receptor and block a response
- - also called blockers
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Bethanechol
- - muscarinic receptor agonist
- - increase intestinal motility
- - causes bladder muscle to contract and opens the involuntary bladder
- Sphincter
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Atropine
- - a muscarinic receptor antagonists
- - slows gut and bladder function
- - slows the release of body secretions
- - high dose increases heart rate
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Structure of the Sympathetic Division
- - more developed and complex then parasympathetic branch
- - uses short presynaptic neurons
- - emerges from T1 - L2 of spinal cord
- - leaves the spinal cord in spinal nerves
- - after leaving spinal nerves, presynaptic neurons synapse in the sympathetic chain
- - there are 23 ganglia of varying size and shape within each chain
- - from the chain, postsynaptic neurons travel in the thoracic, lumbar and sacral
- splanchnic nerves to abdominal organs
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Functions of the Sympathetic Division
- - the sympathetic division is the fight-or-flight system
- - involves E activities - exercise, excitement, emergency and embarrassment
- - promotes adjustments during exercise - blood flow to organs is reduced, flow to
- muscles is increased
- - its activity is illustrated by a person who is threatened
- - heart rate increases, and breathing is rapid and deep
- - the skin is cold and sweaty, and the pupils dilate
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Unique effects of the Sympathetic Division
- - no effect by the parasympathetic branch
- - increases sweat gland activation
- - activates adrenal medulla gland
- - increases cellular metabolic rate
- - increases lipolysis by fat cells
- - increases blood sugar via glucose release from the liver
- - activates RAS (brain becomes more alert)
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Neurotransmitter - Sympathetic
- - presynaptic neurons release ACh
- - postsynaptic neurons release epinephrine or norepinephrine
- - these bind to adrenergic receptors
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Alpha Receptors
- - two subtypes
- - alpha (a 1) receptors are on blood vessels, not on cardiac muscles
- - alpha (a 2) receptors are on platelets
- - both types bind epinephrine and norepinephrine equally
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Beta Receptors
- - three subtypes
- - Beta 1 (b 1) commonly on the heart, blood vessels and kidneys
- - Beta 2 (b 2) common on lungs and abdominal organs
- - Beta 3 (b 3) common on adipose tissue
- - Beta receptors bind epinephrine better than norepinephrine
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Propanolol
- - broad beta receptor antagonist
- - used to slow heart and treat arrhythmias
- - however, blocking beta 2 receptors can cause bronchoconstriction
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Metoprolol
- - beta 1 specific antagonist
- - used to slow heart rate and treat arrhythmias
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Albuterol
- - a beta 2 agonist
- - used to dilate bronchioles, increases air flow
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Doxazosin
- - an alpha receptor antagonist
- - relaxes blood vessels, which lowers blood pressure
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Ephedrine or phenylephrine
- - alpha receptor agonists
- - used to excite the body
- - found in cold medicines to mask symptoms
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Raynaud’s Disease
- - caused by excessive sympathetic activity
- - constricts blood vessels, particularly in extremities
- - causes pain and paleness in the fingers and toes
- - triggered in response to cold weather and stress
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Mental Stress
- - causes excess sympathetic activity
- - increases blood pressure
- - increases brain alertness
- - inhibits intestinal and breeding functions
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Localized vs Diffuse Effects
- - the parasympathetic division exerts short-lived, highly localized control
- - the sympathetic division exerts long-lasting, diffuse effects
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Referred Pain (Figure 14.8)
- - pain stimuli arising from the viscera are perceived as somatic in origin
- - this may be due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers
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