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Flashcards in Chapter 13 Deck (64)
1

Peripheral Nervous System (PNS)

Provides links from and to world outside of body
All neural structures outside brain
Example
-Nerves

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Sensory Receptors

Specialized to respond to changes in environment (stimuli)
Activation results in graded potentials that trigger nerve impulses

3

Sensation Vs. Perception

Sensation- Sensory Nerves- Touch
-Awareness of changes in environment
Perception- Either Brain or Spinal Cord- Thought
-Interpretation of changes in environment

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Classification by Stimulus Type

Mechanoreceptors
Thermoreceptors
Photoreceptors
Chemoreceptors
Nociceptors

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Mechanoreceptors

Movement, Pressure

6

Thermoreceptors

Temperature

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Photoreceptors

Light

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Chemoreceptors

Chemicals, Taste, Smell

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Nociceptors

Pain, Spicy, Too Hot

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Sensory Integration

Somatosensory system- part of sensory system serving body wall and limbs
Receives inputs from:
-Exteroceptors
-Proprioceptors
-Interoceptors
Input relayed toward head, but processed along way

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Levels of Sensory Integration

Receptor Level
Circuit Level
Perceptual Level

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Receptor Level

Sensory Receptors

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Circuit Level

Processing in ascending pathways

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Perceptual Level

Processing in cortical sensory areas

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Processing at Receptor Level

To produce sensation
-Receptors activation
-Stimulus location
-Transduction occurs
Graded potentials must reach threshold

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Adaptation of Sensory Receptors

Adaptation is change in sensitivity in presence of constant stimulus
-Receptor membranes become loss responsive
-Receptor potentials decline in frequency or stop

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Processing at the Circuit Level

Pathways of 3 neurons conduct sensory impulses upward to appropriate cortical regions
First Order Sensory Neurons
Second Order Sensory Neurons
Third Order Sensory Neurons

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First Order Sensory Neurons

From receptor to second neuron

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Second Order Sensory Neurons

From spinal cord to third region

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Third Order Sensory Neurons

Thalamus to perception or somatosensory system

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Perception of Pain

To recognize outside threat- to warn us of danger

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Pain Tolerance

Tolerance not threshold
"Sensitive to pain" means low pain tolerance, not low pain threshold
Genes help to determine pain tolerance
Response to pain medications

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Hyperalgesia

Long lasting intense pain.
Same intensity but feels like hyper-stimulated

24

Phantom Limb Pain

Felt in a limb that is no longer present, like feeling a hand on the distal end of an amputated arm

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Referred Pain

Pain from one body region perceived from different region
Example:
-Heart Attack- heart pain but felt in left arm and jaw
-Neck and shoulder pains

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Structure of a Nerve

Connective Tissue Coverings
-Endoneurium- loose connective tissue
-Perineurium- coarse connective tissue
-Epineurium- tough fibrous sheath

27

Ganglia

Contain neuron cell bodies associated with nerves in PNS
Afferent nerve fibers- sensory neurons
Efferent nerve fibers- autonomic motor neurons

28

Regeneration of New Fibers

PNS- yes if cell body is intact
CNS- no

29

Cranial Nerves

12 Pairs; mixed nerves, numbered from 1 to 12

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Olfactory Nerves

Smell: Olfactory Bulbs to Olfactory Cortex

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Optic Nerves

Sight: Retinas to Thalamus Occipital Cortex

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Vagus Nerves

Only Cranial Nerve that extend beyond head and neck region
-Heart
-Lungs
-Abdominal Functions

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Compostition of Cranial Nerves

Some mixed nerves contain both somatic and autonomic fibers

34

Spinal Nerves

31 Pairs of mixed nerves named for point of issue from spinal cord
-8 Cervical (only 7 cervical vertebrae, 1 exits canal below 7)
-13 Thoracic
-5 Lumbar
-5 Sacral
-1 Coccygeal

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Spinal Nerves: Roots

Each spinal nerve connects to spinal cord with two roots
-Ventral
-Dorsal

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Ventral Roots

Contain efferent fibers from ventral horn motor neurons
Fibers innervate skeletal muscles

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Dorsal Roots

Contain afferent fibers from sensory neurons in dorsal root ganglia
Conduct impulses from peripheral receptors

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Brachial Plexuses

5 Nerves
-Axillary
-Musculocutaneous
-Median
-Ulnar
-Radial

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Axillary

Innervates much of shoulder region

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Musculocutaneous

Innervates much of upper arm

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Median

Innervates much of the forearm flexors

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Ulnar

Innervates forearm flexors and intrinsic hand

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Radial

Innervates forearm extensors

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Lumbar Plexus

Innervates thigh, abdominal wall
L1 to L4

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Femoral Nerve

Innervates anterior and medial thigh

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Obturator Nerve

Innervates adductor muscles

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Sacral Plexus

Innervates buttocks, lower limb, pelvis, and perineum
L4 to S4

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Sciatic Nerve

Longest, thickest nerve of body
Innervates posterior/medial thigh and most muscles in leg and foot
Composed of 2 nerves
-Tibial
-Fibular

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Dermatome

Area of skin supplied to one spinal nerve
All spinal nerves except C1 participate in dermatomes
Extent of spinal cord injuries ascertained by affected dermatomes
Overlapping areas

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Innervation of Skeletal Muscle

1. Takes place at neuromuscular junction
2. Neurotransmitter acetylcholine (ACh) released when nerve impulses reaches axon terminal
3. ACh binds to receptors, resulting in:
-Movement of Na+ and K+ across membrane
-Depolarization of muscle cell
-At end plate potential, which triggers an action potential- muscle contraction

51

Reflexes

Rapid, voluntary, predictable motor response to stimulus
Learned/acquired reflexes result from practice or repetition

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Reflex Arc

1. Receptor
2. Sensory Neuron
3. Integration Center
4. Motor Neuron
5. Effector

53

Reflexes: Functional Classification

Somatic Reflexes
Autonomic (visceral) reflexes

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Spinal Nerves: Plexuses

Within plexus fibers criss-cross
-Each branch contains fibers from several spinal nerves
-Fibers from ventral ramus go to body periphery via several routes
--Each limb muscle innervated by more than one spinal nerve

55

Cervical Plexus and the Neck

Formed by ventral rami of C1 to C4
Most branches form cutaneous nerves
-Innervate skin of neck, ear, back of head, and shoulders
-Other branches innervate neck muscles

56

Phrenic Nerve

Major motor and sensory nerve of diaphragm (receives fibers from C3 to C5
Irritation= hiccups

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Brachial Plexus and Upper Limb

Formed by ventral rami of C5 to C8 and T1 (and often C4 and T2)
Gives rise to nerves that innervate upper limb
Numerous major branches of the plexus

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Somatic Reflexes

Activate Skeletal Muscle

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Autonomic (Visceral) Reflexes

Activate visceral effectors (smooth or cardiac muscle or glands

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Spinal Somatic Reflexes

Integration Center: Spinal Cord
Effectors: Skeletal Muscle

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Testing of somatic reflexes allow assessment of nervous system

If exaggerated, distorted, or absent- degeneration/pathology of specific nervous system regions

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Stretch and Tendon Reflexes

To smoothly coordinate skeletal muscle nervous system must receive proprioceptor input regarding
-Length of muscle
-Amount of tension in muscle

63

Muscle Spindles

Contracting muscle reduces tension on muscle spindle

64

Stretch Reflex

Maintains muscle tone in large postural muscles, and adjusts it reflexively
-Causes muscle contraction in response to increased muscle length (stretch)