KAAP309 Lecture Notes - Lecture 13: Sensory Nerve, Axon, Sensory Neuron
18 May 2018
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Ch. 13 Peripheral Nervous System & Reflex Activity
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I. Peripheral Nervous System (PNS)
A. All neural structures outside the brain
1. Sensory receptors
2. Peripheral nerves and assocatied ganglia
3. Motor endings
II. Sensory Receptors
A. Specialized structures which respond to changes in their environment (stimuli)
B. Some receptors are simply ends of sensory nerve fibers. Other receptors are
cells adjacent to sensory nerrve fibers. Other receptors are sensory nerve fiber
endings plus specialized supporting cells and/or extracellular material
C. Receptor activation results in graded potentials that may trigger action
potentials
D. Sensation (awareness of stimulus) and perception (interpretation of the meaning
of the stimulus) occur in the brain
III. Classifying receptors
A. Receptors have been classified according to:
1. The type of stimulus they detect (best)
2. Receptor location in the body
3. Structural complexity of the receptor
B. 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 chemicals (e.g., smell, taste, changes in
blood chemistry)
5. Nociceptors—sensitive to pain-causing stimuli (e.g. extreme heat or
cold, excessive pressure, inflammatory chemicals)
C. Classification by Location
1. Exteroceptors: respond to stimuli arising outside the body: receptors in
the skin for touch, pressure, pain, and temperature; also most special
sense organs (eyes, ears, etc)
2. Interoceptors (visceroceptors): respond to stimuli arising in internal
viscera and blood vessels: chemical environment, tissue stretch,
temperature
3. Proprioceptors: respond to stretch in skeletal muscles, tendons, joints,
ligaments, and connective tissue coverings of bones and muscles;
ifor the rai of oe’s oeets
D. Classification by Structural Complexity
1. Complex receptors: Special sense organs
a) Vision, hearing, equilibrium, smell, taste (ch. 15)
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2. Simple receptors: General sensation
a) Tactile sensations (touch, pressure, stretch, vibration),
temperature, pain, and muscle sense
b) Unencapsulated (free) dendritic endings
c) Encapsulated dendritic endings
IV. From Sensation to Perception
A. Survival depends upon sensation and perception
B. Sensation: awareness of changes in the internal and external environment
C. Perception: conscious interpretation of those stimuli
V. Processing at the Receptor Level
A. Different receptors respond to different stimuli
1. Light, pressure, temperature, chemicals, etc.
B. Receptive field
1. Physical region over which each receptor can detect stimuli
C. Transduction occurs
1. Stimulus energy is converted into a graded potential called a receptor
potential
VI. Receptor processing in general sense receptors (receptors in which there are not
separate receptor cells)
VII. Receptor processing in special sense receptors
VIII. Adaption of Sensory Receptors
A. Change in response in the presence of a constant stimulus
1. Receptor membranes become less responsive
2. Receptor potentials decline in frequency or stop
B. Phasic (fast-adapting) receptors signal beginning or end of stimulus
1. Examples: receptors for pressure, touch, smell
C. Tonic receptors adapt slowly or not at all
1. Examples: nociceptors; most proprioceptors
IX. Processing at the Circuit Level
A. 3-neuron pathway conducts sensory impulses upward to appropriate brain
regions
B. First-order neurons (cell body in DRG or other peripheral ganglion): conduct
impulses from receptor to second-order neurons in the CNS
C. Second-order neurons (in CNS): transmit impulses to thalamus or cerebellum
D. Third-order (thalamic) neurons: conduct impulses from the thalamus to the
somatosensory cortex (perceptual level)
X. Processing at the Perceptual Level
A. Identification of the sensation depends on the specific location of the target
neurons in the sensory cortex
B. Aspects of sensory perception
1. Stimulus detection: requires multiple impulses
2. Magnitude estimation: intensity coded by frequency of APs & number
of neurons active
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3. “patial disriiatio: idetify the site or patter of stiulus (e.g.
two-point discrimination test)
C. Feature abstraction—identification of more complex aspects and several
stimulus properties
D. Quality discrimination: identification of submodalities of a sensation (e.g., sweet
or sour tastes)
E. Pattern recognition: identification of familiar or significant patterns in stimuli
(face, melody, etc.)
XI. Nerve Structure
A. Bundle of myelinated and unmyelinated peripheral axons enclosed by
connective tissue
B. Connective tissue coverings, from inside to outside:
1. Endoneurium, perineurium, epineurium
XII. Classification of Nerves
A. Most nerves are mixed: afferent and efferent fibers and somatic and autonomic
(visceral) fibers
B. Pure sensory (afferent) or motor (efferent) nerves are rare
C. Cranial and spinal nerves (12 pair cranial, Roman numerals; 31 pair spinal,
named for the nearby vertebra, e.g. C5 or L4)
D. Ganglion (plural: ganglia)
1. A group of neuron cell bodies outside the CNS (analogous to nuclei
inside the CNS)
2. associated with nerves
3. Examples
a) dorsal root ganglia (sensory, somatic; ch. 12)
b) autonomic ganglia, such as sympathetic trunk ganglia (motor,
visceral; ch.14)
Ch. 13B Cranial Nerves
I. Cranial Nerves
A. Twelve pairs of nerves associated with the brain
B. Most are mixed in function; two pairs are purely sensory
C. Each nerve is identified by a number (I through XII) and a name
D. On occasion, our trusty truck acts funny—very good vehicle anyho
II. List of Cranial Nerves
A. I Olfactory
B. II Optic
C. III Oculomotor
D. IV Trochlear
E. V Trigeminal
F. VI Abducens
G. VII Facial
H. VIII Vestibulocochlear
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Document Summary
Peripheral nervous system (pns: all neural structures outside the brain, sensory receptors, peripheral nerves and assocatied ganglia, motor endings. Sensory receptors: specialized structures which respond to changes in their environment (stimuli, some receptors are simply ends of sensory nerve fibers. Other receptors are cells adjacent to sensory nerrve fibers. 15: simple receptors: general sensation, tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense, unencapsulated (free) dendritic endings, encapsulated dendritic endings. From sensation to perception: survival depends upon sensation and perception, sensation: awareness of changes in the internal and external environment, perception: conscious interpretation of those stimuli. Receptor processing in general sense receptors (receptors in which there are not separate receptor cells) Nerve structure: bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue, connective tissue coverings, from inside to outside, endoneurium, perineurium, epineurium. 12: autonomic ganglia, such as sympathetic trunk ganglia (motor, visceral; ch. 14)
