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Nervous System Part Three
Sec 1: Peripheral NS
Name: ___________________________
Sec 2: Autonomic NS
Section 1: PNS
Peripheral Nervous System (PNS)
A. All neural structures outside the brain
o Includes:
 Sensory Receptors
 Peripheral Nerves and associated Ganglia
 Motor Endings
B. Sensory Receptors
o Specialized to respond to changes in their
environment (stimuli)
o Activation results in graded potentials that
trigger nerve impulses
o Sensation (awareness of stimulus) and
perception (interpretation of the meaning of
the stimulus) occur in the brain
C. Classification of Sensory Receptors
o Stimulus Type
 Mechanoreceptors- respond to touch,
pressure, vibration, stretch, and itch
 Thermoreceptors- sensitive to changes in
temperature
 Photoreceptors- respond to light energy
(retina)
 Chemoreceptors- respond to chemicals (smell,
taste, changes in blood)
 Nociceptors- sensitive to pain- causing stimuli
(extreme heat or cold, excessive pressure,
inflammatory chemicals
o Location
 External: Exteroceptors- receptors on skin
 Internal: Interoceptors (visceroceptors)receptors in internal viscera and blood vessels
 Proprioceptors- receptors in bones and
muscles
o Structural Complexity
 Complex receptors- for special sense organs
 in localized areas
 Sight, smell, taste, hearing & equilibrium
 Simple receptors- for general senses
 Widely distributed receptors
 Somatic senses (pain, temp, muscle
distortion, chemical)
Sec 3: Special Senses
D. Sensory Integration
o Input comes from exteroceptors,
proprioceptors, and interceptors
 Input is relayed toward the head, but is
processed along the way
 Levels of neural integration in sensory systems
o Receptor Level – The sensory receptors
 In General Receptors
 In Special Sense Organs
stimulus

receptor potential in receptor cell

release of neurotransmitter

generator potential in first-order sensory
neuron

action potentials (if threshold is reached)
o Circuit level- ascending pathways
 Pathways of three neurons conduct sensory
impulses upward to the appropriate brain
regions
 First-order neurons- conduct impulses from
the receptor level to the second-order neurons
in the CNS
 Second-order neurons- transmit impulses to
the thalamus or cerebellum
 Third-order neurons- conduct impulses from
the thalamus to the somatosensory cortex
(perceptual level)
o Perceptual level- neuronal circuits in the
cerebral cortex
 Identification of the sensation depends on the
specific location of the target neurons in the
sensory cortex
 Aspects of sensory perception:
o Perceptual detection- ability to detect a
stimulus (requires summation of impulses)
o Magnitude estimation- intensity is coded
in the frequency of impulses
o Spatial discrimination- identifying the site
or pattern of the stimulus (studied by the
two-point discrimination test)
o Feature abstraction- identification of more
complex aspects and several stimulus
properties
o Quality discrimination- the ability to
identify submodalities of a sensation
(sweet or sour)
o Pattern recognition- recognition of familiar
or significant patterns in stimuli (melody in
a piece of music)
E. Transmission Lines
o Nerves and associated ganglia
 Structure of a nerve
o Cordlike organ of the PNS
o Bundle of myelinated and unmyelinated
peripheral axons enclosed in connective tissue
 Connective coverings:
o Endoneurium- loose connective tissue that
encloses axons and their myelin sheaths
o Perineurium- coarse connective tissue that
bundles fibers aka fascicles
o Epineurium- tough fibrous sheath around a
nerve
o Ganglia
 Contain neuron cell bodies associated
with nerves
 Dorsal root ganglia (sensory, somatic)
 Autonomic ganglia (motor, visceral)
o Regeneration of nerve fibers
 Mature neurons are amitotic
 If the soma of a damaged nerve is
intact, axon will regenerate
 Involves coordinated activity among:
o Macrophages- remove debris
o Schwann cells- form regeneration
tube and secrete growth factors
o Axons- regenerate damaged parts
 CNS oligodendrocytes bear growthinhibiting proteins that prevent CNS
fiber regeneration
 Spinal nerves
o 31 pairs of mixed nerves named according
to their point of issue from the spinal cord
 8 cervical  (although only 7 vertebrae)
 12 thoracic
 5 lumbar
 5 sacral
 1 coccygeal
 Spinal nerve roots
o Each spinal nerve connects to the spinal
cord via two roots
 Ventral roots- fibers innervate skeletal
muscles
 Dorsal roots- conduct impulses from
peripheral receptors
 Dorsal and ventral roots unite to form
spinal derives, which emerge from the
vertebral column via the intervertebral
foramina
 Each spinal nerve branches into mixed
rami (ramus)
 Rami form plexus
 Innervation of Nerves
o Hilton’s law- any nerve serving a muscle
that produces movement at a joint also
innervates the joint and the skin over the
joint
F. Motor Endings and Activity
o Peripheral Motor Endings
 are PNS elements that activate effectors by
releasing neurotransmitters
o Levels of Motor Control
 Segmental level- lowest level of motor
hierarchy, controls locomotion and specific,
oft-repeated motor activity
 Projection level- projection motor pathways
keep higher command levels informed of what
is happening
 Pre-command level- regulate motor activity
G. Reflex Activity
o Inborn (intrinsic) reflex: a rapid, involuntary,
predictable motor response to a stimulus
o Learned (acquired) reflexes: result from
practice or repetition
o The Reflex Arc
 Components of a reflex arc (neural path)
1. Receptor- site of stimulus action
2. Sensory neuron- transmits afferent
impulses to the CNS
3. Integration center- either monosynaptic or
polysynaptic region within the CNS
4. Motor neuron- conducts efferent impulses
from the integration center to an effector
organ
5. Effector- muscle fiber or gland cell that
responds to the efferent impulses by
contracting or secreting
o Spinal Reflexes
 Spinal somatic reflexes
o Integration center is in the spinal cord
o Effectors are skeletal muscle
 Testing of somatic reflexes is important
clinically to assess the condition of the nervous
system
 Types of reflexes
o 1. Stretch reflexes- maintain muscle tone
in large postural muscles
o 2. Golgi tendon reflexes- help to prevent
damage due to excessive stretch
o 3. Flexor withdrawal reflex - initiated by a
painful stimulus
o 4. Crossed extensor reflex- flexor reflexes
in weight-bearing limbs to maintain
balance
o 5. Abdominal reflexes- contraction of
abdominal muscles from touching of skin
(varies between person)
o 6. Plantar reflexes- stroking lateral aspect
of the sole of the foot causes toes to have
downward flexion
 Babinki’s sign- if toes fan out, common
in infants. In adults indicates
corticospinal or motor cortex damage
Section 2: ANS
Autonomic Nervous System (ANS)
A. The ANS consists of motor neurons that:
o Innervate smooth and cardiac muscle & glands
o Make adjustments to ensure optimal support
for body activities
o Operate via subconscious control (involuntary
nervous system)
B. Differences between Somatic Nervous Sys. (SNS)
and Autonomic Nervous System (ANS):
o Effectors
 SNS is skeletal muscles
 ANS is cardiac and smooth muscles & glands
o Efferent pathways
 SNS- thick heavily myelinated somatic motor
fiber makes up each pathway from the CNS to
the muscle
 ANS- two neuron chain (preganglionic neuron
and ganglionic neuron)
C. Division of the ANS
o Divisions of the ANS
 Sympathetic division- mobilizes the body
during activity. (fight or flight system)
 Parasympathetic division- promotes
maintenance activities and conserves body
energy. Illustrated in a person who relaxes, is
reading, and after a meal
D. Control of ANS Functioning
o Hypothalamus- main integrative center of ANS
activity
o Subconscious cerebral input via limbic lobe
connections influences hypothalamic function
o Other controls come from the cerebral cortex,
the reticular formation, and the spinal cord
E. Developmental aspects of ANS
o During youth, ANS impairments are usually due
to injury
o In old age, ANS efficiency declines, partially due
to structural changes at preganglionic axon
terminals
Section 3: Special Senses
A. Eye and Vision
o 70% of all sensory receptors are in the eye
o Nearly half of the cerebral cortex is involved in
processing visual information
o Most of the eye is protected by a cushion of fat
and the bony orbit
o Structure of the eye
 Eyebrows- shade the eye and protect it from
perspiration
 Eyelids (palpebrae)- protect the eye
anteriorly, eyelashes initiate reflex blinking
 Conjunctiva- transparent membrane that
produces a lubricating mucous secretion
 Lacrimal apparatus- lacrimal glands and
ducts that connect to the nasal cavity and
produce tears
 Extrinsic eye muscles
o 6 strap-like extrinsic eye muscles that
enable the eye to follow moving objects
 4 rectus muscles provide movement to
the eye
 2 oblique muscles move the eye
laterally and rotate the eye
o Structure of the eyeball
 Wall of eyeball contains three layers
o 1. Fibrous- outer most layer that contains
the sclera and cornea
o 2. Vascular- middle pigment layer and
contains three regions1. choroid (supplies blood)
2. ciliary body (controls lens shape)
3. iris (colored part of the eye).
(Pupil controls amount of light
entering the eye.)
o 3. Sensory- the retina
 Pigmented layer absorbs light and
stores vitamin A
 Neural layer has photoreceptors and
transmits signals
 Optic disc is your blind spot due to lack
of photoreceptors
 Photoreceptors (rods: operate in dim
light and provide indistinct, fuzzy, noncolor peripheral vision, cones: operate
in bright light and provide a high-acuity
color vision)
 Internal cavity is filled with humors fluid
 Lens separate internal cavity into anterior
and posterior segments
B. Taste
o Receptor organs are taste buds
o Taste sensations
 Sweet- sugars, saccharin, alcohol, and some
amino acids
 Sour- hydrogen ions
 Salt- metal ions
 Bitter- alkaloids such as quinine and nicotine
 Umami- amino acids glutamate and
aspartate
o Taste is 80% smell
o Thermoreceptors, mechanoreceptors,
nociceptors in the mouth also influence taste
o Temperature and texture enhance or detract
from taste
C. Smell
o Organ of smell is the olfactory epithelium in the
roof of the nasal cavity
o Olfactory receptor cells-bipolar neurons with
radiating olfactory cilia
o Bundles of axons of olfactory receptor cells form
the filaments of the olfactory nerve (cranial
nerve 1)
o Supporting cells surround and cushion olfactory
receptor cells
o Basal cells lie at the base of epithelium
D. Hearing and Balance
o Three Parts to the Ear:
o External ear (hearing)- composed of the auricle
(pinna), external acoustic meatus (auditory
canal) and tympanic membrane (eardrum)
o Middle ear (hearing)- composed of a small airfilled, mucosa-lined cavity in the temporal bone,
and the pharyngotympanic (auditory) tube
equalizes pressure in the middle ear cavity with
the external air pressure
o Internal ear (hearing and balance)
 Composed of three parts: vestibule,
semicircular canals, and cochlea
 Three bones (ossicles) in the inner ear:
malleus, incus, and stapes
o Receptors for hearing and balance
 Respond to separate stimuli
 Are activated independently
o Properties of sound
 Sound is the pressure disturbance produced by
a vibrating object
 Pitch is the perception of different frequencies
 Loudness is subjective to interpretation of
sound intensity
o Transmission of sound to the inner ear
 Sound waves vibrate the tympanic membrane
 Ossicles vibrate and amplify the pressure at
the oval window.
 Pressure waves move through perilymph of
the scala vestibule
 Waves of frequencies below the threshold of
hearing travel through the helicotrema and
scali tympani to the round window
 Sounds in the hearing range go through the
cochlear duct, vibrating the basilar membrane
at a specific location, according to the
frequency of sound
o Auditory pathways to processing
 Impulses from the specific hair cells are
interpreted as specific pitches
 Loudness is detected by increased numbers of
action potentials that result when the hair
cells experience larger deflections
 Localization of sound depends on relative
intensity and relative timing of sound waves
reaching both ears
o Equilibrium and orientation
 Vestibular apparatus consists of the
equilibrium receptors in the semicircular
canals and vestibule
o Vestibular receptors monitor static
equilibrium
o Semicircular can receptors monitor
dynamic equilibrium
 Three modes of input for balance and
orientation
o Vestibular receptors
o Visual receptors
o Somatic receptors
Diagrams
Special Senses Diagrams