Peripheral Nervous System Flashcards
PNS
all neural structures outside of brain and spinal cord
parts of PNS
sensory receptors
peripheral nerves
ganglia
motor endings
goal of PNS
provides links to and from external environment
classification of nerves
somatic- voluntary
visceral- autonomic
sensory- afferent (ascending)
motor- efferent (descending)
groups of cell bodies in PNS
ganglia
groups of cell bodies in CNS
nuclei
what prohibits CNS axon regeneration?
oligodendrocytes have growth inhibiting proteins and astrocytes form scar tissue
regeneration of PNS nerves
if soma of peripheral nerve is intact, axon will regenerate, but might not function as well
cells involved with regerenation?
macrophages- remove debris
schwann cells- form regeneration tube and secrete growth factors
axons- regenerate damaged part
cranial nerves
12
originate in brain
spinal nerves
31 pairs
originate in spinal cord
mixed nerves (both sensory and motor functions)
how are cranial nerves identified?
by Roman numeral and name
combination of only motor, only sensory, or both
I olfactory nerve
receptor cells in nasal cavity
through cribriform plate of ethmoid bone
pathway leads to primary olfactory cortex
sensory - sense of smell
II optic nerve
from retina
pass through optic canal and converge/cross over at optic chiasma
synapse in thalamus, then to visual cortex
sensory- sense of sight
III oculomotor nerve
fibers control extrinsic eye muscles
raise eyelid, direct eyeball up, down, or inward
constrict iris
control lens shape
motor
IV trochlear nerve
motor nerve that directs eyeball inferolaterally
V trigeminal nerve
3 branches: ophthalmic, maxillary, mandinular
both
sensory- impulses from areas of face
motor- chewing muscles
VI abducens nerve
motor function of lateral rectus muscle
abduct eye, move laterally
VII facial nerves
from pons through internal acoustic meatus to face
5 branches: temporal, zygomatic, buccal, mandibular, cervical
both
motor- voluntary facial expression, lacrimal and salivary glands
sensory- taste from anterior 2/3 of tongue
VIII vestibulocochlear nerve
hearing and balance
sensory
IX glossopharngeal nerve
both
motor- tongue and pharynx for swallowing
sensory- taste and sensory impulses of posterior tongue, impulses from carotid chemoreceptors and baroreceptors
X vagus nerve
only cranial nerve that extends beyond head and neck
both
motor- skeletal muscles, regulate heart, lungs, various abdominal viscera (digestion)
sensory- impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds
XI accessory nerves
ventral rootlets from cervical spinal cord
motor- trapezius and sternocleidomastoid muscles
XII hypoglossal nerve
motor- extrinsic and intrinsic muscles of tongue for swallowing and speech
ventral roots
motor (efferent) fibers from ventral horn
innervate skeletal muscles
dorsal roots
sensory (afferent) fibers from sensory neurons in dorsal root ganglia
conduct impulses from peripheral receptors
dorsal ramus
supply back
ventral ramus
supply thorax, abdomen, and limbs
form plexuses
plexus
interlacing nerve networks
meningeal branch
innervate meninges
innervation
more than one spinal nerve supplies a muscle in many parts of body
nerve connecting to muscle also connects to the joint and skin above joint
dermatome
area of skin innervated by a cutaneous branch of single spinal nerve
all nerves beside C1 participate in dermatomes
overlap (destruction of one spinal nerve wont cause complete numbness)
sensory receptors
specialized structures that respond to stimuli
sensation and perception
sensation
the awareness of changes in internal and external environment
perception
the conscious interpretation of those stimuli
classification of PNS receptors
stimulus type
location
structural complexity
5 types of stimulus receptors
mechanoreceptors
thermoreceptors
nociceptors
photoreceptors
chemoreceptors
mechanoreceptors
respond to touch, pressure, vibration, stretch, and itch
Merkel cells in epidermis
hair follicle receptors
thermoreceptors
respond to changes in temperature
cold- 10-40 C superficial dermis
heat 32-48 C deep
nociceptors
sensitive to painful and irritating stimuli
pinching, chemicals from damaged tissue, temperature outside of thermoreceptor range, chili peppers
photoreceptors
respond to light energy
chemoreceptors
respond to chemicals: odors, tastes, changes in blood chemistry
activated by histamine
3 types of location receptors
exteroceptors
interoceptors
proprioceptors
exteroceptors
respond to stimuli outside of body
in skin for touch, pressure, pain and temperature
most special sense organs
interoceptors
respond to stimuli from internal viscera and blood vessels
sensitive to chemical changes, tissue stretch, and temperature changes
proprioceptors
respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
inform brain of one’s movements (position of body)
2 types of structural receptors
complex
simple
complex receptors
special sense organs
vision, hearing, smell, equilibrium, taste
simple receptors
general sense
tactile senations, temperature, pain, stretch
nonencapsulated or encapsulated dendritic endings
nonencapsulated free nerve endings
found throughout body
unmyelinated, small diameter axons
thermoreceptors
chemoreceptors
nociceptors
light touch mechanoreceptors
encapsulated nerve endings
nerve enclosed by connective tissue capsule
mechanoreceptors (some proprioceptors)
encapsulated endings in integumentary system
meissner corpuscles- tactile, discriminative touch
pacinian corpuscles- deep pressure, vibration
ruffini endings- deep continuous pressure
encapsulated endings in muscles and joints
muscle spindle- muscle stretch
tendon organs- tendon stretch
joint kinesthetic receptors- stretch in articular capsules of synovial joints
levels of neural integration of sensory info
receptor level- sensory receptors
circuit level- processing in ascending pathway
perceptual level- processing in cortex sensory areas
general sense signals in somatosensory cortex
receptor is sensory neuron
stimulus -> generator potential -> action potential
special sense signals in somatosensory cortex
receptor is separate cell
stimulus -> receptor potential in receptor cell -> release of neurotransmitter -> graded potential in first order sensory neuron -> action potential
adaptation
change in sensitivity in presence of constant stimulus
receptor membrane becomes less responsive
receptor potentials decline in frequency or stop
which receptor does not exhibit adaptation?
proprioceptors and pain receptors
always need to know information of pain or body position
phasic receptors
signal beginning or end of stimulus
fast adapting
receptors for pressure, touch, and smell
tonic receptors
adapt slowly or not at all
nociceptors and most proprioceptors
ascending pathways
circuit level
uses three neurons to conduct sensory impulses upward to appropriate brain regions
first order, second order, and third order neurons
first order neurons
conduct impulses from receptor level to second order neuron in CNS
second order neurons
transmit impulses to the thalamus or cerebellum
third order neurons
conduct impulses from thalamus to somatosensory cortex
identification of sensation
perceptual level
depends on specific location of target neurons in sensory cortex
perceptual detection
ability to detect stimulus
summation of impulses
magnitude estimation
intensity is coded in frequency of impulses
spatial discrimination
identifying the site or pattern of stimulus
feature abstraction
combination of several features into overall idea
quality discrimination
ability to differentiate sub qualities (taste)
pattern recognition
ability to identify patterns
perception of pain
warns of actual/impending tissue damage
pain stimuli
extreme pressure, temperature, tissue damage
chemicals released: histamine, K+, ATP, acids, bradykinin
pain neurotransmitters
glutamate and substance P activate 2nd order spinothalamic tracks
fight or flight in pain
pain impulses blocked by inhibitory endogenous opioids (natural)
temporary override
role of genetics in pain?
influence a person’s pain tolerance
hyperalgesia
pain amplification - pain receptors always activated
chronic pain and phantom limb pain
activated NMDA receptors
visceral pain
thorax, abdominal cavity
dull, aching, burning
caused by extreme stretching, chemicals, muscle spasms, low blood flow
referred pain
pain from one area of body is perceived as coming from another part
brain interprets pain coming from spinal nerves as somatic rather than visceral
3 levels of somatic control of motor division
segmental level
projection level
pre-command level
segmental level
spinal cord reflexes
automatic repeated movements- CPGs central pattern generators set crude rhythms and alternating patterns of movement
don’t need higher brain levels to control
projection level
primary motor cortex and direct descending tracts for voluntary skeletal movement
brain stem nuclei (red, vestibular, and reticular formation)
control and modify reflex and CPGs
precommand level
cerebellum and basal nuclei
control and coordinate output of projection level
start and stop movements, coordinate posture, prevent unwanted movements, monitor muscle tone
unconscious planning in advance
inborn/intrinsic reflex
rapid, involuntary, predictable motor response to stimulus
stay upright, alive, and intact without thinking about it
learned/acquired reflex
result from practice or repetition (overtime)
how to play instrument, driving, sewing, riding bike
reflex arc
- receptor- site of stimulus action
- sensory neuron- transmit afferent impulses to CNS
- integration center- CNS structure
- motor neuron- conducts efferent impulses from integration center to effector organ
- effector- muscle fiber or gland cell that responds to efferent impulses by contracting or secreting
monosynaptic
two neuron circuit of reflex
polysynaptic
3 or greater neuron circuit of reflex
somatic reflex
integration center- spinal cord
effectors- skeletal muscles
brain not necessary, but can adapt/facilitate reflex
testing important for assessing condition of nervous system (absent, exaggerated, or absent means degeneration or pathology)
muscle and tendon stretch somatic reflex
muscle spindles inform the nervous system of length of muscle
tendon organs inform brain the amount of tension in tendons
muscle spindles
small short intrafusal fibers in connective tissue capsule
sensory neurons wrapped around sense rate and degree of stretch
motor neurons stimulate them to contract along with rest of muscle
muscle spindle intrafusal fibers excitement
- external stretch of muscle and muscle spindle
- contraction of spindle along whole muscle
change in length causes increased rate of impulses
stretch reflex
maintain muscle tone and upright posture
cause muscle contraction in response to increased muscle length
all are monosynaptic and ipsilateral
how stretch reflex works
- stretch activates muscle spindle
- sensory neurons synapse directly with motor neurons in spinal cord
- motor neurons cause stretch muscle to contract
reciprocal inhibition
fibers synapse with interneurons that inhibit motor neurons of antagonistic muscles
tendon reflex
inform brain the amount of tension in muscle tendons
cause muscle relaxation - antagonistic muscle contracts for reciprocal activation
polysynaptic
help prevent damage due to extensive stretch
flexor reflex
withdrawal reflex
initiated by painful stimulus
causes automatic withdrawal of threatened body part
ipsilateral and polysynaptic
brain can override (shots)
