Lesson 1 - General Senses Flashcards
receptor
structure specialized to detect a stimulus
some receptors are _____ _____ _____
bare nerve endings
sense organs
structure that combines nerve tissue surrounded by other tissues that enhance response to a certain type of stimulus
accessory tissue of a sense organ may include… (3)
added epithelium, muscular, or connective tissue
sense organs range in _____ and _____
size, complexity
transduction
the conversion of one form of energy to another
a fundamental purpose of any sensory receptor
convert stimulus energy into nerve signals
two stages of the sensory process
- sensation
- perception
sensation
sensory receptor detects stimulus and creates a small, local, electrical charge called the receptor potential
if the receptor potential is high enough…
the neuron fires action potentials and nerve signals to the brain
perception
conscious experience and interpretation of a stimulus
not all sensations lead to _____
perception
sensory receptors transmit four kinds of information
modality, location, intensity, and duration
modality
type of stimulus or the perception it produces
what is modality determined by?
which region of the brain is “wired” to receive the information
information is sent to the CNS via _____ _____
labeled line
labeled line
the electrical signal of each modality is passed along a chain of neurons to the CNS so that the information is separated from each other
location
where a stimulus is located
what is location encoded by?
which nerve fibers are firing
receptive field
the area within which a sensory neuron detects stimuli
the size of the receptive field determines what?
resolution; the ability to distinguish between two close-together stimuli
intensity
strength of stimulus
intensity is encoded in three ways
- which fibers respond
- how many fibers respond
- hot fast the fibers are firing
- intensity - which fibers respond (2)
weak stimulus can only activate most sensitive neurons
strong stimuli also activates less sensitive neurons with a higher threshold
- intensity - how many fibers respond
more intense stimuli activate more neurons
- intensity - how fast fibers are firing
as stimulus intensity rises, firing frequency increases
duration
how long a stimulus lasts
what is duration encoded by?
changes in firing frequency over time
sensory adaptation
if a stimulus is prolonged, firing of the neuron gets slower over time and we become less aware of it
phasic receptors (2)
adapt quickly; burst of signals when stimulus starts, then reduces or stops signaling even if stimulus continues
examples of phasic receptors (3)
smell, hair movement, cutaneous pressure
tonic receptors (2)
adapt slowly; action potentials continue more steadily while stimulus is present
examples of tonic receptors (4)
body position, muscle tension, joint motion, pain
classification of receptors by stimulus modality (5)
- photoreceptors
- thermoreceptors
- nociceptors
- chemoreceptors
- mechanoreceptors
photoreceptors (2)
located in the eyes and respond to light, provides the sense of vision
thermoreceptors (3)
respond to heat and cold, are free nerve endings, and use the same pathways as pain sensation
where are thermoreceptors located? (4)
the dermis, skeletal muscle, the liver, and hypothalamus
what is the pathway in which thermoreceptors send information? (3)
reticular formation in the brainstem -> thalamus -> primary sensory cortext
nociceptors (2)
respond to noxious stimuli and are free nerve endings with large receptive fields
where are nociceptors commonly found? (4)
superficial portions of the skin, joint capsules, within the periostea of bones, around the walls of blood vessels
analgesia
inability to feel pain
hyperalgesia
increased sensitivity to pain
nociceptors may be sensitive to… (3)
temperature extremes, mechanical damage, dissolved chemicals
pain information can be sent to the CNS by two types of axons
- type A
- type C
type A axons
large myelinated fibers that are fast, sends prickling/fast pain to the CNS to trigger somatic reflexes before reaching primary somatosensory cortex
type C axons
small unmyelinated fibers that are slow, sends burning/aching/slow pain and activated the reticular formation and thalamus - not very specific to exact location or area affected
chemoreceptors
respond to only water-soluble and lipid-soluble substances dissolved in fluid
chemoreceptors can monitor what three things in the blood
pH, carbon dioxide, and oxygen levels in arterial blood
carotid bodies
located near the origin of the internal carotid arteries on each side of the neck; chemoreceptor
aortic bodies
where and what is it?
located between the major branches of the aortic arch; chemoreceptor
mechanoreceptors
respond to stimuli that physically distort the receptor’s plasma membrane; contains mechanically-gates ion channels that open/close in response to stretching, compression or twisting
three classes of mechanoreceptors
- tactile receptors
- baroreceptors
- proprioceptors
tactile receptors
include fine touch, pressure receptors, and crude touch receptors
tactile receptors provide detailed information about the stimulus, including… (5)
- exact location
- shape
- size
- texture
- movement at the location
two characteristics of fine touch and pressure receptors
very sensitive and have a relatively narrow receptive field
three characteristics of crude touch and pressure receptors
- less sensitive
- have a relatively large receptive field, poor localization of stimulus
- provides little information about the stimulus
baroreceptors
monitors change in pressure; free nerve endings that branch with elastic tissue
where can you find baroreceptors? (2)
the walls of distensible organs such as blood vessels, and digestive organs
proprioceptors
monitors the position of joints, tension in tendons and ligaments, and the amount of skeletal muscle contraction
three major groups of proprioceptors
- receptors in join capsules
- Golgi tendon organs
- muscles spindles
- proprioceptors - receptors in joint capsules (3)
free nerve endings that detect pressure, tension, movement at the joint
- proprioceptors - Golgi tendon organs (2)
located between skeletal muscle and its tendon; monitor external tension generated during skeletal muscle contraction and are stimulated by tension in the tendon
- proprioceptors - muscle spindles (2)
monitor skeletal muscle length; used to trigger stretch reflexes
unencapsulated nerve endings
dendrites with no connective tissue wrapping
free nerve endings
what are they? what do they detect?
tonic receptors with small receptive fields that are bare dendrites that detect temperature and pain (warm/cold receptors and nociceptors)
tactile (Merkel) discs
tonic receptors with small receptive fields that are flattened nerve endings that terminate at tactile cells in the basal layer of the epidermis; very sensitive and detect light, touch, texture, edges, shapes
hair receptors (root hair plexuses)
actual hair
phasic receptors that are dendrites coiled around a hair follicle and respond to movements of the hair, are very sensitive
types of unencapsulated nerve endings (3)
- free nerve endings
- tactile (Merkel) discs
- hair receptors (root hair plexuses)
encapsulated nerve endings
nerve fibers wrapped in glial cells or connective tissue; wrapping enhances sensitivity of selectivity of response
types of encapsulated nerve endings (4)
- tactile (Meissner) corpuscles
- end (Krause) bulb
- bulbous (Ruffini) corpuscles
- lamellar (Pacinian) corpuscles
tactile (Meissner) corpuscles
two or three nerve fibers within a fluid filled capsule of flattened Schwann cells
end (Krause) bulbs
sensory nerve fiber surrounded by a connective tissue sheath
what are tactile (Meissner) corpuscles linked to? (6)
linked to the edges of dermal papillae, especially areas of hairless skin like the fingertips, palms, eyelids, nipples, genitals
bulbous (Ruffini) corpuscles (2)
flattened, elongated capsules containing a few myelinated axons in an incomplete fibrous capsule; tonic receptors located in the reticular layer of the dermis
what do bulbous (Ruffini) corpuscles detect? (5)
heavy touch, pressure, stretching of skin, deformation of fingertips, and joint movement
lamellar (Pacinian) corpuscules
large, ovoid receptos with a single dendrite surrounded by layers of flattened Schwann cells and fibroblasts
what do lamellar (Pacinian) corpuscles detect?
they are phasic receptors that detects deep pressure and vibration, most sensitive to pulsing or high-frequency vibration
where are lamellar (Pacinian) corpuscles located? (5)
found in the periosteum of bone, joint capsules, some viscera, and deep in the dermis especially of the hands, feel, breasts, and genitals
exteroceptors
sense stimuli external to the body
exteroceptors include receptors for…(8)
receptors for vision, hearing, taste, smell, and cutaneous sensations like touch, heat, cold, and pain
interoceptors
detect internal stimuli
where are interoceptors located? (3)
stomach, bladder, intestines
what do interceptors sense? (4)
stretch, pressure, visceral pain, nausea
proprioceptors
sense body position and movements, purely somatic sensation
where are proprioceptors located? (3)
muscles, tendons, joint capsules
general (somatosensory/somesthetic) senses
widely distributed in skin, muscles, tendons, joints, viscera; receptors may be simple, and some are just bare dendrites
special senses
limited to head, innervated by cranial nerves, and involve complex sense organs
afferent division of the nervous system
includes receptors that detect stimuli and replay the sensory information towards the CNS
efferent division of the nervous system
include motor neurons that send commands to effectors through motor tracts or nerves taking information away from the CNS
bundles of axons located in the PNS
nerves
clusters of cell bodies located in the CNS
nuclei
bundles of axons located in the CNS
tracts
somatic nervous system
motor neurons and pathways that provide voluntary control of skeletal muscles
somatic motor commands travel from motor center in the brain along these pathways (3)
- motor nuclei (CNS)
- tracts (CNS)
- nerves (PNS)
autonomic nervous system
sends involuntary commands to viscera
two divisions of the autonomic nervous system
sympathetic and parasympathetic
sensory projection (2)
transmission of information from receptor to specific locations in the cerebral cortex; signals travel along projection pathways
most somatosensory signals travel by way of three neurons
- first-order neuron
- second-order neuron
- third-order neuron
first-order neuron (4)
- signals from the head travel to pons/medulla via cranial nerves
- signals from below the head enters the posterior horn of the spinal cord via dorsal root of the spinal nerves
- touch, pressure, and proprioception fibers are large, myelinated, fast
- heat and cold fibers are small, unmyelinated, slower
second-order neuron (2)
- decussate (cross) to opposite side (contralateral) in spinal cord, medulla, or pons
- end in thalamus, except for proprioception which ends in the cerebellum
third-order neuron
where do they span?
thalamus to primary somatosensory cortex of cerebrum
three major somatic sensory pathways
- spinothalamic pathway
- posterior column pathway
- spinocerebellar pathway
spinothalamic pathway
what info does it provide?
provides sensations of poorly localized (crude) touch, pressure, pain, and temperature
spinothalamic pathway: first-order neurons
axons of the first-order sensory neurons enter the spinal cord and synapse on second-order neurons within the posterior grey horns
spinothalamic pathway: second-order neurons
they cross to the opposite side of the spinal cord and then ascends up the spinal cord within the anterior or lateral spinothalamic tracts
spinothalamic pathway - anterior tracts
what info do they carry?
carry crude touch and pressure
spinothalamic pathway - lateral tracts
what info do they carry?
carry pain and temperature
spinothalamic pathway: third-order neurons
they synapse in the thalamus, the information is sorted and processed before being transmitted to the primary somatosensory cortex
posterior column pathway
what info does it carry?
carries highly localizes (fine) touch pressure, vibration, and proprioception
posterior column pathway: first-order neurons
enter the spinal cord and ascend up on the ipsilateral (same) side of the spinal cord and synapse onto the second-order neurons at the medulla oblongata
posterior column pathway: second-order neurons
project axons that cross to the contralateral side and ascend to the thalamus
posterior column pathway: third-order neurons
located in the thalamus, receives input from second order neurons, processes the info, and sends the information to the somatosensory cortex
spinocerebellar pathway
p
carries proprioceptive info from skeletal muscles, tendons, and joints; information terminated at the cerebellum for processing
pain
unpleasant perception of actual or potential tissue damage
what does the perception of pain usually lead to?
evasive action
what is pain perception lost from? (4)
diseases and injuries?
leprosy, diabetes mellitus, nerve damage, neglect of injuries
peripheral neuropathy
peripheral nerve damage
nociceptive pain
stems from tissue injury; occurs when nociceptors are activated
neuropathic pain
stems from injuries to nerves, spinal cord, meninges, or brain
visceral pain
arises from internal organs; diffuse, dull, and hard to locate
visceral pain creates sensations of… (3)
squeezing, cramping, nausea
what is visceral pain caused by? (3)
stretch, chemical irritation, ischemia
deep somatic pain
where does it come from?
arises from bones, joints, muscles
examples of deep somatic pain (3)
arthritis, sprains, bone fractures
deep somatic pain can be caused by
excessive stretch, like a sprained ankle
superficial somatic pain
usually arises from the skin
examples of superficial somatic pain (3)
cuts, burns, insect stings
fast pain
immediate, sharp, localized pain
fast pain is carried by type _____ fibers
A; very fast
discriminative pain
aka fast pain; we can tell exactly where its coming from
slow pain is carried by type _____ fibers
C; slower, but still fast
slow pain
burning, dull, aching pain, less localized
pain signals from the head travel to the _____ via _____ _____
brainstem, cranial nerves
pain signals from the head travel through these cranial nerves (4)
5, 7, 9, and 10
pain signals from the neck and below travel through the ______ tract
spinothalamic tract
referred pain
pain in viscera often perceived as originating from superficial sites
what causes referred pain?
convergence of neural pathways in the CNS, and the brain cannot distinguish the source
endogenous opioids
analgesic peptides secreted by the CNS, pituitary, digestive tract, and other organs; act as neuromodulators and block pain
neuromodulators that block pain and give pleasure
enkephalins, endorphins, dynorphins
opioids block pain through what process?
spinal gating
spinal gating (3)
stops pain signals at the posterior horn, interneurons are stimulated to release enkephalins, and it inhibits second-order pain neurons
amyotrophic lateral sclerosis (ALS)
progressive degenerative disorder affecting motor neurons in the spinal cord, brain stem, and cerebral hemisphere
amyotrophic lateral sclerosis (ALS): cause
inherited by 5-10% in people but the rest is unknown
amyotrophic lateral sclerosis (ALS): treatment
oral medication such as riluzole cannot reverse damage but can mitigate symptoms
cerebral palsy (CP)
number of disorders affecting voluntary motor control, motor skills, posture/balance, memory, speech, learning; but is not progressive
cerebral palsy (CP): possible causes (3)
unusually stressful birth, maternal exposure to drugs, genetic defect
cerebral palsy (CP): treatment
muscle relaxants and pain relievers, various therapies like physical/speech
