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General senses
Temperature, pain, touch, pressure, vibration, proprioception
Special senses
Olfaction, gustation, vision, equilibrium, and hearing
what are free nerve endings (dendrittes)
a highly branched terminal portion of a sensory neuron
What are sensory receptors?
Interface between internal and external environment of the CNS
what is the conversion process of sensory receptors called
transduction
what is transduction
When a receptor reaches its action potential the neuron communicates the information to the CNS
characteristics of free nerve endings
Very common, do not have structures to shield them from other stimuli, can be stimulated by temp, pressure, chemicals and trauma, the size of its receptive field affects its specificity
free nerve endings with large receptive fields
Have difficulty with localization (sense, temp, chemicals, mechanical damage)
what are the complex receptors
visual, gustation, hearing, equilibrium, proprioception
receptors to the central nervous system location
routed to CNS tracts to special location in the CNS
Where do touch and pain info enter the CNS?
primary somatosensory cortex (post central gyrus)
where does visual information go in the CNS
occipital cortex
where does hearing information go?
temporal
where does gustation go?
insula
where does smell information go?
temporal
what activates a tonic receptor?
Stimulus increases and decreases according to the frequency of action potentials
tonic receptor
always active
phasic receptor
normal inactive
what activates a phasic receptors
action potential reaches, then the stimulus lasts a short amount of time
what is adaptation
eduction of receptor sensitivity when there is a constant stimulus
peripheral adaptation
when the level of receptor activity changes. It has an initial strong response by the receptor but then gradually decreases
Reduces information that reaches the CNS
central adaptation
At the subconscious level it restricts the amount of information that reaches the cerebral cortex
example of fast adapting
phasic
what is an example of a slow adapting receptor
tonic
where is sensory information processed
in the brainstem and spinal cord
what is a nocioceptor
pain- found in superficial portion of skin, joint capsules, periosteum of bones, walls of blood vessels
types of nocioceptors
type A, type B
Type A nocioceptor
fast pain- prickling an sharp
Type B nocioceptor
Type B- burning and aching
thermoceptors
temperature
mechanical receptors
physical distortion (touch or pressure)
chemoreceptors
chemical concentration
step 1 in pain perception process
receptors are stimulated until the tissue damage has ended but central adaptation will reduce the perception of pain. It can decrease and inhibit center within thalamus, reticular formation, lower brainstem, and spinal cord
step 2 in pain perception process
neurotransmitters like glutamate or substance p facilitate pain pathways to the CNS
step 3 in pain perception process
the level of pain experienced (especially chronic pain) can be out of proportion to the amount of painful stimuli and apparent tissue damage
step 4 in pain perception process
neuronal pathways especially interneurons can be hyperexcitable
What are endorphins and enkephalins?
Neuromodulators that reduce the level of pain a person experiences
where are endorphins and enkephalins found
Found in the limbic system, hypothalamus, and reticular formation (dry brain v wet brain)
What are the distributions among thermoreceptors
Cold receptors are more numerous than warm receptors, they are conducted along the same pathway as nociception.
where are thermoreceptor info sent
reticular formation, thalamus and the primary somatosensory cortex.
mechanoreceptors
sensitive to physical stimuli that distort plasma membrane
what are three types of mechanoreceptors
tactile, baroreceptors, proprioceptors
tactile receptors
touch, pressure, vibration-
Where are tactile receptors located?
Free nerve endings, tactile, root hair plexus, tactile discs, bulbous, lamellar corpuscles
baroreceptors
free nerve endings that detect pressure changes in blood vessels and parts of digestive respiratory and urinary tracts
Proprioceptors
monitor the joints and skeletal mm positions
where are proprioceptors
Muscle spindle and golgi tendon organ, free nerve endings in joint capsule. Utilized receptors in inner ear
chemoreceptors
detect small changes in the concentration of specific chemicals and compounds
where are chemoreceptors found
In respiratory centers of medulla oblongata-,Chemoreceptors in carotid bodies and aortic bodies
what do chemoreceptors detect?
change in pH, CO2, and O2
sensory information
Monitors specific conditions inside and outside the body
where is sensory information detected?
sensory receptors in the peripheral nervous system
what happens when sensory information/receptors are detected?
pass action potentials through the sensory neurons
What is a receptive field?
The region of the body that a single receptor cell monitors
Vary in size
The larger the field=harder to localize the stimulus
Touch receptive fields=7cm diameter
Touch receptive fields on fingertips=<1mm
what are the neurons that transmit somatic sensory information to the cerebral cortex
sensory pathways
first order neuron
Sensory neuron that carries information into the CNS and spinal cord
second order neuron (interneuron)
Sensory neuron that carries info to the thalamus
where is the first order neuron found
Cell body in dorsal root ganglion
What is decussation?
the crossing over of an axon before reaching the thalamus
where does second order neuron happen
medulla oblongata
third order neuron
Carries information from the thalamus to the cortex
what are the somatic sensory pathways
posterior column pathway and spinothalamic pathway
what is the posterior column pathway
Ascending tract in white column
what does the posterior column pathway carry
localized fine touch, pressure, vibration and proprioception
What is the spinothalamic pathway?
Ascending tracts in lateral and anterior white columns
what does the spinothalamic pathway carry
poorly localized touch pressure, pain, and temperature
what are somatic motor pathways
Control the skeletal muscles
Involve at least two motor neurons
what make up the somatic motor pathways
upper, lower motor neurons
upper motor neuron
Cell body is in CNS processing center (primary motor cortex)
lower motor neuron
Cell body is in nucleus in the brainstem (cranial nerves) or the spinal cord (spinal nerves)
Innervates a motor unit in skeletal muscle in the PNS
what are the three somatic motor pathways
activity is adjusted by the basal nuclei and the cerebellum (for coordinated movements)
corticispinal
medial
lateral
what is the corticospinal pathway
cortex to the spinal cord
upper motor neuron of the corticospinal pathway
come from primary motor cortex, Synapse in motor nuclei for cranial nerves in brainstem or spinal cord
lower motor neuron of the corticospinal pathway
Come from cranial nerve nuclei or horns of spinal cord, Motor unit in skeletal muscle
visceral pathways
visceral sensory system, visceral motor system
what is the visceral sensory system
Carry sensory information from internal organs to regions of brainstem
what is the visceral motor system
autonomic nervous system
what are the five special senses
olfaction, gustation, vision, equilibrium, and hearing
how many layers does the eye have
three layers
fibrous tunic
vascular tunic
neural tunic
what is the fibrous tunic
the outer layer of the eye containing the sclera and the cornea
was is the vascular tunic
the middle layer of the eye containing the iris, ciliary body, and choroid
what is the neural tunic
the inner layer of the eye with the retina (phototreceptors)
what two cavities are in the eye
anterior cavity and the posterior cavity
posterior cavity
Contains vitreous humor - thick gel that holds retina flat against choroid coat
anterior cavity
contains aqueous humor, which is produced by the ciliary body in the posterior chamber. drains through the schlemm into the veins of the sclera
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