special senses

General senses

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