Chapter 16 Flashcards
As sensory impulses reach CNS, they become part of?
large pool of sensory input
→each piece of incoming info is combined with other arriving & previously stored info in integration process
Integration occurs at?
many places along pathways in spinal cord, brain stem, cerebellum, basal nuclei & cerebral cortex
Sensations
conscious perception or subconscious awareness of changes occuring in external or internal environment
Sensory Modality
each unique type of sensation
A given sensory neuron carries info for how many modalities?
jus`t one
2 classes of sensory modalities
1) general senses
2) special senses
General senses
somatic senses
visceral senses
somatic senses
include:
tactile → touch, pressure, vibration, itch, tickle
thermal → warm/cold
pain
proprioception→ awareness of limb & joint position in space
- conscious awareness
visceral senses
provide info about conditions within internal organs
only become conscious when pain receptors stimulated
Process of sensation begins in?
sensory receptor
- can be either specialized cell or dendrites of sensory neuron
Selectivity of sensory receptors
characteristic of sensory receptors
particular kind of stimulus (change in env) activates certain sensory receptors, while others only respond weakly or not at all
Process of Sensation (4 steps)
1) Stimulation of Sensory Receptor
2) Transduction of Stimulus
3) Generation of Nerve Impulses
4) Integration of Sensory Input
1) Stimulation of Sensory Receptor
an appropriate **stimulus **must occur within receptor’s **receptive field **(region where stimulation activates receptor & produces response)
2) Transduction of the stimulus
sensory receptor converts energy in stimulus to **graded potential **
(GPs vary in amplitude (size) depending on strength of stimulus & are not propagated)
exhibits **selectivity **(can only transduce 1 kind of stimulus)
3) Generation of Nerve Impulses
when sum of GPs in (first-order) sensory neuron reaches **threshold, **triggers 1+ **nerve impulses **which propagate towards **CNS **
4) Integration of Sensory Input
particular region of CNS integrates # or variety or sensory nerve impulses
results in **conscious sensation/perceptions **in cerebral cortex
**Sensory Receptors **can be grouped into several classes based on **structural **& **functional characteristics **(3)
1) microscopic structure
2) location of receptors & origin of stimuli that activate them
3) type of stimulus **detected **
Receptors named according to:
1) microscopic structure
1) Free nerve endings of first-order sensory neurons
2) encapsulated nerve endings of first-order sensory neurons
3) seperate nerve cells that synapse with first-order neurons
1) Free nerve endings of first-order sensory neurons
bare dendrites without structural specifications
- include: **pain, temperature, tickle, itch **
2) encapsulated nerve endings of first-order sensory neurons
dendrites enclosed in CT capsule
**pressure & vibration **
3) seperate nerve cells that synapse with first-order neurons
include **specialized receptor cells **for special senses
**taste buds, hair cells **for hearing, photoreceptors
Receptors named according to:
2) location & origin of stimuli that activates them
1) Exteroceptors
2) Interoceptors
3) Proprioceptors
1) Exteroceptors
located at or near external surface of body and respond to external stimuli
2) Interoceptors
visceroceptors
- located in **blood vessels, organs, muscles **
produce impulses which usually are not consciously percieved
3) Proprioceptors
located in **muscle, tendon, joints & inner ear **
- provide info about **body position, muscle length & tension, **movement ofjoints **
Receptors named according to **type of stimulus detected **
1) Mechanoceptors
2) thermoreceptors
3) nociceptors
4) photoceptors
5) chemoreceptors
6) osmoreceptors
1) Mechanoceptors
sensitive to deformation
2) thermoreceptors
detect changes in temp
3) nociceptors
respond to painful stimuli
4) photoceptors
activated by photons of light
5) chemoreceptors
detect chemicals in mouth (taste), nose (smell) & body fluids
6) osmoreceptors
detect osmotic pressure of body fluids
Adaptation
characteristic feature of most sensory receptors
in which **generator or receptor **potential **decreases **in amplitude during sustained or constant stimulus
Why does the perception of a sensation fade or disappear even though stimulus persists?
because of **adaption **
*bc of accommodation response at receptor level, frequence of nerve impulses traveling to cerebral cortex decreases & perception of sensation fades despite persisting stimulus *
Receptors vary in how quickly they adapt (2)
Rapidly adapting receptors - **specialized for signaling changes in stimulus **(pressure, touch, smell)
Slowly adapting receptors - **adapt slowly & continue to trigger nerve impulses as long as stimulus persists **(pain, body position & chemical composition of blood)
Thermoreceptors (2)
**cold & warm **receptors
- both adapt quickly at onset of stimulus
What temperature range will stimulate pain receptors instead of thermal receptors?
**below 10 degrees celsius **
**above 48 degrees celsius **
Nociceptors
chemoreceptive free nerve endings activated by tissue damage from intense thermal, mechanical or chemical stimuli
- found in **every tissue of body EXCEPT brain **
(2) types of pain
1) fast
2) slow
Fast pain
- Perception (acute, well localized) occurs rapidly bc nerve impulses propagate along medium-diameter, myelinated A fibers
Slow Pain
begins after stimulus applied & gradually increases in intensity over period of several seconds/minutes
- impulses conduct along **small-diameter unmyelinated C fibers **
- may be excruciating, often burning, aching, throbbing
**Superficial **somatic pain
pain that arises from stimulation of receptors in **skin **
Deep somatic pain
caused by stimulation of receptors in **skeletal muscles, joints, tendons & fascia **
**Visceral **pain
from stimulation of **nociceptors **in visceral organs
- felt in or just deep to skin overlying stimulated organ or in surface area far from stimulated organ (referred pain)
**Proprioceptive sensations **allow us to know?
where are limbs are even with closed eyes
**proprioceptors **inform us of?
degree of **muscle contraction, tension in tendons & joint positions **
Tendon Organs
located at **junction of tendon & muscle **
- monitor tension
Muscle Spindles
**proprioceptors **in skeletal muscle that monitor changes in length & participate in stretch reflexes
How does brain set overall level of muscle tone (small degree of contraction that is present while muscle is at rest)
By adjusting how vigorously muscle spindle responds to stretching of skeletal muscle
Muscle Spindles consist of?
several slowly adapting sensory nerve endings wrapped around **3-10 **specialized muscle fibers (intrafusal muscle fibers)
Location of Muscle Spindles
plentiful in muscles that control fine movements
more sparse in those that **control course/forceful movements **
**2 **kinds **of graded potentials produced by sensory receptors
1) **generator **potentials
2) **receptor **potentials
1) **generator **potentials
- produced by?
produced by dendrites of **free nerve endings, encapsulated nerve endings **& receptive part of **olfactory receptors **
- if large enough to reach **threshold, **triggers 1+ nerve impulses in first-order neuron axon which propogate along axon into CNS
2) receptor potentials
produced by sensory receptors that are seperate cells
- triggers release of neurotransmitters through **exocytosis **of synaptic vesicle
- diffuse across synaptic cleft & produce postsynaptic potential in first-order neuron
- may trigger 1+ nerve impulses which propogate along axon into CNS
