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physiology chapter 10- peripheral NS: sensory
Terms in this set (51)
the rule in sensory physiology that the stimulus
whether touch, heat or pain is encoded by a specific receptor and decoded by specific location(s) in the brain
all sensory signals are transported by
action potential (AP) flows
multiple modalities of sensation or perception can subsequently be
associated into a complete experience or recorded memory
*the whole brain remembers
effector responses are monitored by
a broad range of intrinsic and extrinsic receptors that feedback the outcomes completing process control loops
neurological loops are foundational for
reflexes and regulator mechanisms
the law of specific nerve energies (rule)
the nature of perception is defined by the pathway over which the sensory information is carried- the origin of the sensation is not important.
the difference in perception of seeing, hearing, and touch are not caused by differences in the stimuli themselves but by the different nervous structures that these stimuli excite.
each sensory receptor detects a
unique form of energy: light, sound, pressure, heat, etc.
respond to chemical ligands that bind to the receptor (taste and smell, for example)
respond to various forms of mechanical energy, including pressure, vibration, gravity, acceleration, and sound (hearing, for example)
respond to temperature
for vision respond to light
net receptor stimulation above its threshold level
triggers an AP in the sensory nerve that can be conducted to the CNS for interpretation
is receptor potential a graded potential or an action potential?
The change in sensory receptor membrane potential is a graded potential (graded potential in a special senses receptor)
In some cells, the receptor potential initiates an action potential (if the net stimulation threshold is met) that travels along the sensory fiber to the CNS.
3 dimensions to any stimulus
intensity, duration and location
explain how stimulation intensity is coded into a sensory neuron action potential
stimulus intensity is coded in two types of information: the number of receptors activated and the frequency of action potentials coming from those receptors.
If a stimulus is below threshold, the primary sensory neuron does not respond. Once stimulus intensity exceeds threshold, the primary sensory neuron begins to fire action potentials. As stimulus intensity increases, the receptor potential amplitude (strength) increases in proportion, and the frequency of action potentials in the primary sensory neuron increases, up to a maximum rate.
explain how stimulation duration is coded into sensory neuron action potentials
the duration of the stimulus in the sensory neuron. In general, a longer stimulus generates a longer series of action potentials in the primary sensory neuron.
location of stimulus is determined by
mapping the body onto the sensory cortex
summarize the specificity of sensory pathways from receptor to brain region
1. Each receptor is most sensitive to a particular type of stimulus.
2. A stimulus above threshold initiates action potentials in a sensory neuron that projects to the CNS.
3. Stimulus intensity and duration are coded in the pattern of action potentials reaching the CNS.
4. Stimulus location and modality (nature of stimulus) are coded according to which receptors are activated or (in the case of sound) by the timing of receptor activation.
5. Each sensory pathway projects to a specific region of the cerebral cortex dedicated to a particular receptive field. The brain can then tell the origin of each incoming signal.
know that receptors can be classified as either ___ or _____ based on the action potential patterns of their response
tonic or phasic
do tonic or phasic receptors adapt faster to a change in the stimulus level?
features of tonic receptors
are slowly adapting receptors that fire rapidly when first activated, then slow and maintain their firing as long as the stimulus is present.
features of phasic receptors
are rapidly adapting receptors that fire when they first receive a stimulus but cease firing if the strength of the stimulus remains constant.
This type of response allows the body to ignore information that has been evaluated and found not to threaten homeostasis or well-being.
describe the anatomic sequence for somatosensory input to reach the primary somatosensory cortex
pathways carrying somatosensory information project to the thalamus, which acts as a relay and processing station before passing the information on to the cerebrum--> eventually reaching primary somatosensory cortex (parietal lobe)
what sequence is required for sensory input to reach the parietal sensory cortex
3 sequential nerves (primary sensory neuron, secondary sensory neuron and tertiary neuron) and a synapse in the thalamus- (the secondary sensory neuron and tertiary sensory neuron synapse in the thalamus)
brainstem injury to ____ side will affect touch modalities more
right side- that is because level of crossover to contralateral cortex is different for pain vs. touch modalities.
pain modalities are on the left side.
the "homunculus" (little man) representation of the body provides a map for
locating the stimulus origin on the post-central gyrus of the parietal lobe
phantom limb occurs when
the corresponding area of the "homunculus" (or area of parietal lobe) is excited despite absence of the limb
1. the responses of primary sensory neurons A,B and C are proportional to the intensity of the stimulus in each receptor field.
2. primary sensory neuron B which is closest to the stimulus inhibits A and C.
3. inhibition of lateral neurons (neurons on each side) enhances perception of stimulus.
pain sensation is detected by
nociceptors- neurons with free nerve endings, respond to strong noxious stimulus (chemical, mechanical or thermal) that may damage tissue
2 types of pain fibers
Ab fibers (immediate pain)-sharp and localized
C fibers (long term pain)-duller and more diffused
conduct at different velocities
is there a difference in myelination between the 2 pain fibers
yes, Ab fibers is myelinated (because pain is conducted rapidly) and C fibers are unmyelinated
2 neurotransmitters for pain
substance p and glutamate
nociceptor neurons are the _____ flow for ______
afferent (PNS -> CNS), spinal withdrawal reflex
what is referred pain and how is this faulty perception explained?
Pain that is felt in a location away from the actual site of the stimulus.
occurs because visceral and somatic sensory pain inputs converge on a single ascending tract- when painful stimuli arise in visceral receptors (coming from internal organs), the brain is unable to distinguish visceral signals from the more common signals arising from somatic receptors (coming from the skin, muscles and soft tissues)
it interprets the pain as coming from the somatic regions rather than the viscera.
stimulation of an inhibitory interneuron can also modulate ____ signals
this is the ____ model for pain perception
gate control model- Mechanically rubbing an injury to decrease pain sensation.
recognize the components of the vestibular apparatus
Portion of the inner ear that contains sensory receptors for balance and equilibrium.
utricle, saccule, the 3 semicircular canals and the endolymph with them
identify a sequence for the equilibrium pathway from vestibular apparatus to cerebellum and thru the thalamus to the cerebral cortex
Vestibular hair cells (receptors in semi circular canals) are tonically active and release neurotransmitter onto primary sensory neurons of the vestibular nerve.
Those sensory neurons either synapse in the vestibular nuclei of the medulla or run without synapsing to the cerebellum, which is the primary site for equilibrium processing.
vestibular nuclei of medulla-> reticular formation -> thalamus -> cerebral cortex
recall that sound waves are measured in _____ and ________
frequency (hertz) and intensity/amplitude (decibels- dB)
remember that visual fields project to the ____ half of the retina, and are sent to ______ cortex
opposite, contralateral occipital cortex
recognize that the image on the retina is ________ and the brain reverses it
because the retina is at the top part of the eye
the importance of visual input in orienting the body in space
receptors in eyes -> visual input -> vestibular nuclei in brainstem -> coordinated processing -> cerebellum
visual input produces output to motor neurons of limb and torso muscles-> maintenance of balance and desired posture
the retina has two types of photoneurons which are _____ and ______ that point ______ from the direction of incoming light
rods and cones- away
the level of light affects pupil diameter reflexively via cranial nerve ___
provide black and white vision in low level light.
*note the removal of old rod disks by phagocytosis and their renewal
provide sharp color vision in bright light
know that humans are trichromats
three types of cones for blue, green, and red corresponding to their frequency absorption maximum
all color perception is generated from these three color receptors (blue, green, red) over a wavelength spectrum from
*this is a very limited range in the entire electromagnetic spectrum
recall the area of sensory fibers receptive field is ____ related to the density (level) of receptors found there
convergence of receptive fields
the convergence of 3 primary sensory neurons creates one large receptive field - 2 stimuli are perceived as a single point (less sensitive area of body)
small receptive fields
are found in more sensitive areas of the body
what is demonstrated by the two point discrimination threshold
-in some regions of the skin, such as the arms and the legs, 2 pins placed within 20mm of each other are interpreted by the brain as a single prick (less sensitive)
-the fingertips have smaller receptive fields, 2 pins separated by as little as 2mm can be perceived as 2 separate touches (more sensitive areas of the skin)
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