Sensory Physiology Flashcards
All senses share 3 common steps
1- a physical stim
2- a set of events that transformed that stim into electrical impulses (that the brain can make sense of)
3- A response to the original stim in the form of perception or conscious awareness
interneuron
housed entirely with in the CNS. It links 2 neurons
- locally projecting
- neither motor nor sensory
afferent
conveying info toward a center
-sensory
efferent
conveying info away from a center
-motor
proprioception
- conscious awareness of ones own posture and movements
- this relies on receptors present in skeletal muscles and surrounding the joint capsule.
- without proprioception our movements would be awkward
exteroception
-sense of direct interaction with the external world as it impacts the body; principally via our sense of touch
interoception
sense of the function of the major organ systems
conscious (senses)
2 categories and list
- somatic senses: touch/pressure, temp, pain, proprioception
- special senses: vision, hearing, taste, smell equilibrium
Unconscious (stimuli)
2 categories and list
somatic stimuli: muscle length/tension
visceral stimuli: bp, pH/O2 content of blood, pH CSF, lung inflation, osmolarity of bodily fluids, blood glu
5 major groups of sensory receptors
1- chemo receptors 2-mechano receptors 3-photo receptors 4-noci receptors 5- thermo receptors
Chemo Rs are sensitive to
pH, O2, organic molecules
they are sensitive to different chemicals
Mechano Rs are sensitive to
vibration, acceleration, sound
mechanical stimuli
Photo Rs are sensitive to
light
Noci Rs are sensitive to
tissue damage – we experience this as painful stimuli
Thermo Rs are sensitive to
temp
what kinds of neurons are in somatic sensation?
simple and complex
simple neuron
- have free nerve endings
- unmyelinated axon
- part of somatic sensation
complex neuron
- have accessory structure (layers of connective tissue) that encloses free nerve ending
- myelinated axon
- part of somatic sensation
The axons of which neurons are myelinated?
Complex and special
Special neuron
- receptor is really pre syn terminal. but don’t fire AP. they do release NT in response to receptor pot though
- each special sense has unique sensory cell located in specialized R organ.
- can be modified neurons or modified epithelial cells
(T/F) all sensory Rs respond to the application of a stim by a change in membrane pot.
T
What is the key to Rs transducing and electrical signal, and how does this happen?
- key is meissners corpuscle
- the flattened epithelial (laminar) cells have primary afferent terminals bw them. when force applied to dermal papilla (surface of skin) that contains meissners corpuscles, the laminal calls slide past each other. this creates a shearing force and distorts the membranes of the axon terminals bw these laminar cells and causes mechanically gated Na channels to open.
- creates depolarization of membrane pot. If it reaches threshold, sensory cell can fire AP
Receptive field
spatial region where application of a stim causes a sensory neuron to respond.
-this is where the receptors are
sensory unit
consists of primary sensory afferent and the receptors that define its receptive field.
neural code
- AP freq codes stimulus strength (intensity)
- The freq of APs discharged will mirror the magnitude (strength) of the stim.
Labeled line code
(modality)
components of a sensation are coded and transmitted via separate pathways to the brain
-R is selective for a particular type of stim. Axon functions as a modality specific line of communication. (ex- optic nerve carries info about light)
-when light touch is applied to skin- only touch Rs are activated
-when more painful stimuli is applied- both touch and pain receptors are activated
the axon from the touch Rs travel in separate pathways than the axons from the pain Rs
Modality, stim, R type, Rs
for vision
vision
-stim- light/ electromag
-R type- photo R
Rs- rods and cones
Modality, stim, R type, Rs
for hearing
stim- sound
R type- mechano R
Rs- cochlea hair cells
Modality, stim, R type, Rs
for balance
stim- head movement
R type- mechano Rs
Rs- vestibular hair cells
Modality, stim, R type, Rs
for taste
stim- chemical
R type- chemo R
Rs- taste buds
Modality, stim, R type, Rs
for somatic/touch
stim- mechanical, thermal, noxious
R type- mechano R, thermo R, noci R, chemo R
Rs- DRG neurons
Modality, stim, R type, Rs
for smell
stim- chemical
R type- chemo R
Rs- olfactory sensory neurons
What does not exist outside the brain?
color, taste and tone
-they are as essential construction that represents the envir in a way that makes subjective experience
Modality is defined by
the specific stimulus
(T/F) Some sensory Rs are transformers that convert a stim into a graded pot
F, all sensory Rs
Spatial awareness of a stim involves 3 diff perceptual abilities
1- location (site of stim on body or in space)
2-descrimination (size and shape of objs)
3-resolution (fine detail of stim)
large receptive field yields
- where on the body do we see these?
- a lot or a little convergence?
poorer resolution and we won’t be able to discriminate size and shapes of objects well.
- 2 points can be perceived as 1
- we see these on the back (large receptive fields far apart from each other)
- a lot of convergence
small receptive field yields
- where on the body do we see these?
- a lot or a little covergence?
good resolution and good discrimination
- 2 points can be perceived as 2 points
- we see these in the finger tips – densely packed small receptive fields
- a little convergence
Convergence takes place at the level of
the secondary sensory neuron
population coding
(intensity)
uses multiple sensory units to encode the strength of a stim.
single large sensory unit stimulated- weak stim stimulates a few receptors of the unit, strong stim stimulates all receptors of the unit
multiple small sensory units stimulated- weak stim, stimulates all Rs of one unit. Strong stim stimulates all Rs of all units
basically the strength of a stimulus can help recruit sensory units
duration
length of time sensory cells can fire APs
adaptation
sensory cells need to be able to remain sensitive to new stim
tonic Rs
-slowly adapting and respond for the duration of a stim
phasic Rs
-rapidly adapt to a constant stimulus and turn off. they fire once more then the stim turns off
specialized cortical regions allow
conscious awareness of all attributes of a stim
(T/F) each sensory pathway projects to the same cortical region in the brain
F, they project to different cortical regions
topographic map: somatosensory cortex
- main sensory receptive area for touch
- homonculus
- amount of primary sensory cortex devoted to a body part is proportional to the relative density of sensory Rs on that body part
- lips and hands have high area (less convergence)
touch Rs
- type of mechano R
- has free nerve endings, merkels disks and meissners corpuscle, pacinian corpuscle and ruffinis endings
thermo Rs
-type of mechano R warm Rs (30-45 C) cold Rs (20-35 C)
nociceptors
- type of mechano receptor
- respond to noxious stim
meissners corpuscle
- small receptive field.
- in epidermis
- phasic adaptation (rapid)
pacinians corpuscle
- large receptive field
- located in dermis
- phasic adaptation (rapid)
merkels disk
- small receptive field
- in epidermis
- tonic adaptation (slow)
ruffinis ending
- large receptive field
- in dermis
- tonic adaptation (slow)
The conversion of an external stim to an electrical signal by a sensory cell is called ____
transduction
Key attributes of sensation that must be encoded by a sensory receptor
modality, location, intensity, duration
(T/F) The labeled line code is best exemplified by the convergence of pain and touch info in the dorsal horn of the spinal cord.
F
What are 2 mechs for encoding stimulus intensity?
1- AP freq
2- population coding
What defines a sensory modality?
physical properties of a stim
A secondary sensory neuron in the spinal cord receives input fro 2 diff primary sensory neurons. What would you expect the receptive field of the secondary neuron to include? what is the name of this process?
- receptive field of both primary sensory neurons
- process is called convergence
Why is a 2 point discrimination task easier when the stim is applied to the lips as opposed to the back?
lips have smaller and more densely packed receptors
Why is the sensory map of the body surface in the sensory cortex distorted?
different body parts no matter the size, have different density of receptors, so if there is a high density of receptors (like in a small body part like the lips), it requires a larger processing area within the sensory cortex.
what is the purpose of adaptation
sensory systems can remain sensitive to new stim in the presence of ongoing stim
