Nervous system - Lectures 6-7 (Sensory + vision) Flashcards
difference btw special sense and somatic senses?
- touch, taste, pain, itch, equilibrium, proprioception, hearing, vision, temperature, smell
- special –> can link to specific organ
- somatic/general senses –> not linked to a specific organ
SPECIAL: - taste
- equilibrium
- hearing
- vision
- smell
SOMATIC: - touch, pain, itch, proprioception, temp
3 different types of stimuli? –> all as ________ energy
- visible light
- sound waves
- mechanical energy
PHYSICAL energy
how can a stimulus produce action potential in CNS? (2 steps ish)
- stimulus has to reach threshold to produce graded potential –> graded potential need to reach threshold to produce action potential!
simple vs complex sensory systems?
- simple: single sensory neuron
- complex: multicellular sense organs
examples of conscious vs unconscious senses
CONSCIOUS
- special and somatic senses –> vision, touch, temp, hearing, equilibrium, proprioception
UNCONSCIOUS:
- somatic stimuli: muscle length and tension, proprioception
- visceral stimuli: blood pressure, blood glucose concentration, internal body temp, osmolarity, pH…
receptors are sensitive to particular forms of E
- neural receptors (2)
- nonneural receptors for 4 special senses (2)
- ___________ structures enhance sensory system (ie?)
NEURAL (2 types)
- naked (“free”) nerves (simple receptor)
- complex neural receptors encased in connective tissue capsules
NONNEURAL
- highly specialized cells
- associated with sensory neurons
ACCESSORY structures –> somatosensory receptors
(think of the figure)
4 types of sensory receptors depending on type of _________
- most common type?
stimuli!
1. chemoreceptors: O2, pH, organic molecules like glucose
2. mechanoreceptors: pressure, cell stretch, vibration, acceleration, vibrations, texture, sound
3. photoreceptors: photos of light
4. thermoreceptors: varying degrees of heat
- most common = touche receptors! (mechanoreceptors)
what is a receptive field of the neuron?
- overlap?
- neighboring fields may exhibit ________
- what determines sensitivity?
- physical area where a stimuli activates a neuron (think of needle example)
- frequently overlap!
- convergence!
-SIZE! - sensitive areas have smaller receptive fields
- less sensitive areas have larger receptive fields (back, leg)
how does sensory information reaches (which part of the brain)? (2 steps)
- spinal cord to brain by ascending pathways
- directly to brain stem via cranial nerves
which type of reflexes in (2 parts of NS) usually do not reach conscious perception?
- visceral reflexes (ie blood pressure, pH)
- in brain stem or spinal cord (or diencephalon (?))
what is the perceptual threshold?
level of stimulus necessary to be aware of particular sensation
- need to reach threshold to induce pathway
3 sensory pathways in the brain:
1. olfactory
2. equilibrium
3. most senses
- olfactory pathways from nose project through the olfactory bulb to olfactory cortex (DOESN’T pass through thalamus)
- equilibrium pathways project primarily to the cerebullum (from the inner ear) (but also a bit to thalamus? selon schéma)
- most sensory pathways project to the thalamus. the thalamus modifies and relay information to cortical centers
4 things to consider to distinguish stimulus properties + explain
- sensory modality: which sensory neurons are activated and where neurons terminate in brain + 1:1 association of receptor with sensation
- location of stimulus: which receptive fields are activated –> lateral inhibition and population coding
- intensity of stimulus: number of receptors activated and frequency coding
- duration of stimulus: duration of action potentials + receptors adapt (tonic vs phasic receptors)
what is lateral inhibition?
it enhances contrast and makes a stimulus easier to perceive
- neuron B will inhibit action potential in neurons A and C –> enhances contrast so you can detect exactly where stimulus comes from
What is population coding?
ie: purple stimulus: neuron that recognizes blue + neuron that recognizes red are both stimulated
ie: punching someone strong = more sensory neurons will respond
will a longer and stronger stimulus increase frequency of action potentials?
yes! longer and stronger stimulus will increase receptor potential strength –> frequency and number of AP increase –> more neurotransmitter release!
- frequency of APs is proportional to stimulus intensity
tonic vs phasic receptors?
TONIC
- slowly adapting receptors that respond for duration of stimulus
- degree of stimulus = degree of response
- ie pain
PHASIC
- rapidly adapt to a constant stimulus and turn off
- ie: put on a coat = stimulus = feel how heavy it is –> but then adapt and don’t feel its weight anymore so APs disappear –> until you remove and feel a weight lifted off
3 pathways for stimulus to brain
- for what senses?
- pathway
- DORSAL COLUMN SYSTEM
- pathway for fine touch and proprioception sensations from R side of body
- 1st sensory neuron goes up spinal cord –> synapses to 2nd interneuron which crosses over to L side at medulla and ascends to reach thalamus –> where a 3rd order neuron goes to somatosensory cortex - SPINOTHALAMIC TRACT
- pain and temperature sensations on R side of body
- first order neuron synapses in dorsal horn of spinal cord –> 2nd order neuron crosses to L side in spinal cord and ascends through spinal cord –> reaches thalamus –> where 3rd order neuron goes to somatosensory cortex - DIFFUSED PATHWAY
- for pain!
- same as 2nd pathway –> but 2nd neuron stops at brain stem at reticular formation and spreads signal to many many pathways through different neurons (lots of 3rd order neuron)
somatic senses
- 5
- pathways for somatic perception project to ________ and __________
- receptors for somatic sense are located in _______ and _________
- tertiary sensory neurons project to __________ cortex and many project to _________ __________ cortex
- nociception (pain & itch), proprioception, temperature, touch
- cortex and cerebellum
- skin and viscera
- somatosensory cortex and to cerebellum somatosensory cortex
blood clot damages sensory tracts on lower right side of medulla. which of these signals (departing from left and right side) would be abnormal/not felt?
1) pain
2) proprioception
3) temperature
- the person would NOT feel pain and temperature from left side + proprioception from right side.
- they would feel pain and temp from right side and proprioception from right side
what is the homunculus?
where each body part is represented next to the area of the sensory cortex that processes stimuli for that body part
which type of receptor for temperature, noxious stimuli (pain) and hair movement?
- adapation?
- Free nerve endings!
- variable adaptation
which type of receptor for vibration?
- where is it located?
- is it encapsulated or as a whole cell?
- adaptation?
- Pacinian corpuscules
- deep layers of skin
- encapsulated!
- rapid adaptation! –> phasic receptor
what type of receptors are skin temperature receptors?
- terminated in ___________ layers
- cold vs warm receptors activated at what temp?
- thermoreceptors use _______ channels called ________ receptor ________ channels
- free nerve endings
- subcutaneous
- cold: lower than body temp VS hot: above body temp to about 45°C VS pain warm receptors activated about 45°C
- cation channels –> transient receptor potential (TRP) channels
3 classes of somatosensory nerve fiber
- (hint: letters)
- big/small?
- myelinated?
- speed of conduction
- associated with ?
Ab (beta):
- large
- myelinated
- 30-70m/sec
- mechanical stimuli
Ad (delta):
- small
- myelinated
- 12-30 m/sec
- cold, fast pain, mechanical stimuli
C:
- small, unmyelinated
- 0.5-2m/s
- slow pain, heat, hold, mechanical stimuli
how does action potential go through axon when myelinated vs unmyelinated?
- myelinated: saltatory conduction
- unmyelinated: local current flow
