Chapter 10 Flashcards
Special Senses
Vision Hearing Taste Smell Equilibrium *Conscious Stimulus processing
Somatic Senses
Touch
Temperature
Pain/ Itch (Nociception)
Proprioception
*Conscious Stimulus processing
- Pathways go to the cortex and cerebellum.
Somatic Stimuli
Muscle length/tension
Proprioception
*Unconscious stimulus processing
Visceral Stimuli
Blood pressure Distension of GI Blood glucose concentration internal body temp osmolarity of fluids lung inflation pH of CSF *Unconscious stimulus processing
Simple sensory system
single sensory neuron with branched dendrites that function as receptors Pain and itch receptors
Complex sensory system
includes multicellular sense organs–> ear and eye
Special Sense Receptors
most are very specialized non-neuronal accessory structures (except for nose, which are just plain old neurons) -cornea of the eye -hair on arms
Chemoreceptors
sense oxygen, pH, glucose, etc.
Mechanoreceptors
sense pressure (baroreceptors), cell stretch (osmoreceptors), vibration, sound, etc.
Photoreceptors
Sense light
Thermoreceptors
sense temperature
Signal transduction
in order to propagate a sense, you need to send the signal. Signal transduction: stimulus energy converted into information that can be processed by CNS. in many cells, there are ion channels or second messenger systems that initiate a membrane potential change.
Adequate stimulus
a form of energy to which a receptor is most responsive. (receptors can respond to most other forms of energy as well, if the intensity if high enough–> seeing stars from falling down). sensory receptors can be very sensitive to their preferred form of stimulus (single odorant molecule).
Threshold
the minimum stimulus required to activate a receptor
Receptor Potential
the change in sensory receptor membrane potential. Is a graded potential. Will initiate an action potential that travels.
Graded potential
variable strength signal that travels over short distances and loses strength as it travels through the cell
Receptive field
A sensory neuron has a receptive field, which is the region surrounding it that can sense the stimulus. Simplest case is one neuron/receptive field, but they can overlap. more sensitive areas have smaller receptive fields (fingertips vs your leg)
Convergence
multiple presynaptic neurons providing input to a smaller number of postsynaptic neurons. Creates a larger overall receptive field.
Sensory system –> the brain
- can travel up the spinal cord via ascending pathways 2. can get directly to the brain via cranial nerves *Each major area of the brain processes at least one major category of sensation. *Most pathways, once in the brain, go through the thalamus.
Sensory pathway that does NOT pass through the thalamus
Olfactory senses. These are one of the oldest senses. They are chemoreceptors
Proust phenomenon
the ability of odors spontaneously to cue autobiographical memories which are highly vivid, affectively toned and very old
Perceptual threshold
level of stimulus intensity necessary for you to be aware of a particular sensation- most senses get filtered out by the brain, otherwise you would be aware of the noises your organs make, etc.
habituation
decreased perception of a stimulus
inhibitory modulation
diminishes a suprathreshold stimulus until it is below the perceptual threshold. often occurs in secondary and higher neurons in a sensory pathway
The CNS must distinguish 4 properties of a stimulus:
- nature, or modality
- location
- Intensity
- duration
Stimulus property: Modality
- what sensory neurons are activated? 2. where are they synapsing in the brain?
Labeled line coding
1:1 association of receptor with sensation ex: stimulation of a cold receptor is always perceived as cold, whether the actual stimulus was cold or an artificial depolarization of the receptor.
Stimulus property: Location
Coded according to which receptive fields are activated (auditory coding is an exception to the location property because sensitive to different frequencies and timing). –> the homunculus
Lateral inhibition
Increases contrast between activated receptive fields and inactive neighbors
Population Coding
–Multiple receptors functioning together to send the CNS more information than would be possible from a single receptor
Stimulus property: Intensity
–Coded by number of receptors activated and frequency of action potentials (frequency coding)
-As a stimulus increases in intensity, additional receptors are activated; the CNS then translates the number of active receptors into a measure of stimulus intensity (the system can react appropriately)
Frequency of action potentials
is proportional to stimulus intensity
Duration of a series of action potentials is proportional to:
the stimulus duration
Stimulus duration
Depends on the duration of the action potentials.
Affected by ADAPTATION
Tonic receptors
slowly adapt to a sustained stimulus.
- iritants
- tactile
- proprioceptors
- barorecptors
Phasic receptors
rapidly adapt to a sustained stimulus, and will shut off if the stimulus doesnt stop.
- Allows body to ignore information that has been evaluated and found not to threaten homeostasis
- Lets us focus on what is new, different or essential
- Sense of smell
Somatosensory pathway
- Pain, temperature and Coarse touch cross the midline in the spinal cord
- Fine touch, vibration, and proprioception cross the midline in the medulla
- All synapse in the thalamus
- Senses all percieved in the primary somatosensory region of the cortex–> recognizes where the sensation originated from (homunculus)
Free nerve endings
are unmylenated nerve endings, located around hair roots and under surface of the skin. Respond to temperature, noxious movement and hair movement.
Meissner’s corpuscles
these are in the superficial layers of skin, encapsulated in the connective tissue. Respond to flutter and stroking of skin. Have rapid adaption.
Pacinian corpuscles
Receptors encapsulated in connective tissue in the deep layers of skin. Respond to vibration and have rapid adaptation.
Ruffini corpuscles
Enlarged nerve endings in the deep layer of skin. Respond to the stretching of skin, and have a slow adaptation.
Merkel receptors
Enlarged nerve endings in the superficial layers of skin. Respond to steady pressure and texture and have a slow adaptation.
Temparature Receptors
Free nerve endings in the subcutaneous layers.
Cold receptors respond to temps below body temp
Hot receptors respond to temps above body temp, 45C.
Above 45C activates PAIN receptors.
Noxious Receptors
Respond to things that may damage tissue. Are free nerve endings that are modulated by local chemicals- Substance P released in response to inflammatory pain.
Have reflexive properties (pull away reflex) in the brain.
Nociceptors are not found in the CNS.
•Activitation of nociceptor pathways initiates adaptve, protective repsonses
Itch
From skin nociceptors
–Histamine activates C fibers, causing itch
Pain
Subjective to perception
–Fast pain
–Sharp and localized—by Ab fibers (mylenated)
–Slow pain
–Duller and more diffuse—by C fibers (unmylenated)
In the absense of a stimulus from C fibers, there is an interneuron that inhibits the pain pathway. When pain is sensed, C fibers activate, and the interneuron is supressed.
pain can then be modulated by input from the Ab fibers
inflammatory pain
increased sensitivity to pain at sites of tissue damage.
Local Chemicals:
–K+, histamine, prostaglandins released from damaged cells
–Serotonin released from activated platelets
–Substance P is secreted by primary sensory neurons
Ischemia
•lack of adequate blood flow
Vs. Chronic pain, which is pathological pain.
Analgesic drugs
- Aspirin, less potenti
- Opiods, more potent
- Act directly on CNS opiod receptors
Olfactory System
olfactory neurons in the olfacory epithelium of the nose activate CN I, which converges at the olfactory bulb–> olfactory tract–> olfactory cortex–> cerebral cortex and limbic system.
Gustatory System
•Taste is a combination of five basic sensations: sweet, sour, salty, bitter, umami
•Taste cells are non-neural epithelium
•Each taste cell is sensitive to only one taste
•Taste transduction: gustducin
1.
Sound Sensory Pathway
- sound waves hit TM and beceome vibrations
- the 3 bones of the middle ear vibrate
- the stapes, the last of the 3 bones, hits the oval window–> fluid waves in cochlea
- Hair cells bend and ion channels open in the cochlea, creates an electrical signal.
- AP fired at the cochlear nerve to the brain.
*Goes primarily to the cerebellum.
*High pitch percieved at stiffer region closer to the round window.
Conductive hearing loss
–No transmission through either external or middle ear
Central Hearing loss
–Damage to neural pathway between ear and cerebral cortex or damage to cortex itself
Sensorineural hearing loss
–Damage to structures of inner ear
Vestibular Apparatus
of the inner ear, responds to changes in the body’s position in space.
is a series of connected, fluid-filled chambers.
- Otolith organs- linear accelleration and head position.
- Semicircular canals- rotational accelleration.
Crista
sensory receptors of the ear for rotational acceleration.
Movement of the endolymph pushes on the gelatinous cupula and activates the hair cells.
When the head turns right, endolymph pushes the cupula to the left.
maculae
sensory receptors in the ear for linear acceleration and head position
The Pupil
- Size of the pupil modulates light that reaches photoreceptors
- Pupillary reflex is a consensual reflex
–Standard part of neurological examination
The Lens
- A concave lens scatters light rays.
- A convex lens causes light rays to converge.
- The lens is flatter for distant objects, and becomes more round for closer objects.
- Changes in lense shape controlled by the ciliary muscle, when relaxed, the lense is flat, and when contracted, the lense is round (contraction releases tension on the ligaments, allowing the lense to go loose)
Focal length
the distance from the center of the lens to the focal point.
Accommodation
•Process by which the eye adjusts lens shape to keep objects in focus
Near point of accommodation
Presbyopia
loss of accommodation
Myopia
near-sightedness,
occurs when the focal point falls in front of the retina.
Gets corrected with a concave lens.
Hyperopia
far-sightedness,
occurs when the focal point falls behind the retina
Corrected with a convex lens
Astigmatism
•Usually caused by a cornea that is not a perfectly shaped dome, resulting in distorted images
Phototransduction
Converts light energy into electrical signals
Photoreceptors- rods and cones and gaglion cells with melanopsin (changing light cues)
Most acute vision occurs at the fovea and macula
Optic disk has no photoreceptors and is called the blind spot
Rods
function well in low light
Contain rhodopsin
Cones
responsible for high-acuity vision and vision during the daytime
Contain three pigments –> Color-blindness
