Sensory Physiology Flashcards
What do sensory receptors do?
They are transducers: they sense a change in environment and convert it to action potential to relay to the nervous system
What is a modality?
The form information takes
Why are modalities perceived as different from one another?
Because of the CNS pathway they take
What are the different receptors (as classified by stimulus type)?
Chemoreceptors - Chemical
Photoreceptors - Light
Mechanoreceptors - Heat
Nocireceptors - Pain
Propioceptor - Balance & Position
What are the cutaneous/somatic receptors?
Touch & Pressure
-Merkel’s discs in stratum basale: sustained pressure
-Ruffini corpuscles - sustained pressure
-Meissner’s corpuscles - changes in texture, slow vibrations
-Pacinian Corpsucles - Deep pressure, fast vibrations
Heat (Cold in upper, warm in lower)
Pain
What are tonic receptors?
Sensors that respond at a constant rate as long as stimulus is being applied
What are phasic receptors?
Receptors that respond with a burst of AP but quickly stop as they adapt
Ex. Smell, Light touch (clothes on body)
What is sensation?
The state of awareness of an internal or external condition
What is perception?
Conscious recognition of a sensation
What is sensory modality?
The quality or distinct property of a sensation (we have more then 20)
Are we conscious of all sensory modalities?
No, some are unconscious, such as those in the stomach
What is an adequate stimulus?
The type of stimulus to which as receptor is most sensitive
What is the law of specific nerve energies?
The sensation perceived when a receptor responds is always the same, regardless of strength or type
True or False: The stimulation of a sensory fiber evokes only the sensation of its modality
True
True or false: Stimulation of sensory fibers requires no energy.
False. This is why different kinds if energy can activate sensory neurons that don’t respond to that stimulus (ie why getting punched in the eye makes you see light)
True or False: The sensors on a body correspond to that side of the body
False. The left side of the body goes to the right side of the brain and vice versa
Where is the somatosensory pathway for touch and proprioception?
The dorsal columns of the spinal cord
Where are the somatosensory pathways for pain and temperature?
The lateral spinothalmic tract
What increases the sensitivity of receptive fields in the skin?
The density of receptors: the more endings closer together, the more sensitive
What is 2-point discrimination?
If the distance between two points is on the same receptive field it will not be perceived as 2 points
What is tactile acuity?
The minimum distance at which two points can be perceived as separate
What is the olfactory pathway?
Receptor cells synapse with secondary cells in the olfactory bulb called mitral cells, which Amplify, Refine, and Relay to olfactory cortex, hypothalamus, amygdala, and limbic sysem
What kind of messenger system does the olfactory pathway use?
Secondary Messenger System:
Oderants bind to 1 of 350 specific receptors, then cilia in the nasal cavity communicates to receptor neurons
Which sensation is the only one that skips the thalamus and goes directly to its cortex?
Olfactory
What are the receptors in gustation?
Sweet
Sour (H+)
Salty (Na+)
Bitter
Unami (amino acids)
What do we call a modified epithelial cell covered with microvilli?
A taste bud
True or False - Each taste bud responds to one type of taste
False - Each bud responds to all categories of tastants
Which two tastants do not have membrane receptors?
Salty and Sour
What is the 3 Order Sensory Neuron Pathway?
1st Order - Vagus, Facial, and Glossopharugeal nerves all carry sensation to the medulla oblangata
2nd order go to the thalamic nucleus
3rd order go to the sensory cortex
What are the three tunics if the eye?
Exterior - The fibrous (sclera and cornea)
Middle - The vascular (cilliary body)
Interior - The sensory (retina)
What is the path of light?
Cornea to Anterior Chamber if Aqueous Humor past the iris through the pupil through the lens to the posterior chamber of vitreous humor and onto the retina
How does the ANS regulate pupil size?
The Sympathetic controls radial fibers, which dilate the pupil
The Parasympthetic controls circular fibers, which constrict the pupil
What does the ciliary body do?
It supports the lens with suspensory ligaments and constricts or relaxes to control the shape of the lens.
It secretes aqueous humor
What happens as aqueous humor circulates in the eye? What happens if this stops?
It is secreted into posterior chamber, circulates to anterior chamber, and is drained through the canal of Schlemm.
If drainage is blocked it causes an increase in pressure called glaucoma
What is refraction?
The change in direction of a wave passing from one medium to another
What is accommodation?
The “plumping up” of a lens during vision.
When the ciliary muscles tense the lens becomes more convex
What 3 adjustments happen to our eyes during close vision and what muscles control these adjustments?
Accommodation - The ciliary body
Constriction if the Pupil - Circular fibers of iris
Convergence - Medial rectus of the eyes
Why do we lose visual acuity as we age?
The dilator muscles become less efficient, this condition is called Presbyopia
What is emmetropia?
Normal vision
What is used to test for sharpness of vision aka visual acuity?
The Snellen eye chart
What is the most common form of color blindness? Why?
RG Colorblindness. It is most common in males because red and green cones are carried on the X chromosome and males only inherit one from their mothers, while females inherit one from each parent
What is hyperopia?
Far-sightedness - rays focus behind the retina, corrected with a convex lens
What’s myopia?
Near-sightedness - rays focus in front of the retina, a concave lens to correct
What is an astigmatism?
Tays do not focus do to an uneven curvature of the lens
What is the the organization of the retina?
Photoreceptor cones on the macula lutea
Light is focused on the fovea centralis
Axons of neurons gather at optic disc
-This creates a blind spot, which the brain accommodates for
The choroid is a dark layer behind the retina
How do visual pigments respond to light?
Light hits the retina and passes through ganglion cells
Piloral celles send info to bipolar cells, which send info to occipital lobe
What is the difference between retinal, opsin, and rhodopsin?
Retinal is a light-absorbing molecule that combines with opsin (synthesized from Vitamin A) to form visual pigments called Rhodopsin in rod cells
Explain the cis/trans isomer distinction of retinal
When light shines onto pigment molecules rhodopsin changes cis isomers to trans isomers
Trans retinal uses g protein to cayse a chain reaction closing gated channels and the cell hyperpolarizes
When light goes dark enzymes slowly covert all the trans retinal back to cis retinal
How do we perceive color?
RBG cone cells
What is light adaptation?
When moving from darkness to light
Pupils constrict and visual acuity improves over 5-10 minutes
What is dark adaptation?
When moving from bright light to darkness
Cones cease to function, pupils dilate and rhodopsin slowly accumulates over 20-30 minutes
What is the difference between rods and cones in terms of sensitivity and resolution?
Rods (all to to one bipolar neuron) - High sensitivity, low resolution
Cones (1 per neuron - 50% of visual cortwz, 1% of photorecptors)
Low sensitivity, high resolution
Where do the majority of optic tracts go and what does it do with this info?
The thalamus
-relays information on movement
-segregates axons for depth perception
-sharpens and contracts information
What are the visual regions of the primary visual cortex?
(All in Occipital Lobe)
Striate Cortex - creates depth perception from fusion of two different images
Prestriate Cortex - Process form, color, motion input
What are the complex processing regions for sight?
Temporal Lobe - identities objects
Parietal Cortex
Postcentral gyrus
True or False: Each part of the retina is responsible for a different part of the visual field
True
What are sound waves?
Change in the pressure in the air
How do we differentiate between pitch and loudness?
Pitch is the measure if the frequency of the waves, measured in Hertz
Volume is coded as amplitude
How is sound transduced from outside to cochlear nerve cells?
- Sound enters the auricle through the external auditory meatus
- The tympanic membrane vibrates
- This vibration pivots the auditory ossicles
- The stapes vibrates the oval window
- The perilymph in the vestibule is displaced by vibrations
- Vibrations ascend scala vestibuli to cochlea
- As they ascend they pass over scala media (filled with endolymph), and scala tympani (filled with perilymph), moving Reissner’s and basal membranes
- These membranes stimulate hair cells in the spiral organ of Corti
- The bending of hair cells opens mechanically gated channels which send an influx of K+ and Ca2+ into the cell
- The cell releases NT glutamate signals via Facial Nerve VIII
What are the auditory pathways to the brain?
Cochlear nuclei in brainstem > spiral ganglion of cochlear nerve > vestibulocochlear nerve > midbrain > thalamus > Primary auditory cortex of temporal lobe
What is meant by tonotopic organization?
In the cochlea higher tones are perceived in different parts of the auditory cortex
How do we localize sound in our environment?
There is relative intensity in both ears ie the right here will receive more physical stimulation from sounds on the right side and brain will code that the sound is coming from that side
(does not work front/back, only left/right)
What is difference between conduction deafness and sensorineural deafness?
conduction - sound is blocked (impacted earwax, perforated tympanic membrane, otosclerosis of ossicles)
Sensorineural - Damage to nerves or part of brain or hair cells
Where are dynamic (rotational) equilibrium receptors?
Semicircular canals
In Crista Ampullaris, in ampula of each canal, and cupila which moves in same direction of direction bent
Which 3 sensory inputs play a role in equilibrium?
Vestibular receptors
Visual recetors
Propiosomatic receptors in joints/tendons
What is vestibular nystagmus?
The involuntary oscillations afters spinning stops
What is vertigo?
The loss of equilibrium
What is the neural pathway for equilibrium?
(complex and poorly traced)
Sensory inputs go to vestibular nuclei in brainstem, cerebellum AND to oculomotor center if eyes and spinal cord
69?
Nice.
True or False: Where there is a high receptive field more physical brain space
True.
ie Hands have leas surface area than one’s back but the hand’s sulcus is larger because there are more receptors
What do basal nuclei do?
Adjust the starting, stopping, and intensity of movements after receiving input from the cerebral cortex and substantia nigra
What happens if there is damage to the basal nuclei?
Parkinson’s, Huntington’s
Increased motor output, muscles tone, difficulty initiating movement, involuntary muscle movement’s, “mask face”
What are the association areas of the brain?
The prefrontal cortex and cerebra cortex
What is the function of the prefrontal cortex?
Intellect. Recall, judgment, concern for others, personality, emotional management
Case of Phineas Gage and personality change
True or false: the prefrontal cortex develops early in life and has little to no impact on our later life actiona
False. Develops later, is heavily impacted by one’s social environment, and there is a correlation between and underdeveloped pfc and incidences of violent crime
What are the language centers of the brain?
Wernicke’s area - Comprehension. temporal lobe near parietal sulcus. Damage = speak but make no sense
Broca’s area - speech production, frontal cortex (opposite hemisphere as writing hand)
Damage = struggle saying correct words
What is aphasia?
A partial or total loss of language skills due to brain damage
When reading what parts of the brain are engaged?
Sensory input to eyes
skeletal muscles of the eye
smooth muscle of the iris
Cerebral cortex
Prefrontal cortex
basal nuclei
What is cerebral lateralization?
Distribution of functional areas are not always symmetrical
Ex. Left hemi has general interpretive center for math. right side has spacial visualization and analysis
What is the emotional brain?
The lymbic system
What are the structures in the limbic system?
Medical cerebrum (anterior thalamus, hypothalamus)
Cingulate gyrus - expressing emotion, resolving conflicts
Hippocampus - role in memory
Amygdala - memory/recognition if fearful expressions and danger anaylsis
How do emotions influence our physiological functions?
Both emotions and the autonomic nervous system are controlled by the HYPOTHALAMUS so emotional responses stimulate autonomic, endocrine, and immune responses
What is memory?
The storage and retrieval of information
What are the 3 principles of memory?
- Storage - Occurs in stages, constant change
- Processing - Hippocampus and surrounding structures
- Traces - Chemical or structural changea in neurons encode the memory
What are the differences in capacity for stages of memory?
Short Term (Working) Memory - lasts seconds-hours, limited to 7-12 pieces of information. Only 5% or so of sensory input is transferred
Ex. Crossing the road to see if it is clear
Long Term Memory - Limitless capcity
What are the factors thar affect the transfer from short term to long term memory?
“Remember for an ERAA”
Emotional State - Learn when alert, aroused, motivated
Rehearsal - Repetition enhances memory
Association - Associating new with okd enhances LTM
Automatic - Subconscious info is stores in the long term memory
What is the order of memory processing?
Outside stimulus provides afferent inputs to cerebral cortex. which stores it temporarily
(If not needed, permanently lost)
Selective transfer to short term
Selective transfer to longterm
“Retrieval” sends from longterm to shortterm
What are the categories of memory?
Declarative (factual) - Explicit information
(names, dates). Conscious thoughts. Stores in context in which it was learned
Procedural (skill) - aka Muscle Memory
Acquired through repetition
Do not retain context of original learning
Stored in premotor cortex
Which structures are involved in declarative memory?
Thalamus
Temporal Lobe Structures (Hippocampus)
Basal Forebrain
Prefrontal cortex
What structures are involved in procedural memory?
Basal Nuclei
Premotor Cortex
Thalamus
Substantia Nigra
What is the physiological mechanism for memory formation?
Long term potentiation
-Repetitive stimulation modifies synapses
-Increases the amount of time a neuron is depolarized
-More NT released, dendrites change shape, number of membrane receptors increases
What are the structures in the diencephalon?
Thalamus, Hypothalamus, Epithalamus
What is the function of the thalamus?
Relay station for all afferent (incoming) sensory impulses
Has two nuclei - one under each hemisphere
Screens sensory impulses and decides whether to send to cortex or no (and where)
What is the function of the hypothalamus?
Maintains homeostasis
Autonomic control center - releases catecholamine, ANS centers in spinal cord
Emotions
Body Temperature
Sleep-Wake Cycles
Food Intake
Thirst/H2O Balance (Anti-diuretic hormone)
What is the function of the epithalamus?
Contains the choroid plexus, which secretes CSF
Suprachiatic Nucleus (SCN) controls melatonin release and circadian rhythms
What are the structures of the midbrain? What are their functions?
Cerebral Peduncles - Superior brain stem
4 grey matter nuclei called corpora quadrigemina (superior - visual, inferior - auditory)
Substantia nigra - linked to basal nuclei, releases dopamine, controls motor output
Ventral Tegmental Area - dopamine neuron tract with prefrontal cortex (addiction path)
Why does the substantia nigra appear dark?
It produced dopamine, which is synthesized from the amino thyocin, which is pigmented
What is the function of pons?
Pontine nuclei - relay station between motor cortex and cerebellum
Pneumotaxic/apneustix respiratory center - Works with medulla oblongata to maintain rhythmic breathing
What is the function of the medulla oblongata?
Motor tracts that desuccate (cross over one another) before going to spinal cord
Cardiovascular Center - adjusts heart rate and blood pressure
Respiratory Center - (with Pons) controls rate and depth of breathing
Integrating Center for - Vomit, swallowing, coughing, sneezing, hiccups
What is the function if the cerebellum?
Maintains and coordinates posture, balance, plays a role in procedural learning
Sensory and motor maps of body to create “awareness map”
Monitors movements from motor cortex and basal nuclei
Monitors proprioceptors, motor sensors
Compares intended movements, sensory input, and actual movement/placement of muscles
Sends corrective feedback
What happens if there is damage to the cerebellum?
Ataxia - disruption in muscle coordination (drunk walk), abnormal speech patterns
What is the reticular activation system? (RAS)
The many neurons sending constant impulses to the cortex via the thalamus to keep the cortex conscious and alert
What inhibits the RAS?
Adenosine, Alcohol, Tranquilizers, The Hypothalamus
What is the Reticular Formation?
The loose cluster if neurons extending through the brain stem to the thalamus, hypothalamus, cerebellum, and spinal cord
What is the Reticular Formation responsible for and where is it? What is the effect of caffeine on it? What can damagin it cause?
Alertness
The brain stem
Caffeine binds to adenosine receptors (but will eventually be overwhelmed)
Coma
What are different types of sleep?
NREM (4 stages)
REM
What are the 4 stages of NREM sleep?
In the first 30-45 minutes of sleep
Stage 1: Dozing Off (when myoclonic twitch happens)
Stage 2: Difficult to Arouse, Grogfy
Stage 3 - Delta waves emerge, deep sleep
Stage 4 - REM
When does sleepwalking typically occur?
In NREM sleep
What happens during REM sleep?
Vital signs increase (BP, HR, Resp)
Neural activity high in pons and limbic
Skeletal muscles are inhibited
-Eyes muscles still popping off
Dreaming takes place
Reduced activity in prefrontal cortex
Long-Term memories formed
What structures regulate sleep?
The suprachiasmatic nucleus and preoptic nucleus
True or False: Our sleep requirements increase with age
False, they decrease
What are the characteristics of sleep disorders? What are their causes?
Narcolepsy - Abruptly enter REM from wake state
Cause - Unknown
Insomnia - Chronic inability to obtain the amount of sleep needed
Cause - stress
Sleep apnea - temporary cessation of breathing during sleep
Cause - blocked airway due to overly relaxed muscles
Night terrors - abrupt anxious awakefullness from deep sleep
Cause - Unknown, more common in children
Sleepwalking - Doing daily activites during sleep, occurs in stages 3 and 4 of NREM
What is EEG? What are the different types of waves?
ElecetroEncephaloGram - a recording of brain activity in the cortex
Alpha Waves - Parietal, Occipital, Awake, Relaxed, eyes closed
Beta Waves - Frontal, visual stimuli
Theta Waves - Temporal, Occipital, REM (indicator of HIGH stress in waking adults)
Delta Waves - Common in adults during sleep, indicates brain damage during wakefulness
What is the biorhythm of the body?
Dynamic Equilibrium that is constantly fluctuating between normal ranges. The fluctuations are called biorthythms
Cycles completely approx. every 25 hours, called circadian rhythm
What structures control circadian rhythms?
The SCN in the hypothalamus
“Clock proteins” change their concentration throughout the day
Melatonin keeps in tune with environment. Light causes production of melanopsin, which destroys melatonin
What are some examples of circadian rhythms?
Plasma cortisol is high in the morning, declines
Body temp is high during day, lowers at night
What do we call the disruption of Circadian Rhythm (when internal clock is out of tune with external environment)
Desynchronis
What is the function if the spinal cord?
Sends information between the brain and the body
What is an example of the ASCENDING (sensory) spinal tract?
Spino Thalamic Tract - Touch receptors up dorsal column go to dorsal root ganglia to 1st order sensory neurons to medulla oblongata to medial leminsicial tract to 2nd order neurons to thalamus to 3rd order neurons in cerebral cortex
How are the descending spinal tracts organized?
2 Neurons - Upper (Cortex and spinal cord)
and Lower (Between spinal cord and skeletal muscles)
What are the different spinal cord injuries? Does this affect the brain?
Cervical - Quadriplegia
Thoracic - Paraplegia
One Side - Heniplegia
Does not usually affect the brain, the muscles receive no information and atrophy
What is the difference between upper and lower neuron damage?
Upper - Spastic paralysis, irregular/exaggerated reflexes and no voluntary control
Lower - Flaccid Paralysis (polio, stroke) severe damage to anterior horn cells
What is the difference between upper and lower neuron damage?
Upper - Spastic paralysis, irregular/exaggerated reflexes and no voluntary control
Lower - Flaccid Paralysis (polio, stroke) severe damage to anterior horn cells
Where are the receptors for static left/right) equilibrium?
in Vestibular apparatus
In The Maculae in utricle walls and saccules
Also monitor position of head in space for posture
