Pt6 Sensory System I Flashcards
What are the 6 sensory pathways?
- Sensory reception
- Transduction
- Amplification/adaptation
- Transmission
- Integration
- Perception
What is the general functional organization of the nervous system?
PNS = sensory & motor input (to environment internal/external)
CNS = integration (unconscious/conscious)
What is the hierarchical organization in the nervous system?
(LOW to HIGH)
1. Receptors distributed with axons projecting via cranial & spinal nerves into CNS.
2. Fibers connect w local circuit for reflex functions (dont need CC for reflexes) or travel cranially to synapse in brain. brainstem, cerebellum, thalamus, CC
3. Primary receiving areas: auditory, sensory, visual, olfactory
4. Association areas integrate input & connect with motor areas via interneurons (takes into account previous experiences) to plan a response.
Describe sensory receptors.
-present in every tissue
-sensory info acquired at terminal end of spinal & cranial sensory nerve fibers & conveyed to CNS
-conscious: pain, touch, temp, bladder
-unconscious: BP, O2/CO2 levels
What are somatosensory signals?
-originate from cutaneous areas: muscle & joints
-respond to mechanical/chemical/thermal stimuli
-produce sensation of: pain, pressure/vibration, touch, temp
-vision & hearing = somatic special
What are viscerosensory signals?
-originate from internal structures
-some signals are conscious (ex. Bladder, full stomach)
-taste & gustation = visceral special
What is the “labeled line” principle?
-nerve fibers transmitting only ONE modality of sensation
-when a sensory fiber is stimulated the perception is related w the type of fiber regardless of the type of stimulus excites it
EX:
~stimulus = overheating, electricity, crushing, damage to fiber
~Perception = pain
EX:
Pain receptors dont respond to normal touch/pressure, only active when stimuli is severe to damage tissue
What is a sensory receptor?
-nerve ending, a cell or group of cells, or sense organ
-when stimulated = produces afferent/sensory impulse
What are the 3 sensory receptors?
- Simple receptors
-free nerve endings
-not myelinated
-common - Complex receptors
-sheathed by CT capsule (enclosed nerve ending)
-encapsulated portions of axon are not myelinated - Special senses receptors
-specialized receptor cells (ex. Hair cell)
-sensory ganglion
-myelinated
-synaptic vesicle
What are mechanoreceptors?
Receptors for:
1. Skin tactile sensibilities: (dermis & epidermis)
-free nerve ending (pain, heat, temp)
-merkles discs (touch)
-Ruffinis endings (pressure)
-meissners corpuscules (touch)
-Krauses corpuscules
-hair end organs (touch)
2. Deep tissue sensibilities
-ruffinis endings
-pacinian corpuscles (strong pressure)
-muscle spindles
-golgi tendon receptors
3. Hearing
-sound receptors of cochlea
4. Equilibrium/balance
-vestibular receptors
5. Arterial receptors
-baroreceptors of carotid sinuses and aorta
What are muscle spindles?
-encapsulated group of 3-12 skeletal muscle fibers (receptors)
-contractile elements = restricted to the ends
>none in middle (lacks myofibrils)
>affect sensitivity for transducing muscle stretch
>contractile part = innervated by gamma motor neurons (give rise to Type A gamma fibers)
» gamma motor neurons from CNS innervate intrafusal fibers to CNS
-middle part innervated by sensory neurons and carry AP from spindle to the CNS
Describe muscle spindle structure.
-buried in extrafusal fibers of muscle = contractile fibers
-sends info about muscle stretch to CNS
-golgi tendon organ links muscle & tendon
-intrafusal fibers found in muscle fibers
What is the function of muscle spindles?
-stretch receptors = to correct changes in muscle length
-stretching middle segment of intrafusal muscle fiber = generates AP along spindle sensory neurons
>stretch ion channels open
>leads to membrane depol & AP gen
>muscle contraction
What are the 5 steps for the muscle stretch reflex?
- Stretching of muscles stimulates muscle spindles
- Activation of sensory neurons
- Info processing at motor neuron
- Activation of motor neuron
- Contraction of muscle
Describe the gamma and alpha motor neurons?
-muscle spindle participates in sensory & motor function
-co-activation of alpha & gamma neurons = allow brain to test whether the amount of contraction intended by the brain was what actually occurred
-alpha = extrafusal
-gamma = infrafusal
What is the golgi tendon organ?
-helps control muscle tension
-encapsulated sensory receptor = muscle tendon fibers pass
>10-15 muscle fibers connected to each golgi
-stimulated when small bundle of muscle fibers are tensed by contraction
What’s the difference between muscle spindle & the golgi tendon organ?
MUSCLE SPINDLE:
-detects muscle length & changes in muscle length
GOGLI TENDON ORGAN:
-detects muscle tension reflected by the tension in itself
What is the golgi tendons role in the nervous system?
-provides nervous system w info on the degree of tension
-signals conducted through sensory nerve fibers
>excite inhibitory interneurons in spinal cord
>inhibit alpha motor neuron activity
>causes muscle relaxation
prevents excessive tension on muscle
What are the 5 sensory receptors?
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
- Photoreceptors
- Chemoreceptors
Describe thermoreceptors.
-temp
-warm/cold receptors
-free nerve ending receptors
Describe nociceptors.
-pain
-free nerve endings
Describe photoreceptors.
-vision
-rods & cones
Describe chemoreceptors.
Receptors for:
-taste = taste bud receptors
-smell = receptors of olfactory epithelium
-arterial oxygen = receptors of aortic & carotid sinus
-osmolality = neurons in/near supraortic nuclei
-blood CO2 = surface of medulla & in aortic & carotid bodies
-blood glucose, AA, FA = receptors in hypothalamus
Describe the transduction of receptor stimulus.
-the type of stimulus that excites the receptor = change the membrane electrical potential
-change = receptor potential or generator potential
-4 ways to stimulate a receptor potential
What are the 4 ways to stimulate a receptor potential?
- Mechanical deformation
- Application of a chemical to the membrane
- Change of temp of membrane
- Effects of electromagnetic radiation
>light on a retinal visual receptor
all are related with changes in membrane permeability = allows ions to diffuse more/less
stimulation change resting membrane potential
Ex. Pacinian corpuscle = onion like structure in dermis & hypodermis
What is the relationship between receptor potential & action potentials (amplification).
-more receptor potential rises above threshold level = greater becomes the action potential freq.
-more intense stimulus = greater the # of receptors stimulated
Describe the adaptation of receptors.
-can adapt either partially/completely to constant stimulus
-continuous sensory stimulus = receptor responds at a high impulse rate at first & then at a slower rate
-rate of AP decrease to few or none
-diminish extent of their depol despite sustained stimulus strength
Describe slow adapting receptors.
“Tonic receptors”
-transmit impulses to brain as long as stimulus is present
EX: baroreceptors & chemoreceptors
pain never adapts
Describe fast adapting receptors.
“Phasic receptors”
-stimulated when stimulus strength changes
EX: pacinian corpuscle
Describe stimulus perception in the dog.
-detect diff modalities of stimulus & know location of stimulus applied to the body
-segments of spinal cord innervates a receptive field of body
>dermatoma
-trigeminal nerve (CN V) fibers have receptive fields on the face
areas of skin innervated by cutaneous branches from a single spinal nerve = “dermatome”
cutaneous areas supplied by adjacent spinal nerve overlap
The precision of stimulus location is acuity and depends on:
receptive fields of afferent neurons (tactile sensations in skin) code for stimulus location
-size & # receptive fields = smaller the receptive field the greater the acuity
>lips and fingertips have better acuity than back & shoulder bc of ability to perceive 2 fine points presses against skin as two points & not one (two-point distribution)
-lateral inhibition = occurs when a strong stimulus applied to receptive field of one neuron = neuron inhibits transmission of signals by neurons w neighboring receptive fields
>increases acuity bc it increases contrast of signals in NS
