Group 8/23/19 Flashcards
Learning issues
- anatomy of joints (Moore)
- physiology of somatic sensation (Guyton and Hall ch 48 and 49)
- physiology of types of sensory receptors (Guyton Hall ch 47)
mechanoreceptors
detect mechanical compression or stretching of the receptor or of tissues adjacent to the receptor
thermoreceptors
detect changes in temperature
nociceptors
pain receptors; detect physical or chemical damage occurring in the tissues
electromagnetic receptors
detect light on the retina of the eye, e.g. rods and cones for vision
chemoreceptors
detect taste in the mouth, smell in the nose, oxygen level in the arterial blood, osmolality of body fluids, carbon dioxide concentration, and other factors that make up the chemistry of the human body
modality of a sensation
a principal type of sensation that we experience, like pain, touch, sight, sound, etc.
labeled line principle
nerve fibers are specific and transmit only one mode of sensation
what is the relationship between stimulus intensity and receptor potential?
with stronger stimulus intensity, amplitude of the receptor potential increases rapidly at first and then gets progressively less rapid at high stimulus strength
with greater frequency of action potentials, receptor potential increases proportionately
adaptation of receptors definition
sensory receptors adapt partially or completely with constant stimulus after time
receptor responds at high impulse rate initially, then at a progressively slower rate until few action potentials firing
mechanisms of adaptation
- when the receptor becomes deformed, a fluid within the corpuscle quickly brings shape back and receptor potential no longer elicited
- accommodation: nerve fiber tip becomes accommodated, inactivated sodium channels prevent depolarization
tonic receptors
these slowly adapting receptors will continue to transmit impulses to the brain as long as the stimulus is present; lets the brain know continuously about stimulus strength
rate/movement/phasic receptors
these receptors adapt rapidly and can’t be used to transmit a continuous signal. They are stimulated only when stimulus strength changes. Can be used to predict future changes.
what are the main differences between type A and type C nerve fibers?*
type A- large, medium sized myelinated fibers of spinal nerves
type C- small, unmyelinated nerve fibers, low velocity of impulses
spatial summation
increasing signal strength is transmitted using progressively greater numbers of fibers
temporal summation
transmits signals of increasing strength by increasing the frequency of nerve impulses in each fiber
excitatory/subthreshold stimulus
a stimulus that is above the threshold required for excitation, might have more than enough terminals to cause the neuron to discharge
subthreshold/facilitated stimulus
when fibers contribute terminals, but not enough to cause excitation. However, makes it so that the neurons are more likely to be excited by additional incoming nerve fibers
facilitated vs discharge vs inhibitory zone in neuronal pool
discharge- in central portion, all fibers are stimulated by incoming fiber, reaches excitation threshold
subthreshold- on the peripheral portions, the neurons are facilitated not excited
inhibitory- incoming fibers that inhibit the neurons congregate here
amplifying type of divergence
an input signal spreads to an increasing number of neurons as it passes through successive orders of neurons in the path
divergence into multiple tracts
signal transmitted into two different directions from the pool
convergence of signals
signals from multiple units unite to excite a single neuron, or signals can come from multiple sources, to create a summated effect
reciprocal inhibition circuit
incoming signal to a neuronal pool may cause one output excitatory signal in one direction and an inhibitory signal going in another direction
responsible for antagonisitic muscle pairs
afterdischarge
a signal entering a pool can cause a prolonged output discharge, that lasts after the signal is over
can happen in synapses to continue exciting a neuron so it produces a continuous train of impulses
reverberatory/oscillatory circuit
circuits that have a positive feedback mechanism so it will re-excite the input of the same circuit. Once stimulated, the circuit may discharge repetitively for a long time.
inhibitory circuits as a mechanism for stabilizing nervous system function
inhibitory circuits can help prevent the excessive spread of signals in the brain
some inhibitory feedback networks go from the termini of one network back to the initial excitatory neurons
there are neuronal pools that have inhibitory control over widespread areas of the brain
synaptic fatigue as a means of stabilizing the nervous system
synaptic transmission becomes progressively weaker the more prolonged and intense the period of excitation
overused pathways become fatigued and sensitivity decreases; underused ones are rested and sensitivities increase
long-term changes in synaptic sensitivity can be caused by down- or up-regulation of the synaptic receptors
what are the 3 physiological types of somatic senses?
- mechanoreceptive somatic senses, include tactile and position senses
- thermoreceptive senses, detect heat and cold
- pain sense
what are the tactile vs position senses?
tactile- touch, pressure, vibration, tickle
position- static position and rate of movement
although touch, pressure and vibration are detected by the same tactile receptors, what makes them individually triggered?
touch- stimulation of tactile receptors at skin or tissues immediately beneath
pressure- deformation of deeper tissues
vibration- rapidly repetitive sensory signals
Meissner’s corpuscle: fiber type, location, senses*
fiber type- large, myelinated fibers that adapt quickly
location- glabrous (hairless) skin
senses- dynamic, fine/light touch, position
expanded tip tactile receptors
feature of some touch receptors, such as those in fingertips. Transmit signals that are initially strong but partially adapting signal, then it becomes a weak signal that adapts slowly, to allow determination of continuous touch. Example is a Merkel disc.
iggo dome receptor
a receptor organ where Merkel discs group together, innervated by one large myelinated fiber. Protrudes through the epithelium of the skin and creates very sensitive receptor. Locate touch sensations and feel textures.
hair end-organ
type of touch receptor that adapts readily. Detects movement of objects on surface of body or initial contact with body.
Ruffini’s endings: fiber type, location, senses*
fiber- dendritic endings with capsule, adapt slowly
location- finger tips, joints
senses- pressure (esp continuous), slippage of objects along surface of skin, joint angle change
Pacinian corpuscles: fiber type, location, senses*
fiber type- large, myelinated fibers that adapt quickly
location- deep skin layers, ligaments, joints
senses- vibration, pressure
what transmits tickle and itch sensations?
there are very sensitive, rapidly adapting mechanoreceptive free nerve endings, usually in superficial areas of skin, slowly transmitted.
almost all sensory information from the somatic segments of the body enter the spinal cord through the ?
dorsal roots of spinal cord
what are the two alternative sensory pathways that sensory signals can be carried through once they enter the spinal cord? where do these systems come back together?
- dorsal column- medial lemniscal system
- anterolateral system (aka spinothalamic tract)
They come back together partially at the thalamus.
what kind of signals are carried in the dorsal column-medial lemniscal system?
Has large, myelinated fibers with high velocity transmission. Mainly carries sensory information that must be transmitted rapidly with temporal and spatial fidelity.
what kind of signals are carried through the anterolateral system?
Composed of small, myelinated fibers with slow velocity transmission. Less critical signals that don’t require highly discrete localization or discrimination of fine gradations of intensity. Examples are pain, hot/cold, itch/tickle, sexual sensations
Brodmann’s areas
human cerebral cortex is divided into 50 distinct areas with histological structural differences
central fissure/sulcus
fold that extends horizontally across the brain. Sensory signals terminate immediately posteriorly to this.
where do visual and auditory signals terminate in brain?
visual- occipital lobe
auditory- temporal lobe
motor cortex
region of cerebral cortex anterior to the central fissure
controls muscle contractions and movements
which lobes are the somatosensory cortices located in?
anterior parietal lobe
main differences between somatosensory areas I and II
I- more extensive and important, high degree of localization for different parts of the body, immediately behind central fissure
II- poor localization, mainly has leg, arm, and face, behind area 1
what are some functions that would be lost without somatosensory area 1?
localizing sensations precisely on the body, judging degrees of pressure, judging weights of objects, judging shapes or forms of objects, judging textures of materials
astereognosis
person is unable to judge the shape or forms of objects
somatosensory association areas
located behind somatosensory area 1. Important for deciphering deeper meanings of the sensory information in the somatosensory areas, by combining information arriving from multiple points.
amorphosynthesis
happens when the somatosensory association area is removed. Person loses ability to recognize complex objects and feel forms on opposite side of body to loss. The person forgets about their opposite side of the body and forgets about the other side of objects.
two-point discrimination
a test for tactile discrimination where two points pressed on the skin, and the person determines where one or two points were felt. Ability to discriminate the two points depends on lateral inhibition. Greater space for less sensitive areas.
