Flashcards in Chapter 46 - Guyton Deck (37):
detect compression or stretching of tissues
detect changes in temperature
pain receptors, detect damage occurring in tissues
detect light in the retina
detect taste, smell, oxygen level in arterial blood, osmolality of body fluids, carbon dioxide concentration, other chemical factors
Differential sensitivity of receptors.
they are sensitive to one type of stimuli and not others (rods and cones to light but not heat/cold, pain only receptive to pressure once it is enough to cause damage)
What is the "labeled line" principle?
each nerve tract terminates at a specific point in the central nervous system, and the type of sensation felt when a nerve fiber is stimulated is determined by the point in the nervous system to which the fiber leads
What is the receptor potential?
type of stimulus that excites the receptor, its immediate effect is to change the membrane electrical potential of the receptor
Mechanisms of receptor potentials.
1) mechanical deformation of the receptors (stretching of the receptor membrane and ion channels open) 2) application of chemical to the membrane (ion channels open) 3) change of temperature (alters the permeability of the membrane) 4) electromagnetic radiation (changes the receptor membrane characteristics and allows ions to flow through channels)
Maximum amplitude of most sensory receptors.
The more the receptor potential rises above threshold level, the greater the frequency of what?
What allows sensory receptors to have an extreme range of response, from very weak to very intense?
frequency of repetitive action potentials
transmitted from sensory receptors increases approx. in proportion to the increase in receptor
potential; very intense stimulation of the receptor causes progressively less and less additional increase in numbers of action potentials
What is adaptation of sensory receptors?
adapt either partially or completely to any constant
stimulus after a period of time; pacinian corpuscle
adapts extremely rapidly and hair receptors adapt
within a second or so, whereas some joint capsule and muscle spindle receptors adapt slowly
How do mechanoreceptors adapt?
receptor potential occurs at onset of compression; accommodation (inactivation of Na channels as fiber gradually accommodates stimulus)
What are tonic receptors?
slowly adapting receptors that can transmit signal as long as stimulus is present; examples are muscle spindles, Golgi tendons, pain, baroreceptors, chemoreceptors of carotid and aortic bodies
Rapidly adapting receptors are also called?
rate, movement, or phasic receptors
If you haven't done so (because you are only reading the outlines), go to page 576 in the 11th edition and read the heading: Importance of the Rate Receptors—Their Predictive Function.
that's pretty cool.
increasing signal strength by using greater number of fibers
increasing the frequency of nerve impulses in each fiber
Type A nerve fibers
typical large and medium-sized myelinated fibers of spinal nerves (alpha, beta, gamma, delta)
Type C nerve fibers
small unmyelinated nerve fibers that conduct impulses at low velocities; constitute more than one half of the sensory fibers in most peripheral nerves as well as all the postganglionic autonomic fibers
Group Ia nerve fibers
Fibers from the annulospiral endings of muscle spindles, alpha A fibers
Group Ib nerve fibers
Fibers from the Golgi tendon organs, alpha A fibers
Group II nerve fibers
Fibers from most discrete cutaneous tactile receptors and from the flower-spray endings of the muscle spindles, beta and gamma A fibers
Group III nerve fibers
Fibers carrying temperature, crude touch, and pricking pain sensations, delta A fibers
Group IV nerve fibers
Unmyelinated fibers carrying pain, itch, temperature, and crude touch sensations, type C fibers
Two ways to increase sensation of pain?
spatial and temporal summation
Give an example of amplifying divergence?
type of divergence is characteristic of the corticospinal pathway in its control of skeletal muscles, with a single large pyramidal cell in the motor cortex capable, under highly facilitated conditions, of exciting as many as 10,000 muscle fibers
Give an example of divergence into multiple tracts?
information transmitted up the dorsal columns of the spinal cord takes two courses in the lower part of the brain: (1) into the cerebellum and 2) on through the lower regions of the brain to the
thalamus and cerebral cortex
The signals from the interneurons ______ on the anterior motor neurons to control muscle function.
converge (convergence can come from a single source or multiple sources)
Give an example of reciprocal inhibition.
at the same time that an excitatory signal is transmitted by one set of neurons in the spinal cord to cause forward movement of a leg, an inhibitory signal is transmitted through a separate set of neurons to inhibit the muscles on the back of the leg so that they will not oppose the forward movement
What is a reverberatory, or oscillatory,
circuits are caused by positive feedback
within the neuronal circuit that feeds back to
re-excite the input of the same circuit. Consequently, once stimulated, the circuit may discharge repetitively for a long time.
Give an example of reverberating circuit in the body.
autonomic nervous system to control such functions as vascular tone, gut tone, degree of constriction of the iris in the eye, and heart rate
What occurs during epileptic seizures?
uncontrolled reverberating signals due to the areas of the brain being interconnected directly or indirectly
What are the two basic mechanisms that prevent reverberating signals in the brain?
inhibitory circuits and fatigue of synapses
Two types of inhibitory circuits in widespread areas of the brain help prevent excessive spread of signals:
inhibitory feedback circuits and neuronal pools that exert gross inhibitory control over widespread areas of the brain