Chapter 10: Sensory Physiology Flashcards
Sensory, Reflexes, ANS, PNS
what is sensory physiology?
- the afferent branch of peripheral nervous system
- transmits information from the periphery to the central nervous system
2 classes of receptors in sensory physiology
1) sensory receptors = detect stimuli in the external environment
2) visceral receptors = detect stimuli that arise within the body
what are visceral afferent neurons?
a class of afferent neurons that transmit information to the CNS from stimulus occurring inside the body
what is perception?
the conscious interpretation of the world based on
sensory systems, memory, and other neural processes
what is the somatosensory system?
- part of the sensory system concerned with the conscious perception of touch, pressure, pain, temperature, position, movement
- necessary for perception of sensations associated with skin and position of the limbs and the body
what is somesthetic sensations?
sensations that arise from receptors in the skin
what is proprioception?
perception of the position of the limb and body
what are special senses?
are necessary for:
- vision
- smell
- taste
- hearing
- equilibrium/balance
what are sensory receptors?
specialized structures detect a specific form of energy in the external environment
what modalities can be detected from sensory receptors?
- light waves
- sound waves
- pressure
- temperature
- chemicals
what is the law of specific nerve energies?
states that a given sensory receptor is specific for a particular modality
–> this means cells in the eye called photoreceptors detect light waves, but not sound waves
what is the adequate stimulus?
refers to the idea that a sensory receptor is adapted to respond best to a certain modality/stimulus
i.e photoreceptors can respond to visible light
–> modalities other than the adequate stimulus may activate the sensory receptor BUT only at higher energy levels
5 types of sensory receptors in somatosensory system
- photoreceptors (light)
- chemoreceptors (taste and smell)
- thermoreceptors (temperature)
- mechanoreceptors (touch and pressure)
- nocireceptors (pain)
what is the function of sensory receptors?
sensory transduction!
–> they convert the energy of a sensory stimulus into changes in membrane potential (called receptor potential)
–> converts from one energy type to another (electrcial)
–> activation of these receptors by stimuli causes graded potentials triggering nerve impulses along the afferent PNS fibers reaching the CNS.
what is sensory transduction?
- is the conversion of stimulus energy into electrical energy
- sensory receptors convert the energy of a sensory stimulus into changes in membrane potential called receptor potentials/ generator potentials
what are receptor potentials?
- are graded potentials (magnitude varies with strength of a stimulus) resulting from changes in membrane potential
- receptor potentials are caused by the opening or closing of ion channels in response to sensory receptors detecting a sensory stimulus in the external environment
how do sensory receptors perform their function?
when a sensory receptor is exposed to a specific stimulus (i.e light), the receptor cell is activated
- this leads to changes in the permeability of its membrane to ions, so ion channels may open or close.
- as a result, the flow of ions across the membrane changes and alters the membrane potential of the receptor cell
- receptor potentials are graded. this means the magnitude of depolarization depends on intensity of the stimulus
–> A stronger stimulus leads to a larger receptor potential (more depolarization)
–> A weaker stimulus results in a smaller receptor potential (less depolarization)
- if the receptor potential exceeds threshold, it can
generate an action potential
- the action potential is a rapid and all-or-nothing electrical signal that is propagated to the CNS (brain or spinal cord)
- the electrical signals are then processed and interpreted, leading to the perception of the original stimulus.
how are post-synaptic potentials different from receptor potentials?
- postsynaptic potentials are triggered by the binding of neurotransmitter to receptors
- receptor potentials are triggered by sensory stimuli
two basic forms of sensory receptors
1) the sensory receptor exists as a specialized structure at the peripheral end of an afferent neuron
–> if the receptor is depolarized to threshold, an action potential is generated in the afferent neuron and propagated to the CNS
2) the sensory receptor is a separate cell that communicates through a synapse with an associated afferent neuron
–> a change in the receptor’s cell membrane potential via calcium channel causes the release of a neurotransmitter (big stimuli = more released)
–> the transmitter binds to the receptors on the afferent neuron and causes a change in membrane potential of that cell, causing depolarization to threshold and generation of an action potential which is transmitted to CNS
what is receptor adaptation? what happens?
- is a decrease in the magnitude of the receptor potential when a stimulus is constant
–> results in decrease in frequency of action potentials = perception of the stimulus decreases
what are slowly adapting/tonic receptors?
- show little adaptation
- the receptors keep firing as long as the stimulus is present but the firing rate decreases over time.
what are rapidly adapting/phasic receptors
- adapt quickly
- they respond respond maximally at the onset of a stimulus but then adapt briefly after
- their response decreases if the stimulus is maintained
what are sensory pathways?
- a chain of neurons, from receptor organ to cerebral cortex, that are responsible for relaying information for the perception of sensations
what are labeled lines in sensory pathways?
- a specific neural pathways that transmits information of a specific particular modality (i.e light, temperature)
- each sensory modality follows its own labeled line
what is a sensory unit?
- a single afferent neuron and all the receptors associated with it
- all the receptors are of the same type
- an action potential may occur in the afferent neuron if any of the associated sensory receptors are triggered
what is a receptive field?
- the region containing receptors on an afferent neuron in which a stimulus can produce a response (excitatory or inhibitory)
what is the sensory transduction mechanism for somatic senses?
- sensory transduction begins with sensory receptors such as photo, mechano, therom, nociceptors
–> each sensory receptor has an adequate stimulus which is the specific modality they are designed to respond to - when the adequate stimulus is applied to a sensory receptor, it activates the receptor, leading to depolarization of the cell and graded receptor potential.
- if the receptor potential exceeds threshold based on the strength of the stimulus, it can generate an action potential
- the action potentials travel along sensory (afferent) neurons to reach the brain or spinal cord (CNS)
- once the sensory signals reach the central nervous system, they are processed and interpreted in various regions of the brain
- each modality follows their own labeled line (a neural pathway) to the be perceived
what are the 3 orders of neurons?
first order = directly receive input from sensory receptors and carry signals from the periphery to the spinal cord
second order = carry signals from the spinal cord to the thalamus (a relay station)
third order = carry signals from the thalamus to the cerebral cortex, where sensory perception occurs
what is sensory coding?
the process of how sensory stimuli are translated and read by the brain so it can interpreted and perceived.
what are the 3 components of sensory coding?
- the type of stimulus
- the location of the stimulus in the receptive field
- the relative intensity of the stimulus
what is coding for stimulus type?
the stimulus type is identified by the particular receptor and pathway that is activated when the stimulus is applied
–> Each sensory modality (i.e vision) has specific receptors and neural pathways dedicated to processing and coding information related to it
i.e light waves activate photoreceptors which communicate via a specific pathway to the visual cortex
what is coding for stimulus intensity?
the intensity of the stimulus is coded/identified by the frequency of action potentials (frequency coding) and the number of receptors activated (population coding)
–> it’s how the body determines if a stimulus is strong or weak, loud or soft, bright or dim, etc.
–> allows you to differentiate the stregnth of a stimulus
what is frequency coding?
- a stronger stimulus results in a larger receptor potential = exceed threshold = stronger depolarization to overcome relative refractory period = generate a second action potential
–> therefore, as the intensity of a stimulus increases, the frequency of action potentials increases
what is population coding?
- a stronger stimulus may activates/recruits a greater number of receptors
- more receptors that are activated = more receptor potentials that are generated = frequency of action potentials sum and cause a stronger signal being transmitted to the CNS for perception
what is coding for stimulus location?
- the coding of where a stimulus is located in the external environment is based on a sensory units receptive fields
- includes the size of the receptive fields (small or big) and degree of overlap (over the same area) = affects 2 point discrimmination
what is acuity?
the ability of a sensory systems to distinguish fine details and precision in the perception of stimuli.
what is lateral inhibition?
- refers to when a stimulus that strongly excites receptors in a given location inhibits activity in the afferent pathways of other nearby receptors
what is the purpose of lateral inhibition?
- increases acuity (preciseness of stimuli)
–> this occurs because it increases the contrast of signals in the nervous system
–> this means it allows the transmission of strong signals in some neurons BUT suppresses the transmission of weaker signals arising in nearby neurons
what is two-point discrimmination?
- the ability of a person to perceive two fine points pressed against the skin as two distinct points
- only occurs if the two points are applied to the receptive field of two different afferent neurons
–> the minimum distance that exists to be perceived as two separate points is called the two-point discrimination threshold - if the two points are closer together than the threshold, then it will be perceived as a single point
- the smaller the receptive field, the greater ability to discriminate the two points
what is pain perception?
is the sensation produced by potentially tissue-damaging stimulus
what does perception of pain depend on?
- depends on your past experiences and the circumstances under which the stimulus was applied
–> i.e tooth ache during a busy day at work is less noticeable than when trying to fall asleep at night
what is fast and slow pain?
fast = sharp sensation that is easily localized
slow = dull ache that is poorly localized
what is visceral pain?
is pained that originates in internal organs, and not limited to just the body surface
what is referred pain?
- when a sensation is “referred” to a body surface
- you may have hurt one area of your body but feel pain somewhere else
what is the gate control theory?
suggests that the spinal cord has a neurological ‘gate’ that controls pain signals to the brain
–> if certain interneurons are active, then transmission of pain signals can be suppressed and the perception of pain is lessened
