Class 8 Flashcards
What is Sensory Receptor?
Structure that recognizes stimulus. Stimulus is detectable change in internal or external environment. Under appropriate circumstances, receptor can transduce
(convert) stimulus into nerve signal. These signals are then
carried into CNS to be analyzed.
May be specialized portion of neuronal membrane, a separate cell associated with neuron ending, or group of
such cells. Sometimes receptor & neuron itself are together referred to as receptor.
EACH SENSORY RESPONDS MOST READILY TO ONE PARTICULAR FORM OF ENERGY. THIS IS CALLED ITS ADEQUATE STIMULUS. Receptors also respond to forms of energy other than the adequate stimulus, but threshold for these nonspecific responses is much higher.
What is threshold?
Magnitude or intensity that must be exceeded for a certain
reaction or condition to occur.
Between stimulus & perception of the stimulus is a series of 4 complex electrochemical events. The nerve impulse consists of an _________________ and a _____________________.
• electrical event
• chemical event (the neurotransmitter)
What is Transduction?
Process by which stimuli are converted to action potentials (APs) by sensory receptors. This is typically done by first order neurons
What is Transmission?
Process by which nerve signals enter & ascend the CNS in various tracts. This is done by second order neurons
What is Modulation?
Process by which electrochemical activity from other ascending inputs for example, touch, or signals descending from brain (emotions) can increase or decrease sensory transmission. In this manner the intensity of sensory input to cerebral cortex can be controlled. Typically done by third order neurons
What is Perception?
Process which results in subjective feelings. It’s a
poorly understood combination of transduction, transmission, & modulation. Can be altered by many phenomena including sleep & emotions such as fear, rage, & depression. Perception of touch sensation delivered by someone touching your arm during a happy moment has quite different results than one that has been delivered in middle of an argument.
what is the Relationship between Sensory Receptors and Unipolar Neurons?
Unipolar neurons have only one structure extending from the soma. It branches into two axons.
All unipolar neurons are attached to some sort of sensory receptor.
All unipolar cell bodies form cluster called dorsal root ganglion at every level of spinal cord
Their peripheral axons enter dorsal horn at each level & on both sides of spinal cord.
Every receptor has a defined area in the _______________, over which it can receive input. This is called the ____________________.
• periphery
• receptive field
What is Spatial discrimination?
Ability to accurately locate site of stimulation & to detect that neighbouring stimuli are actually separate.
Tactile sensitivity depends in part on _____________________ & ______________________________ in a particular skin region.
• density of receptors
• size of the receptive fields
More sensitive areas have smaller fields and a ____________________________ of receptors.
• higher concentration
What is the The two-point threshold?
The two-point threshold is the minimal distance in which two separate stimuli can be distinguished as separate.
In different parts of the skin, the concentration of various sensory receptors changes & this accounts for varying abilities in _________________________ in different regions. For Eg, on the back, density of tactile receptors is greatly reduced, & spatial discrimination is relatively poor.
spatial discrimination
What are Normal thresholds for two-point discrimination?
Tips of fingers are 3mm, forearm is 4mm, centre of back is about 6-7mm.
Continuous monitoring of an unchanging, static situation is usually ________________. It is much more important to ______________________.
• wasteful
• note changes
The receptors that respond best to change are called?
Fast adapting receptors or phasic receptors, for example, olfactory receptors.
