-
Describe presynaptic modulation (inhibition and
facilitation)
- axoaxonic
- may only affect a few postsynaptic cells
- inhibition is due to decrease of neurotransmitter release from the presynaptic cell by blocking calcium channels
- facilitation is due to an increase in neurotransmitter by keeping calcium channels open
-
Describe postsynaptic modulation (inhibition and
facilitation)
- axosomatic or axodendritic
- affects all target cells
- summation of inhibitory vs excitatory signals can result in varying levels of neurotransmitter release
-
Define Sensory Receptor
specialized neuronal structures that detect specific types of energy
-
Name the stimuli that are detected by visceral
(interoceptor) and somatic senses.
- Visceral receptors detect stimuli that arise with the body
- Somatosensory receptors detectsensations associated with receptors in the skin, and proprioception
-
Define modality
The energy form of a stimulus is called its modality
-
Define the law of specific nerve energies
Sensory receptors are specific for a particular modality.
-
Define adequate stimulus
Specific modality to which receptor is most sensitive
-
Under what circumstances will a receptor respond to an
“inadequate stimulus”?
If the strength of an “inadequate stimulus” is high enough, the receptor will respond
-
List the major groups of receptors and their
adequate stimuli
- chemo receptors : smell, taste, blood concentration of O2 and CO2
- mechano receptors: pressure, stretch eg.baroreceptor
- photo receptors: light wavelengths
- thermo receptors: sensations of coldness and warmth
- noci ceptors: tissue damage interpreted as pain stimulated by intense mechanical, thermal or chemical stimuli
-
List the 3 structural types of sensory receptors
- simple
- complex
- special senses
-
Define neural and non-neural receptors
- neural receptors have free nerve endings (if surrounded by connective tissue or not)
- non-neural receptors are cells that release NT onto sensory neurons to initiate an AP
-
Explain how a sensory stimulus is transduced
into electrical signals
- convert the energy of the stimulus into changes in membrane potential
- to cause direct/indirect change in membrane potential must open/close ion channels
- results in generator potentials or receptor potentials (in non-neural cells)
-
Define Adaptation
process in which sensory receptors decrease their response to a stimulus over time.
-
define Tonic Receptors
adapt slowly, transmit signals to the CNS as long as the stimulus persists
-
define Phasic Receptors
fire when the first stimulus is received, then switch off when the stimulus is at constant intensity
-
define Labelled Lines
Specific neural pathways transmitting specific modality information
-
Define sensory unit and receptive field
- sensory unit is a single afferent neuron with all its receptor endings
- the region within which a sensory neuron can detect a stimulus is called the receptive field
-
Describe a generalized pathway for sensory
information
stimulus-receptor-afferent first order neuron-spinal cord or brain stem-second order neuron-thalamus-third order neuron-cortex
-
Describe the Spinothalamic Tract
transmits pain/temp stimulus - primary neuron - dorsal horn of spinal cord - secondary neuron crosses over at spinal cord - acends anterolateral column of spinal cord - VPL of thalamus - tertiary neuron - somatosensory cortex
-
Describe the the Dorsal Column pathways
transmits touch/pressure stimulus - primary neuron - dorsal horn of spinal cord - secondary neuron crosses over at medulla - VPL of thalamus - tertiary neuron - somatosensory cortex
-
Describe the various fibers types involved in
the transmission of somatic sensation
- A-β : largest, myelinated, fastest, sense pressure/vibration
- A-δ : small, myelinated, fast, sense very hot/cold, sharp pain
- C fibers : small, unmyelinated, slow, sense dull pain and moderate temps
-
To what parts of the CNS are painful stimuli
transmitted?
- Signals from painful stimuli are transmitted to the cortex(perceived)
- also to the limbic system and the hypothalamus hence emotional and autonomic reactions occur
-
Define referred pain and describe the
physiological cause
- Caused by multiple primary sensory neurons converging on single ascending tract
- brain gets confused between signals coming from somatic (skeletal) sources versus those which are visceral.
-
Describe the Gate Control Theory of Pain
- somatic signals of non-painful stimuli can inhibit signals of pain at the spinal level
- inhibitory interneurons can be stimulated by collaterals of A-β fibers associated with pressure and touch to stop transmission of painful stimuli from proceeding
|
|
