Nervous System IX Flashcards
Examples of chemoreceptors
- blood chemoreceptors
- nociceptors
- hypothalamic glucose sensing neurons
- taste, smell
Examples of stimulus of mechanoreceptors
- touch
- proprioceptors
- nociceptors
- auditory (hair cells)
- balance
What are examples of photoreceptors
Vision (rods and cones)
Examples of thermoreceptors
Thermal receptors
Nociceptors
What do mechanically gated channels do?
Convert mechanical stimulus into electrical signal
- receptor potential or generator potential
What are receptive fields
Sensory neurons are activated by stimuli that fall within a specific physical area
What determines size of receptive fields?
Type of sensory receptor and if there is convergence of multiple primary neurons onto a secondary neuron
How many neurons do somatosensory neurons have?
3 neurons
Primary sensory neuron: converts physical stimulus to electrical signal (in skin or muscle)
Secondary: projection neurons carry info up spinal cord to brain
Tertiary: from thalamus to relevant cerebral cortex area
What creates large receptive fields?
Convergence
Areas where fine touch is less important
Ex) leg or back
- 3 primary sensory neurons with own receptive fields overlap but all synapse on same secondary
- sub threshold stimuli sum and initiate AP at secondary neuron
- two stimuli that fall within same secondary receptive field are perceived as single point
Where are small receptive fields found?
More sensitive areas
- 1 primary sensory neuron communicates with 1 secondary
-ex) fingers
- two stimuli perceived as distinct (two-point discrimination)
Where is visceral info integrated?
Brainstem and spinal cord
Where are special and somatic sensory info routed?
Through thalamus before projection to relevant cortical centres
Where are olfactory pathways routed?
From nose through olfactory bulb to olfactory cortex
Not through thalamus
Where are equilibrium pathways projected to?
Cerebellum
What do all special senses have?
Dedicated cortical regions
Where are all somatic sense integrated?
Primary somatosensory cortex
If all stimuli are converted to APs and all APs are similar, how does CNS distinguish?
- Modality
- Location
- Intensity
- Duration
What is modality?
Physical stimuli being sense, determined by sensory receptor activated, where pathways terminated in brain
How is location of stimulus distinguished?
Coded according to which receptive fields are activated
- sensory stimuli projected to areas of somatosensory cortex
What is sound localization?
Depends on the timing which sound reaches the auditory cortex from each ear
What can increase accuracy of localization
Lateral inhibition
Pathways closest to stimulus inhibited neighbours in secondary neurons or tertiary
Enhances perception
How is intensity determined?
- cannot be determined by amplitude
- determined by number of receptors being activated (population coding) and the frequency of APs coming from those receptors (frequency coding)
How is duration of stimulus determined?
How long APs are being activated
What are tonic receptors?
Slowly adapting receptors that respond for the duration of a stimulus
- parameters that need to be monitored constantly
- ex) BP
What are phasic receptors?
Rapidly adapt to constant stimulus and turn off
- respond to change, stop once stimulus constant
- can be reactivated if stimulus changes
- ex) feel shirt go on then once wearing stop feeling it
What does autonomic or visceral nervous system control and what are the subdivisions?
Involuntary control of smooth muscle, cardiac muscle, many glands, liver, lymphoid tissue and some adipose tissue (targets)
- parasympathetic and sympathetic
How do sympathetic and parasympathetic work together?
Antagonistically control any given tissue
When does parasympathetic activity dominate?
Rest and digest
- reducing HR, decrease ventilation rate, increase blood flow to GI tract, etc.
When does sympathetic activity dominate?
Fight or flight
- increase HR, ventilates, delivery of blood to muscle, pupil dilation, decrease blood to GI tract
