Unit 3 Flashcards
What are the ways that receptors can be grouped?
By the types of stimulus. Chemoreceptors, mechanoreceptors, photoreceptors and thermoreceptors
What is a neuronal “visual field?
The zone around a neuron that, if a anything occurs in this area above threshold, there will be signal transduction
How is a receptive field defined?
It is defined by the neurons further up in the pathway - due to convergence
What is convergence? What does it allow for? What do we gain and what do we lose with convergence?
Convergence is the gathering of several primary neurons onto one secondary neuron. it allows for the summation of multiple stimuli, and it creates a larger receptive field. we gain greater sensitivity because with a larger receptive field and the ability for summation, there is a higher chance that the neuron will reach threshold. But we also lose resolution, and we are incapable of two point discrimination (if two stimuli fall within the same receptive field of the secondary neuron, only one signal goes to the brain)
What is associated with a smaller receptive field?
Better two point discrimination.
What is so unique about the sensory pathway for olfaction?
There is no thalamic relay, and the sensory information goes directly fro the olfactory bulb to the olfactory cortex. It is a primal/basal sense.
What characteristics of senses does the CNS need to be able to decode?
The modality (type), the location, the intensity and the duration.
How is modality of a stimulus determined? What is labelled-line coding?
Determined by the type of neuron that is activated, and where the pathway terminated in the brain.
Example - if you stimulate the sensory neurons that is coming from the big toe halfway up the calf, the brain will still interpret that information as coming from the big toe
How is location of a stimulus determined? What is lateral inhibition?
Receptors from a particular part of the body project to a specific location in the somatosensory cortex.
The inhibition of the adjacent neurons to enhance the signal coming from the most central and strongest neuron. It enhances contrast and improves stimulus localization interpretation.
How is intensity determined? Which type of intensity neuron is recruits first?
Coded by the number of receipts activated (population coding). The most sensitive (lowest intensity level) are recruited first, and ad the stimulus intensifies, more receptors are recruited.
Frequency coding - the frequency of Ads coming from an individual receptor correlates with the intensity.
How is duration of a stimulus determined?
The duration of a series of APs is proportional to the duration of a stimulus.
What is the difference between tonic and phasic receptors?
Tonic receptors are slow adapting, but are specialized to respond throughout a stimulus. While a phasic receptor responds to on and off
What are the two ascending pathways in the spinal cord? What do they respond to and where do they cross?
The dorsal column and the spinothalamic tracts. The dorsal columns respond to fine touch. vibration and proprioception, and they cross high within the medulla. The spinothalamic tracts cross at the level of the spinal cord and respond to pain, temperature and coarse/crude touch
What are the two descending tracts in the spinal cord? What do they innervate and where do they cross?
The lateral and anterior corticospinal tracts. The lateral carries motor information to the limbs and crosses high within the medulla, and the anterior corticospinal tracts carry information to the trunk muscles and crosses at the level of the spinal cord.
Where are each of the sensory receptors in the skin located? What do they respond to?
Merkel’s Disk - superficial, and responds to sustained touch/pressure, and texture (braille)
Meissner’s Corpuscle - superficial and responds to the on and off of fine touch and pressure
Ruffini’s Corpuscle - deep and responds to sustained gross touch and stretch
Pacinian Corpuscle - deep and responds to the on and off of gross touch and VIBRATION
Is pain transmitted fast or slowly?
Slowly, relative to all the other senses
Why is visceral pain so poorly located? (referred out)
This is because the organ uses the same dorsal root as many more commonly used other senses (skin and kidney for example)
How are neural reflexes classified?
Based on the effector (autonomic for smooth muscle, glands and cardiac muscle and somatic for the skeletal muscle)
Based on the integrating centre (spinal vs. cranial reflexes)
Innate vs. born
Number of neurons in the pathway (monosynaptic vs. polysynaptic)
Can autonomic reflexes be monosynaptic? Why or why not?
No they cannot be monosynaptic because all autonomic reflexes involve pre- and post-gangliocin neurons
What is the integrating centre for proprioception?
Within the spine of in the higher brain structures
What is the name of the efferent neurons and the effectors for a skeletal muscle reflex?
Somatic motor neurons (ALPHA motor neurons) and they innervate the extrafusal muscle fibres
What are the names of the two organs that monitor the state of muscles, and what do they each monitor? What are the names of the neurons that bring this sensory information to the CNS?
Muscle spindles - measure the muscle length/stretch. 1a afferent neurons.
Golgi tendon organs - they measure the muscle tension. 1b afferent neurons.