Flashcards in Unit 3 Deck (55):
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.
How does the CNS monitor muscle length?
There is a tonic stream of APs to the CNS even at resting length and changes in this length causes a change in the ping rate the the CNS
Explain alpha-gamma co-activation.
If the spindle is too loose, there is a signal sent to the brain. This signal causes two signals - 1) increased APs down the alpha motor neurons that contract the exrafusal muscle fibres in turn causing a decrease in the afferent discharge down the 1a neuron 2) increased APs down the gamma motor neurons that contracts the ENDS of the spindles and therefore tightens the muscle
Where are the Golgi Tendon Organs located?
They are between he muscle fibres and the tendon.
What type of contraction are GTO's most sensitive to? Isometric or isotonic? How do they sense information?
Isometric. When the muscle shortens, it pulls on the GTO, and there is an increase in the ping rate from 1b afferent neurons
What type of fibres does proprioception travel on?
The fastest ones we have. Faster than pain, touch or itch.
What is so special about olfaction? (x3). What type of neuron are they?
It does not go to the thalamus first, and it does not cross the midline and it is the only sense that the sensory cell itself is the neurone that carries the information to the brain.
They are true bipolar neurons
At what point in an olfactory axis are you within the CNS? The bodies of which order neurons are within the olfactory bulb?
As soon as you cross the bony plate/boundary. the bodies of the SECONDARY order neurons
How are olfactory neurons generated?
The olfactory epithelial cells develop and become olfactory neurons, and they are replaced every ~60 days.
What are olfactory receptor proteins?
They are the receptor portion on the first order neurons int he olfactory pathway. Each ORNexpresses only one type of odourant receptor, but each receptor can recognize more than one oroudant, and each odourant can stimulate more than one receptor
What are the 5 basic tastes?
Sweet, bitter, sour, salty and Umami (protein).
What are taste receptor cells?
They are non-neural epithelial cells tat synapse with the primary neuron, and each TRC corresponds to one of the basic tastes.
What do each of the tastes use as neurotransmitters?
Sweet, Umami and Bitter all use ATP as a nt, and sour uses calcium. We don't know what salty uses.
What two characteristics of a sound wave correspond to volume and pitch?
Volume is the amplitude and the pitch is the frequency.
How does a sound wave travel in the ear?
tympanic membrane > (malleus > incus > stapes for amplification and transduction) > oval window > cochlea (vestibular dust > tympanic duct) > round window
What is the place code hypothesis?
Sound waves trigger activity at different places along the cochlear basilar membrane based on the frequency of the original sound wave = Higher pitch = closer to the oval window, lower pitch = furthest from the source
What is the temporal code hypothesis?
The frequency of the sound wave determines the frequency of action potentials that travel along the auditory nerve and is perceives as pitch
What is the current hypothesis of how pitch is encoded in the ear?
A mixture of the place code and temporal code hypotheses. At low pitches the temporal code dominates (because at high pitches, our neurons cannot transmit information that quickly) and at high pitches, the place code theory dominates.
What are the three forms of hearing loss? Explain each (x3)
Conduction - the sound wave is not transmitted to the tympanic membrane - often caused by a middle ear infection and there is a fluid/wax build up the dampens the bone vibrations
Central - the cochlear nerve is unable to transmit information to the brain - damage to the neural pathway due to damage to the cortex itself (stroke)
Sensorioneuroal - damage to the structures of the inner ear (death of the hair cells due to loud noises
How is equilibrium monitored? What type of sense receptor?
Detected by hair cells within the semilunar canals and the otolith organs (utricle and saccule)
What do the otolith organs monitor? How?
LINEAR ACCELERATION - The hair cells are grouped with the maculae and are embedded within a gelatinous membrane. Atop this gelatinous membrane are the otolith crystals to increase drag and make the hair cells more sensitive
What do the semilunar canals monitor? How?
ROTATIONAL ACCELERATION - Hair cells are within Christie within the cupula. When you turn or spin the endolymph fluid moves, but the cupula is left behind and this tells you what direction you are spinning in
What is the Canal of Schlemm?
The circular canal that drains liquid out of the aqueous humous
What is the optic disk?
The space right in from of the option nerve that has no sensory receptors (the blind spot)
What is the fovea? What is special about the anatomy within this space?
The special sensory patch of the eye that allows for very fine focus. It is full of cones, so you need a lot of light, and this is why you cannot focus in dim/dark lighting
What is the neural conduction pathway from a light/visual stimulus?
eye > optic nerve > optic chasm > optic tract > visual cortex with a thalamic relay
Explain a pupillary non-visual reflex. What is the nerve conduction pathway?
It is an autonomic reflex with a thalamic relay. Photoreceptors within the retina > bipolar cells > ganglion cells > optic nerve > thalamus > oculomotor nerve > smooth muscles that regulate pupil diameter
Where do the optic nerve and the oculomotor nerves cross within the brain?
Optic nerve - cross at the optic chasm
Oculomotor nerve - cross at the midbrain
What is phototransduction?
The conversion of light into changes in membrane potential by photoreceptor cells in the retina
What does it mean that the design of the eye is inverted?
Light has to reach the furthest part of the eye in order to reach the pigment epithelium which contains the photoreceptors.
What type of convergence and resolution occurs within the fovea?
There is almost. 1:1 relationship between cones and ganglion cells, so there is LOW convergence and HIGH resolution
What is the dark current theory?
The dark is the "standard" and the eye at "rest".
What are the characteristics of rods in the dark?
There is inactive rhodopsin and high levels of cGMP and K+ channels are open and the membrane is slightly depolarized at -40. There is a tonic release of glutamate onto the bipolar neurons