NSB 6. Sensory Receptors and Pathways Flashcards
What are Receptors? (definition)
they are TRANSDUCERS that convert external or internal STIMULI into ELECTRICAL POTENTIALS
What are Sensory Pathways? (definition)
they carry information from RECEPTORS to CNS integrating centres
What are the 2 types of receptors that turn stimuli into electrical signals?
[1] Central Receptors
[2] Peripheral Receptors
What type of receptor is more complicated?
Central Receptors are more complicated than Peripheral Receptors.
- central receptors have multiple cell types that work together
- peripheral receptors have individual cell types
What is the relay nucleus?
it is where the 1st and 2nd neuron synapse
- after the relay nucleus the 2nd neuron may decussate
What are the types of mechanoreceptors for?
[1] Touch
[2] Audition
[3] Vestibular (balance)
What is the receptor type for touch?
pacinian corpuscle
What is the receptor type for audition?
hair cell
What is the receptor type for vestibular (balance)?
hair cell
Where are the receptors for touch located?
skin
Where are the receptors for audition located?
organ of corti
Where are the receptors for vestibular stimuli located?
macula, semicircular canal
What are the photoreceptors for?
for vision
What is the receptor type for photoreceptors?
rods and cones
Where are the receptors for photoreceptors located?
retina
What are the types of chemoreceptors?
[1] Olfaction
[2] Taste
[3] Arterial pO2
[4] pH of CSF
What are the receptors for olfaction stimuli called?
olfactory receptor
Where are the olfactory receptors located?
olfactory mucosa
What are the receptors for taste stimuli called?
taste buds
Where are the receptors for taste located?
tongue
Where are the arterial pO2 receptors located?
carotid + aortic body
Where are the receptors to measure the pH of CSF located?
ventrolateral medulla
What are the receptors for thermoreceptors called?
temperature receptors – cold/warm receptors
Where are the thermoreceptors located?
skin
What are nociceptors used for? What are the different types of nociceptors?
- extremes of pain and temp.
[1] Thermal Nociceptors
[2] Polymodal Nociceptors
Where are the nociceptors located?
skin
What are the 3 types of sensory receptors?
[1] Simple Neural Receptor
[2] Complex Neural Receptor
[3] Special Senses Receptor
List some of the characteristics of the simple neural receptor.
- unmyelinated (impulses are quite slow)
- has free nerve endings
- e.g. pain receptor
List some of the characteristics of a complex neural receptor.
- myelinated (fast impulses)
- enclosed nerve ending by layers of connective tissue
- e.g. mechanoreceptors (pacinian corpuscle)
List some of the characteristics of a special senses receptor.
- has specialized receptor (e.g. hair cell)
- has a synapse between the specialised receptor and neuron
- myelinated (fast impulses)
- e.g. hair cells in the auditory system
List the most important receptors in the skin. [5]
[1] Hair Receptor [2] Merkel's Disc [3] Pacinian Corpuscle [4] Ruffini Endings [5] Meissner's Corpuscle
What are the traits and characteristics of hair receptors in the skin?
- fast adapting
- – react really quickly and then they return to normal (e.g. displacement of the hair)
- located in hairy skin
What are the traits and characteristics of merkel’s disc receptors in the skin?
- they have open nerve endings
- found in hairy + non-hairy skin
- they respond to indentation (e.g. pressing on the skin)
What are the traits and characteristics of pacinian corpuscle receptors in the skin?
- most rapidly adapting
- they encode vibration
- found in both hairy and non-hairy skin
What are the traits and characteristics of ruffini endings receptors in the skin?
- they are activated by stretching of skin
- found in both hairy and non-hairy skin
What are the traits and characteristics of meissner’s corpuscle receptors in the skin?
- they are abundant in the fingertips and lips
- they are for fine touch
- they are found in non hairy skin (!)
What are receptive fields?
Definition: a receptive field defines an area of the body that when stimulated results in a change in firing rate of a sensory neuron
- — basically a part of the body that is supplied by the neuron
- receptive fields exist for 1, 2 and 3 order neurons
- you can have overlapping receptive fields
Can you have overlapping receptive fields?
Yes
- for example, one area may have more than one sensory receptor there
What is the difference between a small and a large receptive field?
Small Receptive Field:
- the patch of skin is innervated by only ONE sensory receptor
Large Receptive Field:
- the patches of skin are innervated my multiple sensory receptors
- the sensory receptors all synapse onto the same 2nd order neuron
- think of it as a duster (it spreads out like that)
What is the purpose of both excitatory and inhibitory receptive fields to synapse on the same 2nd order neuron?
in order for the brain to have a better idea where the stimulus is coming from (increase in accuracy), they have inhibitory receptive fields
– they inactivate the 2nd order neuron
What is 2-point discrimination?
it is to determine how finely innervated an area of skin is
- if the 2 points only send ONE signal to the brain, this means that the primary sensory neurons merge into the same 2nd order neuron
- if the 2 points send 2 separate signals to the brain, this means that the primary sensory neurons do not merge into the same 2nd order neuron
The intensity of a stimulus is encoded in 3 ways which are:
[1] # of receptors activated
[2] difference in firing rates of sensory neurons
[3] activation of different types of receptors
What are tonic receptors?
- they fire as long as the stimulus is present at threshold levels
- they do not stop firing
- e.g. baroreceptors, nociceptors, merkel’s receptors
What are phasic receptors?
- they fire at stimulus onset, but they adapt or cease to fire when constant (steady state) stimulus
- they filter out unnecessary stimuli to focus on new, essential info
- e.g. olfactory receptors, pressure, pacinian corpuscle
- – for example, you don’t smell a smell anymore
Describe the structure and location of primary sensory afferents?
- the cell body is in the dorsal root ganglion
- axon part connects with the sensory receptor
- the other part of the sensory afferent transmits the info from the receptor into the dorsal horn of the spinal cord
What are the 3 types of polarity of neurons?
[1] Multipolar Neuron
- most abundant
[2] Bipolar Neuron
[3] Unipolar Neuron
What are the 2 types of fibre types? How do they differ?
[1] Proprioception, Vibration + Discriminative Touch
- travels in HEAVILY MYELINATED, LARGE DIAMETER, FAST conducting peripheral nerve fibres (A-alpha and A-beta)
[2] Pain, Temperature
- travels in THINLY MYELINATED + UNMYELINATED, MODERATE to SLOWLY conducting peripheral nerve fibres (A and C)
What is the spinothalamic pathway important for?
pain + temperature
Explain how the spinothalamic pathway works.
[1] 1st order neuron recieves the stimulus
[2] the 1st order neuron axons transmit from receptor to spinal cord via dorsal root
- they synapse in dorsal horn of spinal cord (with the 2nd order neuron)
[3] 2nd order neuron cross the spinal cord in anterior commissure
- they cross the midline (decussate)
[4] the 2nd order neuron ascend in the contralateral spinothalamic tract
[5] 2nd order neurons synapse with 3rd order neurons in thalamus
[6] the 3rd order neurons have axons that project from the thalamus to sensory cortex
What is the dorsal column/medial lemniscus system important for?
encodes for proprioception (only in arms, not in legs), vibration, discriminative touch
Explain how the dorsal column-medial lemniscal pathway works. (this one is a little more complicated)
LUMBAR CORD: for LOWER LIMBS
[1] 1st order neuron enters the lumbar cord and travels up the spinal cod until it meets the NUCLEUS GRACILIS in the medulla
[2] at the nucleus gracilis, the 2nd order neuron decussates in the lower medulla and goes to the thalamus
[3] the 2nd order neuron travels up into the thalamus where it synapses with the 3rd order neuron
[4] the 3rd order neurons have axons that project from the thalamus to sensory cortex
CERVICAL CORD: for UPPER LIMBS
[1] the 1st order neuron travels up until it meets the NUCELUS CUNAEUS in the medulla
[2] at the nucleus cunaeus, the 2nd order neuron decussates in the lower medulla and goes to the thalamus
[3] the 2nd order neuron synapses in the thalamus
[4] the 3rd order neurons have axons that project from the thalamus to sensory cortex
What is the spinocerebellar pathway important for?
it is for unconscious proprioception
- it does NOT pass through the thalamus
- it is a 2 neuron pathway
- it provides info to the cerebellum about the position of the body in space
How is the spinocerebellar pathway different than the other 2 pathways?
it is for unconscious activites and so, the neurons do NOT pass through the thalamus
- and it only has 2 neurons in its pathway
What are the 3 main neuron pathways/system?
[1] Spinothalamic Pathway/Anterolateral System
[2] Dorsal-Column-Medial Lemniscal System
[3] Spinocerebellar Pathway
Explain how the spinocerebellar pathway works. (this one is a little more complicated)
- UNCONSCIOUS PROPRIOCEPTION OF UPPER LIMBS
[a] 1st order neuron carries impulse into spinal cord through dorsal root where it enters FASCICULUS CUNEATUS
[b] 1st order neuron continues to carry impulse upwards in CUNEOCEREBELLAR TRACT terminating in the ACCESSORY CUNEATE NUCLEUS in medulla
[c] 1st order neuron synapses with 2nd order neuron in medulla
[d] 2nd order neuron carries impulse to ipsilateral (same side) cerebellum through the inferior cerebellar peduncle
[e] the 2nd order neuron continues to carry the impulse to the appropriate region of the cerebellar cortex
- UNCONSCIOUS PROPRIOCEPTION OF LOWER LIMBS
[a] 1st order neuron enters spinal cord through dorsal root where it enters the FASCUCULUS GRACILIS
[b] the axon of the 1st order neuron ascends for a number of segments util it reaches CLARKES COLOUMN
[c] 2nd order neurons arising in Clarkes Coloumn carry the impulse and enter the ipsilateral (same side) DORSAL SPINOCEREBELLAR TRACT
[d] the 2nd order neuron continues upwards towards the medulla through the dorsal spinocerebellar tract
[e] from the medulla, the 2nd order neuron entesr the ipsilateral (same side) CEREBELLUM via the inferior cerebellar peduncle
[f] the 2nd order neuron carries the impulse to an inappropriate area of the cerebellar cortex
What is convergence and divergence of sensory input along the spinothalamic pathway? Why is it important?
CONVERGENCE: a # of 1st order neurons synapse into a single 2nd order neuron
DIVERGENCE: only one 1st order neuron supplies multiple 2nd order neurons
- it influences the quality of the sensation at the conscious/subconscious level within the CNS
What are the 2 types of unconscious perceptions?
[1] Somatic Stimuli
- muscle length/tension
[2] Visceral Stimuli
- blood pressure
- blood + CSF + pH
- blood pO2
- body fluid osmolarity
- temperature
- blood glucose
- GIT distension
- lung inflation
