Sensory Receptors and Pathways

Question 1

what are receptors?

Answer 1

transducers that convert external or internal stimuli into electrical potential s

Question 2

what are sensory pathways?

Answer 2

carry information from the receptors to the central nervous system integrating centres

Question 3

what are some examples of central receptors? How about peripheral receptors?

Answer 3

central receptors = organs = eyes, ears, nose and tongue

peripheral receptors = chemoreceptors (pH, gases, chemicals) osmoreceptors (osmolarity) thermoreceptors (temp) baroreceptors (pressure), proprioreceptor (body position)

Question 4

sensory receptors run in what direction?

Answer 4

they run in one direction - they are pretty much one big axon -

Question 5

what kind of sensory receptors are pain receptors?

Answer 5

= simple neural receptor - not myelinated, b/c you don’t want them to constantly fire

Question 6

a weak stimulus will produce what kind of action potential?

Answer 6

A low frequency action potential

Question 7

Describe the normal transmision on a sensory receptor

Answer 7

Question 8

Describe the terms - receptive field, modality and location of stimulus coding and processing?

Answer 8

Receptive field = region within which a sensory neuron can sense a stimulus

modality = each central neurone recognizes the receptor type activated and therefore the nature of the stimulus

location = each sensory pathway projects to a region of the cerebral cortex dedicated to a specific receptive field

Question 9

What does the size of the receptive field vary inversely with?

Answer 9

the size of the receptive field varies inversely with the density of receptors - high receptor density gives rise to small receptive fields which lead to greater acuity or discriminative ability of the input

•Overlapping receptive fields (of identical sensory receptors) allows interactions between sensory inputs and refines sensory discrimination.

Question 10

what is phasic receptors?

Answer 10

• Fire at stimulus onset
• Adapt or cease to fire when constant (steady state) stimulus
• Filter out unnecessary stimuli to focus on new, essential information

•Examples: smell, pressure

*when you go to anatomy room you can smell the formeldehyde, but then your nose desensitizes after a while and stops firing*

Question 11

what is a ‘tonic receptors’ ?

Answer 11

Fire as long as stimulus is present at threshold level - example baroreceptors and nocireceptors

Question 12

What do the dorsal root ganglion contain?

Answer 12

They contain cell bodies of unipolar primary sensory neurons

Question 13

What does the dorsal root contain?

Answer 13

contains mainly sensory axons

Question 14

what does the ‘ventral’ root contain ?

Answer 14

contains mainly motor axons

Question 15

what types of fibers are thinly myelinated or unmyelinated?

Answer 15

Pain, temperature

• travel in thinly myelinated & unmyelinated, moderate to slowly conducting, peripheral nerve fibres (Ad, C= unmyelinated)

Question 16

what region of your brain connects all of the sennsory pathways?

Answer 16

Thalamus = all pathways except the olfacotyr pathways and the equilibrium pathways which project ot the cerebellum

Question 17

describe the different appearnaces of multipolar neurons, bipolar neurons and unipolar neurons

Answer 17

Question 18

Describe a first order neuron

Answer 18

1st order neurones

• axons transmit from receptor to spinal cord via dorsal root
• ascend in dorsal columns
• synapse with 2nd order neurones in gracile & cuneate nuclei of medulla

Question 19

Describe 2nd order neurones

Answer 19

2nd order neurones- located in spinal cord

• axons cross in lower medulla to form contralateral Medial Lemniscus
• synapse with 3rd order neurones in thalamus

Question 20

Describe 3rd order neurons

Answer 20

3rd order neurones

•axons project from thalamus to sensory cortex

Question 21

non-specific pathways convery information from where?

Answer 21

•Non-specific pathways convey information from more than one type of sensory unit to the brainstem reticular formation and regions of the thalamus that are not part of the specific ascending pathways.

Question 22

the arrangement of the spinothalamic pathway gives rise ot what?

Answer 22

•convergence or divergence of the sensory input- meaning that they can go to different regions of the brain (divergence) , or convergence - where the brain stem combines a bunch of sensory information from multiple nerves

Question 23

what section of the medulla is responsible for lower limb segments?

Answer 23

Gracile Fasciculus

Question 24

what portion of the medulla is repsonsible for upper limb segments?

Answer 24

Cuneate Fasciculus -

Question 25

the spinocerebellar pathway is responsible for what?

Answer 25

provides information to the cerebelum about position of body in space and position of body parts relative to one another

Question 26

.1 A 40 year old man presents to his GP for a routine check up and the GP notices burn marks on his fingers of which the patient was unaware. Following investigation, a diagnosis of syringomyelia was established (pathophysiology: cavitation of the central canal of the spinal cord). From your knowledge of the sensory pathways, explain the patient’s clinical presentation.

Answer 26

pain temp information follows this path…

1storder neurones

• axons transmit from receptor to spinal cord via dorsal root
• synapse in dorsal horn of spinal cord

2ndorder neurones

• axons cross spinal cord in anterior commissure
• ascend incontralateralspinothalamictract
• synapse with 3rd order neurones in thalamus

3rd order neurones

•axons project from thalamus to sensory cortex

*note he’ll have proprioception/vibration sensory deficits on the other side of his body b/c proprioception/vibration signals do not cross until the lower medulla

Question 27

Describe the different regions of the spinal cord

Answer 27