Mason Sensory Pathways

Front 1

Receive information from the environment via specialized receptors in the periphery and transmit this information through a series of neurons and synaptic relays to the ____.

Back 1

CNS

Front 2

What are Sensory receptors activated by?

Back 2

are activated by stimuli in the environment.

The nature of the receptors varies from one sensory modality to another. In the visual, taste and auditory systems, the receptors are specialized epithelial cells. In the olfactory and somatosensory systems the receptors are first order or primary afferent, neurons.

The function of the receptors is the same, to convert a stimulus into electrochemical energy by a process called sensory transduction.

Once sensory transduction has occurred, the electrical signal results in either depolarization or hyperpolarization of the sensory receptor. This change in membrane potential is called the receptor potential.

Front 3

After transduction and generation of the receptor potential, information is transmitted to the CNS along a series of afferent neurons which are designated as what?

Back 3

first order, second order, third order, and fourth order neurons.

Front 4

What is first order?

Back 4

First order refers to those neurons closest to the sensory receptor

The higher order neurons are those closer to the CNS.

the first order neuron is the primary sensory neuron (remember it is also the receptor cell in Somatosensory and olfactory).

Front 5

When the sensory receptor is a specialized epithelial cell, it synapses on a ___ order neuron.

Back 5

first

When the receptor is also the primary afferent neuron, there is no need for this synapse.

Front 6

T or F:

The primary afferent neuron has its cell body in a dorsal root or spinal cord ganglion.

Back 6

True

Front 7

What are second order neurons?

Back 7

first order neurons synapse on second order neurons in relay nuclei, which are located in the spinal cord or brain stem.

Usually many first order neurons synapse on a single second order neuron within the relay nucleus

Front 8

T or F
Interneurons, also located in the relay nuclei, are excitatory .

Back 8

False
Interneurons, also located in the relay nuclei, may be excitatory or inhibitory.

Front 9

The _______ process and modify the sensory information received from the first order neurons

Back 9

interneurons

Front 10

axons of second projection neurons leave the relay nucleus to synapse on _____ order neurons in the next relay pathway.

Back 10

third

Front 11

The axons of second order neurons decussate en route to the ______ where they synapse on third order neurons.

Back 11

thalamus

Front 12

T or F
Decussation may occur in the spinal cord or it may occur in the brain stem.

Back 12

True...medulla and pons

Front 13

third order neurons typically reside or are located in relay nuclei in the _______.

Back 13

thalamus

Front 14

T or F
a single second order neuron synapses on a single third order neuron.

Back 14

False
As before, many second order neurons synapse on a single third order neuron.

Front 15

The ____ _____ process the information they receive vial local interneurons, which may be excitatory or inhibitory.

Back 15

relay nuclei

Front 16

What are fourth order neurons?

Back 16

reside in the appropriate sensory area of the cerebral cortex.

Eg: In the auditory pathway, fourth order neurons are found in the primary auditory cortex in the visual pathway, they are found in the primary visual cortex.

There are secondary and tertiary areas as well as association areas in the cortex, which integrate complex sensory information.

Front 17

There are two pathways for the transmission of somatosensory information to the CNS, what are they?

Back 17

The dorsal column system &
The antero-lateral (spinothalamic) system

Front 18

What is the dorsal column system used for? What kind of fibers are in this system?

Back 18

Used for transmission of somatosensory information about discriminative touch, pressure, vibration, proprioception, and two-point discrimination.

The dorsal column system consists mainly of group II nerve fibers.

Front 19

As part of the dorsal column system, The first order neurons have their cell bodies in the dorsal root ganglion cells or in the cranial nerve ganglion cells and ascend ipsilaterally to the ____ ____ (upper body) or ____ ____ (lower body) in the medulla.

Back 19

nucleus gracilis, nucleus cuneatus

Front 20

As part of the dorsal column system, In the medulla, first order neurons synapse on second order neurons, which cross the midline, this is called what?

Back 20

decussate

Front 21

As part of the dorsal column system, The second order neurons ascend to the contralateral ______ where they synapse on third order neurons.

Back 21

thalamus...contralateral because they cross

Front 22

As part of the dorsal column system, The third order neurons ascend to the ______ _____ and synapse on fourth order neurons.

Back 22

somatosensory cortex

Front 23

What is The antero-lateral (spinothalamic) system? What type of fibers?

Back 23

The antero-lateral (spinothalamic) system transmits Somatosensory information about pain, temperature, and light touch.
The anterio-lateral system consists mainly of group III & IV fibers. (Remember Group IV fibers have the slowest conduction rate or velocity).

Front 24

In the antero-lateral system, first order neurons have their cell bodies in the dorsal horn and synapse on ________ and ________ in the skin.

Back 24

thermoreceptors, nociceptors

Front 25

In the antero-lateral system, The first order neurons synapse on second order neurons in the ____ _____.

Back 25

spinal cord

Front 26

As part of the antero-lateral system, In the cord, the second order neurons decussate and ascend to the _____ _____

Back 26

contralateral thalamus

Front 27

As part of the antero-lateral, In the thalamus, second order neurons synapse on third order neurons, which ascend to the __________cortex and synapse on fourth order neurons

Back 27

somatosensory