Exam 2: Anterolateral Pathways

Question 1

What is the function of anterolateral pathways?

Answer 1

pain, temperature sense, and crude touch

Question 2

What type of axon pathways does this sensory system involve?

Answer 2

ascending axonal pathways

Question 3

how many neurons does this sensory system have?

Answer 3

4 (incl. primary), ascending

Question 4

where is the decussation

Answer 4

spinal cord

Question 5

What is the first neuron and what is its shape?

Answer 5

• The first neuron in both somatosensory pathways is a primary sensory neuron that contains specialized receptors in the axon terminal to detect specific stimuli
• Sensory neurons have a unique shape:
  1. Sensory neurons are pseudounipolar, where they have one axon and no dendrites
  2. One end of the axon innervates the sensory organ and the other goes to the CNS

Question 6

what type of myelination do these axons have?

Answer 6

Ao and C axons of sensory neurons are lightly myelinated or not myelinated at all, respectively. They detect temperature and pain primarily. Part of the anterolateral pathways.

Question 7

What three tracts does this pathway consist of?

Answer 7

Spinothalamic
Spinoreticular
Spinomesencephalic

Question 8

Where does the primary sensory neuron enter and synapse onto?

Answer 8

The primary sensory neurons that are a part of this pathway enter the spinal cord as a dorsal root and immediately synapse onto a second neuron within the spinal cord dorsal horn

Question 9

What/when is the decussation

Answer 9

The second neuron immediately decussates, forming the anterior commissure as they cross over

Question 10

Where do spinal cord neurons apart of the spinothalamic anterolateral tract synapse onto?

Answer 10

Axons as part of the spinothalamic anterolateral tract synapse onto the third neuron in this sequence at the ventral posterior lateral nucleus in the thalamus

Question 11

Where do neurons from the VPL Thalamus synapse onto?

Answer 11

The neurons from the VPL thalamus then synapse onto the primary somatosensory cortex. Like the motor cortex, there are association areas for higher order sensory processing

Question 12

Functions of the primary somatosensory cortex

Answer 12

1. Basic processing of the tactile information originating from the skin, muscles, and joints.
2. Only processing somatosensory information from the opposite side of the body
3. Encodes the type and intensity of the sensory inputs

Question 13

Functions of the secondary somatosensory cortex

Answer 13

1. Tactile information and information concerning limb position are combined to create representations of the texture and size of objects.
2. Somatosensory information from both sides of the body is integrated.
3. Also involved in tactile learning and memory.

Question 14

Functions of the thalamus

Answer 14

A. The thalamus is a major processing center in the brain and sensory relay station
B. The thalamus consists of multiple nuclei. The nuclei are defined by their inputs and outputs
C. Every sensory system (except for the olfactory system) projects to a specific thalamic nucleus, the receives sensory signals and sends them to the associated primary cortical area

Question 15

Inputs and Outputs of thalamic nuclei

Answer 15

1. The thalamus conveys nearly all inputs to the cortex, including motor inputs from the cerebellum and basal ganglia and inputs involved in arousal and sleep
2. Cortical areas also send axons backs to the thalamus, called corticothalamic projections. In fact the thalamus receives more cortical input than sends out thalamic information

Question 16

Relay Nuclei

Answer 16

They receive input from many brain regions (e.g., reticular formation, hypothalamus, retina) and projects to cortex.
Also, they receive massive reciprocal connections back from cortex.

Question 17

INtralaminar Nuclei

Answer 17

They receive input from the basal ganglia and projects back to the basal ganglia, as well as to cortex.

Question 18

Reticular Nucleus

Answer 18

It is the only nucleus in the thalamus that does NOT project to the cortex. Instead, it receives inputs mainly from other thalamic nuclei and the cortex and then projects back to the thalamus.