The Sensory Nervous System: Proprioception and Nocioception

The function of the nervous system can be thought of as a ___________ part or a ___________ part

motor; sensory

Sensory nervous sytem

detects stimuli and transmits information from receptors to the CNS

Once a sensory receptor detects a stimulus, the information participates in two types of activity:

1.) reflex

2.) relay

reflex activity of sensory information:

stimulated receptors that send information and participates at a local/regional level of the nervous system

Reflex activity is associated with a defined __________ of the nervous system

segment

relay activity of sensory information:

stimulated receptors sends information to higher levels in the nervous system

Two "higher levels" info from relay activity is sent

1.) cerebrum

2.) cerebellum

Relay information is sent to the cerebrum if sensory stimulus is going to achieve a _________ level of activity

Relay information is sent to the cerebellum if sensory stimulus is going to achieve a _________ level of activity

conscious; subconscious

Reflex exams are used to check the _________ integrity of a reflex circuit

local

Two types of reflexes that can be assessed:

1.) spinal reflex

2.) brain stem reflex

spinal reflex

active throughout the trunk and the limbs; involve spinal nerves

brain stem reflex

active through the head and face; involve cranial nerves

components of a general reflex arc

1.) sensory cell in the periphery picks up a stimulus

2.) stimulus travels up the sensory nerve going toward the spinal cord in the CNS

2.) sensory neuron axon synapses with motor cell

3.) motor neuron axon travels back to the periphery to a neuromuscular junction and causes end result, such as muscle contraction

Two classifications for reflexes based on anatomy:

1.) monosynaptic reflex

2.) polysynaptic reflex

monosynaptic reflex

Reflex pathway with only one synapse between the sensory and motor neurons (ex: knee-jerk).

Monosynaptic reflexes are relatively __________ in the body

rare

Example of monosynaptic reflex arc

knee jerk reflex

Polysynaptic reflex

at least one interneuron between the sensory neuron and motor neuron

Role of interneurons

help spread the effect of the stimulus along a few localized segments so that the proper muscle units can be recruited to cause full contraction of muscle

Example of interconnections produced by the interneuron

-interneuron will recieve information from the sensory neuron

-it then can recruit various motor neurons located agross multiple spinal cord levels (such as L4, L5, and L6)

Five locations of a motor neuron that an interneuron can send information to:

1.) motor neuron at same side of spinal cord

2.) motor neuron on opposite side of spinal cord

3.) motor neuron up the cord

4.) motor neuron down the cord

5.) motor neuron in high centers

Polysynaptic reflexes are relatively __________ in the body

common

Three examples of polysynaptic reflex arcs

1.) toe pinch: pinching the toe of animal the animal will flex the joint to try to draw toe away

2.) perineal reflexes: sharp object poked around the perineal area elicits a response

3.) skin twitch reflex

Fasciculus proprius

specialized pathway that is formed by all the connections of interneurons traveling up and down the cord

Function of fasciculus proprius

makes sure all of the neurons on the motor side receive the sensory input to cause full contraction of a muscle

Example of how the fasciculus proprius works

Knee jerk reflex

-patellar tendon is tapped which sends sensory information up to synapse with a motor neuron; that motor neuron's axons are sent back to periphery to cause contraction of quadriceps muscle

-however, in order for stifle to extend, quadriceps have to be contracted while the flexor muscles are inhibited

-some of the information from the sensory neuron, by way of interneurons of the fasciculus proprius, travel along the cord to find the flexor muscles that need to be inhibited

Where is the fasciculus proprius located?

bundle of white matter located all the way around gray matter of the spinal cord

Clinical application example for fasciculus proprius

skin twitch reflex

How does the skin twitch reflex work?

-sensory stimulus goes into the spinal cord and has to reach the location where the motor neurons are to cause the cutaneous trunci muscles to twitch

-the motor neurons are located far away in the cervical vertebrae

-the stimulus travels through the fasciculus proprius to reach the motor neuron

-once the motor neuron receives information, the lateral thoracic nerve is stimulated to cause muscle contraction

Relay pathway

stimulated receptors sends information to higher levels in the nervous system

Four things to know for relay pathways

1.) modality

2.) location of neurons

3.) site of synapse

4.) location of crossing pathways

modality of a relay pathway

type of sensation that is being evaluated; conscious (proprioception) or subconscious (nocioception)

How many neurons will there be for a proprioceptive relay pathway?

one, two, or three; always at least one

caudate nucleus

upper motor neuron nucleus in the cerebrum

internal capsule

white matter fiber bundle formed by mylentated axons

putamen

upper motor neuron nucleus in the cerebrum

pallidum

upper motor neuron nucleus in the cerebrum

ventral caudal lateral nucleus

relay center for somatic pathways located in the thalamus

ventral caudal medial nucleus

relay center for cranial pathways

pons/cerebellum

two components of the metencephlaon

medulla

mylencephalon

Nerves that carry sensory information fall into what nervous system classification?

GSA (general somatic afferent)

Two GSA pathways

1.) Proprioception pathways

2.) Nocioception pathways

Nocioception pathways

Perception of pain, temperature, and itch.

Proprioceptive pathways

relay pathways that are involved in the position of limbs and body parts in space

Two subsets of proprioception

1.) General proprioception

2.) Special proprioception

Is proprioception a spinal or cranial nerve system?

spinal nerve

Conscious proprioception

detects changes in limb position when an animal is standing still/when limbs are at rest

Subconscious proprioception

detects changes in limb position when the animal is moving

Proprioceptors

specialized nerve endings of sensory ells that are designed to detect position and movement of limbs

Where are proprioceptors located?

muscles, tendons, and joints

Three types of proprioceptors

1.) muscle spindles

2.) golgi tendon organs

3.) joint receptors

There is _______ conscious pathway and ________ subconscious pathways of proprioception in the pelvic limb

one; two

conscious proprioception pathway of pelvic limb is called...

fasciculus gracilis

How many neurons are there in the fasciculus gracilis pathway?

three

Location of first order neuron of fasciculus gracilis pathway

spinal ganglion or dorsal root ganglion

Where do first order axons of fasciculus gracilis pathway go?

travel up through the spinal cord

First order axons of fasiculus gracilis pathway travel as...

fasciculus gracilis

Location of second order neuron of fasciculus gracilis pathway

nucleus gracilis

Where do second order axons of fasciculus gracilis pathway go?

immediately cross to the opposite side and ascend through the brain stem

Second order axons of fasiculus gracilis pathway travel as...

deep arcuate fibers, then the medial lemniscus

Location of third order neuron of fasciculus gracilis pathway

ventral caudal lateral nucleus (VCL) of thalamus

Where do third order axons of fasciculus gracilis pathway go?

leave the thalamus until they reach their cytosynapse in the parietal lobe of the cerebrum

Third order axons of fasiculus gracilis pathway travel as...

internal capsule

Is the fasciculus gracilis pathway contralateral or ipsilateral?

contralateral

After which point in the fasciculus gracilis pathway do axon fibers cross over?

after first order axons synapse with the second order nucleus

The fasciculus gracilis pathway begins on the _______ side of the brain and crosses over to the _______ side

right; left

Steps of the fasciculus gracilis pathway:

1.) paw of pelvic limb is flipped upside down, which is detected by proprioceptors

2.) that stimulus travels along the sensory nerve to reach the first order neuron in the spinal ganglion

3.) first order axon comes out of the cell body and travels up through the spinal cord as fasciculus gracilis

4.) the first order axon then synapses on the second order neuron located in the nucleus gracilis

5.) second order axons immediately cross to the opposite side

6.) as second order axons cross, they form arcuate fibers

7.) the second order arcuate fibers then turn and ascend to the brain stem, forming a bundle called medial lemniscus

8.) second order fibers synapse on the third order neuron located in the VCL of the thalamus

9.) third order axons leave the thalamus, enter into and help form the internal capsule until they reach their cytosynapse in the parietal lobe of the cerebrum

the two subconscious proprioception pathways of pelvic limb are...

1.) dorsal spinocerebellar tract

2.) ventral spinocerebellar tract

How many neurons are there in the dorsal spinocerebellar tract pathway?

two

First order neuron of dorsal spinocerebellar tract pathway

spinal ganglion/dorsal root ganglion

Where do first order axons of dorsal spinocerebellar tract pathway go?

enter into the spinal cord

Second order neuron of dorsal spinocerebellar tract pathway

dorsal gray column in Clarke's nucleus

The dorsal gray column in Clarke's nucleus is aka...

thoracic nucleus

Where do second order axons of dorsal spinocerebellar tract pathway go (3)?

1.) leave Clarke's nucleus and continue to ascend through the spinal cord

2.) enter brain stem and pass through base of the caudal cerebellar peduncle

3.) continue to synapse in the appropriate portion of the cerebellum

Second order axons of the dorsal spinocerebellar tract pathway travel as what in the spinal cord?

dorsal spinocerebellar tract

Second order axons of the spinocerebellar tract pathway travel as what in the brain stem?

superficial arcuate fibers at

the base of the caudal cerebellar peduncle

Is the dorsal spinocerebellar tract pathway contralateral or ipsilateral?

ipsilateral

The dorsal spinocerebellar tract pathway begins and ends on the _______ side

right

Steps of the dorsal spinocerebellar tract pathway:

1.) paw of pelvic limb is flipped upside down, which is detected by proprioceptors

2.) that stimulus travels along the sensory nerve to reach the first order neuron in the spinal ganglion

3.) first order axons then enter into the spinal cord and synapse on the second order neuron in Clarke's nucleus (thoracic nucleus)

4.) second order axons leave Clarke's nucleus and continue to ascend through the spinal cord where the fibers then form the dorsal spinocerebellar tract

5.) dorsal spinocerebellar tract continues to ascend up through the spinal cord into the brain stem, and pass through superficial arcuate fibers at

the base of the caudal cerebellar peduncle

6.) then fibers continue

to synapse in the appropriate portion of the cerebellum

How many neurons are there in the ventral spinocerebellar tract?

two

First neuron of ventral spinocerebellar tract

spinal ganglion/dorsal root ganglion

Where do first order axons of ventral spinocerebellar tract pathway go?

enter into the spinal cord

Second neuron of ventral spinocerebellar tract

dorsal gray column

Where do second order axons of ventral spinocerebellar tract pathway go (3)?

1.) immediately cross to the other side of brain

2.) continue through the brain stem to reach the level of the rostral spinal cerebellar peduncle

3.) cross back to the opposite side to reach their appropriate area in the cerebellum

Second order axons of the ventral spinocerebellar tract pathway travel as what in the spinal cord?

ventral white commissure

Second order axons of the ventral spinocerebellar tract pathway travel as what in the brain stem?

rostral cerebellar peduncle

Is the ventral spinocerebellar tract pathway contralateral or ipsilateral?

contralateral

The ventral spinocerebellar tract pathway begins on the _________ side and ends on the _______ side

right; right

Steps of the ventral spinocerebellar tract pathway:

1.) paw of pelvic limb is flipped upside down, which is detected by proprioceptors

2.) that stimulus travels along the sensory nerve to reach the first order neuron in the spinal ganglion

3.) first order axons then enter into the spinal cord and synapse on the second order neuron in the dorsal gray column of spinal cord

4.) second order axons then immediately cross to the other side and form part of the ventral white commissure

5.) then second order axons turn and ascend through the spinal cord, forming the ventral spinal cerebellar tract

6.) then second order axons continue through the brain stem to reach the level of the rostral spinal cerebellar peduncle

7.) they help to contribute the formation of the rostral peduncle and then cross back to the opposite side to reach their appropriate area in the cerebellum

Clinical signs of a conscious deficit

knuckling; turn the paw upside down and animal walks on the dorsal surface of the paw

Clinical signs of a subconscious deficit

sensory ataxia; wide stance, wobbly, and unsure of where limbs are

There is _______ conscious pathway and ________ subconscious pathways of proprioception in the thoracic limb

one; two

Conscious pathway of proprioception in the thoracic limb

fasciculus cuneatus

How many neurons are there in the fasciculus cueatus pathway?

three

First order neuron of fasciculus cuneatus pathway

dorsal root ganglion

Where do first order axons of fasciculus cuneatus pathway go?

enter into the spinal cord

First order axons of fasiculus cuneatus pathway travel as...

fasciculus cuneatus

Second order neuron of fasciculus cuneatus pathway

medial cuneate nucleus

Where do second order axons of fasciculus cuneatus pathway go (2)?

1.) cross to the opposite side of the brain

2.) enter brain stem