King Ch 9 - Special senses

Question 1

Describe the visual pathway

Answer 1

Light > retina > CN II > optic chiasm > optic tract > lateral geniculate nucleus (80%) (diencephalon) > optic radiation (part of the internal capsule) > visual cortex

Question 2

What is the first neuron in the pathway of vision?

Answer 2

The bipolar cell of the retina

This neuron receives impulses from the neuroepithelial cells of the retina, i.e. the rods and cones.

Question 3

What is the second neuron in the pathway of vision?

Answer 3

The ganglion cell of the retina

Its axon lies in the optic nerve and continues through the optic canal to the optic chiasma.

Question 4

What occurs at the optic chiasma?

Answer 4

Partial decussation of the axons of neuron 2

Decussation is almost complete in mammals with laterally directed eyes.

Question 5

What percentage of fibers decussate in horses, dogs, and cats?

Answer 5

• Horses: 80-90%
• Dogs: 75%
• Cats: 66%

This refers to the proportion of fibers that cross to enter the opposite optic tract.

Question 6

Where does neuron 3 in the visual pathway reside?

Answer 6

The lateral geniculate nucleus

This is within the lateral geniculate body, and the axon projects to the visual area of the occipital cerebral cortex.

Question 7

What is the optic radiation?

Answer 7

A band of fibers projecting from the lateral geniculate nucleus to the visual area of the occipital cerebral cortex

This is part of the pathway for visual processing.

Question 8

What is the role of the rostral colliculus?

Answer 8

Projects to motor nuclei of CNN III, IV, VI controlling conjugate movements of both eyeballs towards a source of light

Colliculus is in the tectum of the mesencephalon

It also initiates pupil dilation and contributes to alertness.

Question 9

Describe the PLR pathway

Answer 9

Light > retina > CN II > optic chiasm > optic tract > Pretectal nucleus (in midbrain border between di and mes) > decussation at the caudal commissure and bilateral innervation > parasympathetic nucleus of CN III > CN3 > ciliary ganglion > short ciliary nerve > ciliary muscle

Question 10

Fill in the blanks

Answer 10

Question 11

What is the function of the mesencephalic pretectal nucleus in the visual pathway?

Answer 11

Involved in controlling pupil constriction

Approximately 20% of optic tract axons synapse here.

Question 12

What is the direct reflex in pupil response?

Answer 12

Contraction of the pupil receiving the light stimulus

The consensual reflex is the constriction in the opposite eye.

Question 13

What is the tectospinal tract?

Answer 13

Pathway that controls reflex turning of the head and neck towards a source of light or movement

Neurons in the rostral colliculus project to this tract.

Question 14

What does the ascending reticular formation do in relation to visual input?

Answer 14

Receives visual input contributing to alertness

This structure is involved in regulating arousal and attention.

Question 15

What is the first neuron in the pathway of hearing?

Answer 15

The cell of the spiral ganglion of the cochlear nerve (CN VIII)

This neuron receives impulses from neuroepithelial cells in the spiral organ of Corti.

Question 16

What is the cell location of neuron 2 in the auditory pathway

Answer 16

The cochlear nuclei

Many of the axons decussate at once, forming the trapezoid body. These axons synapse with the dorsal and ventral nucleus of the trapezoid body.

Question 17

Where does neuron 3 in the auditory pathway project?

Answer 17

To the auditory area of the temporal cerebral cortex

This occurs through the auditory radiation in the internal capsule.

Question 18

Describe the hearing pathway

Answer 18

Neuroepithelial cells in the spiral organ of Corti (in the cochlea) > cell of the spiral ganglion of the cochlear nerve (first neuron) > axons pass through the internal acoustic meatus > enter the medulla > synapse in the cochlear nuclei with neuron 2 > many axons decussate at one, forming the trapezoid body > turns rostrally into the contralateral lateral lemniscus > synpase with the caudal colliculus > neuron 3 in the contralateral medial geniculate nucleus > axons project through the auditory radiation in the internal capsule > auditory area of the temporal cerebral cortex

Other axons of neuron 2 do not decussate but project to the ipsilateral medial geniculate nucleus, so each ear is projected to both sides of the forebrain

Question 19

How are the trigeminal and facial nerves involves in auditory regulation?

Answer 19

Regulation of the sound wave frequency occurs through neuronal connections between the
cochlear nuclei and the efferent motor neurons of the trigeminal and facial nerves that
innervate respectively the tensor tympani and the stapedius muscles: these muscles control
the degree of mobility of the ear ossicles.

Question 20

Describe the vestibular pathway

Answer 20

Impulses from the crista of the ampulla of each of semicircular ducts, the macula of the utricle, and the macula of the saccule > neuron 1 is the vestibular nerve, the ganglion is located within the petrous portion of the temporal bone > axons through the internal acoustic meatus into the ipsilateral vestibular nuclei, in the medulla oblongata and pons > four nuclei are rostral, medial, lateral, and caudal > projections to the spinal cord, brainstem, and cerebellum

Question 21

Describe the anatomy of the vestbular nuclei

Answer 21

• Receive afferents from the vestibular division of CN VIII
• Located on either side of the dorsal part of the pons and medulla adjacent to the lateral wall of the fourth ventricle
• The four nuclei are the rostral, medial, lateral, and caudal vestibular nuclei, which form a continuous column on either side of the pons and medulla
• Project to the spinal cord, brainstem, and cerebellum

Question 22

Describe the anatomy and functions of projections from the vestibular nuclei to the spinal cord

Answer 22

1. Lateral vestibulospinal tract - cell bodies in the lateral vestibular nucleus > courses caudally in the ipsilateral ventral funiculus through the entire spinal cord > axons terminate in all of the spinal cord segments on interneurons in the ventral gray columns
2. Medial vestibulospinal tract - cell bodies in the rostral, medial, and caudal vestibular nuclei > passes caudally in the ipsilateral ventral funiculus of the cervical and cranial thoracic spinal cord segments > axons terminate on interneurons in the ventral gray columns. In addition, the medial vestibular nucleus projects axons into the medial longitudinal fasciculus, which courses caudally in the dorsal portion of the ventral funiculus through the cervical and cranial thoracic spinal cord segments.

Question 23

Describe the function of the lateral vestibulospinal tract

Answer 23

Facilitatory to ipsilateral alpha and gamma motor neurons to extensor muscles, inhibitory to the ipsilateral alpha motor neurons to flexor muscles, and some interneurons cross to the opposite ventral gray column, where they are inhibitory to the contralateral alpha and gamma motor neurons to extensor muscles. Thus the effect of stimulation of the neuronal cell bodies, the axons of which are in the vestibulospinal tract, is an ipsilateral extensor tonus and contralateral inhibition of this mechanism.

Question 24

Describe the function of the medial vestibulospinal tract

Answer 24

Axons terminate on interneurons in the ventral gray columns, which influence the activation of the alpha and gamma motor neurons that innervate neck muscles primarily

Question 25

What is the function of the maculae in the vestibular system?

Answer 25

Record the position of the head ## Footnote Gravity acts on the statoconial membrane, affecting the firing of neuroepithelial cells.

Question 26

Describe the three terminations in the brainstem for neurons from the vestibular nuclei

Answer 26

* Axons course rostrally in the medial longitudinal fasciculus to terminate in the motor nuclei of cranial nerves VI, IV, and III - provide coordinated conjugate eye movements associated with changes in the position of the head. * Axons project into the reticular formation. Some of these axons provide afferents to the vomiting center located there. * Conscious perceptions through a thalamic nucleus and then internal capsule to cortex, probably in temporal lobe – pathway not well defined.

Question 27

Describe the vestibulocerebellar pathways and functions

Answer 27

* Axons of neuronal cell bodies in the vestibular nuclei, in addition to some in the vestibular ganglia, project to the cerebellum through the caudal cerebellar peduncle and terminate mostly in the cortex of the flocculus of the hemisphere and the nodulus of the vermis (the flocculonodular lobe). These axons have collaterals that synapse in the fastigial nucleus, which is the most medial of the three nuclei in the cerebellar medulla. * Functions to coordinate the position of the eyes, neck, trunk, and limbs with the position and movements of the head.

Question 28

How many vestibular nuclei are there?

Answer 28

Four: rostral, medial, lateral, and caudal ## Footnote These nuclei are located near the cochlear nuclei in the medulla oblongata and pons.

Question 29

What is the function of the medial longitudinal fasciculus in the context of the vestibular system?

Answer 29

Connects vestibular nuclei to motor nuclei of cranial nerves III, IV, and VI ## Footnote This tract is involved in coordinating eye movements and head position.

Question 30

What is the role of commissural fibers in the vestibular system?

Answer 30

They connect the right and left semicircular ducts with the contralateral vestibular nuclei.

Question 31

Which cranial nerves are influenced by the vestibular nuclei?

Answer 31

Cranial nerves III, IV, and VI.

Question 32

Where does the direct vestibulocerebellar tract go?

Answer 32

Projects directly to the ipsilateral cortex of the flocculonodular lobe and the fastigial nucleus of the cerebellum.

Question 33

What is nystagmus?

Answer 33

An involuntary rhythmic oscillation of the eyeball, usually from side to side.

Question 34

What distinguishes physiological nystagmus from pathological nystagmus?

Answer 34

Physiological nystagmus occurs with head movement; pathological nystagmus occurs when the head is still.

Question 35

What is jerk nystagmus?

Answer 35

A type of nystagmus characterized by a quick and slow phase of eye oscillation.

Question 36

What is the most common sign of vestibular disease in humans?

Answer 36

Spontaneous nystagmus.

Question 37

Describe the taste pathway

Answer 37

CN VII (facial) for taste buds of rostral two-thirds of tongue and CN IX (glossopharyngeal) for caudal two-thirds and CN X for mucosa of the caudal pharynx and larynx > cell locations in the geniculate ganglion (VII) and distal ganglion (IX) > contralateral solitariothalamic tract > nucleus of the solitary tract > contralateral ventral caudal medial nucleus of the thalamus > internal capsule > sensory neocortex

Question 38

Describe this diagram

Answer 38

Question 39

In which part of the nervous system are taste neuron 1 cell bodies located?

Answer 39

In the ganglion of the VIIth, IXth, and Xth nerves.

Question 40

Describe the olfactory pathway

Answer 40

Central process of the olfactory neuroepithelial cell, on the ethmoturbinate bones > axons pass through the cribriform plate of the ethmoid bone > synapses in the olfactory bulb, characterised by four organised layers of neuronal cell bodies > axon of neuron 2 passes caudally into the olfactory peduncle > division into the medial and lateral olfactory tracts (ventral surface of forebrain) > some axons in the lateral olfactory tracts and end in the olfactory tubercle via the lateral olfactory stria. Some other axons in the medial olfactory tract decussate, and project to the olfactory tubercle on the contralateral side. Other axons synapse with the olfactory tubercle > some pathways project from the olfactory bulb through the medial olfactory stria to the septal nuclei and subcallosal area > axons project into the medial forebrain bundle and end in the hypothalamus > olfactory tubercle > piriform lobe ## Footnote Some pathwayd from the olfactory bulb continue caudally in the medial forebrain bundle to reach the reticular formation of the brainstem > further projections make synapses in the parasympathetic motor nuclei of the facial, glossopharyngeal and vagus nerve, thus completing pathways by which olfactory stimuli induce salivation and gastric secretion.

Question 41

What is the olfactory neuroepithelial cell?

Answer 41

The first neuron in the olfactory pathway.

Question 42

What distinguishes the olfactory pathway from other sensory pathways?

Answer 42

It projects to the cerebral cortex without a relay in the thalamus.

Question 43

What are the components of the rhinencephalon?

Answer 43

* Olfactory components * Limbic components

Question 44

What is the role of the hippocampus in the limbic components of the rhinencephalon?

Answer 44

Involved in the control of motor expression of emotion, learning, and memory.

Question 45

Label the diagram

Answer 45

Question 46

What is the paradoxical vestibular syndrome?

Answer 46

A condition where the head tilts to the opposite side of a central vestibular lesion.

Question 47

What area of the brain is involved in the control of motor expression of emotion and rage?

Answer 47

The hippocampus ## Footnote The hippocampus is also involved in learning, memory, and instinct.

Question 48

Where is the amygdaloid body located?

Answer 48

Buried deeply in the piriform lobe ## Footnote The amygdaloid body consists of a complex of nuclei.

Question 49

What are the main sources of afferent connections to the amygdaloid body?

Answer 49

* Lateral olfactory tract * Areas of the neocortex * Thalamus * Rostral hypothalamus * Hippocampus * Nucleus of the solitary tract

Question 50

What is the primary function of the amygdaloid body?

Answer 50

Involved in autonomic, endocrine, and somatic motor responses associated with emotion ## Footnote This includes responses like respiration, circulation, and expressions of fear, rage, and aggression.

Question 51

What are the septal nuclei?

Answer 51

A small area of grey matter in the septum pellucidum, connected with the habenular nuclei via the habenular stria, and have afferent and efferent connections with the hippocampus via the fornix

Question 52

What type of behavioral reactions are the septal nuclei involved in?

Answer 52

Reactions to external stimuli, particularly sexual and aggressive behaviors

Question 53

Where do the habenular nuclei lie?

Answer 53

In the roof of the third ventricle

Question 54

What types of impulses do the habenular nuclei receive?

Answer 54

Olfactory impulses via the septal nuclei

Question 55

What is the primary function of the habenular nuclei?

Answer 55

Participate in autonomic responses to olfactory and emotional stimuli

Question 56

What does the term 'limbic system' refer to?

Answer 56

Parts of the forebrain concerned with visceral processes associated with emotion, memory, behavior, and personality

Question 57

What are the main components of the limbic lobe?

Answer 57

* Hippocampus * Parahippocampal gyrus * Cingulate gyrus

Question 58

What additional structures are now generally included in the limbic system?

Answer 58

* Amygdaloid body * Septal area * Fimbria and fornix * Cingulum * Stria terminalis * Medial forebrain bundle * Habenular nuclei * Rostral thalamic nuclei * Hypothalamus * Mamillary body

Question 59

What are the geniculate nuclei considered part of?

Answer 59

The caudal group of thalamic nuclei

Question 60

What is unique about the olfactory pathway in relation to the thalamus?

Answer 60

It bypasses the thalamus

Question 61

How many conscious modalities are there?

Answer 61

12

Question 62

What are the four distinct groups of conscious modalities?

Answer 62

* Group 1: Touch, pressure, joint proprioception * Group 2: Superficial pain, heat, cold * Group 3: Deep pain * Group 4: Vision, hearing, balance, taste, olfaction

Question 63

What do the pathways of modalities in groups 1 and 2 share?

Answer 63

They converge on and share the medial lemniscus

Question 64

What is the typical arrangement of the pathways conducting modalities in groups 1, 2, and 4?

Answer 64

Built on a chain of three neurons

Question 65

Where does the first neuron in the pathway typically originate?

Answer 65

In a dorsal root ganglion (spinal or cranial)

Question 66

What is the function of the ascending reticular formation in relation to pathways of modalities?

Answer 66

Connects to specific systems conducting the modalities

Question 67

Which modality is conducted by the ascending reticular formation instead of the medial lemniscal system?

Answer 67

Deep pain (group 3)