Exam 2 Flashcards
(164 cards)
1
Q
Organization of Spinal Cord Segments
A
- Dorsal horns-> gray matter; recieve and process somatosensory info
- Ventral horns–> grey matter; process and send somatic motor info
- T1-L2–> sympathetic preganglionic neurons
- S2-S4–> parasympathetic preganglionic neurons
- Tracts are found in consistent locations in the funiculi
2
Q
A
-Surface bumps and ridges indicate cell groups or axon tracts
3
Q
A
4
Q
Colliculi
A
- Roof structures of the midbrain
- Cell group underneath surface
- 4–> organized into superior and inferior
- Superior–> recieve visual info and process it into visual reflexes
—–Tracking motions of eyes
-Inferior–> Auditory info relayed up to brainstem on route to medial geniculate nucleus
—–Auditory relexes such as turning to a noise
5
Q
Cerebellum’s location in regard to the brainstem
A
- Roof structure over the pons and rostral medulla
- Important for unconcious coordination and planning and executing movements
6
Q
A
SCP= superior cerebellar peduncles
MCP= middle cerebellar peduncles
ICP= inferior cerebellar peduncles
-Two areas= cerebellar cortex and deep gray
7
Q
Ventricular Components of the Brainstem
A
-Midbrain= the cerebral aqueduct
—-Surrounded by the periaqueductal gray
——-Gray matter important for modulation of pain
-Pons/Medulla= 4th ventricle
8
Q
The Tegmentum
A
- Grey and white matter in the central part of the brainstem
- Grey matter: Cranial nerve nuclei, the reticular formation, and “other” nuclei
- White matter: axon tracts and fibers of cranial nerves
9
Q
Reticular Formation
A
-Diffuse groups of neurons, often vital centers
—Respiratory control
—Cardiovascular control
—Wakefulness and arousal
*Cell group in the brainstem
Specific Cell Groups:
—Substantia Nigra
—Raphe Nuclei
–Locus Ceruleus
10
Q
Relay Nuclei
A
- Part of the longitudinal pathway
- Somatosensory system- gracile and cuneate nuclei
11
Q
Red Nucleus
A
-Motor nucleus regulating upper limb flexor muscles
12
Q
Inferior olivary nucleus
A
-Motor learning loop
13
Q
Cranial Nerve Nuclei
A
- Sensory Nuclei- Processing and relaying incoming sensory info
- Motor Nuclei-Processing and sending motor information out of the CNS
*Some cranial nerves can carry both sensory and motor fibers, but these axons are associated with different cell groups!!
14
Q
Brainstem Nuclei associated with cranial nerves
A
-Each cell group is related to a single function- somatic or autonomic motor, somatic, visceral, or special sensory
15
Q
What does it mean by motor nucleus?
A
-Motor nucleus A
—-A cluster of somatic motor or branchial motor neuron cell bodies that send axons out through cranial nerve A to innervate skeletal muscles
-Motor nucleus B
—A cluster of autonomic parasympathetic preganglionic neuron cell bodies that send axons out through cranial nerve B toward smooth muscle, cardiac musvle, or cranial nerve target
16
Q
Cortical control of a motor nucleus
A
- Brainstem motor nuclei often recieve compands from the contralateral cerebral cortex (premotor, primary motor areas
- Corticobulbar fibers of the cortical efferents
17
Q
What do we mean by a sensory nucleus?
A
-All relay info to the cortex by communicating with another cell group in the CNS as a tract
**Sensory Nucleus A- A cluster of neuron cell bodies that recieves synpases from somatosensry neurons of cranial nerve A whose cell bodies lie in a ganglion outside the brainstem
**Sensory nucleus B- A cluster of neuron cell bodies that recieves synapses from VISCERAL sensory neurons of cranial nerve B whose cell bodies lie in a ganglion outside the brainstem
**Sensory nucleus C- A cluster of cell bodies that recieve synapses from SPECIAL SENSORY neurons of cranial nerve C carrying info from special sense organs
—-Cell bodies lie in a ganglion outside the brainstem
18
Q
Dopaminergic Projections in the midbrain
A
- Arrise from 2 cell groups
1. Ventral tegmental nuclei
2. Substantia nigra
19
Q
Substantia Nigra
A
- Distinct population of dopaminergic neurons in the ventral midbrain
- Project to the caudate and putamen of the basal ganglia
- Death of these cells–> Parkinsons
20
Q
Serotonergic Projections
A
- In the Brainstem midline reticular formation
- Raphe Nuclei
21
Q
Norepinephrine Projections
A
- From the pons and medulla oblongota
- Locus Coeruleus
22
Q
Area Postrema
A
- Chemoreceptor trigger zone
- Sends noxious chemical stimuli to vomit center–> triggers vomit reflex
*Located in the reticular formation of the medulla
23
Q
Circumventricular Organs of the Brain
A
- Where there is a focal breakdown in the blood brain barrier
- Some release hormones
—-Ex: Pineal gland, posterior pituitary
-Some contain chemosensitive celld mediating different homeostatic responses
—-Ex: area postrema
24
Q
Solitary Nucleus
A
-Sensory nucleus recieving info from sensory axons of cranial nerves 7, 9, and 10
-Extends the length of the medulla
—Diff parts serve as centers for diff modalities
—–Taste, GI tract, Cardiovascular, Respiratory
25
Solitary Nucleus and Taste
- Rostral solitary nuc
- CN 7, 9, and 10 from taste buds--\> responses of salivation and early digestive processes
------superior and inferior salivatory nucleus
26
The Solitary Nucleus and GI tract
- Caudal solitary nuc
- Feedback from GI tract via CN 10--\> response of motor output to enteric NS regulating digestive processes
27
Solitary Nucleus and Cardiovascular
- One area in caudal solitary nuc
- Feedback from baroreceptors via CN 9 and 10--\> sympathetics (T1-T2 preganglionic neurons) and parasympathetics (CN X) to heart up or down,
28
The Solitary Nucleus and Respiration
- One area of the caudal SN
- Feedback from chemoreceptors via CN 9,10 and brainstem chemoreceptor cells
- Response= turns sympathetics (T1-T2 pregang neurons) and parasympathetics (CN 10) of lungs up or down
29
Respiratory Centers
-Recieve input from many sources
---chemoreceptors, higher brain centers, etc
- Located in reticular formation
- Send axons to the spinal cord motor neurons controlling breathing movements
- Control diaphram (main muscle of respiration)
---Motor neurons of C3-C5
-SC injuries above C3--\> damage to respiratory pathways, brainstem can no longer regulate breathing
30
Autonomic Pathways
- Descend from the hypothalamus
- Travel through the brainstem to influence many of the reticular system regulatory centers in addition to parasympathetic nuclei and symapthetic spinal neurons
\*Brainstem damage= fatal
31
Brainstem Arousal System
- Part of the reticular system
- Damage leads to coma
- Stimulation--\> wakefulness
- Resides in the lower midbrain/upper pons
-----Locus coeruleus (NE)
-----Raphe nuc= ser and dop
--ACh and Histamine
32
Cortical Efferent Component
-Created from long projection fibers of the cerebral cortex from layer 5
---Corona radiata, internal capsule, cerebral peduncles of midbrain, longitudinal fibers of the pons, pyramids of the medulla, corticospinal tract
\*\*\*\*The fiber bundle decreases in size from midbrain to SC
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Cranial Nerves 1 and 2
1. Olfactory Nerve
2. Optic Nerve
- Originate from cerebrum, NOT THE BRAINSTEM
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Sensory Nuclei in the Brainstem
-Contain neurons that recieve synapses from CNs carrying sensory info:
---Somatosensory
---Special Sensory
---Visceral Sensory
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Motor Nuclei of the Brainstem
-Contain neurons that send axons out through a cranial nerve to innervate some peripheral target
---Somatic and branchial motor
---Autonomic motor (parasympathetic)
36
Cranial Nerves III, IV, and VI
-3= oculomotor
---Somatic motor to 4 skeletal eye muscles and upper eyelid
---Autonomic motor to internal eye targets
- 4=Trochlear Nerve---\> Somatic motor to one skeletal muscle of eye
- 6=Abducens Nerve--\> Somatic motor to one skeletal muscle of the eye
37
Skeletal Muscles of the eye
- LR6, SO4, all of the rest are oculomotor
- Lateral rectus= 6
- Superior oblique= 4
- Superior rectus, medial rectus, inferior rectus, and inferior oblique= 3
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Oculomotor Nucleus
-Contains cell bodies of somatic motor neurons innervating skeletal muscle targets of oculomotor nerve
----Superior, inferior, and medial rectus muscles
----Inferior oblique muscle
----Skeletal muscle raising upper eyelid
-Originates in the upper midbrain
39
Edinger Westphal Nucleus
-Contains cell bodies of parasympathetic preganglionic neurons that innervate autonomic targets in eye (oculomotor nerve)
---Ex: smooth muscle for pupil constriction, ciliaris muscle
40
Two Functions of Parasympathetic Fibers of CN III
1. Constriction of the pupil to limit light striking the retina
2. Focusing the lens for near vision
41
The Pupillary Light Reflex
-Light info carried back from one eye through the optic nerve is carried to the midbrain and triggers and parasympathetic to contstrict the pupils of both eyes
-----Consensual
42
Cranial Nerve 4 and its nucleus
- Trochlear nerve
- Controls the superior oblique
---Turns eyes down and out to lateral side
\*Originates from trochlear nucleus in lower midbrain
43
Cranial Nerve 6
- Abducens
- Controls the lateral rectus
---Turns eye laterally
-Originates from the abducens nucleus in the middle of the pons
44
Cranial Nerve V
- The trigeminal nerve
1. Motor to skeletal muscles controlling the jaw
2. Somatic sensation from face, dura, head, and jaw (touch, pain, proprioception)
- Attaches to the rostral pons, but its axons connect to nuceli at all levels of the brainstem
45
The Trigeminal Motor Nucleus
-Cluster of motor neurons whose axons Innervate muscles of mastication (chewing)
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Sensory Nuclei of the Trigeminal Nerve
- 3 separate sensory nuclei of the trigeminal nerve
1. Mesencephalic Nucleus
2. Principal Nucleus
3. Spinal Nucleus
47
The Mesencephalic Nucleus
- Lies in the midbrain
- Mediates jaw jerk reflexes
- Sensory neurons collecting feedback from muscle spindles and golgi tendon organs in jaw muscles
- Axons synapse on motor neurons in motor nuc of trigeminal
\*Sensory-motor loop; monosynpatic jaw reflex
48
The Principal Nucleus
- Located in the rostral pons
- Recieves axons of somatosensory afferent neurons conveying touch and vibration info
49
The Spinal Nucleus
- Long column of neurons
- Recieving axons of somatosensory afferent neurons conveying pain and temp info
50
Cranial Nerve VII
- The Facial Nerve
1. Motor to skeletal muscles of the face (facial expression)
2. Special sensory taste fibers from front 2/3 of tongue
3. Parasympathetic preganglionic motor fibers to salivary glands and the tear glands
4. Small piece of somatosensory behind ear
- Facial nucleus= motor to skeletal, muscles of facial expression
- Solitary nucleus= taste
- Superior salivatory nucleus= parasympathetic, salvation and lacrimation
- Trigeminal sensory nuclei= small number of sensory fibers of CN VII
51
The Facial Nucleus
- Located in the pons
- Motor nucleus
- Its axons innervates the skeletal muscles of the face; move the skin to alter facial expression
52
Effect of Damage to the right facial nerve
- Complete facial nerve paralysis on the patient's right side
- Also would result in the loss of tears and salivation
53
Cranial Nerve VIII
- The Vestibulocochlear Nerve
- 2 types of special sensory fibers
- Formed from two separate structures of the inner ear
- Cochlea detects sound; cochlear nerve carries auditory info from cochlea to the brain
- Vistubular organ= vestibule and semicircular canals; detect balance; Vestibular nerve carries balance info to brain
\*Cochlear and vestibular nerves bundled together to create vestibulocochlear nerve
54
Vestibulocochlear nerve at the brainstem
- Separates back into cochlear and vestibular nerve
- Cochlear portion synapses in cochlear nuclei of rostral medulla--\> relays info to brainstem to inferior colliculus and on the medial geniculate nucleus and primary auditory cortex
- Vestibular nerve--\> synpases in the vestibular nuclei of the caudal pons and cerebellum; mediates reflexes that adjust body and eye position in response to changes relative to gravity
55
Vestibular Schwannoma/ Cerebellopontine angle (CPA) tumor
- Vestibular portion of cranial nerve forms a schwann cell tumor btwn pons and cerebellum
- Compression from growth leads to balance and hearing problems
- Discovered when changes in facial expressions may be noticable
- Can also affect CN VII
56
Nucleus Ambiguus
- Motor nucleus in medulla
- Controls muscles of the throat (pharynx) and voicebox (larynx)
---Speech and swallowing
57
Cranial Nerve IX
- Glossopharyngeal nerve
1. Motor to one swallowing nerve (from nuc ambig)
2. Special sensory taste fibers from back 1/3 of the tongue (solitary nuc)
3. Somatic sensory fibers in back of the tongue and throat (spinal trigeminal nuc)
4. Visceral sensory fibers from baroreceptors (solitary nuc)
5. Parasympathetic preganglionic motor fibers to salivary gland (from inferior salivatory nuc)
58
Cranial Nerve 10
- Vagus nerve
1. Motor to swallowing muscle and speech muscle (nuc ambig)
2. Somatic sensory fibers from throat (spinal trigeminal nucleus)
3. Visceral sensory fibers from baroreceptors and organs (solitary nuc)
4. Parasympathetic preganglionic motor fibers to glands, cardiac and smooth muscle in organs of neck, thorax, and abdomen (dorsal motor nuc of vagus)
5. Taste from area around epiglottis in back of throat (solitary nuc)
59
Cranial Nerve XI
- The accessory nerve
- Motor to two skeletal muscles of the neck and bacl
---Trapezius and sternocleoidomastoid
\*\*\*Does NOT arise from brainstem
-Damage leads to weakness or paralysis of affected muscles
---Visible effects of right-sided XI paralysis
--Scalloping of the neck and drooping of the shoulder
60
Cranial Nerve XII
- the Hypoglossal Nerve
- Motor to the tongue
- Hypoglossal nucleus= long cell column in rostral medulla
--- motor axons from hyp nuc control the skeletal muscle on the same side of the tongue
-----Contraction of these muscles bring tongue to midline
\*Damage= causes tongue to deviate toward the weaker damaged side and will eventually lead to atropy on that side
61
Trigeminal ganglion
- Collection of sensory cell bodies just outside the pons in the middle cranial fossa
- Cells= pseudounipolar
- Collect info about somatosensation from face, oral cavity, nasal cavities, and orbit
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Somatosensory targets inside the head
- Ophthalmic branch of V: skin of forehead and nose, eye, upper nasal cavity
- Maxillary branch of V: skin of cheek, upper lip and side of head; nasal cavity and upper teeth, palate
- Mandibular branch of V: skin of chin, lower lip and lateral head; floor of oral cavity and anterior tongue
- Glossopharyngeal: back of nasal and oral cavities, middle ear
- Vagus: lining of espophagus and airway below epiglottis
63
Dorsal Column-Medial Lemniscus Pathway
- Fine touch, vibration sense, mechanosensation
- Receptors are associated with 1a, 1b, and Abeta sensory fibers
- Gracile fasiculus contains axons from lower body, cuneate fasiculus from upper body
- Medial lemniscus carries info to thalamus: VPL nuc
64
Thalamic Nuclear Groups
-Divided into functional groups, only some of which are identifiable in the lab
---anterior nuclear group
---Pulvinar
---MGN
---LGN
\*All project to diff area of the cerebral cortex ipsilaterally
65
Gracile and Cuneate Nuclei
- Located in the lower half of the medulla; dorsal aspect adjacent to gracile and cuneate faciculi
- Gracile axons synapse on gracile nuc neurons
- Cuneate axons synapse on cuneate nuc neurons
66
Internal Arcuate Fibers and the Medial Lemniscus
- Internal arcuate fibers- axons leaving the gracile and cuneate nucleus that sweep ventrally before turning rostrally to become the medial lemniscus
- Info synapses in VPL nucleus of thalamus and is relayed to primary somatosensory cortex
- In rostral medulla, no gracile or cuneate structures, only medial lemniscus
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- Level= caudal pons
- Sensory decussation
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Fiber Bundles of the Dorsal Column-Medial Lemniscus Pathway
- Dorsal columns in the spinal cord (upper and lower body)
- Medial lemniscus in the brainstem
\*\*Head info joins this pathway in the upper pons via the trigeminal lemniscus
69
The Dorsal Column-Medial Lemniscus Pathway
-3 neuron system relaying sensory inputs from body or head to primary somatosensory cortex
Body: 1st= DRG 2nd= gracile or cuneate nuc 3rd: VPL
Head: 1st trigeminal sensory neuron, 2nd: principal sensory nucleus, 3rd: VPM
70
Anterolateral Pathway
- Carries pain and temp info
- Receptors associated with Adelta and C fibers, slow conducting
- Projects to primary somatosensory cortex for discriminative aspects of pain, and limbic areas for affective-motivational aspects of pain (emotions)
For body: 1st= DRG, 2nd= dorsal horn of SC, 3rd= VPL
Head: 1st= trigeminal sensory neuron, 2nd= spinal trigeminal nucleus, 3rd= VPM
71
Spinal Trigeminal Nucleus
- Processes pain and temp info from head
- CN V, VII, IX, X feed into this nuc.
- Located in the lateral tegmentum of the lower 1/2 of the brainstem
\*Largest at lower medulla levels
72
Neospinothalamic Pathway
- Pain projections through aterolateral tract direct to thalamus
- Later to evolve
- Crosses in SC and ascends on side contralateral to origin
- Direct to thalamus VPL/VPM
- Topographically maintained all the way to cortex
73
Paleospinothalamic Pathway
- Formed from C-fiber mediated pain
- Formed earlier, more primitive
- Ascends bilaterally in SC
- Synapses in reticular formation of brainstem, including PAG
- Relayed by brainstem neurons to intralaminar and medial nuclei of thalamus
- Relayed to limbic areas of cortex-- including prefrontal, cingulate gyrus and insula
74
Descending Pathways of the Brainstem
- Modulate pain transmission at the spinal level
- Ascending sensory axons stimulate the PAG, locus coeruleus, and reticular formation
- PAG stimulates raphe--\> raphe sends axons down to dorsal horn releasing Serotonin
- Locus coeruleus sends axons down to dorsal horn--\> Norepinephrine
\*\*\*All activate inhibitory interneurons in the substantia gelatinosa
75
Pain Modulation
- Occurs in substantia gelatinosa of the dorsal horn
- Where C fibers synapse
- Inhibitory neurons release opiate compounds
- Target of pain medicines
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Reffered Pain
- From viscera to body surface
- Pain originating in an organ is often percieved as coming from another area of the body
- Dorsal horn neurons carrying pain info may recieve inputs from both an organ and a specific point on body surace
77
Sensory Systems
Divergent- Info diverges from a single input and is relayed to multiple targets
-Use of vocab= 1st order, 2nd order, etc
78
Motor Pathways
- Convergent- info from multiple sources are integrated into a response by a single cell
- Upper and lower motor neurons
---Upper= from the brain, control LMNs
---Lower= projec to skeletal muscles
79
Lower Motor Neurons
- A neuron that innervates a skeletal muscle or a motor unit
- Cell bodies in CNS- Rexed Lamina IX
---Medial= trunk
---Lateral= limbs
- Axons leave through a spinal or cranial nerve
- Damage leaves muscle cells without control--\> atrophy
80
Spinal Accessory Nucleus
- LMNs to neck muscles innervated by XI
- Located mostly in the upper cervical spinal cord
81
Ventral (anterior) Horn of the Spinal Cord
- Medial LMNs to axial muscles
- Lateral LMNs to appendicular muscles
---Upper extremity- C5-T1
---Lower extremity- L2-S3
82
Groups of Lower Motor Neurons in the Brainstem
- Oculomotor nucleus
- Trochlear nucleus
- Motor trigeminal nucleus
- Abducens nuc
- Facial nuc
- Nuc abiguus
- Hypoglossal nuc
83
Oculomotor, Trochlear Nuc, and Abducens Nuc- LMNs
- LMNs to extraocular eye muscles
- Not driven by direct cortical stimuli; activities are coordinated by brainstem gaze centers
- Connected to each other and the vestibular nuclei by the MLF--\> CNS tract essential for conjugate gaze
84
Motor V, Facial Nuc, Nuc Abiguus, Hypoglossla Nuc- LMNs
- Motor V- LMNs to muscles of mastication
- Facial- LMNs to muscles of facial expression
- Nuc Ambig- LMNs to muscles of swallowing and speech
---All skeletal muscles innervated by IX and X
-Hypoglossal Nuc--LMNs to most tongue muscles
85
Control of Lower Motor Neurons
- Upper motor neurons from brain (cortex/corticospinal tract)
- Brainstem--\> reticulospinal, tectospinal, vestibulospinal, rubrospinal
- Sensory inputs from CNS can drive reflex activation
------All 3 lead to LMNs activation
--------Damage to 1+ UMN pathways has a diff effect on muscle function
86
Reflexes
- Primative control of skeletal muscles
- No thought involved
- Components- sensory receptor, sensory neuron, CNS integration, motor neuron
87
The Stretch Reflex
-Rapid stretch of muscle elicits a reflex contraction of the same muscle
---Protects muscle from too much stretch
1. Stretch--\> muscle spinds send impulses to SC
2. Sensory neurons synapse with alpha motor neurons, excite extrafusal fibers of stretched muscle; also synapse with interneurons that inhibit motor neurons controlling antagonistic muscles
3. Stretched muscle contracts, impulses to antagonist muscles are reduced
Ex: Knee-jerk reflex
88
Golgi Tendon Organ and its reflexes
-Prevents muscle from generating too much tension
Ex:
1. Quadricepts strongly contracts; tendon organs are activated
2. Afferent fibers synapse with interneurons in the SC
3A. Efferent impulses to muscle with stretched tendon are damped; muscle reflexes, reducing tension
3B. Efferent impulses to antagonist muscle cause it to contract
89
The Withdrawal Reflex
- Also called crossed extensor reflex
- Pain causes:
---Withdrawal of injured limb (flexion)
---Shifting of weight to other side (crossed extension)
90
Higher level control by thr Upper Motor Neuron
- Located in the CNS
- Innervate lower motor neurons
\*\*\*DONT SYNAPSE DIRECTLY TO SKELETAL MUSCLE
-Influence activity of skeletal muscles by influencing LMNs
91
Cortical Efferents
- Example of an upper motor neuron cell group
- Contain axons that innervate pools of LMNs along the length of the brainstem and SC
- Influence LMNs of volitional (voluntary) movement
- Sometimes called pyramidal motor system buz its origin is in pyramidal neurons of the cerebral cortex
\*\*Axons arise from premotor, primary motor, primary somatosensory, and other parietal cortical areas (nOT ALL MOTOR)
92
What are the three fiber groups of the cortical efferent pathway?
- Corticospinal
- Corticopontine
- Corticobulbar
93
Corticospinal Fibers
-From the cerebral cortex descend through the cerebral peduncles and continue into the spinal cord as either the anterior corticospinal tract or the lateral corticospinal tract
94
Corticopontine Fibers
- Fibers from the cerebral cortex descend through the cerebral peduncles and synapse in the pons on pontine nuclei
- Axons of the pontine nuclei cross the midline and travel through the middle cerebellar peduncle to synapse in the cerebellum
- Fibers “inform” the cerebellum of the motor plans made in the cerebral cortex
95
Corticobulbar Fibers
- Fibers from the cerebral cortex descend through the cerebral peduncles and synapse in one of the motor nuclei (for example, hypoglossal nucleus, shown in green) within the brainstem
- Nuclei project out through cranial nerves
96
The Cortical Efferent Pathway
-Axons descend from cortex in a fiber bundle that changes names as it moves from cerebrum through the brainstem
---Part of corona radiata
---Part of internal capsule
---Cerebral peduncles of midbrain
---Longitudinal fibers of the pons
---Pyramids of medulla
---Corticospinal tracts of SC
\*\*\*Decreases in size at each level of brainstem from midbrain to medulla (rostral to caudal)
97
Cortical Efferents in the Cortex
1. Cell bodies of the cortical efferents are loccated in layer V of primary motor cortex
2. Projections from cortex become part of the corona radiata in the white matter
98
Cortical Efferents and the Internal Capsule
3. Cortical efferents of corona radiata coalesce in the posterior limb of the internal capsule--\> become cerebral peduncle
4. Cerebral peduncles= cortical efferents of the midbrain
----Some corticobulbar fibers terminate here
------Red nucleus, reticular formation
----Corticopontine and corticospinal fibers just passing through
99
Cortical Efferents- Longitudinal Fibers of the Pons
5. Cortical efferents in the pons
- Some corticobulbar fibes terminate here (facial nuc, reticular formation)
- ALL corticopontine fibers terminate in ipsilateral pontine nuceli
- Corticospinal fibers continue on
100
Cortical Efferents- Pyramids and Pyramidal Decussation
6. Pyramids= cortical efferents in the medulla
- Last of the corticobulbar fibers terminate in the medulla (hypoglossal nuc, nuc ambig, reticular formation)
- Corticospinal fibers continue on
7. At inferior end of the medulla
- 80% of corticospinal fibers cross the midline to form the lateral corticospinal tract
101
Cortical Efferents- Lateral and Anterior Corticospinal Tract
8. Lateral Corticospinal tract--\> Terminates ipsilatterally in the lateral ventral horn on the motor neuron pool of apendicular (limb) muscles
9. Anterior Corticospinal Tract---\> Forms from uncrossed pyramidal fibers (the 20% that did not cross)
--Terminates bilaterally in the medial ventral horn on the motor neuron pools of axial (postural) muscles
102
Corticospinal and Corticopulbar axons
- Direct volitional (voluntary) movement)
- In MOST cases cortical axons direct LMNs on the contralatetal side of the body
103
The Motor Decussation
-80% of the corticospinal fibers cross the midline at the transition btwn the SC to the medulla
----Leads to the lateral corticospinal tract
----Fibers that remain in the ventral position= anterior CST
104
Lateral Corticospinal Tract and Anterior Corticospinal Tract
- LCST- Travels in the dorsolateral potion of the lateral funiculus and carries cortical commands driving voluntary movement of the ipsilateral limbs (distal limbs)
- ACST- Travels in the anterior funiculus and carries commands of voluntary movement of the postural limbs (bilateral)
105
Descending and Ascending Motor Tracts
-Descending motor tracts
---Decrease in size due to fewer axons at lower levels of the SC
---Tracts innervating limbs located in lateral fasiculus
---Tracts innervating postural muscles= ventral fasiculus
-Ascending tracts are larger at higher levels of the SC
106
Corticopontine Fibers
- Synapse on neurons in the ventral pons (pontine nuclei)- Which relay the info to the contralateral cerebellum via transverse fibers of the pons and MCP
- Cerebellum compares this info as well as vestibular info, and sends it back to cortex to adjust cortical plan
----Smoothes out motions; lack of coordination= cerebellar problems
107
Circuitry of the Cerebellum
- Major inputs:
1. Contralateral pontine nuclei
2. Ipsilateral dorsal spinocerebellar tract
3. Vestibular system
4. Contralateral olive (motor learning loops)
- Major Outputs:
1. Contralateral Red Nucleus
2. Contralateral Thalamus (relay to cerebral cortex)
3. Brainstem UMN cell groups
108
Brainstem's Upper Motor Neuron Groups
- Work with the cortical efferent system
- Pathways travel in the tegmentum of the brainstem and the ventral funiculus of the spinal cord
1. Upper midbrain= origin of rubrospinal tract
2. Tectum= origin of tectospinal tract
3. Reticular formation=origin of pontine and medullary reticulospinal tracts
4. Vestibular nucleus= origin of vestibulospinal tract
109
Rubrospinal Tract
- Rostral Midbrain
- The red nucleus contains a pool of UMNs that project to LMNs innervating the contralateral upper limb
- These axons project through the brainstem tegmentum and lateral fasiculus of the SC adjacent to the lateral corticospinal tract
110
The Tectosponal Tract
- Rostral Midbrain
- At the level of superior colliculus; pool of UMNs= origin
- Axons descend through the tegmentum of the brainstem to synapse on LMNs at cervical and upper thoracic levels
- LMNs innervate axial muscles of neck and trunk, mediate turning of the head and upper trunk toward auditory or visual stimuli
111
The Vestibulospinal Tract
- At level of medulla
- Cell group w/in the vestibular complex= origin
- Axons of this pathway synapse on LMNs in the ventral horns innervating axial muscles
- Pathway reflexly adjusts posture to keep center of gravity aligned over feet
112
The Pontine Reticulospinal Tract
- Originates in the pons
- Axons innervate LMNs in the SC initaiting extension of postural and limb muscles
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The Medullary Reticulospinal Tract
- Originates in the medulla
- Axons inhibit LMNs in SC to extensor muscles, facilitating flexion of postural and limb muscles
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Development of the Eye
- Formed from outgrowths of the diencephalon
- Therefore, retina and optic nerve/tracts= CNS tissue
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Retina
-Contains photoreceptors- Rods and cones
---Sensory receptors that transduce light into electrical signals
---When light hits photoreceptor, causes change in mV, altering the amount of transmitter it releases into bipolar cells, influencing pattern of AP firing
- Bipolar cells transmit to ganglion cells, the output cells of retina
- Rods= sensitive to dim light,motion
- Cones= color vision, bright light
- Bipolar neurons= 1st order
- Ganglion cells= 2nd order
---Axons create the optic nerve
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Optic Nerve
- Axons leaving the retina
- Surrounded by dura matter
- Myelinated by Oligodendrocytes
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Iris
- Pigmented
- Pupillary constrictor muscle and pupillary dilator muscle
- Pupil= hole in center of iris
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Sclera
- Tough, outer coat of eye
- Attachment site for muscles
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Tear Gland
- Washes cornea clean
- Regulated by parasympathetic axons from facial nerve (VII)
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Squit and Eyelid Muscles
- Squint muscles controlled by CN VII
- Two eyelid muscles
----Smooth muscle controled by sympathetic system
----Voluntary muscle controlled by CN III
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Smooth Muscles of Iris
- Regulate pupil diameter via autonomic NS
- Pupillary dialator muscles= radial
---decreased light= increased sympathetic stim (sympathetics from symapthetic chain), contracts
-Pupillary constrictor muscles (spincter)
---Increased light= increased para stim (parasympathetics of edinger-westphal nuc), contracts
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The path of light in the eye
1. Cornea--\> transparent, damage alters normal bending of light
2. Aqueous Humor--\> clear fluid washes cornea from inside
3. Lens--\> transparent, bends light for near vision
Other:
--Choroid- pigment absorbs stray light; high blood supply removes heat
--Vitreous Body- Transparent gel mass maintains shape of eye
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Lens of the eye
-Clear, crystalline-like structure centered behind the pupil
---Can change shape and the degree to which it bends light
-Mediated through CN III parasympathetic axons from Edinger-Westphal nucleus
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The Posterior Retina
- Stray light is absorbed in pigmented layer of retina immediately behind photoreceptors
- Vascular choroid layer- lies behind the retina; photoreceptors have high metabolic demandand generate great heat
----Detachment of retina from choroid= blindness
@Fovea centralis, ganglion and Bipolar cells shifted laterally and don't impair light pathway--\> strikes photoreceptors directly
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Fovea Centralis
- Where our most sensitive vision occurs
- Portion of the retina directly behind the pupil
- Optic nerve lies medial to this area
\*\*\*ONLY CONES--\>Increases visual acuity
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Rod and Cone distribution in the retina
Rods= 125 million, peripheral of fovea centralis
Cones= 6.5 million, clustered in fovea
---3 types, each w maximal sensitivity to a diff wavelength
-----Red, green, blue
-----Overlapping sensitivities so we responsd to other colors by signal to brain stating degree to which we see red, blue, and green
\*Colorblindness= when 1+ cones are absent
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Connectivity Patterns of Rods and Cones
photoreceptors\> # bipolar cells \> ganglion cells
-Convergence occurs at rods
----10,000 rods per 1 ganglion; 1 cone in fovea per 1 ganglion
\*rods and cones are equally sensitive to light, but convergence of rod system leads to rods more sensitive to low light and motion (no detail)
-Cones= visual acuity
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Blind spot
-No photoreceptors at point where gang cell axons converge to form optic nerve
---Convergence of gang cells to optic nerve= optic disk
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Destinations of Axons of the Optic Nerve
1. Hypothalamus (Suprachaismatic nucleus)
2. Thalamus (LGN)
3. Midbrain (SupColl)
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Suprachiasmatic Nucleus
- Located in the hypothalamus
- Where come of the axons of the optic nerve terminate
- Drive body changes associated with circadian rhythms
---Body temp, cortisol release, BP
\*Melatonin= sleep promoting hormone released from pineal gland
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The Visual Pathway for Visual Perception-General Order
1. Optic Nerves
2. Optic Chiasm
3. Optic Tracts
4. Lateral Geniculate Nucleus
5. Optic Radiations
6. Primary Visual Cortex
7. Visual Association Cortex
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Eyes and the Visual Field
- Each eye seems more than just half its visual world
- At optic chiasm, only some optic nerve fibers cross the midline
----Nasal fibers cross midline
----Results in separation of visual info into L and R halves of the visual world
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Damage to parts of the visual pathway
- Optic nerve= loss of sight in one eye on ipsilateral side
- Optic tract= loss of one half of visual field in both eyes
- Damage to cortex= cortical blindness
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Retinotopic Map
- Preserved in every stage of the visual pathway
- Within LGN, info is already being segregated into different modalities
---Binocular comparisons
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The "What" Channel
- Dorsal pathway
- Connections into inferior temporal lobe
- Damage leads to deficits in object recognition
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The "Where" Channel
- Ventral pathway
- Connection into parietal lobe
- Damage leads to deficits in object localization
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Types of Eye Movement
- Automatic Scanning: flicking motion of eyes to novel movement in the visual field; involuntary and mediated by superior colliculus
- Voluntary scanning: mediated by frontal eye fields turning eyes to contralateral side
- Visual attention: Mediated by parietal cortex driving frontal eye fields to fix on an object
- Smooth pursuit: following a moving object and need to match velocity of object
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Reflexes in the Eye
- Reflex connections of the optic nerve project directly to the superior colliculus
- Reflex tracking involved: SupColl, pulvinar, and parietal eye fields in the where channel
----Primitive object recognition, but not identification (blindsight)
-Midbrain connections drive reflex orientation to visual stimuli by connections in SupColl
---- Auditory info from interior colliculus also activates this pathway
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Conjugate Gaze
- Aligns light with the fovea in order to increase visual acuity
- Eyes work together to turn to the same target; meaning one eye turns medially while the other turns laterally
---Synchronized activity by CN III, IV, and VI
\*Nuclei connected by MLF
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Lateral Conjugate Gaze
-Regulated by abducens nucleus/nucleus of MLF
---Neurons activate ipsilateral lateral rectlus and contralateral medial rectus--\> "same side gaze"
-The MLF= a fiber bundle on each side of the midline connecting cranial nuc of III, IV, and VI
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Voluntary Gaze
- Sychronized by frontal eye fields of the cortex
- Left side activation drives eye to right and vice versa
- Connections work via a reticular system nucleus (PPRF) which activates MLF
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Voluntary Gaze Pathway
-Left Frontal Eye fields (L cortex)
--\>
-Right PPRF (contralateral to cortex)
---\>
-Right nucleus of MLF
---\>
-Right abducens nuc---\> right lateral rectus muscle
(right eye to right)
AND
-Left oculomotor nuc drives L medial rectus muscle via MLF
(left eye to right side)
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Reflex Gaze
- Synchronized by the vestibular nuclei in the brainstem
- Vestibular nuclei send axons to MLF to drive both eyes together to the opposite side in response to postural changes
\*\*Keeps eyes oriented to target
Ex: turning head to R activates vestibular system, activating L nuckeus of MLF, eyes turn left
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Perception
- Depends on cortical "predictions" as well as interferences based on prior experience
- Brain biased toward novel info
- Perception depends on the context in which it occurs
---Ex: good v bad, important v unimportant
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* Orange= thalamus
* Black= hypothalamus
* Red= midbrain
* Blue= pons
* Yellow= Medulla
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- blue- thalami
- green= third ventricle
- Red= epithalamus
\*\*Dorsal view with cerebellum removed
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- Red= basal ganglia
- Pink= optic tract
- Blue=optic chiasm
\*\*\*Ventral view
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- Green= medial and lateral geniculate nuclei
- Blue= pulvinar
- Red- Anterior Tubercle/Anterior Nucleus
\*\*\*Dorsal View w cerebellum removed
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- Blue= superior colliculi
- Red= inferior colliculi
- Pink= brachium of the inferior colliculus
----Connects the inferior colliculus to the MGN
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- Black= Optic chiasm
- Blue= optic nerve
- Red= optic tract
- Orange= LGN
- Purple= Superior Colliculus
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- Middle Cerebellar Peduncles= blue
- Superior cerebellar peduncles= pink
- Inferior cerebellar Peduncles= green
- Facial colliculi= red
----Floor of the 4th ventricle
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-Red= obex
---Cells= area postrema
- Blue= gracile tubercles
- Pink= cuneate tubercles
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- Yellow= 3rd ventricle
- Red= midbrain
- Blue= pons and medulla
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- Red= cerebral peduncles
- Blue= interpeduncular fossa
----CSF filled space called interpeduncular cistern
-Yellow arrows= CN III
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- Blue= the olives
- Red= the pyramids
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- Yellow= cerebral peduncle
- Black= substantia nigra
- Red= red nucleus
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- White=X/SCP
- Black= substantia nigra
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- Yellow- Middle Cerebellar Peduncle
- Green= transverse fibers of the pons
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