Nerves, Spinal cord, and Pathways Flashcards

Question

Somatic Motor Output

Answer 1

* Two types of motor neurons contribute to majority of output: * **𝛼-motor neurons** * **large, myelinated, and fast** **conducting** axons * synapse on **extrafusal muscle fibers** * produce tension when contracted * **𝛾-motor neurons** * **smaller, myelinated, and fast conducting** axons * synapse on **muscle spindles** * regulate muscle spindle excitability * _𝛽-motor neurons_ * poorly characterized in humans * believed to innervate both intrafusal & extrafusal fibers * _Motoneurons_ _located_ in **ventral horn** of _spinal cord_ * _Axons exit_ via **ventral root**

Answer 2

DTRs used clinically to **assess sensory and motor functions**. **Reflex arc** consists of a sensory and a motor component. * _Sensory side:_ * stretch of tendon detected by **muscle spindle** * activation of **Ia fiber** * _Motor side:_ * Ia afferent fiber synapses in _ventral horn_ on **𝛼-motor neuron** which innervates the _stretched muscle_ * excitation of the 𝛼-motor neuron results in muscle _contraction_ **Hyporeflexia or areflexia** seen if sensory or motor branch of reflex arc compromised (spinal nerve or peripheral nerve lesions). **Hyperreflexia** seen if a upper motor neuron lesion compromises descending spinal cord regulation of the pathway.

Answer 3

1. **Pain** ⇒ safety pin & **Light touch** ⇒ brush * patient with eyes closed * stimulated alternatively with needle and brush * report if there is a difference between sensations 2. **Vibration** ⇒ 128 Hz tuning fork * tested on large toes or fingers * report when vibration stops 3. **Two-point discrimination** ⇒ pair of calipers * alternate between touching patient with one or both points * find the minimal seperation that can be distinguished between two points 4. **Position** sense * examiner manually moves patient's toe or finger * ask the patient to report direction of movement

Answer 4

1. Motor strength * strength of each muscle compared to contralateral conunterpart * rated on a scale of 0-5/5 * 0/5 = no contraction, 5/5 = normal strength 2. Deep tendon reflexes * reflex hammer used to stretch the muscle and tendon * reflexes rated on a scale of 0-5+ * 0 = absent reflex, 2+ = normal, 5+ sustained clonus

Answer 5

* **White matter** * Dorsal funiculus * Lateral funiculus * Ventral funiculus * **Grey matter** * Dorsal horn * Intermediate zone * Ventral Horn * **Small lateral horn** starts **at T5 and above** * contains **intermediolateral nucleus** * **Grooves** * dorsal mediun sulcus * **dorsal intermediate sulcus** starting **at T5 and above** * dorsal lateral sulcus * corresponds to dorsal root entry * ventral median fissue * Ventral/anterior white commissure

Answer 6

Contains the dorsal columns Consists of 2 large fasciculi of _myelinated fibers_. Carries sensory information about _fine touch, proprioception, and vibratory sense._ * **Fasciculus gracilis (FG)** * carries _ipsilateral_ information from _lower body_ * only fasciculus **at T6 and below** * **Fasciculus cuneatus (FC)** * carries _ipsilateral_ information from _upper body_ * present from T5 to C1

Answer 7

**_Contains 3 motor tracts:_** 1. **_Lateral corticospinal tract (LCST)_** * fibers originate from the contralateral motor cortices * voluntary control of distal motor neurons * suppression of infantile reflex 2. **Medullary reticulospinal tract (MRST)** * originates from the medullary reticular formation * inhibits extensor and facilitates flexor motor neurons * opposite action of the PRST 3. **Rubrospinal tract (RST)** * originates from the red nucleus of the midbrain * facilitates upper limb flexors * tract present only at _cervical and upper thoracic levels_ **_Contains 3 sensory tracts:_** **The anterolateral system** 1. **_Spinothalamic tract (STT)_** * carries contralateral pain and temperature sensation 2. **Dorsal spinocerebellar tract (DSCT)** * carries uncouscious proprioception from lower body * present only _at and above L2-L3_ 3. **Ventral spinocerebellar tract (VSCT)** * reports to cerebellum about spinal motor output

Answer 8

**_Contains 6 motor tracts:_** 1. **Pontine reticulospinal tract (PRST)** * originates from the pontine reticular formation * faciliates extensors and inhibits flexors * opposite action of the MRST 2. **_Ventral corticospinal tract (VCST)_** * voluntary control of axial motor neurons 3. **Lateral vestibulospinal tract (LVST)** * originates from the lateral vestibular nucleus * facilitates extensor antigravity muscles 4. **Medial longitudinal fasciculus (MLF)** * originates from the medial vestibular nucleus * vestibular * eye movements * balance function 5. **Medial vestibulospinal tract (MVST)** * controls head and neck position in relation to gravity * runs within the descending MLF tract * only present at cervical and upper thoracic levels 6. **Tectospinal tract (TST)** * controls head and neck movements for reflex of orientation towards visual, auditory, and somatosensory stimuli * only present at cervical and upper thoracic levels

Answer 9

Allows **collaterals** of entering **pain and temperature fibers** to ascend and descend **1-3 segment** before terminating in grey matter. Associated with the **anterolateral system**. Found near the **entrance of the dorsal root**.

Answer 10

Contains _short and long fibers_ **interconnecting spinal segments** to each other.

Answer 11

Contains the _crossing fibers_ of: ## Footnote **Spinothalamic tract (STT)** **Ventral spinocerebellar tract (VSCT)** **Ventral corticospinal tract (VCST)**

Answer 12

**Only fasciculus gracilis** present → dorsal column is carrying _only information from the legs_. **Small amount of white matter relative to grey matter.** **Large ventral horn** → indicates section is from the l_umbosacral enlargement (L2 → S3)_

Answer 13

**Only fasciculus gracilis** present → dorsal column is carrying _information only from the legs_. **Increase in proportion of white matter** to grey matter compared to sacral level. **Large ventral horn** → indicates this section comes from the _lumbosacral enlargement (L2 → S3)._

Answer 14

_Below T5_ **Only faciculus gracilis** present → dorsal column carrying information _only from the legs and lower trunk_. **Higher proportion of white matter relative to grey matter.** **Lateral horn present.** **Small ventral horn** → indicating there are _no limbs to innervate_ at this level.

Answer 15

**Both fasciculus gracilis and fasciculus cuneatus present** → dorsal column contains _information from both legs and arms_. **Dorsal intermediate sulcus** present between FG and FC. **Greater amount of white matter than at lumbar level.** **Large ventral horn** → indicates this section comes from the _cervical enlargement (C4 → T1)_

Answer 16

**Both fasciculus gracilis and fasciculus cuneatus present** → dorsal column carrying information from _legs and arms._ **Dorsal intermediate sulcus** present. _Lissauer's tract replaced by_ the **spinal tract of CN V**. **Large amount of white matter.** **Small ventral horn** → no limbs to innervate. This section is just below the decussation of the pyramids.

Answer 17

* Divided into 3 parts: 1. **Dorsal horn** 2. **Intermediate zone** 3. **Ventral horn** * Divided into 10 laminae → **Rexed's lamina I → X** * _Dorsal root fibers_ enter spinal cord * **medial division** * **lateral division** * **Lissauer's tract** utilized by l_ateral division fibers_

Answer 18

Grey matter containing **Rexed's laminae I → VI** * **Pain processing** * **Lamina I** → posterior marginal nucleus * **Lamina II** → substantia gelatinosa * **Lamina V** * **Sensory integration** * **Lamina III-IV** → nucleus proprius * **Lamina V-VI**

Answer 19

Grey matter containing **Rexed's lamina VII.** Only present at **T1 → L2 (+/- 1)** are: * **Clarke's nucleus** (nucleus dorsalis of Clarke) * Carries info about **unconscious proprioception from the legs** * Neurons are at the **origin of the dorsal spinocerebellar tract (DSCT)** * **Intermediolateral cell column (IML)** * Found within the **lateral horn** * Neurons are **preganglionic sympathetic neurons**

Answer 20

Grey matter containing **Rexed's Laminae VIII and IX**. **Laminae IX** contains **𝛼 and 𝛾 motor neurons.** Axons exit via the **ventral root.**

Answer 21

_Prominent_ **substantia gelatinosa** (RL II) and **nucleus proprius** (RL III-IV). **Large ventral horn** → section is at the _lumbosacral enlargement_ (L2 → S3). Contains a **medial and lateral motor neuron pool** responsible for _innervation of the legs._

Answer 22

_Decreased size_ of **substantia gelatinosa** (RL II) and **nucleus proprius** (RL III-IV) in _dorsal horn_ compared to sacral level. **Clarke's nucleus** _begins to appear_ in the _intermediate zone_. **Large ventral horn** → indicating segment is from the _lumbosacral enlargement_ (L2→S3). Contains both **medial and lateral motor neuron pools** for _innervation of the legs_.

Answer 23

Below T5. _Minimal presence_ of the **substantia gelatinosa** (RL II) and **nucleus propriu**s (RL III-IV) in _dorsal horn_. **Clarke's nucleus prominent** within _intermediate zone_. **Lateral horn present.** **Small ventral horn** → only **medial motor neuron pool** present. No limbs to innervate.

Answer 24

_Slightly increased_ presence of **substantia gelatinosa** (RL II) and **nucleus proprius** (RL III-IV) in _dorsal horn_ compared to thoracic level. **Large ventral horn** → indicates segment at level of _cervical enlargement_ (C4 → T1). Both **medial and lateral motor neuron pools** for _innervation of the arms_.

Answer 25

_Dorsal horn replaced by_ **spinal nucleus of CN V**. _Lissauer's tract replaced by_ **spinal tract of CN V**. Together relay _pain and temperature from the face_. **Small ventral horn** → only _medial motor neuron pool_. No limbs to innervate. **Spinal accessory nucleus** present which appears _similar to a lateral horn_. Contains motor neurons innervating _trapezius and sternocleidomastoid muscles_. This section is at spinal cord level ~ C1 just below the pyramidal decussation.

Answer 26

* Proportion of _grey matter to white matter greatest_ at **sacral level.** * _Ventral horn enlarged_ at the **lumbosacral (L2⇒S3) and cervical enlargements (C4⇒T1)** * Differentiate between the two using presence of the _dorsal intermediate septum_. * **Thoracic levels** characterized by * a _small ventral horn_ * presence of a _lateral horn_ (intermediolateral nucleus) * _Clarke's nucleus_ should be present at all thoracic levels * if section is **thoracic below T5**, _dorsal intermediate septum will be absent_ * if section is **T5 and above**, _dorsal intermediate septum will be present_ * **Thoracic and high cervical** appear similar * _no Clarke's nucleus or intermediolateral nucleus_ at **high cervical levels** * If _Clarke's nucleus_ can be identified in a **lumbar section**, then section is probably between **L1 ⇒ L3**

Answer 27

Innervate **nuclear bag and chain fibers of muscle spindles** via _annulospiral endings_. Carry information about **muscle length** and **rate of change of muscle length**. **Analogous to type A-𝛼 fibers.**

Answer 28

Innervate **Golgi tendon organs**. Carry info about **muscle tension**. **Analogous to type A-𝛼 fibers.**

Answer 29

Innervate **only static** _bag and chain fibers of muscle spindles_ via _flower spray ending_s. Carries info about **muscle length only**. **Analogous to type A-𝛽 fibers.**

Answer 30

From **alpha motor neurons**. Controls **muscle contraction**. **Analogous to type Ia and Ib fibers.**

Answer 31

Innervate **tactile receptors**. (Meissner, Merkel, Pacinian, Ruffini, hair, joint receptors) Carries **fine touch and vibratory** information. **Analogous to type II fibers.**

Answer 32

Terminate as **free nerve endings**. Carry **sharp pain and cold** sensation. **Analogous to type III fibers.**

Answer 33

Terminate as **free nerve endings**. Carries **dull pain and warmth** sensation. **Analogous to type IV fibers.** **Unmyelinated**.

Answer 34

From **gamma motor neurons**. Adjusts the **sensitivity of muscle spindles**.

Answer 35

Classified according to function and diameter. Schemes utilize either **Roman numerals (function)** or **letters (diameter)**

Answer 36

**Ia, Ib, II, and A-𝛽** fibers. * **Large, myelinated, fast** * Carry **epicritic** information * _proprioception_ * _fine touch_ * _vibratory sense_ * Project into the **dorsal column** * _Fasciculus gracilis and cuneatus_ * Project on **laminae III-IX** of the spinal cord * _integrates_ with other sensory modalities * participates in _reflex circuits_

Answer 37

**A-𝛿 and C fibers** * _A-delta fibers_ are **slow, small, and slightly myelinated** * _C fibers_ are **slow, small, and unmyelinated** * Carry **protopathic information** * _pain_ * _temperature_ * __Enters first in **Lissauer's tract** * Sends ascending and decending collaterals * Can be used by local circuits to organize complex reflexes i.e. flexion/withdrawal * Project predominantly to **laminae I, II, and V** of _dorsal horn_ in spinal cord

Answer 38

* Types **Ia, IIb, II, and A-𝛽 fibers** enter via the **dorsal root medial division fibers**. * Form **dorsal columns** → **brainstem dorsal column nuclei** * _Fasciculus gracilis (FG) → nucleus gracilis_ * _Fasciculus cuneatus (FC) → nucleus cuneatus_ * **Somatotopy** organized with **cervical fibers closest to grey matter.** * **Gracile fasciculus** runs _medially_ * Contains **sacral, lumbar, and thoracic fibers (up to T6)** * **Cuneate fasciculus** runs _laterally_ * Contains **upper thoracic (T5 → T1) and cervical fibers**

Answer 39

* **Unilateral lesion** of **dorsal column** results in **ipsilateral** _loss of fine touch and proprioception_ **at and below** the level of the lesion * If lesion **isolated to fasciculus gracilis** → **only info from lower body** is lost.

Answer 40

* Types **A-𝛿 and C fibers** enter through **dorsal root lateral division fibers**. * Joins **Lissauer's tract** * ascending/descending collaterals reaching _1-3 segments rostrally and caudally_ * Most fibers _enter spinal cord_ **at level of entry and +/- 1** * Synapses on **second neurons** in dorsal horn **laminae I, II, and V.** * **Laminae I and V neurons** at the **origin of STT**. * Axons **cross midline** in the **ventral white commissure**. * Forms the **contralateral STT**. * _Destination of STT fibers_ in the **ventral posterior lateral nucleus (VPL) of thalamus**. * _Somatotopy_ of STT with **cervical fibers closes to the gray matter**.

Answer 41

**Lesion of STT** results in **contralateral** _loss of pain and temperature_ sensation **starting 1 segment below the lesion.** Due to redundancy provided by Lissauer's tract.

Answer 42

* LCST formed from _pyramidal tract fibers_ which **crossed within the pyramidal decussation (~85%)** * Fibers _originated_ in the **contralateral cerebral cortex** * 15% which do not cross form the ventral corticospinal tract (VCST) * main target is the medial (axial) motor neuron pool in ventral horn * Destination: * **intermediate zone** * **ventral horn of spinal cord** * main target is the **lateral motor neuron pool** * Functions: * **voluntary control of distal skeletal muscles** * **suppression of infantile reflexes** * _Somatotopy_ of LCST with **cervical fibers closest to gray matter**

Answer 43

* Unilateral lesion of LCST @ cervical level * Loss of motor control of ipsilateral arm and leg * Lesion which affects only the lateral part of LCST tract (L & S fibers only) * May spare motor control of ipsilateral arm * Only impacts motor control of ipsilateral leg

Answer 44

LMN axons synapse on skeletal muscles. Located in **ventral horn** of spinal cord. * MN innervating **axial and proximal muscles** situated more **medially** ⇒ **medial motor neuron pool**. * MN innervating **distal muscles** situated more **laterally** ⇒ **lateral motor neuron pool.** * **Flexor** MN situated more **dorsally**. * **Extensor** MN situated more **ventrally**. _Both medial and lateral motor neuron pools present_ at the **sacrolumbar enlargement (L2 → S3)** and **cervical enlargement (C4 → T1)**. **VCST** controls _axial muscles_. **LCST** controls _distal muscles_.

Answer 45

Lesion of the **lateral portion of ventral horn** destroys the **lateral motor neuron pool**. Produces **motor deficit** in the **ipsilateral** **distal muscles** that receive innervation from this segment. In such a case, control of _axial-proximal muscles is not affect._

Answer 46

A stretched muscle elicits a reflex contraction to oppose the stretch. Important for the constant automatic corrects with movement and posture. * Tapping tendon stretches the muscle activating **annulospinal endings** within the **muscle spindle**. * **Ia afferent fibers** enter spinal cord via **medial division** of dorsal root. * Send **collaterals to ventral horn** that: * synapse directly onto **𝛼-MNs** causing contraction of homonymous muscles. * excite motor neurons supplying **agonist** (synergistic muscles) via **Ia excitatory interneurons** * inhibit **antagonist** muscles via **Ia inhibitory interneurons**

Answer 47

GTO's detect an increase in muscle tension and mediate an inhibition of the motor neurons producing the tension. Protective mechanism to relax an active muscle before tendon tension becomes too high. * Contraction of muscle activates GTO. * **Ib afferents** enter via **medial division** of dorsal root. * Sends collaterals into **dorsal and intermediate horn**. * **Laminae V, VI, and VII** * Synapse onto **Ib inhibitory interneurons** * Inhibition of **𝛼-motor neurons** in **lamina IX** innervating homologous muscle * **Autogenic inhibition**

Answer 48

Stimulation of cutaneous receptors causes flexion of an entire limb in response to noxious stimuli. * Noxious tactile stimulus activates **free nerve ending** **nociceptors** on **A-𝛿 and C fibers**. * A-𝛿 and C fibers enter spinal cord via **lateral division** of dorsal root. * Pathway must spread over several spinal segments: * A-𝛿 and C fibers send branches into **Lissauer's tract** to reach +/- 1 segments * A-𝛿 and C fibers branches also synapse on **interneurons in spinal gray** which have _processes extending over several segments_ * **Axons of interneurons**: * activate MNs innervating flexor muscles of ipsilateral extremity * inhibit MNs innervating ipsilateral extensor muscles * Through crossed connections, flexor reflex accompanied by **adaptive extension of contralateral leg** to support the body.

Answer 49

* **CNS** * Integrates and regulates information. * Determines how and when we will respond. * _Neurons_ grouped into **nuclei or laminae**. * _Axons_ organized into **pathways**. * **PNS** * Gets signals to CNS (**afferents**) and relays information to the periphery from the CNS (**efferents**). * _Neurons_ organized into **ganglia**. * _Axons_ organized into **nerves**.

Answer 50

Nervous system organized to send information in two kinds of circuits: 1. **Reflex circuits:** * shorter and faster * results in **involuntary reactions** 2. **Relay circuits:** * longer distances * will often include cortical processing * results in **awareness of sensation** or **voluntary control of movement**

Answer 51

* **Named by location of cell body and destination of fibers.** * Ex. Spinothalamic tract * Cell bodies orginate in spinal cord * Axons terminate in the thalamus * Some pathways called "tracts" do not meet this definition * Ex. Lissauer's tract * Many alternate names for axon fibers * lemnicus * peduncles * commissure * bundle * stria * etc

Answer 52

Pathways whose **cell bodies of origin are similar in location** but **destination of axons is varied.** * Ex. Faciculus gracilis * Cell bodies originate in dorsal root ganglia * Axons terminate in several brainstem nuclei including * Gracilis nucleus * Clarke's nucelus

Answer 53

Geographical term describing an **anatomical area that contains several pathways**. * May include both ascending and descending pathways. * Cell bodies of origin may be in several locations. * Axons located within funiculus have various destinations. * Most offen applied to the 3 funiculi of the spinal cord. Ex. Lateral funiculus of the spinal cord Contains spinothalamic tract, lateral corticospinal tract, reticulospinal tract, and dorsal spinocerebellar tract, and more.

Answer 54

Refers to **several related tracts** _and/or_ **fasciculi linked to relay a given piece of information over many levels of the CNS**.

Answer 55

**Afferent information entering the CNS.** * **Sensory receptors** transduce _sensory information_ into _nerve impulses_. * **Primary neuron** located in **dorsal root ganglia**. * _Pseudounipolar_ neurons * Info ⇒ _peripheral process_ ⇒ past _DRG cell bodies_ ⇒ through _central processes_ * Axons synapse on: * Cells in **spinal cord grey matter** at level of entry * functions in reflex circuits * Sends **collaterals** further up and down the _spinal cord_ or into _brainstem_. * Grey matter neurons relay to CNS via various **relay stations** (synapases).

Answer 56

**Efferent information traveling away from CNS.** **Output neuron** in the CNS is a **motor neuron**. * **Upper motor neurons** * located in _motor cortex_ and _brain stem_ * projects within the CNS * **Lower motor neurons** * located in _ventral horn of spinal cord_ * located in _intermediate zone_ * contains the **intermediolateral cell column (IML)** * preganglionic sympathetic nucleus * LMN exits CNS in _ventral root_ ⇒ joins **peripheral nerve**

Answer 57

**Major motor pathway from the cortex.** Includes the **Corticospinal tract (CST)**, corticobulbar, and corticoreticular pathways. Extends throughtout the brain and spinal cord. Susceptible to major insult including vacular damage so lesions common.

Answer 58

**Control of voluntary movements.** & **Suppression of innate reflexes.** **[Cortex]** **Pyramidal neurons** (_lamina V_ of cerebral cortex) mostly in _precentral gyrus_ but also other cortical areas ⇒ _corona radiata_ ⇒ _posterior limb of internal capsule_ **[Midbrain]** _Middle 1/3 portion_ of **cerebral peduncle** (_Crus cerebri_ and _Basis pedunculi_) **[Pons]** **Pyramidal tract** in _basal pons_ (_Longitudinal pontine fibers_) **[Open Medulla]** **Pyramid** **[Closed Medulla]** _85% of fibers_ cross at the **Pyramidal decussation** _15% of fibers_ remain on **ipsolateral side** [**Spinal Cord** - starting at cervical] Decussated fibers form the **Lateral Cortical Spinal Tract (LCST)** Cervical fibers closer to gray matter Controls _distal motor neurons_ for fine movements Remainder of fibers form the **Ventral Cortical Spinal Tract (VCST)** Cross at _segmental level_ Influences _bilateral neurons_ controlling _axial muscles_

Answer 59

* **Descending pathways** from the brain **continuously modulate transmission in spinal circuits**. * Damage to these pathways results in **removal of inhibitory influence** * LMN brought closer to threshold for AP * Increases background activity of 𝛼-MN * 𝛾-MN overactivity increases muscle spindle sensitivity * Results in a **strong faciliation of transmission from Ia efferent fibers → 𝛼-MNs** * Leads to hypertonia and hyperreflexia * Treat with **baclophen** to **presynaptically inhibit Ia fibers** * Drug injected into the spinal cord * Binds to **GABA-B receptors** * **Decreases influx of Ca²⁺** into presynaptic terminal of Ia fibers * Reduces the amount of neurotransmitter released into synapse * Also **increases K⁺ conductance** in **postsynaptic neuron** causing **hyperpolarization**

Answer 60

**Voluntary control** over LMN is lost resulting in **lack of inhibitory influence** by **regulatory descending tracts** on **local reflex circuits**. * Presents with: * **Spastic paralysis** * **Hyperrefelxia** * **Hypertonicity** * **Babinski reflex** * **Diffuse atrophy** **** UMN syndrome typically involves the corticospinal tract and reticulospinal tracts plus other descending pathways (corticobulbuar and corticoreticular). Lesion confined to the LCST or its neurons rare & presents with Babinski reflex but otherwise shows LMN signs.

Answer 61

Damage to motor neurons of the spinal cord or brainstem nuclei results in * flaccid paralysis * muscle weakness * hypotonia * hypo or areflexia * pronounced denervation atrophy * faciculations * fibrillations

Answer 62

Carries afferent **epicritic sensation**. **Fine touch, vibration sense, proprioception.** Type **A𝛼** and **A𝛽** (or **Ia**, **Ib**, and **II**) [**Lumbar Spinal Cord**] _Primary neuron_ enters via **medial division of dorsal root ganglion** (DRG). Carries **lower limb** information. Axons form the **gracile fasciculus**. [**Cervical Spinal Cord**] _Primary neuron_ enters via **medial division of dorsal root ganglion** (DRG). Carries **upper limb** information. Axons form the _lateral_ **cuneate fasciculus** _at or above T5._ Somatotopy: _cervical fibers_ located laterally _next to gray matter_ [**Medulla**] Gracile and cuneate fasciculi run **ipsolaterally** up to medulla. Axons terminate on secondary neurons in **gracile and cuneate nuclei**. _Second neurons_ cross midline as **internal arcuate fibers**. Somatotopy: _lower limb_ info **ventral**; _upper limb_ info **dorsal** [**Pons and Midbrain**] Axons form the **medial lemniscus** (ML). Somatotopy: _lower limb_ info **lateral**; _upper limb_ info **medial** [**Thalamus**] Medial lemniscus terminates in the **ventral posterior lateral (VPL) nucleus**. _Third neurons_ in **VPL thalamus**. Somatotopy: _lower limb_ info **lateral**; _upper limb_ info **medial** [**Cortex**] VPL axons terminate in the **postcentral gyrus** (_primary somatosensory cortex_) Somatotopy: _lower limb_ info **medial**; _upper limb_ info **lateral**

Answer 63

_Fine touch and proprioception_ transmitted via the **trigeminal nerve (CN V)**. ## Footnote **[Pons]** Enters at the **mid-pons**. Majority of fibers **crosses midline.** Travels _medially_ within **longitudinal pontine fibers**. Some fibers travel via **Dorsal trigeminal tract**. **[Midbrain]** _Anterior position_ within **medial leminiscus**. Some fibers travel via **Dorsal trigeminal tract**. **[Thalamus]** Project into the **ventral posterior medial (VPM) thalamus.** **[Cortex]** Project to _lateral somatotopy_ of **post-central gyrus**.

Answer 64

Part of the **anterolateral system** along with spinoreticular and spinotectal fibers. Carries protopathic sensation from **contralateral** side of the body. **Pain**, **temperature**, and **crude touch**. Type **A-𝛿** and **C** fibers. [**Spinal cord**] _Primary neurons_ in dorsal root ganglion (DRG) Axons enter via **lateral division of DRG** Sends _collaterals_ into **Lissauer's tract** (~ 1 level rostrally and caudally) Axons terminate in **dorsal horn** (lamina **I**, **II**, and **V**) _Second neurons_ in **Lamina I and V** Axons _decussate_ immediately in **ventral white commissure** Axons form the **spinothalamic tract (STT)** Stomatotopy: _cervical fibers_ located **ventrally** **next to gray matter** [**Pons, Medulla, Midbrain**] Axons ascend as the STT carrying information from _contralateral_ side of the body. Somatotopy: cervical ⇒ sacral goes ventral ⇒ dorsal _Medulla_: STT is **lateral/dorsal to inferior olive** _Pons/Midbrain_: STT **lateral to medial lemniscus** [**Thalamus**] STT axons terminate at the _ventral posterior lateral nucleus (VPL)_ _Third neurons_ in the **VPL thalamus**. Somatotopy: _lower limb_ **lateral**, _upper limb_ **medial** [**Cortex**] _VPL axons_ terminate in the **postcentral gyrus** Somatotopy: _lower limb_ **medial**, _upper limb_ **lateral**

Answer 65

Pain and temperature information carried via **Trigeminal nerve (CN V)** **[Pons]** _Enters spinal cord_ at the **mid-pons**. **Descends down** to the **caudal medulla** and **crosses midline**. Ascends via the **Spinothalamic tract (STT)**. **[Midbrain]** _Anterior position_ within the **STT** **[Thalamus]** Fibers terminate within the **ventral posterior medial (VPM) thalamus.** Third neuron originates in the VPM. **[Cortex]** VPM fibers terminate **laterally** within the **postcentral gyrus.**

Answer 66

**Preganglionic sympathetic neurons** in the _T1 intermediolateral nucleus_ (aka _ciliospinal center of Budge_) ⇒ **postganglionic neurons** in _cervical ganglion_. **Postganglionic sympathetic neurons** ⇒ ipsilateral dilator muscle of pupillae, superior tarsal muscle, and sweat glands of face. Lesion of this pathway results in **Horner's syndrome**. **Characterized by ipsilateral:** miosis (constricted pupil) ptosis (drooping eyelid) anhidrosis (lack of sweating) on the face

Answer 67

**Degenerative disease** of unknown etiology **affecting both upper and lower motor neurons**. * As disease progresses, **upper limb LMN die** _before_ those innervating **lower limbs** * **LMN signs in arms** * **UMN signs in legs** * Terminal stage results in **total flaccid paralysis** involving all voluntary motor systems with _exception of eye movements_ * Eventually leads to **respiratory failure and death**

Answer 68

**Tabes dorsalis** seen in _late stages of neurosyphilis_. * Spinal cord **DRG neurons compromised**, especially in **lumbosacral region** * Results in **degeneration** of axons forming the **dorsal columns** * Tabetic patients have: * **sensory losses in BLE** * **sensory ataxia** * **high-stepping tabetic gait** * **incontinence** * **Romberg's test** used to assess deficits * Diagnosis: * blood tests for treponemes * CSF with lympocyte predominant meningitis * Treat with IV penicillin G

Answer 69

**Fluid-filled cylindric enlargement of the central canal.** * Secondary to: * spinal cord tumors * congenital abnormalities * trauma * Usually develops at **lower cervical or upper thoracic levels** * As **syrinx enlarges**, it first compresses **fibers crossing ventral white commissure** * **Segmental loss of pain and temperature sensation** * As **syrinx enlarges rostrally and laterally,** other structures compromised ⇒ **ventral horn and lateral funiculus** * **LMN signs in affected segments** * **UMN signs below the syrinx**

Answer 70

Viral disease kills **ventral horn motor neurons**. **LMN symptoms bilaterally** in _myotomes affected_ by polio virus. Usually isolated to the lower extremities. Plasticity and mixed motor units can result in spastic movements and muscle failure.

Answer 71

**Autoimmune inflammatory disorder affecting CNS.** * Like caused by T-cells reactive against **oligodendrogial myelin of CNS** * PNS myelin spared * Demyelination causes **dysfunctional conduction in large myelinated fibers** * **dorsal columns** * **LCST** * Localized **plaques of demyelination/inflammation in CNS** can be episodic * Eventually forms **sclerotic glial scars** * Spinal cord associated symptoms include: * bladder dysfunction * b/l deficit in fine touch and proprioception * b/l UMN symptoms * optic neuritis * cerebellar ataxia * vertigo * vomiting * nystagmus * trigeminal neuralgia * transient pain * fatigue

Answer 72

* **Anterior spinal artery** supplies **anterior 2/3 of spinal cord** * **Lateral and ventral funiculus** affected * Stroke may present with: * **bilateral loss of pain and temperature** * **bilateral LMN** **symptoms** _at the lesion_ * **bilateral UMN symptoms** _below the lesion_ * **Fine touch and proprioception preserved** because dorsal columns supplied by posterior spinal arteries

Answer 73

Cuteneous Reflex * Uses T8 → T12 * Initiated by stroking skin of abdomen * Produces contraction of abdominal wall muscles * Movement of umbilicus towards stimulus * Paradoxically attenuated or absent with UMN lesions

Answer 74

Cutaneous Reflex * uses L1 * initiated by stroking skin of medial thigh * produces contraction of cremaster muscle * causes elevation of the testis ipsilaterally * paradoxically attenuated or absent with UMN lesions

Answer 75

Cutaneous Reflex * uses L5→S1 * initiated by coarsely running blunt object up the lateral aspect of foot from heel to big toe * normal reflex is toe flexion * abnormal finding is toe extension → called positive Babinski's sign * seen with UMN lesions

Answer 76

Cutaneous Reflex * produced by stimulation of cutaneous pain afferents * goal is to move the body part away from painful stimulus * multisynaptic * can initiate a cross-extension reflex in order to maintain balance

Answer 77

Tests S1 Mediates plantar flexion (Achilles reflex) Gastrocnemius muscle

Answer 78

Tests L2→L4 Mediates leg extension Quadriceps muscle

Answer 79

Tests C5→C6 Mediates flexion of the elbow Biceps muscle

Answer 80

Tests C5→C6 Slight elbow flexion and wrist extension Brachioradialis muscle

Answer 81

Tests C7→C8 Mediates elbow extension Triceps muscle

Answer 82

* Located within the intermediolateral cell column at T1. * (Between C8→T2) * Contains preganglionic sympathetic neurons * Axons synapse on postganglionic neurons in superior cervical ganglion * Controls the dilator muscle of the pupillae

Answer 83

* Group of neurons in ventral horn at C3→C5 * Axons form phrenic nerves * Contracts diaphragm during inspiration

Answer 84

* In ventral horn from S1→S3 * Contains motor neurons that form pudendal nerve * Innervates striated muscles of rectum and external urethral sphincter * Involved in control of micturition and defecatory continence

Answer 85

* within intermediate zone between S2→S4 * contains preganglionic parasympathetic neurons * origin of pelvic splanchnic nerve * controls pelvic viscera

Answer 86

Malformation of the brain. * Type I * caused by herniation of cerebellar tonsils through foramen magnum * interfers with CSF circulation * associated with hydrocephalia and syringomyelia * some cases asymptomatic * symptoms include headache, weakness, paresthesias, loss of pain sensation especially in hands, imbalance

Answer 87

* results from compression of multiple lumbosacral nerve roots below level of conus medullaris * L3→L5 * S1→S5 * coccygeal roots * Symptoms * low back pain * sciatica * saddle sensory distrubances * bladder and bowel dysfunction * lower extremity motor and sensory losses

Answer 88

* aka hereditary motor and sensory neuropathy or peroneal muscular atropy * one of the most common inherited neurological disorders * involves demyelination and axonopathy * several types * symptoms * foot drop * muscle weakness * sensory losses

Answer 89

* spinal cord injury affecting lower sacral and occygeal spinal cord segments * symptoms * saddle anesthesia * loss of bladder control * rectal incontinence * impotence

Answer 90

* recessive X-linked form of muscular dystrophy * caused by defective gene for dystrophin * results in a progressive neuromuscular disorder * symptoms * muscle weakness * muscle wasting * muscle necrosis

Answer 91

* AR disease * defect in Frataxin gene on chromosome 9 * results in progressive degeneration of nerve tissue * predominantly affects spino-cerebellar pathways, DRG, LCST, and dorsal columns * symptoms * sensory ataxia * muscle weakness * hyporeflexia * loss of vibratory and proprioceptive sensation

Answer 92

* Autoimmune disorder affecting PNS * usually triggered by an infection * myelin of PNS damaged by attack * leads to conduction block * see muscle paralysis and polyneuropathy * life-threatening if respiratory muscles affected

Answer 93

* AR form of spinal muscular atrophy * appears after 18 m/o * wasting and weakness of muscles in arms and legs

Answer 94

* auto-immune disorder * Ab against presynaptic voltage-gated calcium channels at NMJ * results in decreased release of neurotransmitter at synapse * characterized by muscle weakness

Answer 95

* autoimmune neuromuscular disease * Ab against ACh receptors at postsynaptic NMJ * results in fluctuating muscle weakness and fatigability * detection using tensilong test (edrophonium) * treated with acetylcholinesterase inhibitors, immunosuppressants, and thymectomy

Answer 96

* temporary loss or depression of most spinal cord neuronal activity below the level of injury * includes loss of motor, sensory, reflex, and autonomic funciton * transient atoic or flaccid bladder may be present * can start within minutes of spinal cord injury * can last days or weeks * return of reflexes generally indicates end of spinal shock

Answer 97

* caused by tetanospasmin, neurotoxin by gram + clostridium tetani * enters body through an injury & penetrates nervous system at NMJ * tetanus toxin blocks release of inhibitory neurotransmitters * GABA and glycine * causes generalized contractions of agonist and antagonist muscles * symptoms * muscle spasms * risus sardonicus * lockjaw * opisthotonos

Answer 98

**Subacute Combined Degeneration** * Due to poor diet or malabsorption of Vit B₁₂ (pernicious anemia) * Produces **demyelination in dorsal and lateral funiculi and peripheral nerves** * Symptoms include: * muscle weaknes * diffuse paresthesias * loss of position and vibratory sense * ataxia * spacticity * bowel and bladder problems * elevated serum homocysteine and methylmalonic acid

Answer 99

* AR form of spinal muscular atrophy * caused by defect in gene coding for protein necessary for motor neuron survival * age of onset 0→6 m/o * produces LMN signs of lesion * problems feeding and swalling * 80% of deaths occurs within first 2 years