The CNS & Spinal Cord

Question 1

Spinal Cord

Answer 1

• cylindrical cable of pathway to & from brain and rest of body
• extends from base of skull (medulla) to L(1-2 - between the vertebrae)
• has cervical (brachial plexus) & lumbar (lumbosacral plexus) enlargements
• meninges cover it like the brain (identical)
• central canal continuous with ventricles of the brain
• organized into inner gray & outer white matter (opposite to brain)
• Dorsal & Ventral roots join up to form a SPINAL nerve (mixed)

Question 2

Dorsal Horns & Roots

Answer 2

posterior, sensory input

Question 3

Ventral Horns & Roots

Answer 3

anterior, motor output

Question 4

Lateral Horn

Answer 4

protrusion = sympathetic

• pre-ganglionic nerve cell bodies
• enlargement due to appendages
• normally about diameter of little finger

Question 5

Parts of the Spinal Tract

Answer 5

Medulla Oblongata –> L1-L2 Conus Medullaris –> Cauda Equina –> Filum Terminale

Question 6

Conus Medullaris

Answer 6

Spinal nerves extending directly from the end of the spinal cord

Question 7

Cauda Equina

Answer 7

part of the spinal tract between the conus medullaris and the filum terminale

Question 8

Sensory & Motor Pathways

Answer 8

• communication between CNS, PNS, and peripheral organ systems
• involves ascending and descending pathways - relay sensory and motor information between the periphery & higher centres
• ascending = sensory, descending = motor
• each pathway consists of a chain of neurons and associated nuclei or ganglia
• the number of neurons and synapses (inter-neuronal connections) vary from one pathway to another

Question 9

Pathway Nomenclature

Answer 9

pathways are names according to their site or origin and destination

Question 10

Somatic Sensory Pathways (3)

Answer 10

1. Dorsal Column/Medial Lemniscal Pathway
2. Spinothalamic (anterolateral) Pathway
3. Spinocerebellar Pathway

Question 11

Dorsal column/medial lemniscal Pathway

Answer 11

somatic sensory pathway
two names - depends on location (dorsal column within spinal column, medial lemniscal within brain stem)
- joint position & vibration sense (proprioception) & discriminative touch (3D + fine touch), stereogenesis & graphethesia (can build mental images of structures we touch - not all parts of body have the same ability to do this)

Question 12

Discriminative Touch

Answer 12

ability to discriminate 2 points of contact (before no longer able to separate them)

Question 13

Proprioception

Answer 13

awareness of position of body in space

Question 14

Spinothalamic (anterolateral) Pathway

Answer 14

somatic sensory pathway

• pain, temperature & crude touch
• unable to describe structure

Question 15

Spinocerebellar Pathway

Answer 15

somatic sensory pathway

- unconscious proprioception

Question 16

Dorsal Columns (2)

Answer 16

1. Fasciculus Cuntaneous

2. Fasciculus Gracilis

Question 17

Function of the Dorsal Columns

Answer 17

• conveys perception & discriminant touch + stereogenesis (3D recognition of objects) from trunk and extremities

Question 18

Fasciculus Gracilis

Answer 18

info from the lower extremities and lower trunk (more medial - longer)

Question 19

Fasciculus Cutaneous

Answer 19

info from the upper extremities and upper trunk (more lateral)

Question 20

Pathway of the Dorsal Columns

Answer 20

• 1st order neuron from skin/joint receptor –> medulla (same side) (fasciculus gracilis and cutaneous)
• 2nd order neuron from medulla –> crosses to opposite side –> ascends as the medial lemniscus –> thalamus
• 3rd order neuron from thalamus –> primary sensory cortex (thalamocortical projections)

Question 21

Anterior Spinothalamic Tract

Answer 21

crude touch (non-discriminant)

• 1st synapse in posterior (dorsal) horn, then passes contralateral to ventral horn –> up anterior spinothalamic tract
• 2nd synapse at ventral nuclei of thalamus

Question 22

Dorsal Columns Pathway

Answer 22

• 1st neuron travels in dorsal horn and up dorsal column to medulla (1st synapse) –> passes contralateral to medial lemniscus –> 2nd synapse at ventral nuclei of thalamus

Question 23

Lateral Spinothalamic Tract

Answer 23

pain and temperature (often linked)
- 1st synapse in dorsal horn –> crosses contralateral up lateral spinothalamic tract –> 2nd synapse at ventral neuclei of thalamus

Question 24

Spinocerebellar Pathway

Answer 24

unconscious proprioception (tone of muscles & stress of tendons)

• *synapses ipsilaterally and contralaterally
• posterior (ipsilateral) tract and anterior (contralateral) tract
• 1st synapse for both is in the dorsal horn –> travels to cerebellum (regulates posture)

Question 25

Upper Motor Neuron (UMN)

Answer 25

cell body in CNS processing centres of a somatic motor pathway

Question 26

Lower Motor Neuron (LMN)

Answer 26

cell body in ventral horn of spinal cord or motor cranial nerve nucleus in brainstem of a somatic motor pathway

Question 27

Motor Systems

Answer 27

- CNS issues motor commands - commands are distributed to the body by the PNS - somatic motor commands effect contraction of skeletal muscle (conscious) - always involve at least 2 motor neurons: UMN & LMN

Question 28

Modulation of the LMN by UMN

Answer 28

UMN --excitatory/inhibitory synapse--> LMN | CNS --brainstem/spinal cord--> periphery

Question 29

UMN Lesion

Answer 29

in most cases, causes UMN to only synapse in an inhibitory way - leads to dis-inhibition --> SPASTIC PARALYSIS

Question 30

LMN Lesion

Answer 30

UMN produces excitatory or inhibitory synapse but no response by LMN - leads to flaccid paralysis (no muscle tone)

Question 31

Common Final Pathway

Answer 31

LMN, the only axon to extend to the skeletal muscle for motor contraction

Question 32

Pathways of Motor Systems (2)

Answer 32

1. Corticospinal (pyramidal) pathway | 2. Corticonuclear (corticobulbar) pathway

Question 33

Corticospinal Pathway

Answer 33

Aka Pyramidal Pathway - UMNs extend from the cerebral cortex (cortico) to the spinal cord (spinal) - regulate distal musculature in limbs & trunk - convergences from motor & sensory cortex --> internal capsule --> CRUS CEREBRI in midbrain --> pyramids in medulla --> decussation of the pyramids --> synapses 85% to lateral LMN & 15% to anterior LMN

Question 34

Corticonuclear Pathway

Answer 34

Aka Corticobulbar Pathway - UMNs extend from the cerebral cortex (cortico) to motor cranial nerve nuclei in the brainstem (Nuclear (bulbar)) - regulate muscles of the head & neck

Question 35

Extrapyramidal Pathways

Answer 35

subsidiary descending pathways important as back-up systems

Question 36

Basal Nuclei and Cerebellum

Answer 36

modulate and modify activity in the corticospinal tract to ensure smooth, coordinated, purposeful movement

Question 37

Central Motor Program

Answer 37

1. Identification and localization of targets in space --> posterior parietal cortex 2. Formation of a plan of action --> premotor cortex & supplementary motor cortex

Question 38

Primary Motor Cortex

Answer 38

receives info from cortex (central motor program), conveys motor commands by descending motor pathways (execution of the movement)

Question 39

Simple Finger Flexion (Performance)

Answer 39

involves motor cortex and somatic sensory cortex

Question 40

Finger Movement Sequence (Performance)

Answer 40

involves premotor area & supplementary motor area of cortex + motor cortex

Question 41

Finger Movement Sequence (Mental Rehearsal)

Answer 41

involves premotor & supplementary motor area ONLY

Question 42

Origins of the Corticospinal Pathway

Answer 42

1/3 Primary Motor Cortex 1/3 Premotor + Supplementary Motor Cortex 1/3 Primary Sensory Cortex

Question 43

LMN Injury

Answer 43

spinal nerve injury

Question 44

UMN Injuries

Answer 44

- Middle Cerebral Artery Stroke - Internal Capsule lesion - Brainstem Lesion (above red nucleus = decorticate & spastic, below red nucleus = decerebret & flaccid) - spinal cord injury