HMB320 > Lecture 3 Spinal Cord and Motor Systems > Flashcards

Lecture 3 Spinal Cord and Motor Systems Flashcards

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1
Q

What is the spinal cord function and where does it start and end?

A
  • Receives Sensory input
  • Carries motor output
  • Extends from the medulla to the second lumbar vertebrae (L2)
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2
Q

How many segments are in the spinal cord?

A
  • 31 segments
  • 31 pairs of mixed spinal nerves
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3
Q

How many bones does the vertebral column have?

A
  • 26 bones
  • 5 sacral and 4 coccygeal vertebrae which are fused together
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4
Q

What is the spinal canal?

A
  • Canal extends length of vertebral column
  • Houses spinal cord
  • Cord enclosed by the Body (ventral portion) and the Laminae (dorsal portion)
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5
Q

What are the intervertebral discs?

A
  • Discs positioned inbetween the vertebrae as shock absorbers for the vertebral column
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6
Q

What is the Intervertebral Foramina?

A

Openings between the vertebrae on either right or left side
- exit points for mixed spinal nerves leaving spinal cord
- Left and right spinal nerves exit on either side

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7
Q

What other interior protection exists for the spinal cord?

A
  • Cord protected by the meninges, similar to the brain
  • Fat filled epidural space, sits between the dura and periostium of the bone
  • EXISTS ONLY IN SPINAL CORD
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8
Q

Nerve roots exiting the spinal cord are ensheathed by what? This eventually fuses with the what?

A
  • Ensheathed by the meninges
  • Fuses with the Epineurium
    (outer layer of connective tissue of the spinal nerves)
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9
Q

What are the Denticulate Ligaments and how many are there?

A
  • Tooth like extensions of the PIA that anchor the spinal cord to the arachnoid and Dura
  • Stabilize spinal cord, NOT found in cranium meninges
  • 21 pairs of denticulate ligaments
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10
Q

How is the spinal cord organized?

A
  • Consists of two identical halves
  • Grey matter is butterfly interior
  • White matter surrounds grey matter
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11
Q

Of the grey matter core in the spinal cord, what are the divisions of neurons?

A
  • Dorsal horn = sensory neurons (secondary)
  • Ventral horn is motor neurons (lower motor neurons)
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12
Q

What are the three portions of white matter that surround the spinal cord? What is another name for the nerve bundles?

A
  • Dorsal, lateral, and ventral
  • Funiculus
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13
Q

What are the dorsal root ganglion?

A
  • group of cell bodies of sensory neurons that exist outside of the spinal cord
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14
Q

What is the sensory innervation that the spinal cord supplies to a specific area of skin?

A

Dermatome

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15
Q

What is the sensory innervation that the spinal cord supplies to a specific target muscle?

A

Myotome

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16
Q

What is the caudal tip of the spinal cord called?

A

The Conus Medullaris

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17
Q

What are the individual dorsal and ventral roots that exit in the lumbar and sacral region after the end of the spinal cord?

A

Cauda Equina “Horse Tail”

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18
Q

For Lower motor neurons, describe their position and function

A
  • ventral horn
  • send their axons out of the ventral roots
  • contributes to motor function at that level of the spinal cord
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19
Q

For Primary sensory neurons, describe their position and function

A
  • Cell bodies in dorsal root ganglia
  • axons travel through dorsal roots
  • Carrying somatic sensation from the region of the body
  • Synapse on to secondary neurons in the spinal cord
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20
Q

What is unique about the Lumbar 2 vertebrae of the spinal cord?

A
  • Subarachnoid space enlarged
  • forms Lumbar Cistern containing CSF
  • Surrounded by the meninges
  • Point for spinal tap procedure
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21
Q

What segments of the spinal cord contain sensory and motor neurons to the upper and lower limbs?

A
  • (upper) C3-T1
  • (Lower) L1-S3
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22
Q

What is unique about the areas of spinal cord that are responsible for the limbs?

A
  • Dorsal (sensory) and ventral (motor) horns are larger in these regions
  • higher neuronal density
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23
Q

What levels of the spinal cord has lateral horns in the grey matter?

A
  • T1 to L2
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24
Q

What do the lateral horns of the grey matter contain?

A
  • Preganglionic Sympathetic Neurons of the ANS
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25
Which region of the spinal cord has the smallest dorsal and ventral horns? Why?
- Thoracic region - The Torso has small sensory and motor innervation
26
How are neurons in the ventral horn organized?
- Somatotopic manner - the more lateral ventral horn is responsible for the distal muscles (forearm and hand) - The more medial ventral horn is responsible for axial muscles (shoulder near the chest) - The more Dorsal neurons innervate the Flexor muscles - The more ventral neurons innervate Extensor muscles
27
What does the motor pathway consist of?
- Upper Motor Neuron (UMN) - cell body higher up in the CNS (motor cortex or brainstem) PROJECTS TO... - Lower Motor Neuron (LMN) - cell body in the brain stem (for head) or Ventral horn (for body)
28
In the motor pathway which neuron decussates in the CNS?
The upper motor neurons decussate or cross over the the contralateral side
29
What is the function and composition of the lateral motor system of the descending motor pathway?
1. The lateral Motor System - Lateral corticospinal tract (dorsal portion) - Rubrospinal tract (ventral portion) - Projects to LMNs influences skilled voluntary movement of limbs
30
What is the function and composition of the medial motor system of the descending motor pathway?
2. Medial Motor System - Tectospinal tract (Most Ventral) - Vestibulospinal tract (Medial Ventral) - Reticulospinal Tract (more dorsal ventral) - Medial system projects mainly to the LMNs of the trunk, influences posture, balance, and stance
31
What is another name for the Lateral Corticospinal Tract?
- Pyramidal Tract
32
What are the percentages of the fibers that do and do not decussate? What percentage of the motor neurons making up the corticospinal tract are located in the primary motor cortex?
- 90% decussate (Form the Lateral Corticospinal tract) travel to contralateral side - 10% do not decussate (Form the Ventral Corticospinal Tract - 50% upper motor neurons in the cortex
33
Where is the Cerebral Peduncle located? What does it contain?
- Located in the Midbrain - Contains descending corticospinal fibers on the anterior surface of the midbrain
34
What are the Pyramids in the brain stem? What is Decussation of Pyramids?
- Descending corticospinal fibers form a bump on the anterior side of the medulla - Point at which the descending corticospinal fibers cross over to the controlateral sides
35
What is the organization of the corticospinal fibers in the Internal Capsule?
- Head (Anterior) - Arm (Medial) - Leg (Posterior)
36
What do the Corticorubral fibers do?
- Provide cortical motor imput to the red nucleus - Gives rise to the rubrospinal tract
37
What do the Corticofugal Fibers do
- Connect the cortex to subcortical structures
38
What do the Thalamocortical fibers do?
- Carry output from the thalamus to the cerebral cortex - Relay sensory information
39
Explain where the primary motor cortex is on the brain and how is it arranged?
- Precentral Gyrus - Motor Homunculus - Disproportionately large areas of cortex dedicated to hands and face - Top of the cortex is responsible for Feat and lower limbs - Bottom of the cortex responsible for face and upper limbs
40
Where does the Red Nucleus arise from? Why is it red?
- Rostral Midbrain - Iron containing pigment makes it red
41
Where does the red nucleus receive input and what does it control?
- Input from the motor cortex and cerebrellum - Controls proximal limbs (locomotion) and tone of flexor muscles - Become more vestigial as Lateral Corticospinal Tract assuming function
42
Where does the Rubrospinal Tract decussate?
- Fibers Decussate at the (Ventral Tegmental Decussation (MIDBRAIN) - Travel down the contralateral side of the spinal cord along side the Lateral Corticospinal Tract
43
Where does the tectospinal tract arise from? What does Tectum mean?
- Arises from the Superior Colliculus - Tectum = "Roof"' of the midbrain
44
What does the Tectospinal Tract control?
- Controls reflex movements of the head and eyes towards visual stimuli
45
Where does the Tectospinal Tract decussate?
- Decussation at Dorsal Tegmental Area - Travels down contralateral side of the spinal cord in the ventral Funiculus (white matter tract)
46
Where does the Vestibulospinal tract arise from? Where does it receive input from?
- Vestibular Nuclei of the Pons and the medulla - Input from the vestibular apparatus (ear) and Cerebellum
47
What does the Vestibulospinal tract control?
1. Anti-gravity extensor muscles of the leg and trunk (upright posture and balance (standing still)) 2. coordinate movements of head via innervation of neck muscles
48
Describe the fiber organization of the Vestibulospinal tract in the spinal cord.
- Some fibers run ipsilateral in Ventral Funiculus - Some Bilateral projections
49
Where does the Reticulospinal tract arise from? Where does it receive input?
- Arises from the Reticular Formation of the pons and medulla - Receives input from almost all areas of the brain - travels down ipsilaterally
50
What does the Reticulospinal tract control?
1. Anti-gravity extensor muslces of legs and trunk (Upright posture and locomotion (walking)) 2. Regulates ANS functions (HR, Breathing)
51
Describe the fiber organization of the Reticulospinal tract in the spinal cord
- Fibers remain ipsilateral - Run in Ventral Funiculus of the spinal cord
52
What do lower motor neurons in the ventral horn of the spinal cord innervate? How are lower motor neurons activated?
- Activate striated voluntary skeletal muscles - activated by upper motor neurons
53
What are the two types of skeletal muscle fibers?
- Extrafusal Muscle Fibers - Intrafusal Muscle Fibers
54
What are the Extrafusal Muscle Fibers composed of and what neuron innervates it?
- Large contrictile fibers - Innervated by Alpha Motor Neurons (Lower motor neuron)
55
What are the Intrafusal Muscle Fibers composed of and what neuron innervates it?
- Small Fibers hidden in the muscle - Gamma Motor Neurons (Lower motor neuron)
56
What is a Muscle Spindle and what does it detect?
- Group of intrafused fibers - Encapsulated Sensory organ - Detects stretch
57
What does the number of muscle spindles determine?
- Degree of fine control over contracting muscle
58
What is a reflex?
- Involuntary, stereotyped, graded motor response to a particular stimuli
59
Describe the Reflex neural circuitry
- Contained entirely in the spinal cord - Reflex Circuit (Arc) = connection of Afferent (sensory) to Efferent (Motor) output
60
What type of synapes are invoved in reflexs?
- Monosynapse (sensory to motor) - Polysynapse (having one or more interneurons)
61
Descending influences from what region can modulate the behavior of the spinal reflex circuits?
- Cortex and Brainstem (e.g. Reticulospinal Tracts)
62
What are muscle spindles responsible for?
- Monitor changes in muscle length - Important for coordination
63
Describe the neuronal reflex arc pathway
- Load or force applied - 1a Afferent Neurons (Sensory) stimulated - in turn activate Alpha motor neurons - Innervate Extrafusal contractile fibers - Produces additional contraction to maintain muscle tone and limb position
64
Aside from holding up a force/load, what else is the muscle stretch reflex pathway important for?
- Control of skeletal muscle tone - Posture - Activates Anti-gravity extensor muscles in the neck trunk and lower limbs
65
What is the purpose of the gamma motor neuron in Intrafusal fibers?
- Adjustment of sensitivity of the muscle spindles by maintaining constant tension on intrafusal fibers
66
What are the Golgi Tendon Organs and where are they located?
- Encapsulated sensory organs located at the Myotendinous Junction between muscle and bone - Intermingled with Collagen bundles
67
What happens in the Golgi Tendon Reflex?
- Muscle contraction squeezes sensory ending - Monitors muscle tension
68
What is the babinski reflex?
- Upper motor neuron lesion - toes fan out similar to babies when sole of the foot is stoked

HMB320 (12 decks)

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