General Neuroanatomy & Neuronal Regeneration

Question 1

The spinal cord at which vertebral levels has lateral horns? What is located here?

Answer 1

• from T1 - L2/L3
• the cell bodies of the preganglionic sympathetic fibers are located in these lateral/intermediate horns
• sympathetic innervation above T1 (ie, for neck and head) arises from the T1/T2 ganglia (they then ascend)

Question 2

Name the major ascending and descending tracts of the spinal cord.

Answer 2

• ascending (afferent, sensory): dorsal column tract, lateral and anterior spinothalamic tracts, dorsal and anterior spinocerebellar tracts
• descending (efferent, somatic): lateral and anterior corticospinal tracts, rubrospinal tract, tectospinal tract, vestibulospinal tract, reticulospinal tract, septomarginal and interfascicular fasciculi (these are descending tracts found within the ascending dorsal column tract)

Question 3

What is the thalamus? What are the five major nuclei that are found here? What info does each nucleus deal with?

Answer 3

• the thalamus is the major relay for all ascending sensory information EXCEPT for olfaction; it is part of the forebrain, located near the center of the brain, and has fibers projecting out to the cerebral cortex in all directions
• VPL (ventral posterolateral nucleus): pain, temperature, pressure, touch, vibration, proprioception
• VPM (ventral postermedial nucleus): facial sensation, taste
• LGN (lateral geniculate nucleus): vision
• MGN (medial geniculate nucleus): hearing
• VL (ventral lateral nucleus): motor

Question 4

What is the limbic system? What structures are a part of it? What actions/roles is the limbic system responsible for?

Answer 4

• the limbic system is a collection of neural structures involved in emotion, long-term memory, olfaction, behavior modulation, and autonomic function
• structures: hippocampus, amygdala, fornix, mammillary bodies, cingulate gyrus
• responsible for the “Famous Five F’s”: feeding, fleeing, fighting, feeling, and fucking (sex)

Question 5

What are the two parts of the forebrain? What does each contain?

Answer 5

• telencephalon: cerebral cortex, basal ganglia, hippocampus, amygdala, lateral ventricles
• diencephalon: thalamus and hypothalamus, 3rd ventricle
• (note that the forebrain is also called the prosencephalon)

Question 6

What makes up the midbrain?

Answer 6

• mesencephalon: tectum, tegmentum, cerebral peduncles, cerebral aqueduct

Question 7

What are the two parts that make up the hindbrain? What does each contain?

Answer 7

• metencephalon: pons and cerebellum, upper part of 4th ventricle
• myelencephalon: contains the medulla, lower part of 4th ventricle
• (note that the hindbrain is also called the rhombencephalon)

Question 8

What’s the difference between spinal roots and spinal rami?

Answer 8

• the ventral (motor) and dorsal (sensory) spinal roots merge to form the spinal trunk, from which emerge (from the intervertebral foramina) the dorsal and ventral rami (these contain MIXED fibers!)
• the dorsal ramus carries motor and sensory fibers to/from the posterior, while the ventral ramus carries motor and sensory fiber to/from the anterior
• note that the ventral ramus is thicker than the dorsal ramus

Question 9

Generally speaking, how many white columns are found on each half of the spinal cord?

Answer 9

• generally speaking, 3: dorsal, lateral, and ventral

- dorsal is strictly ascending, while lateral and ventral are ascending and descending

Question 10

What are the basic general functions of each cerebral lobe?

Answer 10

• frontal: consciousness, motor control
• parietal: sensory, speech, taste, reading
• temporal: hearing, swallowing, auditory
• occipital: visual

Question 11

At what spinal segment does the spinal cord terminate? At what segment does the subarachnoid space end?

Answer 11

• (at birth it ends at L3)
• in an adult, the spinal cord ends at L1/L2
• the SAS ends at S2

Question 12

How many pairs of spinal nerves do we have?

Answer 12

• 31 pairs

- 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal

Question 13

How many laminae zones are there in the spinal cord grey matter?

Answer 13

• 10 laminae
• laminae I - III are in the dorsal horn; they make up the substantia gelatinosa (2nd order neurons for nociception/pain)
• laminae IX is in the ventral horn; neurons here innervate skeletal muscle

Question 14

Are spinal and cranial nerves part of the CNS or the PNS?

Answer 14

• they are a part of the PNS!
• EXCEPT, CN II (optic) is technically part of the CNS (it is myelinated by oligodendrocytes and is surrounded by the meninges)
• (CN I is also part of the CNS - it does it’s own thing)

Question 15

What embryonic layer does the nervous system develop from?

Answer 15

• the ectoderm (forms the skin and nervous system)
• (mesoderm forms skeletal, muscular, and connective tissues; forms the microglia of the nervous system)
• (endoderm forms the alimentary, respiratory, and genitourinary tracts)

Question 16

What are neural crests? What do they develop into?

Answer 16

• neural crests are groups of cells that lie dorsolaterally to the neural tube
• they develop into the sensory ganglia of the spinal and cranial nerves, as well as into the autonomic ganglia (they basically form the PNS and Schwann cells)

Question 17

What embryonic structure develops into the dorsal horn of the spinal cord? What about the ventral horn?

Answer 17

• alar plate (dorsal plate) becomes the dorsal horn

- basal plate (ventral plate) becomes the ventral horn

Question 18

What has developed by the 5th week of embryonic development? By the 7th week?

Answer 18

• by 5th week: the 3 primary brain vesicles are formed (prosencephalon, mesencephalon, and rhombencephalon)
• by 7th week: the 5 secondary brain vesicles are formed (telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon)

Question 19

What is the corpus callosum?

Answer 19

• corpus callosum is the bundle of commissural fibers that link corresponding regions of the 2 cerebral hemispheres

Question 20

What basic functions are controlled by the brainstem?

Answer 20

• breathing, blood circulation, and consciousness

Question 21

What’s the difference between tracts, commissural fibers, and association fibers?

Answer 21

• tracts ascend up and down
• commissural fibers move left and right, linking related centers on opposite hemispheres
• association fibers move forward and backward, linking centers on the same hemisphere

Question 22

What general higher functions are associated with each cerebral lobe?

Answer 22

• frontal: executive function
• parietal: praxis
• temporal: memory
• occipital: perceptual and spatial function
• language involves an area made up by the inferior parietal lobe and superior temporal lobe

Question 23

What is the basic role of the basal ganglia? What about of the cerebellum?

Answer 23

• basal ganglia: facilitation of appropriate movement and inhibition of unwanted movement
• cerebellum: generated movement is compared with sensory feedback for accurate and coordinated movements

Question 24

Is damage to a neuron’s dendrites repairable? How about to a neuron’s axon? A neuron’s cell body?

Answer 24

• dendrites: usually repairable
• axon: can be slowly regrown in the PNS (not in the CNS because of its environment)
• cell body: irreparable (neuons are post-mitotic cells)

Question 25

What happens in axonal damage?

Answer 25

• the portion distal to the injury undergoes Wallerian degeneration
• the portion proximal to the injury also degenerates, but only up to the next node of Ranvier
• regeneration of the nerve will then be attempted

Question 26

What is axon guidance?

Answer 26

• this is how the regenerating nerve knows where to go (to make sure it innervates the proper structure)
• tissues along the growth pathway release repellent and adhesive cues to the growth cone (the filodopia; the regenerating axon)

Question 27

Give some examples of guidance cues and repellent cues

Answer 27

• guidance: CAMs, the ECM, NTs, growth factors, etc.

- repellant: slits and ephrins, chondroitin sulphate proteoglycans

Question 28

What is the approximate rate of neuronal regeneration?

Answer 28

• about 1 mm/day

Question 29

Why does axonal regeneration not occur in the CNS?

Answer 29

• because the astrocytes here release inhibitory growth factors and because gliosis occurs following an injury, creating a physical “road-blocking” scar

Question 30

Neural crests develop into what part of the nervous system? What about the walls of the neural tube? What about the lumen of the neural tube? What are developmental defects of the neural tube associated with?

Answer 30

• neural crests: PNS and Schwann cells
• wall of neural tube: CNS, ependymal cells, oligodendrocytes, astrocytes (remember, microglia are formed by the mesoderm)
• lumen of neural tube: ventricular system
• (developmental defects in these structures is associated with low folate levels; these result in elevated alpha-fetoprotein and acetylcholinesterase in the amniotic fluid)

Question 31

What is anencephaly? What results from this disorder?

Answer 31

• anencephaly is the absence of the brain and skull due to failure of the rostral end of the neural tube to close; associated with type I maternal diabetes
• the fetus’ eyes are relatively prominent as a result, giving a characteristic “frog-like” appearance
• additionally, polyhydramnios will result because of the inability of the fetus to swallow the amniotic fluid

Question 32

What is spina bifida? What are the possible variations/presentations of this disorder

Answer 32

• spina bifida results from the failure of the caudal end of the neural tube to close
• can result in a simple dimple (or patch of hair) overlying the defect (spina bifida occulta) OR
• can result in herniation of the meninges (meningocele) or of the meninges and the spinal cord itself (meningomyelocele)