Anatomy/Histology Session Oct. 20
Spectrum Access: http://diagnostics.vetmed.ucalgary.ca
TIPS TO INTERPRET MUSCLE CROSS-SECTIONS
Look for bone landmarks  hind limb vs front limb  medial vs. lateral  cranial vs caudal (red = front + blue = hind)
o Ulna lateral + caudal to radius
o Olecranon of ulna easy to recognize
o Accessory carpal bone lateral
o Head of femur easy to recognize
o Patella cranial to femur and tibia (may see patellar ligaments as well)
o Fibula lateral to tibia
o Calcaneus lateral
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Look for distinct muscle groups
o Flexor foursome  3 heads of deep digital flexor (radial, humeral, ulnar) + superficial digital flexor caudally
o Quadriceps  vastus lateralis/medialis/intermedius + rectus femoris make a neat little bundle of four
o Gastroc sandwich  2 heads of gastroc with superficial digital flexor sandwiched in between
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Remember the general patterns of muscle location
o Extensors cranial + lateral (distal to elbow)
o Flexors caudal + medial (distal to elbow)
o Biceps femoris  long, flat muscle on lateral side of thigh
o Peroneus tertius  thick, fibrous band directly lateral to tibia in equine hind limb
o Tibialis cranialis + long digital extensor  always directly cranial to tibia
o Medial tibia has no muscle covering (just skin on bone) – very helpful to identify lateral vs medial
NEURO HISTOLOGY
Big Picture Concepts (BURN INTO YOUR BRAIN!)
Central nervous system (CNS) = brain + spinal cord
Peripheral nervous system (PNS) = everything else!
o Cranial nerves
o Spinal nerves (motor + sensory)
o Autonomic nervous system (parasympathetic + sympathetic)  more on this later…
Grey matter = cell bodies + glia
White matter = myelinated axons + glia
In CNS, cell bodies form collections called nuclei
In PNS, cell bodies form collections called ganglia
Nuclei + ganglia are collections of cell bodies of neurons with a similar function
1: Ventral horn (motor neuron cell bodies)
2: Dorsal horn (sensory neuron axons enter spinal cord + synapse on
interneurons – NO cell bodies)
3. Commissure (interneurons)
Note: nuclei are present in the grey matter of the spinal cord. Sensory =
blue, interneurons = green, motor = red. All the cell bodies within a
nucleus belong to neurons with a similar function.
4/5/6: White matter (myelinated axons of neurons)
8: Ventral sulcus (shows which side of spinal cord is ventral)
10: Central canal (contains cerebrospinal fluid (CSF) and is lined by
ependymal cells)
11: Efferent motor nerve (axons of motor neurons)
12: Afferent sensory nerve (axons of sensory neurons)
13: Dorsal root ganglion (cell bodies of sensory neurons + satellite cells)
3 Types of Cells in Nervous System
Working cells
o Neurons
Lining cells
o Ependymal cells
Supporting cells (glia)
o Satellite cells
o Oligodendrocytes (CNS) + Schwann cells (PNS)
o Astrocytes
o Microglia
How to Recognize Nervous System Cell Types
Microglia
Fxn: phagocytes in the brain (consume bacteria or debris
from dying neurons and glia)
Cannot see them in any of the Aperio slides
Astrocytes
Fxn: modulate neurotransmission, break down
neurotransmitters, regulate blood-brain-barrier using foot
processes lined up along brain capillaries
CNS (brain)
Star-shaped (stellate)
Usually located close to blood vessels
Oligodendrocytes
Fxn: fatty lipid cell membrane wraps around axons  forms
an insulation covering that increased speed of impulse
transmission along the length of the axon (Nodes of Ranvier)
CNS
Fried-egg appearance: pale cytoplasm surrounding a small,
dark, round nuclei
Schwann Cells
Same as oligodendrocytes, except in PNS
Ependymal cells
Fxn: produce CSF
CNS
Dark purple columnar cells lining the central canal of the spinal cord (also line the ventricles in the brain but you don’t see any
ventricles in the Aperio slides)
Neurons (appearance depends on transverse section or longitudinal section)
Neurons in brain: small, dark, round cell bodies. Oligodendrocytes right beside them.
Motor neurons in spinal cord: large, dark, elongated or diamond-shaped cell bodies in the ventral horn.
Sensory neurons in dorsal root ganglion: huge circular pale cell bodies surrounded by satellite cells.
Axons pretty much always look the same
o Transverse: small round pink/purple dots, surrounded by white space. Dots are axons, white space is myelin.
o Longitudinal: long, thin pink/purple strands, surround by segmented white space. Strands are axons, white spaces
are myelin.
Satellite Cells
Fxn: supply nutrients to the neurons, some structural fxn as protective/cushioning cells
PNS only (in peripheral ganglia)
Small, dark oval cells surrounding neuron cell bodies in peripheral ganglia
Slide 267/236 – brain (cortex or cerebellum - I’m not sure which one)
Astrocytes: star-shaped, often near capillaries
Neurons: round dark cell bodies
Oligodendrocytes beside neuron cell bodies
Opposite to spinal cord: in brain white matter is on the inside, gray matter on the outside. In this slide, white matter is the
darker material in the middle – fewer cell bodies, long strands (axons). Gray matter on the outside is lighter stained – lots of
cell bodies, no strands (axons).
Slide 295/264 – transverse section of spinal cord
Ventral sulcus on top so you know the spinal cord is upside down!
Dura + arachnoid + pia maters: connective tissue, contain blood vessels
Ventral spinal artery
Central canal lined with ependymal cells
Ventral horn gray matter: motor neuron cell bodies + small, round dark cells which are probably interneurons
Dorsal horn gray matter: no large cell bodies, a few interneurons
White matter: myelinated axons
Capillaries in white + gray matter (look like empty round spaces)
Slide 562/531 – transverse section of spinal cord + dorsal root ganglion
Same structures as above: dura/arachnoid/pia, ventral sulcus, central canal + ependymal cells, ventral horn + dorsal horn
Dorsal root ganglion
o Sensory neuron cell bodies
o Satellite cells
o Myelinated axons
Slide 288/257 – peripheral nerve
Endoneurium (surrounds individual axons)
Perineurium (surrounds clusters of axons)
Epineurium (surrounds entire nerve)
Myelin very obvious around axons
Lots of adipose tissue
No cell bodies!
Vasa nervosum = blood supply to nerve
Slide 549/518 – don’t worry about this slide. It looks scary, but it’s just the same stuff we saw in slide 288/257 above. We’ll take a quick
look at it during the review session.