### body part:

Spine
* More spines form when a neuron receives insufficient levels of activation.
* Most spines are connected by membranes
  - part of endoskeletons
  - facilitate dispersals
* Most spines grow out of spinal vertebrae
* Most spines have bases
  - shapes
  - vascular tissue
* Most spines protect bellies
  - urchins
* Some spines are located in sharks
  - consist of keratin
* Some spines deter animals
  - graze animals
* Some spines emerge from dorsal surfaces
* Some spines have grooves
  - sides
  - inflict injuries
  - move from sides
* Some spines penetrate human skin
  - pierce flesh
  - provide protection
* also come in handy for burrowing and trapping food
  - help to reduce heat load, and dissipate heat
* are able to swivel towards a predator because they are connected to muscles
* are found along the edges of leaves near the base and at the tips of some of the lobes
  - in a wide range of animals both vertebrate and invertebrate
  - included in the shark anatomy as a form of protection
  - modified leaves, and thorns are modified stems
* are part of backs
  - bodies
  - books
  - human bodies
  - poisonous and cause severe nettling when brought in contact with skin
  - present on juvenile leaves, however, they are lost when the plant matures
  - specialized structures at synapses
  - the first line of physical defense for a sea urchin
  - used for protection against predators and for communication
  - where important connections between neurons are made
* become needles for sewing, or interesting pieces in the creation of jewelery.
* can be soft or rigid, straight or curved, arranged in rows or scattered
  - move in a wide range of directions by contraction of muscles
* cause painful stinging if they penetrate human skin.
* cover backs.
* cut horizontally through the caudal aspect of the fifth cervical vertebral body.
* form intercellular bridges.
* further keep grazing herbivores from nibbling the heads from above.
* grow in clusters out of small lumps or mounds, called areoles, on the stem.
* grow on the stem in clusters called areoles
* harden soon after birth.
  - the added advantage of making the organism harder to eat
  - to be as important as teeth
* help to protect it from predators
  - reflect light away from the cactus stem theoretically lowering the stem temperature
* includes bone cells
  - marrow
  - mast cells
  - tail bones
* make an effective barrier and plants produce loads of healthy orange hips in fall.
* produce puncture wounds and can stay in skin
* protect a hedgehog from predators and also cushion the animal if it falls out of a tree
* protect the plant from animals, shade it from the sun and also collect moisture
  - the plant from the sun and also collect moisture
  - vertebral column
* serve functions
  - important functions
* skeletal structure
* undergo morphological changes in vivo.
* usually produce puncture wounds.

### body part | spine:

Cactus spine
* Most cactus spines occur in clusters and some have spines modified as coarse hair.
* are structural adaptations that provide shade and protection from herbivores.
* come in a wide variety of lengths, widths, textures, and stiffnesses.
* keep the plant safe.

Dendritic spine
* are ephemeral structures and are continually being formed and removed
  - the site of most excitatory synaptic input in the brain
* assume very different shapes.

Dorsal spine
* Some dorsal spines penetrate human skin
* are present when the host leaf is hairy and absent when the host leaf is smooth.

Lateral spine
* Most lateral spines have tissue
* have no vascular tissue