Overview of the Nervous System in Animals

Sea sponges

Lack a true nervous system structure.

Jellyfish

Possess a nerve net, no brain.

Echinoderms

Have nerve cells bundled into fibers called nerves.

Flatworms

CNS with small brain and two nerve cords.

Insects

Complex decentralized nervous system with ganglia.

Octopi

Neurons in specialized lobes, similar eyes to vertebrates.

Vertebrates

Full CNS includes brain and spinal cord.

Neurons

Specialized cells for chemical and electrical signal transmission.

Dendrites

Tree-like structures that receive messages from neurons.

Synapses

Junctions where nerve cells communicate.

Axon hillock

Integrates signals and connects cell body to axon.

Glia cells

Support neurons, outnumber them 10 to 1.

Astrocytes

Type of glia that supports and nourishes neurons.

Microglial cells

Scavenge dead cells and protect from microorganisms.

Oligodendrocytes

Form myelin sheaths in CNS for multiple neurons.

Schwann cells

Provide myelin sheath for one PNS axon.

Blood-brain barrier

Restricts substances from entering the brain.

Resting membrane potential

Neuron at rest, negatively charged inside.

Sodium-Potassium pump

Uses ATP to maintain ion concentration gradients.

Action potential

Rapid reversal of resting membrane potential.

Nodes of Ranvier

Gaps in myelin sheath with voltage-gated channels.

Synaptic transmission

Process of transmitting signals across synapses.

Presynaptic neuron

Neuron sending the signal.

Postsynaptic neuron

Neuron receiving the signal.

Chemical synapse

Involves neurotransmitter release and receptor binding.

Meninges

Protective coverings of the brain and spinal cord.

Cerebral cortex

Outer layer of the brain, divided into hemispheres.

Autonomic nervous system

Controls involuntary bodily functions.

Parasympathetic nervous system

Governs restful bodily activities.

Sympathetic nervous system

Prepares body for stress or emergencies.

Sensory somatic nervous system

Transmits sensory information and directs voluntary movements.