Nervous Systems

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Insect (arthropod)

Segmental

ganglia

Ventral

nerve cord

Brain

Anterior

nerve ring

Longitudinal

nerve cords

Chiton (mollusc)

Ganglia

Slide 10

Annelids and arthropods have segmentally arranged clusters of neurons called ganglia.

Nervous system organization usually correlates with lifestyle.

Sessile molluscs (e.g., clams and chitons) have simple systems, whereas more complex molluscs (e.g., octopuses and squids) have more sophisticated systems.

Slide 11

Squid (mollusc)

Ganglia

Brain

Brain

Spinal

Cord

dorsal

nerve

cord

Sensory

ganglia

Salamander (vertebrate)

Slide 12

In vertebrates

The CNS is composed of the brain and spinal cord.

The peripheral nervous system (PNS) is composed of nerves and ganglia.

Slide 13

Organization of the Vertebrate Nervous System

The spinal cord conveys information from the brain to the PNS.

The spinal cord also produces reflexes independently of the brain.

A reflex is the body’s automatic response to a stimulus.

For example, a doctor uses a mallet to trigger a knee-jerk reflex.

Slide 14

knee-jerk Reflex

White

matter

Cell body of

sensory neuron in

dorsal root

ganglion

Spinal cord

(cross section)

Gray

matter

Hamstring

muscle

Quadriceps

muscle

Sensory neuron

Motor neuron

Interneuron

Slide 15

Invertebrates usually have a ventral nerve cord while vertebrates have a dorsal spinal cord.

The spinal cord and brain develop from the embryonic nerve cord.

Slide 16

Vertebrate Nervous System

Peripheral nervous

system (PNS)

Cranial

nerves

Brain

Central nervous

system (CNS)

Ganglia

outside

CNS

Spinal

nerves

Spinal cord

Slide 17

Ventricles, gray matter, and white matter

White

matter

Ventricles

Gray matter

Slide 18

The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid.

The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord.