Types of Nervous Systems

Types of Nervous Systems

Cephalization

• The concentration of neurons in a brain located in the head.– Bilateral symmetry– Allows for a concentration of sensory organs in the

head.– Flatworms—simple brain and 2 nerve cords

Vertebrate Nervous System

• Central nervous system (CNS)– Brain – Dorsal nerve cord

• Peripheral nervous system (PNS)– Nerves-– Ganglia-clusters of

nerve cells

Information pathway

Vertebrate Nerve cells

• Neuron-Functional cell • Glia-Supporting cell– Astrocytes-CNS, maintain

blood/brain barrier– Oligodendrocytes-

insulation in CNS– Schwann cells-insulation

in PNS

Anatomy of a Neuron•Cell body~ nucleus and organelles•Dendrites~ impulses from tips to neuron•Axons~ impulses toward tips•Myelin sheath~ supporting, insulating layer made of schwann cells•Synaptic terminals~ neurotransmitter releaser•Synapse~ neuron junction

Reflex Arc

Membrane Potentials• Membrane potential (voltage differences across the plasma membrane)• Intracellular/extracellular ionic concentration difference• K+ diffuses out (Na+ in); large anions cannot follow….selective permeability

of the plasma membrane• Net negative charge of about -70mV

Resting Potential• Nontransmitting neuron• -60 to -80 mV• Na+ and K+diffuse down concentration gradient• Neurons at rest are more permeable to K+ and less permeable to Na+-more

ungated ion channels open

Action potentials• Signals conducted by neurons• Gated channels-open and close in response to stimuli– Na+ and K+ voltage gated channels control action

potential– Depolarization (inside of the cell becomes less negative)

opens Na+ gated channels– Opening of K+ gates causes hyperpolarization (inside of

cell becomes more negative)

Conduction of Action Potentials

• Na+ influx in rising spase depolarizes adjacent section of the membrane, bringing them to threshold.

Speed of Action Potentials• Axon diameter (larger = faster; 100m/sec)• Nodes of Ranvier (concentration of ion channels);

saltatory conduction; 150m/sec

Synaptic communication

• Presynaptic cell: transmitting cell• Postsynaptic cell: receiving cell• Synaptic cleft: separation gap• Synaptic vesicles: neurotransmitter

releasers• Ca+ influx: caused by action potential;

vesicles fuse with presynaptic membrane and release….

• Neurotransmitter

Vertebrate PNS

The Vertebrate Brain• Forebrain– cerebrum~memory, learning,

emotion– cerebral cortex~sensory and

motor nerve cell bodies – corpus callosum~connects left and

right hemispheres – thalamus; hypothalamus

• Midbrain – inferior (auditory) and superior

(visual) colliculi• Hindbrain

– cerebellum~coordination of movement

– medulla oblongata/ pons~autonomic, homeostatic functions