Introduction to Vertebrate Nervous Systems Chapter 48

Functions of NS Receiving information from environment Integrating information received from environment Motor output in response

Neuron Structure

Neurons have different shapes for different jobs

Vertebrate NS Structure Central Nervous System: brain and spinal cord Peripheral Nervous System: peripheral nerves

Nervous Conduction All cells have a voltage potential across their membranes Changes in this potential give rise to nervous signaling

Resting Potential Inside the neuron is more negative than the outside Ion channels allow only some ions to cross the membrane

Action Potential 1. At rest, there is more K+ inside and more Na+ outside. Both ions’ channels are closed. Membrane potential: -70mV 2. A stimulus causes the threshold potential to be reached, so sodium channels open and sodium ions flow in and cause more Na+ channels to open. MP: -50mV

Action Potential 3. During depolarization, the Na+ channels are open, but the K+ channels are closed. Cell interior becomes more positive due to Na+ ion influx. MP: +35mV 4. During repolarization, Na+ channels close and K+ channels open, causing K+ to exit. The inside of the cell is more negative than the outside. MP: <+35mV

Depolarization and Repolarization: what it looks like http://www.tvdsb.on.ca/westmin/science/sbioac/homeo/action.htm

Action Potential 5. As the membrane potential heads back toward resting, the K+ channels have not had a chance to close. The membrane is hyperpolarized and membrane potential dips slightly below -70mV: undershoot 6. Eventually, ion concentrations return to normal and resting potential is restored. MP: -70mV

Membrane Potential

Principles of Neural Firing When a nerve fires, it does not fire “halfway” when stimulated It will fire completely once a stimulus is received and threshold potential is reached: “all or nothing” principle No threshold, no action potential

Saltatory Conduction Axons are myelinated--increases nervous signal conduction speed by making signal jump between Schwann cells.

Chemical Communication Occurs at synapses: gaps between neurons Uses neurotransmitters: substances released from vesicles when action potential reaches end of pre-synaptic axon

Synaptic transmission 1. An AP depolarizes the synaptic terminal membrane and Ca+2 ions rush in. 2. Synaptic vesicles with neurotransmitter fuse with presynaptic membrane. 3. Vesicles fuse with membrane, releasing neurotransmitter into cleft.

Synaptic transmission 4. Neurotransmitter binds to receptors on post-synaptic membrane, which gets depolarized. 5. Neurotransmitter is degraded by enzymes or taken up by another neuron. This prevents the synaptic response from persisting.

Synaptic transmission

Divisions of the NS Somatic NS Autonomic NS Controls the voluntary actions an organism does Example: voluntary muscle movements Autonomic NS Controls involuntary actions in an organism Example: control of heartbeat, breathing, GI tract

Divisions of the autonomic NS Sympathetic NS Activation is correlated to arousal and energy generation Examples: heart beat increases, liver converts glycogen glucose Parasympathetic NS Activation is correlated to calming actions Opposite actions of SNS

Brain structures Cerebrum: conscious thought Cerebellum: motor coordination Medulla oblongata: involuntary functions Meninges: tough protective membranes

Brain structures Corpus callosum: connects left and right hemispheres Thalamus: relay center for messages Hypothalamus: controls 4F’s: feeding, fleeing, fighting, flirting

Regions of the Brain Frontal Lobe: personality, control of voluntary muscle movements, thoughts words

Regions of the Brain Parietal Lobe: interpretation of textures, understanding symbols, verbal articulation of thoughts words

Regions of the Brain Occiptal Lobe: organizes sight, conscious seeing

Regions of the Brain Temporal Lobe: speech, olfaction, interpretation of auditory sensations, emotional behavior