Nervous System

Function of the Nervous System

• Receive sensory information, interpret it, and send out appropriate commands to form a response

• Composed of neurons (functional unit of the nervous system)

Nervous System Endocrine System

Divisions of the Nervous System

• Central Nervous System (CNS) – processes, interprets and stores information, composed of the brain and spinal cord

• Peripheral Nervous System (PNS) – peripheral nerves that carry signals to and from the CNS

Divisions of the Nervous System

Structure of a Neuron

Schwann Cells and Myelin

• Schwann cells are supporting cells that produce myelin (lipid insulator)

Types of Neurons

Three Types of Neurons

• Sensory Neurons – Convey signals to the CNS from sensory receptors

• Interneurons – Located within the CNS, integrate data and then relay signals to other neurons

• Motor Neurons – Convey signals from the CNS to effector cells

Reflex Arc

Reflex Arc (Neural Circuit)

Stimulus (External or Internal)

Sensory Receptor Cell

(5 Types)

Interneuron (Brain and Spinal

Cord)

Motor Neuron (Efferent)

Sensory Neuron (Afferent)

Response (Behavior, Secretion)

Effector (Muscle, Gland)

The Synapse

The Synapse

• Site of communication between an axon (or synaptic) terminal of one neuron and another cell

• Transmission of information between neurons occurs across synapses

Molecular Mechanism of Synaptic Function

How Cone Snails Paralyze Fish

When Cone Snails Attack

Watch the following three videos on synaptic function:

What do you already know about action potentials?

Nerve Impulse Animation

Watch the following video:

Membrane Potential

• Neurons, like most cells, have an electrical charge difference (membrane potential)

Resting Potential • At rest, the membrane potential is -70mV

(resting potential) - maintained by the Na+/K+ pump

• At rest, the neuron is said to be “polarized”

Threshold (“All or None”) • A neuron remains at rest until it receives a

stimulus strong enough for the membrane to reach a voltage of ~ -55 mV (threshold)

Action Potential (Nerve Impulse)

• An action potential is the rapid reversal of electrical charge of the neuron membrane (depolarized)

Steps of an Action Potential

1. Stimulus causes Na+ gated ion channels to open and Na + rushes into the cell (initiation of action potential and depolarization)

Steps of an Action Potential 2. As Na + gated channels close, K + gated

channels open allowing K + to rush out of the cell (repolarization)

Steps of an Action Potential

3. Na + /K + pump restores resting potential by pumping Na + ions back out of the neuron and K + ions into the neuron (refractory period)

How Nerves Work Animation

Crossing the Divide: Neurotransmitters and the

Synapse

Watch the following two videos:

Release of Neurotransmitters

• As the action potential reaches the axon terminal, it causes Ca2+ gated channels to open allowing Ca2+ ions to rush into the cell

• Causes synaptic vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft

Release of Neurotransmitters

• Neurotransmitters (ligand):

– bind to receptors on the postsynaptic cell

– cause ion channels to open

– Initiate an action potential by changing the membrane potential (depolarization

• Esterases: enzymes that breaks down and recycles neurotransmitters in the synaptic cleft

Neurotransmitters

• Chemical messengers that transmit nerve impulses (or action potentials) across the synapse

• Neurotransmitters can be stimulatory (excitatory) or inhibitory

Neurotransmitters

Stimulatory Inhibitory

Acetylcholine

Epinephrine GABA

Serotonin

Acetylcholine

• Stimulatory neurotransmitter released at the neuromuscular junction

GABA

• Inhibitory neurotransmitter released between neurons

• Motor control, vision, regulates anxiety

A little bit more about the nervous system…..

Evolution of Nervous Systems

Brain Evolution in Vertebrates

Vertebrate Brain