Nervous System Physiology

3 functions of the nervous system 1) Sensory Input 2) Integration- decisions 3) Motor Output

Two types of Cells 1) Neuroglial Cells- “glial” cells 2) Neurons-stimulus conducting cells

Glial cells: Astrocytes

Glial Cell: Microglial

Glial Cell: Ependymal Cells

Glial Cells: Oligodendrocytes

Glial Cells: Schwann Cells

Neurons- transmit impulses Characteristics: 1) High longevity (  100 years) 2) amitotic-cell division 3) high metabolism / needs a lot of oxygen

Parts of a neuron

Parts of a Neuron 1) Dendrites  impulses to cell body 2) Cell Body – located in the CNS 3) Axon  impulses away from the cell body Direction of impulse-impulse travels from dendrite to cell body to axon

Types of Neurons Sensory (afferent) neuron – brings impulse from a receptor to CNS Motor (efferent) neuron- brings impulse from CNS to an effector Intergration (interneuron or association neuron) between sensory and motor in the CNS

Reflex Arc

Receptor- monitors stimuli Sensory neuron- transmits message to CNS Integration Neuron- makes a decision in the CNS Motor neuron- takes the message from the CNS to an effector Effector- a muscle or gland that responds

The impulse is Electochemical because of ion distribution A neuron that can conduct an impulse must be irritable Irritability is set up by the Na + / K+ pump A neuron that is not conducting is resting In a resting state there is a potential difference in charge between the inside of the membrane and the outside of the membrane The difference is negative ( about – 70 mV)

Na + (Sodium) ions are greater on the outside of the membrane K + (Potassium) ions are greater on the inside of the membrane The difference is maintained by the sodium/ potassium pump

Stimulation of the neuron: 1) Na gates open 2) Na rushes in 3) potential difference of the membrane changes from -70 mV to + 30 mV = depolarization

The K gates open and potassium leaves The potential difference goes from +30 mV back down to -70mV = repolarization

Depolarization + Repolarization = Action Potential

Before the Sodium/ Potassium Pump starts again to restore the resting potential hyperpolarization occurs

Conductivity- how an impulse leaves a neuron and stimulates another neuron, or a muscle, or a gland

Chemicals are released into the synapse and react with the post synaptic muscle, gland, or another neuron

Step 1 Calcium gates open in the synaptic axon terminal membrane and Calcium rushes in

Step 2 Calcium ions act as a messenger signaling the synaptic vesicles to fuse with the pre- synaptic membrane

Step 3 The vesicles empty the neurotransmitter into the synaptic cleft by exocytosis

Step 4 Neurotransmitter binds to post synaptic receptors

Step 5 Ion channels open and produce a change in the membrane potential

Step 6 Depending on the receptor protein to which the neurotransmitter binds – the post synaptic neuron may be excited or inhibited

Step 7 The neurotransmitter will degrade, diffuse away, or be removed by enzyme activity