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

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