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