Neurons and Neurotransmitters

RVS Chatianya KoppalaAssistant Professor Lovely Professional University

Nervous System

– Central nervous system (CNS):• Brain• Spinal cord

– Peripheral nervous system (PNS):• Sensory neurons• Motor neurons (somatic and

autonomic)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Central Nervous System (CNS)

Brain Spinal Cord

Peripheral Nervous System (PNS)

Sensory NeuronsMotor Neurons

Somatic Nervous System• voluntary movements via

skeletal muscles

Autonomic Nervous System• organs, smooth muscles

Sympathetic- “Fight-or-Flight” responses

Parasympathetic - maintenance

The Nervous SystemThe Nervous System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Divisions of the autonomic nervous system

The Nervous System• A physical organ system like any other

• 2 main kinds of cells – Neurons– Glia

Basic units of the nervous system Receive, integrate, and transmit information Operate through electrical impulses Communicate with other neurons through chemical signals More about neurons and neuronal anatomy later

Neurons

Glial cells

• 100 billion neurons• 10x more glial cells• Glial cells

– Support neurons (literally, provide physical support, as well as nutrients)

– Cover neurons with myelin– Clean up debris– “Housewives”

• Regulate external environment (ions, etc.)• Most abundant glial cell • May contribute to blood-brain barrier and to synapses

Astrocytes

Three main types of neurons

• Sensory Neurons

• Interneurons

• Motor Neurons

Sensory (Afferent) vs. Motor (Efferent)Sensory (Afferent) vs. Motor (Efferent)

e.g., skin

e.g., muscle

Gray’s Anatomy 38 1999

sensory (afferent) nerve

motor (efferent) nerve

Neurons that send signals from the senses, skin, muscles, and internal organs to the CNS

Neurons that transmit commands from the CNS to the muscles, glands, and organs

The Withdrawal Reflex

Neuron Anatomy and Neural Communication

Neurons

Axon of anotherneuron

Cell BodyDendrites

Axon

MyelinSheath

Dendrites of another neuron

Neural Anatomy Dendrite

the bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body

Axon the extension of a neuron, ending in

branching terminal fibers, through which messages are sent to other neurons or to muscles or glands

Neural Anatomy and communication

Synapse junction between the axon tip of the sending

neuron and the dendrite or cell body of the receiving neuron

tiny gap at this junction is called the synaptic gap or cleft

Synapse movie

Specific Parts: The NeuronStructure

Specific Parts: The Neuron Function

Neurons = 3 functions: Reception, Conduction, Transmission

1.3.

2.

Action Potential

When dendrites stimulated, the delicate balance is altered

Membrane breaks downPositively charged ions rush in

(depolarization)Charge = less negativeCauses release of chemicals from

terminal buttons

W. W. Norton

Relay Race

• Action Potential starts at dendrite– Through cell body– Down Axon– Axon Terminals

• How does it get to the next cell’s dendrites?

• Neurons don’t touch– Synapse = millionth inch gap– In synapse = vesicles w/ neurotransmitters

» Chemical messengers that transmit info

Communication

• Impulse releases neurotransmitter from vesicles

• Neurotransmitter enters synaptic gap

• Neurotransmitter binds to receptors on the receiving neuron

Myelin Sheath– Fatty material made by glial cells– Insulates the axon– Allows for rapid movement of

electrical impulses along axon– Nodes of Ranvier: gaps in myelin sheath

where action potentials are transmitted– Multiple sclerosis is a breakdown of

myelin sheath– Speed of neural impulse Ranges from 2 –

200+ mph

Myelinization clipMyelin conduction clip

Neurotransmitters

chemical messengers that traverse the synaptic gaps between neurons

when released by the sending neuron, neurotransmitters travel across the

synapse and bind to receptor sites on the receiving neuron, thereby influencing whether it will generate a neural impulse

Neurotransmitters (>60)• Acetylcholine (ACh)

– 1st substance identified as NT– Links motor neurons and muscles (contract or relax)

• e.g. curare vs black widow spider– Also involved in memory, learning, sleep, dreaming

(acetylcholine movie)• Endorphins (the brain’s own morphine)

– 1973 injected rats with morphine– Bound like NTs– Brain had receptors for exogenous substance?

• Brain must produce its own morphine• Released during pain and discomfort

More neurotransmitters Receptor binding movie

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