Neuroanatomy

• Neuroanatomy refers to the study of the parts and function of neurons.• Neurons are individual nerve cells

that combine to create the body’s nervous system (communication system).

• Neural Communication

Types of Neurons

• There are three types of neurons:–Afferent Neurons (Sensory

Neurons)–Interneurons–Efferent Neurons (Motor Neurons)

•Afferent Neurons are responsible for taking information from the senses TO the brain.

• Interneurons are located in the spinal cord and the brain, and are primarily responsible for processing information.

•Efferent Neurons are responsible for taking information FROM the brain and the spinal cord back to the rest of the body.

• Most information travels from the body, up the spinal cord, is processed by the brain, sent back down the spinal cord, and then back to the body with behavior instructions. The exception to this general pathway is reflexes.

•Reflex behaviors are controlled by the spinal cord and brain stem without any conscious effort on behalf of the upper brain.

• Can you not kick your leg out when the patella nerve is struck?• Can you not contract your pupil

when a bright light is shined in your eyes?

Parts of a Neuron

• A. Dendrites–Thin, branching fibers attached to the

cell body that are lined with receptors from which the dendrite receives information from other neurons.

• B. Cell Body/Soma–Contains the (C) nucleus and other

parts of the cell needed to sustain life

C. Nucleus

• The function of the nucleus is to control the activities of the cell

• D. Axon–Wire-like structure ending in the

terminal buttons that extends from the cell body and carries messages towards the intended destination (neuron, muscle, gland, etc.)

• E. Myelin Sheath–An insulating, fatty covering around the axon

that speeds neural transmissions. Made of Schwann cells.–Axons that are myelinated appear white.

Known as “white matter.”

F. Schwann Cells

• Provide for the growth of the myelin sheath.

• G. Nodes of Ranvier– Regularly spaced gaps in the myelin sheath

around an axon or nerve fiber. This is where depolarization takes place.

• H. Terminal Buttons–The branched end of the axon that

contains neurotransmitters

• I. Synapse–The space between the terminal

buttons on one neuron and dendrites of the next neuron

• Neurotransmitters–Chemicals contained in the terminal buttons

that enable neurons to communicate. Neurotransmitters fit into receptor sites on the dendrites of neurons like a key fits into a lock.

Neural Transmission

• In its resting state (resting potential or polarization), a neuron is waiting for input. Housed in the neuron are positively charged potassium ions. Outside are positively charged sodium ions. They are kept separate by the cell walls of the neuron.

• A neuron has a pre-set level of stimulation that needs to be met or exceeded in order for it to pass the received impulses on to the next neuron. This is called a neuron’s threshold.

• If the threshold has been met or exceeded, a chain reaction begins.

• With threshold being met, the cell becomes depolarized. The cells walls open at the nodes and allows positively charged ions into the axon. This overwhelming positive charge causes an electrical charge to form (an action potential). At 120 meters per second, the action potential travels to the terminal buttons via the axon.

• If enough neurotransmitters have been sent, the next neuron will fire. If not, the message ends. This is called the all-or-nothing principle. There are no half-charges or lesser messages sent.

• Action Potential• Myelin and Action Potential

http://www.youtube.com/watch?v=SCasruJT-DU

• At the terminal buttons, neurotransmitters are released into the synapse and passed along to the dendrites of the next neuron. These neurotransmitters tell the recipient what to do next.

• After a neuron fires its message, there is a brief period of time before it can fire again. This is called a neuron’s refractory period.• During the refractory period, excess

neurotransmitters are reabsorbed by the sending neuron, called re-uptake, as well as the cell becoming polarized once again.

• Depending on what type of neurotransmitter has been released, the next neuron will react differently. Since nerve cells are connected to the brain, muscles, glands, etc., the entire human body reacts different depending upon what type of neurotransmitter has been released.

• Part I• Part II• Part III

Neurotransmitters

• Neurotransmitters

Acetylcholine (ACh)

• Enables muscle action, REM sleep, and memory

• Undersupply, as ACh-producing neurons deteriorate, marks Alzheimer’s disease

Dopamine

• This is the reward drug. After doing something well, you “feel” good. Alos plays a part in the motor control over voluntary movements

• Excessive dopamine receptor activity is linked to schizophrenia; a lack of dopamine produces the tremors and lack of mobility of Parkinson’s disease.

Serotonin

• Affects mood, hunger, temperature regulation, sleep, and arousal• Undersupply is linked to depression;

Prozac and other anti-depressants raise serotonin levels.

Norepinephrine

• Helps to control alertness, dreaming, waking from sleep, reactions to stress

• Undersupply can depress mood.

GABA

• Neural inhibitor with a tranquilizing effect.

• Undersupply linked to seizures, tremors, and insomnia.

Glutamate

• Involved in memory

• Oversupply can overstimulate the brain, producing migraines or seizures

Endorphins

•Natural opiates (pain killers) that are released in response to pain and vigorous exercise.

Endorphins

Epinephrine

• Adrenaline Burst of Energy (small amounts in brain)

Drugs and Chemical Interactions with Neural Transmission

• Some drugs that people put into their bodies are classified as agonists.• Agonists may either speed up

the neural process, cause an over-release or absorption of a neurotransmitter, or block the re-uptake process.

• After a neuron fires, if re-uptake is blocked, the lingering neurotransmitters in the synapse will continue to be absorbed by the receiving neuron until it is gone. • Therefore, a lingering feeling will

occur.

Examples of Agonists

•Cocaine – blocks the re-uptake of dopamine•MDMA (Ecstasy) –

excessive release of serotonin

• Some drugs that people put into their bodies are classified as antagonists. • Antagonists may slow or stop the

transmission of a neurotransmitter, or they may bind themselves to receptors on a neuron’s dendrite, thus not allowing a message to be passed on.

Examples of Antagonists

• Curare – a poison that stops the flow of Ach – causes paralysis