Neurons and Glial Cells Overview

Neurons and Synapses

• Neurons are specialized cells in the nervous system for information processing and communication.
• They receive and transmit information to other cells.
• Glia (or neuroglia) are cells that support neurons' activities.
• Glia do not transmit information long distances like neurons do.

Cells of the Nervous System

• The cerebral cortex and its associated areas contain 12 to 15 billion neurons.
• The spinal cord has 1 billion neurons.
• The cerebellum has 70 billion neurons.
• Obtaining an exact neuron count is difficult due to their small size and varying density.

Types of Glia

• Astrocyte: Structural and nutritional support for neurons, synapse isolation, debris cleanup, blood-brain barrier participation, and chemical signaling. Located in the central nervous system.
• Oligodendrocyte: Myelination of axons in the central nervous system.
• Schwann cell: Myelination of axons in the peripheral nervous system.
• Microglia: Debris cleanup in the central nervous system.
• Astrocytes help transport nutrients to neurons and block toxic movement. They also hold neurons in place.

Structure of Neurons

• Neurons have a cell body (soma) containing organelles.
• Dendrites receive information from other neurons.
• The axon carries signals to other neurons.
• The synapse is the junction between two neurons, where information transfer occurs.
• Myelin sheath is fatty insulation around many axons.

Neuron Membranes

• The neural membrane is a two-molecule thick phospholipid layer.
• Ion channels and pumps are embedded in the membrane and allow chemical transport.

Neural Cytoskeleton

• The neural cytoskeleton supports the neuron and transports substances.
• Microtubules transport materials within a neuron.
• Anterograde transport is the movement of materials from the cell body to the axon terminal.
• Retrograde transport moves materials from the axon terminal back to the cell's body.
• Neurofilaments provide structural support, and microfilaments may play a role in learning.

Functional Variations in Neurons

• Sensory neurons receive information from the external environment.
• Motor neurons send commands from the central nervous system to muscles and glands.
• Interneurons connect sensory and motor neurons.

Types of Neurons

• Sensory neurons (afferent) receive information from the environment.
• Interneurons (associative) connect other neurons.
• Motor neurons (efferent) transmit information to muscles and glands.

Classification of Neurons

• Unipolar neurons have one process extending from their cell body.
• Bipolar neurons have two processes extending from their cell body.
• Multipolar neurons have more than two processes extending from their cell body.
• Interneurons have short axons or no axons at all.

Blood-Brain Barrier

• The blood-brain barrier prevents toxins from entering the brain.
• It consists of an unbroken wall of cells surrounding brain blood vessels.

Neural Impulse

• A neural impulse is the electrochemical discharge of a neuron.
• Polarize a neuron to ready for firing creating an internal negative charge.
• Resting potential is the electrical potential across the neural membrane when not responding to other neurons.
• Depolarize to reduce resting potential of a cell membrane.
• Action potential is the conduction of neural impulses along axons.

Firing: Neuron to Neuron

• Neuron fires when incoming messages reach a threshold strength.
• All-or-none principle describes a neuron firing with the same strength, or not at all.
• Refractory period is the recovery time period between firings.

Synapse

• Synapse is a junction between the axon terminals of one neuron and the dendrites or cell body of another neuron.
• Neurotransmitters are chemical substances that communicate from one neuron to another.
• Synaptic vesicles contain neurotransmitters in axon terminals.
• Receptor sites are tailored locations on dendrites to receive neurotransmitters.
• Excitatory neurons cause other neurons to fire.
• Inhibitory neurons prevent other neurons from firing.

Chemical and Electrical Synapse

• Chemical synapse uses neurotransmitters to transmit messages between neurons.
• Electrical synapse directly transmits information via ion flow.

Synaptic Transmission

• Neurotransmitters are synthesized, packaged, and released into the synaptic cleft after an action potential.
• Neurotransmitters bind to receptors on the postsynaptic membrane and trigger a response.
• Transmission is terminated by the removal of neurotransmitters from the synaptic cleft.

Methods for Deactivating Neurotransmitters

• Deactivation occurs through diffusion away from the synapse, action of special enzymes, or reuptake.

Neurotransmitters

• Neurotransmitters are chemical messengers that communicate across synapses.
• Most produce either excitation or inhibition.

Summary Table of Neurotransmitters

• Specific neurotransmitters are linked to distinct functions and locations.

Hormones

• Hormones are chemicals secreted by cells and conveyed by the blood to influence other cells.
• They coordinate long-lasting changes in multiple body parts.
• They regulate growth, metabolism, and some behaviors.
• Maintain homeostasis.

Hormones Regulated by Pituitary Gland

• Pituitary gland is the "master gland" regulating several hormones.
• Hormones like growth hormone, prolactin, vasopressin, and oxytocin have various functions.

Endocrine Glands

• Pineal gland secretes melatonin, regulating the sleep-wake cycle.
• Thyroid gland produces thyroxin affecting metabolism; hypothyroidism and hyperthyroidism represent deficiencies and excesses respectively.
• Adrenal glands are located above the kidneys increasing stress resistance and promoting muscle development.
• Testes and ovaries produce testosterone (androgens) and estrogen/progesterone, responsible for sex characteristics.

Steroids, Behavior, and Mental Processes

• Steroids increase muscle mass, resist stress, and increase the body's energy supply.
• Anabolic steroids enhance athletic performance but may have negative impacts on behaviour and cognitive functions.

Drugs and Behavior

• Drugs can either facilitate or inhibit neurotransmitter transmission.
• Antagonists block neurotransmitters; agonists increase their effects.
• Drug effectiveness and side effects vary among individuals.

Psychoactive Drugs

• Psychoactive drugs are administered to cause psychological effects.
• These drugs frequently bypass the blood-brain barrier.

Drugs: Dependence and Abuse

• Substance abuse is persistent substance use despite causing problems in daily life.
• Substance dependence is loss of control over substance use.

Drugs: Addiction

• Addiction is a compulsive craving for drug effects.
• Some addictive drugs increase dopamine activity to create a reinforcing experience.
• Tolerance occurs when more of a drug is needed to produce the same effect.
• Withdrawal symptoms occur when a drug use is discontinued.

Types of Drugs

• Stimulants speed up the central nervous system (e.g., caffeine, nicotine, amphetamines).
• Depressants slow down the central nervous system (e.g., alcohol, opiates).
• Hallucinogens alter the user's state of consciousness (e.g., LSD, marijuana).

Summary Table: Drugs and Effects

• Different drugs produce various effects, having unique mechanisms of action and impacting the body in distinct ways.

St. John's Wort and Hallucinogenic Mushroom

• Information about these specific drugs and their effects, including images of the plants.