1.2 & 1.3 Psych

Overview of the Nervous System

1.2 Learning Objectives

• Differentiate among the subsystems of the human nervous system and their functions.

  • Central Nervous System (CNS): Comprises the brain and spinal cord.

  • Peripheral Nervous System (PNS): Relays messages from the CNS to the rest of the body. It encompasses:

  • Autonomic Nervous System: Regulates involuntary actions.

    • Parasympathetic Nervous System (PNS): Responsible for the rest-and-digest response.

    • Sympathetic Nervous System (SNS): Responsible for the fight-or-flight response.

  • Somatic Nervous System: Controls voluntary actions.

The Nervous System Structure

• Central Nervous System: Consists of the brain and spinal cord.

• Peripheral Nervous System (PNS): Includes somatic and autonomic systems.

Autonomic Nervous System

• Split into Sympathetic and Parasympathetic systems.

  • Sympathetic System:

  • Activates the fight or flight response and speeds bodily functions.

  • Parasympathetic System:

  • Promotes rest and digest, helping to slow down bodily functions.

Neurons

1.3 Learning Objectives

• Explain how the structures and functions of typical neurons affect behavior.

• Differentiate between neurons and glial cells.

• Understand the reflex arc involving sensory, motor, and interneurons.

• Explain the basic process of neural transmission including key concepts:

  • All or Nothing

  • Depolarization

  • Refractory period

  • Resting potential

  • Reuptake

• Discuss conditions such as Multiple Sclerosis and Myasthenia Gravis.

Neuron Structure

• Neurons are the messenger cells of the nervous system, receiving and transmitting information.

• They vary in size and shape and there are approximately 100 billion neurons in the brain.

• Neurons contain fibers called axons and dendrites that are utilized to send and receive information.

Parts of a Neuron

• Dendrites:

  • Origin of the term comes from the Greek word for tree.

  • Receive messages from other neurons and transmit them to the cell body (like hands catching a football).

• Soma (Cell Body): Contains the nucleus and is central to the neuron's operations.

• Axon:

  • A long fiber that carries outgoing messages from the cell body to other neurons.

  • Length can range from 1 mm to 3 feet.

  • Ends in terminal branches that split into terminal buttons or synaptic knobs where neurotransmitters are stored before release.

Types of Neurons

Sensory Neurons

• Collect messages from sense organs and relay them to the spinal cord or brain.

Interneurons

• Relay messages from one neuron to another (also called association neurons).

• Example:

  • Sensory Neuron: "That hurts!"

  • Interneuron: "Got it!"

Motor Neurons

• Convey messages from the spinal cord or brain to muscles and glands, enabling movements.

• Example:

  • Interneuron: "Pain in the hand, pull it away!"

  • Motor Neuron: "Got it, hand move!"

Glial Cells

• Greek term meaning glue.

• Hold neurons in place, provide nourishment, remove waste, and form myelin sheath.

• Speeds up neural impulses and protects the brain from harmful substances.

Neural Impulse

• Neural communication is facilitated through the exchange of charged particles called ions across the cell membrane.

• Intraneural transmission: Occurs within a neuron and is an electrical process due to ion exchange.

Resting Potential

• At rest, more negative ions are found inside the neuron leading to a resting potential of approximately -70 mV.

• The neuron is likened to a compressed spring, ready to explode when stimulated.

Action Potential

• When stimulated causing depolarization, the neuron's charge rapidly shifts, reaching +30 mV at its peak.

• This shift initiates the action potential, causing the neuron to fire.

• Impulse moves down the axon at speeds up to 400 ft/sec (approximately 275 mph).

• Referred to as the All or Nothing Principle: once the threshold of excitation (usually -55 mV) is reached, the impulse fires fully or not at all.

Refractory Period

• Two phases exist:

  • Absolute Refractory Period: Approximately 1/1000 of a second where the neuron cannot fire.

  • Relative Refractory Period: Cell returns to resting potential but can only fire if stimulated by a stronger-than-normal impulse.

Interneural Communication

• After an impulse travels down the axon, it reaches terminal buttons.

• The neurotransmitters released during firing must cross the synaptic space to reach neighboring neurons and trigger their firing.

Synapse and Chemical Communication

• Composed of the terminal button of one neuron, synaptic cleft, and the dendrites or cell body of the receiving neuron.

• Neurotransmitters have specific receptors thus following a lock and key model guiding their interactions.

Neurotransmitter Reuptake

• After neuronal firing, neurotransmitters are either:

  1. Received by neighboring neurons to open ion channels (post-synaptic).

  2. Reabsorbed and recycled by the sending neuron (pre-synaptic) in a process called reuptake.

  3. Disposed of if not reabsorbed.

Functions of Neurotransmitters

Excitatory and Inhibitory

• Excitatory (EPSP): Increase the likelihood of the neuron firing (e.g., glutamate).

• Inhibitory (IPSP): Decrease the likelihood of the neuron firing (e.g., GABA).

• Neurotransmitters play a crucial role in regulating behavior; imbalances can lead to maladaptive behavior.

Specific Neurotransmitters

• Acetylcholine (ACh): Linked to arousal, attention, memory, motivation, and movement. Degeneration relating to Alzheimer’s.

• Dopamine (DA): Associated with pleasure, emotion, reward-seeking, and motor control. Key in Parkinson’s disease and affected by various substances (e.g., cocaine).

• Serotonin: Regulates sleep, arousal, and mood. Low levels associated with depression.

• Endorphins: Involved in pain perception, released during exercise to alleviate pain.

• GABA: The primary inhibitory neurotransmitter, modulating anxiety and sleep.

• Glutamate: The most abundant excitatory neurotransmitter, vital for learning and memory, but can lead to overstimulation and seizures.

• Substance P: Related to pain perception and immune response; excess can lead to chronic pain experiences.

Comparison of Neurotransmitters and Hormones

• Neurotransmitters:

  • Internal (nervous system)

  • Quick-acting effects

• Hormones:

  • Internal (endocrine system)

  • Slow-acting, long-lasting effects

  • Organize and activate behaviors, such as sexual behavior.

Role of Drugs in Neurotransmission

• Agonists: Facilitate or enhance the effects of neurotransmitters. Examples include L-dopa (for Parkinson’s) and Adderall (for ADHD).

• Antagonists: Prevent or reduce neurotransmitter effects. Examples include Seroquel (antipsychotic) and Revia (alcoholism treatment).

Drug Mechanisms

Conclusion

• Understanding the nervous system, neurons, and neurotransmission provides key insights into behavior and psychological functioning.

• The implications of these mechanisms extend to drug interactions, neurological conditions, and behavioral outcomes.