Nervous System Functioning

Overview of the Nervous System

• The nervous system is a complex network of specialized cells that enable the body to:
  • Receive information (sensory input)
  • Process information (integration)
  • Respond to information (motor output)
• It allows us to interact with the external world and regulate internal bodily functions.
• The nervous system is divided into two major divisions:
  • Central Nervous System (CNS): Consists of the brain and spinal cord.
  • Peripheral Nervous System (PNS): Consists of all the nerves outside the CNS.

KEY TAKEAWAY: The nervous system is the body’s control center, enabling communication and coordination between different parts.

Central Nervous System (CNS)

• Brain:
  • The control center of the nervous system.
  • Responsible for higher-order functions such as thought, memory, emotion, and language.
  • Divided into several regions, each with specific functions.
• Spinal Cord:
  • A long, thin bundle of nerve tissue that extends from the brainstem down the back.
  • Connects the brain to the PNS.
  • Responsible for transmitting sensory information to the brain and motor commands from the brain to the body.
  • Controls reflexes.

EXAM TIP: Understand the distinct roles of the brain and spinal cord within the CNS.

Peripheral Nervous System (PNS)

• Connects the CNS to the rest of the body.
• Carries sensory information to the CNS and motor commands from the CNS to muscles and glands.
• Divided into two main divisions:
  • Somatic Nervous System (SNS):
    • Controls voluntary movements of skeletal muscles.
    • Involved in conscious control of bodily functions.
  • Autonomic Nervous System (ANS):
    • Controls involuntary functions such as heart rate, digestion, and breathing.
    • Operates without conscious control.
    • Further divided into two branches:
      • Sympathetic Nervous System:
        • Prepares the body for action; “fight-or-flight” response.
        • Increases heart rate, breathing rate, and blood flow to muscles.
        • Dilates pupils.
      • Parasympathetic Nervous System:
        • Calms the body down after a stressful event; “rest-and-digest” response.
        • Decreases heart rate, breathing rate, and blood flow to muscles.
        • Constricts pupils.

COMMON MISTAKE: Confusing the roles of the sympathetic and parasympathetic nervous systems. Remember: Sympathetic = “fight-or-flight”, Parasympathetic = “rest-and-digest.”

Conscious and Unconscious Responses

• Conscious Response:
  • A reaction to a sensory stimulus that involves awareness.
  • The individual is aware of the stimulus and the response.
  • Examples: Deciding to wave hello, feeling the sensation of touch.
  • Typically involves the brain processing the sensory information.
• Unconscious Response:
  • A reaction to a sensory stimulus that does not involve awareness.
  • The individual is not aware of the stimulus or the response.
  • Examples: Spinal reflex, heart rate regulation.
  • Can be autonomic or somatic.

Spinal Reflex

• An unconscious, involuntary, and automatically occurring response to certain stimuli.
• Occurs without any involvement of the brain.
• Example: Touching a hot stove and quickly pulling your hand away.
• Reflex Arc:
  1. Sensory receptor: Detects the stimulus.
  2. Sensory neuron: Transmits the signal to the spinal cord.
  3. Interneuron: Relays the signal to the motor neuron (some reflexes bypass interneurons).
  4. Motor neuron: Transmits the signal to the muscle.
  5. Effector (muscle): Contracts, producing the response.

STUDY HINT: Create a flowchart to visually represent the reflex arc.

Comparing Conscious and Unconscious Responses

REMEMBER: Unconscious responses are faster and protect us from harm.

Neurons

• Neurons (nerve cells) are the basic building blocks of the nervous system.
• They transmit information in the form of electrical and chemical signals.
• Types of Neurons:
  • Sensory Neurons: Carry information from sensory receptors to the CNS.
  • Motor Neurons: Carry information from the CNS to muscles and glands.
  • Interneurons: Connect sensory and motor neurons within the CNS.

Structure of a Neuron

• Cell Body (Soma): Contains the nucleus and other organelles.
• Dendrites: Branch-like extensions that receive signals from other neurons.
• Axon: A long, slender projection that transmits signals away from the cell body.
• Myelin Sheath: A fatty insulation layer that surrounds the axon and speeds up signal transmission.
• Nodes of Ranvier: Gaps in the myelin sheath where the axon membrane is exposed.
• Axon Terminals (Terminal Buttons): Branch-like endings of the axon that release neurotransmitters.
• Synapse: The junction between two neurons where communication occurs.

VCAA FOCUS: Be able to label the different parts of a neuron and describe their functions.

Neural Communication

• Communication between neurons occurs at the synapse.
• The neuron sending the signal is called the presynaptic neuron.
• The neuron receiving the signal is called the postsynaptic neuron.
• Neurotransmitters are chemical messengers that transmit signals across the synapse.

Process of Synaptic Transmission

1. Action Potential: An electrical impulse travels down the axon of the presynaptic neuron.
2. Neurotransmitter Release: The action potential triggers the release of neurotransmitters from the axon terminals into the synaptic cleft.
3. Binding to Receptors: Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron’s dendrites.
4. Postsynaptic Potential: The binding of neurotransmitters to receptors causes a change in the electrical potential of the postsynaptic neuron.
   • Excitatory Postsynaptic Potential (EPSP): Makes the postsynaptic neuron more likely to fire an action potential.
   • Inhibitory Postsynaptic Potential (IPSP): Makes the postsynaptic neuron less likely to fire an action potential.
5. Neurotransmitter Removal: Neurotransmitters are removed from the synaptic cleft through:
   • Reuptake: Reabsorption by the presynaptic neuron.
   • Enzymatic Degradation: Breakdown by enzymes in the synaptic cleft.

APPLICATION: Understanding synaptic transmission is crucial for understanding how drugs affect the nervous system.

Neurotransmitters and Neuromodulators

Neurotransmitters

• Chemical substances produced by a neuron that carry a message to other neurons or cells.
• They are released into the synapse to bind to receptors on postsynaptic neurons.
• Examples:
  • Glutamate: Primary excitatory neurotransmitter in the brain; involved in learning and memory.
  • GABA (gamma-aminobutyric acid): Primary inhibitory neurotransmitter in the brain; involved in calming the nervous system.
  • Dopamine: Involved in reward, motivation, and motor control.
  • Serotonin: Involved in mood, sleep, and appetite.
  • Acetylcholine: Involved in muscle contraction and memory.
  • Norepinephrine (Noradrenaline): Involved in alertness and arousal.

Neuromodulators

• Chemical substances that modulate the activity of neurons.
• Unlike neurotransmitters, neuromodulators do not directly cause EPSPs or IPSPs.
• They can enhance or inhibit the effects of neurotransmitters.
• They can have longer-lasting and more widespread effects than neurotransmitters.
• Examples:
  • Endorphins: Natural pain relievers; involved in mood and pleasure.
  • Substance P: Involved in pain perception.

EXAM TIP: Be able to distinguish between neurotransmitters and neuromodulators, and provide examples of each.

Summary of Nervous System Functioning

• The nervous system enables psychological functioning by allowing us to receive, process, and respond to information from the environment.
• The CNS (brain and spinal cord) is the control center, while the PNS (somatic and autonomic) connects the CNS to the rest of the body.
• Neurons communicate through electrical and chemical signals at the synapse, using neurotransmitters and neuromodulators.
• Conscious responses involve awareness and brain processing, while unconscious responses are automatic and may involve the spinal cord (reflex arc).

KEY TAKEAWAY: The nervous system is a complex and interconnected network that enables us to interact with the world around us.