Neurons 2021

Neurons and Neurotransmitters Overview

  • Neurons and neurotransmitters are key components of the nervous system, responsible for transmitting signals throughout the body.

Nervous System Structure

  • Central Nervous System (CNS): The control center of the body, consisting of the brain and spinal cord.

  • Peripheral Nervous System (PNS): Connects the CNS to the rest of the body, divided into:

    • Sensory Neurons: Carry sensory information to the CNS.

    • Motor Neurons: Carry commands from the CNS to muscles and glands, further divided into:

      • Somatic Nervous System: Controls voluntary movements via skeletal muscles.

      • Autonomic Nervous System: Controls involuntary actions; further divided into:

        • Sympathetic: Activates fight-or-flight responses.

        • Parasympathetic: Conserves energy and maintains homeostasis.

Function of the Autonomic Nervous System

  • Sympathetic Functions:

    • Eyes: Dilates pupils

    • Lungs: Relaxes bronchi

    • Heart: Accelerates heartbeat

    • Stomach/Intestines: Inhibits activity

    • Blood Vessels: Constricts vessels

  • Parasympathetic Functions:

    • Eyes: Contracts pupils

    • Lungs: Constricts bronchi

    • Heart: Slows heartbeat

    • Stomach/Intestines: Stimulates activity

    • Blood Vessels: Dilates vessels

Types of Nervous Cells

  • Neurons:

    • Basic units of the nervous system that receive, integrate, and transmit information via electrical impulses and chemical signals.

  • Glial Cells:

    • Support neurons by:

      • Providing physical support and nutrients

      • Covering neurons with myelin

      • Cleaning up debris

Types of Neurons

  • Sensory (Afferent) Neurons:

    • Send signals from sensory receptors to the CNS (e.g., skin).

  • Motor (Efferent) Neurons:

    • Transmit commands from the CNS to muscles and glands (e.g., muscle).

  • Interneurons:

    • Connect neurons within the CNS.

Neural Anatomy

  • Dendrites:

    • Branching extensions that receive messages and conduct impulses towards the cell body.

  • Cell Body:

    • Contains the nucleus and processes incoming information.

  • Axon:

    • Long projection that sends messages to other neurons or muscles.

  • Myelin Sheath:

    • Fatty layer insulating the axon, enhancing speed of signal transmission.

Synaptic Transmission

  • Synapse:

    • The junction between the ending of the axon of one neuron and the dendrite or cell body of another. Contains:

      • Synaptic Gap/Cleft: The tiny space where neurotransmitters diffuse.

Action Potential

  • A rapid rise and fall in membrane potential that occurs when a neuron is stimulated:

    • Dendrites stimulated → Positively charged ions rush in (depolarization) → Chemical release from terminal buttons.

  • Relay Race Analogy:

    • Action potential travels from dendrite → through cell body → down axon → to axon terminals → neurotransmitter release into synapse.

Neurotransmitters

  • Chemical messengers that transmit information across the synaptic gap.

    • When released by the sending neuron, they bind to receptors on the receiving neuron, influencing neural impulse generation.

Types of Neurotransmitters

  • Acetylcholine (ACh):

    • First identified neurotransmitter, involved in muscle action, and also plays a role in memory and learning; antagonists like curare and stimulants like black widow venom affect action.

  • Endorphins:

    • Natural painkillers released during stress or pain, similar to morphine.

  • Other Key Neurotransmitters:

    • Dopamine: Influences movement, attention, learning; linked to disorders like schizophrenia and Parkinson's.

    • Serotonin: Affects mood, sleep, and hunger; low levels associated with depression.

    • Norepinephrine: Regulates alertness and arousal; critical for stress response.

    • GABA: Major inhibitory neurotransmitter; low levels linked to seizures.

    • Glutamate: Major excitatory neurotransmitter; involved in learning and memory.