Neurons and their Components

• Neurons are cells in the nervous system that communicate to perform information processing.
• Thoughts, feelings, and behaviors originate from brain cells producing outputs; there are 86 billion neurons in the body.
• Ramon y Cajal discovered that components of the neuron include:

Neuron Components

• Cell Body (soma): The largest component, coordinating information-processing tasks and maintaining cell life. Functions include protein synthesis, energy production, and metabolism, and contains the nucleus with DNA.
• Dendrites: Receive information from other neurons, relaying it to the cell body in a tree branch-like manner.
• Axon: Carries information to other neurons, muscles, or glands; axons can be very long.
• Myelin Sheath: An insulating fatty layer covering the axon, composed of glial cells that support nervous system cells.
• Synapse: The junction between the axon of one neuron and the dendrites or cell body of another.
• Process include dendrites receiving a signal, the cell body processing it, the axon transmitting it, and axon terminals (synapse) releasing neurotransmitters to communicate with the next neuron.

Neuron Types by Function

• Sensory Neurons receive external information and convey it to the brain via the spinal cord related to light, sound, touch, taste, and smell.
• Motor Neurons carry signals from the spinal cord to the muscles to produce movement, often with long axons reaching muscles at our extremities.
• Interneurons connect sensory neurons, motor neurons, or other interneurons, primarily in the nervous system, and perform simple tasks like identifying sensory signals or recognizing faces.

Electric Signals in Axons

• An electric signal moves down an axon, and a chemical signal from one neuron is transmitted to another across the synapse.
• The neuron's cell membrane contains ions that flow in and out, creating electric current:
• Resting Potential: The difference in electric charge between the inside and outside of a neuron's cell membrane is -70 millivolts.
• Threshold: The cell membrane restricts movement until a threshold is reached.
• Action Potential: An electric signal conducted along the length of a neuron's axon to a synapse, fundamental to thinking, feeling, and doing.
• Refractory Period: The time following an action potential when a new action cannot be initiated.
• Terminal Buttons: Knob-like structures branching out from an axon containing tiny vesicles filled with neurotransmitters.
• Neurotransmitters: Chemicals that transmit information across the synapse to a receiving neuron's dendrites.
• Receiving neurons' dendrites contain receptors which are parts of the cell membrane that receive neurotransmitters and initiate or prevent an electric signal.

Synaptic Transmission

• Action potential travels down the axon, stimulating neurotransmitter release from vesicles.
• Neurotransmitters are released into the synapse, binding with receptor sites on a postsynaptic neuron's dendrite, initiating a new action potential.
• Reuptake occurs into the sending neuron, or neurotransmitters are broken down by enzymes in the synapse, or diffuse away from the synapse.
• Neurotransmitters bind to autoreceptors on the sending neuron, stopping further neurotransmitter release.

Neurotransmitters Functions

• Acetylcholine (ACh): Involved in voluntary motor control, muscle movement, and regulation of attention, learning, and sleeping.
• Dopamine: Regulates motor behavior, motivation, pleasure, and emotional arousal.
• Glutamate: Enhances the transmission of information between neurons.
• Norepinephrine: Involved in states of vigilance or heightened awareness of dangers.
• Serotonin: Involved in the regulation of sleep, wakefulness, eating, and aggressive behavior.
• Endorphins: Chemicals that act within pain pathways and emotion centers.

Drugs Mimic

• Drugs increase the action of neurotransmitters (agonists).
• Drug L-dopa (from dopamine): Treats Parkinson’s
• Opioids: Create calmness and euphoria.
• Prozac: Treats depression.
• Cocaine: Prevents neurotransmitter reuptake.
• Drugs diminish neurotransmitter function (antagonists).
• Propranolol: Obstructs heart receptor sites, slowing heart rate and can treat a fast heartbeat.

Nervous System Organization

• The nervous system is an interacting network of neurons conveying electrochemical information throughout the body.
• The central nervous system (CNS) is composed of the brain and spinal cord.
• The CNS receives sensory information from the external world, processes and coordinates it, and sends commands to skeletal and muscular systems for action.
• Spinal reflexes are simple nervous system pathways generating rapid muscle contractions.
• The peripheral nervous system (PNS) connects the central nervous system to the body's organs and muscles:
• Somatic Nervous System: A set of nerves conveying information between skeletal muscles and the central nervous system.
• Autonomic Nervous System (ANS): A set of nerves carrying involuntary commands controlling blood vessels, body organs, and glands.
• Sympathetic Nervous System: Prepares the body for action in challenging situations (dilates pupil, relaxes bladder, accelerates heart).
• Parasympathetic Nervous System: Helps return the body to a normal resting state (slows heart, contracts pupil, contracts bladder).
• Reflex arcs: A neural pathway controlling reflex actions including sensory, interneurons, and motor neurons.

Brain Structure

• Hindbrain: Coordinates information coming into and out of the spinal cord and basic life functions:
• Medulla: An extension of the spinal cord into the skull, coordinates heart rate, circulation, and respiration.
• Reticular Formation: Regulates sleep, wakefulness, and levels of arousal.
• Cerebellum: A large hindbrain structure controlling fine motor skills, movements, balance, and coordination.
• Pons (bridge): Relays information from the cerebellum to the rest of the brain.
• The midbrain is important for orientation and movement, located on top of the hindbrain, relatively small in humans:
• Tectum: Orients organism in the environment receiving input from eyes, ears, and skin for sensory reactions.
• Tegmentum: Involved in movement and arousal, orienting an organism towards sensory stimuli.
• Forebrain: The highest level of the brain that controls complex cognitive, emotional, sensory, and motor functions:
• Cerebral Cortex: The outermost layer of the brain, divided into two hemispheres connected by the corpus callosum:
• Occipital lobe: Processes visual information.
• Parietal lobe: Handles touch and other functions.
• Temporal Lobe: Responsible for hearing and language.
• Frontal Lobe: Specialized for movement, , planning, memory and judgement.
• Subcortical Structures: Areas of the forebrain housed near the brain's center:
• Basal Ganglia: Subcortical structures directing intentional movements with role in reward processing.
• Thalamus: Relays and filters sensory information, transmitting it to the cerebral cortex.
• Hypothalamus: Regulates body temperature, hunger, thirst, and sexual behavior.
• Hippocampus: Is critical for creating new memories and integrating them into knowledge.
• Amygdala: Plays a role in emotional processes.
• Pituitary gland: The "master gland" releasing hormones.
• Left hemisphere controls the right side of the body and handles language, logic, and analytical thinking.
• The right hemisphere controls the left side of the body and is responsible for creativity, spatial awareness, and emotions.
• The endocrine system produces hormones for functions like metabolism, growth, and sexual development.
• The corpus callosum connects both halves of the cerebral cortex and supports communication.
• Association areas composed of neurons help register sense and information.
• Mirror neurons become active when an animal performs or observes a behavior.
• The brain can adapt in response to plasticity, patients can feel missing limbs moving, and cultural nueroscience studies culture.