Nervous System: Central and Peripheral Divisions

• The nervous system's primary roles include receiving sensory input, integrating information for decision-making, controlling muscles and glands, maintaining homeostasis, and supporting mental activities like thinking and memory.

Central vs. Peripheral Nervous System

• The central nervous system (CNS) consists of the brain and spinal cord, responsible for processing sensory data and issuing motor commands.
• The peripheral nervous system (PNS) includes all nervous tissue outside the CNS.
• The sensory (afferent) division carries signals from sensory receptors to the CNS.
• The motor (efferent) division carries signals from the CNS to effector organs such as muscles and glands.
• The somatic nervous system (SNS) controls skeletal muscles under voluntary control.
• The autonomic nervous system (ANS) regulates cardiac muscle, smooth muscle, and glands involuntarily.
• The enteric nervous system (ENS), located in the digestive tract, manages local reflexes within the digestive system.

Neurons and Glial Cells

• Neurons receive stimuli, conduct action potentials, and transmit signals.
• Glial cells support neurons without conducting action potentials, maintaining neuron function.
• Astrocytes support neurons, form the blood-brain barrier, and regulate the neuron environment.
• Ependymal cells line ventricles and produce cerebrospinal fluid (CSF).
• Microglia act as immune cells, clearing debris and pathogens in the nervous system.
• Oligodendrocytes form myelin in the CNS.
• Schwann cells form myelin in the PNS.

Myelin Sheath and Action Potential Conduction

• The myelin sheath is a fatty layer around axons that speeds up action potential conduction.
• Nodes of Ranvier are gaps in the myelin sheath that facilitate saltatory conduction, where action potentials "jump" between nodes.

Gray Matter vs. White Matter

• Gray matter contains neuron cell bodies and dendrites (unmyelinated), found in the center of the spinal cord.
• White matter is composed of myelinated axons and is located on the outer part of the spinal cord and throughout the brain.

Action Potentials and Membrane Potentials

• Resting membrane potential involves a higher concentration of sodium (Na+) outside the cell and potassium (K+) inside, with the cell's interior being more negative relative to the outside.
• An action potential includes depolarization (Na+ influx), repolarization (K+ efflux), and hyperpolarization.
• The sodium-potassium pump actively transports Na+ out and K+ in to maintain resting potential.

Threshold and All-or-None Principle

• Threshold is the minimum membrane potential required to trigger an action potential.
• The all-or-none principle dictates that if the threshold is reached, an action potential occurs fully; otherwise, it does not occur at all.

Neuronal Synapse

• Neurotransmitter release occurs when an action potential causes Ca2+ channels to open, leading to neurotransmitter release into the synaptic cleft.
• Neurotransmitters affect the postsynaptic cell by binding to receptors, opening or closing ion channels (Na+, K+, Cl−), which can depolarize or hyperpolarize the cell.
• Excitatory neurotransmitters (e.g., acetylcholine) depolarize the cell, increasing the likelihood of an action potential.
• Inhibitory neurotransmitters (e.g., GABA) hyperpolarize the cell, reducing the chance of an action potential.

Converging vs. Diverging Pathways

• In converging pathways, multiple neurons synapse with a single postsynaptic neuron.
• In diverging pathways, one neuron synapses with multiple postsynaptic neurons.

Spatial vs. Temporal Summation

• Spatial summation occurs when local potentials from different locations on the postsynaptic neuron combine.
• Temporal summation occurs when local potentials from the same neuron overlap in time and combine.

Spinal Cord Function and Tracts

• Ascending tracts carry sensory information from the body to the brain.
• Descending tracts carry motor commands from the brain to the body.
• Dorsal (ascending) columns carry sensory information.
• Ventral and lateral (descending) columns carry motor commands for movements.

Reflexes and Reflex Arcs

• Reflexes are involuntary, rapid responses to stimuli.
• A reflex arc includes a sensory receptor, sensory neuron, interneuron (sometimes), motor neuron, and effector organ.
• The stretch reflex involves muscle contraction in response to being stretched such as the patellar reflex.
• The withdrawal reflex is a protective response to a painful stimulus, like pulling a hand away from a hot surface.

Dermatome and Plexus

• A dermatome is a specific area of skin supplied by a spinal nerve.
• A plexus is a network of nerves serving a specific region, examples being the cervical, brachial, and lumbar plexuses.

Brain Anatomy and Functions

• Medulla Oblongata controls vital functions like heart rate, breathing, and swallowing.
• Pons relays signals between the cerebrum and cerebellum and is involved in breathing.
• Midbrain is involved in visual and auditory reflexes.
• Cerebellum coordinates muscle movements and balance.
• Diencephalon includes the thalamus, which relays sensory information, the hypothalamus, which controls homeostasis and autonomic functions, and the epithalamus.
• Cerebrum controls conscious activities like thought, sensation, and voluntary movement.
• Frontal, parietal, occipital, and temporal lobes control different sensory and motor functions.
• The insula is involved in emotion and perception.

Limbic System

• The limbic system is responsible for emotions, memory, and motivation, which includes the hippocampus, amygdala, and other structures.

Meninges and CSF

• Meninges are three layers of connective tissue surrounding the CNS, these include:
  • Dura mater, the tough, outermost layer.
  • Arachnoid mater, the thin, middle layer.
  • Pia mater, the delicate, innermost layer tightly bound to the CNS surface.
• CSF provides cushioning, waste removal, and nutrients and is produced in the ventricles.

Autonomic Nervous System and Enteric Nervous System

• The autonomic nervous system (ANS) regulates involuntary functions (smooth muscle, cardiac muscle, glands). It is divided into:
  • The sympathetic division: "Fight or flight," preparing the body for physical activity.
  • The parasympathetic division: "Rest and digest," promoting relaxation and digestion.
• The enteric nervous system controls the digestive system independently of the CNS.

Overview of the primary roles and divisions of the nervous system. The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). Each division has specific roles in sensory input, motor output, and regulation of bodily functions.