Nervous System: Neuron Function and Action Potentials

Resting Membrane Potential

The resting membrane potential is the electrical potential difference across the plasma membrane of a neuron when it is not actively transmitting a signal. This potential is primarily established by the movement of ions through channels, especially the sodium-potassium (Na+/K+) pump.

• Na+/K+ pump: Actively transports 3 Na+ ions out and 2 K+ ions into the cell, maintaining a negative charge inside.

• Resting potential value: Typically around -70 mV in neurons.

• Importance: Prepares the neuron for rapid depolarization during action potentials.

Equation:

Action Potentials and Signal Propagation

Action potentials are rapid changes in membrane potential that travel along the axon, allowing neurons to communicate.

• Electrical synapses: Use gap junctions for direct ion flow between cells.

• Chemical synapses: Use neurotransmitters to transmit signals across a synaptic cleft.

• Excitatory vs. Inhibitory synapses: Excitatory synapses increase the likelihood of action potential firing; inhibitory synapses decrease it.

• Myelin: Insulates axons, increasing the speed of action potential transmission via saltatory conduction.

Example: Myelin is essential for rapid signal transmission in motor neurons controlling muscle movement.

Brain Structure and Function

Hypothalamus and Thalamus

The hypothalamus and thalamus are key brain regions involved in homeostasis and sensory relay.

• Hypothalamus: Regulates autonomic functions, hormone release, and homeostasis.

• Thalamus: Acts as a relay station for sensory information to the cerebral cortex.

Cerebellum

The cerebellum is responsible for coordination, balance, and fine motor control.

• Function: Integrates sensory input and motor commands to produce smooth, coordinated movements.

• Location: Posterior to the brainstem, beneath the occipital lobes.

Meninges and Cerebrospinal Fluid (CSF)

Meninges are protective membranes surrounding the brain and spinal cord. Cerebrospinal fluid cushions the brain and provides nutrients.

• Meninges layers: Dura mater, arachnoid mater, pia mater.

• CSF: Produced in the ventricles, circulates in the subarachnoid space.

Example: Meningitis is inflammation of the meninges, which can disrupt brain function.

Selective Barrier: Blood-Brain Barrier

The blood-brain barrier protects the brain from harmful substances while allowing essential nutrients to pass.

• Function: Maintains CNS homeostasis and prevents toxins from entering neural tissue.

Autonomic Nervous System (ANS)

Somatic vs. Visceral Nervous System

The nervous system is divided into somatic (voluntary) and visceral (involuntary) components.

• Somatic: Controls skeletal muscle and voluntary movements.

• Visceral: Regulates internal organs, glands, and smooth muscle.

• Location: Somatic motor neurons are found in the anterior horn of the gray matter in the spinal cord.

Parasympathetic vs. Sympathetic Nervous System

The parasympathetic and sympathetic divisions of the ANS have opposing effects on body functions.

• Parasympathetic: "Rest and digest"; conserves energy, slows heart rate, stimulates digestion.

• Sympathetic: "Fight or flight"; increases heart rate, dilates pupils, inhibits digestion.

• Cholinergic receptors: Activated by acetylcholine (ACh), leading to muscle movement or organ responses.

Example: Parasympathetic stimulation slows the heart rate after a stressful event.

Spinal Cord Sensation and Reflexes

The spinal cord is responsible for transmitting sensory information and mediating reflexes.

• Dermatomes: Specific skin regions innervated by sensory fibers from a single spinal nerve.

• Reflex arc: Simple neural pathway mediating automatic responses, such as the patellar reflex.

Example: The knee-jerk reflex is a classic example of a spinal reflex.

Clinical Terms and Disorders

Key Neurological Terms

• Neurologist: Medical specialist in nervous system disorders.

• Dyslexia: Learning disability affecting reading and writing.

• Neuropsychology: Study of the effects of brain injury or disease on behavior.

• Dystonia: Involuntary muscle contractions causing abnormal postures.

• Vagotomy: Surgical cutting of the vagus nerve.

• Horner's syndrome: Condition due to damage to the sympathetic trunk, causing ptosis, miosis, and anhidrosis.

• Analgesia: Reduced ability to feel pain without loss of consciousness.

Cranial Nerves

Overview of Cranial Nerves

The cranial nerves are twelve pairs of nerves that emerge directly from the brain, each with specific sensory and/or motor functions.

Example: Damage to the facial nerve (VII) can result in facial paralysis.

Additional info: Some content was inferred and expanded for clarity and completeness, including definitions, examples, and the full cranial nerve table.