Nervous System Flashcards

Nervous System Overview

• Nerves are not the functional units of the nervous system; that is a misconception.
• Substance P plays a key role in transmitting pain signals from the spinal cord to the brain.
• Hormones and neurotransmitters can perform dual roles; some can act interchangeably in different contexts.

Neurons and Neuroglia

• Neuroglia cells greatly outnumber neurons, contrary to the claim of a 50:1 ratio.
• Receptor cells detect stimuli, while afferent neurons transport this information to the Central Nervous System (CNS).
• Interneurons, also known as association neurons, facilitate communication within the CNS.
• Effectors, such as muscles and glands, execute responses generated by the nervous system.

Neuron Structure and Function

• Efferent neurons carry signals away from the CNS, while sensory neurons bring information to the CNS.
• The central integrative function of the nervous system is primarily fulfilled by the CNS, comprising the brain and spinal cord.
• Neurons respond to stimuli with an "all-or-none" action potential mechanism.

Neuronal Responses

• Nerves exhibit graded responses, differing from the binary action potentials of neurons.
• The terminal end foot of a neuron houses neurotransmitter vesicles.
• Dendrites receive input from other neurons, while axons transmit impulses away from the neuron’s soma.

Divisions of the Nervous System

• Two anatomical divisions: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• Two physiological divisions: Autonomic Nervous System (ANS) and Somatic Nervous System (SNS).
• The CNS is composed of the brain and spinal cord; the PNS connects these to limbs and organs.

Myelination and Signal Conduction

• Myelinated neurons transmit signals 10-20 times faster than their non-myelinated counterparts.
• Oligodendrocytes form the myelin sheath in the CNS, while Schwann cells perform this function in the PNS.

Types of Neurons and Cells

• Multipolar neurons are characterized by multiple dendrites and a single axon.
• Ependymal cells are responsible for the production and movement of cerebrospinal fluid within the brain.
• Astrocytes are the most abundant glial cells in the CNS and do not move freely within nervous tissue areas.

Membrane Potentials and Action Potentials

• The resting membrane potential (RMP) is influenced by potassium (K+) concentration inside cells and proteins present within the intracellular fluid (ICF).
• There are 40 times more potassium and 12 times more sodium outside the neuron than inside.
• For action potentials, the threshold potential is typically -55 mV, at which point a neuron fires.

Local vs. Action Potentials

• Local potentials are not irreversible, contrary to some beliefs, while action potentials are distinct and also not reversible.
• The internal voltage of a neuron can transition through phases: depolarization (becoming more positive) and repolarization (returning to a negative state).

Key Terminology

• Threshold potential: the specific internal voltage that must be reached for a neuron to fire.
• Trigger zone: also referred to as the axon hillock, where action potentials are initiated.
• Relative refractory period occurs during hyperpolarization when a neuron is more difficult to activate than at rest.