Nervous System: Structure, Function, and Physiology Study Guide

Nervous System Overview

Functions of the Nervous System

The nervous system is responsible for coordinating and regulating bodily activities by transmitting signals between different parts of the body.

• Sensory Input: Detects changes inside and outside the body.

• Integration: Processes and interprets sensory input, deciding what should be done.

• Motor Output: Activates effector organs (muscles and glands) to respond.

Organization of the Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for integration and command.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; connects the CNS to limbs and organs.

Neuroglia and Neurons

Neuroglia

Neuroglia are supporting cells in the nervous system that provide structural and metabolic support to neurons.

• CNS Types: Astrocytes, oligodendrocytes, microglia, ependymal cells.

• PNS Types: Schwann cells, satellite cells.

• Functions: Support, insulation, protection, and maintenance of homeostasis.

Neurons

Neurons are the functional units of the nervous system, specialized for transmitting electrical impulses.

• Structure: Cell body (soma), dendrites (receive signals), axon (transmits signals).

• Myelination: Myelin sheath increases impulse speed; produced by oligodendrocytes (CNS) and Schwann cells (PNS).

• Classification: Based on structure (multipolar, bipolar, unipolar) and function (sensory, motor, interneurons).

Physiology of Nerve Impulses

Resting Membrane Potential

The resting membrane potential is the voltage difference across the neuron membrane when the cell is at rest.

• Typical Value: -70 mV (inside negative relative to outside).

• Maintained by: Sodium-potassium pump and selective permeability of the membrane.

Equation:

$V_m = V_{inside} - V_{outside}$

Action Potentials

Action potentials are rapid changes in membrane potential that allow neurons to transmit signals over long distances.

• Phases: Depolarization, repolarization, hyperpolarization.

• Key Channels: Voltage-gated sodium and potassium channels.

• Propagation: Movement of the action potential along the axon; speed affected by myelination and axon diameter.

• Refractory Period: Time during which a neuron cannot fire another action potential.

Steps of Action Potential:

1. Resting state: All voltage-gated channels closed.

2. Depolarization: Na+ channels open, Na+ enters.

3. Repolarization: K+ channels open, K+ exits.

4. Hyperpolarization: K+ channels remain open briefly.

Synapses and Neurotransmission

Synapse Structure and Function

A synapse is the junction between two neurons or between a neuron and an effector cell.

• Components: Presynaptic neuron, synaptic cleft, postsynaptic neuron.

• Types: Electrical and chemical synapses.

• Neurotransmitters: Chemical messengers released from presynaptic terminals.

Postsynaptic Potentials

Postsynaptic potentials are changes in membrane potential of the postsynaptic neuron due to neurotransmitter binding.

• Excitatory (EPSP): Depolarizes membrane, increases likelihood of action potential.

• Inhibitory (IPSP): Hyperpolarizes membrane, decreases likelihood of action potential.

• Summation: Multiple EPSPs/IPSPs can combine to influence action potential generation.

Central Nervous System (CNS) Structure

Major Divisions

• Cerebrum: Higher brain functions, divided into lobes and functional areas.

• Diencephalon: Includes thalamus (relay center), hypothalamus (homeostasis), epithalamus.

• Brain Stem: Midbrain, pons, medulla oblongata; controls basic life functions.

• Cerebellum: Coordinates movement and balance.

• Spinal Cord: Conducts signals to and from the brain; reflex center.

Functional Areas of the Brain

• Motor Areas: Control voluntary movements.

• Sensory Areas: Receive sensory input.

• Association Areas: Integrate information.

Peripheral Nervous System (PNS)

Components and Functions

• Cranial Nerves: 12 pairs, serve head and neck.

• Spinal Nerves: 31 pairs, serve rest of body.

• Reflexes: Rapid, automatic responses to stimuli; can be monosynaptic or polysynaptic.

Special Senses

Sensory Receptors

Sensory receptors detect changes in the environment and initiate nerve impulses.

• Classification by Stimulus: Mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, nociceptors.

• Location: Exteroceptors, interoceptors, proprioceptors.

Vision

• Eye Structure: Three layers (fibrous, vascular, inner); components include cornea, lens, retina.

• Photoreceptors: Rods (dim light), cones (color vision).

• Pathway: Light → photoreceptors → optic nerve → brain.

Hearing and Equilibrium

• Ear Structure: Outer, middle, inner ear; cochlea for hearing, vestibular apparatus for balance.

• Equilibrium: Maintained by semicircular canals and otolith organs.

Chemical Senses

• Olfaction (Smell): Olfactory receptors in nasal cavity.

• Gustation (Taste): Taste buds on tongue; five basic tastes: sweet, sour, salty, bitter, umami.

HTML Table: Comparison of CNS and PNS Neuroglia

Neuroglia Type	Location	Main Function
Astrocytes	CNS	Support neurons, maintain blood-brain barrier
Oligodendrocytes	CNS	Form myelin sheath in CNS
Microglia	CNS	Phagocytosis of debris and pathogens
Ependymal cells	CNS	Line ventricles, produce cerebrospinal fluid
Schwann cells	PNS	Form myelin sheath in PNS
Satellite cells	PNS	Support neuron cell bodies in ganglia

Additional info:

• Some details (e.g., specific neurotransmitters, exact pathways) were inferred based on standard Anatomy & Physiology curriculum.

• For exam preparation, focus on understanding the flow of information in the nervous system, the role of different cell types, and the mechanisms of signal transmission.