Biology Nervous System Overview

Study Notes

The Nervous System

Consists of central (CNS) and peripheral (PNS) systems
The CNS includes the brain and spinal cord
The PNS extends throughout the body

The Spinal Cord

Encased in the vertebral column
Protected by three membranes: dura mater, arachnoid mater, and pia mater
Connected to the peripheral nervous system via spinal nerves

Spinal Nerves

Consist of afferent (sensory) and efferent (motor) fibers
Afferent fibers carry impulses from sensory receptors to the CNS
Efferent fibers carry impulses to organs (muscles and glands)

Nerve Fibers

Bundles of nerve fibers form a nerve
Enclosed by connective tissue layers called endoneurium
Schwann cells are located under the endoneurium
Myelinated fibers (wrapped by Schwann cells several times) have faster conduction speed
Myelination creates regular interruptions called nodes of Ranvier

Nerve Cells (Neurons)

Consist of a cell body, dendrites, and an axon
Dendrites receive stimuli
Axons conduct electrical impulses
Terminal buttons at the end of the axon form the first part of a synapse
Terminal buttons contain calcium channels and vesicles with neurotransmitters

Synapses

Allow communication between neurons
Terminal buttons release neurotransmitters via exocytosis
Neurotransmitters bind to receptors on the postsynaptic cell membrane
This converts the chemical signal back to an electrical impulse

Spinal Ganglion (Dorsal Root Ganglion)

Thickening in the spinal nerve that houses cell bodies of sensory neurons
Neurons in the spinal ganglion are pseudo-unipolar (axon is divided into two branches)

Myelinated vs. Unmyelinated Nerve Fibers

Myelinated fibers have faster conduction speed due to the presence of Schwann cells forming a myelin sheath
Unmyelinated fibers lack myelination, resulting in slower conduction speed

Sensory Receptors in the Skin

Located in various layers of the skin
Can be rapidly adapting or slowly adapting
Meissner's corpuscles: rapidly adapting mechanoreceptors, respond to changes in pressure
Merkel cells: slowly adapting mechanoreceptors, respond to both dynamic and static stimuli
Ruffini corpuscles: slowly adapting mechanoreceptors, respond to tissue stretch

Spinal Cord: Gray and White Matter

Gray matter: contains cell bodies of neurons
White matter: contains axons of neurons
Sensory impulses are transmitted through both gray and white matter in the spinal cord

Reflexes

Sensory impulses can be processed directly in the spinal cord
Sensory fibers can transmit impulses directly or indirectly to motor nerve fibers, causing muscle contraction or relaxation
Example: Burning yourself triggers a reflex where sensory receptors send impulses to interneurons, which then activate motor neurons to contract muscles.

Description

Explore the intricacies of the nervous system, including its central and peripheral components. This quiz covers the structure and function of the spinal cord, spinal nerves, nerve fibers, and neurons. Test your knowledge on how these elements work together to facilitate communication within the body.