Nervous System: Spinal Cord and Nervous Tissue – Study Notes

Nervous System: Spinal Cord and Nervous Tissue

Objectives

• Locate and identify the major structures of neurons on slides, models, and diagrams.

• Locate and identify the major structures of the spinal cord on models and diagrams.

Introduction to Nervous Tissue

The nervous system is a highly complex, interconnected network that receives and conducts impulses. Nerve cells (neurons) are specialized for communication and integration of information throughout the body.

Neuron Cell Structure

• Cell body: The rounded end of the neuron that contains the nucleus.

• Dendrites (DEEN-drits): Numerous extensions from the neuron that project from the cell body; they receive electrical impulses from other neurons and conduct them to the cell body.

• Axon: A single long extension of the neuron that transmits the nerve impulse away from the cell body; axons may be myelinated (covered by a myelin sheath) to increase conduction speed.

• Axon terminals: The fine branches at the end of the axon; specialized for release of neurotransmitters.

• Synaptic knobs: Expanded ends of the axon terminals where neurotransmitter release occurs.

• Nodes of Ranvier: Gaps in the myelin sheath; nerve impulses "jump" from node to node, increasing conduction speed.

Example

Motor neurons transmit impulses from the spinal cord to skeletal muscles, enabling movement.

Spinal Cord Models

The spinal cord contains distinct regions and columns that organize sensory and motor pathways.

• Anterior horns: Contain somatic motor nuclei; provide nerve impulses for contraction of skeletal muscles.

• Lateral horns: Contain autonomic motor nuclei; regulate activity of smooth muscle, cardiac muscle, and glands.

• Posterior horns: Contain somatic and autonomic sensory nuclei.

• Anterior column: Contains bundles of axons (not in PAL).

• Lateral column: Contains bundles of axons (not in PAL).

• Posterior column: Contains bundles of axons (not in PAL).

• Dorsal roots (also called posterior roots): Contain sensory axons only; each dorsal root has a dorsal root ganglion (cell bodies of sensory neurons).

• Ventral roots (also called anterior roots): Contain motor axons only; transmit impulses from the spinal cord to effectors.

Table: Spinal Cord Horns and Columns

Structure	Main Function
Anterior Horns	Somatic motor nuclei; skeletal muscle control
Lateral Horns	Autonomic motor nuclei; smooth/cardiac muscle, glands
Posterior Horns	Sensory nuclei; receive sensory input
Dorsal Roots	Sensory axons; input to spinal cord
Ventral Roots	Motor axons; output from spinal cord

Spinal Cord Meninges and Spaces

The spinal cord is protected by three connective tissue membranes called meninges, and several associated spaces.

• Dura mater: The tough, outermost membrane.

• Arachnoid mater: The middle, web-like membrane.

• Pia mater: The delicate, innermost membrane that adheres to the spinal cord surface.

• Subarachnoid space: The space below the arachnoid mater; contains cerebrospinal fluid (CSF).

• Epidural space: The space above the dura mater; filled with adipose tissue and blood vessels.

• Central canal: The small channel in the center of the spinal cord; contains CSF.

Table: Spinal Cord Meninges and Spaces

Layer/Space	Description
Dura mater	Outermost, tough membrane
Arachnoid mater	Middle, web-like membrane
Pia mater	Innermost, delicate membrane
Subarachnoid space	Contains cerebrospinal fluid (CSF)
Epidural space	Contains adipose tissue and blood vessels
Central canal	Channel for CSF within spinal cord

Key Terms and Definitions

• Neuron: A nerve cell specialized for transmitting electrical impulses.

• Synapse: The junction between two neurons where communication occurs via neurotransmitters.

• Myelin sheath: Insulating layer around axons that increases impulse conduction speed.

• Ganglion: A cluster of neuron cell bodies outside the central nervous system.

• Cerebrospinal fluid (CSF): Fluid that cushions and protects the brain and spinal cord.

Additional info:

• Neurons communicate via both electrical impulses and chemical neurotransmitters.

• Spinal cord organization is essential for reflexes and transmission of sensory/motor information.