Nervous System Overview

Main Functions and Core Sequence

The nervous system is the body's primary controlling and communicating system, operating through rapid electrical impulses. Its three main functions are:

• Sensory input: Gathers information by monitoring changes (stimuli) inside and outside the body.

• Integration: Processes and interprets sensory input, deciding what action is needed.

• Motor output: Responds to integrated stimuli by activating muscles or glands (effectors).

The sequence is: Sensory input → Integration → Motor output.

Structural and Functional Classification

• Central Nervous System (CNS): Command center consisting of the brain and spinal cord.

• Peripheral Nervous System (PNS): Nerves extending from the CNS; includes cranial and spinal nerves.

• Sensory (afferent) division: Carries information to the CNS.

• Motor (efferent) division: Carries impulses away from the CNS to effectors.

• Somatic nervous system: Voluntary control of skeletal muscles.

• Autonomic nervous system: Involuntary control of smooth/cardiac muscle and glands; subdivided into sympathetic and parasympathetic divisions.

Nervous Tissue: Support Cells (Neuroglia)

Types and Functions of Neuroglia

Neuroglia (glial cells) are support cells in the CNS and PNS. They do not transmit electrical impulses and retain the ability to divide.

Oligodendrocytes = CNS myelin; Schwann cells = PNS myelin.

Neuron Anatomy and Terminology

Structure and Function of Neurons

Neurons are specialized cells for transmitting electrical signals. Their major regions are:

• Cell body: Contains nucleus; metabolic center.

• Dendrites: Conduct impulses toward the cell body; numerous per neuron.

• Axon: Conducts impulses away from the cell body; one per neuron.

• Axonal terminals: Branches at axon end; contain neurotransmitter vesicles.

• Synaptic cleft: Gap between adjacent neurons.

• Synapse: Junction between nerves.

Myelin sheath is a fatty covering that insulates axons and increases impulse transmission speed. Nodes of Ranvier are gaps in the myelin sheath.

CNS terminology: Cell bodies = nuclei; nerve fibers = tracts. PNS terminology: Cell bodies = ganglia; nerve fibers = nerves.

Gray matter: Unmyelinated fibers. White matter: Myelinated fibers (tracts); cell bodies (nuclei).

Classification of Neurons

Functional Classification

• Sensory (afferent) neurons: Carry impulses from sensory receptors to CNS; include cutaneous sense organs and proprioceptors.

• Motor (efferent) neurons: Carry impulses from CNS to muscles/glands.

• Interneurons (association neurons): Connect sensory and motor neurons within CNS.

Proprioceptors detect stretch/tension in muscles, tendons, and joints.

Structural Classification

• Multipolar neuron: Many dendrites, one axon.

• Bipolar neuron: One dendrite, one axon.

• Unipolar neuron: Single short process with peripheral and central branches.

Reflexes and Reflex Arcs

Types and Elements of Reflexes

Reflexes are rapid, predictable, involuntary responses to stimuli, occurring over neural pathways called reflex arcs. Types include:

• Somatic reflex: Stimulates skeletal muscles (e.g., withdrawal from heat).

• Autonomic reflex: Regulates smooth muscle, heart, glands, blood pressure, digestion.

The five elements of a reflex arc are:

1. Sensory receptor – reacts to stimulus

2. Sensory neuron – carries message to CNS

3. Integration center – processes information

4. Motor neuron – carries message to effector

5. Effector organ – muscle or gland stimulated

Central Nervous System: Brain

Major Brain Regions

• Cerebral hemispheres (cerebrum): Paired superior parts; >50% of brain mass.

• Diencephalon

• Brain stem

• Cerebellum

Gyri: Elevated ridges. Sulci: Shallow grooves. Fissures: Deep grooves dividing lobes.

Cerebral Cortex Functional Areas

• Primary somatic sensory area: Receives impulses from sensory receptors (pain, cold, touch).

• Primary motor area: Sends impulses to skeletal muscles.

• Broca's area: Speech/vocalization.

• Gustatory area: Taste.

• Visual area: Vision.

• Auditory area: Hearing.

• Olfactory area: Smell.

• Interpretation areas: Speech/language and comprehension.

Cerebral White Matter

• Fiber tracts: Deep to gray matter; transmit impulses to/from cortex.

• Corpus callosum: Connects hemispheres; transmits impulses between them.

Diencephalon, Brain Stem, and Cerebellum

Diencephalon

• Thalamus: Sensory relay station; transfers impulses for localization/interpretation.

• Hypothalamus: Autonomic center; regulates temperature, metabolism, drives; part of limbic system; pituitary gland attached.

• Epithalamus: Pineal body; choroid plexus forms CSF.

Brain Stem

• Midbrain: Mostly tracts.

• Pons: Fiber tracts; nuclei for breathing control.

• Medulla oblongata: Control centers for heart rate, blood pressure, breathing, swallowing, vomiting.

Cerebellum

• Two hemispheres; convoluted surfaces.

• Outer cortex = gray matter; inner region = white matter.

• Involuntary coordination for balance/equilibrium.

• Interprets equilibrium info from ears, eyes, proprioceptors.

Protection of the Central Nervous System

Meninges

The meninges are connective tissue membranes surrounding the CNS:

• Dura mater: Outermost, double-layered covering.

• Arachnoid mater: Middle, web-like layer; villi protrude through dura.

• Pia mater: Internal layer; clings to brain/spinal cord surface.

Order: Dura mater → Arachnoid mater → Pia mater (D-A-P).

Cerebrospinal Fluid (CSF)

• Similar to blood plasma.

• Formed by choroid plexuses.

• Watery cushion protecting brain from trauma.

• Circulates in subarachnoid space and central canal; reabsorbed at subdural sinuses.

Blood-Brain Barrier

• Allows passage of water, glucose, essential amino acids, fats, respiratory gases, alcohol, nicotine, anesthesia.

• Excludes urea, toxins, proteins, most drugs.

Spinal Cord

Anatomy and Function

• Extends from foramen magnum to L1-L2 vertebra.

• Two-way conduction pathway to/from brain.

• Internal gray matter: Cell bodies; dorsal (posterior) and anterior (ventral) horns; surrounds central canal.

• Central canal: Filled with CSF.

• Exterior white matter: Conduction tracts; divided into dorsal, lateral, ventral columns.

• Meninges: Cover spinal cord.

• Spinal nerves: Leave at each vertebra level.

• Dorsal root: Associated with dorsal root ganglia (cell bodies outside CNS).

• Ventral root: Contains axons.

Quick-Review Table: Nervous System Terms

Practice Questions (with Answers)

1. Which part of the nervous system contains the brain and spinal cord? Answer: CNS

2. Which division carries nerve impulses toward the CNS? Answer: Afferent

3. Which glial cell forms myelin in the PNS? Answer: Schwann cell

4. Which glial cell disposes of debris? Answer: Microglia

5. Dendrites conduct impulses in which direction? Answer: Toward the cell body

6. A bundle of nerve fibers in the CNS is called a: Answer: Tract

7. Which neuron connects sensory and motor neurons in the CNS? Answer: Interneuron

8. Which is the first element of a reflex arc? Answer: Sensory receptor

9. Which reflex type stimulates skeletal muscles? Answer: Somatic reflex

10. Which structure is the relay station for sensory impulses? Answer: Thalamus

11. Which area sends impulses to skeletal muscles? Answer: Primary motor area

12. Broca's area is associated with: Answer: Speaking/vocalizing

13. Which structure connects the two cerebral hemispheres? Answer: Corpus callosum

14. Which brain-stem region contains control centers for heart rate and blood pressure? Answer: Medulla oblongata

15. Which structure provides involuntary coordination for balance and equilibrium? Answer: Cerebellum

16. Put the meninges in order from outside to inside: Answer: Dura → arachnoid → pia

17. What forms cerebrospinal fluid according to the slides? Answer: Choroid plexuses

18. The spinal cord extends to approximately which vertebral level? Answer: L1-L2

19. In the spinal cord, gray matter is mainly: Answer: Internal

20. The dorsal root is associated with the: Answer: Dorsal root ganglion

• Neuroglia transmit electrical impulses. Answer: False

• Nodes of Ranvier are gaps in the myelin sheath. Answer: True

• The somatic nervous system allows voluntary control of skeletal muscles. Answer: True

• The pia mater is the outermost meningeal layer. Answer: False

• The central canal of the spinal cord contains cerebrospinal fluid. Answer: True

Additional info: This guide covers the core concepts and terminology for Chapter 7: The Nervous System, suitable for exam preparation in Anatomy & Physiology college courses.