Functions of the Nervous System

Functions of the Nervous System

• Maintains homeostasis through electrical signals.
• Facilitates sensation and higher mental functions, including emotions.
• Controls and activates muscles and glands.

Roles of the Nervous System

• Sensory Input: Gathers information about internal and external stimuli.
• Integration: Processes and interprets sensory information to determine action.
• Motor Output: Executes responses to stimuli by activating muscles or glands.

Structural Classification of the Nervous System

• Central Nervous System (CNS): Comprises the brain and spinal cord; located in the dorsal cavity; serves as the command center for processing information.
• Peripheral Nervous System (PNS): Consists of nerves outside the CNS; facilitates communication between the CNS and the body.

Functional Classification of the PNS

• Sensory (Afferent) Division: Carries information to the CNS.
• Motor (Efferent) Division: Carries impulses away from the CNS; divided into:
  • Somatic Nervous System: Voluntary control over skeletal muscles.
  • Autonomic Nervous System: Involuntary control over smooth muscles and glands.

Neuroglia vs. Neurons

• Neuroglia can divide; neurons cannot.
• Most brain tumors (gliomas) originate from neuroglial cells.

Support Cells in the CNS

• Astrocytes: Provide structural support, regulate neuronal signaling, assist in repair.
• Ependymal Cells: Line brain ventricles and spinal canal; produce and circulate cerebrospinal fluid (CSF).
• Microglia: Act as phagocytes to protect against infection.
• Oligodendrocytes: Form the myelin sheath in the CNS.

Support Cells in the PNS

• Schwann Cells: Produce myelin sheaths around peripheral nerves.
• Satellite Cells: Offer support and nutrition to neurons and protect from toxins.

Neuron Anatomy

• Neurons consist of a cell body (with nucleus) and processes (dendrites and a single axon).
• Dendrites convey impulses toward the cell body; axons transmit impulses away.

Nerve Impulses and Axon Terminology

• Axonal terminals contain neurotransmitter vesicles, separated from adjacent neurons by the synaptic cleft.
• Synapse: The junction where neuron communication occurs.

Nerve Fiber Coverings

• Schwann Cells: Myelinate peripheral axons.
• Nodes of Ranvier: Gaps in myelin sheaths that facilitate faster signal transmission.

Neuron Cell Body Location

• Most neurons reside in the CNS, forming gray matter (cell bodies and unmyelinated fibers) and white matter (myelinated axons).
• Nuclei: Clusters of cell bodies within the CNS white matter.
• Ganglia: Collections of cell bodies in the PNS.

Classification and Function of Neurons

• Sensory Neurons: Transmit impulses from sensory receptors to the CNS.
• Motor Neurons: Convey impulses from the CNS to muscles and glands.
• Interneurons: Connect sensory and motor neurons within the CNS.

Physiology of Neurons

• Irritability: Neurons can respond to stimuli.
• Conductivity: Ability to transmit impulses.
• Neurons at rest have a polarized membrane.

Starting a Nerve Impulse

• Depolarization: Stimulus triggers sodium ions to enter the neuron, initiating an action potential.

Action Potential Propagation

• If initiated, the action potential spreads along the axon.
• Sodium influx followed by potassium efflux repolarizes the membrane.

Nerve Impulse Propagation

• Myelinated fibers transmit impulses more rapidly due to saltatory conduction.

Synaptic Transmission

• Impulses bridge the synapse through neurotransmitter release, affecting receptor-stimulated dendrites of adjacent neurons.

Reflex Arc

• Reflexes are rapid, involuntary responses; the reflex arc provides a direct route from sensory neurons, through interneurons, to effectors.

Central Nervous System Development

• CNS originates from the embryonic neural tube, evolving into the brain and spinal cord.

Brain Structure Regions

• Major parts are the cerebral hemispheres, diencephalon, brain stem, and cerebellum.

Cerebral Hemispheres

• Consist of left and right halves; contain more than 50% of brain mass.
• Structurally defined by gyri (ridges) and sulci (grooves).

Lobes of the Cerebrum

• Cerebrum is divided into frontal, parietal, occipital, and temporal lobes, each with specific sensory and motor functions.

Specialized Areas of the Cerebrum

• Regions for speech, language comprehension, and general interpretation.

Cerebral Layers

• Gray Matter: Outer layer that initiates thoughts and actions.
• White Matter: Composed of myelinated axons, facilitating impulse conduction.

Diencephalon Structure

• Comprised of the thalamus, hypothalamus, and epithalamus; functions in sensory relay, homeostasis, and endocrine regulation.

Brain Stem Components

• Includes the midbrain, pons, and medulla oblongata; controls vital functions such as heart rate and breathing.

Cerebellum Function

• Coordinates balance and voluntary movements through its convoluted surface structure.

Protection of the CNS

• Encased by scalp, skull, and vertebral column; protected by meninges and cerebrospinal fluid.

Meninges Structure

• Dura Mater: Tough outer layer.
• Arachnoid Layer: Web-like middle layer.
• Pia Mater: Thin inner layer adhering to the brain.

Cerebrospinal Fluid

• Provides cushioning for the brain; composition changes can indicate medical conditions.

Blood-Brain Barrier

• Comprised of tightly sealed capillaries; selectively excludes harmful substances while allowing some essential nutrients to pass.

Spinal Cord Characteristics

• Extends from the medulla to the T12 region; serves as a conduit for nerve impulses and spinal reflex centers; contains 31 pairs of spinal nerves.