Chapter 11: Nervous System (Part 1,2,3)

Nervous System

Master controlling and communicating system of body

• It is reflected in every thought, action, and emotion

• Cells communicate via electrical and chemical signals

Rapid and specific

Usually cause almost immediate responses

Communication Method

Cells use electrical & chemical signals

Primary Functions

Sensory input, intergration, motor output

Sensory input

sensory receptors gather info about internal & external changes.

Integration

system processes & interprets sensory input to decide on appropriate action

Motor output

effector organs (muscles & glands) activated to produce response to stimulus

Divisions of the Nervous System

Central Nervous System (CNS), Peripheral Nervous System (PNS)

Central nervous system (CNS)

• Consists of brain & spinal cord

• Integration & control center

• Interprets sensory input + dictates motor output

Peripheral nervous system (PNS)

• Portion of nervous system outside CNS

- Consists of spinal nerves to & from spinal cord

- Cranial nerves to and from the brain

Two Divisons:

Sensory (Afferent) Divison

Motor (Efferent) Division

Sensory (Afferent) Divison

• Keeps CNS informed about events happening on the inside & outside of the body

• Has nerve fibers (axons) that carry info to the CNS from sensory receptors found throughout the body

Subdivisons:

Somatic sensory fibers

• Visceral sensory fibers

Somatic sensory fibers

convey impulses from skin, skeletal muscles, and joints to CNS

Visceral sensory fibers

convey impulses from visceral organs to CNS

Motor (Efferent) Division

• Transmits impulses from CNS to effector organs (muscles & glands)

- Impulses cause muscles to contract and glands to secrete

Two subdivisions:

1 - Somatic nervous system (SNS)

2. Autonomic nervous system (ANS)

Autonomic nervous system (ANS) Two functional subdivisions:

Sympathetic

Parasympathetic

Work in opposition to each other

Somatic nervous system (SNS)

somatic motor nerve fibers that conduct voluntary impulses from the CNS to skeletal muscles

(voluntary nervous system since we have conscious control over these skeletal muscles)

Autonomic nervous system (ANS)

composed to visceral motor nerve fibers that

regulate involuntary activity (smooth/cardiac muscles & glands)

( Involuntary nervous system since we have no control conscious control over these muscles)

Two functional subdivisions:

Sympathetic (mobilizes systems)

Parasympathetic (conserves energy) divisons

Work in opposition to each other

Histology of Nervous System

Highly cellular; little extracellular space so they are tightly packed

Two principal cell types:

• Neuroglia (Glial cells) - small cells that support + protect neurons

• Neurons (nerve cells)—excitable cells that transmit electrical signals

Neurologia (Glial cells)

• Have a branching extensions (processes) and central cell body

• Much smaller in size and have a dark nuclei

• Make up half of the brain mass

Types:

• Astrocytes (CNS)

• Microglial cells (CNS)

• Ependymal cells (CNS)

• Oligodendrocytes (CNS)

• Satellite cells (PNS)

• Schwann cells (PNS)

CNS= brain & spinal cord

PNS= peripheral nerves

CNS Neurologia

Astrocytes: Most abundant; support neurons and control the chemical environment.

Microglial Cells: Defensive cells that monitor neuron health and phagocytize debris.

Ependymal Cells: Line central cavities and circulate cerebrospinal fluid (CSF) via cilia.

Oligodendrocytes: Form insulating myelin sheaths around CNS nerve fibers.

PNS Neurologia

Satellite Cells: Surround neuron cell bodies; function similarly to astrocytes of CNS.

Schwann Cells: Form myelin sheaths around peripheral nerve fibers; vital for (peripheral nerve) fiber regeneration (fix damage).

Neurons (Nerve Cells)

Large, specialized, amitotic cells that conduct electrical impulses.

Structural Characteristics: High metabolic rate requiring continuous oxygen and glucose.

Types:

Cell Body (Soma)

Dendrites

Axon

Neuron Structural Characteristics

High metabolic rate requiring continuous oxygen and glucose

Cell Body (Soma)

Biosynthetic center containing the nucleus and organelles.

Dendrites

Short, branched processes that serve as the main receptive (input) region.

Axons

Conducts impulses away from the cell body toward axon terminals to release neurotransmitters.

Specialized Neuron Processes and Myelination: Axonal Transport:

 Movement occurs in two directions: Anterograde (away from cell body for renewal) and Retrograde (toward cell body for degradation or signaling.

Specialized Neuron Processes and Myelination: Myelin Sheaths

Whitish, protein-lipoid substance that insulates axons and increases the speed of nerve impulse transmission.

Types of Myelination:

PNS Myelination

CNS Myelination

PNS Myelination:

Formed by Schwann cells wrapping in a "jelly roll" fashion, leaving gaps called Nodes of Ranvier

CNS Myelination

Formed by multiple flat processes of oligodendrocytes

Tissue Classifications: of Myelination Sheaths in CNS

White matter contains dense collections of myelinated fibers, while gray matter consists mostly of cell bodies and nonmyelinated fibers.

Structural Classification of Neurons

Based on the number of processes.

Types:

Multipolar

Bipolar

Unipolar

Multipolar

Three or more processes (1 axon, many dendrites); most common in CNS

Bipolar

Two processes (1 axon, 1 dendrite); rare, found in retina and olfactory mucosa.

Unipolar

One short process that divides T-like into two branches.

Functional Classification of Neurons

Based on the direction of impulse travel.

Types: (3)

Sensory (Afferent)

Motor (Efferent)

Interneurons

Sensory (Afferent)

Transmit toward the CNS; mostly unipolar.

Motor (Efferent)

Carry away from the CNS to effectors; multipolar.

Interneurons

Lie between sensory and motor neurons; shuttle signals through CNS pathways (99% of all neurons).

Principles of Electricity

Voltage measures potential energy from separated charges; current is the flow of ions; resistance is the hindrance to that flow.

Ion channels

Selective proteins that control ion flow.

Types:

Leakage Channels

Gated Channels

Leakage Channels

Always open.

Gated Channels

 Open/close in response to chemical binding (ligand-gated), voltage changes (voltage-gated), or physical deformation (mechanically gated).

Resting Membrane Potential (RMP)

Potential Difference across membrane of resting cell. Exists only across the membrane.

• Typically –70 mV in neurons.

• Maintained by differences in ion concentrations (High Na+ outside, High K+ inside) and differential permeability.

• Sodium-Potassium Pump

Sodium-Potassium Pump

Stabilizes RMP by pumping 3 Na+ out and 2 K+ in.

Changes in Membrane Potential

Depolarization, Hyperpolarization, Signal Types

Depolarization

The membrane potential becomes less negative (toward zero), increasing the likelihood of a nerve impulse.

Hyperpolarization

The membrane potential becomes more negative, reducing the likelihood of a nerve impulse.

Signal Types:

Graded potentials are short-distance signals, while action potentials are long-distance signals along axons