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Nervous System (Part A-1) Module 8 -Chapter 14

Overview

Cellular structure of the

nervous system

Neurons

Neuroglia

Nervous System Divisions

Central nervous

system

Peripheral nervous

system

Susie Turner, M.D. 1/9/13

Nervous System

• Most complicated system of body

– Senses physical and chemical changes in the internal and external environments

– Coordinates, regulates and integrates voluntary & involuntary activities

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Nerve Impulses

• Also called action potentials – Convey information from

cell to cell. • Charges change across

plasma membrane • Because of flow of Na & K

ions

– Provide Instantaneous response.

Nervous System

• 2 Major Divisions – Central nervous system

• Brain

• Spinal cord

– Peripheral nervous system • Nerves

– Cranial

– Spinal

• Sensory Receptors – Actually nerve endings

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Homeostatic Regulation

• Adjustments in the body’s physiological systems

– To maintain its stable internal environment.

– When environmental change occurs

• Called a stimulus

Homeostatic Mechanisms • 3 NECESSARY COMPONENTS • 1. Receptor

– Receives the stimulus – Transmits stimulus to control

center

• 2. Control Center – Directs or controls – Receives and processes the

information supplied by the receptor • Also called the Integration Center

• 3. Effector – Bodily response

• Causes an effect to happen that opposes the change

• In certain situations can enhance the change

Receptor

Control Center

Effector

(Nerve Endings)

(Brain)

(Muscle)

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Effectors • Cells that produce an action

– “Do Something” upon nerve stimulation

• a. Muscle Cells – Skeletal – Cardiac – Smooth

• b. Glandular Cells

Homeostatic Regulation

• Teacher asks a question in class

• Ears are receptors

• Brain is control center

• Effectors are muscles that control mouth & pharynx

– Action is muscle contraction to answer question.

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Cellular Structure of the Nervous System

• 2 Principal Types of Cells

• Neurons – Transmit nerve impulses

• Neuroglia – Support Cells

Neuron Classification

• Identified by direction the impulse travels – Sensory (Afferent)

• Bring impulses in to CNS – Motor (Efferent)

• Take impulses out of CNS

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Neuroglia

• “Nerve Glue”

• Functions

– Support Neurons & Bind them to other tissues

– Supply nutrients & O2 to neurons

– Assists when neurons injured

• Different types in CNS vs PNS

Neuroglial Cells in CNS • 4 Types

• Astrocytes – “Astro” means star

– "Blood Brain Barrier"

• Oligodendrocytes – “Oligo” means few

– “Dendro” tree-like

– Myelinate "insulate" neuron cytoplasm extensions.

• Microglia – Phagocytes

– Help fight infection

• Ependymal cells – Assist with CSF circulation

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Neuroglial Cells in PNS

• Schwann cells

– Myelinate the cytoplasm extensions

– Many Schwann cells per nerve fiber

Neuron • 3 Major Structures • Cell Body

– Enlarged area – Contains nucleus, organelles, part of cytoplasm

• Dendrites – Receive & transmit impulses to cell body – Dendron = Many tiny branches

• Axons (Nerve Fiber) – Generate & transmit nerve impulse away from cell body

• To muscles, glands & other neurons

– Only one process • End is called axon terminal

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Myelin Sheath

• Lipid-like covering of some axons.

• Functions to; – Insulate fibers

– Speeds nerve impulse transmission

• Axons appear white because sheath is made of Fat.

• Formed by Plasma Membrane of some neuroglia

Myelin Sheath of PNS • Schwann Cell wraps

around axon to form 2 layers. – “Jelly Roll Wrap”

– 1. Inner layer is myelin sheath • Mainly plasma membrane

– 2. Outer layer is Neurilemma • Squeezed plasma

membrane & nucleus of the Schwann cell.

• Assists in healing of peripheral nerves

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CNS Myelin Sheath

• Oligodendrocytes

– One cell wraps many fibers

• Do not have “neurilemma effect”

• Do not help in healing of injured axons

Nodes of Ranvier

• Nodes of Ranvier

– Gaps or indentations between Schwann cells.

– Impulse jumps or leaps across nodes.

– Speeds transmission of impulse.

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Synapse

• Small fluid-filled space between 2 neurons or between a neuron & its target

– Effector cell

• Nerve impulse must travel across this space.

Neurotransmitters

• Chemical messenger released at synapse for communication – Electrical events trigger its release from synaptic vesicles.

• Chemical crosses synapse & binds to certain receptor sites. – To generate next electrical impulse

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Meninges of Brain & Spinal Cord

• 3 Connective Tissue Membranes

– Cover & protect brain & spinal cord

• Dural Mater

• Arachnoid Mater

• Pia Mater

Meninges

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Meninges of Brain & Spinal Cord

• Dura Mater

– Outer layer • Fibrous Connective Tissue

• “Hard or Tough mother”

• Arachnoid Mater

– Middle layer • Delicate & spider-web like

• “Spider mother”

• Spinal fluid circulates in space below

– Subarachnoid Space

Meninges of Brain & Spinal Cord

• Pia Mater – Innermost delicate layer

• “Little or Tender Mother”

• Clings tightly to surface of brain & spinal cord

• Contains blood vessels & lymphatics

– Nourish outer brain

– Leptomeninges • Term for arachnoid &

pia mater

• Due to thinness & delicacy

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Cerebrospinal Fluid (CSF)

• Colorless fluid

– Contains proteins, glucose, urea, salts, & some WBCs

– Circulates around spinal cord & through ventricles of brain

– Provides nutritive substances to the CNS & cushions it

Ventricles of the Brain

• Total of 4 Ventricles – Contain CSF – Connect with each other thru canals & foramens

• 2 Lateral Ventricles – “Ram horn shaped”

• 3rd Ventricle • 4th Ventricle