Chapter 11 Functional Organization of Nervous Tissue BIOL-3301

Neurons
Glial cells

What are two cells of Nervous tissue?

Neurons

electrically excitable cells of the nervous system

Glial cells

supportive cells

Neurons
Microglia
Astrocytes
Ependymal
Oligodendrocytes

CNS cells

Neurons
Satelittle cells
Schwann cells

PNS cells

Microglia

Innate immunity

Astrocytes

Maintain blood brain barrier integrity, participate in synapses

Ependymal

Build barriers between compartments

Oligodendrocytes

Produce myelin sheaths

Satellite cells

Support other cells bodies

Schwann cells

Produce myelin sheaths around axons

-Maintaining homeostasis
-Receiving sensory input
-Integrating information
-Controlling muscles and glands
-Establishing and maintain mental activity

Functions of the nervous system

Central nervous system
Peripheral nervous system

Divisions of the nervous system are

CNS

-Receives information from and sends information to the body
-Decision maker
-Consists of the brain and spinal cord

PNS

-Detects stimuli in and around the body
-Carries information to the CNS and from the CNS to the body
-Consists of nerves, ganglia, and sensory receptors

Brain
Spinal cord

What does the CNS consist of?

Nerves
Ganglia
Sensory receptors

What does the PNS consist of?

Nerves

Collection of axons outside the brain and spinal cord and can carry electrical signals away or towards the CNS?

12

How many pairs of cranial nerves are there?

31

How many pairs of spinal nerves are there?

Plexus

bundle of nerves outside the brain and spinal cord

Ganglia

Group of neuron cell bodies outside the brain and spinal cord

Sensory receptors

Cells that respond to a specific stimuli that can be neurons or specialized cells that are distributed throughout the body

Sensory division
Motor division

Divisions of the PNS

Sensory division

Transmits electrical signals from receptors to the CNS

Motor division

Transmits electrical signals from the CNS to the effector organs (includes muscle and glands)

Somatic
Autonomic

Divisions of the Motor Nervous System

Somatic nervous system

Voluntary division that regulates movement of skeletal muscles

Autonomic nervous system

Involuntary division that regulates contract of cardiac and smooth muscles and secretions of glands

Sympathetic
Parasympathetic
Enteric

Divisions of autonomic nervous system

Sympathetic nervous system

Prepares body for physical activity; "fight or flight"

Parasympathetic nervous system

Regulates resting functions (digesting food); "rest and digest"

Enteric nervous system

Neuronal networks in the wall of digestive tract

50%

How much of the brain's weight is glial cells?

Cell body
Dendrites
Axons

Neurons Structure

Cell body (Soma)

-Single, centrally located nucleus with nucleolus; contains nissl bodies
-Abundant intermediate filaments and microtubules forming bundles in the cytoplasm

Nissl bodies

extensive rough endoplasmic reticulum

Dendrites

-Processes off the cell body
-Short, often highly branched
-Tapered from base to tip
-Receives input from other neurons and other sensory receptors

Dendritic spines

small extension on the surface where synapses are formed

Axons

-Single process off the cell body
-Constant diameter with varied length

Axoplasm
Axolemma
Axon hillock
Initial segment
Trigger zone
Presynaptic terminal

Structure of Axons

Axoplasm

cytoplasm of the axon

Axolemma

plasma membrane of the axon

Axon hillock

cone shaped area coming off cell body

Initial segment

formed by narrowing of axon hillock

Trigger zone

axon hillock and initial segment, where action potentials are generated

Presynaptic terminal

region at the end of the axon that house synaptic vesicles storing neurotransmitters

Synapse

point of contact between the axon ending and its effector

Direction of action potential conduction

What is the functional classes of neurons based on?

Sensory neurons
Motor neurons
Interneurons

Functional Classes of Neurons

Sensory neurons

conduct action potentials toward CNS

Motor neurons

conduct action potentials away from the CNS toward muscles or glands

Interneurons

conduct action potentials within the CNS

Number of Dendrites

What is structural classes of neurons based on?

Multipolar neurons
Bipolar neurons
Pseudo-unipolar neurons
Anaxonic nurons

Structural classes of neurons

Multipolar neurons

Many dendrites and a single axon; motor neurons of the PNS and most neurons within CNS

Bipolar neurons

One dendrite and one axon; located in sensory organ

Pseudo-unipolar neurons

Single process that exits the cell body and divides into two branches that function as a single axon

Anaxonic neurons

Do not have axons only dendrites; found in brain and retina

Peripheral process

extends to periphery and has dendrites that act as sensory receptors or communicate with sensory receptors

Blood brain barrier

-Controls substances that pass from blood into brain and spinal cord
-Protects neurons from toxins
-Allows nutrients and waste products to be exchanged
-Prevents fluctuations in blood composition

Reactive astrocytosis

Astrocytes wall off injury site; limit spread of inflammation; and limit regeneration of axons of injured neurons; caused by injury of CNS

Choroid plexuses

-Specialized ependymal cells and blood vessels located in regions of the ventricles
-Secretes cerebrospinal fluid

Neurilemma

-Outermost layer of each Schwann cell
-Contains majority of Schwann cell cytoplasm, nucleus, and organelles

Myelinated Axons

-Wrapped up in either Schwann cells pr oligodendrocytes
-Forms layers of phospholipids with small amounts of cytoplasm
-Protect and electrically insulate the axons

Nodes of Ranvier

gaps in the myelin sheath

Unmyelinated Axons

Protects axons and axons rest in invaginations of Schwann cells or oligodendrocytes

Starts in late fetal development and rapidly until 1 year old; slowly after

When is the development of Myelin sheath?

Multiple sclerosis

-Chronic disease of CNS
-Gradual loss of myelin sheath
-Slows action potential transmission
-Impairs control of skeletal and smooth muscle

Gray matter

Contains neuron cell bodies and dendrites

Gray Matter (CNS)

Cortex and Nuclei

Gray Matter (PNS)

Ganglia

White Matter

Bundles of myelinated axons

White Matter (CNS)

Nerve tracts

White Matter (PNS)

Nerves

Action Potentials

electrical signals produced by the ervous system

Membrane Potential

measure of electrical properties of the plasma membrane

Causes of membrane potential

-Ionic concentration differences across the plasma membrane
-Permeability characteristics of the plasma membrane

Ion channels and pumps

What determines the permeability of the plasma membrane?

Sodium-potassium pump
Leak Channels
Gated Channels

Types of Pumps and Ion Channels

Sodium-Potassium pump

contribute to the maintaining the differences in cytoplasmic and extracellular concentrations of ions

Leak Channels

-Always open
-Specific for one type of ion

Leak channel

What type of channel is responsible for permeability of the plasma membrane at rest?

Gated-Ion Channels

Open and close due to specific signal

Ligand-gated
Voltage-gated
Mechanically-gated
Thermoreceptors

Types of Gated ion channels

Ligand-gated ion channels

Opened by binding of a specific molecule on the extracellular side; channel crosses membrane

Voltage-gated ion channels

Open and close in response to specific voltage changes across the plasma membrane and is required for action potentials

Mechanically-gated ion channels

Open in response to mechanical stimulation

Thermoreceptors

Respond to temperature changes

Potential difference

electrical charge difference across the plasma membrane

Resting membrane potential

potential difference in a resting cell

Depolarization
Hyperpolarization

Two types of changes in resting membrane potential

Depolarization

Inside of cell becomes more positive; Excitatory

Na+ and Ca2+ entry

Factors for depolarization of neurons

Excitatory

always moves the membrane closer to the point of action potential generation

Hypocalcemia

Lower levels of Ca2+ in the blood
-Symptoms-nervousness and uncontrolled skeletal muscle contractions

Hyperpolarization

Inside of cell becomes even more negative; Inhibitory

K+ exits
Cl- enters

Two ways to hyperpolarize neurons

Inhibitory

makes the cell less likely to generate an action potentials

Hypokalemia

lowers blood K+ concentration
-Symptoms-muscular weakness, abnormal heart function, sluggish reflexes