Chapter 7The Nervous System

Functions of the Nervous SystemFunctions of the Nervous System1. Sensory input – gathering

information

monitor changes inside and outside the body

Changes = stimuli

2. Integration

process and interpret input and decide on action

3. Motor output

response to stimuli

activates muscles or glands

Structural ClassificationStructural Classification

1. Central nervous system (CNS)

Brain

Spinal cord

2. Peripheral nervous system (PNS)

Nerves outside the brain & spinal cord

2 Divisions of the PNS2 Divisions of the PNSSensory (afferent) division

Nerve fibers that carry information to the central nervous system

Motor (efferent) division

Nerve fibers that carry impulses away from the central nervous system

2 Parts of Motor Division2 Parts of Motor Division1. Somatic = voluntary

2. Autonomic = involuntaryWhich side is fight or flight response?

Neuroglia : Support CellsNeuroglia : Support Cells

1. Astrocytes

Abundant, star-shaped cells

Brace neurons

Form barrier between capillaries and neurons

Control chemical environment of brain

2. Microglia

Spider-like phagocytes

Dispose of debris

3. Ependymal cells

Line cavities of brain and spinal cord

Circulate cerebrospinal fluid

4. Oligodendrocytes

Produce myelin sheath around nerve fibers in CNS

5. Satellite cells

Protect neuron cell bodies

6. Schwann cells

Form myelin sheath in the peripheral nervous system

Neurons = nerve cellsNeurons = nerve cells

1. specialized to transmit messages

2. Major regions

Cell body – nucleus and metabolic center of the cell

Processes – fibers that extend from the cell body

Neuron AnatomyNeuron Anatomy Cell body

a. Nissl substance – specialized rough endoplasmic reticulum

b. Neurofibrils – intermediate cytoskeleton that maintains cell shape

c. Nucleus

d. Large nucleolus

Processes -Extensions outside the cell body

a. Dendrites – conduct impulses toward the cell body

b. Axons – conduct impulses away from the cell body

Axons and Nerve ImpulsesAxons and Nerve Impulses

Axons end in axonal terminals

terminals contain vesicles with neurotransmitters

Synaptic cleft – gap between adjacent neurons

Nerve Fiber CoveringsNerve Fiber Coverings Schwann cells –

produce myelin sheaths in jelly-roll like fashion

Nodes of Ranvier – gaps in myelin sheath along the axon

Figure 7.5

Neuron Cell Body LocationNeuron Cell Body Location In CNS (Most)

1. Gray matter – cell bodies and unmylenated fibers

2. Nuclei – clusters of cell bodies within the white matter of the central nervous system

Outside CNS

1. Ganglia – collections of cell bodies

1. Sensory (afferent) neurons

Carry impulses from sensory receptors to CNS

a. Cutaneous sense organs

b. Proprioceptors – detect stretch or tension

2. Motor (efferent) neurons

Carry impulses from CNS

3. Interneurons (association neurons)

Found in neural pathways in CNS

Connect sensory and motor neurons

Functional Classification of NeuronsFunctional Classification of Neurons

Structural Classification of NeuronsStructural Classification of Neurons

1. Multipolar neurons – many extensions from cell body

2. Bipolar neurons – one axon and one dendrite

3. Unipolar neurons –short single process leaving cell body

Properties of NeuronsProperties of Neurons1. Irritability –respond to stimuli

2. Conductivity –transmit impulses

plasma membrane at rest is polarized

Fewer + ions inside than outside the cell

Starting a Nerve ImpulseStarting a Nerve Impulse

Depolarization – a stimulus depolarizes the neuron’s membrane

allows Na+ to flow inside membrane

exchange of ions initiates an action potential in neuron

The Action PotentialThe Action Potential

If action potential (nerve impulse) starts, it is propagated over the entire axon

K+ rush out after Na+ rush in, which repolarizes the membrane

Sodium-potassium pump restores the original configuration - requires ATP

Impulse moves toward the cell body

Impulses travel faster when fibers have a myelin sheath

Impulses are able to cross the synapses

Neurotransmitter released from nerve’s axon terminal

Dendrite of the next neuron has receptors that are stimulated by neurotransmitter

Action potential is started in the dendrite

Continuation between NeuronsContinuation between Neurons