Chapter 10 Basics of the Nervous System 10-1. Chapter 10 Nervous System I Composed mainly of neural tissue Cell Types of Neural Tissue neurons transmit.

Chapter 10

Basics of the Nervous System

10-1

Chapter 10Nervous System I

Composed mainly of neural tissue•Cell Types of Neural Tissue

• neurons• transmit impulses

• neuroglial cells• assist neurons

10-2

Divisions of the Nervous System

• Central Nervous System• brain• spinal cord

• Peripheral Nervous System• peripheral nerves

• cranial nerves• spinal nerves

10-1

Divisions of Peripheral Nervous System

Sensory Division• picks up sensory information and delivers it to the CNS

Motor Division•carries information to muscles and glands

•Somatic – carries information to skeletal muscle•Autonomic – carries information to smooth muscle, cardiac muscle, and glands

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Divisions Nervous System

10-5

Functions of Nervous System

Sensory Function• sensory receptors gather information• information is carried to the CNS

Integrative Function• sensory information used to create

• sensations• memory• thoughts• decisions

Motor Function• decisions are acted upon • impulses are carried to effectors

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Neuron Structure

10-7

Myelination of Axons

White Matter• contains myelinated axons (lipid)

Gray Matter• contains unmyelinated structures

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Classification of Neuronsbased on shape

Bipolar• two processes• eyes, ears, nose

Unipolar• one process• ganglia

Multipolar• many processes• most neurons of CNS

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Classification of Neuronsbased on function

Sensory Neurons• carry impulse to CNS (afferent)• most are unipolar• some are bipolar

Interneurons• link neurons/ neuronal pathways• multipolar• in CNS

Motor Neurons • carry impulses away from CNS (efferent)•multipolar• carry impulses to effectors 10-10

Types of Neuroglial Cellsprovide scaffolding, position neurons, remove ions/neurotransmitters,

produce growth factors

Schwann Cells• PNS• myelinating cell

Oligodendrocytes• CNS• myelinating cell

Astrocytes• CNS• scar tissue• mop up excess ions, etc• induce synapse formation• connect neurons to blood vessels

Microglia• CNS• phagocytic cell (immune)

Ependyma• CNS• ciliated• line central canal of spinal cord• line ventricles of brain

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Types of Neuroglial Cells

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Regeneration of A Nerve Axon

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Resting Membrane Potential

•Before stimulation, nerve must be in its resting potential•Active transport keeps sodium (Na+) ions out and potassium (K+) ions inside cell•inside is negative relative to the outside (because of other ions); negative inside/positive outside• polarized membrane• due to distribution of ions• Na+/K+ pump

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Potential Changes• at rest membrane is polarized (- in)

• sodium channels open and membrane depolarizes (Na rushes in)

• potassium channels open and membrane repolarizes (K rushes out) (- in)

• threshold stimulus reached (causes action potential)

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•Creates momentary hyperpolarization (+ in)

•Na is now in and K is now out•whole process takes 1/1000 of a second

Action Potentials

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•An action potential in one region stimulates an action potential in the adjacent region•Action potential travels down axon (one way)

Action Potentials/Nerve Impulse

•caused by various stimuli•chemicals•temperature changes•mechanical forces

• occur on dendrites, cell bodies, and axons• all-or-none• refractory period

• absolute - time when threshold stimulus does not start another action potential• relative – time when stronger threshold stimulus can start another action potential

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Saltatory Conduction

10-20

•Action potential occurs only at nodes, jumps from node to node•Myelin and diameter of fiber determine speed of potential.•Thick/myelinated fiber- 120 meters/sec ; thin/unmyelinated- 0.5 meters/sec

The Synapse

Nerve impulses pass from neuron to neuron at synapses – space between neurons

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Synaptic Transmission

Neurotransmitters are released when impulse reaches synaptic knob

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Neurotransmitters

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Impulse Processing

Neuronal Pools• groups of interneurons that make synaptic connections with each other • interneurons work together to perform a common function • each pool receives input from other neurons• each pool generates output to other neurons

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Convergence

• neuron receives input from several neurons• incoming impulses represent information from different types of sensory receptors• allows nervous system to collect, process, and respond to information• makes it possible for a neuron to sum impulses from different sources

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Divergence

• one neuron sends impulses to several neurons• can amplify an impulse• impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction 10-28