April 9, The Nervous system can be organized by. The Nervous system can be organized by i STRUCTURE i FUNCTION. Central Nervous System (CNS) CNS

(1)

The Nervous system can be organized by

i

STRUCTURE

i FUNCTION

The Nervous system can be organized by

i FUNCTION

_{Central Nervous}

System (CNS)

(2)

The Nervous system can be organized by

i FUNCTION

_{Central Nervous}

System (CNS)

Peripheral Nervous System

(PNS)

The Nervous system can be organized by

i FUNCTION

_{Central Nervous}

System (CNS)

(PNS)

1. Collecting information:

• Sensory receptors in the PNS detect changes in the internal and external environment ➟ pass the information on to the CNS

2. Processing and evaluating information:

• CNS determines the required response

3. Responding to information:

• CNS sends nerve impulses via motor neurons in the PNS to the effectors (muscles or glands!), which then react

The Nervous system can be organized by

i FUNCTION

_{Central Nervous}

System (CNS)

(PNS)

The Nervous system can be organized by

i FUNCTION

_{Central Nervous}

System (CNS)

(PNS)

(3)

The Nervous system can be organized by

i FUNCTION

_{Central Nervous}

System (CNS)

(PNS)

3. Responding to information:

• CNS sends nerve impulses via motor neurons in the PNS to the effectors (muscles or glands!), which then react

The Nervous system can be organized by

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• A nerve = a cablelike

bundle of parallel axons

(similar to the arrangement found in muscles)

• Surrounded by three

connective tissue

wrappings

1. Endoneurium: Around each axon 2. Perineurium: Around individual 3. Epineurium: Around the entire nerve

• A nerve = a cablelike

bundle of parallel

axons

(similar to the arrangement found in muscles)

• Surrounded by three

connective tissue

wrappings

1. Endoneurium: Around each axon 2. Perineurium: Around individual fascicles 3. Epineurium: Around the entire nerve (bundles of fascicles)

1. Neurons (nerve cells): Electrically excitable cells that initiate, transmit, and receive nerve impulses

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Receive information

A neuron has three main structural regions:

1. Cell body • aka the “soma” • Contains organelles that

allow neuron to function as a cell, manufacture neurotransmitters, carry out cellular respiration, etc.

• Serves as attachment point and junction between its own dendrites and axon(s) • Can itself synapse with

other neurons to receive messages

• Nervous signals can be transmitted along its plasma membrane!

A neuron has

three main

structural

regions:

2. Dendrites

• Short processes that branch from the cell body

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A neuron has

three main

structural

regions:

3. Axon

• transmit nerve impulses away from the cell body and transmit information to other cells • The region where

the axon connects to the cell body is the axon hillock

1. Axon collaterals: Side branches off the main axon (not found in all neurons) 2. Telodendria: Fine terminal

extensions at the end of the axon and its collaterals 3. Synaptic knobs (aka axon

terminal; aka synaptic bulbs): Expanded regions at the tip of telodendria

extensions at the end of the axon and its collaterals

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terminal; aka synaptic bulbs): Expanded regions at

the tip of telodendria

• Nervous signal

conduction velocities vary

widely among neurons

• Rate of impulse

propagation is determined

by:

1. Axon diameter – the larger the diameter, the faster the impulse 2. Presence of a myelin sheath:

• made of lipids and acts like an electrical insulator around the axon • myelination dramatically increases

nerve signaling speed

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• A typical

synapse

consists of:

• Presynaptic neuron • Postsynaptic neuron • Synaptic cleft

• Specialized for the release and reception of neurotransmitters • Typically composed of

two parts:

• Axonal terminal of the presynaptic neuron, which contains synaptic vesicles

• Receptor region on the dendrite(s) or cell body of the postsynaptic neuron

• Specialized for the release and reception of neurotransmitters • Typically composed of

two parts:

• Axonal terminal of the presynaptic neuron, which contains synaptic vesicles

• Receptor region on the dendrite(s) or cell

SYNAPTIC CLEFT

• Fluid-filled space separating the presynaptic and postsynaptic neurons

• Prevents nerve impulses from directly passing from one neuron to the next

• Transmission across the synaptic cleft:

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SYNAPTIC CLEFT

• Nerve impulses reach the axonal terminal of the presynaptic neuron • Neurotransmitter crosses

the synaptic cleft and binds to receptors on the postsynaptic neuron • Postsynaptic membrane

permeability changes, causing an excitatory or inhibitory effect

Structurally, neurons are classified into 3 major groups, depending on the number of cell processes emanatingdirectly from the cell body:

• Single, short cell process that branches like a T

• Peripheral dendrites are often , specifically for pain, touch, pressure, or temperature detection

• Two processes, one dendrite and one axon, extend directly from the cell body

• Not very common in the human body

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• Many dendrites and a single axon

There are 3 functional classifications of neurons:

• Specialized dendrites (aka sensory receptors!) detect stimuli inside or outside of the body

• Send message regarding the stimuli to the CNS (brain or spinal cord) • Responsible for sensory reception (pain, touch, taste, vision, hearing, smell,

etc.)

• Most are either unipolar (pseudo-unipolar) or bipolar neurons

Can this brain feel the pressure of the hands holding it?

How about the light? Can it see the light?

...receives information from the

internal or external environment

that information

into electrochemical impulses

(action potentials!)

activates an afferent neuron

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Stimuli: Chemicals Examples: Taste, smell

Stimulus: Example:

Stimulus: Temperature

Examples: Hot or cold sensation Stimuli: Disruption of blood

flow??? Example: Pain

Located close to body surfaces (cutaneous receptors)

Located internally, around viscera

Located in muscles, joints, and tendons

There are 3 functional classifications of neurons:

• Only found in CNS (brain or spinal cord) • Facilitates communication between sensory

neuron input and motor neuron output • This occurs in the spinal cord or brain. • These cells can make decisions about

which nervous signals to transmit and where to transmit them.

• Based on the synapses they make with other cells and whether they are inhibited/stimulated by other neurons (These are , and they get very complex!)

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There are 3 functional classifications of neurons:

• Conducts nerve impulses from the CNS to the effectors (muscles or glands)

• Structurally they are multipolar.

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• Can possibly transmit nervous signals, similar to neurons!

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• Ciliated cuboidal epithelial cells that line the ventricles of the brain and the central canal of the spinal cord

• In conjunction with other glial cells, the ependymal cells produce cerebral spinal fluid (CSF) and form the choroid plexus

• Small cells that are motile

• Function in defense and recycling

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• Associated with CNS axons only

• Wrap themselves around the axons like electrical tape wrapped around a wire

• Produce myelin, which is an insulator of electrical activity • Also called Schwann cells • Wrap themselves around the

axons like electrical tape wrapped around a wire • Produce myelin, which is an

insulator of electrical activity • Similar structure and

function as oligodendrocytes

• Also called Schwann cells

• Wrap themselves around the axons like electrical tape wrapped around a wire

• Produce myelin, which is an insulator of electrical activity • Similar structure and

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• Action potentials in a myelinated axon only happen at the

(spots in between the myelin sheaths where the plasma membrane of the axon is exposed)

• Action potentials are triggered only at the nodes and jump from one node to the next (saltatory

conduction!)

• Action potentials in a myelinated axon only happen at the

(spots in between the myelin sheaths where the plasma membrane of the axon is exposed)

• Action potentials are triggered only at the nodes and jump from one node to the next (saltatory

conduction!)

The Nervous system can be organized by

i

STRUCTURE

aka the “AFFERENT” Nervous System

aka the “EFFERENT”