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2.2THE NERVOUS SYSTEM

The body’s communication systems help maintain homeostasis.

A stimulus causes a response. Responses can be chemical, cellular, or

behavioral. The nervous system responds to stimuli.

The nervous system controls thoughts, movement, and emotion.

The nervous system works quickly, using chemical and electrical signals.

spinal chord

nerves

– interconnected network of cells– signals move through cells – divided into central nervous

system (CNS) and peripheral nervous system (PNS)

The nervous system’s two parts work together. The CNS includes the brain,

brain stem, and spinal cord. The PNS includes four

systems of nerves.

The CNS processes information.

The brain has three parts. 1. cerebrum controls

thought, movement, emotion

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Lobes of the Brain

There is a fifth lobe, known as the limbic lobe, that is responsible for emotions

The CNS processes information.

The brain has three parts. 1. cerebrum controls

thought, movement, emotion

2. cerebellum allows for balance

3. brain stem (reptilian brain) controls basic life functions midbrain

pons

medulla oblongata

Brainstem

The brain stem has three parts.

1. midbrain controls some reflexes

2. pons regulates breathing

3. medulla oblongata controls heart function, swallowing, coughing

midbrain

medulla oblongata

pons

The spinal cord controls reflexes. – sensory neuron sends impulse to spinal cord– spinal cord directs impulse to motor neuron – does not involve the brain

– See simulation with online textbook

interneuron

motor neurons

sensory neuron

The PNS gathers and transmits information

links the CNS to muscles and other organs.

The somatic nervous system regulates voluntary movements.

The PNS gathers and transmits information

The autonomic nervous system controls involuntary, functions sympathetic nervous system:

“fight vs. flight” Involved in all internal adjustments

that prepares the body for action or increased levels of stress.

parasympathetic nervous system: sends impulses that return a body

to “normal” functioning after a period of stress is over,

conserves energy

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Fine adjustments made so glands and organs are functioning at levels appropriate to a body at a particular time:

Sympathetic Parasympathetic

Dilates pupilsInhibits saliva

Constricts blood vessels

Accelerates heartBronchi dilate

Glycogen converts to glucose

Bladder relaxes

Constricts pupilStimulates salivation

Dilates blood vessels

Reduces heart rateConstricts bronchi

Stimulates bile release

Contracts bladder

The CNS and PNS pass signals between one another.– Sensory receptor generates impulse. – PNS passes impulse to CNS. – CNS interprets impulse.– CNS passes impulse to PNS. – PNS stimulates a response.

Basic Organization

Sensory Input triggered by stimuli conduction of signals to

processing center

Integration interpretation of sensory signals

within processing centers

Motor output conduction of signals to effector

cells (i.e. muscles, gland cells)

sensory receptor (sensory input) integration (motor output) effector

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Nerves Nerves, which carry the electrical

impulses to various parts of the nervous system, are made up of a bundles of cells, known as neurons

Neurons are highly specialized cells. A neuron has 3 main parts.

1. cell body contains nucleus and organelles

1Cell body

Neurons are highly specialized cells. A neuron has three parts.

1. cell body has nucleus and organelles2. dendrites receive impulses

2 dendrites

Neurons are highly specialized cells. A neuron has three parts.

1. cell body has nucleus and organelles2. dendrites receive impulses3. axon carries (transmits) impulses

3 axon

Neurons have other structures to transmit signals.

4. Schwann cell makes up the myelin sheath, which insulates the axon

Neurons have other structures to transmit signals.

5. Nodes of Ranvier – the gaps between the myelin sheath that speed up the process of transmitting impulses.

4. Schwann cell makes up the myelin sheath, which insulates the axon

6. Axon terminal – part through which the impulse leaves.

Neurons have other structures to transmit signals.

axon terminal

5. Nodes of Ranvier – the gaps between the myelin sheath that speed up the process of transmitting impulses.

4. Schwann cell makes up the myelin sheath, which insulates the axon

6. Axon terminal – part through which the impulse leaves.

7. synapse gap between the neuron and the next cell.

Neurons have other structures to transmit signals.

synapse

5. Nodes of Ranvier – the gaps between the myelin sheath that speed up the process of transmitting impulses.

4. Schwann cell makes up the myelin sheath, which insulates the axon

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Types of Neurons1. Sensory Neuron: detect stimuli and transmit

signals to the brain and the spinal cord, which are both made up of interneurons.

2. Interneurons: receive signals from sensory neurons and relay them within the brain and the spinal cord. Process information and pass signals to motor neurons.

3. Motor neurons: pass messages from the NS to other tissues in the body, such as muscles