Download Unit 3: Chapter 10 How Nerve Signals Maintain

Unit 3: Chapter 9
How Nerve Signals Maintain
Homeostasis
Section 9.1 (pages 414-417)
Recap
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Endocrine system (location of endocrine glands)
Hormones
Pituitary Gland
Proteins vs. Steroid Signaling
Blood sugar levels (Insulin, Glucagon)
Metabolism (T4, T3)
Adrenal Glands (Short vs. Long term response)
The Importance of
the Nervous System
• Communication
system that contains
100 billion nerve
cells in the brain
alone
• Nerve cells detect
air temperature,
light intensity and
odours
The Importance of the Nervous System
• Responds to internal/external environments
through electrochemical message or a series of
chemical messengers (hormones)
• Hormones require more time than nerves
require
• Memories, learning and language  functions of
the nervous system.
Vertebrate Nervous Systems
• The nervous system has 2 main divisions:
1.Central Nervous System (CNS)
2.Peripheral Nervous System (PNS)
Vertebrate Nervous Systems
CNS
• Consists of the nerves of the
brain and spinal cord
• Coordinating Center for
incoming/outgoing
information
PNS
• Nerves that carry information
between the organs of the body
and the CNS
• Subdivided into: somatic and
autonomic nerves
• Somatic nerves: skeletal muscle,
bones and skin
• Autonomic nerves: special
motor nerves that control
internal organs of the body
• Autonomic nerves 
sympathetic and
parasympathetic nervous system
Figure 1. page 412
Anatomy of a Nerve Cell
• Two types of cells exist in the nervous system:
1.Glial cells
2.Neurons
Glial cells:
• Non-conducting cells that are important for the
structural support and metabolism of the nerve
cells
The Types of Neurons
Neurons:
• Are the functional units of the nervous system.
• These specialized nerve cells are categorized into
three groups:
1.The sensory neurons
2.Interneurons
3.Motor Neurons
1. Sensory Neurons
• Sense and relay information
(stimuli) from the environment to
the CNS for processing
• Example: photoreceptors,
chemoreceptors and
thermoreceptors
• Sensory neurons are located in
clusters  ganglia
2. Interneurons
• Link neurons within the body
• Predominantly located in the brain and spinal
cord
• Integrate and interpret sensory information
and connect neurons to outgoing motor
neurons
3. Motor Neurons
• Relay information to the effectors
• Effectors include muscles, organs and glands
 because they produce responses
Anatomy of the
Neuron
• All neurons contain
dendrites, cell bodies,
and axons
Dendrites
• Receive information
from either sensory
receptors (sensory
neurons) or nerve cells
(motor neurons)
• Conduct nerve impulses
toward the cell body
Axon
• An extension of the cytoplasm
that carries nerve impulses
away from the cell body
• Carries nerve impulse toward
other neurons or to effectors
Myelin Sheath
• Insulted covering over the
axon of a nerve cell
Schwaan Cells
• Special type of glial cell that
produces the myelin sheath
Nodes of Ranvier
• Regularly occurring gaps between sections of myelin
sheath along the axon
• Nerve impulses jump from one node to another
Neurilemma
• Within the PNS, some nerve cells have a delicate
membrane that surrounds the axon
• Promotes the regeneration of damaged axons
Speed of an impulse increases if:
• Nerve fiber is myelinated
• The axon has a small diameter
Figure 2. Page 413
Let’s suppose you touch a hot stove…
1. Heat is detected by temperature receptors in
the skin
2. A nerve impulse is carried to your spinal cord
3. Sensory neuron  interneuron  motor
neuron
4. Motor neuron causes the hand to contract and
pull away from the stove
5. All this happens in less than 1 second, before
information travels to your brain
Neural Circuits: Reflex Arc
• Reflexes are involuntary and often unconscious
• The simplest nerve pathway is the reflex arc
• Most reflexes occur without brain coordination
• Reflex arcs contain 5 essential components:
1.Receptor
2.Sensory Neuron
3.Interneuron in the spinal cord
4.The motor neuron
5.Effector
Figure 6. Page 416
Any Questions?