Transcript 9.1: The Importance of the Nervous System

9 How Nerve
Signals Maintain
Homeostasis
9.1 The Importance
of the Nervous
System
9.1: The Importance of the Nervous
System
• The nervous system is an elaborate
communication system that has more than
100 billion nerve cells in the brain alone.
• Memory, learning and language are all a
part of the nervous system.
• Has two divisions: the central nervous
system (CNS) and the peripheral
nervous system (PNS).
Vertebrate Nervous System
Central nervous System
(CNS):
• The nerves in the
brain and spinal cord
Peripheral Nervous
System (PNS):
• Nerves that carry info.
Between the organs
and the CNS
• CNS is all the nerves of the brain and
spinal cord and is the coordinating centre
for incoming and outgoing information.
• The PNS include the nerves that carry
information between the organs of the
body and the CNS
– PNS can be divided further into the somatic
and autonomic nerves.
• Somatic: controls the skeletal muscle, bones and
skin.
• Autonomic: special motor nerves that control the
internal organs of the body.
– Autonomic can be subdivided into the sympathetic and
the parasympathetic.
Peripheral Nervous System
Somatic Nerves:
• Controls skeletal
muscles, bones and
skin
• Brings information
from the external
environment to the
CNS
• Motor somatic nerves
What do the somatic nerves control?
Controls the skeletal
muscles
Peripheral Nervous System
Autonomic Nerves:
• Motor nerves that
control organs
Is this sensory, integrative, or motor input?
SENSORY
– monitor:
• temperature, light, and
sound, ETC.
– Inside the body receptors
detect variations in:
• pressure, pH, carbon
dioxide concentration, and
the levels of various
electrolytes.
Is this sensory, integrative, or motor
input?
– signals are brought together to:
• create sensations, to produce thoughts, or to add to
memory.
– Decisions are made based on the sensory input.
This is integration.
Integrative
Is this sensory,
integrative, or motor
input?
– nervous system responds by:
• sending signals to muscles,
causing them to contract, or to
glands, causing them to produce
secretions.
– muscles and glands are called
effectors
• they cause an effect in response to
directions from the nervous
system.
– This is the motor output or
response
motor input
Anatomy of a Nerve Cell
Glial Cells:
• Structural support and
metabolism of nerve
cells
• Non-conducting
Neurons:
• Sensory neurons
• Interneurons
• Motor Neurons
Sensory Neurons
• Afferent neurons
• Sense and relay stimuli (information) from
the environment to the CNS
• Located in clusters outside of the spinal
cord
Interneurons/Association Neurons
• Neurons that link together
neurons in the body
• Mainly in the spinal cord
and brain
• human brain contains
~100 billion (1011)
interneurons averaging
1000 synapses on each
or some 1014
connections
Motor Neurons
• Efferent Neurons
• Relay information to the effectors
– Muscles, organs and glands
– The axons connecting your spinal cord to your
foot can be as much as 1 m long (although
only a few micrometers in diameter).
What are the three parts of all
neurons?
1. Dendrites
2. The cell body
3. The axon
Neuron Structure
Dendrites:
• Receive information
• Conduct nerve impulses
toward the cell body
Axon:
• Sends nerve impulses
from the cell body to
other neurons (effectors)
Myelin Sheath:
• White coat of fatty protein
that covers some axons
Neuron Structure
Schwann Cells:
• Individual cells that compose the myelin
sheath
• Insulates the nerve cell
Nodes of Ranvier:
• Areas between the sections of myeline
sheath
ANIMATIONS
• http://www.sumanasi
nc.com/webcontent/
anisamples/neurobi
ology/neurobiology.h
tml
The Speed of Nerve Impulses
• Myelinated nerve
fibres speed up nerve
impulses
• Nerve impulses jump
from one node to
another… speeding
up nerve action
Reflex Arcs
• What are the 3
overlapping
nervous system
functions?
–Sensory
–Integrative
–Motor
• Does this describe
the autonomic or
somatic nervous
system?
– Control the internal
organs of the body
– operate without
conscious control
– constant interplay of
balance between
sympathetic and
parasympathetic
autonomic nerves
http://itc.gsw.edu/faculty/gfisk/anim/a
utonomicns.swf
Does this describe the
sympathetic nervous
system or
parasympathetic?
– Prepares the body for
stress:
• increases heart
rate,
• increases the
release of
glucose,
• dilates the pupils,
• increases blood
flow to the skin,
• causes release of
epinephrine
• sympathetic nervous system
parasympathetic
nervous system
–Restores
normal balance:
• decreases
heart rate,
• stores glucose,
• constricts
pupils,
• decreases
blood flow to
the skin
Neuron Repair
Neurilemma:
• Thin membrane that surrounds the axon
• Promotes regeneration of damaged neurons
• Not in all nerve cells
White Matter:
• Nerve cells in the brain that contain myelinated fibres
and a neurilemma
Grey Matter:
• Nerve cells in the brain and spinal cord that lack a myelin
sheath and neurilemma
• Why are spinal and brain injuries often permanent?
How to Fix “Irreparable” Damage to
the CNS
1. Reattach two torn nerves
Limited success
2. Grafts from the PNS
More successful…CNS cells that are left
alone however, had no regeneration
Stem Cells
• Cells that have not
specialized into tissue
cells
• Experiments are being
done on replacing
damaged cells using
stem cells
• E.g. pp. 415…rats with
reconnected spinal cords
• Page 417 # 1-6