Transcript The Nervous System

The Nervous System
The Nervous System
• The master controlling and communicating system of the
body.
• Vital in maintaining homeostasis
• Two divisions:
– Central Nervous System (CNS) = brain and spinal cord
– Peripheral Nervous System (PNS) = nerves that
extend from CNS
PNS Structures
• Sensory / Afferent Division – Nerves that convey impulses to the CNS
from sensory receptors in the body.
• Motor / Efferent Division – Nerves that convey impulses from the CNS
to organs, muscles, and glands.
• Two divisions of motor / efferent nerves:
• Somatic nervous system – voluntary control
• Ex: skeletal muscle contraction
• Autonomic nervous system (ANS) – automatic or involuntary
regulation
• Ex: cardiac muscles
Basic Divisions of the Nervous System
Figure 12.2
THREE BASIC FUNCTIONS OF THE NERVOUS SYSTEM
• Sensory - gathers info
• Integrative - information is brought together
• Motor - responds to signals, homeostasis
Neurons
Neurons – nerve cells
Parts:
•Cell body – metabolic
center
•Dendrites – convey
signals toward the cell
body
•Axons – convey signals
away from the cell body
•Myelin sheath – enclose
axon, increase
transmission rate
•Nodes of Ranvier – gaps
between myelin
White vs Grey Matter
Myelinated (white matter) – myelinated axons
Unmyelinated (grey matter) - unmyelinated
Types of Nerves
•Sensory Neurons - conduct impulses into the brain or
spinal cord
•Motor Neurons - carry impulses to muscles of glands
•Interneurons- contain both sensory and motor nerves
Neurons Classified by Function: Sensory vs. Motor Neurons
Figure 12.11
Neuroglial Cells – “nerve glue”
- support cells
for the neurons
1. Microglial
Cells: scattered
throughout,
digest debris or
bacteria
Microglial cells respond to
immunological alarms
Neuroglial Cells
2. Oligodendrocytes:
Produce Myelin sheath
around axons of
neurons in CNS
Neuroglial Cells
3. Astrocytes: connect
blood vessels to
neurons
I connect to
blood
vessels
Neuroglial Cells
4. Ependymal Cells: form a protective
membrane (Blood-brain barrier), allow diffusion
5. Schwann cells: form the insulating myelin
sheath around neurons in PNS
Practice with neuroglia coloring!
Supporting Cells - NEUROGLIA
Supporting Cells- NEUROGLIA
Label
Interesting Facts about the Neuron
• Longevity – can live and function for a lifetime
• Do not divide – fetal neurons lose their ability to undergo
mitosis; neural stem cells are an exception
• High metabolic rate – require abundant oxygen and glucose
The nerve fibers of newborns
are unmyelinated - this
causes their responses to
stimuli to be course and
sometimes involve the whole
body. Try surprising a baby!
Cell Membrane Potential
• Membrane of a resting, or inactive, neuron is
polarized – meaning it is internally more negative
(more negative ions) and there are more positive
ions outside.
•During stimulation, often by a neurotransmitter, the sodium
channel will open, allowing sodium ions to flow into the cell.
•This will change the polarity of the neuron locally, an event
called depolarization. Locally the inside is now more
positive and the outside less positive. This is called a graded
potential.
•If stimulus is strong enough (threshold reached; threshold
= minimum stimulus needed for response) and enough Na+
ions enter cell, the graded potential activates the neuron to
begin a long-distance signal called an action potential (or
nerve impulse)
•Action potential propagates along the entire length of the
axon, making it an All-or-none response.
•After the sodium influx, the membrane becomes impermeable
to sodium and permeable to potassium, causing K+ ions to
diffuse into cell.
•This loss of positive ions leads to the membrane becoming
polarized, at rest, in a process called repolarization.
• Until repolarization, cell cannot conduct another impulse
(this time is called the refractory period)
• After repolarization, the neuron’s initial
concentrations of ions are restored by the
sodium-potassium pump.
Nerve Impulses
Animations of Nerve Impulses
http://highered.mcgrawhill.com/sites/0072495855/student_
view0/chapter14/animation
__the_nerve_impulse.html
http://outreach.mcb.harvard.edu/
animations/actionpotential.swf
The Synapse
• Junction between two
communicating neurons
• Neurons do not touch–
synapse
• To complete a signal, a
neurotransmitter is
released across synaptic
cleft to reach next neuron
Structure of a Synapses
Events at the Synapse
1. Arriving action potential depolarizes
the synaptic knob and presynaptic
membrane
2. Calcium ions enter cytoplasm of knob
3. Neurotransmitter released through
diffusion and exocytosis of
neurotransmitter vesicles
4. Neurotransmitter goes across synapse
and binds to receptors on post-synaptic
membrane
5. Sodium channels open on new neurons
6. Neurotransmitter is broken down
• This ends depolarization
Neurotransmitters
•Excitatory - increase membrane permeability,
increases chance for threshold to be achieved
•Inhibitory - decrease membrane permeability,
decrease chance for threshold to be achieved
Examples of Neurotransmitters
• Acetylcholine - stimulates muscle contraction
• Catecholamines – Epinephrine and Norepinephrine
(fight-or-flight response) & Dopamine (sense of
feeling good, low levels = depression)
• Serotonin (happiness, sleepiness, metabolism)
• GABA (gamma-Aminobutyric acid) – chief inhibitor
Common Neurotransmitter
Disorders
Disorder
•
•
•
•
•
•
•
•
•
Alzheimer’s
Depression
Epilepsy
Huntington’s
Insomnia
Mania
Parkinson’s
Schizophrenia
SIDS
Neurotransmitter
• Deficient ACh
• Def serotonin/norepinephrine
•
•
•
•
•
Excess GABA
Deficient GABA
Deficient serotonin
Excess norepinephrine
Deficient dopamine
• Def. GABA / excess dopamine
• Excess dopamine
Reflexes
•Reflexes – rapid, predictable, involuntary responses to stimuli
•Reflex arc – neural pathways that involve both CNS and PNS
on which reflexes occur
•Somatic reflexes – stimulate skeletal muscles (hot pan)
•Autonomic reflexes – regulate smooth muscles, heart, glands
(secretion of saliva, dilation of pupils)