Download Unit 8 - Perry Local Schools

https://www.youtube.com/watch?v=qPix_X-9t7E
https://www.youtube.com/watch?v=OZG8M_ldA1M
Unit 8
Nervous Tissue
Overview of the Nervous System
Objectives:
•
List the structures and basic functions of the
nervous system
•
Describe the 3 basic functions of the nervous
system
Structures of the Nervous System



Brain: Neurons enclosed within skull
Spinal cord: Connects to brain - Enclosed within
spinal cavity
Nerves:





Cranial nerves (12 pairs) emerge from brain
Spinal nerves (31 pairs) emerge from spinal cord
Ganglia: Groups of neuron cell bodies located
outside of brain and spinal cord
Enteric plexuses: Networks in digestive tract
Sensory receptors: Monitor changes in internal or
external environments
Structures of the Nervous System
Copyright 2010, John Wiley & Sons, Inc.
Functions of Nervous System
1. Sensory Function
Afferent nerves
– Carry information into brain and spinal cord
– Sensory receptors and sensory nerves
PNS
• Receptors detect changes in surroundings
• Neurons
Functions of Nervous System
2. Integrative Function (Association)

CNS (brain and/or spinal cord)

Perception = Awareness of sensory input
Sensations

Memory

Thoughts

Decisions
Occurs in interneurons
Link neurons together




(sensory neuron  interneuron  motor neuron)
Functions of Nervous System
3. Motor Function

Efferent nerves
PNS
Response of a body part/decisions are acted upon


Impulses are carried from CNS to effectors
Effectors – 2 types





Muscles (that contract)
Glands (secrete a hormone)
Neurons
Histology of Nervous Tissue
Objectives:


Contrast the histological characteristics and
the functions of neurons and neuroglia
Distinguish between gray matter and white
matter
Histology of the Nervous System

Neurons


Can respond to stimuli and convert stimuli to
electrical signals (nerve impulses) that travel along
neurons
Neuroglia cells:

Critical for homeostasis of interstitial fluid around
neurons
Neuronal Structure




Cell body: Nucleus, cytoplasm with typical
organelles
Dendrites: Highly branched structures that carry
impulses TO the cell body
Axon: Conducts AWAY from cell body toward
another neuron, muscle or gland
Axon terminals: Contain synaptic vesicles that can
release neurotransmitters
Neuronal
Structure
Copyright 2010, John Wiley & Sons, Inc.
Structural Classes of Neurons

Multipolar



Bipolar



Have several or many dendrites and one axon
Most common type in brain and spinal cord
Have one dendrite and one axon
Example: In retina of eye and inner ear
Unipolar

One process from cell body



Fused dendrite and axon
Only distal ends are dendrites
Sensory neurons of spinal nerves
Copyright 2010, John Wiley & Sons, Inc.
Neuroglia





Cells smaller but much more numerous than
neurons
Can multiply and divide and fill in brain areas
Gliomas: Brain tumors derived from neuroglia
Do NOT conduct nerve impulses
DO support, nourish and protect neurons
Types of Neuroglial Cells
PNS –
Schwann Cells
• produces myelin
Satellite Cells
• Support neurons and regulate exchange of materials
between neurons and interstitial fluid
CNS – 4 types
Provide bulk of brain and spinal cord tissue
• Oligodendrocyte
• Microglia
• Astrocyte
• Ependyma
10-11
CNS – 4 types
1. Oligodendrocytes

Function - Produces myelin in CNS

Looks like eyeball
2. Microglia

Function - Phagocytosis


Protect CNS cells from disease
Looks like spider
3. Astrocytes
 Function

Nourishes neurons




Connect neurons to blood vessels
Help form blood brain barrier
Mop up excess ions, etc.
Induce synapse formation
Star-shaped
 Scar tissue
4. Ependyma
 Function – Lines spaces in CNS





Brain – Ventricles
Spinal cord – Central canal
Epithelial-like layer
Ciliated
Myelination

Many layers of lipids and proteins:




Increases speed of nerve conduction
Appears white
Nodes of Ranvier:



Insulates neurons
Gaps in the myelin
Important for rapid signal conduction
Some diseases destroy myelin:


Multiple sclerosis
Tay-Sachs
Gray and White Matter


White matter: Primarily myelinated axons
Gray matter:


Cell bodies, dendrites, unmyelinated axons, axon
terminals, neuroglia
Location:

Spinal cord:



White matter (tracts) surround centrally located gray matter
“H” or “butterfly”
Brain:

Gray matter in thin cortex surrounds white matter (tracts)
Subdivisions of the Nervous System
Objective:
 Describe the organization of the nervous
system
Subdivisions of the Nervous System

Central Nervous System (CNS)


Brain and spinal cord
Peripheral Nervous System (PNS)

All nervous system structures outside of the CNS
Organization of the Nervous System

Somatic (SNS)



Sensory neurons FROM head, body wall, limbs, special
sense organs
Motor neurons TO skeletal muscle: voluntary
Autonomic (ANS) nervous systems


Sensory neurons FROM viscera
Motor neurons TO viscera
(cardiac muscle, smooth muscle, glands): Involuntary
 Sympathetic: “fight-or-flight”
 Parasympathetic: “rest-and-digest”

Organization of the Nervous System

Enteric Nervous System (ENS):
“Brain of the Gut”


Sensory neurons - Monitor chemical changes and
stretching of GI wall
Motor neurons - Regulate contractions and endocrine
secretions (involuntary)
Organization of the Nervous System
Copyright 2010, John Wiley & Sons, Inc.
Action Potentials
Objective:
 Describe how a nerve impulse is generated
and conducted
Cell membrane potential
Distribution of Ions
 Potential Difference (PD) = the difference in
electrical charge between 2 points (across cell
membrane)
Resting Membrane Potential (RMP) = results from the
distribution of ions across the cell membrane
 Resting neuron’s cell membrane – polarized
 K+ high inside
 Na+ high outside
 Cl- high outside
 Negatively charge proteins or Anion high inside
Resting Membrane Potential
Copyright 2010, John Wiley & Sons, Inc.
Local Potential Changes
• Occur on membranes of dendrites and cell bodies
caused by various stimuli
• Chemicals
• Temperature changes
• Mechanical forces
• If membrane potential becomes more negative,
hyperpolarized
• If membrane potential becomes more positive (less
negative), depolarized
Action Potentials
• When RMP of a neuron is depolarized to -55mV –
threshold potential is reached
 rapid opening of Na+ channels results in rapid
depolarization
Action potential - Start of the nerve impulse - occur on
axons
K+ channels open (while Na+ channels close) and
repolarization occurs = Recovery
• Occurs very quickly = 1/1000 sec
Potential Changes
Copyright 2010, John Wiley & Sons, Inc.
10-15
Action Potential

Recovery


Refractory period (brief): even with adequate
stimulus, cell cannot be activated
All-or-none principle


If a stimulus is strong enough to cause
depolarization to threshold level
Then the impulse will travel the entire length of the
neuron at a constant and maximum strength.
Action Potential
Copyright 2010, John Wiley & Sons, Inc.
Conduction of Nerve Impulses

Nerve impulse conduction (propagation)

Each section triggers the next locally as even more
Na+ channels are opened


Row of dominos
Types of conduction

Continuous conduction


Saltatory conduction


In unmyelinated fibers; slower form of conduction
In myelinated fibers; faster as impulses “leap” between
nodes of Ranvier
Factors that increase rate of conduction

Myelin, large diameter and warm nerve fibers
Conduction
of Nerve
Impulses
Copyright 2010, John Wiley & Sons, Inc.
Synaptic Transmission
Objective:
 Explain the events of synaptic transmission and
the types of neurotransmitters used
Synaptic Transmission
Synapse (neuron-neuron)
 Neuromuscular junction (neuron-muscle fiber)
 Neuroglandular junction (neuron-gland)
 Components of synapse:




Sending neuron: Presynaptic Neuron (releases
neurotransmitter)
Space between: Synaptic Cleft
Receiving neuron: Postsynaptic Neuron
The Synapse
Copyright 2010, John Wiley & Sons, Inc.
10-21
Synaptic Transmission
• Ca++ channels open
• Synaptic vesicles release NT
(exocytosis)
• NT depolarizes the post-synaptic
neuron’s membrane
• Action potential  NI begins in
the post-synaptic neuron
10-22
Synaptic Transmission

One-way transmission



Presynaptic release NT
Postsynaptic have receptors for NT binding
NT must be removed from the cleft



Diffusion out of cleft
Destruction by enzymes (such as ACh-ase)
Transport back (recycling) into presynaptic cell
Signal Transmission at the Chemical Synapse
Copyright
Copyright 2010,
2009 John
John Wiley
Wiley &
& Sons,
Sons, Inc.
Inc.
40
Neurotransmitters
At least 30 different produced by CNS
 Some neurons release only one while others
release many
Most typical = Acetylcholine
 All motor neurons



Stimulatory (on skeletal muscles)
Inhibitory (on cardiac muscle)
Other NT include
Monoamines (modified amino acids)
 Widely distributed in the brain
 Emotional behavior
 Circadian rhythm
 Some motor neurons of the ANS
 EX: Epinephrine, norepinephrine, dopamine,
serotonin, histamine
Unmodified amino acids
 Ex: Glutamate, aspartate, GABA, glycine
Neuropeptides
 Synthesized by CNS neurons
 Act as NT or Neuromodulators


Alter a neuron’s response to a NT
Block the release of a NT
Enkephalins
 Synthesis is increased during painful stress
 Bind to same receptors in the brain as the narcotic
morphine
 Relieve pain
Endorphines
 Same as above, with more potent and longer lasting
effect
Synaptic Potentials
EPSP
• Excitatory postsynaptic potential
• Graded
• Depolarizes membrane of postsynaptic neuron
• Action potential becomes more likely
IPSP
• Inhibitory postsynaptic potential
• Graded
• Hyperpolarizes membrane of postsynaptic neuron
• Action potential becomes less likely
Summation of EPSPs and IPSPs
• EPSPs and IPSPs
are added together
in a process called
Summation
10-24
Impulse Processing
Neuronal Pools – neurons that synapse and work together
• Interneurons work together to perform a common
function
• Working together results in facilitation
• General excitation that makes stimulation easier to
achieve
Convergence
Neuron receives input from
several neurons
• Allows nervous system to
collect, process, and respond to
information
Typical motor pathway
• Many inputs from brain, but
usually only one motor response
Copyright 2010, John Wiley & Sons, Inc.
10-27
Divergence
One neuron sends
impulses to several
neurons
• Signal amplifies
• Typical sensory
pathways
• Reason that a stimulus
(odor) can cause many
responses
10-28
Neuron Regeneration

PNS neurons

Axons and dendrite
If cell body is intact and Schwann cells functional
 Form a regeneration tube  grow axons or dendrites if scar
tissue does not fill the tube


CNS neurons


Very limited even if cell body is intact
Inhibited by neuroglia and by lack of fetal growthstimulators
Regeneration of A Nerve Axon
Copyright 2010, John Wiley & Sons, Inc.
10-13
Disorders Associated with NT Imbalances








Alzheimer's = deficient Ach
Clinical Depression = deficient
norepinephrine/serotonin
Epilepsy = Excess GABA leads to excess
norepinephrine & dopamine
Hypersomnia = excess serotonin
Insomnia = deficient serotonin
Mania = excess norepinephrine
Schizophrenia = deficient GABA leads to excess
dopamine
SIDS = excess dopamine
Clinical Application
Multiple Sclerosis
Symptoms
• Blurred vision
• Numb legs or arms
• Can lead to paralysis
Treatments
• No cure
• Bone marrow transplant
• Interferon (anti-viral drug)
• Hormones
Causes
• Myelin destroyed in various
parts of CNS
• Hard scars (scleroses) form
• Nerve impulses blocked
• Muscles do not receive
innervation
• May be related to a virus