Transcript Functional Organization of Nervous Tissue Chapter 11

Functional Organization of
Nervous Tissue
Chapter 11
The Nervous System
• Components:
– Brain, spinal cord, nerves, sensory receptors
• Responsible for…
– Sensory perceptions, mental activities,
stimulating muscle movements, secretions of
many glands
• Subdivisions:
– Central Nervous System (CNS)
– Peripheral Nervous System (PNS)
Central Nervous System
• Consists of brain and
spinal cord
• The structural &
functional center of
the entire nervous
system which
integrates incoming
pieces of information
& initiates an outgoing
response
Peripheral Nervous System
• All other nerves
• All pathways going
toward and away
from the CNS
Nervous System Organization
Concept Check
• What are the two divisions of the nervous
system? What are their parts?
– CNS: Brain & Spinal Cord
– PNS: nerves
• What are the functions of the CNS?
– Integrates incoming information & initiates an
outgoing response
• What is the function of the PNS?
– Conducts action potentials to and away from the CNS
• What are some functions of the Nervous
system?
– Sensory perceptions, mental activities, stimulating
muscle movement, secretions of many glands
Cells of Nervous System
• Neurons or nerve cells
– Receive stimuli and
transmit action
potentials
– Organization
• Cell body or soma
• Dendrites: input
• Axons: output
• Neuroglia cells
– Support and protect
neurons
Types of Neurons
• Functional Classification
– Sensory or afferent: action potentials toward
CNS (receives stimuli; could be a special sense
organ)
– Motor or efferent: action potentials away
from CNS (attached to a muscle or gland)
– Interneurons or association neurons: within
CNS from one neuron to another
Myelinated and Unmyelinated Axons
• Myelinated axons
– Myelin protects and
insulates axons from
one another
– Not continuous
• Nodes of Ranvier
• Impulse “jumps” from
node to node
• Fast impulse
• Unmyelinated axons
– Slower impulse
Electrical Signals
• Cells produce electrical signals called
action potentials
• Transfer of information from one part
of body to another
• Electrical properties result from ionic
concentration differences across
plasma membrane and permeability
Nerve Impulses
• A wave of electrical fluctuation that
travels along the plasma membrane; due
to changes in chemical concentrations.
Impulse
+++-++++++-++++-+
---+---+-----------+--+
++++++-+++-++-+++++-++++++++
----+----+--+--------+
++++-++++++-+++++-
-----+----+-------+--+-------+--------
----+----+---+----------
++++++++-++-++++-++
++++++-++-+++++++
--------+--++----------+----
----+-----++-----------+-----+------+--+++++++-+++++++--++++++++-+++
Resting Potential
Action Potential
Resting Potential
“Polarized”
“Depolarized”
“Repolarized”
Resting Membrane Potential
• Characteristics
– Number of charged
molecules and ions inside
and outside cell nearly
equal
– Concentration of K+
higher inside than
outside cell- negative
proteins in also, Na+
higher outside than
inside
– At equilibrium there is
very little movement of
K+ or other ions across
plasma membrane
Action Potentials
• Series of permeability
changes when a local
potential causes
depolarization of
membrane
• Phases
– Depolarization
• More positive
– Repolarization
• More negative
• All-or-none principle
– Neuron will fire or it won’t
The Synapse
• Junction between two
cells
• Electrical message
transferred across
the synapse by
chemicals called
neurotransmitters
Concept Check
• What are the main parts of a neuron?
– Axon, dendrites, myelin sheath, synapse
• What are the three types of neurons and what
do they do?
– Sensory (afferent)- action potential toward CNS ,
Motor (efferent)- action potential away from CNS, &
Interneurons- within CNS from one neuron to another
• How does an impulse travel along an axon? What
speeds it up?
– Jumps from node to node; myelin
• How does a synapse work?
– Neurotransmitters transfer message across synapse
Stimulus
• Any change in your
environment.
– Temp, sound, smell
• You may or may not
respond to a specific
stimulus
Reflex
• A predictable response to a stimulus which
may or may not be conscious
– A reflex consists of either muscle contraction
or glandular secretion
– Neurons involved in reflex
• Afferent neuron- sensory
• Interneuron
• Efferent neuron- motor
Sensory Receptors
• In order for a stimulus to be detected, it
must be strong enough to elicit an impulse
– It must be at the threshold level- the minimum
stimulus to start an impulse
• The all-or-none response means that either
a neuron will fire or it won’t, there is no
partial impulse
• Sensation- the brain’s interpretation of
what the stimulus is
Characteristics of Sensations
• Projection- brain refers a sensation to the
point of stimulation
• Adaptation- loss of sensation even though
the stimulus is still applied
• Afterimage- persistence of a sensation
even though the stimulus is removed
• Referred pain- felt in the skin near or
around the organ sending the impulse
• Phantom pain- sensation of pain in a limb
that has been amputated
Classification of Receptors
1. Mechanoreceptors- activated by
mechanical stimuli or deformation of the
receptor
2. Chemoreceptor- changing of the chemical
concentrations around the body
3. Thermoreceptors- detect hot and cold
4. Nociceptors- any stimuli that can cause
tissue damage; sensation of pain
5. Photoreceptors- respond to light
Somatic Senses
pain, temperature and touch
• These sensations can be felt throughout
the body, yet they are distributed unevenly
through the skin
• Exteroceptors- sense receptors located on
body surfaces
• Proprioceptors- found in the muscles and
joints
• Visceroceptors- found in internal organs
• Nociceptors- pain receptors; free nerve
endings
Review
• Meissner’s corpuscles- touch
• Krause’s End Bulbs- touch
• Ruffini’s corpuscles- continuous touch
• Pacinian corpuscles- deep pressure
The Brain
• Parts/Functions
• Left vs Right Brain Activity??
• Dissection notes…pre-lab??