Transcript Nervous System

Nervous System
Nestor T. Hilvano, M.D., M.P.H.
(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain,
Textbook, 2012.)
Learning Objectives
1. Describe the structural and functional
subdivisions of the nervous system.
2. Describe a reflex arc, noting its components
and types of neurons.
3. Explain how an action potential is produced
and resting membrane potential restored.
4. Define a synapse. Describe the types of
neurotransmitters in man.
5. Describe the parts and functions of the human
brain.
Subdivisions of the Nervous System
•
•
CNS – consists of
brain and spinal cord.
PNS – consists of
nerves (nerve fibers) and
ganglia (cell bodies of
nerves).
•
Functions:
-
The main controlling and
communicating system of
the body through electrical
and chemical signals
Sensory input, integration
of information, and motor
output
-
Figure 28.1A
Sensory input
Integration
Sensory receptor
Motor output
Brain and spinal cord
Effector cells
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Reflex arc
• Reflex- quick, automatic
(unconscious) response to
stimulus
• 3 Components
1. Sensory (afferent) input
- stimulation of receptors (ex.
pain); it travels via the sensory
neuron (sensory ganglia)
2. Integration
- processing centers (CNS)
- interneuron (association
neuron)
3. Motor output
- motor neuron (conduction of
signals from the CNS to
effectors)
4. Effector response- contraction of
muscles or secretion of glands
Figure 28.1B
1
Sensory
receptor
2
Sensory
neuron
Brain
Ganglion
Motor
neuron
Spinal
cord
3
Quadriceps
muscles
4
Interneuron
Nerve
Flexor
muscles
PNS
CNS
__ - short processes;
receive stimuli
__ - long process;
conduct impulses
to target organ
__ - genetic/nutritive
center
a. Axon
b. Cell body
c. Dendrites
Figure 28.2
Signal direction
Cell body
Nucleus
Myelin
sheath
Dendrites
Cell
body
Nodes of
Ranvier
Schwann
cell
Signal
pathway
Node of Ranvier
Layers of
myelin
Synaptic
terminals
Nucleus
Axon
• Myelin sheath is formed in PNS by Schwann cells; and in
CNS by Oligodendrocytes.
Schwann
cell
RMP and Action potential
• Cell Membrane is polarized; inside the cell is negative
(proteins) and outside of cell is positive (Na+)
• Permeability varies; leaky (open all the time), or have
gates ( voltage gated, or chemical gated)
• Resting membrane potential (-70 mV), Na+ outside >
Na+ inside, K+ inside > K+ outside
•
•
•
•
•
Action potentials are all-or-none events:
1) Stimulus opens Na+ channel
2) Threshold reached (-55mv)
3) Depolarization (Na+ rushes into the cell)
4) At +30 mv (Na+ inactivation gate closed, K+
channel opens)
• 5) Repolarization (K+ rushes out of cell), inside the
cell becomes more negative than outside
• 6) Hyperpolarization (below resting, K+ channel
close slowly)
• 7) Return to RMP.
Figure 28.4
Na
Na
Na
Na
K
Additional Na channels
open, K channels are
closed; interior of cell
becomes more positive.
Na
Na
K
2
Sodium Potassium
Na channel channel
Action
potential
3
0
4
Na channels close
and inactivate; K
channels open, and
K rushes out;
interior of cell is more
negative than outside.
5
The K channels
close relatively
slowly, causing a
brief undershoot.
4
2
50 Threshold
100
A stimulus opens some Na
channels; if threshold is reached,
an action potential is triggered.
Na
K
50
Membrane potential
(mV)
3
1
Resting potential
5
1
Time (msec)
Outside
of neuron
Na
Na
Plasma membrane
K
1
K
Inside of neuron
Resting state: Voltage-gated Na
and K channels are closed;
resting potential is maintained by
ungated channels (not shown).
1
Return to resting
state.
* Thin axon- unmyelinated, slow conduction of AP= Continuous Conduction
* Thick axon- myelinated, fastest conduction of AP= Saltatory Conduction
• Synapse- region (junction)
between a neuron and another
cell; where the impulses moves
from one to another.
• Components: pre-synapse (has
neurotransmitter, acetylcholine or
norepinephrine), synaptic cleft,
and post-synapse
• At a synapse, electrical signals in
the axon terminals are converted
into chemical signals through the
release of a specific
neurotransmitter.
• Cerebrum – control/integration center
(Functions: formulation of thought, voluntary
movement, language, reasoning, and
perception); 2 cerebral hemispheres
connected by corpus callosum; consists of
frontal (motor), parietal (sensory), temporal
(auditory cortex), occipital (visual), and limbic
(personality, behavior, short-term memory,
sexuality) lobes
• Thalamus- relay information (sensory/motor)
to higher center
• Hypothalamus- visceral (autonomic) and
endocrine functions; regulates body
temperature, emotions and hunger, thirst, and
circadian rhythms (sleep-wake cycle)
• Midbrain – integrates hearing information and
coordinates visual reflexes to higher brain
centers
• Pons- rate and depth of breathing
• Medulla oblongata – respiratory center and
cardiac center (heart rate, blood pressure)
• Cerebellum – coordinates muscular
movement (equilibrium)
Figure 28.15
Frontal lobe
Parietal lobe
Frontal
association
area
Speech
Somatosensory
association
area
Reading
Speech
Smell
Hearing
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe
Figure 28.19
Thalamus
Cerebrum
Hypothalamus
Prefrontal
cortex
Smell
Olfactory
bulb
Amygdala
Hippocampus
Autonomic N.S.
• Sympathetic
- prepares the body for energy-consuming
activities; fight or flight
• Parasympathetic
- gain and conserve the body’s energy
supply; rest and digest
Figure 28.12A
Peripheral nervous system
(to and from the central
nervous system)
Motor system
(voluntary and
involuntary; to and from
skeletal muscles)
Autonomic nervous system
(involuntary; smooth and
cardiac muscles, various glands)
Parasympathetic
Sympathetic
division
division
(“Rest and digest”) (“Flight and fight”)
Enteric division
(muscles and glands
of the digestive system)
Fig. 49-8
Sympathetic division
Parasympathetic division
Action on target organs:
Action on target organs:
Constricts pupil
of eye
Dilates pupil
of eye
Stimulates salivary
gland secretion
Inhibits salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Relaxes bronchi
in lungs
Slows heart
Accelerates heart
Stimulates activity
of stomach and
intestines
Inhibits activity
of stomach and
intestines
Thoracic
Stimulates activity
of pancreas
Inhibits activity
of pancreas
Stimulates
gallbladder
Stimulates glucose
release from liver;
inhibits gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitals
Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation and
vaginal contractions
Functional comparison of ANS
Organ
SYMPATHETIC
PARASYMPATHETIC
Pupil
dilatation
constriction
Heart (HR/BP)
RR/passages
Digestive glands
increase
decrease
 / bronchodilatation ↓/ bronchoconstriction
Inhibition secretion Stimulate secretion
GIT motility
Decrease
Increase
GIT sphincter
contraction
relaxation
Urinary bladder
Blood vessels
Penis
inhibitory
vasoconstriction
ejaculation
stimulatory
vasodilatation
erection
(contraction)
Homework
1.
2.
3.
4.
5.
Define terms – synapse, reflex, CNS, PNS, sensory
neuron, motor neuron, interneuron, somatic N.S.,
autonomic N.S.
Discuss the events of knee-jerk reflex.
Explain how an action potential is produced in
response to nerve stimulation.
Identify the part of brain being describe: a) cardiac
center, b) coordinate movements, c) relay sensory &
motor information, d) highest control center (reasoning
and language), e) link autonomic and endocrine
functions (thirst, hunger, and temperature regulation)
Identify if the given items below is sympathetic or
parasympathetic effect: a) pupilloconstriction, b)
digestive tract motility and glands secretion, c)
increase respiration rate, d) erection, e)
bronchodilatation, and e) decrease heart contraction
and heart rate.