Transcript Biology 30 NERVOUS SYSTEM

Biology 30
NERVOUS SYSTEM
1. Nervous System Overview
2. The Neuron
3. Reflex Arc
4. The Action Potential
5. The Synapse / Neurotransmitters
6. Nervous System Diseases
7. Drugs
8. PNS
9. CNS
10. The Brain
General Functions
Reception
2. Conduction
3. Interpretation and Organization
1.
4. Transmission
The nervous systems main function is to
maintain homeostasis: a maintenance of the
internal environment i.e. pH, body temp,
glucose levels, BP, water levels, etc
Nervous System Organization
The Neuron- The functional unit
of the nervous system, it
conducts nerve impulses

There are 3 kinds of neurons:
– 1) sensory neurons (afferent)- take impulses from
the body receptors to the CNS
– 2) motor neurons (efferent)-take impulse away
from the CNS and to the muscles and glands
– 3) interneurons- are actually in the CNS (in the
brain and spinal cord)
– ***Neuroglia (glial cells)- supportive cells that aid
the interneurons of the brain. Nourish neurons,
removes waste from neurons, and protect neurons.
The Neuron has 3 basic Basic parts:
1) cell body- nucleus and cytoplasm
 2) Dendrites-finger-like projections of cytoplasm
of cell body. They receive information
 3) Axon-extension of cytoplasm. Transmit impulse
away from the body
Some neurons contain the following
additional parts:
Myelin Sheath-a white fatty covering that insulates
the axon. Schwann cells produce the myelin sheath
– Schwann cells- a special kind of glial cell that
produces a myelin sheath that wraps around the
axons as insulation
– On top of protection, the myelin sheath allows
for faster conduction of impulses and greater
power of regeneration
– The myelin sheath is NOT continuous but rather
forms intermitted gaps called the Nodes of
Ranvier. Impulses will now ‘jump’ from Node
to Node rather then slowly moving through the
entire length of the axon. (faster impulses)

All nerves of the PNS, as well as all motor
and sensory neurons are myelinated, only
some of the nerves in the CNS are
myelinated
– Non- Myelinated neurons in the brain= grey
matter
– Myelinated nerves in the brain are called white
matter

Neuron structure
Nerves
 Individual
neurons are organized into
tissues called nerves.
Repairing Damaged Nerves

Nerves in the PNS are surrounded by a thin
membrane called the neurilemma which helps
to regenerate damaged axons

Nerves in CNS lack neurilemmas and cannot
be repaired

Area of research: stem cells, brain band-aid
Reflex Arc
 automatic,
quick, involuntary responses to
internal or external stimuli.
 does
not immediately involve the brain.
 allows
quicker reaction times to a potentially
harmful stimulus

Stretch Reflex
5 Components of a Reflex Arc:
1. Sensory receptor -senses
something
2. Sensory neuron -sends
signal to the CNS
3. Interneuron- registers
signal
4. Motor neuron -sends
response back
5. Effector- caries out the
action
Action Potential
A
nerve impulse is an action potential
 An action potential is an
electrochemical event with a rapid
change in polarity (relative electrical
potential) down a nerve cell that
results in the conduction of a nerve
impulse.
Potential
1. Resting Potential

Polarization: voltage difference of -70mV across a
nerve cell membrane

caused by the sodium potassium pump (gate):
more sodium is pumped out than potassium is
pumped in, resulting in a negative charge inside
the axon of the neuron

also potassium moves out by diffusion more
easily than sodium moves in

Result: excess positive charge outside the
membrane and negative charge inside the
membrane
2. Stimulation / Depolarization

A threshold stimulus must be applied (a change
in pH, pressure, or an electrical stimulus) This
causes the sodium potassium pump to cause
Na+ gates to open and tons of Na+ rush into the
cell, and small amounts of K+ to move out

membrane becomes depolarized (+ 40 mV)
3. Re-polarization
 After
the wave of impulse has move
through Na+ gates close to stop inflow
 change
in electrical potential causes K+
channels to open and K+ ions rush out of
the cell
 Restores
the polarized state but now is
hyperpolarized – more positively
charged on the outside than the resting
state (over-shoot)
(also the ion concentrations are reversed
from the resting state )
4. Refractory period
 resting
potential (-70mv) must be
restored before the neuron can fire again
 Na+ are pumped out and K+ are pumped
back into the cell using ATP energy.
 The
The Action Potential
The Action Potential in Action
Neuron Action Potential
Propagation
Saltatory Action
• the speed of the nerve impulse is
increased by jumping from node of
Ranvier to node of Ranvier (gated
channels are found only at the nodes)
Propagation of the Action Potential
Threshold level – minimum depolarization that
must be reached (usually around +30mV) before
sufficient Na+ gates open to continue the action
potential
All or None Response – if the threshold level is
not reached, the action potential will not occur at
all. If the threshold is reached or exceeded a full
action potential will result.
The wave of depolarization is self propagating,
meaning that it will continue without any aid until
its passed on to the next neuron
How do we differentiate intensity? Ex
hot vs warm?
Intensity is determined by:
1. the number of neurons that fire
simultaneously
2. the frequency at which the neurons fire
3. the threshold level of different neurons
(lower threshold neurons are more likely to
fire, and are found in more “sensitive”
areas)
The Synapse and
Neurotransmitters
 Neurons
are NOT physically attached
to each other, but are separated by a
gap (synaptic cleft), the electrical
impulse cannot just simply cross the
gap to the next dendrite, something is
needed
 Neurotransmitters are stored in
synaptic vesicles of the axon and are
released to carry the information across
this synaptic gap
The Synapse
Terminal
Axon
Structures in the Synapse
membrane – membrane
found at the synaptic ending of the neuron
sending information
 Pre-synaptic
 Post-synaptic
membrane- membrane
found at the dendrite of the neuron
receiving information
cleft – space between the pre and
post synaptic membranes.
 Synaptic
Neurotransmitters continue the
impulse across the synaptic cleft
Crossing the impulse across the gap is a
chemical reaction
– 1) The end of pre-synaptic axon contains
vesicles that have specialized neurotransmitters
(NTs), as the impulse gets to the end of the
axon the NTs are released in to the gap
– 2) The NTs diffuse across the gap and attached
to specialized receptors found on the post
synaptic dendrite.
– 3) The wave of depolarization continues on the
through the next neuron
Neurotransmitters
1. excitatory neurotransmitters – cause
the opening of Na+ channels to cause
depolarization
2. inhibitory neurotransmitters –block
Na+ channels and open K+ channels ions
which causes hyper-polarization
-inhibits action potentials
Summation – at any given time there are
many neurons acting and releasing NTs
into the synaptic cleft, the net effect of
excitatory and inhibitory neurotransmitters
is called summation
– ONLY if there is adequate excitation to
reach the threshold, the neuron will fire.
-may
require more than one neuron
to release neurotransmitters
A
response may involve both excitatory
and inhibitory neurotransmitters
 Ex)
Throwing a ball: Triceps contracts
and bicep relaxes
Integration – the degree of sensation
felt or the degree of response created
by the brain depends on the number of
neurons that fire
There are 9 universally recognized
neurotransmitters: aspartate, glycine,
GABA, glutamate, dopamine, norepinephrine, epinephrine, seratonin, and
acetylcholine.
Some of the more common neurotransmitters
(and their enzymes) include:
Neurotransmitter Enzyme
Acetylcholine
Cholinesterase Involved with muscle contraction
Dopamine
Monoamine
oxidase
enzyme
Serotonin
Monoamine
oxidase
enzyme
Nor-epinephrine
GABA
Function of Neurotransmitter
of the skeletal muscles
Responsible for voluntary
movement and emotions of
pleasure
Regulates temperature, sensory
perception, sleep and involved in
mood stabilization and control
Regulates the stress “fight or
flight” response
Inhibitory action of motor
behavior
Removing Neurotransmitters
To be effective, the NTs must NOT linger
around in the gap, other wise successive
impulses will occur. NTs are removed
from the gap by:
1. Degradation by enzymes in the synaptic
cleft
2. Re-uptake by the pre-synaptic membrane
3. Diffusion out of the synaptic cleft
4. Inability to bind due to competitive
inhibitors
The Effects of Drugs
– anything that is not food that alters
the normal bio-chemistry of the body in
some way.
 Drug
– mimics neurotransmitter,
decreases rate of breakdown of
neurotransmitter or increases release
of neurotransmitter
 Stimulant
– blocks receptor site,
decreases production of
neurotransmitter, or increases the
breakdown of neurotransmitter
 Depressant
Alcohol:
- depressant
-seems to enhance GABA
-leads to lack of coordinated response, and
loss of normal social inhibitions.
-may also weaken the effect of glutamine, an
excitatory neurotransmitter, leading to
sluggishness and lack of co-ordination.
Close to Home Animation: Alcohol
Marijuana:
- a depressant and hallucinogen
-acts on the canniboid receptors of the brain
that affect concentration, perception and
movement.
-may have an impact on the activity of
seratonin, GABA and norepinephrine in
the brain
Cocaine:
-a stimulant
-blocks the re-uptake of dopamine, causing
an adrenaline like effect from the dopamine
-as dopamine levels increase in the synapse,
the body produces less, thus making
cocaine very physically addicting
Close to Home Animation: Cocaine
Crystal meth:
-a stimulant
-passes directly through neuron
membranes and causes excessive release
of dopamine
-leads to feelings of euphoria, psychosis,
delusions and extreme aggressiveness.
Ecstasy:
- a stimulant and hallucinogen
-affects neurons in the brain by causing an
over-production of serotonin.
-creates shorter feelings of pleasure,
however use can result in brain damage,
and cardiac arrest.
The venom of the black widow spider is
called “latrotoxin”. This toxin results
in a massive release of the
neurotransmitter acetylcholine from
the neuromuscular junctions of victims
and may cause muscle spasms, pain,
increased blood pressure, nausea and
vomiting.
Diseases of the Nervous
System
Parkinson’s Disease: wide-eyed, unblinking
expression, involuntary tremor, muscle
rigidity, shuffling gait. Ex. Muhammad Ali
-dopamine deficiency caused by the
degeneration of dopamine producing cells in
the brain
-
-caffeine may offer protection against
Parkinson’s disease as it prevents loss
of dopamine
Alzheimer’s Disease: characterized by loss
of memory, senility, deterioration of cells
in the basal nuclei, presence of tangles and
plaques
-possibly due to a malfunction of
acetylcholine
- seems to be linked to a gene located on
chromosome #21
Schizophrenia: delusions, random
thoughts, disjointed thoughts, sensory
hallucinations
- may be the result of excessive activity of
brain neurotransmitters such as dopamine
Huntington’s Disease: progressive
deterioration of the nervous system that
leads to writhing movements, insanity
and eventually death
- seems to be caused by the malfunction of
the inhibitory neurotransmitter GABA
Depression: low affect, feeling blue, lack
of or excessive sleep and eating patterns
- seems to be linked to malfunctions in
dopamine and seratonin, perhaps caused
by an excess of monoamine oxidase
enzymes
 Stroke:
caused by interruption of blood
flow to the brain which causes brain cells
to perish.
Epilepsy: is a seizure disorder where
there is a sudden, un-explained surge
of electrical activity through the brain
with no specific known cause.

Epilepsy.com
Chemical Warfare

1) Nerve Gas: inhibit acetylcholinesterase
(enzyme that removed acetylcholine from
the synaptic gap). Causes spastic paralysis
which is continues muscle spasms

2) Strychnine: similar to nerve gas, causes
convulsions and spastic paralysis
Central Nervous System (CNS)
 Is
primarily responsible for the
processing and organization of
information.
 The
CNS consists of two major
structures:
1. The Brain
2. The Spinal Cord
Spinal Cord
•Made of 31 segments
•Protected by the vertebrae
Spinal Cord

Central Cavity – contains cerebrospinal fluid

White Matter – contains myelinated nerve cells

Grey Matter – contains un-myelinated nerve
cells
Spinal Cord
Root Ganglion – entry of
sensory neurons to spinal cord and CNS,
ganglion is the collection of cell bodies
 Dorsal
Root – exit of motor neurons
from the spinal cord
 Ventral
– 3 protective membranes
surrounding the spinal cord and brain
(dura mater, arachnoid, pia mater)
 Meninges
 Meningitis
is an infection of the
meninges (A spinal tap is a needle that
is inserted between 2 vertebrates into
the meninges to check for meningitis)
Fluid – circulates between
the inner and middle membranes of the
brain and spinal cord.
 Cerebrospinal
– Provides protection, nutrient / waste
exchange, etc.
Spinal Cord
Spinal Cord Functions
1.
center for reflex action
2.
provides a pathway for communication
between the brain and peripheral
nerves
The Brain
Hindbrain - The Unconscious
Brain
– important for autonomic functions
required for survival

Cerebellum – responsible for muscle
co-ordination, posture, coordinated
muscle movement and balance
oblongata – controls
heartbeat, respiration, blood pressure,
reflex center for vomiting, sneezing,
hiccupping, coughing and swallowing
 Medulla
– connects the cerebrum to other
parts of the brain, regulates breathing
rate
 Pons
Midbrain – reflex center for head movements
in response to visual stimuli, connects
cerebrum to other parts of the brain
Forebrain – responsible for
conscious and unconscious actions
– central relay station
- directs incoming sensory
information to the cerebrum
 Thalamus
Hypothalamus – contains cells that
produce some hormones, controls
thirst, hunger, and controls many of the
pituitary hormones
 Also aids in sleep regulation, sexual
arousal, emotions (anger, fear, pain,
pleasure)
– largest part of the
brain (80% of brain mass), left and
right hemispheres.
 Cerebrum
– responsible for intellect, memory,
consciousness and language.
Lobes of the Cerebral Cortex
Lobe –voluntary motor muscle
movement, higher intellectual processes,
personality/behavior, language
 Frontal
 Temporal
Lobe – hearing
Lobe –perceptions of touch,
temperature, pressure, pain, etc from
the skin
 Parietal
 Occipital
Lobe –vision
 Olfactory
Lobe –smell
Other parts of the brain
System –emotions, associated
with hypothalamus
 Limbic
 Pituitary
Gland- Master Gland
– attaches to hypothalamus
Corpus Callosum
– Bundle of nerves that connects the
two halves of the brain
– allows for integrated thoughts and
coordinated responses
– Left brain – verbal, linguistic
dominant
– Right brain – spatial, artistic, visual
dominant
PET – Positron Emission Tomography
– Radioactive chemicals are injected into the
bloodstream
– data is used to produce 2D or 3D images of
the distribution of the chemicals throughout
the brain and body.
SPECT-Single Photon Emission
Computed Tomography
– radioactive tracers and a scanner record
data
– computer constructs 2D or 3D images of
the active brain regions.
MRI-Magnetic Resonance Imaging
- magnetic fields and radio waves produce
high-quality 2D or 3D images of brain
structures without injecting radioactive
tracers.
EEG-Electroencephalography
- electrodes placed on the scalp detect and
measure patterns of electrical activity
from the brain.
CT-Computed Tomography Scan
- a series of X-ray beams passed
through the head.
-images are then developed on sensitive
film.
-creates cross-sectional images of the
brain
Peripheral Nervous System (PNS)
nerves – 12 pairs of sensory,
motor and mixed nerves that control the
face, neck and shoulders
 Cranial
Nerves – 31 pairs of nerves that
emerge from the spinal cord by two
roots (one pair for each segment)
 Spinal
root nerves – contain sensory
neurons and ganglia
 Dorsal
 Ventral
root nerves – contain motor
neurons
 All
other nerves not part of the CNS
Spinal Cord Injuries
The PNS is subdivided into two
major parts:
1.
The Somatic Nervous System
-contains all the nerves that serve the
muscular-skeletal system and the sensory
organs.
-conscious and deliberate.
2.
The Autonomic Nervous System
-non-voluntary actions
-contains all the nerves that serve the
internal organs.
-unconscious and automatic.
-made of two parts:
A. Sympathetic nervous system
-responsible for the 4 Fs: fight, flight,
fright, or having sex response
-ex) dilation of the pupils, increased
heart rate, increased breathing rate,
slowed digestion, enhanced
performance, increase in blood sugar
B. Parasympathetic nervous system
– responsible for the relaxation
response (after fight, flight, fright,
having sex)
- brings the body back to normal
levels
– http://itc.gsw.edu/faculty/gfisk/anim/aut
onomicns.swf
Fig 2 p 434