Transcript Biology 30 NERVOUS SYSTEM - Salisbury Composite High School

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
Nervous System Organization
The Neuron- conducts nerve
impulses
The Neuron
Basic parts:
 cell body- nucleus and cytoplasm
 Dendrites-projection of cytoplasm
 Axon-extension of cytoplasm
 Glial Cells-non conducting support and metabolic
cells
Some neurons contain the following
additional parts:
 Schwann
cells- a special kind of glial
cell that produces a myelin sheath
 myelin
sheath-white fatty covering that
insulates the axon
 nodes
sheath
of Ranvier-gaps in the myelin

Myelination allows for faster transmission
of the nerve impulse

The impulse “jumps” the node
 Myelinated
nerves in the brain are
called white matter
 Non-
Myelinated = grey matter
 Nerves
of the PNS are myelinated

Neuron structure
Types of Neurons
Neurons (afferent) – carry
information from the receptors to the
brain/spinal cord
 Sensory
Neurons (efferent) – carry information
from the brain to the muscles and glands
 Motor
(association) – organize
and relay information within the brain
and spinal cord.
 Interneurons
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
2. Sensory neuron
3. Interneuron
4. Motor neuron
5. Effector
Action Potential
 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.
1. Resting Potential

Polarization: voltage difference of -70mV across a
nerve cell membrane

caused by the sodium potassium pump: more
sodium is pumped out than potassium is pumped in

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

change in pH, pressure, or an electrical stimulus
cause the Na+ gates to open and Na+ rush into
the cell.

membrane becomes depolarized (+ 40 mV)
3. Re-polarization
 Sodium
 change
gates close to stop inflow
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
(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 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 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.
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
 the
electrical impulse cannot cross the
gap (synaptic cleft) to the next dendrite
 neurotransmitters
are stored in synaptic
vesicles of the axon and are released to
carry the information across the 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
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 – the net effect of excitatory
and inhibitory neurotransmitters
– 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
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
1.
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
-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
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
meninges
is an infection of the
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
– contains cells that
produce some hormones, controls
thirst, hunger, and controls many of the
pituitary hormones
 Hypothalamus
– largest part of the
brain, left and right hemispheres.
 Cerebrum
– responsible for intellect, memory,
consciousness and language.
Lobes of the Cerebral Cortex
Lobe –voluntary muscle
movement, higher intellectual processes,
personality
 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
 Limbic
System –emotions
 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
root nerves – contain motor
neurons
 Ventral
 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
-contains all the nerves that serve the
internal organs.
-unconscious and automatic.
-made of two parts:
A. Sympathetic nervous system
-responsible for the fight or flight
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 or flight)
– http://itc.gsw.edu/faculty/gfisk/anim/aut
onomicns.swf
Fig 2 p 434