Download Nervous System

The Nervous System
Function
• The nervous system works with the endocrine system to maintain homeostasis.
– sensory receptors monitor changes in and out of the body
– process and interpret sensory input and make decisions on what should be done
– effect a response by activating (muscle, organ, glands)
Nervous System - Overview
Two main components:
1. Central Nervous
system: Brain and
spinal cord
2. Peripheral nervous
system: nerves that
emerge from spinal
cord and brain that
go to other parts of
the body
a. Afferent—
towards CNS
b. Efferent—away
from CNS
Multipolar Neuron
Parts of a neuron
Types of neurons
Neurons in context
Neuroglia (CNS)
Schwann and Satellite Cells (PNS)
ADAM-IAP modules (mount IP10.iso before starting)
• Interactive Anatomy and Physiology Nervous I
Anatomy Review 4, 5, 6, 7, 9
Schwann Cells
Myelin Sheath
How neurons communicate
• Simple animation of how neurons
communicate (action potentials and
neurotransmission)
• http://www.bris.ac.uk/synaptic/public/basics
_ch1_2.html
• Overview of the whole system
Axon - Resting Potential
The normal voltage difference maintained across the membrane of
the neuron. Excess positive charges accumulate on the outside of
the cell while excess negative charges accumulate on the inside of
the cell
This is results in a resting potential of about -70 mV
Gated channels
Proteins that open to allow ions to flow across the membrane in response
to a signal. There are two main types:
--chemical (usually respond to a chemical like a neurotransmitter)
--voltage (respond to a change in membrane potential voltage)
Action potential
-generated at axon hillock—results in a large spike in voltage across the
membrane as ions flow across the axon membrane—this spike tends to
travel down the axon to the axon terminus where it triggers
neurotransmitter release at the synapse
-only triggered when voltage at hillock is greater than threshold potential
(>~55mV)
Action Potential
• Simple animation of how neurons
communicate (action potentials and
neurotransmission)
Propogation of an Action Potential
Action Potential another view
Conduction Velocity
It’s all about resistance.
Axon diameter - larger the diameter, the less
resistance for sodium to move along axon
Myelin sheath - prevents leakage of sodium as it
moves along axon (saltatory conduction)
Note: alcohol, sedatives, anesthetics all block nerve
impulses by reducing the membrane permeability
to sodium ions (by blocking chemically-activated
or voltage-activated channels)
ADAM-IAP Modules
Interactive Physiology and Anatomy Nervous
I
The Action Potential 3, 4, 6, 7, 16
Synapses
• Junction between axon and post-synaptic cell
(another neuron, muscle cell, etc)
• Action potential reaches end of axon, triggers
release of neurotransmitters
• Neurotransmitters cause graded potential on postsynaptic cell
• Can cause excitatory post-synaptic potential
(EPSP) or inhibitory post-synaptic potential
(IPSP)
Synapse
Overview of neuron communication
• http://www.bris.ac.uk/synaptic/public/basics
_ch1_3.html
• http://www.getbodysmart.com/ap/nervoussy
stem/neurophysiology/synapses/menu/menu
.html
Synapses
Excitatory Post-Synaptic Pontentials (EPSPs) and
Inhibitory Post-Synaptic Potentials (IPSPs)
Excitatory or Inhibitory?
• EPSP or IPSP?
• Determined by which ion channels open up in the
postsynaptic cell.
• Spatial summation
• Temporal summation
•
•
•
•
To see:
Interactive Physiology and Anatomy Nervous I
Nervous System 2 Synaptic Potentials 12
Synaptic Potentials and Cellular Integration 4, 5,
6, 7, 8, 9
Neuronal communication
http://thebrain.mcgill.ca/flash/i/i_01/i_01_cl/i_01_c
l_fon/i_01_cl_fon.html
Neurotransmitters - Actions
nt
where
action
glutamate
GABA
Acetylcholine*
Acetylcholine
(parasympathetic)
Norepinephrine*
(sympathetic)
Norepinephrine
serotonin
dopamine
CNS
EPSP
CNS
IPSP
neuro-muscular EPSP
heart
IPSP
heart
EPSP
resp.
CNS
CNS
IPSP
IPSP
EPSP
* Ach and NE are also released at other synapses in the PNS and CNS
Drugs
cold/allergy med.binds to all receptors non-specifically drys mucosae, but also causes some CNS, HR, etc.
amphetamines
- most increase release of NE, epinephrine, dopamine
botulism
- bacterial toxin, prevents Ach release
valium
- receptor for GABA is a fast Cl- channel leading to IPSP
valium binds to another site (allosteric) increasing action of receptor, thus more
IPSP than nomal, relaxes anxiety, less stimulation
LSD/mescalin
cocaine
- bind to serotonin and some dopamine receptors - blocking and thus prevents
normal nt inhibition of certain pathways
- blocks reuptake mechanism, increases nt release
(dopamine, NE, serotonin synapses?)
nerve gas
- inhibits Ach-esterase...problem especially in intercostal skel muscles.
Prozac
- blocks re-uptake of serotonin, relieves anxiety/depression in some
caffeine
- shaped like adenosine, an IPSP nt in brain, blocks receptors, but no action
ecstasy
- broken down into HMMA which stimulates ADH release...alters kidney
function , water conserved...problem with solute dilution in the brain, etc.
opium
- mimics endorphins
Viagra
- a different kind of neurotransmitter....NO is a gas released by some neurons
locally in erectile tissue, causes vasodilation. Viagra blocks an enzyme that
Neuronal circuits
Spinal Cord
Components of a Reflex Arc
Reflex Circuit
Stretch Reflex
A reflex arc also involves inhibiting muscles that
oppose reflex action
The main parts of the human brain
Human brain (another view)
3D Brain (Genes to Cognition)
Brain functions
• Cerebral Cortex—
– “higher” functions, consciousness, creativity, thought,
etc
– Sensory integration and interpretation
– Motor control
• Diencephalon (includes limbic system)
– Limbic system—
• Amygdala: responsible for emotion, emotional learning
• Hippocampus: memory formation
• Hypothalamus—hormonal regulation, thirst, hunger, body
temp, fatigue, anger, circadian rhythms
– Thalamus—relay station for sensory impulses, impulses
to and from cerebral motor cortex and cerebellum
• Brain stem
– Pons—relay station for neurons entering and
leaving brain
– Medulla Oblongata—regulate essential bodily
functions
• Cerebellum
– Coordination of movement
– Physical equilibrium
Human Brain - Superior view
Human Brain - Lateral view
Human Brain - Sectional view
Sheep Brain - ventral and dorsal views
Sheep Brain - Sagittal section
Structure and functional areas of the cerebrum
Localization of brain functionalities: TMS—DVD: “How Does the
Brain Work” Chapter: Magnetic Simulation
Primary motor and somatosensory areas of the human cerebral cortex
Motor Cortex
Somatosensory Cortex
Hemispheric Lateralization
Mapping language areas of the cerebral cortex
Brain circuitry
A more recent view of brain circuitry
(diffusion tensor imaging)
Credit: M. D. Van Wedeen, Martinos Center and Dept. of
Radiology/Massachusetts General Hospital/Harvard U. Medical School
Male (left)/female (right) brain wiring
differences (Diffusion tensor imaging)
Sex differences in the structural connectome of the human brain http://www.pnas.org/content/early/2013/11/27/1316909110
Circuitry used in reading out loud
Syntax
Eyes to Thalamus first
(Understanding words)
From: http://thebrain.mcgill.ca/flash/i/i_01/i_01_cr/i_01_cr_fon/i_01_cr_fon.html
Brain function while listening to
music
Memory formation
http://www.stanford.edu/group/memorylab/Research/Research.html
Brain MRI
Localization of Brain Functions
Case studies of patients with brain damage or
congenital defects reveal information about
the various functions of the brain
The tale of Phineas Gage
• Premature explosion under
a tamping rod resulted in
the meter long rod (4-5
centimeters in diameter)
entering under his left
orbit, destroying much of
his frontal lobe as it was
propelled out of the top of
his head (landing 300 feet
away). Additional tissue
was destroyed by
subsequent infection.
Impact of this injury on Gage’s
personality
• Gage was] fitful, irreverent, indulging at times in the grossest profanity
(which was not previously his custom), manifesting but little deference
for his fellows, impatient of restraint or advice when it conflicts with
his desires, at times pertinaciously obstinate, yet capricious and
vacillating, devising many plans of future operations, which are no
sooner arranged than they are abandoned in turn for others appearing
more feasible. A child in his intellectual capacity and manifestations,
he has the animal passions of a strong man. Previous to his injury,
although untrained in the schools, he possessed a well-balanced mind,
and was looked upon by those who knew him as a shrewd, smart
businessman, very energetic and persistent in executing all his plans of
operation. In this regard his mind was radically changed, so decidedly
that his friends and acquaintances said he was ‘no longer Gage'.
• J. M. Harlow, 1868 (Publications of the Massachusetts Medical
Society 2: pp. 339–340)
Insula involved in addiction (red/orange area in this image)
Fig. 3. Whole-brain region-by-region logistic regression analysis
N. H. Naqvi et al., Science 315, 531 -534 (2007)
Published by AAAS
The limbic system
The Amygdala—seat of emotion in the brain?
Emotions
Fear: S.M. has
damaged
amygdala—can no
longer recognize the
emotion of fear
Associative learning of emotion in the
amygdala
Affective (mood) disorders
Blood flow in the brain of a patient suffering from unipolar clinical
depression, compared to non-depressed patients
Memory formation—case studies that shed light on
location in the brain where new meories are formed
• The case of H.M.—After surgery to treat seizures, in
which the amygdala, uncus, hippocampal gyrus and
anterior two-thirds of the hippocampus were removed,
H.M. could not form long-term memories
• The case of N.A.—a fencing foil poked into his right
nostril damaged part of his thalamus and the medial
temporal lobe on the right side as well as the mammilary
bodies. N.A. has lost much of his ability to form long-term
memories (retaining excellent memory of events prior to
1960)
• The case of R.B.—Suffered damage to the hippocampus
(bilaterally) during cardiac surgery. Also impaired in his
ability to form long-term memories
Brain areas associated with memory formation
Causes of amnesia
(Cerebral cortex?)
Religion and the brain
Increased activity in the frontal lobe, decreased in parietal lobe
Embryonic development of the brain
Brain Comparison
Reflex
• A reflex is a rapid, automatic response to a
stimulus, in which a particular stimulus always
causes the same motor response.
• Reflexes happen over neural pathways called
reflex arcs. Essential components:
–
–
–
–
–
Receptor
Sensory neuron
Integration center
Motor neuron
Effector
Somatic & Autonomic: The Plumbing