Transcript intro to CNS

Introduction to Central Nervous System
Metro Anatomy & Physiology
Spring 2017
Stan Misler
<[email protected]>
1. Why study nervous system?
Contemporary Consensus: (i) the brain is “the engine of reason and the seat of the
mind” and “self” (personality) and likely the seat of the “soul”
(ii) Reality is a function of how regions of brain acquire and interpret features of the
environment at any given time. However some functions (e.g., memory) may be
distributed over many interacting locations.
(iii) Brain as site of major debilitating diseases; attempted treatment likely requires
knowing location(s) of injury. Physicians use history and symptoms of illness, and their
physical exam to hypothesize effected site(s). Afterwards use computerized
tomography (CT or MRI) and functional imaging (PET or fMRI) to carefully localize
lesions in 3D. Examples: (a) finding area of cell death within the brain; (b) as an aid in
investigating origin of coma or existence of brain death; and (c) to evaluate extent of
degenerate brain diseases with cerebral atrophy.
(iv) Brain is seat biology of behavior and
there of social problems such as child
rearing, opioid addition and aggression
(v) Gateway to your future occupation?
Medical care is fastest growing industry
and care of brain diseases such as
Computerized tomography:
dementia is the fastest growing sector
horizontal, coronal and sagittal section
of the medical care industry
2. Central nervous system (brain +
spinal cord) underlies many functions
3. What the nervous system is composed of
Brain weighs ___, is roughly the size and shape of a small
pumpkin on a stalk and has the consistency of soft jello;
contains ________neurons + helper glial cells and blood
vessels; cerebral cortex (outer surface) accounts for 80 % of
mass of brain.
Brain is very active metabolically getting _____ of body’s blood
flow for only 2% of body mass; _______,the major metabolite
is not stored so must be constantly delivered by blood
Sensory perception,
thought, movement
Visual & auditory
reflexes
Bridge between
hemispheres
Thalamus; sensory
motor way station;
hypothalamus:
coordination of
automatic
responses and
hormone release
Motor memory &
smoothness of motion
automatic function:
breathing, heart rate;
reflexes
4. Schematic representation of nervous system
a.
b.
Afferent fibers in carry
impulses from peripheral or
internal sensory receptor
organs to the CNS.
Efferent fibers carry impulses
from CNS to peripheral
effector organs (muscles of
various types and glands)
c.
5. Approaches to functional anatomy of brain
Accidental injuries: Phineas Gage and personality change after pipe
going through frontal brain
Effects of surgical lesions: commissuratomy (division of corpus
callosum) to disconnect left hemisphere from right of cerebrum
Electrical stimulation during deep brain surgery to pinpoint some
regions
Electroencephalogram (EEG) (surface recording of slow currents
passing through glial cells) to localize site of seizure initiation
Imaging: (i) CT (computerized tomography) and MRI (magnetic
resonance imaging) for structure;
(ii) PET = positon emission tomography (with tagged glucose
injection) for areas of high or very low brain metabolism
(iii) fMRI = functional MRI for rapid changes in regional blood flow
(O2 delivery) with stimulation of activity.
The strange case of Phineas Gage,
Survived a railroad track accident where an iron bar passing through
his left skull destroyed his left eye and much of his brain’s left frontal
lobe. His personality and behavior over the remaining 12 years of his
life were altered to the extent that his friends no longer thought he
was the previously patient, polite and mild mannered Gage.
Implication: is this where personality has its origin?
6. What types of cells is the nervous
system is composed of
(i) Neurons: generate impulses (action potentials) and conduct these
down pathway -> synaptic transmission (release of chemical transmitters at
the nerve terminal to excite or inhibit action potential of next cell in
sequence)
(ii) Glia = helper cells for neurons including:
(a) insulation of axons with myelin sheaths (oligodendrocytes)
(b) scaffold for neuronal growth (radial glia)
(c) uptake of released transmitter and excess K from synaptic cleft,
metabolism, blood brain barrier (astrocytes)
(d) scavengers to remove cell debris (microglia)
(iii) Capillary endothelial cells = provision of O2, metabolites from
bloodstream)
7. Cell Biology of neurons:
neurons work electrically & contain four recognizable regions
(1) Dendritic tree = Sensory pole for signal detection: Reception
of transmitter inputs from other neurons at dendritic spines ->
post-synaptic potential (psp = a & b) while sensory transduction
such as membrane vibration (stretch), results in a generator
potential (GP = c)
(2) & (2a) Soma (cell body with nucleus) & initial segment of axon
are sites of integration (summation of over time and space) of
psps and analog to digital conversion of these summed potentials
to trigger action potentials (APs). APs encoded as trains with
stereotyped or changing shapes. Site of protein synthesis
(3) Axon = impulse propagating cable for APs. Axons are often
wrapped in a myelin sheath made of glial membrane for insulation;
Allows interval electrical boosting at nodes of Ranvier (*) to
maintain fidelity. Transports proteins, mRNA and mitochrondria
from soma to nerve terminal
(4) Presynaptic terminal = secretory pole: action potential dependent release of neurotransmitter from synaptic vesicles onto
sensory pole of follower cell by exocytosis (pore formation between
vesicle and cell membranes) + diffusion of neurotransmitter through
pores and across synaptic cleft to interact with post-synaptic
receptors, refilling of vesicles with transmitter
Diseases of Nervous system
Interaction of CNS with rest of body