Transcript The Nervous System

The Nervous System
Or:
What makes me do that Voodoo that I
Do So Well
Nervous System

Central
– Brain
– Spinal Cord

Peripheral
– Everything Else
Central Nervous System
(CNS)

Brain
– Lobes
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Frontal
Parietal
Temporal
Occipital
– Cerebellum
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Spinal Cord
Brain
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Frontal Lobe
The Cerebral Cortex:
Localization of Function

Brodmann’s Area Map
of the brain (Based on
cyto-architecture)
– Language and
–
–
–
–
–
Comprehension
Cognition
Emotion
Motor
Somatosensory
Vision
The Cerebral Cortex: Location
of Function

Can also be organized
into:
– Motor Cortex
– Somatosensory Cortex
– Association Cortex

The Homunculus
– Penfield
Lateralization of Function

Two halves (hemispheres) of our brain
– connected by the corpus callosum

Right Brain / Left Brain specialization
 The right brain
– responsible for movement on the left-side of the body

The left brain
– specialized for language (Stroke victims)

The right brain
– specialized for spatial relationships
Roger Sperry (1913-1994):
Split Brain Research

Two halves of the brain are in constant
communication with each other
 if you cut the corpus callosum you disrupt
the communication (severe epilepsy)
– Visual abilities (L vs. R visual field)
– Tactile stimulation
– Auditory ability
Sperry: Visual Abilities

Flashing lights across both visual
fields,
– PTs responds by saying they only
saw lights on the R side of the board
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Flashing lights to the left visual
field
– the PTs said they saw nothing

But if asked to point to the lights
presented in both visual fields
they would respond correctly
(identifying all the lights)
 Conclusion: Both halves were
perceiving the lights, but only the
left half of the brain could
respond verbally
Sperry: Tactile Abilities

When a hidden object is placed in right
hand, the PT was able to name what it was
 When a hidden object is placed in the left
hand, the PT could not name or describe it
Peripheral Nervous System
PNS

Receptors
 Afferent Neurons
 Efferent Neurons
 Effectors
Receptors - Vision

Rods
– rods are responsible for vision in dim light

do not support colour vision

in very dim light, all objects appear in different
shades of grey
Receptors - Vision (con’t)

Cones
– three types (in humans), each maximally
sensitive to a different wavelength of light
 less sensitive to light than rods, but faster temporal
response
– concentrated mostly in the centre of the retina
(the "fovea")
 (it's hard to read by moonlight due to the low spatial
resolution of the rods)
Receptors - Skin

Hair Follicle Ending
– A-beta
– Responds to hair
displacement
Receptors - Skin

Ruffini Endings
– A-beta
– Responds to pressure
on skin
Receptors - Skin

Krause corpuscle
– A-beta
– Responds to pressure
Receptors - Skin

Pacinian corpuscle
– A-beta
– Responds to vibration.
Most sensitive in 150300 Hz range
Receptors - Skin

Meissner corpuscle
– A-beta
– Responds to vibration.
Most sensitive in 20-40
Hz range
Receptors - Skin

Free nerve endings
– A-delta and C
– Different types of free
nerve endings that
respond to mechanical,
thermal or noxious
stimulation
Skin Receptors

Merkel Cells
– A-beta
– Responds to pressure
of the skin
Receptors - Sound

Cochlea
 Basilar Membrane
– Cilia

Auditory Nerve
Chemical Receptors

Taste Bud
– approximately 10,000
in humans) is made up
of many (between 50150) receptor cells.
Receptor cells live for
only 1 to 2 weeks and
then are replaced
– Each receptor in a taste
bud responds best to
one of the basic tastes.
Olfaction
Olfaction
Reflex Arc

Stimulus
– afferent

Signal Split
 Response
– efferent
The ANS
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Regulates physiological activity
– Involuntary
– Not under conscious control
The ANS
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Consists of two divisions
– The Sympathetic System
– The Parasympathetic System
The ANS

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Eye
Salivary glands
Trachea
Bronchi
Heart
Stomach
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Liver
Gallbladder
Adrenal Glands
Kidney
GI Tract
Urinary Bladder
The ANS
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Function is to maintain Homeostasis
– Tendency to maintain a variable (like
temperature) within a fixed range

Control steady state of the internal
environment
Anatomy of the ANS

Control centers are located within the CNS
– The hypothalamus (the brain)

Peripheral network of afferent and efferent
nerves
The Hypothalamus
The Hypothalamus

Regulation of Body Temperature
 Water Balance
 Blood Pressure
 Emotion
 Sleep
 Sexual Reflexes
Efferent Nerves

These are Motor or Effector nerves
 Comprised of a two-neuron chain
– Preganglionic neuron
 Originates in the CNS
– Postganglionic neuron
 Originates in the ganglion
Ganglion

Loosely organized collection of nerve fibers
and cell bodies
Postganglionic Neurons

Directly innervate effector organs
– Impulse at the neuroeffector junction
Organ
CNS
ANS
Pre
Post
Ganglion
Afferent Neurons

Usually Sensory Nerves
– Transmit unconscious info
 Blood pressure
 Heart rate
 GI motility
 Visceral info (semi conscious)
– Nausea. Hunger
ANS Divisions
Parasympathetic

Ganglia are near the innervated organ
– Long Pre short Post
 The post innervates only a single organ
 Reflects function of discretely regulating processes
such as digestion
Sympathetic

Ganglia are near the vertebrae
– Short pre Long post
 The post has wide diffusion
 Reflects function of a whole body response
– The fight or flight response
– One nerve cell may innervate 25,000 effector cells
Adrenal Glands
Adrenal Glands

Consists of two parts
– Adrenal cortex
– Adrenal Medulla
Adrenal Glands
Adrenal Cortex

Produces a hormone called cortisol
– Mobilizes energy reserves and suppresses
immune system
Physiology of the ANS
Acetylcholine (ACh)

A major NT in the ANS and CNS
 Catalyzed by Choline acetyltransferase
 Acetyl CoA + Choline
ACH + CoA
Dopamine, Norepinephrine
and Epinephrine

Major NTs in the CNS and ANS
Tyrosine
Tyrosine Hydroxalase
DOPA
DA
Aromatic amino-acid
decarboxylase
DA-Beta Decarboxylase
NE
E
Phenylethanolamine N methyl
transferase