Chapter 2: The Biology of the

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Chapter 2: The Biology of the
Mind

Nervous System Hierarchy

Nerves


Nerves consist of neural
“cables” containing
many
axons
. They are part of the
peripheral
nervous system
and connect muscles, glands,
and
sense organs
to the
central nervous system.

Peripheral Nervous System

Links
the CNS to the organs, muscles, and
glands of the
body.


Sensory receptors receive sensory
information. The PNS transmits that
information along sensory nerves to the CNS


Motor neurons transmit commands to
effectors (muscles and glands)


Peripheral Nervous System


PNS has two parts


Somatic or
Somatosensory

(SNS): nerves
controlling voluntary movement and control of
skeletal muscles and receiving sensory
information


Autonomic

(ANS): controls (self
-
regulated)
activity of glands, organs, blood vessels,
heartbeat, digestion


Sympathetic


Parasympathetic


PNS

Sympathetic and Parasympathetic

Sympathetic
Nervous System


Accelerates
heartbeat


Raises B.P. and blood sugar


Slows digestion


Increases respiration and
perspiration


Dilates
pupils


Stimulates
secretion of
epinephrine and
norepinephrine


Diverts
blood flow away
from reproductive organs


Relaxes
bladder


Parasympathetic


Slows
heartbeat


Lowers
blood sugar


Contracts
pupil


Stimulates
digestion,
gall bladder


Contracts
bladder


Allows
blood flow to
sex organs


Sympathetic and Parasympathetic

Sympathetic
Nervous
System
(Arousing)


Fight
or
Flight. In
situations of high stress
(survival
-
wise), expends
energy, increases
alertness and readiness
by diverting
blood/nutrients from
non
-
essential functions
to functions that will
increase chance of
immediate
survival

Parasympathetic Nervous
System (Calming)



When
stress
subsides/threat is no
longer
present, undoes
the effects of the
sympathetic nervous
system


Calms
and conserves
energy, returning to
routine maintenance so
that life can go on.

Sympathetic/Parasympathetic

Stress is
present

Stress has
subsided

Somatic Nervous system


Includes all neurons connected with muscle, skin, or
sensory organs


12 pairs of cranial nerves (connect brain to periphery)


Transmit sensory info about smell, taste, vision, balance,
and general sensation in the head to the brain and transmit
signals from the brain to motor neurons that are involved in
movements of the face and throat


31 Pairs of Spinal Nerves (connect spine to periphery)


Transmit sensory info from body to brain and
transmit signals to innervate motor neurons that
control skeletal muscle


Each spinal nerve has a ventral root and a dorsal
root.

Spinal Nerve

“Mixed” because
it contains both
motor neurons
and sensory
neurons

Arrows are the direction
the stimulus is traveling

Ganglion=mass
of nerve tissue
containing cell
bodies

In the CNS
these are called
nuclei

Autonomic Nervous System


Sensory and motor neurons


Motor neurons that control smooth muscle
or cardiac muscle


Also differs from somatic nervous system
in that it uses two sets of motor neurons
instead of one

PNS

Autonomic Nerves


Preganglionic

neurons arise in CNS and run to a
ganglion in the body where they synapse with
postganglionic nerves.


Postganglionic neurons run to the
effector

organ
(cardiac muscle, smooth muscle, or gland)

Sympathetic Nervous System

The
preganglionic

neurons of the sympathetic nervous system
arise in the spinal cord and pass into the sympathetic ganglia.
These ganglia are organized into two chains that run parallel to
and on either side of the spinal cord.

In the sympathetic ganglia, the
preganglionic

neurons can pass up and
down the chain of sympathetic ganglia to
synapse with postganglionic neurons in a
higher or lower ganglion. These
postganglionic neurons then synapse with
effectors or they can reenter the spinal
nerve and ultimately pass out again later
on. This enables communication of
information to the different organs that
are effected by sympathetic arousal

Sympathetic Nervous system

Sympathetic Nervous System

The
preganglionic

neuron uses Ach as its
NT to stimulate action
potential in the
postganglionic neuron.

The effect is always
excitatory


The postganglionic
neuron uses
norepinephrine

as its NT
where it synapses with
effectors.

The effect is excitatory
or inhibitory depending
on the receptor at each
synapse

Parasympathetic Nervous System


Main nerves are the tenth pair of cranial
nerves (the
Vagus

nerves). They originate
in the Medulla


Preganglionic

parasympathetic neurons also
arise from other areas of the brain and
the lower tip of the spinal cord. These
synapse with postganglionic neurons which
are located near or on effecter organs.


Ach is the NT a most of
these synapses

The Endocrine System


Hormones have to travel
through the blood stream to
target organs. Compared to
neurotransmitters, they take
longer to act (several seconds
compared to fractions of a
second) but the effect is also
longer lasting


The endocrine system and
nervous system work
together. Example: Adrenal
gland and sympathetic
nervous system, the pituitary
gland and hypothalamus

The body’s “slow” chemical
communication system.
Communication is carried out by
hormones.

Hormones


Chemical messengers that are synthesized
and stored in glands of the endocrine
system. When secreted, the travel
through the blood stream and affect other
tissues, including the brain.


Influence growth, reproduction, mood,
metabolism, sex, aggression


Examples: Epinephrine (adrenaline), insulin,
growth hormone, estrogen, testosterone

The Endocrine System


Adrenal Glands


Pituitary Glands


Hypothalamus


Parathyroids


Testis/ovary


Thyroid gland


Pancreas

The Pituitary Gland


Called the “Master Gland”
because it releases
hormones that tell other
endocrine glands to
release hormones. But the
pituitary gland is
controlled by the
Hypothalamus.


Also releases hormones
that influence growth



Hypothalamus


Releases hormones
that stimulate or
inhibit the pituitary
gland.


Also helps control
body temperature,
hunger, thirst, sleep
-
wake cycle,
maintaining
homeostasis


Adrenal Glands


On top of the kidneys


Release epinephrine and
norepinephrine
(adrenaline and
noradrenaline) to
produce “fight or
flight” response under
stressful situations


Regulate salt and
carbohydrate
metabolism

Gonads


Ovaries/Testes


Secrete male or female sex
hormones.


Regulate body development and maintain
reproductive organs


Thyroid and Parathyroid


Regulate metabolism, growth rate, and
calcium levels

Pancreas


Secretes Insulin to regulate blood sugar
levels

Central nervous system


Brain


~2% of body weight, uses ~20% of resources


Composed of bunches of
neurons
, which form
nerves


Spinal cord


Complex tangle of nerves that stretch from
brain to tailbone


Collects & transmits info between brain and
peripheral nervous system


Also initiates
reflexes
: automatic responses to
an event

Simple Spinal Reflexes

Reflex


Automatic response to stimuli


Simplest reflex pathway is a single sensory neuron and a single
motor neuron, often communicating through an interneuron


Knee
-
jerk response, pain reflex, later you will learn about
reflexes that we display only during certain periods of infancy.


What purpose can you see in having actions that don’t require
conscious processing?



Complex Neural Networks

Interconnected
neurons form networks in
the
brain
.
The brain learns by modifying these
connections in response to feedback (inputs)

Major Sections
of the Brain

The Brain


Three important parts


Brain
Stem (including the cerebellum and
thalamus)

Midbrain and Hindbrain


Limbic System
-

Forebrain


Cerebral
Cortex
-

Forebrain

Older Brain Structures/Lower
Level
Functions


Brainstem


Medulla


Pons


Reticular formation (passes through both brainstem
and thalamus)


Thalamus (extends from top of brainstem)


Cerebellum (extends from rear of brainstem)


Limbic
system


Amygdala


Hypothalamus


Hippocampus


Brainstem


Automatic survival functions that occur
without conscious effort


Region
of the brain where the spinal cord enters
the
skull; an extension of the spinal cord


Crossover point where most nerves to and from
each side of the brain connect with body’s
opposite side

Brainstem


Medulla

-

Regulates
heart rate, breathing,
blood pressure and
has pathway for motor
movement


Pons



Helps
coordinate
movement


Reticular Formation


Nerve network that
controls Sleep and
arousal, (
Moruzzi

&
Magoun
, 1961)




Brainstem


Thalamus


Sits at the top of the
brainstem


Receives
sensory
input(except smell)and directs
them to sensory areas in the cortex then
transmits replies to cerebellum and medulla


Cerebellum


“Little Brain”


Nonverbal learning and memory,



C
oordinates voluntary movement and balance


Controls Learned/skilled movements that are
automatic (i.e., walking)

Limbic System


Memory, emotions, basic drives


Hypothalamus


Maintenance functions
-

Hunger, thirst, body temp.,
reproductive behavior


Helps govern endocrine system


Emotion and “Reward Center” (Olds & Milner (1954))


Hippocampus


Processes memory (H.M., amnesia)


Amygdala


Aggression, fear
,
and perception of them


Processing/encoding emotional memories


Regulating feeding

Question?


The limbic system is involved in
controlling basic drives important
for our survival as a species,
feeding and reproducing.
B
ut it is
also instrumental to the experience
of fear and aggression.


What do you make of the fact that
these two particular emotions
(unlike say, happiness or
melancholy) are controlled by the
same system that helps ensure our
survival?


What does Memory have to do with
this?

Cerebral Cortex


Intricate fabric of interconnected neural
cells that covers the cerebral hemispheres


Ultimate
control and information processing
structure


Higher Functions/Newer neural networks


85% of brain weight, billions of nerve cells
and 9 times as many glial cells


Filled mainly with axons connecting the
cortex to other brain regions


Neural networks form specialized teams

Cerebral Cortex


Glial Cells


Provide nutrients to the neuron (Astrocytes) and
myelin to insulate(
oligodendrocytes

and Schwann cells


Guide neural connections


Mop up ions and neurotransmitters


May play a role in learning, thinking, information
transmission and memory

Cerebral Cortex


Two halves, four
lobes, separated by
Fissures


Frontal lobe


Motor cortex


Parietal lobe


Sensory
cortex


Body position


Temporal
lobe


Auditory areas


Occipital lobe


Visual areas

Two Cerebral Hemispheres


Contralateral arrangement


the left
hemisphere receives inputs from and controls
the right side of the body and vice versa


Work together on many functions but can also
simultaneously carry out different functions
with minimal duplication of effort


Corpus callosum


Thick band of nerve fibers connecting the
hemispheres and allowing them to
communicate with each other


Functions of the Cortex


The
Motor Cortex
is the area at the rear of
the frontal
lobes that control voluntary movements
.


The cortex of each hemisphere controls the opposite
side of the body


The
Somatosensory
cortex
in the
parietal lobes,
receives
information from
skin surface and
sense organs.

Motor and Sensory Cortex


The body areas
requiring precise
control occupy
the most cortical
space on the
Motor Cortex


The more
sensitive the
body region, the
larger the
sensory cortex
area devoted to
it.

Functions of the Cortex

Visual Cortex




In the Occipital
Lobe


Receives visual
info from the eyes

Auditory Cortex


In the temporal
lobes


Receives auditory
information from
the ears


Association Areas of the Cortex


The ¾ of the cortex, across all four lobes not devoted to
sensory or muscle activity.


Interpret, integrate information processed by the
sensory areas, link sensory inputs with stored memories


In the frontal lobes enable judgment,

planning, processing memories,

inhibitions, and personality


In parietal lobes, enable mathematical

and spatial reasoning


In right temporal, enable facial

Recognition.

Association Areas

More intelligent animals have
increased
“uncommitted
” or association areas of
the
cortex
.

Specialization and Integration


Complex human behaviors involve multiple
specialized areas and association areas working
together.

The Brain’s Plasticity


Plasticity occurs during normal brain
development but it is also the brain’s
ability to modify itself after injury or loss
of function


Phantom limb


Enhanced peripheral vision in deaf people


The brain is sculpted by our genes and by a
person’s environment and experiences


Neural tissue reorganizes and in some
cases regenerates (neurogenesis)

Our Divided Brain

Corpus Callosum

Split Brain Patients

http
://
www.youtube.com
/watch?v=aCv4K5aStdU


With the corpus
callosum severed,
objects (
apple)
presented
in the right
visual field can be
named. Objects
(pencil) in the left
visual field cannot.


Divided Consciousness

The Right hemisphere is nonverbal but it can still
make itself understood

Hemispheric Specialization

Left brain


G
ood with literal
interpretations of
language


More active when
a person is
deliberating


More “rational”

Right Brain


Making inferences about
words and modulating
speech to convey meaning


Orchestrates sense of
self


Better with quick,
intuitive responses


Perceives objects better


More involved in emotion,
spatial reasoning


Hemispheric Specialization


After damage to the right
hemisphere, some patients
exhibit indifference to the left
side of their world


“hemi
-
neglect”


T
he neglect can be multimodal,
affecting auditory, visual,
somatosensory


Related to the right side’s
involvement in spatial reasoning
and sense of self. Damage to the
left side does not have this
effect.

Left & Right Functions

Theories of lateralization


Why?


May increase neural capacity


Dominance by one side prevents the
simultaneous initiation of incompatible
responses/actions


May increase capacity for parallel
processing in the two hemispheres


But then why do we display a consistent
preference at the population level? Shouldn’t
there be an equal ratio of left to right side
preference?

Theories of Lateralization


How?


Lateral birth position and neonatal head
orientation preference are both
predictors of handedness


Lateral asymmetry in the uterine
environment and maternal anatomy my lead
to the left side of the uterus being more
“favorable” for fetal positioning.


But then why would we have any lefties at all?

Handedness


Lefties are more likely than righties to process language with
either the right hemisphere or with both hemisphere. 96% of
righties process language primarily with left hemisphere.


Left
-
handedness is more common among musicians,
mathematicians, pro baseball players, architects and artists.


Do you think there is a connection?

Handedness


In the past, left
-
handedness was stigmatized in our
society and as children, lefties were “trained” to use
their right hands.


In a
world where

m
ost things are made

for righties
,
lefties are

More susceptible to

accidental injury.


On average, lefties

l
ive 9 years than

p
eople who are right
-

handed

Handedness


Given these facts about left
-
handedness as well as what you have
learned about research methods, what do you make of this graph?