NERVOUS SYSTEM (1):Biological Bases of Behavior, Terminal Buttons

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Introduction to Psychology PSY101

Lesson 12

NERVOUS SYSTEM (1)

Central Nervous System (CNS) and Peripheral Nervous System (PNS)

The brain and its constituent parts are the most complex system ever known. With one trillion separate

cells, each one in a continuous process of changing in response to chemical signals. From the moment of

conception to the moment of death, the biology of the individual is changing. It is in this complexity that

our species has found the capability to store the accumulated experience of thousands of generations to

create human culture. Our language, religions, governments, childrearing practices, technologies, economies

are all man-made; yet all depend upon the remarkable capacity of the brain to make internal representations

of the external world.

Biological Bases of Behavior

The Nervous System

Endocrine Glands

The Nervous system

The system that controls and regulates the structure and function of the brain, spinal cord,

nerves, and the nerve cells; it maintains coordination between the nervous system and the rest

of the bodily systems.

It is responsible for the internal communication system that ensures the integrated functioning

of the various systems.

Some Interesting Facts about the Nervous system

The nervous system consists of billions of highly specialized nerve cells called neurons.

Nerve impulse is an electrical impulse that travels along the nerves at a speed of around

400km/ hour.

Every second, a number of these impulses can pass along nerves.

Brain cells never re grow; once destroyed or dead, they can not be replaced.

Nerve fibers are very thin and fine in size; a hundred of them lying side by side would fit into

just 1mm.

The brain is divided into two visible parts or hemispheres; the left hemisphere controls the

right side of the body, and the right controls the left side.

The total surface area of the cerebral cortex is approximately 2.5sq.ft. if you spread it flat.

Neuron

A nervous system cell is constituted in

Nucleus

such a way that it is specialized in receiving,

processing,

and/or

transmitting

Dendrites

information to other cells.

Cytoplasm

Structure of a Neuron

· Dendrites: Receivers of incoming

signals; branch fibers extending

Myelin Sheath

Soma

outward from the cell body.

· Soma: The cell body containing

Axon

the cytoplasm and the nucleus of

(transmitting end)

the cell; cytoplasm keeps it alive.

Terminal Buttons

· Axon: The nerve impulses travel

from the soma to the terminal buttons through the extended fiber of a neuron i.e., axon.

Introduction to Psychology PSY101

Terminal Buttons: Swollen, bulblike structures at one end of the axon; the neuron stimulates

the nearby glands, muscles, or other neurons

Connection between nerve cells

Synapse: the gap between one neuron and the other.

Synaptic Transmission: the procedure through which information is relayed from one

neuron to another across the synaptic gap.

Neurotransmitters: The post synaptic neuron is stimulated by the chemical messages released

from neurons; they cross the synapse from one neuron to another.

The Chemical Messages

The neurons follow an all-or-none law.... either a neuron will be firing or resting /off.

Excitatory Message: The chemical message that makes it more likely that the receiving

neuron will fire and the action potential will travel down its axon.

Inhibitory Message: The chemical message that inhibits a receiving neuron from firing so

that the action potential does not travel down its axon.

Major Varieties of Neurons

Sensory Neurons (afferent): they carry messages toward the Central Nervous System from

the sensory receptor cells.

Motor Neurons (efferent): they carry messages away from the Central Nervous System

toward the muscles and glands.

Inter-Neurons: they relay messages from sensory neurons to other inter-neurons and/or to

motor neurons.

Main Parts of the Nervous System

The Peripheral Nervous System

The Central Nervous System

Divisions of The Nervous System

Central Nervous System

Brain

Spinal Cord

The Peripheral Nervous System

(PNS)

The part of the

Peripheral Nervous System

nervous system that

Sensory Neurons

Motor Neurons

includes all parts of

(afferent)

(efferent)

the nervous system

except the brain and the

spinal cord

Somatic Division

Autonomic Division

Includes:

(motor nerves to skeletal

(motor nerves to glands,

i. Somatic

muscles)

Smooth & cardiac muscles

Division /

Somatic Nervous

System/ SNS

Sympathetic

Parasympathetic

ii. Autonomic division / Autonomic

Nervous System

Nervous System/ ANS

Somatic Division: controls the voluntary movements of the skeletal muscles.

Autonomic division: controls the involuntary movements all over the body; movements of the heart,

lungs, stomach, glands and other organs.

Introduction to Psychology PSY101

Central Nervous System (CNS)

Brain receives the information from all over the body (primarily in terms of stimulation via

sensation), interprets it, and decides how to respond.

The brain's function is similar to that of a computer; there is a central processing unit (CPU),

the output comes in, and the CPU analyses it and responds to it.

CENTRAL NERVOUS SYSTEM

The Brain

The center of the nervous system.

The vital organ that is responsible for the

Spinal Cord

Brain

functions of seeing, hearing, smelling,

tasting, thinking, feeling, remembering,

speaking, dreaming, information processing,

and a lot more.

The regulator of basic survival

functions such as breathing, resting

FORE BRAIN

MID BRAIN

HIND BRAIN

and feeding.

It is responsible for abstract level

functions such as decision making, foresight, and problem solving.

The spinal cord is an information highway connecting the PNS to the brain.

Information travels to and from the brain by way of spinal cord.

Functions of the Various Structures of the Brain

Regulation of the internal systems

Reproduction

Sensation

Motion

Adaptation to the varying environmental demands

Structure of Brain

The deeply grooved structure lies safely and securely in our skull.

The average adult human brain weighs 1.3 to 1.4 kg (approx. 3 pounds).

If you look at it from the outside the brain is pinkish gray in color; soft, spongy, and mottled.

The brain contains billions of nerve cells (neurons) and trillions of "support cells".

Parts of the Brain

The brain is made of three main parts:

a. Fore brain

b. Mid brain

c. Hind brain

Fore Brain

i. Cerebrum

ii. Thalamus

iii. Hypothalamus

iv. Limbic system

Mid Brain

i. Tectum

ii. Tegmentum

iii. Reticular formation

iv. Substantia nigra

Introduction to Psychology PSY101

Hind Brain

i. Cerebellum

ii. Pons

iii. Medulla oblongata

Brain Stem and Cerebellum

Located underneath the limbic system the brain stem, containing four structures, is found in all vertebrates.

It contains four structures:

1. Medulla

2. Pons

3. Reticular formation

4. Thalamus

o Responsible for basic survival functions such as breathing, heartbeat, and blood pressure.

Medulla/ Medulla Oblongata

· Located at the top of the spinal cord and continuous with it.

· Damage to Medulla can be fatal as it is the center responsible for vital functions i.e.,

respiration, heart beat, and blood pressure.

· Contains ascending & descending tracts that communicate between the spinal cord &

various parts of the brain.

· At medulla, nerves ascending from the body and descending from the brain cross over;

hence the left side of the body is connected to the right side of the brain and vice versa.

· Contains 3 vital centers:

Cardio inhibitory center: regulates heart rate.

Respiratory center: regulates the basic rhythm of breathing.

Vasomotor center: regulates the diameter of blood vessels.

2. Pons

Pons = Latin word for bridge

· Bridge connecting spinal cord with brain and parts of brain with each other.

· The pons seems to serve as a relay station carrying signals from various parts of the cerebral

cortex to the cerebellum.

· Nerve impulses coming from the eyes, ears and touch receptors are sent on the cerebellum.

· The pons also participates in the reflexes that regulate breathing.

· It has parts that are important for the level of consciousness and for sleep.

3. Reticular Formation

· The reticular formation is a region running through the middle of the hindbrain and into the

midbrain.

· A dense network of nerve cells.

· It keeps the brain alert even during sleep.

· It makes the cerebral cortex attend to new stimulation by arousing it.

· Long fibrous tracts of reticular formation run into the thalamus.

· Needed for arousal from sleep & to maintain consciousness.

· Serious damage to reticular formation may result into a coma.

4. Thalamus

The pair of egg-shaped structures located at the top of the brainstem.

· Incoming sensory information is channeled to the appropriate area of the cerebral cortex by

thalamus, so that it is processed there.

· Thalamus acts like a relay station.... the brain's sensory switchboard; it directs messages to the

sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.

Introduction to Psychology PSY101

It receives information from the sensory neurons and routes it to the higher brain regions that

deal with vision, audition, taste and touch.

Cerebellum

"Cerebellum" comes from the Latin word for "little brain". The cerebellum is located behind

the brain stem.

Cerebellum is somehow similar to the cerebral cortex: the cerebellum is divided into

hemispheres and has a cortex that surrounds these hemispheres.

It carries 10% of the weight of the brain.

It contains as many neurons as in the rest of the brain.

Its function is to coordinate body movements i.e. coordination, maintenance of posture &

balance.

Damage to cerebellum results into jerky and uncoordinated body movements.

Limbic System

Evolutionarily the structure of limbic system is rather old.

The limbic system, often referred to as the "emotional brain", is found buried within the

cerebrum.

At the border of the brainstem and cerebral hemispheres it is a doughnut-shaped system of neural

structures; associated with emotions e.g. fear and aggression, and drives like hunger and sex; regulates

body temperature, blood sugar level and blood pressure.

Structures within the Limbic System

i. Hippocampus

ii. Amygdala

iii. Hypothalamus

Amygdala

· Two almond-shaped neural clusters in the limbic system that are linked with emotions.

· They are related with aggression and fear.

Hippocampus

· The hippocampus is the part of the limbic system that is important for memory and learning.

Hypothalamus

· One of the smallest structures in the brain.

· The neural structure lying below (hypo) the thalamus; Composed of several nuclei. Small

bundles of neurons that regulate physiological processes involved in motivated behavior e.g.

hunger, thirst, regulation of body temperature.

· Hypothalamus acts as the body's Thermostat.

· Helps govern the endocrine system via the pituitary gland.

· Is linked to emotions.

Homeostasis

Hypothalamus maintains the body's internal equilibrium e.g. looking for food when energy levels are low,

causing constriction of the blood vessels when body temperature falls.

Cerebrum

Largest part of the human brain, associated with higher brain functions such as thought and

action..

Occupies 2/3 of the brain's total mass

Consists of two symmetrical halves or hemispheres; The right cerebral hemisphere controls the

left side of the body and vice versa.

The hemispheres are connected by Corpus Callosum, a thick mass of nerve fibers.

Cerebrum regulates the brain's higher cognitive and emotional functions.

Introduction to Psychology PSY101

Cerebral Cortex

o Coming from the Latin word for "bark", cortex means covering, or sheath; the cortex is a sheet of

tissue making up the outer layer of the brain.

o About 1/10 of an inch in thickness, the cortex is composed of some 30 billion nerve cells and 300

trillion synaptic connections.

o It is the body's ultimate control and information-processing center.

Sulci and Gyrus

o The cerebral cortex is greatly convoluted in humans. These convolutions include:

1. Sulci (singular Sulcus) i.e. small grooves.

2. Gyri (singular Gyrus) i.e. large grooves also called "Fissures".

Grey matter

Cerebral cortex mostly consists of glia (glial cells), cell bodies, dendrites and

interconnecting neurons; they give the cerebral cortex a grayish brown appearance,

commonly known as `Grey Matter".

White Matter

Beneath the cerebral cortex lie millions of axons that connect the neurons of the cerebral

cortex to those located elsewhere in the brain.

The large myelin gives tissue an opaque white appearance known as "White Matter".

Cerebral Lobes

a. Frontal lobe

b. Parietal lobe

c. Temporal lobe

d. Occipital lobe

· Each lobe controls a different range of activities.

· Each hemisphere is vertically divided by the central sulcus, a groove.

· The lateral fissure, another groove divides each hemisphere horizontally.

a. Frontal lobe

Associated with motor control and cognitive activities; reasoning, planning, decision making, problem

solving, movement and speech (Broca's Area).

b. Parietal lobe

Associated with controlling incoming sensory information; thus affecting movement, orientation,

recognition, perception of stimuli.

c. Temporal lobe

Associated with perception and recognition of auditory stimuli, memory & speech.

Wernicke's area: concerned with the understanding of language is located here

d. Occipital lobe

Associated with visual processing.

Cranium

o The brain is enclosed in the cavity of skull or cranium consisting of eight hard bones; One frontal

bone, two parietal bones, two temporal bones, one occipital bone, one sphenoid bone, and one

ethmoid bone.

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