The nervous system

THE NERVOUS
SYSTEM
Presented by: Group 2
Roll Numbers: 02, 14, 29, 33, 44, 82
Presented to: Ma’am Rabiya Amer
Health Psychology (PSY-508)
BS 6th Morning

INTRODUCTION
■ The nervous system is a complex network of interconnected nerve fibers.
■ It is the body’s main communication system; it gathers, synthesizes, and uses data
from the environment.
■ It controls and coordinates all essential functions of the body including all other
body systems allowing the body to maintain homeostasis or its delicate balance.
■ Without the nervous system, our muscles would not expand or contract, our
pancreas would not release insulin, and consciousness would not be possible.

FUNCTIONS OF THE NERVOUS SYSTEM
1. Sensory Function:
■ The nervous system gathers information from both inside and outside the body.
2. Integration Function:
■ The nervous system transmits information to the processing areas of the brain and
spine and processes the information in the brain and spine.
3. Motor Function:
■ The nervous system sends information to the muscles, glands, and organs so they
can respond appropriately.

OVERVIEW OF THE NERVOUS SYSTEM
 The nervous system can be broken
down into two major parts—the
central nervous system and the
peripheral nervous system.
 The central nervous system, the
main data center of the body,
includes the brain and spinal cord.
 The peripheral nervous system
includes all of the neurons that
sense and communicate data to
the central nervous system.
 The peripheral nervous system can
be further divided into the
autonomic system, which
regulates involuntary actions, and
the somatic system, which
controls voluntary actions.

Neuron: The Basic Unit of the Nervous
System
■ The neuron serves as both a sensor and
communicator of internal and external stimuli.
■ Dendrite – receives stimulus and carries it
impulses toward the cell body.
■ Cell Body with nucleus – nucleus & most of
cytoplasm.
■ Axon – fiber which carries impulses away from
cell body.
■ Schwann Cells- cells which produce myelin or fat
layer in the Peripheral Nervous System.
■ Myelin sheath – dense lipid layer which insulates
the axon – makes the axon look gray.
■ Node of Ranvier – gaps or nodes in the myelin
sheath.
■ Impulses travel from the dendrite to the cell body
to axon.

THREE TYPES OF NEURONS
1. Sensory neurons – bring
messages to the central
nervous system.
2. Motor neurons - carry
messages from the central
nervous system.
3. Interneurons – between
sensory & motor neurons in
the CNS.

THE CENTRAL
NERVOUS SYSTEM
• The central nervous system consists of the brain and the spinal cord.
• Sensory nerve fibers provide input to the brain and spinal cord by carrying signals from
sensory receptors; motor nerve fibers provide output from the brain or spinal cord to
muscles and other organs, resulting in voluntary and involuntary movement.

OVERVIEW OF THE BRAIN
(A) The Hindbrain and Midbrain
(i) Medulla
(ii) Pons
(iii) Cerebellum
(B) The Forebrain
(i) Thalamus
(ii) Hypothalamus
(iii) Cerebral Cortex
(C) The Limbic System
(i) Amygdala
(ii) Hippocampus

■ The hindbrain, which includes the medulla oblongata, the pons, and the cerebellum, is
responsible for some of the oldest and most primitive body functions. It coordinates
functions that are fundamental to survival, including respiratory rhythm, motor activity,
sleep, and wakefulness.
(i) Medulla Oblongata
 The medulla is responsible for the regulation of heart rate, blood pressure, and
respiration.
 Thus, it controls several vital reflexes, including salivation, coughing, and sneezing
alongside other functions outside conscious control.
(ii) Pons
 Located just up from the medulla, the pons consists of two pairs of thick stalks that
connect to the cerebellum.
 The pons contains nuclei that help regulate sleep, breathing, swallowing, bladder
control, equilibrium, taste, eye movement, facial expressions, and posture.

(iii) Cerebellum
 The cerebellum is a separate region of the brain located behind the medulla oblongata and
pons. It is attached to the rest of the brain by three stalks (called pedunculi).
 Its main function is to maintain body balance and coordinate voluntary muscle movement.
 It assists us when we are learning a new motor skill, such as playing a sport or musical
instrument.
 In addition, some studies suggest that specialized parts of the cerebellum contribute to
memory, language, and cognition.
 Damage to the cerebellum produces a loss of muscle tone, tremors, and abnormal posture.
Damage also results in the impairment of fine motor skills.
 Midbrain
 The Midbrain is the part of the brain that lies between the hindbrain and the forebrain.
 The midbrain helps us to locate events in space.
 It also contains a system of neurons that releases the neurotransmitter dopamine.
 The Reticular Formation runs through the hindbrain and the midbrain and is involved in sleep
and wakefulness, pain perception, breathing, and muscle reflexes.

(i) Thalamus
 The thalamus is involved in the recognition of sensory stimuli and the relay of sensory
impulses to the cerebral cortex.
 It is viewed as the brain’s switchboard as it filters and then relays information to various
brain regions.
 Scientists have observed that, upon reception of pain sensory information, there are
consequential changes in the biochemistry, genetic expression, and blood flow of many
thalamic neurons. From this, they have continued to hypothesize that the thalamus plays a
central role in the modulation of pain.
(ii) Hypothalamus
 The hypothalamus interconnects with numerous regions of the brain.
 The hypothalamus helps regulate cardiac functioning, blood pressure, respiration, water
balance, and appetites, including hunger and sexual desire.
 It also is involved in monitoring information from the autonomic nervous system and
controlling the pituitary gland and its hormones.

(iii) Cerebral Cortex
 The cerebral cortex is the largest portion of the brain, involved in higher-order intelligence,
memory, and personality.
 Sensory impulses that come from the peripheral areas of the body are received and
interpreted in the cerebral cortex.
 The cerebral cortex consists of four lobes:
1. Frontal lobe:
 Controls specialized motor control, learning, planning, and speech.
2. Parietal lobe:
 Controls somatic or voluntary sensory functions.
3. Occipital lobe:
 Controls vision
4. Temporal lobe:
 Controls hearing and some other speech functions.

It contains the parietal lobe (green), the occipital lobe (red), the temporal lobe (yellow), and
the frontal lobe (blue).

■ The limbic system is a complex set of structures found on the central
underside of the cerebrum, comprising inner sections of the temporal lobes
and the bottom of the frontal lobe.
■ It combines higher mental functions and primitive emotion into a single
system often referred to as the emotional nervous system.
■ It is not only responsible for our emotional lives but also our higher mental
functions, such as learning and formation of memories.
■ The limbic system is the reason that some physical things such as eating
seem so pleasurable to us, and the reason why some medical conditions,
such as high blood pressure, are caused by mental stress.

(i) Amygdala
 Known as the emotional center of the brain, the amygdala is involved in evaluating the
emotional valence of situations (e.g., happy, sad, scary).
 It helps the brain recognize potential threats and helps prepare the body for fight-or-flight
reactions by increasing heart and breathing rate.
 The amygdala is also responsible for learning on the basis of reward or punishment.
 Some scientists believe that a range of behaviors associated with autism, such as a reluctance
to make eye contact and other deficits in social functioning, may be linked to abnormal size or
functioning of the amygdala.
(ii) Hippocampus
 Psychologists and neuroscientists dispute the precise role of the hippocampus, but generally
agree that it plays an essential role in the formation of new memories about past experiences.
 Some researchers consider the hippocampus to be responsible for general declarative
memory (memories that can be explicitly verbalized, such as memory of facts and episodic
memory).
 When the hippocampus is injured, people typically develop anterograde amnesia, a form of
amnesia in which they are unable to form new memories but retain their memory for
previously learned skills.

The Spinal Cord
■ The spinal cord is a tail-like structure embedded in the vertebral canal of the spine.
■ The adult spinal cord is about 40 cm long and weighs approximately 30 g.
■ The spinal cord is attached to the underside of the medulla oblongata, and is
organized to serve four distinct tasks:
1. To convey (mainly sensory) information to the brain;
2. To carry information generated in the brain to peripheral targets like skeletal
muscles;
3. To control nearby organs via the autonomic nervous system;
4. To enable sensorimotor functions to control posture and other fundamental
movements.

THE PERIPHERAL
NERVOUS SYSTEM
• The peripheral nervous system consists of the rest of the nerves in the body,
including those that connect to the brain and spinal cord.
• It is comprised of sensory receptors, which process changes in internal and
external stimuli and communicate that information to the CNS.

OVERVIEW OF THE PERIPHERAL
NERVOUS SYSTEM
■ The peripheral nervous system is further subdivided into 2 subdivisions:
(A) Somatic Nervous System
(B) Autonomic Nervous System
(i) Sympathetic Nervous System
(ii) Parasympathetic Nervous System

(A) Somatic Nervous System
■ The somatic nervous system – also known as the voluntary nervous system - keeps
the body adept and coordinated, both through reflexes and voluntary action.
(i) Voluntary Action through the Somatic Nervous System:
■ The somatic nervous system connects nerve fibers to voluntary muscles and
provides the brain with feedback about voluntary movement.
■ Thus, it relays information from skin, sense organs & skeletal muscles to the CNS
and brings responses back to the skeletal muscles for voluntary responses.
■ The voluntary action is possible due to the presence of afferent and efferent nerves.

■ Afferent fibers, or nerves that receive information from external stimuli, carry
sensory information through pathways that connect the skin and skeletal muscles
to the CNS for processing. For this reason, afferent nerves are also called sensory
nerves.
■ The information is then sent back via efferent nerves, or nerves that carry
instructions from the CNS, back through the somatic system. For this reason,
efferent nerves are also called motor nerves.
■ These instructions then go to neuromuscular junctions—the interfaces between
neurons and muscles—for motor output.

(ii) Reflexes through the Somatic Nervous System:
■ The somatic system also provides us with reflexes, which are automatic and
do not require input or integration from the brain to perform.
■ The pathway of a reflex action is called a reflex arc.
■ In a reflex arc, the stimulus is received by the receptors (sense organs) and it
passes through the sensory nerves to the spinal cord. From the spinal cord,
the information passes through the motor nerves to the effectors (muscles or
glands) for the response.
■ Reflexes can be categorized as either monosynaptic or polysynaptic based
on the reflex arc used to perform the function.

Monosynaptic reflex arcs, such as the
knee-jerk reflex, have only a single
synapse between the sensory neuron
that receives the information and the
motor neuron that responds.
Polysynaptic reflex arcs, by contrast,
have at least one interneuron between
the sensory neuron and the motor
neuron.

(B) Autonomic Nervous System
■ The autonomic nervous system regulates involuntary and unconscious
actions, such as internal-organ function, breathing, digestion, and
heartbeat.
■ This system consists of two complementary parts that help in its regulation:
the sympathetic and parasympathetic systems.
■ Both divisions work without conscious effort and have similar nerve
pathways, but they generally have opposite effects on target tissues.
■ Together, these two systems maintain homeostasis within the body: one
priming the body for action, and the other repairing the body afterward.

(i) Sympathetic Nervous System
■ The sympathetic nervous system consists of groupings of neuron cell bodies called ganglia
that run along the spinal cord and connect to the body’s internal organs. Thus, all the
ganglia tend to act as a single system in ‘sympathy’ with one another.
■ The sympathetic nervous system activates the “fight or flight” response under sudden or
stressful circumstances, such as taking an exam or seeing a bear.
■ It increases physical arousal levels, raising the heart and breathing rates and dilating the
pupils, as it prepares the body to run or confront danger.
■ These are not the only two options; “fight or flight” is perhaps better phrased as “fight or
flight or freeze,” where in the third option the body stiffens and action cannot be taken. This
is an autonomic response that occurs in animals and humans; it is a survival mechanism
thought to be related to playing dead when attacked by a predator.
■ Post-traumatic stress disorder (PTSD) can result when a human experiences this “fight or
flight or freeze” mode with great intensity or for large amounts of time.

(ii) Parasympathetic Nervous System
■ Unlike the ganglia of the sympathetic division, the ganglia of the
parasympathetic nervous system are not closely linked and therefore
tend to act more independently.
■ This system has opposite effects than those of the sympathetic
ganglia; in helping the body to recover after arousal, it decreases
heart rate, increases digestive activity, and conserves energy

DISORDERS OF THE
NERVOUS SYSTEM

Epilepsy
Epilepsy is often idiopathic, which means that no speciﬁc cause
for the symptoms can be identiﬁed. Symptomatic epilepsy may be
traced to harm during birth, severe injury to the head, infectious
disease such as meningitis or encephalitis, or metabolic or
nutritional disorders
Risk for epilepsy may also be inherited. With the epilepsy more
than 3 million people are affecting in the United State.
Epilepsy cannot be cured, but it can often be controlled through
medication and behavioral interventions designed to manage
stress.
Epilepsy is marked by seizures, which range from barely
noticeable to violent convulsions accompanied by
irregular breathing and loss of consciousness.

Cerebral Palsy
• Cerebral palsy is a chronic,
nonprogressive disorder marked by lack
of muscle control. Apart from being
unable to control motor functions, those
who have the disorder may (but need
not) also have seizures, spasms, mental
retardation, diﬃculties of sensation and
perception, and problems with sight,
hearing, and speech.
• It stems from brain damage caused by
an interruption in the brain’s oxygen
supply, usually during childbirth. In
older children, a severe accident or
physical abuse can produce the
condition.

Parkinson’s
disease
Patients with Parkinson’s disease
have progressive degeneration of
the basal ganglia, a group of nuclei
in the brain that control smooth
motor coordination. Th e result of
this deterioration is tremors, rigidity,
and slowness of movement.
Although the cause of
Parkinson’s is not fully known,
depletion of the
neurotransmitter dopamine
may be involved.
As many as one million
Americans suﬀer from
Parkinson’s disease, which
primarily strikes people age 50
and older men are more likely
than women to develop the
disease.
Parkinson’s patients may be
treated with medication, but
large doses, which can cause
undesirable side eﬀects, are
often required for control of the
symptoms.

Multiple
sclerosis
This degenerative disease can cause paralysis and, occasionally,
blindness, deafness, and mental deterioration.
Early symptoms include numbness, double vision, dragging of the
feet, loss of bladder or bowel control, speech difficulties, and extreme
fatigue. Symptoms may appear and disappear over a period of years;
after that, deterioration is continuous.
Multiple sclerosis is an autoimmune disorder, so called because the
immune system fails to recognize its own tissue and attacks the
myelin sheath surrounding the nerves.
The effects of multiple sclerosis result from the disintegration of
myelin, a fatty membrane that surrounds the nerve fibers and
facilitates the conduction of nerve impulses.
Although there's not yet a cure for MS, there are many effective
medications to help you manage the disease.

Huntington’s
disease
A hereditary disorder of the central nervous system, Huntington’s disease
is characterized by chronic physical and mental deterioration.
Symptoms include involuntary muscle spasms, loss of motor abilities,
personality changes, and other signs of mental disintegration.
The gene for Huntington’s has been isolated, and a test is now available
that indicates not only if one is a carrier of the gene but also at what age
one will succumb to the disease. Genetic counseling with this group of at-
risk people is important. The disease aﬀects 1 out of every 10,000 men
and women in the United States.
There is no treatment to stop or reverse Huntington's disease, however
there are some medications that can help keep symptoms under control.
Treatment includes the drug tetrabenazine, antipsychotic drugs,
antidepressants, and tranquilizers. Patients who exercise tend to do
better than those who do not.

Polio
Poliomyelitis is a viral disease that attacks the
spinal nerves and destroys the cell bodies of
motor neurons so that motor impulses cannot be
carried from the spinal cord outward to the
peripheral nerves or muscles.
Depending on the degree of damage that is done,
the person may be left with diﬃculties in walking
and moving properly, ranging from shrunken and
ineﬀective limbs to full paralysis.
Once the virus that causes polio has infected a person,
there is no treatment that will cure polio. Early diagnosis
and supportive treatments such as bed rest, pain control,
good nutrition, and physical therapy to prevent
deformities from occurring over time can help reduce
the long-term symptoms due to muscle loss.

Paraplegia
and
Quadriplegia
Paraplegia is paralysis of the lower extremities of the body; it results
from an injury to the lower portion of the spinal cord.
Quadriplegia is paralysis of all four extremities and the trunk of the
body; it occurs when the upper portion of the spinal cord is severed.
People who have these conditions usually lose bladder and bowel
control and the muscles below the cut area may lose their tone,
becoming weak and ﬂaccid.
Most spinal cord injuries are caused by accidents, such as car crashes,
falls, and sports injuries are the main causes.
Immediate treatment of spinal cord injuries includes bracing the bony
spine to keep it from moving and further injuring the spinal cord.
Steroids and other medications may be used to lessen damage to
nerves and nearby tissue.

Dementia
Dementia (meaning “deprived of mind”) is a serious loss of cognitive
ability beyond what might be expected from normal aging.
It may be the result of a brain injury, or progressive, resulting in long-
term decline. Although dementia is far more common in the geriatric
population, it may occur at any stage of adulthood.
Memory, attention, language, and problem solving are aﬀected early
in the disorder and often prompt diagnosis.
Some risk factors for dementia, such as age and genetics, cannot be
changed. But researchers continue to explore the impact of other risk
factors on brain health and prevention of dementia.
Treatment of dementia depends on its cause. In the case of most
progressive dementias, including Alzheimer's disease, there is no cure
and no treatment that slows or stops its progression. But there are
drug treatments that may temporarily improve symptoms.

The nervous system

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