THE NERVOUS SYSTEM

Question 1

The nervous system is

Answer 1

responsible for communication between different parts of the body. It’s in charge of voluntary and involuntary actions, and is responsible for cognitive functions in the brain

Question 2

Types of nervous cells:

Answer 2

• Glia

- Neurons

Question 3

Glia

Answer 3

Glia provides support and nutrition. There are few types of this cells, for example:

• Astrocytes – star shaped cells that support and feed neurons. Also create the blood brain barrier. Also connects between neurons.
• Oligodendrocytes – create the myelin sheet in the central nervous system.
• Schwann – do the same in the peripheral nervous system.
• Microglia – immune cells of the central nervous system.

Question 4

Neurons

Answer 4

The functional unit of the system. Comprised of:
* Banditries – branded structures meant for receiving information from other neurons and transmitting it to the axon hillock.
* Soma (body) – contains organelles.
* Myelin - layer that is electronically insulating
* Axon – nerve fiber that is specialized in conducting electrical impulses (carrying messages). It is covered with myelin sheath.
* Presynaptic terminal (synapse) – space between neurons or an effector cells that allows
for message transmission.
* Nodes of Ranvier – small breaks in the myelin sheath that are critical for proper signal conduction.

Question 5

Some facts:

Answer 5

*Blood brain barrier (𝐵𝐵𝐵) –a highly selective semipermeable membrane barrier that separates the
circulating blood from the brain and extracellular fluid in the central nervous system.
* Each neuron is surrounded by 6 to 60 glia cells that protect, feed and insulate it.
* Myelin sheath is a phospholipid layer that is electronically insulating and surrounds neuron’s axons.

Question 6

The Action Potential

Answer 6

Action potential is an electric pulse that is generated close to the soma, travels down the axon and reaches
the synapse. It is often causing the release of neurotransmitters (like acetyl chlorite and norepinephrine).
All action potentials are equal in intensity, and obey the all or nothing principle. The principle states that any sufficient stimulus will generate the same pulse as a stronger stimulus. Whereas, any insufficient stimulus will generate no pulse at all.

Question 7

Resting Potential

Answer 7

All neutrons have a resting potential of −70𝑚𝑣. This is generated by the 𝑁𝑎/𝐾 pump, due to the potential
difference that is created (3 ions of 𝑁𝑎 go out while 2 ions of 𝐾 go in). This making the inside of the cell more negative.
In addition, because the sodium concentration is high outside of the cells and low inside of the it – and the
opposite regarding potassium – 𝑁𝑎 is drawn in, while potassium is drawn out. The pump creates and
electrochemical gradient but the moving of electrons through it.

Question 8

Powers exerted on the sodium and potassium ions are:

Answer 8

• Electrical force – due to the inside of the cell being more negative, positive ions of these elements
  will be attracted to it.
• Diffusion – potassium and sodium will want to go where there is an abundance of such elements
  (potassium would want to go out, while sodium would want to go in)

Question 9

Action Potential Initiation:

Answer 9

• Depolarization – the membrane becomes more positive.
• Hyperpolarization – the membrane becomes more negative.
• Threshold – −55𝑚𝑣. When the membrane reaches this potential value, an action potential is fired.

Question 10

Process of the Action Potential initiation

Answer 10

1. The process begins by the neuron receiving sufficient stimulus.
2. Sodium channels open, allowing to sodium to flow into the cell (making the membrane more
   positive) .
3. After that, potassium channels open, allowing potassium to go out of the cell (making the cell more
   negative) . The sodium channels are closing.
4. Finally, the potassium channels close ending the action potential.

Question 11

Action Potential Probation and Termination

Answer 11

At the end of the action potential, the channels are blocked. This is how the potential is terminated. This
allows conduction in one direction only, because even after a segment of an axon was hyper polarizes, it
cannot have depolarized again. (due to blocked channels). This is called the refractory period.

Question 12

The Synapse

Answer 12

The space between two neurons where information is passes is called the synapse. Neurons sending
information are presynaptic terminal, while neurons receiving information are postsynaptic terminal
(effector cells).
When an action potential reaches the end of the axon and depolarized terminal membrane, neurotransmitters are release into the synapse. These neurotransmitters bind to receptors on the postsynaptic membrane.
This process allows the message to be passed from on neurons to the next. In can be an inhibitory or excitatory.

Question 13

Nervous System Divisions

Answer 13

The nervous system is a complex network of nerves and cell that transmits signals between different parts
of the body, it is responsible for the higher level thinking and mental function.

Question 14

The nervous system is divided into few subsystems.

Answer 14

1. The Central Nervous System (𝐶𝑁𝑆) – brain and spinal cord. It is the body command and control
   system.
2. The Peripheral Nervous System (𝑃𝑁𝑆) – includes all nerve fibers located outside the 𝐶𝑁𝑆. It carries
   out instruction from the 𝐶𝑁𝑆 to various parts of the body.
   * The Somatic nervous system (𝑆𝑁𝑆) – associated with the voluntary control of body movements via skeletal muscles.
   * The Autonomic Nervous System (𝐴𝑁𝑆) – control system that acts largely unconsciously
   and regulates bodily functions
   • The Sympatric Nervous System (𝑆𝑁𝑆) – primary
     process is to stimulate the body’s
     fight-or-flight response.
   • The Para-sympatric Nervous System (𝑃𝑆𝑁𝑆) –
     functions to regulate the body’s
     unconscious actions.

Question 15

The Peripheral Nervous System (𝑷𝑵𝑺)

Answer 15

This system consists of nerves and ganglia cells located outside of the 𝐶𝑁𝑆. Nerves carry signal that allow the brain the spinal cord to communicate with the body’s organs and tissues.
The 𝑃𝑁𝑆 is not protected as the 𝐶𝑁𝑆 , making it more vulnerable to toxins and mechanical injuries. The
𝑃𝑁𝑆 is divided into:
* The Somatic Nervous System (𝑆𝑁𝑆)
* The Autonomic Nervous System (𝐴𝑁𝑆)

Both parts have sensory and moto aspects:
- Sensory – consists of afferent nerves that carry information from receptors or sense organ to the
𝐶𝑁𝑆.
- Motor – consists of efferent nerves that carry information away from the 𝐶𝑁𝑆 to organs

Question 16

The Somatic Nervous System (𝑆𝑁𝑆)

Answer 16

Associated with voluntary control of muscles and body movement(efferent). Sensory fibers carrying information to the 𝐶𝑁𝑆 (afferent).

Question 17

Process of The Somatic Nervous System (𝑆𝑁𝑆)

Answer 17

1. Stimulus detected by receptors (e.g. hand touches something hot)
2. Impulse (action potential) are propagated in sensory afferent neurons that pass the information
   on to the 𝐶𝑁𝑆.
3. 𝐶𝑁𝑆 neurons plan appropriate respond (e.g. movement of the hand).
4. The response is transmitted by motor efferent neurons which conduct impulses to muscle and
   other organs.

** Reflex is when somatic neurons are connected via an inter neuron in the spinal cord. This is still a part
of the somatic system even though its involuntary.
** Nociceptors - receptor (free nerve ending) at the end of a sensory neuron’s axon that responds to
damaging or potentially damaging stimuli, heat and respond to chemical secreted by cells of the
immune system.

Question 18

The Autonomic Nervous System (𝐴𝑁𝑆)

Answer 18

Associated with involuntary control of organs, like smooth muscle in the 𝐺𝐼𝑇, blood vesicles, the bronchi,
sweat glands, pupils and so on…
Divided into two:
* Sympathetic – fight of flight – response to stress, danger, excitement, exercise, adrenaline and embarrassment. Causes to increased respiration, heart rate and the release of adrenaline and other stress hormones. Also decrease digestion.
* Para-sympathetic – rest and digest – response when the body is relaxed, resting or feeding. Causes to a decrease in respiration, heart rate and an increases in digestion

Question 19

Process of the The Autonomic Nervous System (𝐴𝑁𝑆)

Answer 19

1. When receptors detect changes in the viscera, impulses are conducted through autonomic sensory
   afferent neurons to the 𝐶𝑁𝑆.
2. Neurons in the 𝐶𝑁𝑆 generate response which are conducted as impulses by autonomic motor
   efferent neurons to effectors such as smoot muscles and the heart.

Question 20

The Central Nervous System (𝑪𝑵𝑺)

Answer 20

Comprised of the brain and the spinal cord. Both are submerged in a clear, liquid fluid called the
cerebrospinal fluid (𝐶𝑆𝐹). The fluid provides protection and nutrition alongside oxygen. It also removes
waste, and it flows through the ventricles of the brain and through a canal in the middle of the spinal cord
called the central canal.

Question 21

both the brain and the spiral cord are wrapped

Answer 21

Are wrapped by three layers of membrane called meninges:

• Inner – pia
• Middle – arachnid
• Outer – dura

Both also contain white and grey matter:
- Grey matter – made out of the bodies of the neuron cells, dendrites and un-myelinated axons that
receives and store electrical impulses.
* Dorsal horn – pathway that receives sensory from
the environment
* Ventral horn – pathway that excites motor
neurons.
- White Matter – made out of myelinated axons that connect to different parts of the grey matter
by carrying electrical impulses.

Question 22

The position in the brain and the spina

Answer 22

Note that the position in the brain and the spinal cord are opposite – in the brain, the grey matter is in the
outer part of the brain, and the white matter is in the inner part. In the spinal cord, the white is in the outer
part and the grey matter is in the inner side

Question 23

The Brain

Answer 23

The brain is the organ where information is processed and responses originate. It is responsible for higher
mental functions such as consciousness, memory, planning and voluntary actions. It also controls the
maintenance of involuntary actions such as respiration, heart rate, blood pressure and digestion.
The brain is composed of 4 parts:
- Cerebrum
- Cerebellum
- Brainstem
- Diencephalon

Question 24

Cerebrum

Answer 24

Also called the big brain. It is divided into two hemispheres. It is responsible for higher functions (memory, movement and problem solving) and can be divided into 4 lobes accordingly

Question 25

Diencephalon

Answer 25

Responsible for sending motor information to the spinal cord and for hormone production. Also consists the thalamus and the hypothalamus.

• Thalamus – relays sensory and motor signals to the cortex.
• Hypothalamus – regulates involuntary function such as water appetite and temperature (hormones)

Question 26

Cerebellum

Answer 26

Important for balance, muscle memory and coordination.

Question 27

Brainstem

Answer 27

Most posterior part of the brain responsible for transferring information to the spinal
cord as well as the control of arousal heart rate and many reflexes like breathing. It is divided into
three parts:
* Midbrain – superior part that is responsible for integration of optics and auditory
information.
* Pons – middle part that is responsible for arousal and sleep for relaying information
between the cerebrum and the cerebellum. Also accounts for autonomic functions.
* Medulla oblongata – inferior part that is continuation of the spinal cord, and it controls
the body’s blood pressure, heart rate and breathing

Question 28

The Four Lopes

Answer 28

The brain is divided into 4 lobes:
1. Frontal lobe – located at the front of the brain, is the largest of the four major lobes. Accounts for problems solving, social interaction, movement and personality developments.
2. Parietal lobe – integrates sensory information among various
3. Occipital lobe – accounts visual processing center, and containing most of the anatomical region of the visual cortex
4. Temporal lobe – mainly revolves around hearing and selective listening. It is also key to being able
to comprehend, or understand meaningful speech.

Question 29

Additional facts about the brain

Answer 29

*The cranial nerves emerge directly from the brain.
* Taste buds and olfactory receptors are type chemoreceptors.
* Pacinian receptors chemoreceptors that are sensitive to radicals.
* Receptors involved in reception of information concerning the body’s position and movement are
called proprioceptive receptors.

Question 30

The Spinal Cord

Answer 30

The spinal cord is a long tube like structure of nervous tissues that extends from the brain to the lumber
region. It is composed of a series of 31 spinal segments with a pair of spinal nerves extending from each
segment.
Both motor and sensory nerves are located in the spinal cord. Functions of the spinal cord is primarily in
the transmission of neural signals between the brain and the body. It can also generate independent control of reflexes.
The spinal cord is composed of:
* Central canal.
* Ventral canal – motor descending pathway neurons.
* Dorsal canal – sensory ascending pathway neurons.