THE NERVOUS SYSTEM Flashcards
The nervous system is
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
Types of nervous cells:
- Glia
- Neurons
Glia
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.
Neurons
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.
Some facts:
*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.
The Action Potential
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.
Resting Potential
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.
Powers exerted on the sodium and potassium ions are:
- 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)
Action Potential Initiation:
- 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.
Process of the Action Potential initiation
- The process begins by the neuron receiving sufficient stimulus.
- Sodium channels open, allowing to sodium to flow into the cell (making the membrane more
positive) . - After that, potassium channels open, allowing potassium to go out of the cell (making the cell more
negative) . The sodium channels are closing. - Finally, the potassium channels close ending the action potential.
Action Potential Probation and Termination
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.
The Synapse
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.
Nervous System Divisions
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.
The nervous system is divided into few subsystems.
- The Central Nervous System (𝐶𝑁𝑆) – brain and spinal cord. It is the body command and control
system. - 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.
- The Sympatric Nervous System (𝑆𝑁𝑆) – primary
The Peripheral Nervous System (𝑷𝑵𝑺)
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
The Somatic Nervous System (𝑆𝑁𝑆)
Associated with voluntary control of muscles and body movement(efferent). Sensory fibers carrying information to the 𝐶𝑁𝑆 (afferent).
Process of The Somatic Nervous System (𝑆𝑁𝑆)
- Stimulus detected by receptors (e.g. hand touches something hot)
- Impulse (action potential) are propagated in sensory afferent neurons that pass the information
on to the 𝐶𝑁𝑆. - 𝐶𝑁𝑆 neurons plan appropriate respond (e.g. movement of the hand).
- 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.
The Autonomic Nervous System (𝐴𝑁𝑆)
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
Process of the The Autonomic Nervous System (𝐴𝑁𝑆)
- When receptors detect changes in the viscera, impulses are conducted through autonomic sensory
afferent neurons to the 𝐶𝑁𝑆. - 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.
The Central Nervous System (𝑪𝑵𝑺)
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.
both the brain and the spiral cord are wrapped
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.
The position in the brain and the spina
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
The Brain
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
Cerebrum
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
