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nervous system summarized

The Nervous System is the:
•    Master controller and communicating system in the body
•    Every thought, action and emotion reflects its activity.
•    It signals the body through electrical impulses that communicate with the body cells. 
•    Its signaling and responding abilities are highly specific and rapid.
The Nervous System is capable of:
1.    Sensory input – gathering information
•    To monitor changes occurring inside and outside the body
•    Changes = are called stimuli
2.    Integration
•    N.S. is able to integrate the sensory information, process, interpret and decide if action is needed
3.    Motor output
•    A response to the integrated stimuli
•    The response activates muscles or glands

The NS does not work alone in maintaining homeostasis. It enlists the Endocrine system for regulating and maintain body functions.
•     The Neurons (nervous cells) must perform 4 specialized functions
1.    Receive information from the internal or external environment
2.    Integrate the information received and produce an appropriate output signal (or response)
3.    Conduct the signal to its terminal
4.    Transmit the signal to another cell (effector)

The Neurons cells have:
•    Dendrites – that receive information
•    Cell body – that integrates incoming information
•    Axon – conducts electrical impulses (signals)                                                                                    to the synaptic terminals
•    Synapsis (synaptic terminals) – the site that receives  signals and communicates with other cells, tissues,   or organs.

The Neurons are nervous cells that transmit messages.
The structure of the neuron has:
•     A Cell body – with a nucleus, a large nucleolus
•     The Dendrites – conduct impulses toward the      cell body (afferent), away from the receptors
•     The Axons – conduct impulses away from the cell   body (efferent) toward the muscle or endocrine                                                                            

•    Nervous tissue is comprise of 2 types of cells
–    Neurons = nerve cells that transmit impulses
–    Neuroglia = supporting cells. They act as insulators, adhesive, protectors and nourishers.
Nervous Tissue Supporting Neuroglias include:
1.    Astrocytes
•     There are an abundant of these star-shaped cells
•     They brace themselves onto neurons
•     They control the chemical environment of the brain
2.    Microglia
•     These are Spider-like phagocytes that dispose of debris.
3.    Oligodendrocytes
•    Produce myelin sheath around nerve fibers in the central                                                                        nervous system
4.    Ependymal cell
- Epithelial-type cells that line the nervous system (brain                                                                     and spinal cord. They form the Meninges – Dura Mater,                                                   Arachnoid Mater and Pia Mater.
5.   Satellite cells
•    Protect neuron cell bodies
6.    Schwann cells
•    Form myelin sheath in the peripheral nervous system

How is the Human Nervous System Organized?
The Peripheral Nervous System (PNS) has:
•    Sensory (afferent) division - carrying toward a center  Nerve fibers that carry information to the central       nervousystem
•    Somatic sensory - (skin, skeletal muscle)
•    Visceral sensory - (visceral organs)
-- AND --
•    Motor (efferent) division - Nerve fibers that carry impulses away from the central nervous system (effect)  and activate muscles or glands to bring about a response.

                                         
The PNS:
The Motor (efferent) has 2 division
1.    Somatic nervous system is voluntary (skeletal muscles)
2.    Autonomic nervous system = involuntary (smooth and cardiac muscles, glands)
Sensory (afferent) neurons:
  Carry impulses from the sensory receptors 
  Cutaneous (skin) sense organs    Proprioceptors – detect stretch or tension
Sensory Motor (efferent) neurons    Carry impulses from the central nervous systemnterneurons association neurons)
•    Are found in neural pathways in the central nervous system
•    They connect sensory and motor neurons
•    Are capable of Irritability – ability to respond to stimuli
•    Are capable of Conductivity – ability to transmit an impulse
•    Are Excitatory & inhibitory potentials

•    The plasma membrane at rest is polarized
–    Fewer positive ions are inside the cell than outside the cell
Starting a Nerve Impulse
•    Depolarization – a stimulus depolarizes the neuron’s membrane
•    A depolarized membrane allows sodium (Na+) to flow inside the membrane
•    The exchange of ions initiates an action potential in the neuron


The Reflex Arc
•    Reflex – is rapid, predictable, and involuntary responses to stimuli
•    Reflex arc – directs the route from a sensory neuron, to an interneuron, to an effector

Types of Reflexes and Regulation
•    Autonomic reflexes – involves Smooth muscle regulation of the Heart and blood pressure, vessels, Regulation of endocrine glands and the Digestive system regulation. It also involves Somatic reflexes which Activates the skeletal muscles and Voluntary motions.

How do Sensory Receptors Work?
•    Receptors are cells or clusters of cells that transduce the energy of a specific signal into an electrical signal
•    Receptor potential
EXAMPLE:   the ear captures, transmits and converts sound into electrical signals
a.    The Outer ear captures sound waves
b.    Middle ear converts vibrations from sound waves into electrical signals (cochlea)
c.    Cochlea is a fluid-filled chamber with 2 membranes (basilar & tectorial) and sensory receptors called hair cells
d.    The basilar membrane vibrates in response to sound waves
e.    The vibrations causes the hair cells to bend, which generates receptor potentials
f.    Larger vibrations bend the hair cells even more, which is perceived as louder sound.
•    Loud, prolonged sounds damage hair cells
g.    Different parts of the basilar membrane vibrate at different frequencies of sound waves
h.    This allows for perception of different pitches

Visual Sensory
•    The eye collects, focuses and transduces light waves
•    Adjustable lenses allows for distant and nearby focusing.
–    Eyeball long – near sightedness
–    Eyeball short – farsightedness
•    Light strikes the retina’s photoreceptors
•    Rods & cones transduce light signals
•    Electrical signals are transmitted and processed
•    Axons of ganglion cells carry signals to the brain

Rods & Cones
•    Rods – dim vision  (periphery)
•    Cones – color vision  (fovea)

Taste that Smell – the Olfactory receptors
•    Responsible for sense of smell
•    Located at the roof nasal cavity
Olfaction contributes to taste perception.  Taste receptors are located in clusters on the tongue

Other Special Senses
•    Pain receptors – with Specialized chemical sense
•    Echolocation - a type of sonar receptor. Some animals have specialized receptors for navigating and detecting prey. Some birds and fishes use the earth’s magnetic field to navigate long-distance migration
•    Electolocation - Some fish use electrolocation for hunting and commuinicating

THE  BRAIN

Regions of the Brain
o    Cerebral hemispheres
o    Diencephalon
o    Brain stem
o    Cerebellum
Cerebral Hemispheres (Cerebrum)
The surface is made of ridges (gyri) and grooves (sulci)

Lobes of the Cerebrum
- Fissures (deep grooves) divide the cerebrum into lobes
- Surface lobes of the cerebrum
•    Frontal lobe
•    Parietal lobe
•    Occipital lobe
•    Temporal lobe
Lobes of the Cerebrum have Specialized Areas of the Cerebrum
-    Somatic sensory area – receives impulses from the body’s sensory receptors
-    Primary motor area – sends impulses to skeletal muscles
-    Broca’s area – involved in our ability to speak

The Specialized Areas of the Cerebrum have cerebral areas that are involved in special senses
•    Gustatory area (taste)
•    Visual area
•    Auditory area
•    Olfactory area

The brain has Interpretation areas of the cerebrum for
•    Speech/language region
•    Language comprehension region
•    General interpretation area

The DIENCEPHALON
The Diencephalon Sits on top of the brain stem; it is enclosed by the cerebral heispheres and made of three parts:
•    Thalamus
•    Hypothalamus
•    Epithalamus

Thalamus
-    Is the relay station for sensory impulses
-    Transfers impulses to the correct part of the cortex for localization and interpretation
Hypothalamus
-     Under the thalamus
-     Helps regulate body temperature
-     Controls water balance
-     Regulates metabolism
-     An important part of the limbic system (emotions)
-     The pituitary gland is attached to the hypothalamus
Epithalamus
-     Houses the pineal body (an endocrine gland)
-     Includes the choroid plexus – which forms cerebrospinal fluid

The BRAIN  STEM
•    Attaches to the spinal cord. Parts of the brain stem include:
•     The Midbrain, Pons and Medulla oblongata

-    The Midbrain – is the Reflex centers for vision and hearing
-    The Pons – is the center part of the brain stem which is mostly composed of fiber tracts
-    Includes nuclei involved in the control of breathing
-     Medulla oblongata - lowest part of the brain stem
-     Merges into the spinal cord
-     Control center for: Respirations, H.R., B/P swallowing and vomiting

The SPINAL NERVES

-    There are 31 pair of spinal nerves at the level of each vertebrae
-    Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord



This post first appeared on Nervous System, please read the originial post: here

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