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Anatomy & Physiology Nervous System


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Coordination Control is done in two forms
1) electrical

2) chemical
Electrical Coordination control
Ensures rapid transmisssion of info. (The body's nervous system)
Chemical Coordination Control
By the use of hormones. It is important to detect changes int he body's environment and respond to them (Hormones are endocrine system)
What is a Neuron
Specialized cells of the nervous systems that detect changes
3 main types of neurons
Afferent Neurons (sensory) -


Efferent Neurons (motor)
Afferent Neurons-
receptors detects environemntal changes (stimuli) They detect and transmit the info about the changes to the CNS.

Also called SENSORY Neurons
(90% of neurons are these)
Neurons of the CNS, that are located in the spinal cord. They transmit info and and down the spinal cord
Efferent Neurons
Also called motor neaurons. These carry the body's resposes to a stimuli in two ways. It can come from the brain or spinal cord. It prmiarily carries a response back to muscles.
What are the 3 Physiology of a Neuron and what is it?
Excitablity --> Response to a stimuli

Conductivity --> Produces and electrical signal

Secretion --> Secretes chemical neurotransmitters across the synapses. The most common neurotransmitter is Ach (Acetylcholide)
WHat makes one comlete system in the nervous system?
CNS (Central Nervous System) the brain and spinal cord

PNS (Peripheral Nervous System) - Everthing Else
Neuroglia Cells
Also known as glial cells. There are 50 trillion in the body and the are the supportive cells of the neuron. Glial cells or neuroglia cells support, guide the growth and connection of the neurons.
6 main types of glial or neuroglia cells

6 cells are _______
sosame... S's are the so,same
Schwann cells
Satelitte Cells
Satellite Cells
Located in the ganglia where they are surrounded by cells bodies in the PNS. The function is unknown
These form the myelin sheaths in the CNS
Schwann Cells
Winds around the fibers to make the myelin sheaths in the PNS. Regeneration of damaged PNS nerve cells
Control blood to brain substance and form the supportive structure of the CNS
(very small) Macrophages that clean up the dead nervous tissue. There is a cluster of these at sites of injury
Looks very similiar to cuboidal epithilium, they line the cavity of the brain and spinal cord. They also produce spinal fluid
Myelin (myelination) in the PNS
(The myelin sheath provides insulation between adjacent nerve fibers, to prevent crossovers, these are made by the Scwann Cells)

-Ea. Schwann cell wraps around the axon to form a multi-layer insulation with the last layer being loose (the nucleus, cytoplasm, and organelles of the Schwann cell are in this layer)
- spaces occur between ea. Scwann cell (Nodes of Ranvier)
- The Schwann cell interrupts the continues conduction of nerve impulses along the axon and in response the nerve impulse jumps across ea. Schwann cell from one node to the next
Myelin: Myelination in the CNS
The axons are insulated by oligodendrocytes; oligodendrocytes is what makes the myelin sheaths

-The myelin sheath is formed when a process extended by the oligodendrocytes wrap around the axon
-Many axons can be myelinated by multiple processes from a single oligodendrocyte

Its cells body doesn't wrap around any axons
Myelin in general
Occurs from the 14th week of fetal development to late adolescents

Triglycerides are CRITICAL in the laying down of the myelin sheaths and is CRITICAL for the proper functioning of the nervous system
Nerve Growth and Regeneration in general
Nerves develop from stem cells in embryonic development.

The response to nerve re-growth depends on how severe the injury is and where the site of injury is

CNS CANNOT be regenerated, but does suffer less damage than the PNS since it's protected by bone. The nerves in the PNS can regenerate as long as the soma is intact.
Nerve regrowth process
-Within the first few weeks after injury the distal end of the axon and its myelin sheath degenerate, macrophages come in and remove the debris
- a regeneration tube is formed by the neurilemma and endoneurium
- the axon stump puts out several sprouts trying to find its way to the regeneration tube
-Once found the other sprouts are reabsorbed and the regeneration tube helps the growing axon back to its original destination until the neuron reestablishes a connection with the cells that originally innervated.

Skeletal muscles atrophy when their nerve fiber is damaged but regenerate after the connection is reestablished
Membrane potential
It all starts here as the entire nervous system couldn't function with it!
The opposite electrical charges have the potential for doing work when they come together. Opposties attrackt! Ion have charges (+ or -)

Resting Membrane Potential, Graded (local) potential, and action potential...
Voltage-gated Sodium Channels
Resting Membrane Potential
The resting potential is the un-stimulated, polarized state of a neuron (-40 to -75 millivolts)

Na, K-ATPase Pumps:
These help maintain the appropriate concentration of ions and work agasint the concentration gradient so the oins in and out of the cell remain different.

Eg. INSIDE CELL(Na+low, K+High, Cl-low)
OUTSIDE CELL (Na+high, K+low, Cl-high)
Graded Potential
Localized, This is a change in the resting potential of the plasma membranse in response to a stimulus such as light, heat, mechanical pressure, and chemical (neurotrasmitters). Graded potentials occur int he cells bodies and dendrites.

It occurs when the stimulus casue NA+ or K+ gated channel to open.

If Na+ channels open then +Na ions enter and the membrane depolarizes (+)
If the stimulus opens K+ channel then K+ ions exit the membrane and it hyperpolarizes (-)
Voltage gate Sodium Channels
Channels on the membrane that opens and NA ions open trying to reach equilibrium, the membrane depolarizes (+) when the action potential ends. It then restores resting condition and is re-polarized
Action Potential
Capable of traveling long distances

If a depolarizing graded potential is sufficiently large Na+ channels in the trigger zone open. Na+ on the inside of the membrane depolarize and if the stimulus is above the threshold level, additional Na+ channels open increasing the flow, and this causes action potential or complete depolarization. This stimulates neighboring Na gates farther down the axon to open. This is an all or nothing event. The the stimulus fails to produce depolarization that exceeds the threshold then there is no action potential results.
When does depolarization occur?
What is the function of a synapse, what are the 2 types
Function between two neurons and most occur in the CNS

Electrical- gap junctions of adjoining cells allows them to communicate. Most are seen in the cardiac and smooth muscle so they can have uniform contraction

Chemical- Neurotransmitters that are released across the synaptic cleft on the nerve to another neuron to receptors on the plasma membrane on yet another neuron. The chemical has to be received by the receptor on another end, most of these are 1 directional and Ach is the main neurotransmitter
What can affect the Synapses?
Diseases such as tetanus, by locking it all up
Chemical messengers that are usually very fast, there have been over 100 discovered.

ATP and Adanine can also be used as neurotransmitters.

Some of the most important are Ach, monoamines (biolenic amines), amino acids, and neuropeptides

The major one, you can't function without it.

Alzheimer's has been linked to a decrease of Ach in the brain

In the PNS and brain
monoamines (Biolenic Acid)
Dopamine, Neremphiphen, Seratonin, and Histamine

They are catacole ammines and seem to influence states of concienceness, motivation, movement, blood pressure, and regulate hormones
Amino Acids
Most prevalent in the CNS. They affect the CNS neurons. They finction in learning, memory, nerve development, and the may play a role in epilepsy, Parkinson's Disease, Alzheimer's, and stroke nerve damage.
Two or more amino acids that have been linked together by peptide bonds. They act as a neuropeptide transmitter. They regulate pain, give the feeling of a second wind, and drinking, eating, moods, and emotions are all influenced by neuropeptides
Gray Matter
contain the un-myelinated portions of neurons. It is composed of interneurons, cell bodies, and dendrites of the efferent (motor) neurons

The afferent fibers enter the spinal cord at the dorsal root and the efferent exit fromthe ventral root.
White matter
Contains the myelinated portions of neurons. The white color is the color from the myelin sheaths. It surrounds the grey matter and consists of groups of myelinated axons.

The afferent fibers enter the spinal cord at the dorsal root and the efferent exit fromthe ventral root.
Spinal Nerves... How many pairs and where are they
31 pairs.

8 cervical nerves - pherenic nerve, it serves the diapragm to allow breathing. Serves the head, shoulders, and arms
12 thorasic nerves - brachial nerve. it serves the chest and abdominal walls
5 lumbar nerves - anterior lumbar plexis is the abdomen, thigh, leg, and genitals. Serves the hips and legs
5 sacral nerves- sacral is the buttocks, tibia and sole of foot, and also the genitals. It serves the lower digestive tract also.
1 coccygeal nerve - it innervates the skin....tailbone
Generalized sensory pathway
Branchs in cervical nerves and coccygeal nerves are called nerve plexus's, they have a lot of branching to serve many areas and hurt like hell when you land on them
Sensory system pathway
Ascending and descending

Environmental change --> stimulus --> receptor --> graded (local) potential or action potential --> interneurons of the CNS (265 mph, 90% of the body's neuron's) --> brain --> sensation --> perception --> decision --> response
--> interneurons (thought sent through descending pathways) --> efferent (motor) neurons --> muscles --> action response........
Specialized endings of sensory (afferent) neurons or a specialzed cell that effects the ends of the afferent neurons

These do the actual detection of body changes

The energy potential of neurons first produces a local (graded) potential. So there is always local potential only in cases of overload basically do we see an action potential
Various forms of energy that act upon and activate a sensory receptor
Sensory Unit
Single afferent neuron and its receptor endings

The body can have hundreds of thousands of receptors. There are many types throughout the body and each is specific to the type of energy in the stimulus but mostly all of them can be activated by several forms of energy
Receptive fields
The portion of the body that when stimulated results in activity in a particular afferent neuron. Fields are tiny in the face, hands, and genitals...making them very sinsative. Field are large in the back and legs and less sensative
Somatic Receptors
Body recpetors that detect sensations such as touch, pressure, posture, movement, strecth in the body's msucles and joints, temp. changes in the body, and the sensation of pain.
Motor Neuron Pool
The motor neuron pool is all the neurons that control a given muscle.
Levels of organization of the neural systems and what they are
highest level- incluses many regions of the brain. This is where the sensation of intention is constructed

middle level- in the cerbral cortex, cerebellum of the brain, and the sub-cortical nuclei in the brainstem. This is primarily concerned with posture and movement

Local level - found in the brainstem and spinal cord. The recieve input from the receptors and send stimuli back out by the motor (efferent) meurons to the muscles.

All actions have voluntary and involuntary components. Most input to motor neurons is from motor interneurons, so it doesnt take conscience control
Gamma motor neuron and alpha motor neurons
gamma motor neurons are the ones that innerveate the intrafusal fibers

Alpha motor neurons are the ones the control the surrounding extrafusal fibers and they are larger

Both are co-ativated in movement to provide continues info about what the muscle is doing, it also helps the brain plan for future movement. It is a continues smooth operation
Ipsilateral response
Muscles that are activated on the same side of the body as the receptors (hand on hot stove)
Contralateral response
Muscle that are activates on the opposite side of the body that the receptors ( stepping on broken glass, body axis leans opposite way)
Golgi tendon Organ
Locates in the muscles, is a structure that monitors muscle tension. It is important in certain responses and reflexes to environemtnal conditions.
Withdrawel reflexes
ipsilateral and contralateral responses
Muscle Spindle Stretch Receptors Basics
Monitors the body's senses that the muscle length and speed is being changed. As your muscle moves it sends out signals that the muscle is stretching or contracting, it lets the nervous system know that the muscles are working and how. These are inter-graded into the middle level, the cerebral cortex, cerebellum of the brain and in the sub-cortical nuclei in the brains-stem
Muscle Spindle Stretch receptor Function
as the muscle stretches the nerve ending in the muscle spindle fibers fire and action potential are generated

Extra fusal fibers on the outside and intrafusal fibers on the inside of the muscle sheath. The extra give an indication of the entire muscle mass, while the intra give an indication of each muscle bundle.

They act individually, collectively, or grossly.

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