ap test 4

endocrine system

communicates through the release of chemical messengers like hormones in the blood

nervous system

commuicates through electrical and chemical to send messages cell to cell

Three steps of the nervous system

1. sense organs get stimulated by changes in both the body and environment then send messages back to the CNS

2. CNS, which is the brain and spinal cord, process the information and responds in the correct manor

3. CNS issues commands to the muscles and glands to carry given response

Two subdivisions of nervous system

CNS (spinal cord and brain) and PNS (everything else)

PNS is made up of two things

Nerves and ganglion. Nerves are a bundles of axons (nerve fibers) wrapped in fibrous ct that carry electrical impulses and ganglion are clusters of neuron cells (somas) that acts as processing centers.

sensory or afferent division of PNS

Somatic: carries signals from muscles or bones or skin to cns

Visceral: carries singals from the visera like heart, lungs, kidney, stomach

Motor efferent division of PNS

Somatic: Carries the CNS signals to muscles or skin aka voluntary

Visceral: Carries CNS signals to the heart or lung or bladder aka involuntary

PNS motor or efferent division of visceral has two divisions

sympathetic (fight or flight) and parasympathetic (rest and digest)

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Excitability

responds to environment changes (stimuli)

Conductivity

Can produce electrical signal that travels down nerve fibers (axon) to other cells

Secretion

Nerve fiber ends called axon terminals can release chemical neurotransmitters that affect other cells

Sensory or Afferent

Detect then report to CNS

Interneurons

90% of all neurons and lies in the CNS. It is the bridge between the motor and sensory and gets the signals then makes the decisions 

Motor or efferent neurons

Sends out the signals to the muscles or glands from CNS

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Parts of Neuron

Soma, Nucleus, cytoplasm, dendrites, axon, axon terminals, and myelin sheath

Multipolar neuron

One axon with many dendrites (mostly in CNS and interneurons)

Bipolar neuron

one axon and one dendrite (Nose, retina, inner ear) = sensory

Unipolar neuron

singe process away from soma (Sensory cells from skin to spinal cord)

Anaxonic neuron

No axon (Retina, brain, adernal gland)

anterograde transport

Down the axon to the terminal away from soma (use Kinesin)

Retrograde transport

up the axon returning to soma (use Dynein)

Fast anterograde transport

Organelles, enzymes, synaptic vesicles, and small molecules

Fast retrograde transport

Recycled materials and hijacked by pathogens like rabies, herpes and tetanus. 

Slow axonal transport

Stop-and-go movement and always anterograde

Glia

binds neurons, makes framework, cover mature neurons, gives precision

Oligodendrocytes

form myelin sheets in CNS that increase the speed

Ependymal cells

line internal cavities like brain and secrete cerebrospinal fluid

micro gila

phagocytes that develop white blood cells and concentrate in damaged areas

Astrocytes

most abundant gila and covers brain. They…

• Create supportive framework

• Form the blood–brain barrier

• Monitor activity;

• Regulate blood flow to match metabolic need

• Convert glucose to lactate

• Secrete nerve growth factors

• Communicate electrically with neurons.

• Regulate chemical composition of tissue fluid

• form hard scar tissue

Two PNS gila

schwann cells, which form myelin sheets and satellite cells, which surround the somas

Myelin sheath (Oligodendrocytes in CNS & Schwann cells in PNS)

Insulation around the axon and increases action potential conduction velocity, produce myelin 

Myelination

Completed in late adolescence and is why dietary fat is important when growing up

Neurilemma

thick outermost coil of myelin sheath (PNS), which contains Schwann cell nucleus

____ Schwann cells (PNS) or oligodendrocytes (CNS) are needed to myelinate one axon

Many

Nodes of ranvier

gaps between the segments of wrapped axon (internodes)

internodes

myelin covered axon

Initial segment

bare section of axon between the axon hillock and the first glial cell

What has large amount of voltage sodium passages that trigger APs

axon hillock, initial segment, trigger zone (most sodium passgae), help initiate the signals for AP

the larger, more surface area, or more myelin of a axon allows it to

conduct signals faster

PNS can be regenerated if there is

soma and some neurilemma

Steps of PNS regeneration

• Axon distal to the injury degenerates

• Macrophages clean up tissue debris

• Neurosoma swells

• nucleus moves off center

• Axon stump sprouts multiple growth processes

• Schwann cells, basal lamina, neurilemma form regeneration tube

• Regeneration tube guides regrowth to original destination

• the neuroma shrink down 

• could take 2 years or more

four major chemical categories of neurotransmitters

Acetylcholine, Amino acids, Monoamines, Neuropeptides

Acetylcholine

Acetyl acid and choline

amino acids

glycine, glutamate, aspartate, and g-aminobutyric acid (GABA)

Monoamines which are synthesized from amino acids

• catecholamines—epinephrine, norepinephrine, dopaminee

Neuropeptides which are chains of 2 to 40 amino acids that get stored in secretory granules

cholecystokinin and substance P

Gases

Nitric oxide (NO) and carbon monoxide

Purines

adenosine and ATP

Excitatory Cholinergic Synapse

Use acetylcholine (ACh), which ACh diffuses and binds to postsynaptic receptors then the receptors are ligand-gated ion channels that open and allow Na⁺ and K⁺ across the membrane leading to depolarization and action potential

Inhibitory GABA-ergic Synapse

Action potential leads to release of GABA, which binds to Cl, then hyperpolarizes and less likely to fire.

Excitatory Adrenergic Synapse

Monoamines and neuropeptide bind to g protein that then activate seconder messager system

Clearance of the neurotransmitter to stop can occur in three ways

Degradation(Enzyme), reuptake(recycled), and diffusion(go away)

Neuromodulators are chemicals that

get secreted by neurons that have long term modulatory effects on groups of neurons such as altering the rate of neurotransmitter synthesis, release, reuptake, or breakdown

Enkephalins and endorphins

neuropeptides or chains of amino acids that act as neuromodulators to inhibit pain signals in the CNS

Chemical synapses

allow for decision making, but they travel slower

Glutamate and aspartate produce

EPSPs (depolarize)

Glycine and GABA produce

IPSPs (hyperpolarize)

Acetylcholine (ACh) and norepinephrin

ACh inhibits heart

Norepinephrine stimulates heart

Summation

is the process of adding up postsynaptic potentials and responding to their net effect

Temporal summation

Occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades

Spatial summation

Occurs when EPSPs from several different synapses add up to threshold at an axon hilloc

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Presynaptic facilitation

when one presynaptic neuron enhances another one

Presynaptic inhibition

when one presynaptic neuron suppresses another one or halts unwanted transmission

Conduction

nerve fibers conduct sensory and motor info up and down the spinal cord

neural integration

spinal neurons receive information from sources and use it for a output

locomotion

This involves central pattern generators, which are groups of neurons that coordinate repetitive sequences of contractions for walking

reflexes

involuntary response to stimuli

Cauda equina

bundle of nerve roots that occupy the vertebral canal from L2 to S5

Meninges

three fibrous membranes that enclose the brain and spinal cord

Dura mater

Forms loose-fitting sleeve (dural sheath) around spinal cord that is thick

Arachnoid mater

arachnoid membrane adhering to dura (middle layer under dura)

Pia mater

transparent membrane that follows contours of spinal cord and fuses dura (deepest layer)

Gray matter

dull in color (no myelin) that contains neuron cell bodies, dendrites, and proximal portions of axons

White matter

white color due to myelin and has axon bundles

Two posterior (dorsal) horns of grey matter

receive sensory nerve fibers

Two anterior (ventral) horns of grey matter

contain cell bodies of somatic motor neurons

Left and right sides connected by

gray commissure

Know this

Poliomyelitis

Destroys motor neurons in brainstem and anterior horn of spinal cord leads to muscle pain, weakness, and loss of some reflexes, then followed by paralysis, muscular atrophy, and respiratory arrest

ALS or Lou Gehrig disease

Destruction of motor neurons and muscular atrophy that leads to sclerosis (scarring) of lateral regions of the spinal cord

• Astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid which accumulates to toxic levels

• Early signs: muscular weakness; difficulty speaking, swallowing, and using hands

• Sensory and intellectual functions remain unaffected

Endoneurium

loose connective tissue external to neurilemma - covers whole axon (nerve fiber)

Perineurium

layers of overlapping squamous cells that wrap fascicles - bundles of nerve fibers

Epineurium

dense irregular connective tissue that wraps each nerve

There are 31 pairs of spinal nerves

• 8 cervical (C1 to C8)

• 12 thoracic (T1 to T12)

• 5 lumbar (L1 to L5)

• 5 sacral (S1 to S5)

• 1 coccygeal (Co1)

Posterior (dorsal) root

Has cells sensory bodies sending input to spinal cord (PNS) located at Dorsal root ganglion

Anterior (ventral) root

motor output out of spinal cord

Reflexes

quick, involuntary, stereotyped(same every time) reactions of glands or muscle to stimulation

proprioceptors

muscle spindles that sense organs to monitor position and movement of body parts (very abundant in hands)

Stretch (myotatic) reflex

when a muscle is stretched, it “fights back” and contracts

Reciprocal inhibition

reflex phenomenon that prevents muscles from working against each other by inhibiting antagonist when agonist is excited

Intersegmental reflex

one in which the input and output occur at different levels (segments) of the spinal cord like Pain in foot causes contraction of abdominal muscles

Paraplegia

paralysis of both lower limbs

Quadriplegia

paralysis of all four limbs

Hemiplegia

paralysis on one side of the body

Paresis

partial paralysis or weakness of the limbs

ionotropic

direct and fast and short acting (ligand gate)

metabotropic

indirect and slow but long lasting (G protein)