COMPLETE Nervous System

What are the 2 major NT of the autonomic/visceral NS?

Acetylcholine and NE

What days/weeks do you see the 3-part brain and 5-part brain intermediates?

3-part: D26 5-part: W5

What is the synapse?

A junction where the axon bulb of one neuron interacts with another neuron or an effector organ like a muscle or gland - Action potentials (nerve impulses) are transmitted from presynaptic neuron to postsynaptic neuron (or other postsynaptic cell) across a synapse

synaptic delay

- A synaptic delay of 0.2-0.5 msec occurs between: >> Arrival of action potential at synaptic terminal >> And effect on postsynaptic membrane - Fewer synapses mean faster response - Reflexes may involve only one synapse

Sympathetic Stimulation and the Release of NE and E

- Adrenergic membrane receptors 1. Alpha adrenergic receptors (NE more potent) - smooth mm contraction 2. Beta adrenergic receptors - smooth mm relaxation, heart mm contraction Activates enzymes on inside of cell membrane via G protein coupled receptors

Axon Diameter and Propagation Speed

- Axon diameter affects action potential speed - The larger the diameter, the lower the resistance = faster a propagation rate will occur

In addition to the sympathetic release of NE and E --> Sympathetic Stimulation and the Release of ACh and NO

- Cholinergic (ACh) sympathetic terminals • Innervate sweat glands of skin and blood vessels of skeletal mm and brain • Stimulate sweat gland secretion and dilate blood vessels - Nitroxidergic synapses • Release nitric oxide (NO) as NT • Neurons innervate smooth mm in walls of blood vessels in skeletal mm and the brain • Produce vasodilation and increased blood flow

Neuron characteristics

- Conducting potential - Longevity - Amitotic - High metabolic rate

How do NT's and neuromodulators work?

- Direct effects on membrane channels • Ex: ACh, glycine, aspartate - Indirect effects via G proteins • Ex: E, NE, dopamine, histamine, GABA - Indirect effects via intracellular enzymes on target tissues • Ex: lipid-soluble gases (NO, CO)

Sympathetic Stimulation and the Release of NE and E on alpha adrenergic receptors (Alpha-2)

- Lowers cAMP levels in cytoplasm - Has inhibitory effect on the cell (negative feedback) - Helps coordinate sympathetic and PS activities

Axons

- Most neurons have one - Long with uniform diameter - Carry action potentials away from soma, originates at axon hillock - Ends may branch into collaterals - Terminate at axon terminals (or bulb) full of synaptic vesicles

Type A fibers

- Myelinated - Large diameter - High speed (140 m/sec) - Carry rapid information to/from CNS - For example, position, balance, touch, and motor impulses

Type B fibers

- Myelinated - Medium diameter - Medium speed (18 m/sec) - Carry intermediate signals - For example, sensory information, peripheral effectors

synaptic fatigue

- Occurs when NT cannot recycle fast enough to meet demands of intense stimuli - Synapse inactive until ACh is replenished

1. Chemically gated channels

- Open in presence of specific chemicals (e.g., ACh) at a binding site - Found on neuron cell body and dendrites

Neuromodulators

- Other chemicals released by synaptic terminals (not NT) - Similar in function to NT's - Characteristics of neuromodulators > Effects are long term, slow to appear >> Can modulate or enhance NT effects > Responses involve multiple steps, intermediary compounds > Affect presynaptic membrane, postsynaptic membrane, or both > Released alone or with a neurotransmitter

both divisions of the visceral/autonomic NS (sympathetic and parasympathetic) consist of?

- Preganglionic neuron • Cell body in CNS • Axons travel to autonomic ganglia - Postganglionic neuron (also called 'ganglionic' neuron) • Cell body in autonomic ganglia • Axons travel to effector organ

W5: 5-part brain

- Prosencephalon 1. Telencephalon 2. Diencephalon - 3. Mesencephalon - Rhombencephalon 4. Metencephalon 5. Myelencephalon - SC - Flexures: >> mesencephalic (cranial) >> Cervical (caudal) >> Pontine

2. Voltage-gated channels

- Respond to changes in transmembrane potential - Have activation gates (open) and inactivation gates (close) - Characteristic of excitable membrane

3. Mechanically gated channels

- Respond to membrane distortion - Found in sensory receptors (touch, pressure, vibration)

4 steps of an action potential induction and propagation

- Step 1: Depolarization to threshold - Step 2: Activation of voltage gated Na+ channels - Rapid depolarization - Na+ ions rush into cytoplasm - Inner membrane changes from negative to positive - Step 3: Inactivation of Na+ channels and activation of voltage gated K+ channels - At +30 mV -Inactivation gates close (Na+ channel inactivation) - K+ channels open -Repolarization begins - Step 4: Return to normal permeability - K+ channels begin to close >> When membrane reaches normal resting potential (-70 mV) - K+ channels finish closing >> Membrane is hyperpolarized to -90 mV >> Transmembrane potential returns to resting level >> Action potential is over

action potential: refractory period

- The time period from beginning of action potential to return to resting state >> During which membrane will not respond normally to additional stimuli

Type C fibers

- Unmyelinated - Small diameter - Slow speed (1 m/sec) - Carry slower information - For example, involuntary muscle, gland controls,

How do the indirect effects of NT's and neuromodulators on G proteins work?

- Work through second messengers - Enzyme complex that binds GTP - Link between neurotransmitter (first messenger) and second messenger - Activate enzyme adenylate cyclase >> Which produces second messenger cyclic-AMP (cAMP)

the brain can be divided into 2 main parts which are?

- brain stem >> similar in organization to SC >> made up of myencephalon, pons (derivative of metencephalon) and mesencephalon - higher centers >> specialized, organization unlike the SC >> consists of cerebellum (derived from metencephalon) and forebrain

What is stabilization?

- comes after neurite outgrowth - process wherein reinforcement of appropriate connections between neurons, specifically between axons and dendrites of neighboring neurons, become reinforced and more permanent

if the graded potential is sufficient, what happens?

- it will spread to the axon hillock where voltage-gated channels allow for AP. - The AP will travel down the axon to the synaptic knob and cause NT exocytosis. - If the potential change is subthreshold, then no AP will ensue and nothing will happen.

action potentials

- originate at axon hillock - voltage gated sodium channels - all or none - speed is variable

divisions of the functional nervous system (Peripheral NS)

- somatic (SNS) >> innervates skin and most skeletal mm >> operates under conscious control - visceral (autonomic) (ANS) >> innervates viscera and smooth mm and glands >> sympathetic and PS division >> operates without conscious instruction

peripheral nerves

1) Are outgrowths of axons from motor neuroblasts (neuroepithelium) in the basal plate 2) Neural Crest Cells (NCCs) form spinal ganglion a) Growth of neurites (dendrites) toward periphery b) Growth of neurites (axons) toward dorsal horn of SC 3) Interneurons form between sensory neuron termination and motor neurons 4) Primitive reflex arc is formed c) Sensory information --> motor response

What are the 3 main types of Beta receptors?

1. Beta-1 (b1) • Increases metabolic activity, heart rate 2. Beta-2 (b2) • Triggers relaxation of smooth mm along respiratory tract • Vasodilation to heart and skeletal mm 3. Beta-3 (b3) • Leads to lipolysis, the breakdown of triglycerides in adipocytes

What are the 3 classes of gated channels?

1. Chemically gated channels 2. Voltage-gated channels 3. Mechanically gated channels

What are the 2 methods of propagating action potentials?

1. Continuous propagation (unmyelinated axons) - an AP in an axon spreads to a neighboring region of its membrane by a series of small steps 2. Saltatory propagation (myelinated axons) - an AP spreads by jumping from one site to another along the axon

responses to increased parasympathetic activity

1. Decreased metabolic rate 2. Decreased heart rate and blood pressure 3. Increased secretion by salivary and digestive glands 4. Increased motility and blood flow in digestive tract 5. Urination and defecation stimulation

Graded potentials share what 4 basic characteristics?

1. Effect decreases with distance 2. The effect spreads passively, due to local currents - depolarizing or hyperpolarizing in nature 3. Depolarization or hyperpolarization 4. The stronger the stimulus, the greater the change in the transmembrane potential and the larger the area affected

What are the 2 types of synapses?

1. Electrical synapses • Direct physical contact between cells 2. Chemical synapses • Signal transmitted across a gap by chemical neurotransmitters

What are the 2 classes of NT?

1. Excitatory neurotransmitters • Cause depolarization of postsynaptic membranes • Eventually promote action potentials 2. Inhibitory neurotransmitters • Cause hyperpolarization of postsynaptic membranes • Suppress action potentials

what are the 2 types of postsynaptic potentials?

1. Excitatory postsynaptic potential (EPSP) • Graded depolarization of postsynaptic membrane 2. Inhibitory postsynaptic potential (IPSP) • Graded hyperpolarization of postsynaptic membrane

responses to increased sympathetic acitivity

1. Heightened mental alertness 2. Increased metabolic rate 3. Reduced digestive and urinary functions 4. Energy reserves activated 5. Increased respiratory rate and respiratory passageways dilate 6. Increased heart rate and blood pressure 7. Sweat glands activated

initiating an action potential

1. Initial stimulus of sufficient strength • A graded depolarization of axon hillock large enough (10 to 15 mV) to change resting potential (-70 mV) to threshold level of voltage-gated sodium channels (-60 to -55 mV) 2. Once process has begun it's an all-or-none principle • If a stimulus exceeds threshold amount - The action potential is the same - No matter how large the stimulus • Action potential is either triggered, or not

D26: 3-part brain

1. Prosencephalon - Forebrain 2. Mesencephalon- Midbrain 3. Rhombencephalon - Hindbrain >> individual segments = rhombomeres - spinal cord - flexures: >> cephalic (red arrow) (mesencephalic) >> Cervical (purple arrow)

What are the 3 groups of axons?

1. Type A fibers 2. Type B fibers 3. Type C fibers • These groups are classified by: - Diameter - Myelination - Speed of action potentials

3 major divisions of neural crest cells

1. cranial NCC 2. circumpharyngeal NCC 3. trunk NCC are a temporary group of cells that arise from embryonic ectoderm, and give rise to a diverse cell lineage

steps to formation of the neural tube

1. thickening of neural plate 2. elongation of neural plate 3. lateral folding >> neural groove, forms --> >> median hinge point >> lateral hinge points (2) 4. fusion of opposing neural folds and separation from overlying ectoderm >> neural crest cells

origin of parasympathetic division

Brainstem (CN III, VII, IX and X) - sacral SC - "craniosacral division"

neuroglial/glial cells

Cells that: - provide support, insulation and nourishment to neighboring neurons - maintain homeostasis - forms myelin - participates in transmission - don't conduct impulses (non-excitable) outnumber neurons 10:1 6 different types: 4 in CNS and 2 in PNS

What is the most prominent artifact of the Mesencephalon?

Cerebral aqueduct - large tube/channel through which fluid can be trafficked • allows CSF to flow from the forebrain to the 4th ventricle

Graded potentials

Consider a stimulus at the dendrite of a neuron. - rich throughout the dendrites are leaky Na+ channels >> these open >> Na+ from outside cell move inside cell bringing with them their +++ charge --> charge inside cell slowly becomes more positive >> + charge spreads like wave of depolarization thru cytoplasm

Differentiation of Rhombomeres is regulated by what?

HOX genes

What happens if the cerebral aqueduct becomes blocked?

Hydrocephalus • 3rd plus lateral ventricles swollen --> excessive CSF • Cerebral cortex thins • Sutures of skull forced apart allowing the bones to increase in size

propagation of action potentials

Moves action potentials generated in axon hillock along entire length of axon

origin of sympathetic division

T1-L2 of the SC - "thorocolumbar division"

How can hydrocephalus be treated?

VP of VA shunt - relieves pressure on the brain caused by fluid accumulation

each axon is surrounded by _______

an endoneurium (loose vascular tissue)

What does the Mesencephalon (midbrain) change into?

auditory colliculil

groups of axons/fibers are bound together into _________ by a ________

bundles/fascicles perineurium (robust and collagenous)

What does the Telencephalon change into?

cerebrum

Hirschsprung's disease

complete constipation of newborns due to lack of colonization of NCC's in wall of lower colon (PS) - results in lack of PS innervation --> no peristalsis - absence of innervation to the terminal part of the colon - mistakenly the dilated part used to be removed "megacolon/-rectum"

Neurocristopathies

defects in neural crest cell migration

Neurites

differentiate into axons and dendrites - have numerous filopodia - filopodia regularly extend and retract, testing the local environment

All fascicles of a nerve are enclosed by a _________

epineurium (loose collagenous CT)

action potential is produced by _____ and is generated by ______

graded potential changes in V(M)

resting potential

is before stimulation - negative on the inside - differential placement of charged molecules

What does the Myelencephalon change into?

medulla oblongata

Where are voltage-gated channels found in abundance?

on the axon hillock and axolemma - where the leaky channels turn into voltage-gated - skeletal mm sarcolemma, cardiac mm

What does the Metencephalon change into?

pons and cerebellum

What are the 3 major divisions of the autonomic/visceral NS?

sympathetic and PS NS, enteric NS

What does the Diencephalon change into?

thalamus hypothalamus pineal body pituitary gland eyes

equilibrium potential

the magnitude of the membrane voltage at equilibrium for a particular ion - there is no net movement of a paricular ion across cell membrane

Graded potentials are

triggered when dendrites receive stimuli, grated, leaky sodium channels

Mesencephalon is largely made up of what?

white matter, specifically tracts connecting the forebrain with the hindbrain and spinal cord

Graded potentials: depolarization

• A shift in transmembrane potential toward 0 mV > Movement of Na+ through channel > Produces local current > Depolarizes nearby plasma membrane (graded potential) > Change in potential is proportional to stimulus

action potential: absolute refractory period vs relative refractory period

• Absolute Refractory Period (orange) - Sodium channels open or inactivated - No action potential possible • Relative Refractory Period (purple) - Membrane potential almost normal - Very large stimulus can initiate action potential

Sympathetic Stimulation and the Release of NE and E on Beta receptors

• Affect membranes in many organs (skeletal muscles, lungs, heart, and liver) • Trigger metabolic changes in target cell • Stimulation increases intracellular cAMP levels

Parasympathetic Receptors: muscarinic receptors

• At cholinergic neuromuscular or neuroglandular junctions (parasympathetic) • At a few cholinergic junctions (sympathetic) • G proteins >> Effects are longer lasting than nicotinic receptors >> Can be excitatory or inhibitory

Soma

• Cell body (perikaryon) • contains the nucleus and most organelles • Neuronal RER = Nissl body >> Described as "gray matter" • Bundles of intermediate filaments (neurofibrils) maintain integrity • Form clusters >> In CNS called Nuclei >> In PNS called Ganglia

Communication: general

• Communication begins with the stimulation of a neuron. • Once stimulated, a neuron will communicate information about the causative event by relying on affects of: >> Sensory neurons >> Interneurons >> Motor neurons

effect of a NT on a postsynaptic membrane

• Depends on the receptor • Not on the neurotransmitter - For example, acetylcholine (ACh) >> Usually promotes action potentials >> But inhibits cardiac neuromuscular junctions

Graded potentials: hyperpolarization

• Increasing the negativity of the resting potential ex -70mV --> -100mV

2. circumpharyngeal NCC

• Marks the pathway of migration for two groups: 1) Vagal crest cells • Migrate into the developing gut • Precursors to PS innervation > mismigration = Hirschsprung's disease 2) Cardiac crest cells • Outflow tract of the heart and great vessels (vena cava, aorta, pulmonary vessels) • Associate with thymus, parathyroid, and thyroid glands

Sympathetic Stimulation and the Release of NE and E on alpha adrenergic receptors (Alpha-1)

• More common type of alpha receptor • Releases intracellular calcium ions from reserves in endoplasmic reticulum • Has excitatory effect on target cell > Smooth mm in vessels to skin, sphincters (constriction)

What are some examples of Neurocristopathies?

• Neurofibromatosis (peripheral nerve tumors) • Charcot-Marie-Tooth (demyelinating disease) • Albinism (pigmentation defect) • Hirschsprung disease (absence of innervation to the terminal part of the colon) • DiGeorge Syndrome (affects development of craniofacial and cardiovascular system)

Parasympathetic Neurons Release ACh

• Neuromuscular and Neuroglandular Junctions - All release ACh as neurotransmitter - Effects of stimulation are short lived >> Inactivated by acetylcholinesterase (AChE) at synapse

What are some other important NT besides ACh?

• Norepinephrine (NE) • Dopamine • Serotonin • Gamma aminobutyric acid (GABA)

Parasympathetic Receptors: nicotinic receptors

• On surfaces of ganglion cells (sympathetic and parasympathetic) >> Exposure to ACh causes excitation of ganglionic neuron or muscle fiber

passive/leaky channels vs active/gated channels

• Passive Channels (Leaky Channels) - Are always open - Permeability changes with conditions • Active Channels (Gated Channels) - Open and close in response to stimuli - At resting potential, most gated channels are closed

How is the action potential returned to normal?

• Powering the Sodium-Potassium Exchange Pump again - To maintain concentration gradients of Na+ and K+ over longer periods of time >> Requires energy (1 ATP for each 2 K+/3 Na+ exchange) - Without ATP >> Neurons stop functioning

simplified graded potential

• Temporary, localized change in resting potential • Caused by stimulus

3. trunk NCC

• Trunk NCCs leave after NT closes > Sixth somite --> caudal • Three main pathways 1) Dorsolateral • melanocytes 2) Ventrolateral • sensory ganglia 3) Ventral • Sympathoadrenal • Adrenal chromaffin cells • Sympathetic ganglia • Sympathetic neurons

Graded potentials: repolarization

• When the stimulus is removed, transmembrane potential returns to normal • Potassium leaves cell

Function of the cerebellum

• center for balance and posture

Neurons

• functional and structural units that communicate with cells throughout the body - includes: • Sensory (afferent) neurons: signals from receptors to the CNS • Motor (efferent) neurons: signals from the CNS to effector tissues • Interneurons: signals between neurons

1. Cranial NCC

• leave well before closure of neural tube • Origin specifies destination (unlike trunk NCC) • Responsible for tissues of the facial region (including bones of skull), CN ganglia, odontoblasts, pharyngeal arch cartilages, dermis of face

Functions of the medulla oblongata

• relay center b/w the SC and the higher brain centers • Regulates respiration, heartbeat, reflex movements, along with other functions

Function of the pons

• relays signals linking the spinal cord and cerebral cortex with the cerebellum • The pontine nuclei relay input from the cerebrum to the cerebellum