Nervous system deeper questions

ANS for now only

1. Presynaptic Terminal (Axon Terminal)

• The end of the sending neuron’s axon. ​

• Contains synaptic vesicles filled with neurotransmitters. ​

• When an action potential arrives, it triggers neurotransmitter release. ​

Calcium channels open

• The electrical signal causes voltage-gated Ca²⁺ channels in the presynaptic membrane to open.​
  Calcium ions enter the neuron.

Neurotransmitter release

• The calcium influx causes synaptic vesicles to move to the membrane and release neurotransmitters into the synaptic cleft by exocytosis.

6. New signal begins

This binding opens ion channels, changing the membrane potential of the postsynaptic neuron and potentially triggering a new action potential.​

7. Signal ends

Neurotransmitters are removed from the synapse by:​

• reuptake into the presynaptic neuron ​

• enzymatic breakdown ​

• diffusion away

Sympathetic nervous system

part of the autonomic nervous system that prepares the body for Responds to stressful situations (“fight or flight” responses.)

• innervates same organs as parasympathetic​

what are the 3 exceptions of organs that are not parasympathetic

sweat glands & arrector pili muscles of skin (make hairs stand up)​

adrenal medulla​

blood vessels to skeletal muscles​

*These are only sympathetic​

what does sympathetic system neurons do

What it does:

• Increases heart rate ❤

• Dilates pupils 👀

• Increases breathing rate 🌬

• Slows digestion 🍽

• Releases energy (like glucose) 🔋

Muscles generate heat

body temperature increases

Decrease in nonessential organ activities

Adrenal Medulla

Part of peripheral nervous system:

• stimulated by preganglionic fiber of SD​

• acts like postganglionic fiber

• ​is sympathetic

adrenal medulla

Part of endocrine system:​

• releases hormones​

• norepinephrine​

• epinephrine​

Parasympathetic (Craniosacral) Divison

is the “rest and digest” side of the autonomic nervous system

• conserve & and saves energy

• ​preganglionic fibers are long and psotgalionic are short

• release ACh at synapse- excites postsynaptic membrane of postganglionic neuron​

• ​Salivation, Lacrimation, Urination, Digestion, Defecation (SLUDD)

Parasympathetic (Craniosacral) Divison

Preganglionic neurons​

• cell bodies:​

• in brain stem nuclei (for cranial nerves) ​

• in ventral horns of sacral spinal cord segments S2-S4 (for sacral nerves)​

Biofeedback (Control of ANS: Cortical Control)​

training program designed to develop ability to control ANS ​

• learns access of parasympathetic division to control:​

• heart rate (lower) ​

• blood pressure (lower) ​

• skin temperature (lower)​

• relax certain muscles​

• concentrate on thoughts that calm, relax​

• Physical response to emotions ​

🧪 Cholinergic

• Uses acetylcholine (ACh) ​

🧪 Cholinergic

• Found in: ​

• ALL preganglionic neurons ​

• Parasympathetic postganglion​

Receptors:​

• Nicotinic ​

• Muscarinic

⚡ Adrenergic

• Uses norepinephrine (NE)

• Found in: ​

• Sympathetic postganglionic neurons​

• Hormone secreted by the adrenal gland medulla​

⚡ Adrenergic

• Receptors:​

• Alpha (α) ​

• Beta (β)​

• ​

​

Parasympathetic tone (stronger)​

• keeps heart rate lower​

• maintains partial contraction of GI system (6-7 meters in living person versus 9 meters in cadaver)​

• maintains partial contraction of urinary system tubes (ureters)​

Sympathetic tone

used to maintain vasomotor tone (partial constriction) of blood vessels​

Neurotransmitters

primary substances produced by neurons of ANS​

Nicotinic Receptors

are a type of receptor in the nervous system that respond to acetylcholine (ACh)

• Cholinergic (the recpetor it is)

• Found on postganglionic neurons, skeletal muscles, adrenal glands​

  (Excitatory)

Muscarinic receptors

are another type of receptor for acetylcholine (ACh)

• Found on parasympathetic effectors, some sweat glands​

• Excitatory or inhibitory​

• Slower-acting receptors

• G-protein (metabotropic) receptors​

Atropine ​

a drug that blocks muscarinic receptors.

• suppresses salivation & respiratory secretions​

• dilates bronchi ​

• dilates pupils for eye exam (long lasting effect)​

Because it blocks “rest and digest,” it causes more sympathetic-like effects:

↑ heart rate

↓ saliva (dry mouth)

↓ digestion

Pupils dilate

↓ sweating

Dual Innervation

means an organ receives input from both:

(part of ANS)

• the sympathetic division (fight or flight)

• the parasympathetic division (rest and digest)

-Can work alone or both coordinate activities of different structures.​

a 1 -Alpha (Adrenergic Receptor)

• - almost all sympathetic target organs except heart; NE binding:​

• constricts peripheral blood vessels and GI sphincters​

• dilates pupils of eyes by acting on iris​

a 2-Adrenergic Receptor

• membrane of adrenergic axon terminals ​

• Generally inhibitory​

Phenylephrine

• sympathomimetic drug (mimics sympathetic effects).​

• stimulates 1 receptors, which inhibit nasal & lacrimal secretion through peripheral vasoconstriction​

• used to treat hypotension ​

why is Phenylephrine​ used to treat hypotension

due to strong action on blood vessels​

b1 beta (β) Receptors

generally stimulates​

• heart​

• skeletal muscles​

b2 recpetors Beta (β) Receptors​

mainly inhibition (smooth muscle relaxation)​

• lungs (smooth muscle of bronchi & bronchioles)​

• heart blood vessels (vasodilation)​

• stimulates secretion of insulin​

B3 Beta (β) Receptors​

stimulates hydrolysis of stored fat

Effects of Drugs: Beta Blockers

• b-receptor antagonist​

• Used to treat:​

• Various heart conditions​

• Hypertension​

• Anxiety​

Somatic nervous system

part of the nervous system that controls voluntary movement and skeletal muscles. (1st part of ANS)

somatic

Target cell​

Skeletal muscle

sympathetic system

Cell Bodies​ ​

CNS (Brainstem or Spinal cord)

Somatic

Function​

Conscious movement

Somatic

Neurotransmitter​ ​

Ach

Somatic

Receptor​ ​

Nicotinic

Autonomic

Target cell​

Smooth and cardiac muscle; glands

Autonomic

# of Neurons​

2 motor neurons

Autonomic

Cell Bodies​ ​

PNS ganglions

Autonomic

Neurotransmitter​ ​

Ach and NE

Autonomic

Function​

Unconscious regulation

Autonomic

Neurotransmitter​ ​

Ach and NE

Autonomic

Receptor​ ​

Varies

Dendrites

branch-like extensions of a neuron (nerve cell) that receive signals from other neurons and carry those signals toward the cell body (soma)

Node of Ranvier

These are small gaps between the myelin sheath along an axon. They play a key role in how nerve signals travel.

What they do:

• Allow electrical impulses to “jump” from node to node

• This process is called saltatory conduction

• It makes nerve signals travel much faster

Preganglionic neuron

• The first neuron in the pathway

• Starts in the central nervous system (brain or spinal cord)

• Travels to a ganglion (a cluster of neuron cell bodies)

• Releases acetylcholine (ACh)

• Targets nicotinic receptors

Postganglionic neuron

• The second neuron

• Starts in the ganglion

• Travels to the effector organ (heart, glands, muscles, etc.

Parasympathetic

at target organ:

• Releases ACh

• Acts on muscarinic receptors

Sympathetic

• Usually releases norepinephrine (NE)

• Acts on alpha and beta receptors

Nicotinic

always at the ganglion of both systems