Unit 16: The Peripheral Nervous System🧠

Unlike the CNS, the PNS is ____ throughout the body and can be incorporated into ____ ____

spread, other organs

What are the 2 main anatomical structures of the PNS?

1. nerves

2. ganglia

The enteric nervous system (ENS) is a specialized part of the PNS found mainly in the ____ system

digestive

What is a group of neuron cell bodies in the PNS called?

ganglion

What are the 2 main types of ganglion called?

1. sensory ganglia

2. autonomic ganglia

Sensory ganglia → contain cell bodies of ____ ____

Autonomic ganglia → involved in the ____ ____ ____

sensory neurons, autonomic nervous system

What is the most common type of sensory ganglion called?

dorsal root ganglion (DRG)

Dorsal root ganglion (DRG) contains ____ ____ of ____ ____

cell bodies, sensory neurons

Dorsal root ganglion (DRG) axons receive sensory information from the ____ (e.g., ____)

periphery, skin

Dorsal root ganglion (DRG) axons enter the CNS through the ____ ____ ____

dorsal nerve root

The sensory neurons in the dorsal root ganglion are ____ neurons by shape

unipolar

Nerves contain more than nervous tissue: they also have ____ ____ and ____ ____ that provide nourishment

connective tissue, blood vessels

Cranial nerves = 12 pairs connected to the _____

brain

Spinal nerves = 31 pairs connected to the ____ ____

spinal cord

What are cranial nerves primarly responsible for?

sensory and motor functions of the head and neck

What does the vagus nerve do?

reaches organs in the thoracic and abdominal cavities as part of the parasympathetic nervous system

Cranial nerves can be ____, ____, or mixed

sensory, motor

Sensory axons originate from what?

sensory ganglia outside the cranium

Motor axons originate from what?

motor nuclei within the brain stem

All ____ nerves are mixed, containing both sensory and motor axons

spinal

What 2 nerve roots do spinal nerves divide into?

1. dorsal nerve root

2. ventral nerve root

What happens in dorsal nerve root?

sensory axons enter the spinal cord

What happens in ventral nerve root?

motor fibres exit the spinal cord

A nerve's connective tissue is organized into layers:

- Around the ____ nerve

- Around each ____ (bundle of nerve fibers)

- Around each individual ____ ____

entire, fascicle, nerve fiber

What is somatic nervous system?

the division of the peripheral nervous system that controls the body's skeletal muscles

The SNS is responsible for ____ ____ of the environment

conscious perception

____ ____ ____ receive information from environmental stimuli, but the neurons that ____ motor responses originate in the CNS

peripheral sensory neurons, produce

What is a reflex?

an automatic response to a specific stimulus

What are the neurons and pathways involved in a reflex called?

reflex arc

What is stretch reflex?

stretching a muscle causes that same muscle to contract

What does stretch reflex help prevent?

overstretching

What is withdrawal reflex?

rapid spinal reflex that protects you from harmful stimuli

Reading example: Light/visual information → retina → ____ → ____ ____

thalamus, cerebral cortex

The ____ ____ ____ in the occipital lobe processes the visual information, allowing you to consciously recognize the letters

primary visual cortex

During reading, the cortex sends signals to motor neurons in the brain stem, which control the ____ ____ (eye muscles)

extraocular muscles

Eye movement is carried through ____ ____ III, IV, and VI

cranial nerves

Somatic nervous system: ____ ____→ central processing → ____ ____

sensory input, motor output

The autonomic nervous system (ANS) controls involuntary physiological responses, especially during situations involving ____ or ____ emotions

threats, strong

What is fight-or-flight response in ANS?

the body's preparation to fight a threat or run away

During fight-or-flight, ____ is released into the ____

adrenaline, bloodstream

During fight or flight, ____ ____ increases and ____ ____ increases

heart rate, blood pressure

During fight or flight why do sweat glands activate?

to help prepare the body

During fight or flight:

____ dilate → more air can enter the lungs

____ dilate → more visual information can enter the eyes

____ ____ in skeletal muscles dilate → more blood can reach the muscles needed for movement

bronchi, pupils blood vessels

Why can similar (fight or flight) physiological reactions occur with anxiety or panic, even when there is no physical threat?

because the ANS is also connected to emotional responses

What are the 2 main divisions of the autonomic nervous system (ANS)?

1. sympathetic

2. parasympathetic

What is the sympathetic division of ANS for?

preparing the body for action (fight-or-flight)

What is the parasympathetic division of ANS for?

helps the body relax, slow down, and digest food

During "rest-and-digest" of the parasympathetic division, ____ ____ slows, ____ returns to normal, and ____ activity increases

heart rate, breathing, digestive

The ANS controls what three things, while the somatic nervous system controls skeletal muscle

cardiac muscle, smooth muscle, and glands

The ANS regulates internal organs through what?

autonomic (visceral) reflexes

The sympathetic and parasympathetic divisions often provide dual innervation to the ____ organ, with ____ effects

same, opposite

Why does the sympathetic division increase oxygen delivery to skeletal muscles?

because respiratory, cardiovascular, and musculoskeletal systems become more active

Why does the sympathetic division increase sweating?

to help prevent overheating from increased muscle activity

Why does the sympathetic division decrease/shut down digestion?

so blood can prioritize delivering oxygen to skeletal muscles rather than absorbing nutrients

Why is the sympathetic division also called the thoracolumbar system?

because it originates from the thoracic and upper lumbar spinal cord

In the sympathetic division, central neurons in the lateral horn project through the ventral spinal roots to ____ ____ near the vertebral column

sympathetic ganglia

What is the sympathetic chain ganglia?

a network running alongside the vertebral column, most sympathetic ganglia are a part of it

Sympathetic chain ganglia appear as clusters of ____ connected by ____ ____

neurons, axonal bridges

What are the 2 types of axons in the sympathetic division called?

1. preganglionic fibre

2. postganglionic fibre

How does a preganglionic fibre axon carry signals

from a CNS neuron to a sympathetic ganglion

How does a postganglionic fibre axon carry signals?

from a ganglion neuron to a target organ/effector

What are the physical qualities of a preganglionic fibre?

short and myelinated

What are the physical qualities of a postganglionic fibre?

long and unmyelinated

Some preganglionic sympathetic fibres go directly to the ____ ____ instead of a regular ganglion

adrenal medulla

What is the adrenal medulla?

inner part of the adrenal gland

What does the adrenal medulla act like?

modified ganglion

Instead of sending an axon to a target organ, the adrenal medulla releases ____ ____ into the ____, allowing them to affect ____ organs

signaling molecules, bloodstream, many

How does the sympathetic division have such widespread effects throughout the body?

because its pathways diverge/branch extensively

A single preganglionic sympathetic neuron can have how many targets?

10-20

A preganglionic axon from the lateral horn of the thoracolumbar spinal cord enters the sympathetic chain through what?

white ramus communicans

Within the sympathetic chain, the axon can:

Synapse at the ____ level

____ up or down the chain before synapsing

Pass through the chain to a collateral ____

Travel to the ____ ____

same, travel, ganglion, adrenal medulla

When is the parasympathetic division most active?

when the body is not responding to an immediate threat

The parasympathetic increases activity in what 2 bodily systems?

1. digestive

2. urinary

What is the reproductive system regulated by?

both sympathetic and parasympathetic innervation

The activity of an organ depends on what?

which division is releasing more neurotransmitter onto it at that time

Why is the parasympathetic division is also called the craniosacral system?

because its preganglionic neurons originate in the brain stem and sacral spinal cord

Cranial preganglionic fibres, part of the parasympathetic division, travel through ____ nerves, while sacral preganglionic fibres travel through ____ nerves

cranial, spinal

Preganglionic fibres in the parasympathetic division, travel to ____ ____, which are located near or within the target organ

terminal ganglia

Preganglionic fibres are long, while postganglionic fibres are short because why?

the ganglia are close to the target organ

What are terminal ganglia located within the walls of the target organ/tissue called?

intramural ganglia

Postganglionic fibres travel a ____ distance from the terminal ganglion to the effector

short

At an ____ ____, an ____ ____ causes the release of a signaling molecule that binds to receptors on the ____ ____

autonomic synapse, action potential, target cell

What do cholinergic synapses release?

acetylcholine (ACh)

What do adrenergic synapses release?

norepinephrine (NE)

Cholinergic receptors can be what 2 things?

1. nicotinic

2. muscarinic

What are nicotinic receptors?

ligand-gated cation channel

What are muscarinic receptors?

G protein-coupled receptor (GPCR)

____ binds nicotinic receptors, while ____ binds muscarinic receptors; they do not cross-react

nicotine, muscarine

Exogenous = produced ____ the body; endogenous = produced ____ the body

outside, within

Nicotine and muscarine are ____ molecules

exogenous

What are the 2 main receptor types of the adrenergic system?

1. α (alpha) 2. β (beta)

All ____ ____ are G protein-coupled receptors (GPCRs)

adrenergic receptors

The adrenergic system uses what 2 signaling molecules?

1. norepinephrine (NE)

2. epinephrine (E)

Epinephrine = ____

Norepinephrine = ____

adrenaline, noradrenaline

How does epinephrine differ from norepinephrine?

by one CH₃ (methyl) group (nor- means that the methyl group is missing)

Epinephrine/adrenaline is released by what?

adrenal gland

Epinephrine/adrenaline is strongly associated with what response?

fight-or-flight

All preganglionic fibres (sympathetic + parasympathetic) release ____

ACh

Why is ACh a neurotransmitter?

because it is released at synapses

When can norepinephrine act as a neurotransmitter?

when released by sympathetic postganglionic fibres