Nervous System III Flashcards
Learning Outcomes
- Explain how the autonomic and somatic nervous systems differ in structure
and function. - Explain how the two divisions of the autonomic nervous system differ in
structure and function. - Describe an autonomic reflex.
functional organisation photo
Autonomic Nervous System
- Regulates fundamental states and life processes:
- E.g. heart rate, blood pressure, body temperature
- maintains homeostasis
- “Visceral motor system”
- Controls the viscera of thoracic & abdominopelvic cavities:
- glands
- cardiac muscle
- smooth muscle
- Controls some structures of the body wall:
- cutaneous blood vessels
- sweat glands
- arrector pili muscles (hair erector muscles)
- ANS is independent of our will
- Autonomic = “self-governed”
Homeostasis requires communication
Hormones:
* carried by blood to distant targets.
* slow and not
particularly specific.
* (Endocrine system & homeostasis lecture)
Neurotransmitters:
* released at synapses between neurons & target cells.
* fast and specific.
Homeostasis requires communication photo
Autonomic Reflexes
- Visceral reflexes: unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors
- Visceral reflex arc:
- Stimulus: stretch, pressure, blood chemicals, body temperature etc.
- Receptors: nerve endings that detect internal stimuli
- Afferent (sensory) neurons: lead to CNS
- Integrating center: interneurons in the CNS (hypothalamus and brainstem)
- Efferent (motor) neurons: in the spinal cord and peripheral ganglia carry signals away from the CNS (travel through cranial and spinal nerves)
- Effectors: carry out end response
Autonomic
Reflex arc photo
Divisions of the ANS
Two divisions often innervate same target organ
* May have cooperative or contrasting effects
* Sympathetic division: fight or flight
* Prepares body for physical activity: exercise, trauma, arousal, competition, anger, or fear.
* Increases heart rate, BP, airflow, blood glucose levels, etc.
* Reduces blood flow to the skin and digestive tract.
* Parasympathetic division: rest & digest; feed & breed
* Slows many body functions (e.g. heart rate).
* Relaxes sphincters, stimulates glands.
* Regulates functions such as digestion, salivation, urination, sexual response, sweating, heart rate.
ANS versus a somatic motor pathway
Somatic pathway: a motor neuron from brainstem or spinal cord issues a myelinated axon that reaches all the way to skeletal muscle.
Autonomic pathway: signal travels across 2
neurons to get to the target organ.
Must cross a synapse where these 2 neurons meet in an autonomic ganglion.
Presynaptic neuron: the first neuron has a cell body in the brainstem or spinal cord.
Synapses with a postganglionic neuron whose axon extends the rest of the way to
the target cell.
ANS versus a somatic motor pathway photo
Preganglionic and Postganglionic photo
Sympathetic Division
- Arises from the thoracic & lumbar regions of the spinal cord (“thoracolumbar division”)
- Short preganglionic & long postganglionic fibers
- Preganglionic nerve cell bodies in lateral horns and nearby regions of spinal cord gray matter
- Fibers exit spinal cord via spinal nerves T1 to L2
- Lead to nearby sympathetic chain of ganglia
- Sympathetic chain: series of longitudinal ganglia adjacent to both sides of the vertebral column from cervical to coccygeal levels
Sympathetic
Division
- Each sympathetic ganglion is connected to a spinal nerve by 2 branches: communicating rami
- Preganglionic fibers: myelinated fibers that travel from spinal nerve to the ganglion via the white
communicating ramus - Postganglionic fibers: leave the ganglion by the gray communicating ramus (unmyelinated)
- Postganglionic fibers extend to the target organ
Sympathetic
Division photo
The Adrenal Glands
- Paired adrenal (suprarenal) glands located on superior poles of kidneys
- Each is two glands with diferent functions
Adrenal cortex (outer layer): - Secretes steroid hormones (Endocrine system lecture)
Adrenal medulla (inner core): - Essentially a sympathetic ganglion consisting of modified postganglionic neurons (without fibers) =
chromaffin cells - Stimulated by preganglionic sympathetic neurons
- Secretes a mixture of hormones into bloodstream: catecholamines- 85% epinephrine (adrenaline) and
15% norepinephrine (noradrenaline)
Parasympathetic Division
- Arises from the brain and sacral regions of the spinal cord
(“craniosacral division”) - Fibers travel in certain cranial and sacral nerves
- Long preganglionic, short postganglionic fibers
- Origins of preganglionic neurons:
- Midbrain, pons, and medulla
- Sacral spinal cord segments S2 to S4
- Preganglionic fiber end in ganglia in or near target organs
- Oculomotor nerve (III): narrows pupil & focuses lens
- Facial nerve (VII): lachrymal (tear), nasal, & salivary glands
- Glossopharyngeal nerve (IX): parotid salivary gland
- Vagus nerve (X): heart, lung, digestive tract.
Neurotransmitters & Receptors photo
Parasympathetic Division
photo
Control with Dual Innervation photo
Control with Dual Innervation
Most viscera receive nerve fibers from both parasympathetic and sympathetic divisions
* Antagonistic effect: oppose each other
* Sympathetic: pupils dilate
* Parasympathetic: pupils constrict
* Sympathetic: Heart rate increases
* Parasympathetic: Heart rate decreases
* Cooperative effect: two divisions act on different effectors to
produce a unified overall effect
* Sympathetic: increase salivary mucous cell secretion
* Parasympathetic: increase salivary serous cell secretion
* Both divisions do not normally innervate an organ equally.
* Sympathetic has greater effect on ventricular muscle of heart
* Parasympathetic exerts more influence on digestive organs
Neurotransmitters & Receptors
How do autonomic neurons have contrasting effects on organs?
(a) Parasympathetic fiber
1. Sympathetic and parasympathetic fibers secrete
different neurotransmitters
- The receptors on target cells vary
* Acetylcholine (ACh) is secreted by all preganglionic neurons in both divisions and by postganglionic
parasympathetic neurons
* Norepinephrine (NE) is secreted by nearly all sympathetic postganglionic neurons
* Norepinephrine (NE) = Noradrenaline (NA)
Control With Single Innervation
Some effectors receive only sympathetic fibers, e.g. adrenal medulla, arrector muscles, sweat glands, and many blood vessels
* Regulation of blood pressure and routes of blood flow
* Sympathetic vasomotor tone-a baseline firing frequency of
sympathetics
* Keeps vessels in state of partial constriction
* Increase in firing frequency = vasoconstriction
* Decrease in firing frequency = vasodilation
* Can shift blood flow from one organ to another as needed
* During stress:
* blood vessels to muscles and heart dilate, (prioritizes blood to skeletal muscles and heart)
* blood vessels to skin constrict (minimize bleeding if injury occurs)
Raynaud disease/phenomenon
: Mist como on in Young women.
* Intermittent attacks of paleness, cyanosis, and pain in the fingers and toes.
* Caused when cold or emotional stress triggers excessive vasoconstriction in the digits.
* Sometimes treated by severing sympathetic nerves to the
affected regions.
Autonomic tone
Level of normal background activity of the ANS to maintain the resting state of the organ.
Represents the balance of the two systems according to the body’s needs.
Sympathetics & parasympathetics continuously fire at a low level
* Sympathetic tone
* Keeps most blood vessels partially constricted and maintains blood pressure
- Parasympathetic tone
- Maintains smooth muscle tone in intestines
- Holds resting heart rate down to about 70 to 80 beats per minute
Enteric Nervous System
- The nervous system of the digestive tract
- Does not arise from the brainstem or spinal cord (no CNS components).
- Innervates smooth muscle and glands of the digestive system.
- Composed of 100 million neurons found in the walls of the digestive tract.
- Has its own reflex arcs.
- Regulates motility of esophagus, stomach, and intestines and secretion of digestive enzymes and acid.
- Digestive function also requires regulation by sympathetic and parasympathetic systems.
“Fight-or-flight” response
reaction to stress: fight the threat off or flee to safety evolved as a survival mechanism, enabling animals to react quickly to life-threatening situations.
* Threat = Stimulus. Triggers a fear response in the amygdala.
* Amygdala sends a distress signal to the hypothalamus.
* Activates the sympathetic nervous system.
* Sympathetic nerves to the adrenal glands.
* Adrenal glands release epinephrine (adrenaline) into the bloodstream.
* Increases heart rate & blood pressure: increasing blood flow to the muscles, heart, and other vital organs.
* Breathing rate increases.
* Small airways in the lungs dilate increasing oxygen intake.
* Increased oxygen to the brain increases alertness. Sight, hearing, and other senses become sharper.
* Epinephrine triggers the release of glucose and fats from storage sites in the body. These nutrients flood into the bloodstream, supplying energy to all parts of the body.
Exposure to cold:
* Stimulates cold receptors of the skin
* Stimulates sympathetic nervous system
* Causes vasoconstriction in skin
* Decreases heat loss
Rest and digest
Parasympathetic nervous system and enteric nervous system
* Stimulus = food (thought, sight, smell, taste) or mastication
* Hypothalamus & Medulla oblongata (salivary centres)
> Stimulates salivary gland secretion (facial & glossopharyngeal nerves)
* Ingestion of food leads to stretch of the gut
* Response via vagus nerve & enteric nervous system
> Increases motility of gut (acelerates peristalsis)
* Relaxation of sphincters
* Dilation of blood vessels leading to the Gl tract, prioritises blood flow to the gut.
* Mediates digestion of food and absorption of nutrients
The gag reflex (pharyngeal reflex)
* reflex that evolved to prevent aspiration of solid food
particles
* Stimulation of the posterior pharyngeal wall, tonsillar area, or base of the tongue.
* Afferent nerve = glossopharyngeal (CN IX) nerve
* Efferent nerve = vagus (CN X) nerve
* Reflex contraction of the muscles of the posterior pharynx (throat).
The nasolacrimal reflex
* Chemical or mechanical stimulation of the nasal mucosa
* Parasympathetic: Facial nerve (CN VII) stimulates fluid secretion from the lacrimal gland
* Production of tears (lacrimation)
sleep lectrue
Learning objectives:
* Demonstrate how various brain structures and regions presented in previous lectures work together
* Understand the fundamental importance of sleep to the brain, learning and health of other body systems
* Understand the distinction between different stages of sleep and some of their functions.
Cast of brain characters:
* Neurons and glial cells
* CSF
* Hypothalamus & optic nerve (CN Il)
* Thalamus
* Hippocampus
Who sleeps?
Every organism studied to date that lives more than a few days sleeps.
Primitive worms emerged 500 million years ago so sleep predates all vertebrate life.
Why is sleep necessary?
Restorative - sleep = replenishment
Dynamic - brain is physiologically active during sleep
Impacts the health of every organ system in the body In particular, brain, cardiovascular system, immune function & reproduction
Prolonged absence of sleep = death
Lack of sleep = death (traffic & industrial accidents, miscalculations)
Homo sapiens is the only species on the planet that routinely deprives itself of sleep.
How do we recognise sleep?
- Stereotypical position
- Relaxation of muscles (postural)
- Lack of communication or responsivity
- Easily reversible
- Adheres to a reliable timed pattern - diurnal / nocturnal
Universal indicators of sleep:
1. a loss of external awareness.
2. a sense of time distortion.
Thalamus (sensory convergence zone) blocks perception of light, sound, touch, smell, taste
The brain still registers these inputs but the thalamus regulates what gets through to the cortex
Time is still mapped when sleeping but at a non-conscious level
Example = waking up before your alarm goes off
What determines when you want to sleep and when you want to be awake?
Two main factors:
1. Circadian (circa = around; diam = day) rhythm (internal 24 hour clock)
- cycling day-night rhythm
2. Sleep drive - due to chemical build-up in the brain
Circadian Rhythm Driver = Hypothalamus - Suprachiasmatic nucleus - optic nerves
What determines when you want to sleep and when you want to awake pt.1
- Circadian rhythms
metabolism, cardiovascular system, temperature and hormonal processes
Suprachaismatic nucleus by sampling light via the optic nerves controls the release of Melatonin (secreted by the pineal gland)
Melatonin:
* provides the instruction to commence the event of sleep
(Other brain regions, e.g. brain stem, and processes generate sleep.)
* regulates the timing of sleep by signalling “darkness”
throughout our bodies.
* peaks around 2-4am and then decreases in concentration
becoming virtually undetectable by midmorning.
What determines when you want to sleep and when you want to awake pt.2
- Sleep pressure due to a chemical substance that builds up in your brain - Adenosine
* Adenosine is a metabolite that is ejected from cells into the extracellular space when ATP is used to produce cellular energy (mitochondria).
* Levels of adenosine represent time spent awake and levels of toxin buildup within the brain.
* Sleep deprived individuals have unusually high levels of adenosine, which is restored to normal levels only after a recovery sleep.
* Adenosine concentration is reduced during sleep because the glymphatic system removes it, along with other metabolites.
The Glymphatic System (2012)
G = glial + lymphatic
Flushes the brain with CSF via the regulatory actions of astrocytes.
Astrocytes form part of the blood brain barrier.
circadian diagram
The Glymphatic System
Small channels ‘piggybacking’ the blood vasculature allow the CSF to flow into the brain tissue along para-arterial spaces and exit via
a para-venous route.
Flow flushes out metabolites such as adenosine and beta amyloid (protein associated with Alzheimer’s disease)
During sleep, the brain consumes about 40% less energy.
Result = smaller vascular diameter, = expanded para-vascular channel
Plus, glial cells shrink by up to 60% = expanded space around neurons
Makes glymphatic system 60% more effective during sleep
The Glymphatic System
Flushing by the glymphatic system is pulsatile & predictable
* First, neural activity quiets.
* Then, blood flows out of the brain.
* Next, cerebrospinal fluid flows in.
* Lather, rinse, repeat.
* Most active during deep sleep
What does sleep look like?
Sleep verification requires recording signals from:
* eye movement activity (REM & NREM)
* muscle activity
(REM = no muscle tone = paralysis;
NREM = lowered muscle tone)
activity of the glymphatic system
: brainwave activity
Awake = fast frequency brain wave activity
Different parts of waking brain processing different streams of information in different ways at different times.
Light sleep (stage 2) = sleep spindles
Shield the brain from external noises
The more powerful and frequent the sleep spindles, the more resilient the sleeper to external noises.
Deepest stages of NREM (3 & 4) = slow wave sleep
- due to synchronicity in neuronal activity (sleep spindles)
REM sleep looks similar to awake - fast frequency brain waves
What does sleep look like?
8 hours sleep = 5 x 90 minutes cycles
Can differ in amount required
Some people require less (very rare), others more
Can differ in timing sleep and wake early / late
Strongly genetically influenced
Deep NREM (stages 3 & 4) predominates in cycles 1-3 & glymphatic system most active
Light NREM (stage 2) increases from cycles 3-5
REM most prevalent in cycles 4 & 5
Sleep and learning create physical changes in the brain
In 2014 researchers showed for the first time that sleep after learning encourages neuronal growth.
Dendritic spines = tiny protrusions from neurons that
connect to other neurons and facilitate the passage of
information across synapses
Brain cells that activated when a task was learned, reactivated during slow-wave deep sleep (NREM)
Neuronal replay (the process by which the sleeping brain rehearses tasks learned during the day) during sleep is important for growing specific connections between
neurons
Sleep deprivation after learning prevented dendritic spine growth.
NREM sleep and learning
Hippocampus = informational inbox of the brain
(short term only)
= USB stick of the brain (limited capacity)
= active site of neuronal birth
NREM sleep moves memories from short-term storage to a more permanent, safer, long-term storage location.
NREM sleep and learning
Sleep after learning = hitting the save button to store memories
Stages 3 & 4 NREM - Memories are moved from the hippocampus to more permanent long term storage sites in the brain
(file transfer to a hard drive)
Sleep before learning prepares the brain
Stage 2 NREM = freeing up storage space for more learning
40% deficit in ability to make new memories without sleep
= difference between HD & Fail
Sleep deprivation = can’t effectively commit new experiences to memory
AND if prolonged affects birth of new neurons in the hippocampus
REM sleep - dreaming & learning
REM sleep - dreaming & learning
Only found in birds and mammals - evolved twice
Compared to the great apes, humans sleep less
BUT more of that sleep is devoted to REM sleep (9% vs 25%)
Paradoxical sleep: the brain appears awake, yet the body is asleep.
The brain activity during this stage is not that different from the activity our brain experiences when we re awake.
Seconds before you start dreaming you become paralysed - atonia of voluntary (postural) muscles
Brain stem sends a powerful disabling signal down the entire length of you spinal cord
Eliminating muscle activity prevents acting out the dream experience
During REM sleep barrage of movement commands flying around the brain - underlie the movement rich experience of dreams
Two core benefits of REM sleep:
Modulating our emotional and mental health
Problem solving and creativity
REM sleep - dreaming and learning
There are three stages in terms of information processing.
1. Wakeful state - information goes into short term storage
2. NREM sleep - transfer information into long term storage
3. REM sleep is the integration of all that information
- Wakeful state - information goes into short term storage
- NREM sleep - transfer information into long term storage
- REM sleep is the integration of all that information
REM sleep:
* integrates new learning (transferred by NREM
sleep) with all previous learning
* helps constructs vast association networks within
the brain
* allows for novel links to be made between seemingly unrelated pieces of information
(creative insights)
If you go to sleep at 11pm and wake 5am
You’ve lost 25% of total sleep
But more than 50% REM sleep
Sleep and health: sleep deprivation
18 hours sleep deprivation
* Reaction time increases
* Decision making, maths processing ability, spatial awareness deteriorate
24 hours sleep deprivation
* Reaction time triples (= legally drunk)
* Micro-sleeps (10-20 seconds)
48 hours sleep deprivation
: behaviour resembles psychosis
REM sleep critical for: emotional regulation
ability to read facial expression and body language
problem solving
creativity
(cerebral hemisphere functions)
During REM sleep, signals from different emotions, feelings, and memories are played out inside the brain
A key stress related chemical noradrenaline is not released
= ability to replay events and emotions without triggering a stress
related response
Dreaming can create emotional closure of a traumatic experience provided you dream about emotions related to the trauma.
Sleep and health: Sleeping regularly for less that 7 hours per day:
- Decreases testosterone, testicle size, sperm count.
- Reduces follicular-releasing hormone, increases abnormal menstrual cycles, increases infertility issues
- Increases risk of developing coronary heart disease.
Deep sleep prevents an increase in physiological stress synonymous with increased blood pressure, heart attack, and stroke. (sympathetic nervous system) - Disrupts appetite regulation
Hormones that control our appetite:
leptin (lepto - slender), which signals a sense of feeling full & ghrelin (ghre-to grow), which triggers a strong sensation of hunger.
Sleeping less decreases concentrations of leptin (less full)
and increases levels of ghrelin (more hungry),
increasing the chance of gaining weight, becoming overweight, and developing type 2 diabetes. - Sleep helps the body fight against infection and sickness.
inke sto nessicient sleep. (bowel, prostate, breast)
More forms of malignant tumors are being linked to insuficient sleep. (bowel, prostate, breast)
Poor sleep quality provides a toxic fertilizer for rapid and more rampant tumor growth. - Distorts gene activity - decreases gene activity related to the immune system
Increases activity of genes involved in tumor promotion, inflammation and stress (CV system) - Contributes to anxiety and depression. (REM sleep)
Learning Challenge:
Explain the function of the glymphatic system and how it changes during sleep.
Where in the figure above is the nerve cell body of the neuron you identified in (i)
located?
Ventral horn of the grey matter. .
How is grey and white matter arranged in the spinal cord in relation to the central
canal and outer surface?
White on outside and grey on inside.
What is contained in white matter? Why does white matter appear white?
Mainly myelinated axons (myelin makes it white).
How is grey and white matter arranged in the cerebrum and cerebellum?
Grey on outside and white on inside.
How does the diameter of a nerve fibre affect the
speed of transmission?
Signal conduction occurs along the surface of the fibre. Large fibres have
more surface area than small fibres, therefore, signals travel faster along
large fibres.
Name the cells which form myelin in the CNS.
Oligodendrocytes.
Name the cells which form myelin in the PNS.
Schwann cells.
Where are fast myelinated fibres likely to be found?
Where speed is important, e.g. motor control of skeletal muscle, sensory
signals for vision and balance etc.
Where is the cell body of the first order neuron? (1st neuron in this pathway).
In the dorsal root ganglion of the spinal cord.
iii) Where is the cell body of the second order neuron?
In the medulla.
iv) Where is the cell body of the third order neuron?
In the thalamus.
