Nervous System 2

Question 1

Reflexes Basic Steps

Answer 1

1. A stimulus activates a receptor.
2. A nerve impulse travels through a sensory neuron to the spinal cord.
3. A nerve impulse is processed in the integration center by interneurons. The nerve impulse is relayed to the brain by interneuron collaterals.
4. A motor neuron receives the impulse from sensory or interneurons and transmits the nerve impulse to the effector.

Question 2

Reflexes

Answer 2

These are a quick (very few neurons involved meaning less delay), involuntary (automatic so no need for stimuli to register in the brain and awareness comes later), stereotyped (the response is the same every time or predictable) reaction to stimuli (muscles and glands). They are protective.

Question 3

Monosynaptic Reflex

Answer 3

This is a direct communication between a sensory and motor neuron. Its name is gathered from the fact it has only 1 synapse. An example is a stretch reflex.

Question 4

Polysynaptic Reflex

Answer 4

This is when an interneuron facilitates the sensory-motor communication. Its name is gathered from the fact it has more that 1 synapse. An example is a withdrawal reflex.

Question 5

Real World Reflex Response

Answer 5

Example: stepping on glass while walking.
1. The withdrawal reflex occurs where the injured foot is lifted by flexing the knee.
2. A new reflex occurs in order to maintain balance while being on 1 leg.
3. A crossed extension reflex occurs to stabilise the opposite limb so you don’t lose balance. This reflex involves many more muscles in your opposite limb as well as your core, back and hips as balance can’t just be achieved with a leg.
4. The response therefore requires a polysynaptic and multilevel reflex which takes more time than a monosynaptic reflex (this is still quick just slightly slower than a normal one).

Question 6

Gordon Ramsey Example

Answer 6

When Gordon touches the hot pan handle the he immediately moves his hand away from the pan before swearing and shaking his hand showing a registering of pain. This is because the nerves that send proprioceptive messages are larger and more myelinated (meaning faster transmission) than the nerves that send pain signals. This is why the hand waving continues as the proprioceptors override the pain receptors which numbs or dulls the pain.

Question 7

White Matter Tracts

Answer 7

The white matter has 3 anatomically different regions which are the dorsal funiculi, lateral funiculi and ventral funiculi. All nerve fibers (axons) in a named tract have a similar origin, destination and function.

Question 8

Funiculi

Answer 8

The white matter has 3 anatomically different regions which are the dorsal, lateral and ventral. All 3 of these regions have a common name used to describe them.

Question 9

Fasiculi

Answer 9

The axons within funiculi which are organised into small structural units.

Question 10

Ascending & Descending Tracts

Answer 10

The ascending tracts have names that begin with spine and end with a brain region these carry sensory information from the spine to the brain. The descending tracts begin with a brain region and end in spine these carry motor information from the brain down the spine.

Question 11

Sensory Tract Anatomy

Answer 11

These typically have 3 neurons with a primary (1st order) neuron (cell body located in the posterior root ganglion), secondary (2nd order) neuron (cell body located in the posterior horn or a brainstem nucleus), tertiary (3rd order) neuron (cell body located in the thalamus).

Question 12

Motor Tract Anatomy

Answer 12

These typically have 2 neurons with an upper motor neuron (cell body located in the cerebral cortex or brainstem nucleus) and a lower motor neuron (cell body located in the anterior horn or a brainstem nucleus).

Question 13

Decussate

Answer 13

When fibers cross to the opposite side of the body (contralateral origin and destination). In terms of tracts not all undergo this process however many do.

Question 14

Somatic Sensory (Ascending) Pathway

Answer 14

This carries a signal up the spinal cord e.g. proprioception. The 1st order neuron detects the stimuli, the 2nd order neuron synapses at the thalamus, the 3rd order neuron carries the signal to the brain.

Question 15

Fine 2-Point Discrimination

Answer 15

The ability to identify 2 points applied to the skin as 2 and not one. Different areas of the body discriminate different distances between 2 points. This is because sensory neurons detect stimuli within an area called a receptive field which will stimulate only 1 neuron. These regions can be large or small depending on the region of the body.

Question 16

Motor (Descending) Pathway

Answer 16

This carries a signal down the spinal cord. This originates in the brain with the upper motor neuron (sending an exciting or inhibiting signal) and the lower motor neuron (receiving an exciting or inhibiting signal and sending to an effector).

Question 17

Corticospinal Tract

Answer 17

This is the largest descending tract in humans. This has 2 pathways. the lateral corticospinal tract is directed to the limbs (85%) with the ventral corticospinal tract being directed to trunk muscles (15%). Both of these decussate in the medulla as motor control is typically contralateral. The lateral part innervates skeletal muscles that controls skilled limb movement e.g. playing bass, typing.

Question 18

Spinal Injury Specifics

Answer 18

C4: Quadriplegia/Tetraplegia complete paralysis below the neck.
C6: partial paralysis of hands/arms and lower body.
T6: Paraplegia paralysis below the chest.
L5: Paraplegia paralysis below the waist.

Question 19

Spinal Injuries

Answer 19

This most commonly occurs in males aged 16-30 most commonly caused by motor accidents and sports injuries. A complete severance (transection) of the spinal cord interrupts pathways to the brain. Initially spinal shock will occur after which it will pass to a normal flaccid paralysis which will turn to spastic paralysis.

Question 20

Spinal Shock

Answer 20

Caused by spinal injury where a flaccid paralysis below the site of injury and absence of reflexes occurs (patient retains urine and faeces). This process only lasts for a short period of time will diminish.

Question 21

Flaccid Paralysis

Answer 21

Caused by spinal injury where a paralysis of the body below the sight of injury occurs. In this state reflexes will still occur however lack of voluntary control may cause a person to be incontinent.

Question 22

Spastic Paralysis

Answer 22

Caused by spinal injury where the initial flaccid paralysis from injury will changes to this because spinal reflexes lack inhibitory control from the brain.

Question 23

Incontinent

Answer 23

A lack of voluntary control over urination and defecation.

Question 24

What Happens When You Get Scared

Answer 24

Increased heart rate and blood pressure, clench/flinch, scream. These are autonomic responses.

Question 25

What Happens When You Get Cold

Answer 25

Skin goes pale, shivering,

Question 26

Nervous System Divisions

Answer 26

There is a central nervous system and a peripheral nervous system. Another division is the sensory and motor division. These are also divided into 2 other parts or the somatic and autonomic/visceral.

Question 27

Visceral Sensory

Answer 27

Sensory input that is not consciously perceived from receptors of blood vessels and internal organs e.g. heart.

Question 28

Autonomic Motor

Answer 28

Motor output that is not consciously controlled some effectors of this are cardiac/smooth muscle and glands.

Question 29

Autonomic Nervous System

Answer 29

This regulates the fundamental states and life processes e.g. heart rate, blood pressure, body temperature etc. in order to maintain homeostasis. It is made up of the visceral motor system which controls the viscera (glands, smooth/cardiac muscle) of thoracic and abdominopelvic cavities as well as some structures of the body wall e.g. cutaneous blood vessels, sweat glands.

Question 30

Homeostasis

Answer 30

In order to maintain this balance communication is required. This communication can occur via hormones which are carried by blood to distant targets. These are slow and not particularly specific. Communication can also occur using neurotransmitters released at the synapses between neurons and target cells. These are fast and specific.

Question 31

Autonomic Reflexes

Answer 31

These are unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors. It requires a visceral reflex arc to occur which has stimuli, receptors, sensory neurons, integrating centers, motor neurons and effectors.

Question 32

Visceral Reflex Arc

Answer 32

Stimulus: a change caused by stretch, pressure, blood chemicals or body temperature.
Receptors: nerve endings that detect internal stimuli.
Sensory neurons: lead to the CNS.
Integrating center: interneurons in the CNS (hypothalamus and brainstem).
Motor neurons: in teh spinal cord and peripheral ganglia carry signals away from the CNS.
Effectors: carry out the end response.

Question 33

Sympathetic Division

Answer 33

This part of the nervous system prepares the body for physical activity e.g. exercise, trauma, arousal, anger, fear etc. It causes the reduction of blood flow to the skin and digest trick.

Question 34

Parasympathetic Division

Answer 34

This part of the nervous system slows down many bodily functions e.g. heart rate. It helps to relax sphincters and stimulates glands. It also regulates the functions such as digestion, salivation, urination, sexual response, sweating and heart rate.

Question 35

Somatic Motor Pathway

Answer 35

A motor neuron from the brainstem or spinal cord issues a myelinated axon that reaches all the way the the skeletal muscle.

Question 36

Autonomic Motor Pathway

Answer 36

The signal travels across 2 neurons to get to the target organ. It must cross a synapse where these 2 neurons meet in an autonomic ganglion. The neuron before the ganglion is known as preganglionic while the one after the ganglion is referred to as the postganglionic. In the sympathetic system the ganglion is closer to the spine meaning a short preganglionic neuron and uses the neurotransmitters adrenaline/noradrenaline at the target organ and acetylcholine at the ganglion. In the parasympathetic system the ganglion is closer to the target organ meaning a long preganglionic neuron and uses the transmitter acetylcholine.

Question 37

Neurotransmitters & Receptors

Answer 37

The sympathetic and parasympathetic nervous systems can effect the same target organs. The reasons for the different results from the systems is due to the type of neurotransmitters they use and the receptors on the target cells.

Question 38

Acetylcholine (ACh)

Answer 38

This neurotransmitter is secreted by all preganglionic neurons in both divisions of the autonomic nervous system and also by the postganglionic neurons in the parasympathetic nervous system.

Question 39

Noradrenaline (NA)

Answer 39

This neurotransmitter is secreted by nearly all postganglionic neurons in the sympathetic nervous system. This is also known as norepinephrine.

Question 40

Sympathetic Nervous System

Answer 40

This arises from the nerves from the thoracic and lumbar regions of the spinal cord. It has short preganglionic nerves and long postganglionic nerves. The cell bodies of preganglionic nerves are in the lateral horns and nearby regions of the spinal cord gray matter. Fibers exit the spinal cord via spinal nerves T1 - L2 which leads to the sympathetic chain. Each sympathetic ganglion is connected by a spinal nerve by 2 branches called communicating rami.

Question 41

Sympathetic Chain

Answer 41

A series of longitudinal ganglia adjacent to both sides of the vertebral column from the cervical to the coccygeal levels.

Question 42

Preganglionic Fibers

Answer 42

These nerves are myelinated and ttravel from spinal nerves to the ganglion via the white (myelinated) communicating ramus.

Question 43

Postganglionic Fibers

Answer 43

These nerves are unmyelinated and travel from the ganglion via the gray (unmyelinated) communicating ramus. These extend to the target organ.

Question 44

The Adrenal Glands

Answer 44

A pair of glands located on the superior poles of the kidneys. Each is 2 glands consisting of a medulla and a cortex which both have different functions.

Question 45

Adrenal Cortex

Answer 45

This secretes steroid hormones (adrenaline/noradrenaline).

Question 46

Adrenal Medulla

Answer 46

This essentially is a sympathetic ganglion consisting of modified postganglionic neurons (without fivers) called chromaffin cells. It is stimulated by preganglionic sympathetic neurons. It secretes a mixture of hormones known as catecholamines which 85% being adrenaline and 15% being noradrenaline.

Question 47

Parasympathetic Nervous System

Answer 47

This arises from the brain and sacral regions of the spinal cord which is why its sometimes known as the ‘craniosacral division’. The fibers travel in certain cranial and sacral nerves. This has long preganglionic nerves and short postganglionic nerves. The preganglionic neurons originate from the brainstem (midbrain, pons, medulla) and the sacral spinal cord segments S2-S4. The preganglionic fiber ends in the ganglia which is in or near the target organ.

Question 48

Oculomotor Nerve (III)

Answer 48

This narrows the pupil and focuses the lens of the eye.

Question 49

Facial Nerve (VII)

Answer 49

This controls the lachrymal (tear), nasal and salivary glands.

Question 50

Glossopharyngeal Nerve (IX)

Answer 50

This controls the parotid salivary gland.

Question 51

Vagus Nerve (X)

Answer 51

This controls the heart, lungs and digestive tract.

Question 52

Single Innervation Control

Answer 52

Some effectors only receive only sympathetic fibers e.g. adrenal medulla, arrector muscles, sweat glands and many blood vessels. In the regulation of blood pressure there is a sympathetic vasomotor tone (a baseline firing frequency). It keeps the vessels in a state of partial constriction. The sympathetic division can then increase (vasoconstriction) or decrease (vasodilation) the firing frequency. Which allows the blood to flow as needed from organ to organ. During stress blood vessels to the muscles and heart dilate (priority blood) while those under the skin contract (minimise bleeding if injury occurs).

Question 53

Double Innervation Control

Answer 53

Most effectors receive nerve fibers from both the parasympathetic and sympathetic nervous system. These systems will have an antagonistic effect (oppose each other) with the sympathetic increasing heart rate and parasympathetic decreasing it. They can also have a cooperative effect (2 divisions act together to produce a general overall effect) with the sympathetic increasing salivary mucous secretion while the parasympathetic increases salivary serous secretion. There is variable innervation as the sympathetic will have a stronger effect on the heart while the parasympathetic will be stronger on the digestive system.

Question 54

Autonomic Tone

Answer 54

The level of normal background activity of the autonomic nervous system to maintain the resting state of an organ. It represents the balance of the 2 systems according to the body’s needs. Both the sympathetic and parasympathetic systems fire continuously at a low level.

Question 55

Sympathetic Tone

Answer 55

This keeps most blood vessels partially constricted and maintains blood pressure.

Question 56

Parasympathetic Tone

Answer 56

This maintains smooth muscle tone in the intestines and holds the resting heart rate down to 70-80 bpm.

Question 57

Enteric Nervous System

Answer 57

This only effects the digestive tract. This doesn’t arise from the brainstem or spinal cord (no CNS components). This innervates smooth muscle and glands of the digestive system. It is composed of 100 million neurons found in the walls of the digestive tract. This system has its own reflex arcs. It regulates motility (esophagus, stomach and intestines), secretion of digestive enzymes and acid. The digestive system also requires regulation from the sympathetic and parasympathetic nervous system.

Question 58

Fight-or-Flight Response

Answer 58

This is a reaction to stress to fight off or flee from the threat. This is evolved as a survival mechanism, enabling animals to react quickly to life-threatening situations. First a stimulus in the form of a threat occurs causing a fear response in the amygdala. The amygdala sends a signal to the hypothalamus. This activates the sympathetic nervous system. Sympathetic nerves activate the adrenal glands to release adrenaline. This increase heart rate and blood pressure resulting in increased blood flow to the muscles, heart and vital organs. Other effects such as breathing rate increase, increased oxygen intake, glucose released for extra energy etc.

Question 59

Cold Response

Answer 59

First a stimulus in the form of cold stimulates cold receptors on the skin. This stimulates tthe sympathetic nervous system. This causes vasoconstriction in the skin in order to decrease heat loss.

Question 60

Rest and Digestion Response

Answer 60

This is done by the parasympathetic and enteric nervous systems. The stimulus of food (thought, smell or taste) activates the hypothalamus and medulla oblongata (salivary centers). This stimulates salivary gland secretion (facial and glossopharyngeal nerves). The ingestion of food leads to the stretch of the gut as a stimulus which is responded to by the Vagus nerve and enteric nervous system. This increases the motility of the gut (peristalsis) and relaxes the sphincters. The dilation of blood vessels leading to the digestive system prioritises blood flow to the gut and mediates the digestion of food and absorption of nutrients which may lead to a tired feeling which may result in postprandial somnolence.

Question 61

Postprandial Somnolence

Answer 61

This is also known as a food coma.

Question 62

Gag Reflex

Answer 62

This is a survival adaptation to avoid solids from entering the airway. The stimulus from something disturbing the throat. This stimulates the posterior pharyngeal wall, tonsillar area or base of the tongue. This stimulation is sent to the spine via the glossopharyngeal nerve and a signal is returned to the area by the Vagus nerve. This causes the reflex contraction of muscles in the posterior pharynx.

Question 63

Nasolacrimal Reflex

Answer 63

This is stimulated by a chemical or mechanical stimulation of the nasal mucosa. This causes the facial nerve to simulate fluid secretion form the lacrimal glands which results in tears (lacrimation).

Question 64

Sleep

Answer 64

Every organism studied to date that lives more than a few day will sleep. This emerged 500mya meaning it predates life. It is restorative (replenishment), dynamic (the brain is very active). This impacts the health of every organ system in the body especially brain, cardiovascular, immune and reproductive. A prolonged absence of this can lead to death. Homo sapiens are the only species that deprives itself from this activity without a reproductive function.

Question 65

Recognition of Sleep

Answer 65

There is a stereotypical position, muscles are relaxed especially posture, a lack of communication/responsiveness, it is easily reversible and different to unconsciousness. The universal indicators for this are a loss of extrernal awareness and a time distortion.

Question 66

Thalamus

Answer 66

This is the sensory convergence zone which blocks the perception of light, sound, touch, smell and taste. The brain still registers these inputs but the thalamus regulates what gets through to the cortex. Time is still mapped when sleeping however not at a conscious level.

Question 67

What Determines When You Want to Sleep

Answer 67

There are 2 main factors which are the circadian rhythm and sleep drive.

Question 68

Circadian Rhythm

Answer 68

This is driven by the hypothalamus, suprachiasmatic nucleus (sits above the crossing of the optic nerves) and optic nerves. This process control metabolism, cardiovascular system, temperature and hormonal processes.

Question 69

Melatonin

Answer 69

The suprachiasmatic nucleus samples light from the optic nerves and controls the release of this hormone by the pineal gland. This provides the instruction to commence the event of sleep to which other brain regions (brain stem etc.) respond to generate that sleep. This peaks at 2-4am and then decreases becoming undetectable until 9pm at night.

Question 70

Adenosine

Answer 70

This is what causes sleep pressure due to build up of this metabolite in the brain. This is ejected from cells into extracellular space when ATP is used to produce cellular energy (mitochondria). Levels of this represent time spent awake and levels of toxin buildup within the brain. The means the levels increase the more you stay awake which only decrease when you sleep. Sleep deprived individuals have unusually high levels of this which is restored to normal levels after a recovery sleep. The glymphatic system works to remove these types of metabolites.

Question 71

Spider Study

Answer 71

This showed that in comparison to marijuana, speed and caffiene that spiders on caffeine made the worst webs.

Question 72

Caffeine

Answer 72

This binds to adenosine receptors in the brain. The adenosine at the receptors causes sleepiness but due to the blockage of the receptor by this molecule sleepiness is blocked. The average half-life of this is 5-7 hours (50% clearance) however adenosine continues to builds up despite not attaching to receptors causing a big crash as the adenosine then binds to the receptors.

Question 73

The Glymphatic System

Answer 73

This flushes the brain with CSF using the regulatory actions of astrocytes. The astrocytes form part of the blood brain barrier. This consists of small channels piggybacking the blood vasculature which allows the CSF to flow into the brain tissue along para-arterial spaces and exit via para-venous routes. The flow flushes the metabolites such as adenosine out. During sleep the brain consumes 40% less energy meaning smaller vascular diameter meaning expanded para-vascular channels for flushing. The glial cells also shrink by 60% allowing more space around neurons. In combination these make this system 60% more effective during sleep. Flushing is pulsatile and predictable where the neural activity quiets, blood flows out of the brain, CSF enters. This process repeats over again and again.

Question 74

What Sleep Looks Like

Answer 74

Verification of sleep require recording signals from eyes movement activity rapid eye movement (REM). During REM sleep there is no muscle tone meaning paralysis and even in non-REM there is lowered muscle tone. The activity of the glymphatic system occurs and the level of brain activity are also deciding factors.

Question 75

Awake

Answer 75

This is when the fast frequency brain wave activity occurs. The different parts of the waking brain processing different streams of information in different ways at different times.

Question 76

Stage 2 (Light Sleep)

Answer 76

At this point sleep spindles (types of brain waves) begin to form, the brain is shielded from external noise, the sleep spindles become more powerful and frequent and the person that is sleeping is more resilient to external noises.

Question 77

Stages 3 & 4 (Deepest Stages of NREM Sleep)

Answer 77

At this point slow wave sleep occurs due to the synchronicity in neuronal activity (sleep spindles).

Question 78

REM Sleep

Answer 78

This is the deepest level of sleep. Despite this it looks similar to being awake with fast frequency brain waves. This is known as paradoxical sleep as the brain appear awake while the body is asleep. The brain activity during this stage isn’t different to awake brain activity. Before dreaming begins you are paralysed by signals from the brain stem signaling down the spinal cord which prevents dream experiences from being acted out physically.

Question 79

Sleep Time

Answer 79

8 hours of sleep is typical which usually occurs in 5, 90 minute cycles. This can differ in the amount required with some people needing less and others needing more as well as whether they sleep/wake early/late which is strongly genetically influenced. Deep NREM is when the glymphatic system is most active in cycles 1-3. Light NREM increases from cycles 3-5. REM is most prevalent in cycles 4 and 5.

Question 80

Sleep & Learning

Answer 80

In 2014 researches showed that sleep after learning encourages neuronal growth. Dendritic spines are tiny protrusion from neurons that connect to other neurons to facilitate the passage of information across synapses. Brain cells that activated when a task was learned were reactivated during slow-wave deep sleep (NREM). Neuronal replay (sleeping brain rehearses tasks learned during the day) is important for growing specific connections between neurons. Sleep deprivation can after learning can prevent dendritic spine growth.

Question 81

NREM Sleep & Learning

Answer 81

The hippocampus is the informational inbox of the brain (short term). It has a limited capacity and is the active site of neuronal birth. Deep NREM sleep (stages 3 and 4) moves memories moves short-term storage to a more permanent, safer, long-term storage location. Light NREM sleep (stage 2) is important before learning as it frees up storage space for more learning. There is a 40% deficit in the ability to make new memories without sleep. Prolonged sleep deprivation affects the birth of new neurons in the hippocampus.

Question 82

REM Sleep Dreaming & Learning

Answer 82

This is only bound in birds and mammals meaning it has evolved twice. Compared to great apes humans sleep less however more of human sleep is devoted to REM sleep (9% vs 25%). The brain activity during this stage isn’t different to awake brain activity. During REM sleep many commands for movements fly around the brain which underlies the movement experienced in dreams. During REM sleep signals from different emotions, feeling and memories are played out within the brain in which the stress hormone noradrenaline is not released allowing the ability to replay events and emotions without triggering a stress related response.

Question 83

Benefits of REM Sleep

Answer 83

The 2 purposes of this type of sleep is modulating emotional/mental health and problem solving/creativity. This is critical for emotional regulation, reading facial expression/body language, problem solving and creativity. This integration of knowledge allows for association networks to be built helping to find novel links between seemingly unrelated pieces of information. All of these benefits are higher order and done by the cerebral hemisphere. This also allows for the playing out of emotions, memories and events without a stress response being triggered allowing you to potentially gain emotional closure of traumatic experiences.

Question 84

Sleep Cycles & Learning

Answer 84

In a wakeful state information is stored in short-term storage. During deep NREM sleep this information is transferred into long-term storage. During REM sleep the information is integrated.

Question 85

Sleep Deprivation

Answer 85

After 18 hours of this reaction time increases and decision making, maths processing ability and spatial awareness deteriorates. After 24 hours your reaction time triples and you may experience micro-sleeps (10-20 seconds). After 48 hours of sleep deprivation you may experience hallucination and behaviour may resemble psychosis.

Question 86

Sleep Time Issues

Answer 86

Less than 7 hours of sleep per day decreases testosterone, testicle size and sperm count in men whereas for women it reduces follicular-releasing hormone, increases abnormal menstrual cycles and increases infertility issues. It can increase the development of coronary heart disease and physiological stress (high blood pressure leading to stroke or heart attack). This disrupts appetite increasing ghrelin and decreasing leptin making you hungrier potentially causing obesity. It can cause a decrease in immune system effectiveness especially more forms of tumors (bowel, prostate, breast). It can distort gene activity which is involved in tumor promotion, inflammation and stress (cardiovascular system). It can also lead to anxiety and depression.