Nervous system Flashcards
What are the four main functions of the nervous system?
to receive information and transmit it to the CNS for processing
to integrate and analyse different sources of information
to make decisions
to send instructions to muscles and glands to: perform voluntary movement, influence endocrine function, and regulate unconscious activities via the ANS
What are the two main types of nerve cells in the nervous system?
neurons and neuroglia
Where are neurons located?
CNS and PNS
What are three main neuron subtypes?
unipolar, bipolar, multipolar
What is the function of neurons?
to generate action potentials for sending and receiving information
Where are neuroglia located?
CNS - astrocytes, microglia, ependymal cells, oligodendrocytes
PNS - Schwann cells, satellite cells
What are the functions of astrocytes?
to secure neurons to their blood supply
to regulate the external chemical environment of neurons by removing excess ions
to promote the re-uptake of neurotransmitters released in synaptic transmission
to form the blood-brain barrier
What is the function of microglia?
specialised macrophages capable of phagocytosis
protect neurons from pathogens
What are the functions of ependymal cells?
thought to be stem cells in the nervous system
create and secrete CSF and circulate it by cilia activity
involved in CSF reabsorption
What is the function of oligodendrocytes?
to produce myelin to coat axons of neurons in CNS
What are the functions of Schwann cells?
to produce myelin to coat axons of neurons in PNS
phagocytotic and remove debris to allow growth and regrowth of neurons
What are the functions of satellite cells?
to regulate external chemical environment of neurons, particularly calcium ions
thought to have a role in chronic pain as they are sensitive to injury and inflammation
What is a neurotransmitter?
a chemical released by a neuron to transmit an impulse across the synaptic cleft to another neuron
What is the structure and function of a neuron?
soma - contains a nucleus, mitochondria and ribosomes
dendrites - connect to other neurons and carry impulses to the soma
neurofibrils - transport cell material and facilitate axon movement and growth
axon - carries action potentials away from the soma
axon terminal - contains synaptic vesicles holding neurotransmitters
What is the resting potential of a neuron?
the potential difference across the membrane while the neuron is at rest
-70 mV
What causes the potential gradient across the cell membrane of a neuron?
cell membrane contains Na+ channels, K+ channels, and Na+/K+ pumps
pump actively transports 3 Na+ ions out of the cell for every 2 K+ ions transported into the cell
membrane more permeable to K+ ions
negatively charged anions inside neuron
cell membrane is polarised (negatively charged inside compared with outside)
What are the four main stages of an action potential?
depolarisation, repolarisation, hyperpolarisation, refractory period
What happens in depolarisation?
Na+ ion channels open when the cell membrane is deformed by a pressure change
Na+ ions diffuse into the cell
the membrane is depolarised and reaches the threshold value of –50 mV
positive feedback causes voltage-gated Na+ ion channels to open and many Na+ ions diffuse into the cell
the potential difference across the membrane reaches +40 mV
What happens in repolarisation?
Na+ ion channels close and K+ ion channels open
K+ ions diffuse out of the cell bringing the potential difference back to negative inside compared with the outside
What happens in hyperpolarisation?
the potential difference overshoots slightly
What is the refractory period?
the period after an action potential when a neuron will not respond to another stimulus
Na+/K+ pump restores the original resting potential and ionic concentrations
Why is an action potential referred to as an ‘all-or-nothing’ phenomenon?
the change in potential difference must reach +40 mV for the action potential to occur
a stimulus below the threshold will not produce an action potential
a stimulus above the threshold will produce a full action potential
What is saltatory conduction?
a method of rapid impulse transmission in myelinated neurons
the myelin sheath means that action potentials can only occur at the gaps between the Schwann cells
the action potential jumps from one node of Ranvier to the next
What are the two types of synaptic transmission?
electrical and chemical
What is electrical synaptic transmission?
the gap junction between the synaptic bulb and dendrite is much smaller than in a chemical synaptic transmission
the gap junction contains channels which cross the membranes of both neurons
the channels allow ions and small molecules to flow from one neuron to the other which enables depolarisation
What is chemical synaptic transmission?
more common form of transmission
slower and more complex
What are the stages of chemical synaptic transmission?
action potential arrives at the synaptic bulb
voltage-gated calcium ion channels open and calcium ions diffuse into the synaptic bulb
calcium ions cause synaptic vesicles to move to, and fuse with, the pre-synaptic membrane
neurotransmitter is released by exocytosis
neurotransmitters diffuse across the synaptic cleft and bind to receptor sites on sodium channels in the post-synaptic membrane
sodium channels open and sodium ions diffuse across the post-synaptic membrane into the post-synaptic neuron
if sufficient generator potentials combine then the potential across the post-synaptic membrane reaches the threshold potential
a new action potential is created in the post-synaptic neuron
What is the function of acetylcholinesterase?
an enzyme found in the synaptic cleft
hydrolyses acetylcholine to ethanoic acid and choline
this stops the transmission of signals, so the synapse doesn’t continue to produce action potentials in the post-synaptic neuron
ethanoic acid and choline diffuse back into the synaptic bulb and are recombined to acetylcholine using ATP from respiration in the mitochondria
the recycled acetylcholine is stored in synaptic vesicles for future use
What are the four main types of neurotransmitters?
acetylcholine, monoamines (biogenic amines), amino acids, neuropeptides
What are the functions of acetylcholine?
normally an excitatory function (SNS)
parasympathetic effect on some organs (e.g. reduces heart rate)
sometimes classed as a monoamine
What are the functions of monoamines?
synthesised from amino acids
include catecholamines (e.g. adrenaline and noradrenaline)
thought to mediate emotion, arousal and cognition
What are the functions of amino acid neurotransmitters?
inhibitory amino acids (IAA) or excitatory amino acids (EAA)
glycine is inhibitory in the spinal cord, brainstem and retina
glutamate is excitatory and involved in learning and memory
What are the functions of neuropeptides?
work at lower concentrations and are not recycled
effects last longer than other neurotransmitters
associated with analgesia, metabolism, reproduction, social behaviours, learning and memory
What are the two main divisions of the nervous system?
central nervous system (CNS) and peripheral nervous system (PNS)
What are the two divisions of the CNS?
brain and spinal cord
What are the two divisions of the PNS?
sensory and motor
What is the function of the sensory division of the PNS?
to carry information from sensory receptors and special sense organs to the CNS
What are the two divisions of the motor division of the PNS?
somatic nervous system - innervates skeletal muscles under voluntary control
autonomic nervous system - involuntary regulation of muscles and glands
What are the two divisions of the autonomic nervous system?
sympathetic - excitatory, speeds up processes, exceptions exist
parasympathetic - inhibitory, slows down processes, exceptions exist
Nerve fibres are grouped into which two major tracts?
corpus callosum - joins the two sides of the brain
internal capsule - consists of both sensory and motor fibres that carry information to and from the cerebral cortex
What is grey matter?
neuronal bodies
mainly around the outside of the brain with a convoluted surface to increase SA for brain cells
concerned with higher functions
clumps of grey matter deep within the brain
What is white matter?
neuronal axons
connects different parts of the brain by carrying information in and out
spinal cord connects to the base of the brain and runs down within the spinal column
How is the distribution of grey and white matter different in the brain and spinal cord?
grey matter is within the centre of the spinal cord
white matter is around the outside of the spinal cord
What are the three parts of the brain?
forebrain - diencephalon, cerebrum
midbrain - tracts of nerve fibres, nuclei of cranial nerves
hindbrain - pons, medulla oblongata, cerebellum
What is the forebrain?
largest section of the brain
associated with thermoregulation, reproduction, eating, sleeping, cognition and emotional responses
The diencephalon is composed of what three parts?
thalamus, hypothalamus, epithalamus
What is the thalamus?
relay centre for nervous impulses moving to and from the cerebrum
large mass of grey matter positioned deep within the brain on either side
all sensory pathways go via the thalamus to be processed and relayed to the appropriate area of the cerebral cortex (except olfaction)
role in processing painful stimuli, temperature and attention with the RAS
What is the hypothalamus?
lies below the thalamus
includes several nuclei and tracts of axons
What are the three groups of hypothalamic functions?
control of the autonomic nervous system
control of the neuro-endocrine system
control of the limbic system
What is the pituitary gland?
small pea-sized extension below the hypothalamus
part of the endocrine system
links the nervous and endocrine systems
What is the epithalamus?
composed primarily of the pineal gland and the habenula
What is the pineal gland?
secretes serotonin in the day and melatonin at night to regulate the sleep/wake cycle
the large pineal gland in childhood is thought to inhibit the onset of puberty by secreting melatonin in high amounts before shrinking to a small size in adulthood
What is the habenula?
a relay from the limbic system
deals with sleep, stress, pain and reinforcement processing
What are the five groups of thalamic nuclei?
medial geniculate, lateral geniculate, lateral dorsal, mediodorsal, ventrolateral
What is the function of the medial geniculate?
relays auditory information from the midbrain to the primary auditory cortex
What is the function of the lateral geniculate?
relays visual information from the retina to the visual cortex
What is the function of the lateral dorsal?
works with the limbic system to form memories
What is the function of the mediodorsal?
works with the limbic system and prefrontal cortex to manage cognitive processes (e.g. reasoning, thoughts and mood)
What is the function of the ventrolateral?
relays signals from the cerebellum to the primary motor cortex in coordinating movement
What are the eleven groups of hypothalamic nuclei?
paraventricular, preoptic, anterior, suprachiasmatic, supraoptic, dorsomedial, ventromedial, arcuate, posterior, mamillary, lateral
What are the functions of the paraventricular?
fluid regulation, anterior pituitary control, oxytocin production
What are the functions of the preoptic?
thermoregulation, sexual arousal
What are the functions of the anterior?
thermoregulation, sexual arousal
What is the function of the suprachiasmatic?
circadian rhythms (e.g. sleep/wake cycle)
What are the functions of the supraoptic?
fluid regulation, anterior pituitary gland control, oxytocin production
What is the function of the dorsomedial?
emotional expression
What are the functions of the ventromedial?
appetite/hunger, satiety, fear and aggression
What are the functions of the arcuate?
growth, dopamine release
What is the function of the posterior?
thermoregulation
What are the functions of the mamillary?
emotion (via the limbic system), recognition memory
What is the function of the lateral?
hunger
What is the structure of the cerebrum?
consists of the cerebral cortex (grey matter) and underlying white matter, basal nuclei and limbic system
cerebral cortex and some white matter are folded into gyri to maximise surface area
longitudinal fissure divides the cerebrum into two cerebral hemispheres
cerebrum is further divided into five functional lobes by sulci
What are the five lobes of the brain?
frontal lobe, parietal lobe, occipital lobe, temporal lobe, insular lobe
What is the frontal lobe?
regulates voluntary movements
pre-motor cortex enables planning and sequencing of movement
primary motor cortex enables muscles to work in synergy for coordinated movement
neuronal axons in primary motor cortex extend to the spinal cord and down to connect with spinal nerves
Broca’s area located in the frontal lobe
prefrontal cortex involved in higher cognitive functions (reasoning, understanding, foresight and thinking)
it has extensive connections with the other lobes and is associated with personality
What is the parietal lobe?
processes sensory information
primary somatosensory cortex processes sensations of touch, vibration and proprioception
this is located beside the primary motor cortex - enables brain to respond rapidly
somatosensory association area processes stereognosis (recognition of an object by feeling shape, texture and temperature)
parieto-occipital association areas (mainly in right parietal lobe) process spatial perception
left parietal lobe involved in calculations, writing and reading
optic nerve pathways pass through the parietal lobe
What is the insular (fifth) lobe?
small area of dense tissue positioned under the temporal, frontal and parietal lobes
located under arteries and veins - difficult to isolate and access
What is the temporal lobe?
processes special senses, particularly gustation, olfaction and audition
roles in learning, memory, visual recognition and emotional actions
primary auditory cortex interprets volume and tone of sound, and links with Wernicke’s area to interpret spoken language
medial areas of the temporal lobe integrate into the limbic system with learning, memory and emotion
The insular lobe is thought to be responsible for which functions?
thermosensation (perception of temperature)
nociception (perception of pain)
somatosensation (sensations originating mainly in the skin including proprioception, touch and temperature)
viscerosensation (sensations originating in internal organs including pain, palpitations and spasms)
gustation (taste)
role in human emotions and associated behaviours
The insular lobe is thought to be responsible for which functions?
thermosensation (perception of temperature)
nociception (perception of pain)
somatosensation (sensations originating mainly in the skin including proprioception, touch and temperature)
viscerosensation (sensations originating in internal organs including pain, palpitations and spasms)
gustation (taste)
role in human emotions and associated behaviours
What are the basal nuclei/ganglia?
nuclei of grey matter buried within the white matter
include the corpus striatum (caudate nucleus, putamen and globus pallidus), substantia nigra and subthalamic nucleus
role in motor and thought control and inhibit muscle tone
What is the limbic system?
borders the brainstem
focuses on emotional state, instinct and motivation
links into the olfactory system, hypothalamus, midbrain and reticular formation
What are the structures of the limbic system?
amygdala, hippocampus, septum pellucidum, cingulate gyrus, insula, parahippocampal gyrus, mamillary bodies
What are the functions of the amygdala?
contributes to storage of emotional experiences as memories
regulates emotional learning
responds to harmful stimuli
processes distress
recognises and evaluates other emotive stimuli (e.g. facial expressions)
What are the functions of the hippocampus?
associated with formation of short-term and long-term memory
organises sensory and cognitive experiences for storage in the frontal and temporal lobes
What is the difference between short-term and long-term memory?
short-term memory involves quick recall over secs and mins
long-term memory involves memory consolidation
Long-term memory is further subdivided into which two types of memory?
declarative memory - recalling personal experiences and language, facilitated by hippocampus
procedural memory - related to learning and recalling how to complete a task, facilitated by basal nuclei
What is the septum pellucidum?
situated between the lateral ventricles at the midline of the brain
comprises myelinated axons connecting parts of the limbic system
when it is damaged/malformed people experience disorders relating to age, pleasure and mood
What is the function of the cingulate gyrus?
thought to integrate emotion and sensory experiences (e.g. pain sensation and emotional response)
What is the function of the parahippocampal gyrus?
processes declarative memory alongside the hippocampus
What is the function of the mamillary bodies?
thought to be a relay centre with a distinct role in memory operations
What is the midbrain?
joins the part of the brain containing the thalamus and hypothalamus with the pons and medulla oblongata
these parts of the brain contain the nuclei for the cranial nerves
What does the midbrain consist of?
corticospinal tracts and reticulospinal tracts
cranial nerves responsible for eye movement
nuclei of cranial nerves for the response to auditory and visual stimuli
What is the substantia nigra?
component of the midbrain
works with the basal nuclei to regulate movement by inhibiting the neurotransmitter/hormone dopamine produced in the substantia nigra
What does the hindbrain consist of?
pons, medulla oblongata, cerebellum
What is the pons?
anterior to the cerebellum, inferior to the midbrain and superior to the medulla
consists of nerve fibres which connect the two cerebellar hemispheres and fibres passing between the higher levels of the brain and the spinal cord
nuclei act as relay stations and some are associated with cranial nerves
regulates breathing through the pneumotaxic and apneustic centres
What is the medulla oblongata?
links the brain with the spinal cord and fits just within the cranium
grey matter lies centrally surrounded by white matter
nuclei act as renal stations for sensory information from spinal cord
medullary pyramids are where corticospinal and sensory pathways cross over from left to right and vice versa (decussation)
Which vital centres involved in coordination of the ANS are contained in the medulla oblongata?
cardiac centre - regulates heart rate and force of contraction
respiratory centre - regulates the pattern of breathing
vasomotor centre - regulates the diameter of blood vessels
reflex centres - vomiting, coughing, sneezing and swallowing
What is the cerebellum?
coordinates muscles and regulates muscle tone and posture
contributes to the fine-tuning of motor commands and sensorimotor adjustment needed for motor learning
receives information about muscle stretch, position of body parts and other coordinating information from the pons and cerebral cortex
relays back to the thalamus and cerebral cortex to respond appropriately
sends and receives information to non-motor regions of the cerebral cortex (e.g. prefrontal areas that regulate higher cognitive functions)
What is the reticular activating system (RAS)?
contains nuclei that connect throughout the forebrain, midbrain and hindbrain
controls arousal mechanisms used in maintaining consciousness and awake states for selective attention and purposeful responses
arousal regulation is not confined to the RAS
neural pathways descend to the spinal cord and ascend to the cerebral cortex, referred through the thalamus and suprachiasmatic nuclei (pair of neuron clusters in the hypothalamus situated directly above the optic chiasma of the hypothalamus)
the sleep/wake cycle is regulated by these processes
What is the reticular formation?
component of the RAS
core of nerve cell bodies which extend from the spinal cord through the medulla, pons and midbrain to the hypothalamus and thalamus and with connections to the cerebral cortex
What are the functions of the reticular formation?
skeletal muscle tone
autonomic control (forms part of the cardiovascular and respiratory centres in the pons and medulla)
somatic and visceral sensations
What is the difference between the spine and the spinal cord?
the spine refers to the spinal column and the mechanical structures that it is composed of (e.g. vertebrae, ligaments and tendons)
the spinal cord refers to the neural tissue encased within the spine which runs from the medulla (where it joins the brain at the level of the foramen magnum) to the level of the first or second lumbar vertebrae
The spinal cord runs down through the space in the spinal vertebrae within which three groups of neurons?
ascending (afferent) neurons - carry information up the spinal cord to the brain for processing
descending (efferent) neurons - carry instructions down the spinal cord from the brain to muscles and glands
interneurons (association neurons) - connect descending and ascending neurons
What are the two main enlargements of the spinal cord?
cervical enlargement (through the brachial plexus) - provides neurons for the arms lumbar enlargement (through the lumbosacral plexus) - provides neurons for the legs
What is the conus medullaris?
the tapered, lower end of the spinal cord
What is the cauda equina?
nerves resembling a horse’s tail which extend further down to the sacrum
The grey matter of the spinal cord is divided into which three horns?
anterior (ventral) horn, posterior (dorsal) horn, lateral horns
What is the anterior (ventral) horn?
contains cell bodies of the somatic motor nerves that stimulate skeletal muscle
run the length of the spinal cord
What is the posterior (dorsal) horn?
contains cell bodies of the somatic and autonomic sensory (afferent) neurons running the length of the spinal cord
What is the lateral horn?
contains cell bodies of the autonomic motor nerves that stimulate smooth muscle, cardiac muscle and glands
run from T2 to L1
link with the thoracolumbar ganglia running alongside the spinal cord and supplying the sympathetic nervous system
The white matter of the spinal cord is divided into which three columns?
anterior, posterior and lateral columns
subdivided into tracts (distinct sets of fibres going to or from the same place)
the name of the tracts indicates its path (e.g. corticospinal tract carries information from the cortex to the spinal cord)
What is the peripheral nervous system (PNS)?
nerves and ganglia outside the CNS (mainly cranial and spinal nerves)
carries information to and from the CNS where information is processed
two divisions - sensory division and motor division
What is the sensory division of the PNS?
carries sensory information via afferent neurons to the CNS for processing
this includes information from viscera of the thoracic and abdominal cavities (visceral sensations) and the skin, muscles, bones and joints (somatic sensations)
sensory input about the external and internal environment is received in the CNS
some sensory input is consciously perceived
some sensory input is carried directly to the brain by the cranial nerves
other input enters via the spinal nerves and is carried to the brain in various ascending tracts
What is a sensory receptor?
an organ which converts energy from one form (e.g. heart, light, pressure) into electrical energy which is transmitted through the sensory nerve fibres
The sensitivity to a particular modality varies according to which factors?
the density of distribution of the specific receptors for that modality/sensation
the degree of overlap of receptor fields
the size of the receptor fields
Receptors are divided into which three types?
enteroreceptors - internal environment
exteroreceptors - external environment located in the skin
proprioceptors - relative position of body parts
Sensory information is normally carried to the brain through which three sets of neurons?
first-, second- and third-order neurons
Sensory pathways are ascending and organised into which three distinct groups?
anterolateral pathways - temperature, pain and coarse touch sensations to the brain
medial lemniscal pathways - discriminative touch, vibration and proprioception sensations to the brain
spinocerebellar tracts (anterior and posterior) - sensations for muscles and tendons (stretch) to the cerebellum to coordinate skeletal muscle movement
What is the motor division of the PNS?
refers to nervous impulses sent from the CNS to cells/organs/muscles to initiate responses
subdivided into somatic (motor) and visceral (ANS)
What is the somatic nervous system?
responsible for voluntary control of body movements through stimulating contraction of skeletal muscles
motor cortex controls movement of the opposite side of the body and gives instructions to move different body parts
efferent neurons carry impulses to the muscles of the skeleton to stimulate muscle contraction and regulate movement
the area of the cortex concerned with movements of different body parts for a particular activity is related to the importance of that function
Movement is controlled at two levels through which three motor pathways?
direct pathway, indirect pathway, spinal cord (lower motor neuron)
What is the direct pathway?
sends upper motor neurons from the cerebral cortex to the spinal cord
impulses travel directly from the brain to the level of the spinal cord where it synapses with the lower motor neuron (corticospinal tracts)
carry impulses for fast or skilled movement
What is the indirect pathway?
consists of all the other nervous input to motor function and involves upper motor neurons
information passes through a series of synapses between some of the basal nuclei, cerebellum and motor cortex
carry impulses more slowly
How does the cell body of the lower motor neuron receive and integrate impulses?
direct and indirect pathways
sensory nerves carrying information from the tissues at that spinal level
association neurons carrying information from higher and lower segments of the spinal cord
How does the cell body of the lower motor neuron receive and integrate impulses?
direct and indirect pathways
sensory nerves carrying information from the tissues at that spinal level
association neurons carrying information from higher and lower segments of the spinal cord
What are the spinal reflexes?
involved in coordination of movement at a subconscious level
more complex reflexes involve spinal segments
associated nerves higher and lower in the spinal cord and/or on the opposite side of the spinal cord ensure correct coordination
spinal cord contains neural circuits that create walking movements
What is a reflex arc?
exemplifies integration and coordination at the spinal cord level
enables a very rapid response to noxious stimuli
more complex reflexes involve spinal segments and associated nerves higher and lower in the spinal cord and/or on the opposite side of the spinal cord
this ensures that actions are coordinated effectively
What is the autonomic nervous system (ANS)?
subconscious control system for visceral organs including those of the circulatory, digestive and respiratory systems
mainly motor pathways but include some sensory pathways
part of the PNS but has elements in the CNS
cranial and spinal nerves innervate the visceral organs, but the hypothalamus and medulla oblongata represent the control centres for the ANS
two divisions - sympathetic and parasympathetic nervous systems
The parasympathetic nervous system (PNS) decreases bodily activity through which actions?
slowing and pacing the heart rate
constricting bronchioles in the respiratory system
reducing respiratory rate
increasing motility of the digestive system and release of enzymes for digestion
promoting conversion of glucose to glycogen to create an energy store
relaxing GI sphincter muscles to facilitate movement of GI contents
relaxing the internal urethral sphincter muscle and contraction of the bladder to permit micturition
constricting pupils and bulging the lens of the eye to permit close vision
What is the name of the main nerve involved in the PNS?
vagus nerve
The sympathetic nervous system (SNS) decreases bodily activity through which actions?
increasing rate and force of myocardial contraction
vasodilating the coronary arteries
dilating the respiratory bronchioles
increasing respiratory rate
reducing the motility of the digestive system and release of digestive enzymes
constricting GI sphincter muscles to reduce GI activity
promoting conversion of glycogen to glucose for energy for increased activity
constricting the internal urethral sphincter muscle and relaxing the bladder to reduce micturition
producing renin for raising blood pressure
dilating pupils to increase light entering the eye for visual accuracy
What is the name of the main neurotransmitter involved in the SNS?
noradrenaline
Which spinal nerves running through the sympathetic ganglion chain are innervated by the SNS?
thoracic and lumbar spinal nerves
Which spinal nerves running through the sympathetic ganglion chain are innervated by the PNS?
cranial nerves and sacral spinal nerves
What is the difference between cranial and spinal nerves?
cranial nerves emerge directly from the brain and brainstem
spinal nerves emerge from the spinal cord
How many cranial nerves are there?
12
Where are the nuclei for the cranial nerves located within the brain?
nuclei for the first (olfactory) and second (optic) cranial nerves connect with parts of the forebrain concerned with smell and vision
the other cranial nerve nuclei are in the brainstem
What is cranial nerve I?
olfactory (sensory)
What is the function of the olfactory nerve?
olfaction - originates in olfactory mucosa in nasal cavity, terminates in olfactory bulb beneath the frontal lobe
What is cranial nerve II?
optic (sensory)
What is the function of the optic nerve?
vision - originates in retina, terminates in thalamus from where information is relayed to the visual cortex
What is cranial nerve III?
oculomotor (motor)
What is the function of the oculomotor nerve?
eye movement - opening eyelids, constricting pupil, focussing sight, proprioception,
originates in midbrain, terminates in muscles moving eye, iris and lens (ciliary muscles)
What is cranial nerve IV?
trochlear (motor)
What are the functions of the trochlear nerve?
eye movement and proprioception - originates in midbrain, terminates in oblique muscles of the eye
What is cranial nerve V?
trigeminal (motor and sensory)
What are the functions of the trigeminal nerve?
three divisions, originate in face and terminate in pons:
ophthalmic division - main sensory nerve of upper face for touch, temperature and pain
maxillary division - main sensory nerve of middle face for touch, temperature and pain
mandibular division - main sensory nerve of lower face for touch, temperature and pain, motor nerve stimulates the muscles for mastication
What is cranial nerve VI?
abducens (motor)
What is the function of the abducens nerve?
eye movement - originates in pons, terminates in lateral rectus muscles of the eye
What is cranial nerve VII?
facial (sensory and motor)
What are the functions of the facial nerve?
motor for muscles of facial expression, control of tear, nasal palatine, and salivary glands, originates in pons, terminates in facial muscles and glands, and muscles of middle ear
sensory for taste on anterior two thirds of tongue, originates in taste buds, terminates in thalamus
What is cranial nerve VIII?
vestibulocochlear (auditory) (sensory, but some motor)
What are the functions of the vestibulocochlear nerve?
hearing and balance (equilibrium)
sensory fibres originate in inner ear, terminates in pons and medulla oblongata
motor fibres originate in pons, terminate in outer hair cells in cochlea
What is cranial nerve IX?
glossopharyngeal (motor and sensory)
What are the functions of the glossopharyngeal nerve?
sensory - tongue and pharyngeal sensations (touch, pressure, taste and pain), outer ear sensations (touch, pain and temperature)
swallowing - saliva production, gagging, regulation of blood pressure and breathing
motor fibres originate in medulla oblongata and terminate in parotid salivary glands, glands of posterior tongue and stylopharyngeal muscle
sensory fibres originate in pharynx, middle and outer ear, posterior of tongue and internal carotid arteries
What is cranial nerve X?
vagus (motor and sensory)
What are the functions of the vagus nerve?
swallowing, taste, speech, respiratory, cardiovascular and GI regulation, hunger, satiety and intestinal discomfort
motor fibres originate in medulla oblongata and terminate in tongue, palate, pharynx, larynx, thorax and abdomen
sensory fibres originate in thorax, abdomen, root of the tongue, epiglottis, pharynx, larynx, outer ear and dura mater, terminate in medulla oblongata
What is cranial nerve XI?
spinal accessory (motor)
What are the functions of the spinal accessory nerve?
swallowing, head, neck and shoulder movement
originates in medulla oblongata and C1 to C5 or C6 of spinal cord, terminates in palate, pharynx and muscles of shoulder, head and neck
What is cranial nerve XII?
hypoglossal (motor)
What is the function of the hypoglossal nerve?
movements of the tongue for speech, moving food and swallowing
originates in medulla oblongata, terminates in muscles of the tongue
How many pairs of spinal nerves are there?
31
What are dermatomes?
areas of skin normally supplied by a single spinal nerve
What are the four plexuses?
cervical, brachial, lumbar, sacral
How do cells of the nervous system receive adequate nutrient and oxygen?
cerebral and spinal circulation distributes blood to parts of the CNS
CSF provides nutrition to parts of the CNS
What is the cerebral circulation?
two internal carotid arteries and the basilar arteries (arising from the two vertebral arteries) are the main arteries supplying the brain
the Circle of Willis is a circle of blood vessels that supplies blood to the different parts of the brain
it is formed from the main arteries supplying the brain joined by the connecting arteries
it enables regulation of blood flow and blood pressure in the brain and enables collateral circulation if arteries in the brain are narrowed/blocked
blood from the brain drains into sinuses (wide vessels wit no muscle in the walls) which return it to the main circulation at the internal jugular vein in the neck
What is the spinal circulation?
spinal cord is nourished by three main arteries and an arterial network
CSF supplies nutrients and oxygen to tissues of the brain and spinal cord
anterior spinal arteries supply the anterior two thirds of the spinal cord
posterior spinal arteries supply the posterior surface and form the vasocorona which supplies blood to the superficial layer of the anterolateral surface of the spinal cord
anterior and posterior spinal veins drain into radicular veins to return venous blood to the vertebral venous plexus
this drains blood into the larger veins in the neck, thorax and abdomen
The brain and spinal cord are protected by which components?
the bone surrounding them (cranium and spinal column), meninges, CSF, blood-brain barrier (BBB)
What are the meninges?
three layers of connective tissue that surround the brain and spinal cord
What are the three layers of the meninges?
dura mater, arachnoid mater, pia mater
What is the dura mater?
tough outermost layer
consist of the outer periosteal layer (absent from the spinal cord) and inner meningeal layer
these layers are closely joined except where they separate in the cranium to form venous sinuses
prevents friction against the skull, retains CSF within the CNS, and suspends the brain in the cranial cavity
What is the arachnoid mater?
middle layer
separated from the dura mater by the subdural space and from the pia mater by the subarachnoid space
arachnoid and pia mater are connected by web-like extensions
subarachnoid space is filled with CSF
arachnoid mater contains large blood vessels
arachnoid villi reabsorb CSF as it circulates through the CNS
What is the pia mater?
thin, impermeable fibrous membrane adjacent to the brain and spinal cord
ensures that CSF remains within the subarachnoid space
blood vessels pass through the pia mater to the brain and spinal cord
What is the function of the CSF?
to protect and nourish the CNS
What are the components of normal CSF?
glucose, protein and leucocytes (mainly lymphocytes, monocytes and macrophages)
How is CSF produced and circulated?
CSF is created in the choroid plexus
it moves through the foramen of Monro to the third ventricle
it then passes via three apertures (two lateral and one median) to the cerebellomedullary cistern
from here it circulates over the spinal cord and enters the subarachnoid space where it is reabsorbed
How does the BBB create a structural barrier between the circulatory system and the nervous system?
capillary endothelial cells in the brain are packed very tightly together with no fenestrations in the cell walls
capillary lumen has a reduced surface area
How does the BBB create a chemical barrier between the circulatory system and the nervous system?
capillary endothelial cells in the brain have many mitochondria for high energy production
specific proteins inhibit lipid-soluble drugs crossing from the blood into the brain by actively transporting them into the bloodstream
these cells contain drug-metabolising enzymes to eliminate/deactivate substances that pass before they reach CNS tissues
What are the two routes for substances to cross the BBB?
transport mechanisms control movement of water-soluble substances through ion channels, transport proteins, or transcytosis
fats move across by diffusion
How are drugs able to cross the BBB to treat an infection in the brain?
certain drug preparations can be given directly into the ventricles of the brain (intraventricular route) or subarachnoid space (intrathecal route)
What is neurogenesis?
the growth of new neuronal tissue
Neurogenesis appears to be limited to which areas of the brain where there are active stem cells?
hippocampus and olfactory bulb
What is the difference between neurogenesis in the CNS compared to the PNS?
damaged neurons in the CNS do not repair well
neurons in the PNS are better at adapting to injury by growing new axons and making new synaptic connections
Why is neurogenesis in the PNS more effective than neurogenesis in the CNS?
genetic programming - adult CNS neurons no longer express the gene for axonal growth, the same genes can be reactivated in adult PNS neurons
macrophages in the PNS remove cell debris
Schwann cells in the PNS provide optimal conditions to promote regeneration by enhancing cell adhesion molecules, the extracellular matrix, and neurotrophins
Which cells in the CNS inhibit neurogenesis in the CNS?
oligodendrocytes produce a substance called Nogo which inhibits axons extending to form new connections
astrocytes release more factors which inhibit axons extending in the presence of injured cells
Which processes modify and refine neuronal function and efficiency over time and as we develop?
synaptogenesis - formation of synapses between neurons
pruning - removal of unnecessary neuronal connections and strengthening important ones
apoptosis - programmed cell death
What is consciousness?
a state of explicit awareness dependent on both biological arousal in the brain, mainly by the RAS, and the processing of experiences (perception)
a person can process, interact and experience their surroundings, and is influenced by their state of mind
How is consciousness thought to be achieved?
both cerebral hemispheres function simultaneously
both CNS and PNS are involved
reticular formation receives signals from sources in the nervous system and directs them to the thalamus
reticular formation contains the RAS and regulates signals that go to the thalamus
thalamus directs signals out across the cerebral hemispheres to the cerebral cortex
thalamus communicates with the hypothalamus to regulate the sleep/wake cycle
thalamus stimulates prefrontal cortex which regulates perception and experience of the environment
limbic system integrates this to provide an emotional element to that response
What are the three states of human existence?
wakefulness, non-rapid eye movement (NREM) sleep, rapid eye movement (REM) sleep
What are the five types of brain waves?
gamma - wide awake and alert
beta - awake and active
alpha - awake and relaxed
theta - asleep
delta - deep sleep
What is non-rapid eye movement (NREM) sleep?
release of growth hormone for growth and development
proteins for repair and growth (anabolism) are often made in this stage
What is rapid eye movement (REM) sleep?
possible role in regulating energy metabolism in the brain
processes emotional experiences and newly learned information
role in language development and formation of long-term memory
What are the five stages within each sleep cycle?
NREM 1 (4%), NREM 2 (50%), NREM 3 (4-6%), NREM 4 (17-19%), REM 5 (23%)
What is NREM 1?
interim period between wakefulness and sleep
What is NREM 2?
drowsy - alpha waves fluctuate and slow, eyes roll, pupils constrict and dilate in 1-3 second intervals
light stage of sleep, reduced attentiveness
some perceptual distortions possible
What is NREM 3?
slow-wave sleep, delta waves present, reduced body movements
What is NREM 4?
high degree of immobility and intense external stimuli required to wake individual
large increases in growth hormone
What is REM 5?
characterised by dreaming, muscular relaxation, disappearance of muscle tone and high levels of physiological activity
A healthy night’s sleep should consist of approximately how many sleep cycles?
4-5 cycles
How does the hypothalamus regulate sleep?
determines the circadian rhythm
regulates sleep in the nervous system, influenced by social factors regarding time
triggered by light and melatonin from the pineal gland
How does the ascending reticular activating system (ARAS) regulate sleep?
sends signals to the forebrain and hypothalamus to regulate sleep
signals to the thalamus are forwarded to the cerebral cortex - pathways similar to consciousness pathways
How does the forebrain regulate sleep?
works with RAS to regulate NREM sleep
How does the pons regulate sleep?
regulates REM sleep and reactivates the brain from sleep
What three neurotransmitters/hormones from the pons are central to controlling sleep?
noradrenaline - arouses the cerebral cortex to achieve wakefulness, low levels are present in sleep states
acetylcholine - achieves wakefulness and regulates REM sleep, low levels are present in sleep states
serotonin - involved in regulating REM and NREM sleep
What are the social factors that regulate sleep?
exposure to light
social activities (e.g. regular meal times, regular times of going to bed and getting up, stress levels, emotional state, exercise)
What are the four key areas of the brain that contribute to a person’s mental health?
amygdala, hippocampus, anterior cingulate cortex, prefrontal cortex
How does the amygdala contribute to a person’s mental health?
involved with phobic experiences as it links fear with a previous unpleasant experience
that response can be relearnt if the person is exposed to the experience again and it is positive (part of the management of phobias and PTSD)
How does the hippocampus contribute to a person’s mental health?
memories are important to a person’s mental health-related quality of life
role in regulating mood
How does the anterior cingulate cortex contribute to a person’s mental health?
regulates emotional responses
influences feelings of motivation, focus and realisation
people can experience depression when anterior cingulate cortex works ineffectively
How does the prefrontal cortex contribute to a person’s mental health?
accesses short- and long-term memory and regulates the amygdala in times of heightened stress
How is serotonin involved in regulating mental health?
regulates mood and sleep
low serotonin levels linked with depression
some types of antidepressants promote the presence of serotonin within the synaptic cleft so that the receiving neuron works better in regulating mood
this is achieved by drugs that stop serotonin being recycled/reabsorbed back into the pre-synaptic neuron
