18. CNS Morphology 🧠Flashcards
What is the difference in the specificity of the responses brought about by the parasympathetic and sympathetic nervous systems?
Parasympathetic - localised Sympathetic - mass response
Describe the outflow of the sympathetic nervous system.
Thoracolumbar - T1 - L2/L3
Other than the dorsal and ventral horns, what other feature do parts of the thoracolumbar spinal cord have?
Lateral Horn - where the sympathetic preganglionic fibres originate
What is the difference between the White and Grey rami communicantes?
White - going into the sympathetic trunk Grey - going out of the sympathetic trunk
What is the difference in the direction of ventral and dorsal flow?
Ventral - OUTflow Dorsal – Inflow
What can happen to the preganglionic neuron once it reaches the sympathetic ganglion via the white ramus?
It can travel up and down the sympathetic trunk and synapse in another ganglion at a different level. It can synapse at that particular ganglion. It can go through the ganglion and synapse in a subsidiary ganglion (e.g. coeliac ganglion or superior mesenteric ganglion)
State the number of ganglia in each of the four regions.
Cervical = 3 Thoracic = 11/12 Lumbar = 4/5 Pelvic = 4/5
Where do the splanchnic nerves arise and where do they go?
They originate in the thorax and move down to the abdomen through the diaphragm. You get the greater, lesser and least splanchnic nerves.
Describe the outflow of the parasympathetic nervous system.
Craniosacral
State the levels of the sacral outflow and the nerves they go through.
S2-S4 Goes to pelvic viscera via pelvic splanchnic nerves
How many pairs of cranial nerves are there?
12
What four cranial nerves make up the cranial parasympathetic outflow?
Occulomotor, facial, glossopharyngeal, vagus
Where is the ganglion of the occulomotor nerve (III)?
Ciliary ganglion
What does the facial nerve (VII) innervate? State the ganglia of the facial nerve.
Facial muscles and two of the three salivary glands (submandibular and sublinguinal glands) Ganglia: submandibular and pteropalatine
What does the glossopharyngeal nerve (IX) innervate and where is its ganglion?
Innervates the third salivary gland - parotid gland Ganglion = Otic ganglion
What structure does the vagus nerve go through in the neck?
Carotid sheath - contains the carotid artery and internal jugular
State the two plexuses in the enteric nervous system and the layer in which they are found.
Submucosa = Meissner’s Plexus Myenteric plexus = Auerbach’s Plexus
What are the 6 parts of a neurological examination?
Appearance Mental State Gait and Station Motor System Cranial Nerves Sensation
What are the two ways you can do an EMG?
Intracellular - determine the difference in potential (EMF) between inside and outside the axon Extracellular - determine the difference in potential between two points (both outside the neuron) along a nerve
What can an EEG be used to diagnose?
Alzheimer’s, Epilepsy, Tumour
Cervical plexus
C1-C4 muscles in neck diaphragm Nerves : phrenic (C3, C4, C5) cranial nerves: accessory, hypoglossal
Brachial plexus
C5-T1 arm muscles, flexion and extension Nerves: axillary (C5, C6) musculocutaneous (C5, C6, C7) median (C5, C6, C7, C8, T1) ulnar (C8, T1) radial (C5, C6, C7, C8, T1)
Lumbar plexus
T12-L4 some low abdomen genitalia anterior and medial thigh (quads) medial surface of leg from knee to foot Nerves: femoral (L2, L3, L4) obturator
Sacral plexus
L4-S4 butt and low limb (sole of foot) external genitalia Nerves: sciatic (L4, L5, S1, S2, S3) tibial common fibular
cerebral cortex
-motor, sensory and association areas -all neurons in cortex are interneurons and not to be confused with sensory and motor neurons -two hemispheres
fissure
deep groove
gyri
folds
sulci
depressions separating gyri
What is the function of the thalamus?
-relay and processing center for information -information is sorted and edited
What is the function of the hypothalamus?
-hormones -homeostasis
What is the function of the midbrain?
-conduction between higher brain centers and spinal cord -regulates visual reflexes -controls alertness
What is the function of the pons?
–conduction between higher brain centers and spinal cord-assist medulla in breathing -reticular formation -Cranial nerves:V-VII trigeminal & facial
What is function of medulla oblongata?
-conduction between higher brain centers and spinal cord -sensory nuclei controlling skin and proprioceptors -major (motor) center controlling autonomic functions: heart rate, resp rate, blood vessel diameter etc. -Cranial nerves VII-XII
What is function of cerebellum?
-process information from cerebral motor cortex and vision and equilibrium pathways -motor control and coordination -muscle memory
limbic system components
hypothalamus, mammillary bodies. hippocampus, fornix, amygdaloid body
amygdaloid body
-heart rate in fight or flight response -linking emotions with memories
hippocampus
-learning -retrieval of long-term memories
basal nuclei
-caudate and lentiform nucleus -gray matter -subconscious control of skeletal muscle toon -coordinate learned movement patterns -povide general pattern and rythym for movements of trunk and limbs (example: swinging arms when walking or unconsciously stabilizing arm when picking up pencil)
superior colliculi (corpora quadrigemina)
-located at root of midbrain -receives visual inputs from thalamus -in response to visual stimuli: controls reflex movements of the eyes, head, and neck
inferior colliculi (corpora quadrigemina)
-located at root of midbrain -receives auditory input from medulla and pons -in response to auditory stimuli: controls reflex movements of head, neck and trunk
What is the basic function(s) of the frontal lobe?
-executive function -motor function, problem solving, spontaneity, memory, language, initiation, judgement, impulse control, and social and sexual behavior
What is the basic function(s) of the parietal lobe?
-touch -integrates sensory info
What is the basic function(s) of the temporal lobe?
-high level auditory processing
What is the basic function(s) of the occipital lobe?
-vision center
What structures make up the brainstem?
-medulla oblongata -pons -midbrain
What structures make up the hindbrain?
-medulla oblongata -cerebellum -pons
What structures make up the forebrain?
-cerebrum -diencephalon
What is included in the midbrain?
-cerebral aqueduct -quadragemini (superior & inferior colliculus)
How much oxygen is supplied to the brain per minute?
55 ml/100g of tissue/min
Why is there a vast surplus of glucose delivery to the brain?
Because the brain can only metabolise glucose Ketone bodies can be metabolized if there is a shortage of glucose but glucose is the main nutrient
Blood glucose below what value will lead to loss of consciousness, coma and death?
2 mM
On what levels do you get regulation of cerebral blood flow?
Mechanisms affecting total cerebral blood flow Mechanisms that relate activity to requirement in specific brain regions by altered localised blood flow
Between what range in mean arterial blood pressure can autoregulation maintain a constant cerebral blood flow?
60-160 mm Hg
Name one important factor to do with the smooth muscle lining arterioles that allows regulation of blood flow.
Myogenic Mechanism – when the smooth muscle surrounding arterioles is stretched, it will contract to maintain a constant blood flow This occurs when there is a change in blood pressure in the body
What are the two types of control of cerebral blood flow regulation?
Neural and Chemical
What are the four types of neural control of cerebral blood flow?
Sympathetic innervation of the main cerebral arteries – causes vasoconstriction when arterial blood pressure is high Parasympathetic (facial nerve) stimulation – can cause a little bit of vasodilation Central cortical neurons – neurons within the brain itself can release neurotransmitters such as catecholamines that cause vasoconstriction Dopaminergic neurons – produce vasoconstriction (important in regulating differential blood flow to areas of the brain that are more active)
What feature do capillaries in the brain have that allow them tocontract?
They are surrounded by pericytes, which are contractile cells They are a type of brain macrophage that have several functions e.g. contractile, immune function, transport properties
What do the dopaminergic neurons affecting cerebral blood flow innervate?
Pericytes around capillaries and smooth muscle around arterioles
Dopaminergic neurons cause contraction of pericytes via which receptors?
Aminergic and serotoninergic neurons
Which fibres innervate the main arteries in the brain?
Sympathetic fibres
Name some chemical factors that increase blood flow to particular tissues.
Carbon dioxide NO pH Anoxia Adenosine K+ Other (e.g. kinins, prostaglandins, histamine, endothelins)
How does change in pH affect blood flow?
The lower the pH (the higher the H+ concentration) the more the vesselvasodilates
Describe how carbon dioxide indirectly causes vasodilation in the cerebral vessels.
H+ ions can’t cross the blood-brain barrier but carbon dioxide can Carbon dioxide moves from the blood through the blood-brain barrier into the smooth muscle cells Within the smooth muscle cells, in the presence of carbonic anhydrase, the carbon dioxide reacts with water to form bicarbonate and H+ ions This internally generated H+ ions within the smooth muscle cells cause smooth muscle relaxation (vasodilation)
Describe how nitric oxide (NO) causes vasodilation.
Nitric oxide stimulates guanylyl cyclase Guanylyl cyclase converts GTP - cGMP cGMP causes vasodilation
Where is CSF produced?
Choroid plexus – these are specific cells associated with the ventricles (in particular the lateral ventricles)
What name is given to parts of the brain that receive blood flowlike anywhere else but do not have a blood-brain barrier?
Circumventricular organs
Describe the passage of CSF through the ventricular system.
CSF is produced by specialized ependymal cells of the choroid plexus (mainly in the lateral ventricles) From the lateral ventricles it goes through the foramen of Monro to the 3rd ventricle From the 3rd ventricles, CSF flows down the cerebral aqueduct to the 4th ventricle From the 4th ventricle it enters the subarachnoid space (via medial and lateral apertures) and eventually drains back into the venous system via arachnoid granulation
What is the volume of CSF in a normal person?
80-150 mL
What is the volume of CSF formed per day?
450 mL/day
State three functions of the CSF.
Protection (chemical and physical) Nutrient provision to neurons Transport of molecules
Describe the structure of the blood-brain barrier. Which cells areinvolved?
The capillaries in the brain have endothelial cells with very tight junctions so there is tight control of what can pass through the wall of the capillary The capillaries are also surrounded by pericytes with end-feet runningalong the capillary wall When the pericytes contract they make it more likely for the molecules to leave the capillary
What type of molecule can cross the blood-brain barrier easily?
Lipophilic molecules
How do water and glucose cross the blood-brain barrier?
Water pass through aquaporin molecules Glucose passes through Glut 1 transporters
Name three circumventricular organs.
Median eminence region of the hypothalamus Subfornical organ Organum vasculosum of the lamina terminalis
State four components that have a lower concentration in the CSF than the plasma.
K+ Calcium Amino acids Bicarbonate
State two components that have a higher concentration in the CSF than the plasma.
Magnesium Chloride
How is the osmolarity different between the CSF and the plasma?
The same
How is the pH different in the CSF compared to the plasma?
CSF is slightly more acidic
Differences between blood and CSF?
o CSF has fewer cells o CSF has less protein o CSF has lower concentration of K+ and Ca2+ o CSF has higher concentration of magnesium and chloride
Volume and flow rate of CSF?
o Volume: 150 mL o Flow: 500 mL/day
Hydrocephalus is? ______ - all 4 ventricles are affected o Caused by _________ over the brain: • • • • _______ - not all ventricles enlarged o Cause: _____ caused by: • • • Signs and Symptoms: 1. 2. 3. 4. 5. Treatment: 1. 2. 3.
Hydrocephalus: an abnormal increase in the amount of cerebrospinal fluid within the ventricles in the brain COMMUNICATING - all 4 ventricles are affected o Caused by block in CSF absorption or CSF flow over the brain: • Meningitis • Head Injury • Congenital • Haemorrhage (sub-arachnoid) NON-COMMUNICATING - not all ventricles enlarged o Cause: block in the ventricular system caused by: • Aqueduct stenosis • Ventricular tumours • Paraventricular tumours Signs and Symptoms: o Headache o Drowsiness o Blackouts o Raised intracranial pressure o Increased head circumference (in children) Treatment: o Remove cause e.g. papilloma o Divert CSF e.g. shunt o Open alternative pathway e.g. ventriculostomy
• Meninges o EPIDURAL/EXTRADURAL HAEMORRHAGE - usually _______ between the _______ o SUBDURAL HAEMORRAHGE - usually due to _____between the _____ o Distinguishing between the two: • Epidural - symptoms arise ____ • Subdural - symptoms ____ • Meningitis o Structures affected: ___ and ____ o CSF analysis used to distinguish between bacterial and viral: • BACTERIAL 1. 2. 3. 4. 5. • VIRAL 1. 2. 3. 4. 5.
• Meninges o EPIDURAL/EXTRADURAL HAEMORRHAGE - usually due to a damaged meningeal artery between the skull and the dura after head trauma o SUBDURAL HAEMORRAHGE - usually due to a damaged vein between the dura and arachnoid membrane o Distinguishing between the two: • Epidural - symptoms arise promptly after the bleeding begins • Subdural - symptoms may be delayed • Meningitis o Structures affected: Pia Mater and Subarachnoid Space o CSF analysis used to distinguish between bacterial and viral: • BACTERIAL ♣ HIGH WBC count ♣ NEUTROPHILS predominate ♣ Protein concentration = INCREASED ♣ Glucose concentration = INCREASED ♣ Bacteria may be identifiable - cloudy CSF • VIRAL ♣ HIGH WBC count ♣ LYMPHOCYTES predominate ♣ Protein concentration = normal ♣ Glucose concentration = normal ♣ Viral identification is unlikely
Fxn of frontal lobe?
- reasoning, problem solving, parts of speech, movement, and emotion (prefrontal: is planning, consequences of action)
Fxn of parietal lobe?
- perception of stimuli, orientation, recognition of stimuli and movement
Fxn of temporal lobe?
- memory, perception/recognition of auditory stimuli and speech
Fxn of occipital lobe?
- visual processing
Fxn of basal ganglia?
- voluntary motor movemnt, coordination, cognition and emotion
Cerebrum fxn?
- cerebral cortex: higher brain fxn: thought and action, controls all voluntary activity with help of cerebellum
Limbic system?
- thalamus, hypothalamus, and amygdala(in temporal lobe, memory, emotion and fear), and hippocampus (learning, memory, converts short term memory into long memory)
Diencephalon 2 parts and fxns?
- thalamus: deep in forebrain, processes almost all of sensory and motor info, relays info to and from overlying cortex, last relay site to all sensory input (except olfaction) before this info reaches cortex - hypothalamus: base of forebrain - controls homeostasis
Brainstem parts and fxn?
- contrls vital life fxns: breathing, HR and BP - midbrain: controls eye movement, relays visual and auditory info - pons: regulates breathing, relay station b/t cerebral hemisphere and medulla (involved in motor control and sensory output) - medulla oblongata: extension of spinal cord, regulates vital body fxns (along with pons - HR, breathing, autonomic centers, swallowing, coughing)
Fxn of cerebellum?
- maintains posture and balance, coord voluntary movement and control of head and eye movement
What are the brain motor descending pathways?
- pyramidal (fine, isolated precise movements) - extrapyramidal (gross synergistic movements)
Fxn of pyramidal system (direct pathway)?
- directly reaches target in brainstem or spinal cord with only 1 synapse with cranial nerve (in brainstem) with the lower motor neuron in the spinal cord (anterior horn), direct connection allows for faster impulse transmission fxn: controls fine, precise body movements of head, neck and limbs (muscle groups that require concentration and conscious control)
What is the extrapyramidal system? Fxn?
- indirect pathway (multisynaptic): don’t reach their targets by traveling through the pyramids and they make more than 1 synapse. - fxn: controls gross movement and autonomic movements involving larger muscles groups. - selective activation of movement and suppression of other movements ot prevent erratic movements - initiate movements, and coordiante movements - coord with ANS to help with posture and muscle tone, has more effect on midline structures instead of peripheral, controls facial expression (why parkinson pt has little facial expression)
What makes up the PNS? FXN?
- CNs and spinal nerves - fxn: communication lines b/t CNS and rest of body
What makes up the CNS? FXN?
- brain and spinal cors - integrative and control centers
Sensory (afferent) division of PNS?
- somatic and visceral sensory nerve fibers - conducts impulses from receptors to CNS
Motor (efferent) division of PNS? 2 sep divisions of this?
- motor nerve fibers - conducts impulses from the CNS to effectors (muscles and glands) - ANS and SNS
ANS fxn?
- visceral motor control (involuntary) - conducts impulses from CNS to cardiac muscles, smooth muscles and glands - has sympathetic division: mobilizes body systems during activity - has parasympathetic: conserves energy, promtes housekeeping fxns during rest
SNS fxn?
- somatic motor (voluntary) - conducts impulses from CNS to skeletal muscles
How does neural tube form?
- neural plate forms from surface ectoderm 2. neural plate invaginates, forming neural groove, flanked by neural folds 3. neural fold cells migrate to form neural crest, which will form much of PNS and many other structures
Prosencephalon (forebrain) will become?
- telencephalon: cerebrum - diencephalon (thalamus, hypothalamus)
Mensencephalon (midbrain) will become?
- brain stem
Rhombencephalon (hindbrain) becomes?
- Metencephalon: brain stem: pons, and cerebellum - myelencephalon: brain stem: medulla oblongata
How does an AP work?
- all or none event: threshold voltage is usually 15 mV positive to resting potential - initiated by depolarization, APs can be induced in nerve and muscle by extrinsic (percutaneous) sim - - APs don’t summate, info coded by frequency not amplitude - have constant conduction velocity - APs only occur at nodes: increased velocity, and energy conservation
What fibers conduct faster? large or small diameter? Myelinated or unmyelinated?
- fibers with large diameter conduct faster than small fibers - myelinated fibers conduct faster than unmyelinated fibers
Role of ion channels in AP?
- depolarization causes Na cahnnels to open (can cause activation and inactivation) - inactivated channels don’t pass any ions - K+ channels show activation but not inactivation - fall in current at end is deactivation
Parts of brain involved in speech and language comprehension?
- broca’s area - wernicke’s area
How does edema occur in CNS? Why is this such a problem?
- increase in tissue mass that results from excess movement of body fluid from vascular compartment or its abnormal retention in tissue - problem in brain and spinal cord b/c: enclosed space, lack of lymphatics, and lack of anastomoses in venous drainage
What is vasogenic edema?
- occurs when blood-brain barrier is upset: inflammation due to infection, toxic agents that damage capillary endothelium, abnorm capillaries assoc with malignant neoplasm - leakage of protein fluid into interstitial - leads to swelling - plasma filtrate accum alters ionic balance and impairs fxn
What is cytotoxic edema? Causes?
- intracellular phenomenon - hypoxia: cardiac arrest, near drowning, strangulation, focal edema due to blockage of an end artery - toxic substances that: impair Na+/K+ pump, impair production of ATP
Tx of CNS edema?
- swelling often caused by both cytotoxic and vasogenic - tx is diff - if cytotoxicity the cause - can give IV bolus of hypertonic soln such as mannitol to draw water into vasculature and out of the brain - Can’t do this for vasogenic because fluid would be drawn into interstitial space and increase swelling
Normal ICP? Causes of IICP?
- norm: 5-15 mm Hg - IICP: tumor growth edema excess CSF hemorrhage - contents of cranium can cause IICP (tissue of CNS, CSF, blood)
Clinical hallmarks of IICP?
- headache - vomiting - papilledema: don’t do spinal tap (brain will herniate)
Stage 1 of IICP?
- since brain is encased in cranium, only way pressure can be relieved is by decreasing cranial contents, most readily displaced is CSF, and if ICP is still high, cerebral blood volume is altered: stage 1: vasoconstriction and external compression of venous system. Compensating, so only few sxs
Stage 2 of IICP?
- if ICP continues to increase, may exceed brain’s ability to adjust stage 2: IICP (gradually rising) causes a decrease of O2 of neural tissue - systemic vasoconstriciton occurs to increase BP to get blood to brain - clinical manifestations transient: episodes of confusion, restlessness, drowsiness, and slight pupillary and breathing changes (hypoventilation)
Stage 3 of IICP?
- when ICP begins to = arterial pressure, there is a lack of compensation - beginning decompensation stage 3: hypoxia and hypercapnia - lead to cytotoxic edema, decreasing levels of arousal, widening pulse pressure, may begin Cheynes-stokes respirations, bradycardia: due to increased pressure in carotid arteries, pupils are small and sluggish * surgical or medical intervention is needed!!
Stage 4 of IICP?
- When all compensatory mech have been exhausted - stage 4: dramatic rise in ICP in a short time. Autoregulation is lost, and get vasodilation, further increasing intracranial volume. Decreased cerebral perfusion = severe hypoxia and acidosis - brain contents shift (herniate) from area of high pressure to areas of lower pressure - decreased blood flow - small hemorrhages develop, ipsilateral pupil dilation and fixation, progressing to bilateral fixed and dilate pupils - when mean systolic arterial pressure equals ICP - cerebral blood flow ceases
What arteries make up 30% of CBF?
- Basilar and vertebral arteries (verterbrals turn into basilar)
Fxn of blood brain barrier?
- prevent infections - protection from circulating AAs and otehr molecules that might act as neurotransmitters - protects against drugs and abx - has tight jxns and astrocyte foot processes that secure BBB
Purpose of cervical and lumbar enlargements?
- for innervation of upper and lower extremiteis
Where would you perform a lumbar puncture at? Why?
- b/t L4 and L5 b/c spinal cord has already ended (just nerve fibers), easy access of subarachnoid space
Motor neurons route?
- from ventral horn through ventral root and out of spinal nerve - (somatic and visceral motor neurons)
sensory neruon route
- Visceral and somatic sensory neurons coming in - into doral root ganglion (cell bodies) - and then into dorsal horn
Classification of somatic sensations?
-mechanoreceptive: stimulated by mechanical displacement: tactile position or propioceptive - thermoreceptive - nociceptive: (touching hot stove - pull hand back)
Spinocerebellar pathway?
- remains on ipsilateral side up spinal cord and brainstem into cerebellum
2 types of pain fibers?
- neo-spinothalamic tract: fast- sharp pain, feel pain immediately, travel up through reticular formation along with paleo-spinothalamic tract and into ventrobasal compelx and posterior nuclear group - paleo-spinothalamic tract: slow - chronic pain, travel up through reticular formation into intralaminar nuclei of thalamus
Process of reflex?
1 - afferent impulses from stretch receptor to spinal cord 2 - efferent impulses to alpha motor neurons cause contraction of stretched muscle that resists/reverses the stretch 3 - efferent impulses to antagonist muscles are dampened (reciprocal inhibition)
Signs of UMNLs?
- paralysis or weakness of movements of the affected side but gross movements may be produced. No muscles atrophy seen initially but later on some disuse atrophy may occur 2. Babinski sign in present: great toe dorsiflexes and other toes fan outward in response to sensory stimulation along lateral aspect of sole. Normal response = plantar flexion of all toes 3. loss of performance of fine skilled voluntary movements esp at distal end of limbs (babinski) 4. superficial abdominal reflexes and cremasteric reflex are absent 5. spasticity or hypertonicity of muscles 6. clasp-knife rxn: initial higher resistance to movement is followed by lesser resistance 7. exaggerated DTRs and clonus may be present
Signs of LMNLs?
- flaccid paralysis of muscles supplied 2. atrophy of muscles supplied 3. loss of reflexes of muscles supplied 4. muscle fasciculations 5. muslce fibrillation 6. muscle contracture 7. presence of muscle wasting 8. rxn of degeneration to response to electrical stimulus
Neurotransmitters in SNS?
- initially acetylcholine is NT - at ganglion and adrenal medulla but NE and E are NTs that act on target (smooth muscle - gut, glands, cardiac muscle, blood vessel)
Neurotransmitters of PNS?
Acetylcholine is NT at both ganglion and target organ (smooth muscle, glands, cardiac muscle, and blood vessels)
Parasympathetic nerve orgins?
-Cranial - sacral
sympathetic nerve origins?
- sympathetic ganglion in Thoracic and lumbar
Visceral reflex arc?
- stimulus - travels up through sensory receptor through dorsal root ganglion into dorsal horn and integration center - and then ventral horn - to preganglionic axon which next travels to autonomic ganglion and then post ganglionic axon and to visceral effector - get a response
What are neurotransmitters?
- chemical substances that excite, inhibit or modify response of cerebral cells. - these include AAs, neuropeptides, and monoamines/
GABA acts on what sites? FXN of GABA?
- GABA (gamma-aminobutyric acid), AAs: glutamine, and glycine are NTs at most CNS synapses - GABA: mediates most synaptic inhibition in CNS
3 processes a released transmitter can undergo?
- 1: can be broken down into inactive substances by enzymes - 2: can be taken back up into presynaptic neuron (reuptake) - 3: it can diffuse into intercellular fluid until its concentration is too low to influence postsynaptic excitability
Catecholamines?
- NE, epi, dopamine
NE and epi fxn?
Catecholamines can cause excitation or inhibition of smooth muscle contraction depending on set, dose and type of receptor present - NE: potent excitatory activity and low inhibitory activity - Epi: potent excitatory and inhibitory agent - produce excitatory effects on alpha receptors and inhibitory at beta receptors
Cholinergic receptors?
- receptors that respond to acetylcholine - 2 types: muscarinic: PNS and sweat glands nicotinic: skeletal muscle - acetylcholine is excitatory to most muscarinic and nicotinic receptors except those in heart and lower esophagus (inhibitory effect)
What is consciousness?
Processes that enable us to experience the world around us This is distinct from automatic behaviours that occur in a rather unconscious manner
What structure within the brain is heavily involved in regulatingalertness?
Reticular Activating System
What is the reticular formation?
A core of grey matter passing through the midbrain, pons and uppermedulla – it is a polysynaptic network that regulates the activity of the cerebral cortex
What are the sensory inputs to the reticular formation?
Sensory and pain from ascending pathways Vestibular information from medial vestibular nucleus Visual from superior colliculus Auditory from inferior colliculus Olfactory via the median forebrain bundle
The RF modulates cerebral activity via various projections. Whatare these projections?
Noadrenergic projections from the nucleus coeruleus to the cerebral cortex Dopaminergic projections from the ventral tegmental area to the cerebral cortex Cholinergic projections to the thalamus Raphe nuclei in the midline – main source of serotoninergic projections to the brain and spinal cord
Which of these projections is most important in regulating the level of arousal?
Cholinergic projections
What are the three mechanisms by which these projections regulate the level of arousal?
Excitation of individual thalamic relay nuclei –> activation of cortex Projections to intralaminar nuclei –> project to all areas of cortex Projections to reticular nucleus– regulates flow of information through other thalamic nuclei to the cortex
What are the different waveforms seen on an EEG and what levels of arousal do they represent?
Delta (< 4 Hz) – seen in sleep Theta (4-8 Hz) – drowsiness Alpha (8-13 Hz) – subject relaxed with eyes closed Beta (13-30 Hz) – mental activity and attention Gamma range (~40 Hz) – creation of conscious contents in the focus of the mind’s eye, via the recurrent thalamo-cortical feedback
What is a cerebral contusion?
Localised bleeding in the brain (bruise in the brain)
What is a concussion?
Diffuse, widespread, homogenous impairment of brain tissue due tobrain trauma
What is acute confusion/delirium and stupor?
Acute confusion and delirium– sustained disturbance of consciousness where mental processes are slowed. Subject may be inattentive, disorientated and having difficulty carrying out simple commands or speaking Stupor– lack of critical cognitive function and consciousness – only responsive to pain
Damage to the reticular formation can lead to coma. What is a coma?
State of unconsciousness in which the subject cannot be roused even by strong sensory stimuli Different from sleep – metabolic activity of the brain is depressed and there is total amnesia for this period
State some causes of coma.
Metabolic alteration e.g. hypoglycaemia, hypoxia, intoxication Bilateral lesions in the cerebral hemispheres Lesions in the thalamus or brainstem
Describe how the Glasgow Coma Scale is structured.
Eye opening = 4 Verbal responses = 5 Motor responses = 6
What causes a persistent vegetative state?
Disconnection of the brainstem from the cortex or widespread cortical damage Brainstem is still functioning so reflexes, postural movements and sleep-wake cycle may still be present
What is brain death?
Irreversible coma due to brainstem death, but body kept alive artificially NOTE: spinal reflexes and some postural movements may be present
What would the consequences of a right parietal lesion be?
Hemispatial neglect – the patient will not pay attention to the left visual field Information from the left visual field is reaching the primary visual cortex but because of the parietal damage, the patient is not conscious of this visual field
What imaging technique can be used to study consciousness in health and disease?
Functional MRI
What is blindsight?
Brain-damaged (occipito-visual cortex) patients who are perceptually blind of their visual field can demonstrate some responses to visual stimuli e.g. manually interacting with ‘unseen’ objects and avoiding ‘unseen’ objects
