Neuroscience and Mental Health Flashcards
Outline the organisation of the Central Nervous system.
Central Nervous System
Peripheral Nervous system
- Autonomous Nervous system
- Sympathetic nervous system
- Parasympathetic nervous system
- Somatic PNS
Define the central nervous system.
Brain and spinal cord
Define the peripheral nervous system.
Nerves and ganglia (clusters of neuronal cell bodies) outside the brain and spinal cord.
What to the branches of the PNS do?
- Somatic PNS: controls motor and sensory function for the body wall e.g. skin, skeletal muscles
- Autonomic NS: regulates function of the viscera (internal organs, smooth involuntary muscle, pupils, sweating, blood vessels, bladder, intestin, glands etc and controls heart and contraction rate. It had two arms (sympathetic and parasympathetic)
What are the different types of neurones with regard to direction of information flow?
- Afferent axons propagate action potential towards the CNS, away from PNS e.g. sensory neurones
- Efferent axons propagate action potentials from the CNS to the PNS e.g. motor neurones
- Inter-neurones are CNS neurons that synapse with other CNS neurons within the brain or spinal cord
Outline the parts of the brain.
- Cerebral cortex: two hemispheres. Each receives sensory info from and control movement of the opposite side of the body
- Cerebellum: Controls coordination of movement
- Brain stem: Primitive, densely packed fibres, regulates vital functions e.g. consciousness, breathing. Damage is usually serious and could be fatal
Where does the CNS end in the spinal cord?
- Ends at the margins of the spinal cord
- Dorsal and ventral roots that emerge are part of the PNS
Outline axon packing in nerves.
- Spinal nerves contain both afferent and efferent axons
- They’re bundled into fascicles surrounded by a perineurium
- Whole nerve encased in tough epineurium capsule
- Individual axons wrapped in myelin and endoneurium, though some are unmyelinated e.g. nociceptive (pain) neurons
What is the function of a neuron?
To transmit and receive action potentials, or stimulate target tissue e.g. contraction of smooth/skeletal muscle, secretion from gland.
What is the difference between PNS and CNS with respect to regeneration?
- Axons in PNS can regenerate after injury. Though recovery is often compromised by non-specific target re-innervation and aberrant axon sprouting. It can leave to neuropathic pain.
- Axons in CNS are unable to regenerate over long enough distance to be useful.
Why can’t axons in the CNS regenerate?
- Inhibitory molecules in CNS not PNS e.g. myelin differences
- Absence of guidance cues that stimulate axon growth during development
- Some loss of intrinsic axon growth capability by neurons
What is white and grey matter?
White matter - Ascending and descending axons
Grey matter - Neuronal cell bodies
What is the difference in the action potential pathways between a reflex response and conscious registering?
- Reflex: Only somatic sensory input to inter-neurons and motor output from spinal cord are required NO communication with sensorimotor cortex
- Conscious registering: Sensory inputs activate sensory neurons in spinal cord grey matter that transmit action potentials upward to sensory cortex of brain. Similarly neurons of motor cortex transmit action potentials downward to synapse with spinal motor neurons for voluntary movement
What is considered when diagnosing neurological problems?
- Presenting signs and symptoms to identify underlying anatomy and characterise the syndrome
- Mode (and speed) of onset to determine underlying aetiology (pathological cause)
- History: previous medical problems, family history, social history, other symptoms
List common causes of neurological problems in order of speed of onset.
- Trauma
- Vascular
- Toxic/metabolic
- Infectious
- Inflammatory/autoimmune
- Genetic-congenital
- Neoplastic
- Degenerative
Give some features of stroke.
- 80% are infarct
- 20% haemorrhage (often related to high bp)
- Can affect any part of brain including brainstem
- Problems in opposite side of lesion (contralateral)
- Risk factors include smoking, family history, diabetes, alcohol
What are the common areas affected by stroke and the syndromes they cause.
- Middle cerebral artery: most common, results in weakness and loss of sensation on the other side (contralateral)
- Posterior cerebral artery: often affect occipital lobe, result in visual loss on contralateral side
- Anterior cerebral artery: often cause contralateral leg weakness
- Brainstem: problems with balance, eye movemetns, speech and swallowing, breathing
What treatments are available for stroke?
Acute:
- intravenous thrombolysis to dissolve clot
- intra-arterial thrombectomy to remove clot
Treat complications:
- neurosurgery for haemorrhage or dangerously high pressure
Prevent further stroke:
- thin blood with aspirin
- treat diabetes and high cholesterol
- treat dangerously narrow carotid arteries
What are the examinations performed to diagnose neurological problems?
- Cognitive/thinking abilites: e.g. mini mental state examination
- Cranial nerves: smell, vision, eye-movements, facial sensation and movements
- Limbs: power, coordination, reflexes and sensation
Describe the mini mental state examination?=.
- Orientation e.g. what year is it?
- Registration e.g. ask patient to recall 3 things you just said (like items)
Trials: - Attention and calculation e.g. spell world backward, or count back in 7s
- Recall e.g recall 3 objects
- Language e.g. follow a 3 stage command
Outline the features of Parkinson’s disease.
- Slowly progressinve degenerative diseas affecting the basal ganglia
- Clinical features; rigidity, tremor, bradykinesia (reduced movement)
- Loss of neurons from substantia nigra to the caudate and putamen
- Dopamine is associated neurotransmitter
- Treated with levodopa which can cross blood brain barrier
- Also with deep brain stimulation
What is Spastic Parapaesis?
- Axonal degeneration that affects the spinal cord and leads to rigidity and weakness in the leg muscles which gets progressively worse
- Causes include: Trauma, inflammatory/autoimmune, neoplastic, degenerative, vitamin deficiency (B12), vascular
What is multiple myeloma?
- tumour of plasma cells (b cells)
- treated with radiotherapy and chemotherapy
What is stocking and glove distribution?
- Peripheral nervous disease
- Around the hands approx up to wrist
- Around the feet approx up to mid-shin
(Where you’d wear gloves and socks)
What is Acute Polyneuropathy?
- Peripheral nerve damage
Can be caused by
- Infections e.g. diptheria, autoimmune (e.g. Guillain Barre)
- Drugs (chemotherapy)
- Exposure to toxins (organophosphate insecticides)
Outline Guillain-Barre syndrome and Acute inflammatory demyelinating polyneuropathy.
- Common cause of acute neuromuscular weakness
- Progressiv ascending sensorimotor paralysis with areflexia, affectin 1 or mor limbs and reaching nadir (the worst point) within 4 weeks
- Patients may progress to almost complete paralysis and require ventilation
What treatment is available for Guillain-Barre and Acute Inflammatory demyelination polyneuropathy (AIDP)?
- Immunotherapy: Plasma exchange or intravenous immunoglobulin
- Supportive including ventilation if necessary
- Cardiac monitoring
- Anticoagulation to prevent leg clots (and subsequent pulmonary emboli)
What are the investigative methods of diagnosing a neurological problem?
- Brain scans: CT and MRI
- Cerebrospinal fluid: Lumbar puncture
- Nerve conduction studies and electromyography (EMG)
- Electroencephalogram (EEG) and Evoked potentials
- Brain pathology: damage to cells or larger structures
Where is a Lumbar puncture performed?
Between L3 and L4 or L4 and L5
What is a neuron?
- Basic structural and functional unit of the nervous system
- information processing unit
- responsible for generation and conduction of electrical signals
- communicates with other neurons via chemicals at the synapse
- supported by neuroglia, comprising of different types
Describe the structure of a neuron.
- cellular structure of all neurons are similar
- diversity achieved by differences in number and shape of processes
- usually made up of cell body, axon and dendrites
What are the adaptions of neutrons inside the cell?
- large nucleus
- prominent nucleolus
- abundant rough ER
- well developed golgi
- abundant mitochondria
- highly organised cytoskeleton
Highly organised, metabolically active, secretory cell.
Outline the features of dendrites.
- major area of reception of incoming information
- spread from cell body, branching frequently
- greatly increase surface area
- often covered in protrusions called spines
- dendritic spines receive majority of synapses
- large pyramidal neurons may have up to 30,000/40,000 spines
Describe the structure of pyramidal cells.
- triangular (isosceles)
- primary dendrite from each corner
- one large axon from bottom
How are Purkinje cells specialised?
- enormous number of spines on dendrites (>80,0000 per cell)
- human cerebellum has about 15 million Purkinje cells
Outline the features of axons.
- conduct impulses away from cell body
- emerge at the axon hillock
- usually one per cell
- may branch after leaving cell body and at target
- prominent micro-tubules and neurofilaments
Describe the properties of axons.
- contain abundant intermediate filaments and micro-tubules
- can be myelinated or unmyelinated
- axonal membrane in only exposed at node of Ranvier, ion channels at node and juxtanode, not paranode
- cable properties
Describe the features of axon terminals.
- Axons often branch extensively close to target (terminal arbor)
- Form synaptic terminals with target
- Boutons (typical synpaptic knob) OR
- Varicosities ( -O-O-O- )
Outline the ways the synapse is adapted for its function.
- Synaptic vesicles, packaged in Golgi and shipped by fast anterograde transport to synapse
- specialised mechanisms for association of synaptic vesicles with the plasma membrane
- abundant mitochondria about 45% of total energy consumption is required for ion pumping and synaptic transmission, sensitivity to O2 deprivation
Describe organisation of the synapse.
- neurons receive multiple synaptic input
- neurons use a range of chemical transmitters, excitatory and inhibitory
- competing inputs are integrated in the post-synaptic neuron (neuronal integration)
What are the types of synapses?
- Axo-dendritic (often excitatory)
- Axo-somatic (often inhibitory)
- Axo-axonic (often modulatory)
Describe the neuronal cytoskeleton.
- In adult humans axons range in length from micrometres to a metre
- Highly organised cytoskeleton required (microfilaments, intermediate filaments, microtubules)
- neurofilaments play a critical role in determining axon caliber (diametre)
- microtubules are very abundant in the nervous system
Outline axonal transport.
- transport of membrane associated materials
- vesicles associated motors are moved down the axon at 100-400mm per day
- different membrane structures targeted to different compartments
- retrograde moving organelles are morphologically and biochemically distinct from anterograde vesicles
What is the primary cause of Multiple Sclerosis?
Immune system attacking and destroying the myelin sheath of CNS neurons, and therefore their axons.
What are the different morphological sybtypes of neurons?
- Pseudounipolar (one axon) e.g. sensory neurons
- Bipolar (two axons) e.g. retinal bipolar cells
- Golgi type I multipolar (highly branched dendritic trees, long axons) e.g. pyramidal cells, Purkinje cells, retinal ganglion cells
- Golgi type II multipolar (highly branched dendtritic trees, short axons) e.g. stellate cells in cerebral cortex and cerebellum
What are Neuroglia?
- Support cells of the nervous system
- Astroglia, oligodendroglia, microglia, immature progenitors, ependymal cells, Schwann cells, satelite glia
- many and varied functions
- essential for correct functioning of neurons
What are the features of Astroglia?
- Multiprocessed star-like shape
- Most numerous cell type
- Numerous intermediate filament bundles in cytoplasm of fibrous astroglia
- Gap junctions suggest astroglia-astroglia signalling
What are the functions of astroglia?
- Scaffold for neural migration and axon growth during development
- Formation of blood brain barrier
- Transport of substances from blood to neurons
- Segregation of neuronal processes (synapses)
- Removal of neurotransmitters
- Synthesis of neurotrophic factors
- Neuronal-glial and glial-neuronal signalling
- Potassium ion buffering
- Glial scar formation
What are the features of Oligodendroglia?
- the myelin forming cells of the CNS: interfasicular (peripheral white matter), perineuronal (CNS grey matter)
- Small spherical nuclei
- Few thin processes
- Prominant ER and Golgi
- Metabolically highly active
What are the functions of Oligodendroglia?
- Production and maintenance of the myelin sheath
- Each cell produces multiple sheaths (1-40)
What are the features of myelin?
- a lipid rich insulating membrane
- up to 50 lamellae (layer)
- dark and light bands seen in EM images
- loss of oligodendroglia and myelin has disastrous consequences:
e. g. Multiple Sclerosis (MS), Adrenoleucodystrophy
What are Microglia?
- derived from bone marrow during early development
- resident macrophage population of CNS
- involved in immune surveillance
- present antigens to invading immune cells
- first cells to react to infection or damage
- role in tissue modelling
- synaptic stripping
What are Schwann cells?
- myelin producing cells of the PNS
- each Schwann cell produces only on myelin sheath
- surrond unmyelinated axons
- promote axon regeneration
Define flux.
The rate of transfer of molecules.
The number of molecules that cross a unit area per unit of time
What are the properties that affect excitable cells?
- Voltage/Potential difference: Generated by ions to produce a charge gradient (volts)
- Current: Movement of ions due to a potential difference (amps)
- Resistance: Barrier that prevents the movement of ions (ohms)
What is an electrochemical equillibrium?
When electrical forces balance diffusion forces, and prevent further movement.
What is the equilibrium potential?
Potential that prevents diffusion of the ion down its concentration gradient.
Which ions are the most important for maintaining resting potential?
Na+ and K+
What Is Ek and ENa? Why isn’t resting membrane potential eaqual to either?
Ek = -90mV ENa = +72mV
Membranes have mixed K+ and Na+ permeability (but at rest K+»Na+)
Which ions contribute to the membrane potential?
K+, Na+ and Cl-
The size of each ion’s contribution is proportional to how permeable the membrane is to the ion.
What equation is used to calculate the resting memrbrane potential (Em)?
Golman-Hodgkin-Katz equation.
Takes into account the concentration of ions and the membrane’s permeability to them.
Name the stages of an action potential.
- Resting potential
- Depolarizing
- Overshoot
- Repolarizing
- Hyperpolarizing
- Resting potential
What differences in stimulus can be seen when measured?
- Depolarisation causes positive deflection, hyper-polarization causes negative negative deflection
- Weak stimulus causes smaller potential than stronger stimulus
- The further from the stimulus site the smaller the potential
What is a graded potential?
- Changes in membrane potential that vary in size, rather than being all or none.
- Can be less than threshold
Where do graded potentials occur and why?
Occur at synapses and sensory receptors
Function: contribute to initiating or preventing action potentials
Describe the process of an action potential.
- Resting Potential
- Permeability K+» Permeability Na+
- Membrane potential nearer EK+ than ENa+ - Stimulus
- Depolarizes the membrane potential
- Moves it in the +ve direction towards threshold - Depolarization
- Na+ permeability increase greatly, Na+ enters down electrochemical gradient
- K+ permeability slowly increases, K+ leaves cell down electrochemical gradient but less than Na+. Membrane potential shifts to ENa+ - Repolarization
- Na+ permeability decreases, Na+ entry stops.
- K+ permeability increases as more channels open. Membrane potential shifts to EK+ - After Hyperpolarization
- K+ continues to leave electrochemical gradient. Membrane potential shifts to EK+. Some K+ channels.
Outline when during an action potential there is and isn’t possibility for a new action potential.
Absolute refractory period: Start of repolarization
- Inactivation gate closed, no new potential even if strong stimulus
- Later in repolarization activation gate also closes
Relative refractory period: After hyperpolarization
- Inactivation gate is open, but stronger than normal stimulus required to trigger an action potential
What are the features of neurons and action potentials?
- Once threshold is reached action potential is released
- All or nothing nature
- Refractory state where it is unresponsive to threshold depolarization
What restores the electrochemical equilibrium?
Non-voltage gated channels (fast) and sodium-potassium pumps (slow)
What is the difference between passive and active propagation?
Passive: Only resting K+ channels are open, resistance alters it, both directions
Active: Na+ channels involved, different areas are at different stages of the action potential, unidirectional
What is Saltatory conduction?
- Myelin sheath around axon with nodes of Ranvier allow the depolarisation to ‘jump’.
- Voltage-gated channels mostly at nodes creating a circuit
- Faster impulses
What factors affect conduction velocity?
- Axon diametre: velocity increases with axon diameter as there is less resistance
- Myelination: Faster with myelination
- Conduction is slowed by cold, anoxia (lack of oxygen), compression and drugs e.g. some anaesthetics
What are the divisions of the brain?
- Forebrain: Cerebral hemispheres, diencephalon
- Midbrain
- Hindbrain: Pons, medulla, cerebellum
(Brainstem: Midbrain, Pons and medulla)
What are the different parts seen in a cross section of the spinal cord?
- White matter: axons
- Grey matter: Cell bodies
- Dorsal horn: (posterior) Contains sensory neurones
- Ventral horn: (anterior) Contains motor neurones
- Dorsal root ganglion: (posterior) Contains sensory neuron somas/bodies
Identify the different structures of vertebra.
- Inter-vertebral foramen: Openings between verterbrae
- Body of verterbrae
- Arch of verterbrae
What are the spinal and vertebral levels?
- Cervical vertebrae C1-C8 and Cervical nerves C1-C7
- Thoracic vertebrae T1-T12 and Thoracic nerves T1-T12
- Lumbar vertebrae L1-L5 and Lumbar nerves L1-L5
- Sacral Vertebrae S1-S5 and Sacral nerve S1-S5
- Coccygeal nerve
Where does the spinal cord end?
L1/L2
What is the relationship between spinal segments and nerves their corresponding vertebrae?
Lumbar and sacral spinal segments are higher that their corresponding vertebrae.
Spinal nerves run below their vertebrae
What is the Peripheral nervous system?
- Peripheral nerves
- Ganglia
Describe the structure of a ganglion.
- Connective tissue capsule on outside
- Many neurons inside, but no dendrites
- Satellite cells support neurons
- Axons (appear dark, corrugated) in different planes
Describe the structure of a nerve.
- Neuron axons grouped in bundles called fascicles
- Fascicles grouped together with blood vessels into nerves
- Packaged with layers of connective tissue which give protection
