NEU 1 Flashcards
Name the 2 divisions of the nervous system.
CNS - brain and spinal cord
PNS - cranial nerves and spinal nerves, trunks of autonomous nerves, enteric nervous system
Name the divisions of the PNS
Somatic and autonomic
Name the divisons of the autonomic system
Sympathetic and parasympathetic
Describe the somatic nervous system
- Under voluntary control
- Muscle movements
- Motor nerve cell body is contained in the spinal cord
- Does not synapse until at the muscle
Describe the autonomic nervous system
- Involuntary control
- Regulation of glandular secretions, gut motility etc
- Divided into the sympathetic and parasympathetic system
- Alwyas has a synapse before it reaches muscle
State the general functions of the nervous system
Sensory detection, information processing, behaviour, motor function
Describe the distribution of grey matter in the spinal cord
Mainly central and forms a butterfly shape
Describe the distribution of grey matter in the brain
Grey matter is peripheral (in the cortex)
Describe peripheral nervous system plexi
- Formed by peripheral nerves which come from spinal nerves
- Innervation of the limbs from ventral branches of spinal nerves
- Brachial plexus = forelimb
- Lumbosacral plexus = hindlimb
- nerve cells located in ganglia (groups of nerve cells outside CNS) and in CNS (nuclei of cranial nerves or in ventral and lateral horn of spinal cord)
Describe the composisiton of the myelin sheath
Mainly phospholipids
Describe the general neural structure
- Neurons - actual conducting cells
Neuroglia - supporting/maintaining cells, outnumber neurons - Insulation - lipid sheaths around inflow/outflow, myelin
- No connective tissue in CNS - no obvious boundaries, blood vessels supported by neuroglia
- Connective tissue sheaths in PNS
List the various junctions occuring between neurons and other excitable tissues
Synapses, neuromuscular junctions, neuroglandular junctions
List the functional types of neurons occuring in the nervous system
- Afferent
- Efferent
Describe the different macroglia
- Astrocytes - control local environment of CNS
- Satellite cells - similar to astrocytes
- Oligodendrocytes - insulators of CNS
- Schwann cells - insulators of PNS
- Ependymal cells - make CSF and form blood -CSF barrier
- Radial glia - progenitor cells
- Enteric glia - found in GIT ganglia
List the different microglia
- Specialised macrophages
- Mobile
- Control inflammation
Describe the general structure of neurones.
- large cells consisting of cell body (soma, perikaryon) and processes (poles) which include a single axon and one or more dendrites
Describe synapses
- Neuron to neuron
- Can be excitatory or inhibitory
- Only in grey matter
- Constantly made and destroyed (memory)
Describe neuromuscular junctions
- Neuron to muscle cells
- Always excitatory in case of skeletal muscle
Describe neuroglandular junctions
- Neuron to glandular cells
- Most secretory cells
List the different structural neurons found in the nervous system
Multipolar, bipolar, unipolar, interneurons
Describe mulipolar neurons
- single axon and mulitple dendrites
- Most comon
- Single outflow, multiple inputs
- Groups of these nerve cell bodies in CNS termed nuclei
- Tend to group together based on function
Describe bipolar neurons
- single axon, single dendrite
- Relatively uncommon
- Restricted to mainly special sensory pathways
Describe unipolar neurons
- single process leaves the cell and divides into 2
- Structurally both processes resemble acons
- Functionally one acts as dendrite, the other as true axon
- GSE - usually peripheral sensory
- Cell bodies grouped together in ganglia
Describe interneurons
- Association between one point of CNS and another
- Never leave CNS
- Most numerous type of neurons
What is a ganglion and what is its function?
- Collection of nerve cell bodies in the PNS
- Can be site for synapses (GVE - ANS)
- Cell bodies (general afferent)
- general swapping of nerve fibres (middle cervical ganglion particularly
- Exception is part of 5th cranial nerve which has some of its sensory cell bodies in the nucleus rather than a PNS ganlion
What are the functional components of spinal nerves?
All are mixed i.e. sensory and motor
What are the functional components of cranial nerves?
Are either purely sensory, purely motor or mixed
What are the types general afferent fibres?
GSA - general somatic: somatic pain, temperature, touch
GPA - general proprioceptive: kinaesthesia, proprioception
GVA - general visceral: visceral sensation including baroreceptors
What are the types of special afferent fibres?
SSA - special somatic: vision and hearing
SPA - special proprioceptive: balance
SVA - special visceral: tast and olfaction
Where is the outflow for sympathetic nerves?
- spinal outflow T1 to L3
Where is the outflow for parasympathetic nerves?
Outflow in cranial nerves 3, 7, 9, 10 and sacral nerve
Describe the structure of the spinal cord.
- Ends in the filum terminale - meninges fused to a fine cord
- 2 intumescenses with cell bodies for motor outflows (cervical and lumbar intumescences)
- Is a continuation of the medulla
- Some medullary nuclei enter to C1 level (spinal nucleus of V)
- Passes through the intervertebral foramen to exit spine as nerve
Describe the origins of from the spinal cord.
- Spinal cord and spinal nerves are segmental and are named by the segment (e.g. C4, T3)
- Exit at the intervertebral foraminae
- Link to ascending and descending columns of white matter
- Tracts link the brain with the PNS
- Named by origin-destination e.g. spinothalamic tract (start at spine, end in thalamus)
Describe the typical structure of the spinal cord
- Dorsal median septum and ventral median fissure
- White matter (peripheral) made up of ascending and descending tracts
- Grey matter (central) contains neurons and synapses
- Central canal continuous with ventricles in the brain
Describe the exit of nerves from the spinal cord
- Exit via dorsal or ventral roots
- Dorsal is afferent, larger and contains dorsal root ganglion
- Ventral is efferent
- These unite near the intervertebral foramen to make a spinal nerve and leave together
Describe what happens to the nerve after it has left the spinal cord.
- Spinal nerve branches into rami just outside intervertebral foramen
- Dorsal ramus goes to dorsal part of body
- Ventral ramus goes to ventral part of body (incuding limbs)
- Ventral is larger
- Both are mixed fibres (efferent and afferent)
Describe where motor neurones are situated in the spinal cord
- Cell body in ventral horn of grey matter of spinal cord
- Axon leaves via ventral root, into spinal nerve, then D/V rami
Describe where sensory neurones are situated in the spinal cord
- Cell body in dorsal root ganglion (pseudounipolar cell)
- Periperal process from skin etc via D.V rami
- Via dorsal root to dorsal root ganglion
- Central process - dorsal root to dorsal horn of grey matter or spinal cord
Describe spinal cord termination
- Dogs: L6/7, Cats S3, Horse S1, Cattle L7
- After this cauda equina filld vertebral canal
- Space around nerves is epidural space
Describe the enteric nervous system
- Smooth muscle of GIT controlled by 2 local nerve plexi
- Interspaced between/in smooth muscle of GIT
- Operate automatically - controls motility and local hormone reflexes
- Modified by autonomic nervous system
- Stressed animals often get diarrhoea - more forceful contractions rather than mixing contractions
Give the levels of the GIT and what is contained in these
- Lumen/food
- Mucosa - epithelium, lamina propria, muscularis mucosa
- Submucosa - Meissner’s (submucosal) plexus
- Muscularis propria - circular muscle, Auerbach’s (myenteric) plexus, longitudinal muscle
- Serosa
List the image properties of common tissue types on T1 MRI
Cortical bone - black Fat- white Water/fluid - black Soft tissue - grey Pathology - grey
List the image properties of common tissue types on T2 MRI
Cortical bone - black Fat - white Water/fluid - white Soft tissue - grey Pathology - white
Describe the generation and transmission of an action potential
- Opening of gated channels (neuromediator, physical force, ligand gated, voltage gated)
- Leads to influx of positive ions (usually Na+ ions) via gated channels, Na+/K+ ATPase pump stops = no outflow of Na+ = depolarisation of membrane
- Reaches treshold potential (-50mV)
Describe how the resting membrane potential is reached
- Potassium/sodium antiporters present in membrane of animal cells
- Sodium in, potassium out (3 out for 2 in)
- Large anions present in cell = negative membrane potential (-70mV)
- Leak channels allow outflow of ions, mostly potassium
Describe ligand gated channels
- Can have rapid or slow synaptic transmission
- Rapid: nicotinic Ach receptor, inotropic glutamate receptors, gamma-aminobutyric acid receptor. Are faster and direct
- Slow: Muscarinic Ach receptor, alpha and beta adrenergic receptors, metabotropic glutamate receptors. Are slow and indirect
Descrieb action potential propagation
- Schwann cells protect axon
- In myelinated AP propagates in saltatory manner - faste
- In non-myelinated, AP propagated continuously
- Refractory period ensures AP travels in one direction
- Becomes progressively easier to produce an AP
Describe how an action potential triggers the release of neurotransmitters at a synpase.
- Voltage gated Ca2+ channels open when AP at pre-synaptic knob
- Ca2+ enter into cells (axon terminals)
- Promote pre-synaptic vesicle exocytosis
- Released NTs interact with their receptors (ligand gated channels) on the postsynaptic cell (can be organ e.g. muscle or another neuron) to allow influx of Na+ and continue AP
Explain the origins of the neural tube and how it differentiates
- Develops from the nerual plate
- Plate invaginates along axis = neural groove and fold either side
- Folds move together and fuse
- Tube gives rise to tissues of CNS - brain rostrally and spinal cord caudally
- Closure progresses antero-posteriorly
- Once closed, meninges and vertebral structures develop around it
- Series of expansions of neural tube give rise to internal spaces (ventricles and aqueducts) within different regions of the brain
Where is CSF produced?
The choroid plexus - vascular proliferation of the ependymal layer in later 3rd and 4th ventricles
What divisions of the brian are contained in the forebrain?
The telencephalon and diencephalon
What divison of the brain is contained in the midbrain
The mesencephalon
What divisions of the brain are contained in the hindbrain
The metencephalon and the myencephalon
Describe the formation of the eyes
- Intraembyronic mesoderm lateral to notochord and neural tube thickens
- Forms longitudinal columns of paraxial mesoderm
- Differentiation into notochord and paraxial mesoderm depends on inhibition of BMP4
- Differentiation into intermediate and lateral plate mesoderm depnds on bone morphogenetic protein BMP4 and fibroblast growth factor (FGF)
- Eyes form initial as bulges of lateral ventricles
- Outer proportions invaginate, result in formatin of an optic cup and stalk
- Retina produced by optic vesicle invaginating
Describe the differentiation of the spinal cord during development
- Neural canal indentates and deliniates dorsal and ventral columns
- Notochord, floor plate and roof plate release signals to induce ventral (Shh) or dorsal (BMP4) cell types
- Dependent on concentration gradient
- Repression by Shh factors expressed dorsally
- Cell movement restricted by F-cadhedrin in ventricular zone
- Sensory in alar plate, motor in basa plate
- White matter of SC from outer layer that develops from neural tube as axons grow into from brain, ganglia and SC
- Dorsal horn fuses = median septum
- Ventral horn expands = ventral fissure
What is differentiation into notochord and paraxia mesoderm dependent on?
Inhibition of BMP4
What is differentiation into intermediate and lateral plate mesoderm dependent on?
BMP4 and FGF
Describe the myelination of nerve fibres
- In CNS oligodendroglia wrap around multiple axons
- In periphery, Schwann cells wrap around 1 axon
- Schwann cells derived fro neural crest cells
- Wrap around developing axons
- Nodes Ranvier breaks in myelin sheath between adjacent Schwann cells
- During formation of multiple layer, cytoplasm is withdrawn, plasma membranes fuse to form mesaxon that makes up myelin sheath
- Not compelte until after birth
What are the layers of the cerebral cortex going outside in?
Molecular, external granular, external pyramidal, internal granular, external pyramidal, multiform thalamic, subcortical
Describe the structure of a nerve
- Composed of several bundles of nerve axons
- Held together by connective tissue
- Most nerves contain sensory and motor fibres
- Epineurium (outermost)
- Perineurium (surrounds each fascicle)
- Endoneurium (around each nerve fibre)
Describe the structure of neurones
- Cell body: nutritional centre and large molecule production
- Dendrites: receptive area for impulse transmission
- Axons: conduct impulse away from cell body
- Axoplasm: axon’s cytoplasm
- Axolemma: axon’s membrane
- Neurolemma: outermost layer of nerve fibres in the PNS
- Neurones connected to each other by synaptic junctions or to organs
- Presynaptic knobs contain vesicles of NTs
Describe the function of neurons
- Transmit impulses either to or from the CNS
- Sensory: from sensory receptors to CNS
- Association neurons: in CNS, bridge sensory and motor neurons
- Motor: out of CNS to effectors
Describe ependymal cells and their function
- Allow flow of CSF within centra canals
- Line cavities of CNS
- Produce CSF in ventricles by filtering blood form capillaries
- Beat cilia to help circulate CSF
Describe astrocytes and their function
- Form junctions between capillaries and neurons
- Form blood brain barrier
- Have processes that terminate in end-feet surrounding capillaries of CNS
- Feet involved in formation of tight junctions between epithelial cells in capillaries
- Maintain proper ionic environment, express ion channels
Describe oligodendrocytes and their function
- Wrap around several axons
- Form white matter
- Similar properties to Schwann cells
Describe microglia and their function
- Cleaning cells
- Phagocytose pathogens and cellular debris
- Form immune system of the brain and spinal cord
List the supporting cells of the PNS
- Schwann cells
- Satellite cells
- Type A
- Type B
- Type C
List the supporting cells of the CNS
- Oligodendrocytes
- Astrocytes
- Microglia
- Ependymal
Describe association neurons
- Located in CNS
- Provide direct (reflex arcs) or indirect (via brain structures)
- Connection between sensory and motor neurons, as well as between selves
Describe motor neurons
- Conduct impulses out of CNS
- Somatic: reflex and voluntary control of skeletal muscle
- Autonomic: involuntary, cell bodies outside CNS regrouped in ganglia
- Also subdivided into sympathetic and parasympathetic
Describe the roles of synapses and neurotransmitters involved in the generation of a nerve impulse
- Signal transmission between 2 neurons
- Nerve impulse transmitted from presynaptic cell to postsynaptic cells
- Nerve impulse transmitted via neurotransmitters
- must be released to interact with specific receptors on postsynpatic membrane
Describe how a nerve impusle is transmitted across a synapse
- Action potential reaches presynaptic knob
- Opens voltage gated Ca2+ channels
- Influx of calciium triggers exocytosis of NT by fusing vesicles with membrane
- NT travels across cleft and binds to ligand gated ion channels
- Can be inhibitory or excitatory
- Enzymes break down neurotransmitters to be repackaged into vesicles in the presynaptic knob
Describe the kiss and run model
- Limited supply of NTs - need to be controlled
- When AP arrives, only small amount of NTs are released
- Vesicle fuses but not fully, allowing some neurotransmitters to escape
- If strong stimulus, then high frequency of APs so vesicles fuse more frequently, more NT released, more frequent APs on postsynaptic side
Give examples of biological controls of neurotransmitters action
- Once released, control of NTs is central
- Degradation in synaptic cleft by enzymes
- Receptor mediated endocytosis and destruction by intracellular endosomes or lysosomes
- Degradation: acetylcholinesterase breaks down Ach into acetyl and choline
- Receptor mediate endocytosis: usually clathrin endocytosis, clathrin molecules provide coat, adaptor proteins provide link between membrane and coat, dynamin encircles neck of bud and pinches off vesicles, clathrin release from membrane vesicle activated by chaperones, clathrin polymerised on cell membrane
Define a motor unit
A single motor axon of a motor neuron and all of the corresponding muscle fibres it innervates. A single axon can innervate multiple muscle cells
Explain the process of motor unit recruitment
- Slow MUs tend to be smaller and are recruited first during normal exercise
- During ballistic locomotion faster MUs can be recruited initially
Give an overview of how motor unit action potentials are measured
- Motor unit action potential can be used to distinguish a myopathy from neuropathy
- Based upon size, shape and recruitment pattern
- Electromyography
- Needle electrode
- Detects electrical action potential generated by muscle cells
- Insertional activity provides information about state of muscle and its innervating nerve
Explain the functin of stretch and tension receptors in tendon and muscle
- Weakest part of MSK system is junction between tendon and muscle
- Stretch and tension receptors send information to prevent overstretching and damage to this area
- Muscle spinde detects dynamic and static changes in msucle length. Stretch on muscle causes refelx contraction
- Golgi tendon organ monitors tension developed in muscle,, prevents damage during excessive force generation, stimulation results in reflex relaxation of muscle
Explain how neurotransmitters can be excitatory or inhibitory
- If NTs released open Na+ channels then are excitatory as Na+ enters and membrane depolarised
- If NTs open Cl- channels then are inhibitory as influx of Cl- leads to hyperpolarisation of membrane making it more difficult for an action potential to be generated
Explain how an excitatory postsynaptic potential (EPSP) can be generated
- 1 presynaptic neuron releasing several vesicles containing NTs over a short period of time (temporal summation)
- 2 or more presynaptic neurons releasing few pools of NTs over a short period of time (spatial summation)
Give the different interneuronal networks
Diverging, converging and reverberating
Describe a diverging interneuronal network
- One neurone connected to several others which connect to more
- Signals diverge and a single stimulus can activate multiple responses
Describe a converging interneuronal network
- One neurone receives signals from several others
- Signals converge
- Many stimuli cause single response
Describe a reverberating interneuronal network
- One axon sends an acons collateral to a previous neuron in the series
- Series restimulated without a new external signal
- Loop or echo circuit
Describe the neuromuscular junction of skeletal muscles
- AP opens Ca2+ channels, Ach released, Na+ channels open, muscle cell depolarised
- Calcium in muscle stored in sarcoplasmic reticulum
- Released when depolarised, muscle can contract
- Excess sytolic Ca2+ frees actin from tropomyosin, can interact with myosin
- Interact in presence of ATP
- Skeletal muscle contracts
- Resting conditions triggered by outward pumping of Ca2+ via ATPase channels but also passive Na+/Ca2+ exchanger
- Active K+/Na+ antiport maintains final homeostasis
describe the neuromuscular junction of smooth muscles
- 1 neuron to several cells
- Synapses are loose
Give the major classes of neurotransmitters
I - small NTs, mainly involved in nerve impulse generation
II - large NTs, released by NS into circulation
Give the major divisions of the brain
Rostral to caudal: Telencephalon, diencephalon, mesencephalon metencephalon, myencephalon
Describe the structure and function of the brainstem
- Medulla oblongata, pons, midbrain
- Efferent and afferent fibres pass through
- Nuclei of cranial nerves
- Forms floor of 4th ventricle
- Location of respiratory, blood pressure and heart rate regulatory centres
- Functions: hearing, balance, swallowing, masticatory musculature, mimic musculature, salication, parasympathetic
Describe the structure and function of the hindbrain
- Cerebellum, medulla and pons
- Functions: balance and coordinatin of movement
List the components of the forebrain
Telencephalon, diencephalon, cerebral hemispheres
The diencephalon is the part of the brain between the hemispheres
Describe the structure and function of the diencephalon
- Thalamus - thymal gland, relay station for sensory information (all senses apart from olfaction)
- Epithalamus - seasonal breeding
- Hypothalamus (around 3rd ventricle)
Describe the function of the hypothalamus
- Hormonal regulation
- Reproduction
- Appetite
- Fight/flight
- Stress
Describe the structure and function of the telencephalon
- Cortex plus subcortical structures
- Cortex: neocortex, paleocortex
- Subcortical:
- Basal ganglia: motor regulation
- Paleocortex: olfatory sense
- Archicortex: memory generation (spatial memory)
- Neocortex: dominant part of cerebral cortex in mammals
Give examples of inhibitory and excitatory neurotransmitters
Inhibitory: glycine, opens Cl- channels
Excitatory: ACh, opens Na+ channels
Give the regions of the cortex and their functions
Frontal lobe: motor cortex
Parietal lobe: sensory cortex
Temporal lobe: hearing
Occipital lobe: vision
Describe what a membrane potential is and how it is acheived
- The potential difference between the inside of a cell and the outside
- Established by the concentrations of K+ and Na+ ions, as well as large organic anions inside the cell
- Potassium leak channels allow slow efflux of potassium, while the Na+/K+ ATPase pump removes 3Na+ from the cell and brings in 2K+
- This maintains a negative membrane potential
Describe how MP and AP are related together
- An action potential is a membrane potential with a smaller potential difference
- It is brought about by a stimulus that goes above the threshold
- Sodium leaks channels open and potassium channels close
- The membrane is depolarised (becomes more positive) and an electrical current passes along the cell membrane
Describe what a refractory period is
The refractory period is the time in which an action potential can be generated while the membrane returns to its resting potential
Explain what inhibitory and excitatory postsynaptic potentials are
- Inhibitory postsynaptic potentials are ones that inihibit the generation of an action potential. This is done by opening Cl- channels to hypoerpolarise the cell and make it more difficult to acheive the threshold potential
- An excitatory postsynaptic potential is one that majkes it easier for an aciton potential to be geenerated by depolarising the membrane by opening sodium channels
