WEEK 10 - NERVOUS TISSUE

Question 1

Organisation of the nervous system

Answer 1

• Central nervous system (CNS)
  -Brain & spinal cord
  -3 membranes, Outer = dura mater; middle = arachnoid; inner = pia mater
• Peripheral nervous system (PNS)
• NS outside dura mater
• Peripheral nerves (include cranial nerves, nerves at the back of the brain)
• Afferent neuron’s –sensory (signals to the periphery (nerves besides ones from spinal cord or brain i.e. the CNS) → CNS)
• Efferent neurons –motor (CNS → periphery)
• Autonomic nervous system (ANS)
• Comprised of parts of CNS & PNS
• Regulates & controls visceral functions
• e.g. Heart rate, blood pressure, body temperature et

Question 2

Nervous tissue

Answer 2

• Neurons
• Structure varies throughout NS
• BUT share certain features
• 100 billion neurons in brain
• Glial cells
• cells attached to neurones
• Provide support functions
• Out number neurones 10 to
• key structural features of neurones
• all will have a cell body, soma, which will comprise the nucleus and coming off the cell body are dendrites
• they will all have an axon of some sort and an axon terminal

Question 3

Glial cells - CNS

Answer 3

• Astrocytes – found in CNS, provide nutrients, regulate conc. of ions, structural support, key cell in the blood-brain barrier
• Microglia cell – scavenge & degrade dead cells, protect brain from microorganisms, regulated
• Oligodendrocytes – form myelin sheaths in CNS
• Radial cells – scaffolds for developing neurones
• Ependymal cells – line the ventricles (gap) in brain, produce cerebral spinal fluid (CSF)

Question 4

Glial cells -PNS

Answer 4

• Satellite cells – found in PNS, provide nutrients & structural support
• Schwann cells – form myelin sheaths in PNS

Question 5

Nerve cells

Answer 5

• Specialised for sending & receiving signals
• Typical neurone has 4 domains
• Cell body or soma
• Dendrites
• Axon
  -Pre-synaptic terminals

Question 6

Nerve cell domain

Answer 6

• Cell body
• Surrounds nucleus
• Integrates inputs & generates signals
• Synthesis & processing of proteins
• grey matter - collections of cell bodies due to the nucleus making it look grey while white matter is the rest
• Dendrites
• large surface area
• Info receiving area
• Covered with receptors
• Axon
• Point of origin axon hillock
• Message sending –action potentials
• Presynaptic terminals
• Terminal of axon –multiple endings
• Release of neurotransmitter (NT) –synaptic transmission

Question 7

types of neurones

Answer 7

• multipopar neurones - many dendrites
• bipolar neurons
• unipolar neurons
• anaxonic neurone

Question 8

Special features of nerve cell

Answer 8

• Large surface area
• Axons –up to a metre long (in PNS), but short in the brain, not efficient to have lots of a little neurones
• motor neurone and then sensory neurone
• Vast consumers of energy
• Protein synthesis
• Creating and regulating electrochemical gradients, ion pumps use lots of energy

Question 9

Specialised cytology of nerve

Answer 9

• Large nucleus
• produce everything required for nucleus
• Abundant ER, mitochondria & lysosomes
• acts as calcium store
• Well developed golgi complex
• important for packaging proteins and putting into vesicles
• Cytoskeleton, transport network for vesicles and others
• Neurofilaments
• Microtubule

Question 10

microtubule transport

Answer 10

• two types of movement
• anterograde movement
• retrograde movement
• anterograde movement
• movement of proteins, mitochondria (things that are going to move from the cell body to the axon terminal
• proteins are packaged by budding off in the membrane-enclosed vesicles from the Golgi
• the vesicles and mitochondria are carried down the axon on microtubule ‘tracks’ by kinesin motors that are energised by ATP
• retrograde movement
• they happen in the opposite direction
• moving vesicles, mitochondria back from the axon terminals to the cell body
• powered by motors called MAP-1C (related to dynein), which also use ATP and move along the microtubules tracks
• in axons the microtubules have a polarity with the + side pointing away from the soma, but in dendrites the polarity is more random
• microtubules are normally in straight lines but can twist and tangle which causes the movement of the vesicles to become impaired and could cause the neurone to die off. this is one of the causes of Alzheimer’s

Question 11

Axon membrane potential

Answer 11

• Resting membrane potential inside cell is -70mV
• ↑[Na+] in extracellular fluid
• ↑[K+] in intracellular fluid
• Balance actively maintained by ATP-Na+/K+pumps

Question 12

Generation of an action potential

Answer 12

• K has greater conc inside the cell (intracellular fluid) than inside
• Na, Ca and Cl have a greater conc outside (extracellular fluid) the cell than inside

Question 13

What happens during an action potential

Answer 13

• resting potential starts at -70
• stimulus causes an influx in sodium ions
• membrane potential increases
• once reaches threshold potential (-50) the voltage gated sodium channels open and sodium ions flood into the cell - depolarisation where membrane potential becomes more positive
• once we reach the peak sodium channels close (refractory period, cannot be activated) and voltage gated K channels open - repolarisation where K leaves the cell
• hyperpolarisation - some K channels remain open and ATP-Na/K pump restores the resting potential
• resting potential - Na channels get out of refractory period and reach rest

Question 14

Excitatory & inhibitory inputs are summated

Answer 14

• EPSP-IPSP cancellation
  -excitatory and inhibitory graded potentials cancel each other out
• spacial summation
  -excitatory potentials from many neurones rigger threshold potential points
• temporal summation
  -many excitatory potentials from one neurone trigger threshold potential

Question 15

Conductance of an action potential

Answer 15

• spread and increase of membrane potential more and more down the axon
• resting - depolarised - depolarised
• action potential gets pushed along due to refractory period of Na channels

Question 16

Chemical synapse

Answer 16

• gap between neurone and target
• action potential leads to an increase in membrane potential
• Ca channels will open and go down con gradient and calcium will bind to snare proteins
• synaptic vesicles will fuse with the membrane and release the neurotransmitters across to the complementary receptor

Question 17

neurotransmitter release

Answer 17

*

Question 18

Electrical synapse

Answer 18

• action potential interacts with gap junctions
• depolarisation will go from one to another
• bidirectional

Question 19

Chemical vs electrical synapse

Answer 19

• Chemical synapse –delay of ~1ms
• Electrical synapse faster
• Chemical synapse –unidirectional
• Electrical synapse –bidirectional
• Chemical synapse –potential for signal modulation (input from different neurones)
• Electrical synapse –signal relay