BHCS3007 Summary
Introduc4on to neurobiology
Organisa4on
• Divided into the central nervous system (CNS) and peripheral nervous system (PNS)
• CNS
o Brain – 2 major func4ons
§ Control behaviour
§ Regulate body’s physiological processes
§ Thought, forming memories, movement and awareness
o Spinal cord
§ Conducts signals to and from brain
§ Contains circuits of neurones which can control some of our simple reflexes (doesn’t
go through brain)
§ Ganglia and roots connect spinal cord to PNS
§ Divided into 4 sec4ons
• Cervical vertebrate – head, neck, shoulder, arm, hand movement
• Thoracic vertebrate – chest and abdomen movement
• Lumber vertebrate – leg muscles
• Sacrum (sacral nerves) – bowel, bladder, sexual func4on
§ Ventricles
• Open areas of brain
• Manufacture cerebrospinal fluid (CSF)
• Appear as dark structures on MRI
§ CSF
• Plasma-like watery substance
• Cushions and protects brain and spinal cord
• Con4nuously circulates around brain and spinal cord to remove impuri4es
and deliver nutrients
o Cranial nerves
§ 16
§ E.g., op4c nerve relay messages from eyes to brain to create visual images
o Brain terminology
§ Dorsal – top
§ Ventral – bo\om
§ Anterior – front
§ Posterior – back
§ Coronal plane cuts fronts and back
§ Sagi\al plane cuts le] and right
§ Axal (horizontal) plane cuts top and bo\om
o Brain regions (do not need to know for exam)
§ Cerebellum – modulates force, range of movement, learning of motor skills
§ Medulla oblongata – autonomic func4oning, e.g., diges4on, breathing, heart rate
§ Pons – conveys informa4on about movement from cerebrum to cerebellum
§ Midbrain – controls sensory and motor func4ons, eye movement, coordina4on of
visual reflexes
§ Diencephalon
• Thalamus – processes informa4on to cerebral cortex
• Hypothalamus – regulates autonomic, endocrine, visceral func4ons
§ Cerebral cortex (cerebrum)
• 2 hemispheres for learning, personality, decision making
, • Connected by corpus callosum
• Hippocampus – memory
• Basal ganglia – motor performance
• Amygdala – emo4on
• Cortex further divided into 4 lobes
o Frontal – largest, personality decision making
o Parietal – object iden4fica4on, speech, touch, percep4on
o Occipital – vision
o Temporal – short-term memory, speech, smell, rhythm
o Brain is covered in meninges – 3 layers of protec4on
§ Pura ma\er – outermost layer
§ Arachnoid – no blood vessels or nerve 4ssue
§ Pia mater – innermost, rich in veins and arteries
• PNS
o Connects CNS to effectors (muscles, glands etc)
o Sensory (afferent) neurons – flow TO brain
o Motor (efferent) neurons – flow FROM brain
• Grey vs white ma\er
o Myelin is a fa\y, high lipid content substance that appears white
o White ma\er is highly myelinated
§ Inside brain
§ Interprets sensory informa4on received
§ Outer side of spinal cord
o Grey ma\er is s4ll myelinated, but thinly
§ Outer side of brain
§ Inside of spinal cord
§ Contains most of brain’s neuronal cell bodies
§ Conducts, processes and sends informa4on to various parts of the body
Cellular components and cytoarchitecture
• Neurones
o Classified by loca4on, morphology, func4on and neurotransmi\er use
o Human brain contains at least 1 billion neurons
o Each class of neuron has same basic structure, with same basic func4on
§ Dendrite à cell body à axon à axon terminal
§ Energy conversion à integra4on à conduc4on à distribu4on
o 3 classes
§ Bipolar cell – re4na nerve cells
§ pseudo-unipolar cell – sensory neuron
§ mu4lpolar cells – motor neuron
,BHCS3007 Summary
• Glia
o 2-10x more glia than neurons in CNS
astrocytes
§ Fibrous (white ma\er)
§ Proteoplas4c (grey ma\er)
§ Role is trophic, metabolic and protec4ve support of CNS neurons
• Ionic homeostasis
• Cycling neurotransmi\ers (nodula4on of synap4c ac4vity)
• Supply mitochondria to neurons
• Regula4on of cerebral blood flow
• Maintain blood-brain barrier
• Respond to injury, promote repair
§ In a reac4ve state, astrocytes have more processes, are glial fibrillar astrocy4c
protein posi4ve and induce chemokine/cytokine produc4on
o Microglial
§ Highly specialised cells
§ 0.5-16.6% of total cell popula4on in brain
§ Myeloid origin (yolk sac) but enter CNS early in development
§ Func4ons
• Synap4c organisa4on (pruning)
• Trophic neuronal support during development
• Immune sen4nels – potent inflammatory response
• Phagocytosis of apopto4c cells in developing brain
• Myelin turnover
• Control of neuronal excitability
• Phagocy4c debris removed
• Brain protec4on and repair
§ Can change morphology very quickly – reac4ve states is hypertrophic (less processes)
o Oligodendrocytes
§ Myelina4ng cell in CNS
§ Purpose of myelin is to permit fast saltatory conduc@on
§ Myelin also protects and provides trophic support to an axon
§ A single oligodendrocyte can form up to 50 myelin segments
§ Number of myelin segments determined by intrinsic and extrinsic controls
§ Ac4ve progenitor popula4on present in adult brain, capable of repair (remyelina@on)
§ Extends processes around axon to form concentric wraps, squeezes cytoplasm out to
form 4ght myelinated segments, separated by Nodes of Ranvier
o Schwann cells
§ Myelina4ng cell in PNS
§ Axons >1um are sorted (radial sor@ng), ensheathed and myelinated by Schwann cells
§ 1 Schwann cells makes 1 myelin segment
§ Number of myelin wraps determined by axon thickness and neuregulin 1
§ Capable of regenera4on and remyelina4on
Signalling and nerve conduc4on
• Neurons generate electrical signals via ac@on poten@als
• Axon hillock is a specialised trigger region
o Part of soma and forms start of axon
o Where ac4on poten4al begins
• Ac4on poten4al mediated by Na+ and K+ ion channels
, • Ac4on poten4al
o All or nothing event
o Rapid sequence of changes in voltage across a membrane
o Membrane voltage (poten4al) is determined by ra4o of ions, EC to IC and permeability of
each ion
o Rapid rise in poten4al, depolarisa@on, ini4ated by opening of Na+ channels within plasma
membrane
o Subsequent return to res4ng poten4al, repolarisa@on, is mediated by opening K+ ion
channels
• Myelinated axons propagate ac4on poten4al much quicker by using saltatory conduc4on
• The synapse
o Chemical synapse
§ Uses neurotransmi\er release
§ Pre-/post-synap4c terminal
§ Neuromuscular junc4ons
§ Uses Ca2+ ion channels
§ Neurotransmi\er are ligands for ionotropic and metabotropic receptors on post-
synap4c terminals
o Electrical synapses
§ Transmission of electrical signals
§ Between2 nerves, nerve and effector target
§ Uses gap junc4on channels
o Neurotransmi\ers
§ Adrenaline – fight or flight
§ Noradrenaline – concentra4on
§ Dopamine – pleasure
§ Serotonin – mood
§ GABA – calming
§ Acetylcholine – learning
§ Glutamate – memory
§ Endorphin – euphoria
