Neuroanatomy: Lectures 5-8 Flashcards
What are the main types of neurons
- Unipolar neurons - single process with single protrusion from cell body
- Pseudo-unipolar (sensory neurons)
- receptor –> CNS
- peripheral axon –> cell body –> central axon –> CNS
- receptor –> CNS
- Bipolar:
- Dendrites –> Cell body –> axon
- Multipolar:
- Recieve information from the brain
- Info –> dendrites –> cell body (star shaped) –> axon –> spinal cord and muscles
- E.g. hippocampal pyramidal cell
- Cell body in the middle of dendrites
How do you identify neurons
Silver Staining
Stains between 1 in 100 neurons and 1 in 1000
Properties of the nervous system
- 10^12 neurons
- Information flows from dendrites –> axons
- One single neuron can link to many dendrites (star shaped)
- Just after the cell body there is an axon hillock
- Initiation of action potentials
- Increased concentration of Na channels
- Can release hormones or neurotransmitter
What are the three main parts of the nervous system
Afferent: sensory information –> CNS
Interneuron: modulates the CNS; can be excitatory, inhibtiory, local or relay.
Efferent: motor information from CNS –> periphery
What are Glial cells (examples) and what are their function?
Glial cells are support cells for example Oligodendrocytes, Schwann Cells or Astrocytes.
Possible functions: structural support, insulation, debris removal, K+ ion buffering (concentration gradient), removal of neurotransmitters, blood brain barrier, nutritive.
What is the difference between Oligodendrocytes, Schwann Cells and Astrocytes.
Oligodendrocytes myelinate CNS (possibly multiple axons)
Schwann Cells myelinate the periphery (only single axons)
Astrocytes maintain the environment for a neuron (nutrient exchange, blood brain barrier)
Describe neurulation
- An area of the ectoderm known as the neural plate is predetrimed to become neural tissue
- It invaginates to become a neural groove
- Neural groove reseals and pinches off to become a neural tube
- Peripheral ganglia cells compose the majority of the cells.
Describe the main stages of cephalisation
- Three vesicle stage:
- Forebrain, midbrain and hindbrain — spinal cord
- Forebrain becomes cerebral cortex
- Hindbrain becomes medulla + brain stem
- Forebrain, midbrain and hindbrain — spinal cord
- Five vesicle stage:
- Forebrain divides into part a and b
- Hindbrain divides into 2 (pons & cerebellum, medulla)
- Little change in spinal cord length
- Brain must continously fold to become mature
- Vertical column grows faster than the spinal cord
- Back bone becomes longer than spinal cord.
What different modalities do sensory neurons posses
- Mechanoreception
- Pain (thermal or mechanical)
- Temperature
- Proprioception
- Olfaction
- Gustation
- Audition
- Vision
Describe a Dorsal Root Ganglia
- Pseudo-uni-polar neuron
- Uni-polar cell body
- Sensory terminal with a peripheral branch
- Primary afferent fiber
- Central branch goes to CNS
Describe nerve innervation of skin.
Any nerve endings which are bare have a very high threshold
Pacinian corpuscle is used to detect vibration
Ion channels present to trigger depolarisation and initiate and action potential.
What are the three groups of nerve fibres?
Are they myelinated or unmeylinated?
A (alpha, beta, gamma, delta) all myelinated
B = myelinated
C (DR or symp) unmyelinated
Which nerve fibres have the highest rate of conductance
A > B > C
What is the purpose of all of the nerve fibres
- A- alpha: motor-somatic proprioception
- A-beta: touch / pressure
- A- gamma: motor spindle changes
- A- delta: pain (thermal)
- B- preganglionic sympathetic
- C- DR: pain
- C- Sympathetic: postganglionic sympathetic
Which nerve fibres are sensory
A (alpha, beta, delta)
C (DR)
Why are there two types of pain receptors
A delta- fast onsent pain –> withdrawal reflex
C- slow onset pain caused by tissue damage or inflammation –> dull ache
A delta fibres have a far higher conduction velocity than C (DR)
The slow fibres may be an evolutionary throwback (innvertebrates also have them)
What are pain receptors known as
Nocioceptors
What are the main properties of nocioceptors
- Poorly differentiated axons
- Very few varicosities
- Thin axons containing neurofilaments
- Bare nerve endings
Which receptor detects which type of thermal pain?
<5 C, 25, 41, 46
A delta fibres detect smaller changes in skin temperature (cool and warm) so 25 and 41 C
C fibres detect larger changes in temperature <5 and Over 46 C
What are the response properties of mechanoreceptors
- Can adapt rapidly or slowly
- Rapidly- Fire action potentials at the start and at the end of a stimulus
- Slowly- action potentials throughout duration of stimulus but with decrease freq.
- Pacinian corpuscle used to dissapate pressure as connective tissue laminae slides over
- Action potentials fire when normality resumed
- Variety of nerve fibre densities
- Two point discrimination test
- Able to detect vibrations:
- Low frequency: meissiners corpuscle
- High frequency: Pacinian
What are receptive fields? Do they overlap? What is there function
A receptive field is the area where a sensory nerve can detect a stimulus.
They overlap in order to provide total coverage of the body.
Detect stimulus and feedback to different segments of the spinal cord (sensory nerves come off at different points from spinal cord)
How does our body respond to pain
Tissue damage leads to the production of inflammatory mediators which bind to receptors and enhance pain (sensitisation)
This makes it easier to fire action potential which propagate down the nociceptive terminal
How many spinal regions are there and how many segments does each region have
5 regions:
Cervical- 8 segments
Thoracic 12 segments
Lumber 5 segments
Sacral 5 segments
Coccygeal 3 segments
What are dermatomes?
A single pair of nerves comes away from each spinal segment and innervates specific territory.
This allows us to build a predictable map (dermatome) of which segments of the spinal cord control which bodily regions which can then be used in spinal cord injuries.
Label the main structures in the brain
Label the brain mark 2
How is the spinal cord structured?
A fluid filled central canal
Spinal roots (dorasla and ventral) which divide before entering the spinal cord
Dorsal root = sensory
Ventral root = motor
What is the difference between grey and white matter
Grey matter (middle) contains the cell bodies of the nerve fibre.
White matter contains the axons which are travelling to (afferent) and from (efferent) the brain
It is white because of the myelin sheath.
What are the tracts that white matter ascends in?
Fasciculus gracilis
Fasciculus cuneatus
Lateral spinothalamic tract - carries pain fibres (A delta and C fibres)
Spinoreticular and spinomesencephalic
What tracts make up the anterolateral system
Spinoreticular, spinomesencephalic and spinothalamic
What is the purpose of the three tracts which make up the anterolateral system
Carry information from spinal cord –> medulla –> pons –> midbrain
The spinothalamic and spinoreticular tracts then project to the cerebral cortex
Describe the spinothalamic tract
- Pain pathway
- Afferent fibres in superficial dorsal horn
- Descussates in the spinal cord
- Synapses in the thalamus and projects to the somatosensory cortex
Describe the spinoreticular tract
- Temporary pain tract
- Afferent fibres synapse in superficial dorsal horn
- Decussates in the spinal cord
- Synapse in reticular formation and then again at thalamus before terminating in the somatosensory cortex
Describe the spinomesencephalic tract
- Pain pathway
- Decussates in the spinal cord
- Afferent fibres synapse in the superficial dorsal horn
- Ascends and synapses at periaqueductal gray matter, synapses at thalamus and terminates at somatosensory cortex
What is the difference between the anterolateral tracts and the dorsal column-medial leminscal pathway
Anterolateral - pain / temperature
Dorsal column-medal lemniscal pathway - touch / pressure
How does the spinal withdrawal reflex work?
Stimulus –> afferent sensory fibres –> synapses in the spinal cord –> interneuron –> motor efferent fibre –> response
What are the four lobes of the brain?
Frontal
Occipital
Parietal
Temporal
How is the cortex organised?
What is the homunculus?
A somatotopic map which is predictable in all people showing which areas require more neural processing due to increased nerve innervation / neuron density
What are the names of the principal descending tracts and what are their individual functions?
- Corticospinal tracts
- It projects from the motor cortex the whole way down the spinal cord. Controls limb movement
- Corticobulbar tracts
- Motor cortex –> brain stem
- Head and facial movements
- Monaminergic pathway
- Uses NA and serotonin to contral pain
What two tracts make up the corticospinal tracts, and which one is dominant
- Lateral tract: 75%
- Crosses over in the medulla
- Ventral Tract: 25%
- Does not decussate
- There are only 2 neurones used
- Upper and lower motor neurons
Label the transverse section of a spinal cord
How does pain response move from the brain to the body
Label the basal ganglia
How is the basal ganglia organised in order to suppress movement
Direct and Indirect feedback mechanisms
What are the affects of basal ganglia injury / lesion?
- Abnormal movement- tremors, dystonia (distortion), chorea (huntingdons like), increased muscle tome (cogwheel rigidity), Bradykinesia (slow initiation of movement)
- Parkinsons disease:
- Loss of dopaminergic neurons in pars compacta of substainia nigra
- Symptoms: pill rolling tremor, rigity, bradykinesia
- Huntingdons:
- Genetic disorder not environment
- Loss of GABAergic and cholinergic neurons in stratum
- Degradation of motor cortex which can then lead to dementia
