LO: Outline the basic organisation of the nervous system - brain, spinal cord and associated afferent and efferent pathways
Physiology: science of life, emphasis on integrating molecular, cellular, systems and whole-body function
Nervous system
- Communication network
- ~86 billion neurons in brain
- Detect and respond to internal changes and external changes
- Fast, specific, direct, electrical signalling
Divisions
- Divide in terms of structures (structural classification) or activities (functional classification)
- Afferent/Efferent
- Sensory/Motor
- Somatic/Autonomic
- Sympathetic/Parasympathetic
- Enteric
Neuro pathways
- Afferent: Projection to brain
- Efferent: Projection from brain
- Sensory (afferent) - 3 neuron chain
- Motor (efferent) - 2 neuron chain
- Transduction - receptor sensing
- Ascending pathways
- Sorting - redistribution
- Central processing
- Descending pathway to 'effectors'
- Synapses and decussation at key locations
Cells of the nervous system
Neurons
- Excitable cells
- Communicate to neurons, muscles or glands
- Various structures
Glia
- Supportive cells
- CNS - Oligodendrocytes (sheath), Astrocytes (Blood brain barrier)
- PNS - Schwann
LO: Define the types and properties of sensory receptors (mechano, thermo, chemo, nociceptors) and key neurotransmitters involved in sensory and motor pathways
Neurotransmitters
- Chemicals that are produced and released by neurons
- Send/extend signal at synapse/junction
- Bind to neurons, muscles or glands
- NT needs to be cleared from cleft to remain effective
- NT can be inhibitory, excitatory and change sensitivity
- Glutamate - excitatory
- GABA - inhibitory
- Substance P - pain
- Prostaglandins - fever
- Endorphins - pain
- Dopamine - Parkinson's
Sensory receptors
- Allows body to understand sensation
- Transduction
- Location of stimulus - external/internal
- Stimulus modality - taste/touch
| Receptor | Function | Examples |
| Mechanoreceptors | Detect movement | Pascinian corpuscle |
| Thermoreceptors | Detect temperature | Nerve endings in skin |
| Nociceptors | Detect damage | Nerve endings in skin |
| Photoreceptors | Detect photons (light) | Rods and cones in eyes |
| Chemoreceptors | Detect chemicals | Olfactory (smell) receptors, blood glucose detectors |
Nociceptors - multimodal | | |
Ascending pathways - dorsal column
- Active in fine touch, 2 point discrimination and proprioception
- Ascends on the same side as entry
- Synpase/decussate at medulla
- Target - thalamus, somatosensory cortex
Spinothalamic pathway
- Active in pain, temperature and touch
- Ascends on the counter lateral side to entry
- Synpase/Decussate at the point of spinal entry
- Target - thalamus
| Pathway | Active in | Ascends | Synpase/Decussate | Target |
| Medial lemniscus | Fine touch, 2-point discrimination and proprioception | Same side as entry | Medulla | Thalamus |
| Spinothalamic | Pain, temperature, crude/gross/non-discriminative touch | Counter lateral side to entry | Point of spinal entry | Thalamus |
Thalamus - Somatosensory cortex
- Relay station, collects sensory information and redistributes to relevant brain regions for appropriate processing
Somatosensory and motor cortex
- Contralateral processing of information - perception/response
- Homunculus - map of the body
- Disproportionate sizing relative to sensitivity and innervation density
- Sensory association
Descending pathways
Spinal tracts
- Corticospinal - movement
- Reticulospinal - pain modulation
Interactions (1)
- Most sensory pathways experience some degree of modulation and mediation by secondary factors
- Important to understand the mechanics and philosophy of interactions
- Modulation occurs peripherally/locally and centrally
Types
- Additive - statistical H0 of interactions (no differential effect of either stressor)
- Synergistic - net effect is significantly more than the additive effect
- Antagonistic - net effect is significantly less than the additive effect
Characterisation
- Combined effect of 2 or more stressors can be categorised by the net effect
Sub types
- Most severe component takes precedence - the effect of the more dominant/severe stressor overshadows or cancels out the impact of the other
- Relative addition - percentage change remains constant in the prescence of an additional stressor
- Impact nullification - extreme antagonistic response where combined effect is lower than individual effects
Reference
- Lloyd, A. and Havenith, G. (2016). Interactions in human performance: An individual and combined stressors approach. Temperature, 3(4), pp.514–517. doi:10.1080/23328940.2016.1189991.