Subdivisions Of The Nervous System Flashcards
Afferent Neurones
- Sensory
- Afferent info travels toward the brain (ascending)
- Fibres found in dorsal region of the spinal cord
Efferent Neurones
- Motor neurones
- Efferent in for travels away from the brain (to effector)
- Fibres found in the ventral region of the Spinal cord
Peripheral Nervous System (PNS)
Consists of autonomic & somatic NS (peripheral nerves)
PNS do regenerate after injury
Central Nervous System (CNS)
Consists of brain and spinal cord [acts as a single entity], most learned responses occur in SC.
CNS nerves don’t regenerate following injury, instead they undergo Wallerian degeneration & die. [swelling, lack of blood flow kills Neurones]
[but hippocampus - memory area/ learning centre - regeneration found in 2013]
Olfactory can also regenerate
PNS - Peripheral Nerves + Glia:
Peripheral nerves:
A fibres [fast myelinated]
C fibres [ slow unmyelinated]- normally associated with pain response
Muscle spindle afferents [Ia & II]
Golgi tendon organs [Ib]
Alpha & gamma motor fibres - Alpha = goes straight to skeletal muscle, voluntary control. Gamma = actives muscles spindles subconsciously.
Glia:
Schwann cells [myelinated peripheral nerve axons]
Satellite cells [regulate chemical environment] - stem cells
CNS - Neurones + Glia
Neurones:
Pyramidal cells [cortex] - motor control and movement
Beth cells [ motor cortex]
Purkinje cells [ cerebellum]
Motor neurones [spinal cord] - starts in SC goes to muscles
Glia [Glue]:
Oligodendrocytes [myelinate neuronal axons] - same as Schwann Cells.
Astro Yates [matirix/scaffolding] - star look alike, neural support and repairs damage, helps prevent major inflammation
Microglia [may ingest microbes and broken down tissues]
Radial glia - neurogenesis
Ependymal cells [secretes cerebrospinal fluid/circulate CSF with cilia]
Neurones - the basic unit of CNS
Oligodendrocytes in CNS and Schwann cells in the PNS are the glial cells responsible for myelinating the axons of neurones.
Myelin acts as insulation allowing rapid propagation of neural impulses along axon.
Neurones - The Action Potential
Electrochemical potential exists across the membrane of neurone as ion concentrations inside the cell aren’t the same as outside the cell
When a neurone is stimulated Na channels open & Na ions enter the cell along their electrochemical gradient
This changes the voltage across the membrane [becomes less -ve]
Voltage sensitive Na channels open allowing more Na to rapidly enter the cell and further depolarise it
~15mV change in membrane potential pushes neurone beyond ‘threshold’ and action potential ensues.
Resting membrane potential = ~70mV
Threshold = ~55mV
Sensing - Peripheral receptors
Muscles spindles
MS = muscle fibre with sensory organ wrapped around it.
MS are constantly firing to sense where joints are.
Golgi tendon smooths the forces as more motor units are recruited
Pressure and pain receptors are - inhibitory receptors
Muscle spindle receptors
Mechanoreceptors [stretch sensitive]
Important for proprioceptive feedback
Involved in spinal reflec circuitry
Coil around intrafusal muscles fibres
Detect absolute length & changes in muscle length
Are located at the end of Ia and II afferent fibres
Golgi tendon organs
Mechanoreceptors [stretch-sensitive]
Detect muscle tension
Located at muscle-tendon junction
Modulates muscle output in response to fatigue
Joint receptors
Mechanoreceptors [stretch-sensitive]
Location at junction capsule
Only respond to limited range of overlapping angles
Higher level of CNS determines joint position & perception of our position in space by monitoring which receptors are activated at the same time
Some are sensitive to extreme joint angle i.e. Provide danger signal.
Cutaneous receptors
Mechanoreceptors e.g. Pacinian corpuscles detect mechanical stimuli on skin.
Thermoreceptors detect temperature changes.
Notice-toes detect potential damage to skin [pain].
Afferent info goes to the thalamus first, then to cerebellum - it needs a lot of info in order to do a proper comparison
Sensing - The Afferent types
Ia - muscles spindles [stretch reflex]
Ib- Golgi tendon organ [inhibitory reflex]
= senses velocity and length change.
II - muscle spindles [stretch reflex]
III - mechanical stimuli e.g. Pressure
= only detects length change.
IV - chemical stimuli e.g. Pain, temperature.
Sensing - Ascending Pathways
- Dorsal column - medial lemniscal system
Dorsal column - medial lemniscal system
Info on touch, pressure and proprioception
Fasciculus Cuneate pathway- Lateral tract - for upper limb.
Fasciculus Gracillis pathway - Medial tract - for lower limb.