C8 Nervous system Flashcards
(25 cards)
Function of the nervous system
- Receive sensory input (internal&external)
- Integrate information
- Motor output
- Maintaining homeostasis
- Establishing & maintaining mental activity
What does the CNS include
Brain
Spinal Cord
What does the PNS include
- Sensory receptors
- Cranial nerves (12 pairs)
- Spinal nerves (31 pairs)
- Ganglia - neuron cell bodies outside CNS
- Plexuses - extensive network of axons outside CNS
Somatic division
Voluntary, conscious control
CNS -> Skeletal muscles
SIngle neuron system, 1 synapse
Cell bodies in CNS
Skeletal muscle contracts
Myelinated axons
Autonomic division
Involuntary, subconscious control
CNS -> smooth/cardiac muscle / glands
Cell bodies of 1st neuron in CNS
Cell bodies of 2nd neuron in autonomic ganglion
Target tissue stimulated or inhibited
Preganglionic - myelinated
Postganglionic - unmyelinated
Enteric division
Nerve plexuses within wall of digestive tract
- sensory neuron: digestive tact -> CNS
- motor neuron: CNS -> digestive tract
- enteric neurons confined to enteric plexuses
Functions
- stimulate/inhibit
- smooth muscle contraction
- gland secretions
- detect changes in content of lumen
What is in the Neuron cell body
- Nucleus, nucleolus
- Nissl bodies
- Golgi apparatus
Dendrites
- Highly branched
- Generate electric current when stimulated
- Flow of current from tip of dendrites to cell body
Axons
- Few mm-a meter
- sometimes branched - collateral axons
- arise from axon Hillock
- Trigger zone - axon hillock+inital segment
- Axon endings - presynaptic terminal, axon terminal, terminal boutons, synaptic knobs
- Myelin sheath
- Node of Ranvier
Sensory neurons
Afferent div
Detects external & internal stimuli
COllects input from specialised receptors
Transmit input as electric signal to CNS
Cell body - Dorsal root ganglion (outside CNS)
Motor neurons
Efferent div
Transmit electric signals from CNS -> effector (muscle/gland)
Cell body inside CNS
Interneuron
Connects sensory & motor neurons
Interconnections
Resting membrane potential
= difference in charge across the cell membrane in a resting cell
- 70mV
Intracellular -> more -ve
RMP=> leak ion channels & Na+/K+ pump
What happens in the RMP when a neuron is stimulated
All gated Na+ and K+ channels are closed
K+ leak channels open -> movement of K+ to outside of the cell
- creates -ve intracellular change
Na+/K+ pump activates
Difference in conduction velocity of a myelinated cell compared to an unmyelinated cell
Unmyelinated- each segment gets depolarised & repolarised
Myelinated- saltatory conduction, jumps from one Node of Ranvier to next, increases speed of transmission
What occurs at a synapse
- AP arrives at pre-synaptic terminal
- Voltage-gated calcium channels open, Ca2+ diffuses into the cell & acts on vesicle
- Vesicle move to pre-synaptic membrane
- Neurotransmitter released into synaptic cleft via exocytosis
- Neurotransmitter cross the synaptic cleft
- Neurotransmitter bind to receptor of ion channels on post-synaptic membrane
- Ion channels open, diffusion of ions into post-synaptic membrane
- Neurotransmitter removed from synapse by enzyme activity
Main parts of a reflex arc
Sensory receptor -> sensory neuron -> interneuron -> motor neuron -> effector organ
Reflex
Involuntary response w/o involving higher brain centre
Doesn’t require mental processing
Rapid, predictable, unlearnt
Stereotyped, immediate response from spinal cord
Reaction
Voluntary response to stimulus
Slower than reflex
Involves brain & spinal cord
Reaction time improves through repetition
Microglial cells
Migrate to areas damaged by infection, trauma/stroke & perform phagocytosis
Satellite cells
Provides support & nutrition to neuron cell bodies & protect neurons from heavy metal poisoning within the PNS
Oligodendrocyte
Produce myelin which wraps around the axons of several neurons within the CNS
Astrocyte
Provide a supportive framework for blood vessels & neurons and regulate the extracellular composition of brain fluid
Ependymal cells
Line te cavities within the brain & contribute to the production of cerebrospinal fluid
