neural system Flashcards
central nervous system (CNS)
brain
spinal cord
peripheral nervous system (PNS)
cranial nerves- 12 pairs
spinal nerves - 31 pairs
- brain to effectors
- effectors to spinal cord
afferent nerves
- sensory neurons
- impulses from receptors to CNS
efferent nerves
- motor neurones
- impulses from CNS to effectors
the brain
cerebrum- 4 lobes (frontal, parietal, temporal and occipital)
cerebellum- little brain (coordinating movement by cerebral cortex)
diencephalon- thalamus, hypothalamus, pituitary gland (sensory integration and homeostasis regulation)
brain stem- connects brain to spinal cord (CV and respiratory control)
cranial nerves (12 pairs)
- nose, smell - sensory
- eye, vision - sensory
- upper eyelid and eyeball - motor
- movement of eyeball - motor
- touch, pair, chewing - sensory/motor
- eyeball movement - motor
sensory neurones
baroreceptors
chemoreceptors
mechanoreceptors/ proprioceptors
metaboreceptors
thermoreceptors
nociceptors
baroreceptors
stretch receptors, sensitive to changes in blood pressure
chemoreceptors
chemical receptors, chemical environment of the blood
mechanoreceptors/ proprioceptors
muscle tension and length
metaboreceptors
skeletal muscle metabolites
thermoreceptors
temperature regulation
nociceptors
pain
interneurons
pain response example - a shortcut needed
pass afferent transmission to efferent response without need to involve brain
spinal cord can control simple motor reflexes
brain controls more complex and sometimes subconscious motor reactions
myotatic/ stretch reflex
stretch sensed by M-spindles
afferent signal to spinal cord
sensory neurons transmit signal
- motor neurons
- interneurons
motor neurons send efferent impulses to agonist muscle to contract
interneurons block motor neurons signalling antagonist muscle to not contract
efferent division - control
autonomic nervous system
involuntary processes
-SNS and PNS
somatic nervous system
motor neurons
- skeletal muscle function
sensory function
to sense change in the internal and external environment through sensory receptors
afferent functions
integrative function
to analyse the sensory information, store some aspects and make decisions
interneurons
motor function
to respond to stimuli by initiation of action
efferent neurons
neurones
functional unites of nervous system
convert stimuli to nerve impulses
neuroglia (microglia)
do not generate or conduct nerve impulses
protective and supporting
oligodendrocytes
support cells in CNS
astrocytes
regulate electrical transmission in brain
motor unit
two components
- alpha-motor neuron (AMN)
- muscle fibres innervated by the AMN
three types
- slow ( type 1 fibres)
- fatigue resistant (type IIa fibres)
- fast fatiguing ( type IIx fibres)
one motor neuron innervates each single muscle cell
anatomy of a neuron
dendrites (little trees)
- picking up signals
axon hillock
- nerve impulse generated
axon
- carries electrical impulse away from cell body
synapses
- contact point
myelinated neuron
Schwann cells
- myelin sheath: most nerve fibres are surrounded by an insulating, fatty sheath called a myelin sheath
nodes of Ranvier (periodic breaks of myelin sheath)
speed of transmission of the impulses
nerve fibre groups
3 groups
- A ( alpha, beta and gamma) which are all myelinated
largest
5-20 microns and 130m/sec
- B (nerve fibres) moderate myelination
medium
2-3 microns and 15m/sec
- C (nerve fibres) unmyelinated
smallest
0.5-1.5 microns and 2 m/sec
based on size and transmission
velocity of action potential
amount of myelination
-faster in myelination
axon diameter
- faster as diameter increases
temperature
- faster as temp increase
action potentials
sequence of rapidly occurring events that reverse the membrane potential and then restore to a resting state
excitable cells: neurons, muscle, endocrine
membrane potential: difference in amount of electrical charge inside and outside the cell
resting membrane potential
2K+ inside and 3Na+ outside
concentration of ions inside and outside
- extracellular (Na+ and Cl- )
- cytosol (intracellular) (K+, organic phosphate - and amino acids-)
membrane permeability differs for Na+ and K+
- 50-100 times greater for K+
- inward flow of Na+ can’t match outward flow of K+
- Na+/K+ pump removes Na+ as fat as it leaks in
polarised membrane
a cell with a membrane energy difference is termed polarised
occurs when sufficient stimulus depolarises the cell to threshold
membrane ion channels
leakage channels e.g. Na+, K+
voltage gated channels
- Na+ (-55 mV)
- K+ (+30 mV)
ligand-gated ion channels
depolarisation
occurs when sufficient stimulus depolarises the cell
- voltage gates Na+ open (-55mV) and sodium floods in
- delayed closing of sodium channels
- delayed opening of potassium channels
repolarisation
return to resting membrane potential
- Na+ channels close
- K+ leave the cell
voltage gated K+ channels (+30 mV)
hyperpolarisation
delay in closing of voltage gated K+ channels
synapses
neurons need to communicate with other neurons or target cells
- skeletal muscle
membranes do not touch
- separated by synaptic cleft
communication occurs via synaptic transmisson
- chemical synapse
-electrical synapse
neurotransmitters
synaptic vesicles release neurotransmitters by exocytosis
excitatory
-glutamate
inhibitory
- gamma aminobutyric acid
both
-acetylcholine
-noradrenaline
excitatory and inhibitory postsynaptic potentials
excitatory Post Synaptic Potential (EPSP)
- depolarisation via ligand-gated Na+ channels
inhibitory postsynaptic potential (IPSP)
- ‘more’ negative or hyperpolarised via ligand-gated Cl- and K + channels
signal summation
accumulation of multiple EPSPs on a postsynaptic cell
- excitatory
-inhibitory
spatial summation
- summation of effects of neurotransmitters released from several end bulbs onto one neuron
temporal summation
- summation of effect pf neurotransmitters released from 2 or more in rapid succession
refractory periods
excitable membrane needs recovery
during the refractory period the region cannot be excited again
absolute refractory period
- unable to respond
relative refractory period
- stimulus must be substantially greater to evoke action potential
a second action potential can be elicited by a supratheshold stimulus
